Search

14 páginas.- 6 figuras.- 53 referencias, Understanding the chemical composition of our planet's crust was one of the biggest questions of the 20th century. More than 100 years later, we are still far from understanding the global patterns in the bioavailability and spatial coupling of elements in topsoils worldwide, despite their importance for the productivity and functioning of terrestrial ecosystems. Here, we measured the bioavailability and coupling of thirteen macro- and micronutrients and phytotoxic elements in topsoils (3–8 cm) from a range of terrestrial ecosystems across all continents (∼10,000 observations) and in response to global change manipulations (∼5,000 observations). For this, we incubated between 1 and 4 pairs of anionic and cationic exchange membranes per site for a mean period of 53 days. The most bioavailable elements (Ca, Mg, and K) were also amongst the most abundant in the crust. Patterns of bioavailability were biome-dependent and controlled by soil properties such as pH, organic matter content and texture, plant cover, and climate. However, global change simulations resulted in important alterations in the bioavailability of elements. Elements were highly coupled, and coupling was predictable by the atomic properties of elements, particularly mass, mass to charge ratio, and second ionization energy. Deviations from the predictable coupling-atomic mass relationship were attributed to global change and agriculture. Our work illustrates the tight links between the bioavailability and coupling of topsoil elements and environmental context, human activities, and atomic properties of elements, thus deeply enhancing our integrated understanding of the biogeochemical connections that underlie the productivity and functioning of terrestrial ecosystems in a changing world., We acknowledge the following people as additional data contributors: Drs. G. Blume-Werry, V. Bruckman, J. Buss, S. Collins, E. Dorrepaal, K.N. Egger, J. Fridley, Gibson-Roy, R. Harrison, J. Heberling, K. Helsen, E. Hinman, A. K olstad, N. Lemoine, M. Lesser, E. Li, S. E. Macdonald, E. Mallory, E. Massicotte, H.B. Massicotte, T. Moore, C. Morris, L. Nijs, M. Smith, Suojala-Ahlfors, E. Thiffault, K. Trepanier, R. Uusitalo, L. Van Langenhove, S. Vicca, F. Wang, M. Werner, K. White and S. Wilson. R.O.H. was funded by the Ramón y Cajal program of the MICINN (RYC-2017 22032), by the R&D Project of the Ministry of Science and Innovation PID2019-106004RA-I00 funded by MCIN/AEI/10.13039/501100011033, by the program José Castillejo” of the “Ministry of Universities” (CAS21/00125), by a project of the European Regional Development Fund (FEDER) and the Ministry of Economic Transformation, Industry, Knowledge and Universities of the Junta de Andalucía (ERDF Andalucía 2014–2020 Thematic objective “01—Reinforcement of research, technological development and innovation”): P20_00323 (FUTURE-VINES), by the European Agricultural Fund for Rural Development (EAFRD) through the “Aid to operational groups of the European Association of Innovation (AEI) in terms of agricultural productivity and sustainability,” Reference: GOPC-CA-20-0001, and from Fundación Biodiversidad (SOILBIO). M.D-B. was supported by a Ramón y Cajal Grant (RYC2018-025483-I), a project from the Spanish Ministry of Science and Innovation (PID2020-115813RA-I00), and a project PAIDI 2020 from the Junta de Andalucía (P20_00879). JP acknowl-edges funding from MICINN (RYC–2021–033454). S. Bridgham and P. Reed were supported from National Science Foundation Macrosystems Biology Grant 1340847. KVS acknowledges support from the Belgian American Educational Foundation (Paul Vernel Fellow), the Fulbright Program and the Fund for Scientific Research-Flanders. J. Pergl and M. Vítková were partly supported by 17-19025S, EXPRO Grant 19-28807X (Czech Science Foundation), BiodivClim Call 2019 (Grant TACR SS70010001) and long-term research development project RVO 67985939 (Czech Academy of Sciences). Natasja van Gestel was funded by the National Science Foundation Grant 1643871. Stevan Earl was partially supported by the National Science Foundation under Grant DEB-2224662, Central Arizona-Phoenix Long-Term Ecological Research Program (CAP LTER). Lilia Serrano-Grijalva has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 890874. Kevin van Sundert acknowledges support from the Fund for Scientific Research-Flanders. Yuriko Yano acknowledges USDA, National Institute of Food and Agriculture Grant, Award number 2015-67020-23454. A. Leeper, B. Lawrence, and J. LaMontagne acknowledge support from National Science Foundation Grant DEB-1745496, the University Research Council Collaborative Grant from DePaul University, and the Huron Mountain Wildlife Foundation.

