Ecologie fonctionnelle & biogéochimie des sols & des agro-systèmes

Carbon Cycle and Climate Change As climate change accelerates, it is important to know the likely impact of climate change on the carbon cycle (see the Perspective by Reich ). Gross primary production (GPP) is a measure of the amount of CO 2 removed from the atmosphere every year to fuel photosynthesis. Beer et al. (p. 834 , published online 5 July) used a combination of observation and calculation to estimate that the total GPP by terrestrial plants is around 122 billion tons per year; in comparison, burning fossil fuels emits about 7 billion tons annually. Thirty-two percent of this uptake occurs in tropical forests, and precipitation controls carbon uptake in more than 40% of vegetated land. The temperature sensitivity (Q10) of ecosystem respiratory processes is a key determinant of the interaction between climate and the carbon cycle. Mahecha et al. (p. 838 , published online 5 July) now show that the Q10 of ecosystem respiration is invariant with respect to mean annual temperature, independent of the analyzed ecosystem type, with a global mean value for Q10 of 1.6. This level of temperature sensitivity suggests a less-pronounced climate sensitivity of the carbon cycle than assumed by recent climate models.

Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives.

, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.

Life on Earth is sustained by a small volume of soil surrounding roots, called the rhizosphere. The soil is where most of the biodiversity on Earth exists, and the rhizosphere probably represents the most dynamic habitat on Earth; and certainly is the most important zone in terms of defining the quality and quantity of the Human terrestrial food resource. Despite its central importance to all life, we know very little about rhizosphere functioning, and have an extraordinary ignorance about how best we can manipulate it to our advantage. A major issue in research on rhizosphere processes is the intimate connection between the biology, physics and chemistry of the system which exhibits astonishing spatial and temporal heterogeneities. This review considers the unique biophysical and biogeochemical properties of the rhizosphere and draws some connections between them. Particular emphasis is put on how underlying processes affect rhizosphere ecology, to generate highly heterogeneous microenvironments. Rhizosphere ecology is driven by a combination of the physical architecture of the soil matrix, coupled with the spatial and temporal distribution of rhizodeposits, protons, gases, and the role of roots as sinks for water and nutrients. Consequences for plant growth and whole-system ecology are considered. The first sections address the physical architecture and soil strength of the rhizosphere, drawing their relationship with key functions such as the movement and storage of elements and water as well as the ability of roots to explore the soil and the definition of diverse habitats for soil microorganisms. The distribution of water and its accessibility in the rhizosphere is considered in detail, with a special emphasis on spatial and temporal dynamics and heterogeneities. The physical architecture and water content play a key role in determining the biogeochemical ambience of the rhizosphere, via their effect on partial pressures of O 2 and CO 2 , and thereby on redox potential and pH of the rhizosphere, respectively. We address the various mechanisms by which roots and associated microorganisms alter these major drivers of soil biogeochemistry. Finally, we consider the distribution of nutrients, their accessibility in the rhizosphere, and their functional relevance for plant and microbial ecology. Gradients of nutrients in the rhizosphere, and their spatial patterns or temporal dynamics are discussed in the light of current knowledge of rhizosphere biophysics and biogeochemistry. Priorities for future research are identified as well as new methodological developments which might help to advance a comprehensive understanding of the co-occurring processes in the rhizosphere.

Soil provides ecosystem services, supports human health and habitation, stores carbon and regulates emissions of greenhouse gases. Unprecedented pressures on soil from degradation and urbanization are threatening agro-ecological balances and food security. It is important that we learn more about soil to sustainably manage and preserve it for future generations. To this end, we developed and analyzed a global soil visible–near infrared (vis–NIR) spectral library. It is currently the largest and most diverse database of its kind. We show that the information encoded in the spectra can describe soil composition and be associated to land cover and its global geographic distribution, which acts as a surrogate for global climate variability. We also show the usefulness of the global spectra for predicting soil attributes such as soil organic and inorganic carbon, clay, silt, sand and iron contents, cation exchange capacity, and pH. Using wavelets to treat the spectra, which were recorded in different laboratories using different spectrometers and methods, helped to improve the spectroscopic modelling. We found that modelling a diverse set of spectra with a machine learning algorithm can find the local relationships in the data to produce accurate predictions of soil properties. The spectroscopic models that we derived are parsimonious and robust, and using them we derived a harmonized global soil attribute dataset, which might serve to facilitate research on soil at the global scale. This spectroscopic approach should help to deal with the shortage of data on soil to better understand it and to meet the growing demand for information to assess and monitor soil at scales ranging from regional to global. New contributions to the library are encouraged so that this work and our collaboration might progress to develop a dynamic and easily updatable database with better global coverage. We hope that this work will reinvigorate our community's discussion towards larger, more coordinated collaborations. We also hope that use of the database will deepen our understanding of soil so that we might sustainably manage it and extend the research outcomes of the soil, earth and environmental sciences towards applications that we have not yet dreamed of.

Almost half of the total organic carbon (C) in terrestrial ecosystems is stored in forest soils. By altering rates of input or release of C from soils, forest management activities can influence soil C stocks in forests. In this review, we synthesize current evidence regarding the influences of 13 common forest management practices on forest soil C stocks. Afforestation of former croplands generally increases soil C stocks, whereas on former grasslands and peatlands, soil C stocks are unchanged or even reduced following afforestation. The conversion of primary forests to secondary forests generally reduces soil C stocks, particularly if the land is converted to an agricultural land-use prior to reforestation. Harvesting, particularly clear-cut harvesting, generally results in a reduction in soil C stocks, particularly in the forest floor and upper mineral soil. Removal of residues by harvesting whole-trees and stumps negatively affects soil C stocks. Soil disturbance from site preparation decreases soil C stocks, particularly in the organic top soil, however improved growth of tree seedlings may outweigh soil C losses over a rotation. Nitrogen (N) addition has an overall positive effect on soil C stocks across a wide range of forest ecosystems. Likewise, higher stocks and faster accumulation of soil C occur under tree species with N-fixing associates. Stocks and accumulation rates of soil C also differ under different tree species, with coniferous species accumulating more C in the forest floor and broadleaved species tending to store more C in the mineral soil. There is some evidence that increased tree species diversity could positively affect soil C stocks in temperate and subtropical forests, but tree species identity, particularly N-fixing species, seems to have a stronger impact on soil C stocks than tree species diversity. Management of stand density and thinning have small effects on forest soil C stocks. In forests with high populations of ungulate herbivores, reduction in herbivory levels can increase soil C stocks. Removal of plant biomass for fodder and fuel is related to a reduction in the soil C stocks. Fire management practices such as prescribed burning reduce soil C stocks, but less so than wildfires which are more intense. For each practice, we identify existing gaps in knowledge and suggest research to address the gaps.

Soils are the product of the activities of plants, which supply organic matter and play a pivotal role in weathering rocks and minerals. Many plant species have a distinct ecological amplitude that shows restriction to specific soil types. In the numerous interactions between plants and soil, microorganisms also play a key role. Here we review the existing literature on interactions between plants, microorganisms and soils, and include considerations of evolutionary time scales, where possible. Some of these interactions involve intricate systems of communication, which in the case of symbioses such as the arbuscular mycorrhizal symbiosis are several hundreds of millions years old; others involve the release of exudates from roots, and other products of rhizodeposition that are used as substrates for soil microorganisms. The possible reasons for the survival value of this loss of carbon over tens or hundreds of millions of years of evolution of higher plants are discussed, taking a cost-benefit approach. Co-evolution of plants and rhizosphere microorganisms is discussed, in the light of known ecological interactions between various partners in terrestrial ecosystems. Finally, the role of higher plants, especially deep-rooted plants and associated microorganisms in the weathering of rocks and minerals, ultimately contributing to pedogenesis, is addressed. We show that rhizosphere processes in the long run are central to biogeochemical cycles, soil formation and Earth history. Major anticipated discoveries will enhance our basic understanding and allow applications of new knowledge to deal with nutrient deficiencies, pests and diseases, and the challenges of increasing global food production and agroecosystem productivity in an environmentally responsible manner.