Understanding the chemical composition of our planet's crust was one of the biggest questions of the 20th century. More than 100 years later, we are still far from understanding the global patterns in the bioavailability and spatial coupling of elements in topsoils worldwide, despite their importance for the productivity and functioning of terrestrial ecosystems. Here, we measured the bioavailability and coupling of thirteen macro- and micronutrients and phytotoxic elements in topsoils (3–8 cm) from a range of terrestrial ecosystems across all continents (∼10,000 observations) and in response to global change manipulations (∼5,000 observations). For this, we incubated between 1 and 4 pairs of anionic and cationic exchange membranes per site for a mean period of 53 days. The most bioavailable elements (Ca, Mg, and K) were also amongst the most abundant in the crust. Patterns of bioavailability were biome-dependent and controlled by soil properties such as pH, organic matter content and texture, plant cover, and climate. However, global change simulations resulted in important alterations in the bioavailability of elements. Elements were highly coupled, and coupling was predictable by the atomic properties of elements, particularly mass, mass to charge ratio, and second ionization energy. Deviations from the predictable coupling-atomic mass relationship were attributed to global change and agriculture. Our work illustrates the tight links between the bioavailability and coupling of topsoil elements and environmental context, human activities, and atomic properties of elements, thus deeply enhancing our integrated understanding of the biogeochemical connections that underlie the productivity and functioning of terrestrial ecosystems in a changing world.

International audience

Background and aims: the nitrogen isotope composition (δ¹⁵N) of plants in arid and semiarid grasslands is affected by environmental factors, especially water availability. Nevertheless, it is unclear whether the response of δ¹⁵N to water availability differs between C₃ and C₄ photosynthetic pathways. - Methods: we investigated plant δ¹⁵N of coexisting C₃ and C4 species as a function of aridity along a 3200 km aridity gradient across the arid and semi-arid grasslands of northern China. - Results: aridity was positively correlated with plant δ15N values in both C₃ and C₄ plants and also in the entire plant community, whereas soil bulk δ¹⁵N values increased first and then decreased along the aridity gradient. The N uptake by C₄ plants appeared to be more affected by competition pressure of neighboring plants and soil microbes than for C₃ plants along the transect. - Conclusions: the decoupled relationship between plant and soil δ15N values indicated that variations in vegetation and soil δ15N values were driven by differential biogeochemical processes, while different soil N sources were used for plant growth along the climatic gradient. The advantage of C₃ plants in the use of N may counteract the competitive advantage that C₄ plants have over C₃ plants due to their higher water use efficiency under drier conditions. These findings can help understand why C₄ plants do not completely replace C₃ plants in drier environments despite their higher water use efficiency.

Nonsteady state chambers are often employed to measure soil CO2 fluxes. CO2 concentrations (C) in the headspace are sampled at different times (t), and fluxes (f) are calculated from regressions of C versus t based on a limited number of observations. Variability in the data can lead to poor fits and unreliable f estimates; groups with too few observations or poor fits are often discarded, resulting in “missing” f values. We solve these problems by fitting linear (steady state) and nonlinear (nonsteady state, diffusion based) models of C versus t, within a hierarchical Bayesian framework. Data are from the Prairie Heating and CO2 Enrichment study that manipulated atmospheric CO2, temperature, soil moisture, and vegetation. CO2 was collected from static chambers biweekly during five growing seasons, resulting in >12,000 samples and >3100 groups and associated fluxes. We compare f estimates based on nonhierarchical and hierarchical Bayesian (B versus HB) versions of the linear and diffusion‐based (L versus D) models, resulting in four different models (BL, BD, HBL, and HBD). Three models fit the data exceptionally well (R2 ≥ 0.98), but the BD model was inferior (R2 = 0.87). The nonhierarchical models (BL and BD) produced highly uncertain f estimates (wide 95% credible intervals), whereas the hierarchical models (HBL and HBD) produced very precise estimates. Of the hierarchical versions, the linear model (HBL) underestimated f by ~33% relative to the nonsteady state model (HBD). The hierarchical models offer improvements upon traditional nonhierarchical approaches to estimating f, and we provide example code for the models.