Over the last 50 years, the use of nitrogen (N) and phosphorus (P) fertilizers has increased at a faster rate than global food production, resulting in substantial decreases of N and P efficiency in agriculture (Fig. 1). Thus, considerable amounts of N and P fertilizers have been wasted in agroecosystems, and the alteration of N and P biogeochemical cycles is among the most visible impacts of human activities on ecosystem services, far exceeding the hypothesized “planetary boundaries” for N and approaching those for P (Rockström et al., 2009). Projections for the future suggest that a substantial further increase in N and P fertilizer use will occur to cope with increasing food demand (Tilman et al., 2001; Vance et al., 2003). Tilman et al. (2001) predicted that global consumption of fertilizer P will increase from 34.3 Tg year−1 in 2000 to a mean projected value of 83.7 Tg year−1 in 2050 (56.2–118 Tg year−1 depending on the calculation scenario). Such increases in fertilizer consumption will further threaten the global N and P cycles. Bouwman et al. (2009) estimated that in 2000, the total input of fertilizer P in croplands amounted to 21 Tg year−1, of which 9 Tg was accumulated in soils and 1 Tg was lost to erosion. Their projections for 2050 for various scenarios of future agricultural development amounted to 29 to 46 Tg year−1 total P fertilizer input and 10 to 23 and 3 to 5 Tg year−1 accumulated in soil and lost to erosion, respectively. This suggests that even in the most optimistic scenario, the contribution of P fertilization of cropland to P movement by erosion will triple over the period 2000 to 2050. While further intensification of agroecosystems is clearly needed to cover the growing food demand over the next decades, we cannot afford to accept the “business as usual” scenario that relies on ever-increasing agricultural inputs and the resulting waste of nutrients in some regions of the world (Vitousek et al., 2009). Relative increase in world annual production of cereals, and global annual consumption of fertilizer N and fertilizer P over the period from 1961 to 2008. The 100-basis in 1961 corresponds to 876.9 Tg cereals year–1, 11.6 Tg fertilizer N year–1, and 4.8 Tg fertilizer P year–1. In 2008, these values were 2,520.7 Tg cereals year–1, 101.6 Tg fertilizer N year–1, and 17.1 Tg fertilizer P year–1. (Data are from FAOSTAT [http://faostat.fao.org/], accessed February 20, 2011). Contrary to N, P is reasonably abundant in the Earth’s crust (1.2 g kg–1 on average) and thus in soils, where it primarily occurs as inorganic P in apatite minerals derived from the bedrock. However, with soil formation and weathering, total P content decreases over time and organic P content builds up at the expense of inorganic P, as shown in soil chronosequences (Richardson et al., 2004). At early stages of development (in young soils), therefore, terrestrial ecosystems are primarily N limited, while at later stages of development (in older soils), they become P limited (Vitousek and Farrington, 1997). Thus, soil P scarcity is especially critical in the tropics, where deeply weathered soils dominate. In addition, unlike N (especially nitrate), phosphate ions are poorly mobile and present at low concentration in soil solution, due to strong and multiple interactions with soil constituents (Hinsinger, 2001). These comprise adsorption onto soil minerals (metal oxides and clay minerals), precipitation as P minerals (predominantly apatite-like minerals), and immobilization as various organic P compounds (soil organic matter and phytate, which is the P storage form in seeds). P limitation is thus widespread, estimated to affect about 5.7 billion ha worldwide (Gaume, 2000). While, in spite of their considerable energy cost, the reservoir of atmospheric N2 used for manufacturing N fertilizers is much larger than required, the situation for P is rather different. World reserves of P ores are indeed finite, and the exact time when their consumption will peak is a matter for debate. High-grade phosphate rocks are definitely expected to be exhausted within the next decades (Cordell et al., 2009), which calls into question the sustainability of current P fertilizer use in developed and emerging countries. Increasing P efficiency in crops without further increasing P inputs requires better exploration and exploitation of soil resources in agroecosystems. To achieve this, we must breed more P-efficient crop genotypes that will make better use of belowground (root architecture and rhizosphere-related) traits (Vance et al., 2003; Lynch, 2007). Another promising option for achieving ecological intensification of agroecosystems (Cassman, 1999) is to make better use of plant diversity, especially niche complementarity and facilitation occurring in the rhizospheres of intercropped species (Zhang et al., 2010). Enhanced productivity of multispecies agroecosystems (intercropping) compared with that of monospecific agroecosystems (each of the component species being grown alone) may be explained by two major processes that result in improved resource use: complementarity and facilitation (Fridley, 2001). Experimentally, these processes can be difficult to tease apart (Loreau and Hector, 2001). Complementarity may be defined as a decrease in interspecific competition and competitive exclusion through resource partitioning between intercropped species (Fig. 2). Species may use a given resource differently in time, in space, and in forms (Fridley, 2001). A well-known example is the complementarity of N use between cereals and N2-fixing legumes, where both species compete for the same pool of soil N, while only the legume can substantially access the additional pool of atmospheric N2 through symbiotic fixation. Facilitation occurs when one species enhances the growth or survival of another (Callaway, 1995). This can occur through (1) direct positive mechanisms, such as favorable alteration of light, temperature, soil moisture, soil nutrients, etc., and (2) indirect mechanisms, such as beneficial changes in soil mycorrhizal or microbial communities. Hereafter, we use facilitation to mean positive interactions by which a species can modify the biotic/abiotic environment of its roots (rhizosphere), ultimately benefitting the intercropped species by increasing nutrient availability (Callaway, 2007). Direct, root-mediated processes altering P availability in the rhizosphere and indirect, microbially mediated processes will be addressed. Competition (A), complementarity (resource use partitioning; B), and facilitation (C) between two intercropped species. Pools represent different forms of a single resource (e.g. nutrient). Solid arrows indicate uptake of the resource by the intercropped species, while dotted arrows indicate mechanisms by which species B can alter resource availability, increasing the size of the available pool at the expense of the unavailable pool (indicated by the curved arrow), thereby improving uptake of the resource by the intercropped species A (facilitation). Such positive interactions are particularly valuable when resources are limited, as occurs in low-input agroecosystems. For example, beneficial effects of intercropping have been observed at lower rates of P fertilizer application but were no longer significant at higher rates (Li et al., 2007). In ecology, the “stress gradient hypothesis” proposes that positive interactions (facilitation) increase in importance and intensity with increasing environmental stress (Brooker et al., 2005). For both natural and managed ecosystems, nutrient use in multispecies stands has been mainly studied for N and especially for cereal/legume intercropping systems. Few studies have focused on cereal-legume interactions with regard to soil P. Recently, this research field has attracted new interest with the reported evidence of enhanced P acquisition for cereals intercropped with legumes (Li et al., 2007). Given the low mobility of phosphate ions in soils, the volume and geometry of the rhizosphere largely determines the pool of P readily accessible to plants. Spatial complementarity can occur (1) when the two species have contrasting root architecture, exploring different soil horizons, and/or (2) because of the plasticity of root systems, combined with possible avoidance strategies (Hauggaard-Nielsen and Jensen, 2005; Li et al., 2006; de Kroon, 2007). In both cases, intercropping may ultimately result in better exploration of the whole soil volume compared with monocropping. The role of root distribution in resource use in intercropping systems has been mostly documented for N. But the conclusion that cereal has better N uptake efficiency due to faster root growth may also apply to P. The discovery that plants can adjust root location depending on nutrient availability and the presence of neighboring plants within a single species (Gersani et al., 2001; Cahill et al., 2010) raises new questions about how soil P is shared in multispecies stands and how “root decisions” (Hodge, 2009) occur for intercropped species. In addition, intercropped species may exhibit contrasting phenologies (Rose et al., 2007) and/or growth periods (e.g. different sowing dates), which may result in differential P requirements over time (Li et al., 1999, 2007). Contrasted sowing/harvest dates may also reduce competition and increase P availability by mineralization of crop residue, which enhances P acquisition of the intercropping system. Soil P occurs as various pools that require different biochemical or chemical reactions to release phosphate ions that are readily taken up by roots. Complementarity can thus occur for two intercropped species tapping into two distinct pools of soil P resources (e.g. inorganic and organic; Li et al., 2008). Intercropped species may also have access to different fractions of each of these pools (Turner, 2008). Cu et al. (2005) observed that wheat (Triticum aestivum) and intercropped white lupin (Lupinus albus) depleted two distinct inorganic P fractions. In Li et al. (2003a), chickpea (Cicer arietinum) mobilized soil organic P and left more inorganic P available to the intercropped wheat. Li et al. (2008) tested this hypothesis on a larger number of inorganic and organic P fractions for durum wheat (Triticum durum) and common bean (Phaseolus vulgaris). Almost all values of soil P pools in the rhizosphere of the two intercropped species were intermediate between those in the monocropped cereal or legume. As for Cu et al. (2005), the rhizospheres of the intercropped species were not dissociated to measure the changes in P fractions separately for each of the intercropped species. Facilitation of P uptake is defined as the positive interactions that result from the ability of one species to increase soil P availability to the benefit of the intercropped species (Callaway, 2007). Thus, for example, the size of the pool of available P is increased at the expense of the pool that is unavailable to species A (Figs. 2C and 3) as a consequence of exudation by species B. This section will focus on how plant roots are able to directly change rhizosphere P availability through either P uptake and exudation of P-mobilizing compounds or as a consequence of interactions with the uptake of other nutrients (Hinsinger, 2001; Vance et al., 2003; Devau et al., 2010). Root exudates play a major role in P bioavailability via several mechanisms: protons/hydroxyls and carboxylates solubilize inorganic P, while root-borne phosphatases hydrolyze organic P (Hinsinger, 2001; Vance et al., 2003). Most cereal/legume intercropping studies implicitly assume that the cereal shall benefit from the legume species (one-way because legumes are to larger amounts of et al., et al., carboxylates and Vance et al., 2003; et al., and phosphatases et al., in their But cereals can also change rhizosphere P availability, and one the facilitation of legume P acquisition by P-efficient cereals or even facilitation in intercropped cereal/legume systems. and microbially mediated positive interactions (facilitation) altering P availability in the rhizosphere of two intercropped species. arrows indicate how species B can P that is not available to species either directly or via soil such as and mycorrhizal or These processes result in increases in the size of the available P pool at the expense of the unavailable pool (indicated by the curved Solid arrows indicate P uptake by the two species from the available P N uptake and the of N used are to play a role in uptake and changes in rhizosphere and P availability et al., 2003). The intercropped cereal will benefit from due to N2 in soils, where such may increase P availability through of P minerals (Hinsinger, 2001). have shown a lower rhizosphere in legumes than cereals, while rhizosphere of the intercropped cereal/legume is intermediate (Li et al., Cu et al., 2005). However, has a with plant Li et al. (2008) reported a significant benefit when durum wheat was intercropped with common to durum wheat grown but they not the with the observed changes of rhizosphere and P These that release rate by the intercropped legume was than that when the legume was grown This as a result of legume N2 due to lower rhizosphere because of competition for soil N with the intercropped as documented (Hauggaard-Nielsen et al., 2009). when legumes to more on soil N when it is readily available due to the of concentration on N2 fixation. This where competition for one resource may facilitation for the acquisition of another resource only but also release and increase in rhizosphere can substantially increase soil P This occurs as a consequence of enhanced of phosphate ions and changes in of oxides and clay minerals to which phosphate ions are (Hinsinger, 2001). Devau et al. both and the substantial contribution of of the durum wheat rhizosphere to observed increases in P These were documented in a soil but occur for a of soil and that P availability is primarily by These suggest that cereals, which exhibit improved N when intercropped and may P acquisition by the intercropped legume. and other organic by roots can compete with phosphate ions for adsorption on thereby P and enhanced P availability (Hinsinger, 2001). exudation rates are and with plant species and and Vance et al., being much in cereals than in legumes such as chickpea and white lupin and et al., These species can amounts of and which are some of the most P-mobilizing carboxylates (Hinsinger, 2001). Thus, it is expected that legumes P acquisition of the intercropped legume species not carboxylates at rates than most one (Li et al., 2010) focused on and in the rhizosphere of intercropped and white lupin or bean for but no on plant or P The was and additional is needed to the of this in intercropping systems. which have the role of P-mobilizing have mainly focused on (Li et al., et al., et al., phosphatases may soil P availability through organic P. Li et al. reported increased P acquisition from organic in wheat intercropped with chickpea compared with wheat grown with a its roots from those of no such when the of P was inorganic which suggests that chickpea P acquisition by the intercropped wheat as a consequence of its ability to hydrolyze the organic P by Li et al. observed both in and plants that higher was observed for chickpea than for not affect the of either species, and P acquisition were The enhanced and P acquisition of the cereal not be to increased in intercropping compared with grown because it also when only inorganic P was et al. a but with another different species and growth intercropping was observed when P was in organic form but P and P availability all increased when inorganic P was between rhizosphere processes such as and P facilitation have not been clearly is to that a of in the rhizosphere is not directly the consequence of the of root-borne but rather from microbial activities of the on intercropping systems has to the of the due to To a this also to rhizosphere and organic of the rhizosphere processes occur over rather While protons/hydroxyls can several from root carboxylates and most are expected to be onto soil and thus poorly mobile in the over than 1 or et al., 2009). Thus, in the of root or mycorrhizal root is for the of positive interactions that the release of P-mobilizing Thus, in to niche of roots of the two intercropped species is needed for P facilitation to This is by root either in the field or in (Fig. which have shown that better growth and/or P acquisition is when is no between the roots of intercropped species. et al. (2008) that where the of is as be expected to occur in most soils, only the neighboring roots of the species benefit from the increased P availability due to by roots of the species. This not only from the mobility of P-mobilizing compounds by such as but especially carboxylates or is also for the phosphate ions to be able to the roots of the species. The for between roots may be by root and more mycorrhizal which can access to P resources from roots of the intercropped species. of either uptake or release of P-mobilizing compounds be as the of a root can its This has been especially documented for the release of and carboxylates in roots of white lupin and bean intercropping in two field with a root and between the species a that root but and no between the root systems of and bean from Li et al. with from the of of the B and and P uptake (C) of and bean from Li et al. with from For each species, different indicate significant among the exudation of P-mobilizing other processes may also changes in rhizosphere P availability as a consequence of interactions with the uptake of other nutrients, as for example N uptake and its on rhizosphere The role of uptake has been by Devau et al. P availability in the rhizosphere of durum wheat not be explained by P uptake combined with rhizosphere due to However, when for Devau et al. a between and rhizosphere P with P via its on especially for clay minerals at thereby the adsorption of phosphate ions and P The uptake of by roots thus the of increasing P Given that uptake can substantially between species, with legumes up more than cereals, legumes may thereby P acquisition of the intercropped we have evidence to the facilitation of P acquisition in between increased P acquisition and rhizosphere processes altering P availability are in with the role of N facilitation in cereal/legume a studies have to measure both rhizosphere processes and changes in P availability et al., et al., Li et al., or P acquisition in intercropping systems. In addition, rhizosphere processes may with soil and plant species (Hinsinger, 2001; et al., 2009), and P availability in the rhizosphere of intercropped species has been mostly studied in These interactions to be in a of soil soils et al., Li et al., 2010). For the hypothesis of facilitation of cereal P acquisition due to rhizosphere has only been tested in soils (Li et al., Cu et al., 2005). also be tested in soils, where more at increasing P direct chemical processes in the facilitation can also occur as a consequence of in the microbial or (Fig. species a on rhizosphere microbial due to in amounts and of root exudates and et al., et al., 2010). For in in the rhizosphere of white lupin were to while in were to the presence of and et al., In addition, roots a of and that microbial and are in and et al., 2003). can thus with plant species et al., 2006; et al., and/or plant interactions et al., 2004). In to the of is increasing evidence that soil chemical such as have a major on the of soil microbial et al., et al., 2010). To this apply to rhizosphere changes question et al., 2009), which be in cereal/legume intercropping systems. studies have shown significant changes in microbial in the rhizosphere of intercropped species compared with those of crops et al., et al., Li et al., 2010). of roots of the intercropped species can result in a common microbial which be a of the of each of the two species et al., However, in the rhizosphere of a of organic compounds be expected are in root between the intercropped species. In that the microbial of intercropped species not be a of the of each of the two species. effects of intercropping on microbial are et al. of bean intercropping on the of The and growth may also among in microbial are not as as changes in microbial and which can plant growth by altering root growth via production or nutrient availability through mineralization et al., et al., et al., 2011). et al. observed a between microbial P and However, is a between microbial and because of these are by a of which form et al., The consequence of such is that changes in the of a single species have on a given et al., 2003). However, even for with low of and their was not by intercropping et al., 2011). are that changes in microbial can be with changes in microbial activities et al., In to the of microbial on P acquisition of intercropped species, of be such as those in the of inorganic or organic P pools in The to increase the availability of inorganic P is soil as it in the production of organic and which are traits among rhizosphere (Richardson et al., 2009). also use phytate, pool of soil organic P et al., through the production of et al., 2008). These that the of from the rhizosphere of species was that for a legume lupin their was on these suggest that intercropping species such as cereals and legumes may different resulting in to in the To this it will be to to microbial from or to and and have been far only for one the et al., to only in et al., 2007). Another indirect in the rhizospheres of intercropped species is enhanced nutrient mineralization due to the The is defined as the change in soil organic matter resulting from the of organic matter and 2008). Thus, it can occur in the rhizosphere via root and 2009). et al. that use the energy from this to in to release organic N when inorganic N is P limitation has been to a but it may be in ecosystems that are primarily P limited, such as in the A positive of to the of organic N and P and may ultimately plant growth et al., 2000). of the is not accessible to all and is in to with those have not been clearly but a are to this et al., et al., 2011). As a the is on both the microbial and the of the organic be used by that their energy to growth rather than or compounds are more to some than et al., 2011). The and the of may thus the and the of the rhizosphere microbial and intensity (2009) indeed a larger in the rhizosphere of than in that of wheat. The has been in the of cereal/legume but of one of the intercropped species that release P in benefit the growth of the plant species via their The of common mycorrhizal the roots of two plants may also increase P availability to intercropped species. of nutrients between the intercropped species via has been documented for N but not for P. Li et al. (2009) that was of N to the intercropped species when the was the cereal with no significant role of In the of N was much increased by the development of when the species was the legume bean which up to of the N taken up by evidence for improved growth and in cereal/legume intercropping systems for ecological intensification of agroecosystems. of of nutrient efficiency in such systems has N, especially with regard to legume N2 fixation. on P are and of these between complementarity and facilitation or evidence that a rhizosphere the improved P efficiency when cereals and legumes are research is needed to positive interactions occur in intercropped cereals and legumes, which be to P acquisition efficiency for both low input and agroecosystems (Zhang et al., 2010). to be for such Given the of the mechanisms, also be further developed and