Break crops are used in agriculture to reduce soil pathogens and improve yield of subsequent cereal crops. However, they can also affect soil microbial communities beneficial to plant growth including arbuscular mycorrhizal fungi (AMF). Two wheat genotypes (IAW2013 and 249) were planted after crop rotation with canola or chickpea with different nitrogen (N) and phosphorus (P) fertilizer treatments (0 and 100 kg N ha(-1) and 0 or 20 kg P ha(-1)) in the field. Plant and soil available N and P, AMF root colonization, shoot biomass, wheat yield and leaf delta C-13 were examined. While crop rotation did not affect soil available N and P, AMF colonization in wheat was on average 60% higher after chickpea than after the canola rotation. Wheat yield after chickpea increased for genotype IAW2013, and was positively related to AMF colonization for both genotypes. N and P fertilization reduced AMF colonization and yield, but increased shoot biomass and leaf tissue N and P concentrations. Leaf delta C-13 decreased with increased yield, suggesting that higher yielding and AMF colonized plants were less water stressed. In contrast to fertilization, cultivation of certain crops in the previous season, in our case chickpea, can promote AMF colonization of wheat roots, thereby increasing grain yield.

Drought is predicted to increase in many areas of the world, which can greatly influence soil microbial community structure and C stabilization. Increasing soil carbon (C) stabilization is an important strategy to mitigate climate change effects, but the underlying processes promoting C stabilization are still unclear. Microbes are an important contributor of C stabilization through the adsorption of microbial derived compounds on organo-mineral complexes. Management practices, such as addition of organic amendments might increase soil C stock and mitigate drought impacts, especially in agro-ecosystems where large losses of C have been reported. Here, we conducted a drought experiment where we tested whether the addition of organic amendments mitigates drought effects on soil C stabilization and its links to microbial community changes. In a semi-natural grassland system of eastern Australia, we combined a management treatment (compost vs. inorganic fertilizer addition) and a drought treatment using rainout shelters (half vs. ambient precipitation). We measured soil moisture, soil nitrogen and phosphorus, particulate organic C (Porn-C) and organo-mineral C (Min-C). Microbial community composition and biomass were assessed with PLFA analyses. A structural equation modeling (SEM) approach was used to examine the controls of soil moisture, Porn-C and nutrients on soil microbial biomass and community structure and changes in Min-C. Overall, the drought treatment did not affect microbial community structure and Min-C, while fertilizer only marginally increased Min-C, highlighting the resistance to these treatments in this grassland soil. In the surface soil (0-5 cm) Min-C was strongly associated with fungi that may have been stimulated by root exudates, and by gram-negative bacteria in the deep soil (5-15 cm) that were more affected by Porn-C and soil moisture. We conclude that the grassland microbial community and its effect on Min-C at our field-site were non-responsive to our drought treatment, but sensitive to variability in soil moisture and microbial community structure. Our findings also show that surface compost application can moderately increase soil C stabilization under drought, representing a useful tool for improving soil C stability. (C) 2016 Elsevier Ltd. All rights reserved.

1. Drought induces changes in the nitrogen (N) and phosphorus (P) cycle but most plant species have limited flexibility to take up nutrients under such variable or unbalanced N and P availability. Both the degree of flexibility in plant N:P ratio and of root symbiosis with arbuscular mycorrhizal fungi might control plant resistance to drought-induced changes in nutrient availability, but this has not been directly tested. 2. Here, we examined the role of plant N:P stoichiometric status and mycorrhizal symbiosis in the drought-resistance of dominant and subordinate species in a semi-natural grassland. 3. We reduced water availability using rainout shelters (control vs. drought) and measured how plant biomass responded for the dominant and subordinate species. We then selected a dominant (Paspalum dilatatum) and a subordinate species (Cynodon dactylon), for which we investigated the N:P stoichiometric status, mycorrhizal root colonization and water-use efficiency. 4. The biomass of all dominant plant species, but not subordinate species, decreased under drought. Drought increased soil available nitrogen, and thus increased soil N:P ratio, due to decreasing plant N uptake. The dominant P. dilatatum showed a high degree of plant N:P homeostasis and a considerable reduction in biomass under drought. At the opposite, the more flexible subordinate species C. dactylon increased its N uptake and water-use efficiency, apparently due to stronger symbiosis with mycorrhizae, and maintained its biomass. 5. Synthesis. We conclude that the maintenance of N:P homeostasis in dominant species, possibly because of a large root nutrient foraging capacity, becomes inefficient when water stress limits N mobility in the soil. By contrast, we demonstrate that higher stoichiometric N:P flexibility coupled with stronger mutualistic association with mycorrhizae allow subordinate species to better withstand drought perturbations. Using a stoichiometric approach in a field experiment, our study provides for the first time clear and novel understandings of the mechanisms involved in drought-resistance within the plant-mycorrhizae-soil system.