Terrestrial gross primary productivity (GPP) varies greatly over time and space. A better understanding of this variability is necessary for more accurate predictions of the future climate-carbon cycle feedback. Recent studies have suggested that variability in GPP is driven by a broad range of biotic and abiotic factors operating mainly through changes in vegetation phenology and physiological processes. However, it is still unclear how plant phenology and physiology can be integrated to explain the spatiotemporal variability of terrestrial GPP. Based on analyses of eddy-covariance and satellite-derived data, we decomposed annual terrestrial GPP into the length of the CO2 uptake period (CUP) and the seasonal maximal capacity of CO2 uptake (GPPmax). The product of CUP and GPPmax explained >90% of the temporal GPP variability in most areas of North America during 2000-2010 and the spatial GPP variation among globally distributed eddy flux tower sites. It also explained GPP response to the European heatwave in 2003 (r(2) = 0.90) and GPP recovery after a fire disturbance in South Dakota (r(2) = 0.88). Additional analysis of the eddy-covariance flux data shows that the interbiome variation in annual GPP is better explained by that in GPPmax than CUP. These findings indicate that terrestrial GPP is jointly controlled by ecosystem-level plant phenology and photosynthetic capacity, and greater understanding of GPPmax and CUP responses to environmental and biological variations will, thus, improve predictions of GPP over time and space.

Abstract As of 2020, the world has an estimated 290 million ha of planted forests and this number is continuously increasing. Of these, 131 million ha are monospecific planted forests under intensive management. Although monospecific planted forests are important in providing timber, they harbor less biodiversity and are potentially more susceptible to disturbances than natural or diverse planted forests. Here, we point out the increasing scientific evidence for increased resilience and ecosystem service provision of functionally and species diverse planted forests (hereafter referred to as diverse planted forests) compared to monospecific ones. Furthermore, we propose five concrete steps to foster the adoption of diverse planted forests: (1) improve awareness of benefits and practical options of diverse planted forests among land‐owners, managers, and investors; (2) incentivize tree species diversity in public funding of afforestation and programs to diversify current maladapted planted forests of low diversity; (3) develop new wood‐based products that can be derived from many different tree species not yet in use; (4) invest in research to assess landscape benefits of diverse planted forests for functional connectivity and resilience to global‐change threats; and (5) improve the evidence base on diverse planted forests, in particular in currently under‐represented regions, where new options could be tested.

Abstract Soil organic matter (SOM) models are based on the equation d C /d t = − kC which states that the decomposition rate of a particular carbon (C) pool is proportional to the size of the pool and the decomposition constant k . However, this equation does not adequately describe the decomposition of recalcitrant SOM compounds. We present an alternative theory of SOM dynamics in which SOM decay rate is controlled by the size and the diversity of microbe populations and by the supply of energy‐rich litter compounds. We show that the SOM pool does not necessarily reach equilibrium and may increase continuously, which explains how SOM can accumulate over thousands of years. However, the simulated SOM accumulation involves the sequestration of available nutrients. How can plants persist? This question is explored with two models that couple the C cycle with a limiting nutrient. The first model considers a single type of microbe whereas the second includes two functional types in competition for energy and nutrient acquisition. The condition for plant persistence is the presence of these two competing microbial types.

As a major contributor to the reduced nitrogen pool in the biosphere, symbiotic nitrogen fixation by legumes plays a critical role in a sustainable production system. However this legume contribution varies with the physico-chemical and biological conditions of the nodulated-root rhizosphere. In order to assess the abiotic and biotic constrains that might limit this symbiosis at the agroecosystem level, a nodular diagnosis is proposed with common bean as a model grain-legume, and a major source of plant proteins for world human nutrition. The engineering of the legume symbiosis is addressed by participatory assessment of bean recombinant inbred lines contrasting for their efficiency in use of phosphorous for symbiotic nitrogen fixation. With this methodology, in field-sites chosen with farmers of an area of cereal-cropping in the Mediterranean basin, a large spatial and temporal variation in the legume nodulation was found. Soil P availability was a major limiting factor of the rhizobial symbiosis. In order to relate the field measurements with progress in functional genomics of the symbiosis, in situ RT-PCR on nodule sections has been implemented showing that the phytase gene is expressed in the cortex with significantly higher number of transcripts in P-efficient RILs. It is concluded that various tools and indicators are available for developing the ecological engineering of the rhizobial symbiosis, in particular for its beneficial contribution to the bio-geochemical cycle of N, and also P and C.

Healthy soils provide a wide range of ecosystem services. But soil erosion (one component of land degradation) jeopardizes the sustainable delivery of these services worldwide, and particularly in the humid tropics where erosion potential is high due to heavy rainfall. The Millennium Ecosystem Assessment pointed out the role of poor land-use and management choices in increasing land degradation. We hypothesized that land use has a limited influence on soil erosion provided vegetation cover is developed enough or good management practices are implemented. We systematically reviewed the literature to study how soil and vegetation management influence soil erosion control in the humid tropics. More than 3600 measurements of soil loss from 55 references covering 21 countries were compiled. Quantitative analysis of the collected data revealed that soil erosion in the humid tropics is dramatically concentrated in space (over landscape elements of bare soil) and time (e.g. during crop rotation). No land use is erosion-prone per se, but creation of bare soil elements in the landscape through particular land uses and other human activities (e.g. skid trails and logging roads) should be avoided as much as possible. Implementation of sound practices of soil and vegetation management (e.g. contour planting, no-till farming and use of vegetative buffer strips) can reduce erosion by up to 99%. With limited financial and technical means, natural resource managers and policy makers can therefore help decrease soil loss at a large scale by promoting wise management of highly erosion-prone landscape elements and enhancing the use of low-erosion-inducing practices.

There is growing evidence of the importance of extramatrical mycelium (EMM) of mycorrhizal fungi in carbon (C) cycling in ecosystems. However, our understanding has until recently been mainly based on laboratory experiments, and knowledge of such basic parameters as variations in mycelial production, standing biomass and turnover as well as the regulatory mechanisms behind such variations in forest soils is limited. Presently, the production of EMM by ectomycorrhizal (EM) fungi has been estimated at ~140 different forest sites to be up to several hundreds of kg per ha per year, but the published data are biased towards Picea abies in Scandinavia. Little is known about the standing biomass and turnover of EMM in other systems, and its influence on the C stored or lost from soils. Here, focussing on ectomycorrhizas, we discuss the factors that regulate the production and turnover of EMM and its role in soil C dynamics, identifying important gaps in this knowledge. C availability seems to be the key factor determining EMM production and possibly its standing biomass in forests but direct effects of mineral nutrient availability on the EMM can be important. There is great uncertainty about the rate of turnover of EMM. There is increasing evidence that residues of EM fungi play a major role in the formation of stable N and C in SOM, which highlights the need to include mycorrhizal effects in models of global soil C stores.

Cyanobacterial flavodiiron proteins (FDPs; A-type flavoprotein, Flv) comprise, besides the β-lactamase-like and flavodoxin domains typical for all FDPs, an extra NAD(P)H:flavin oxidoreductase module and thus differ from FDPs in other Bacteria and Archaea. Synechocystis sp. PCC 6803 has four genes encoding the FDPs. Flv1 and Flv3 function as an NAD(P)H:oxygen oxidoreductase, donating electrons directly to O2 without production of reactive oxygen species. Here we show that the Flv1 and Flv3 proteins are crucial for cyanobacteria under fluctuating light, a typical light condition in aquatic environments. Under constant-light conditions, regardless of light intensity, the Flv1 and Flv3 proteins are dispensable. In contrast, under fluctuating light conditions, the growth and photosynthesis of the Δflv1(A) and/or Δflv3(A) mutants of Synechocystis sp. PCC 6803 and Anabaena sp. PCC 7120 become arrested, resulting in cell death in the most severe cases. This reaction is mainly caused by malfunction of photosystem I and oxidative damage induced by reactive oxygen species generated during abrupt short-term increases in light intensity. Unlike higher plants that lack the FDPs and use the Proton Gradient Regulation 5 to safeguard photosystem I, the cyanobacterial homolog of Proton Gradient Regulation 5 is shown not to be crucial for growth under fluctuating light. Instead, the unique Flv1/Flv3 heterodimer maintains the redox balance of the electron transfer chain in cyanobacteria and provides protection for photosystem I under fluctuating growth light. Evolution of unique cyanobacterial FDPs is discussed as a prerequisite for the development of oxygenic photosynthesis.

Abstract Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1‐km 2 resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1‐km 2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse‐grained air temperature estimates from ERA5‐Land (an atmospheric reanalysis by the European Centre for Medium‐Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (−0.7 ± 2.3°C). The observed substantial and biome‐specific offsets emphasize that the projected impacts of climate and climate change on near‐surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil‐related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications.

Globally, phosphorus (P) limits productivity of trees in many forests and plantations especially in highly weathered, acidic or calcareous profiles. Most trees form mycorrhizal associations which are prevalent in the organic and mineral soil horizons. This review critically examines mechanisms that enhance the acquisition of P by tree roots. Mycorrhizal roots have a greater capacity to take up phosphate (Pi) from the soil solution than non-mycorrhizal root tips. Factors that contribute to this include the extent of extraradical hyphal penetration of soil and the physiology and biochemistry of the fungal/soil and fungal/plant interfaces. Ectomycorrhizal (ECM) trees are likely to benefit from association with basidiomycetes that possess several high-affinity Pi transporters that are expressed in extraradical hyphae and whose expression is enhanced by P deficiency. To understand fully the role of these putative transporters in the symbiosis, data regarding their localization, Pi transport capacities and regulation are required. Some ECM fungi are able to effect release of Pi from insoluble mineral P through excretion of low-molecular-weight organic anions such as oxalate, but the relative contribution of insoluble P dissolution in situ remains to be quantified. How the production of oxalate is regulated by nitrogen remains a key question to be answered. Lastly, phosphatase release from mycorrhizas is likely to play a significant role in the acquisition of Pi from labile organic forms of P (Po). As labile forms of Po can constitute the major fraction of the total P in some tropical and temperate soils, a greater understanding of the forms of Po available to the phosphatases is warranted.

Land-use practices aiming at increasing agro-ecosystem sustainability, e.g. no-till systems and use of temporary grasslands, have been developed in cropping areas, but their environmental benefits could be counterbalanced by increased N2O emissions produced, in particular during denitrification. Modelling denitrification in this context is thus of major importance. However, to what extent can changes in denitrification be predicted by representing the denitrifying community as a black box, i.e. without an adequate representation of the biological characteristics (abundance and composition) of this community, remains unclear. We analysed the effect of changes in land uses on denitrifiers for two different agricultural systems: (i) crop/grassland conversion and (ii) cessation/application of tillage. We surveyed potential denitrification (PD), the abundance and genetic structure of denitrifiers (nitrite reducers), and soil environmental conditions. N2O emissions were also measured during periods of several days on control plots. Time-integrated N2O emissions and PD were well correlated among all control plots. Changes in PD were partly due to changes in denitrifier abundance but were not related to changes in the structure of the denitrifier community. Using multiple regression analysis, we showed that changes in PD were more related to changes in soil environmental conditions than in denitrifier abundance. Soil organic carbon explained 81% of the variance observed for PD at the crop/temporary grassland site, whereas soil organic carbon, water-filled pore space and nitrate explained 92% of PD variance at the till/no-till site, without any residual effect of denitrifier abundance. Soil environmental conditions influenced PD by modifying the specific activity of denitrifiers, and to a lesser extent by promoting a build-up of denitrifiers. Our results show that an accurate simulation of carbon, oxygen and nitrate availability to denitrifiers is more important than an accurate simulation of denitrifier abundance and community structure to adequately understand and predict changes in PD in response to land-use changes.

An ultra-thin ALD Al ₂ O ₃ architected at the CH ₃ NH ₃ PbI _3−δ Cl _δ /Spiro-OMeTAD interface reduces hysteresis loss and stabilizes perovskite devices against humidity.

In the quest for sustainable intensification of crop production, we discuss the option of extending the root depth of crops to increase the volume of soil exploited by their root systems. We discuss the evidence that deeper rooting can be obtained by appropriate choice of crop species, by plant breeding, or crop management and its potential contributions to production and sustainable development goals. Many studies highlight the potentials of deeper rooting, but we evaluate its contributions to sustainable intensification of crop production, the causes of the limited research into deep rooting of crops, and the research priorities to fill the knowledge gaps.