A. Peyton Smith,Ben Bond-Lamberty,Brian W. Benscoter,Malak M. Tfaily,C. Ross Hinkle,Chongxuan Liu & Vanessa L. Bailey. Shifts in pore connectivity from precipitation versus groundwater rewetting increases soil carbon loss after drought. Nature Communications 8, Article number: 1335 (2017) doi:10.1038/s41467-017-01320-x
Abstract
Droughts and other extreme precipitation events are predicted to increase in intensity, duration, and extent, with uncertain implications for terrestrial carbon (C) sequestration. Soil wetting from above (precipitation) results in a characteristically different pattern of pore-filling than wetting from below (groundwater), with larger, well-connected pores filling before finer pore spaces, unlike groundwater rise in which capillary forces saturate the finest pores first. Here we demonstrate that pore-scale wetting patterns interact with antecedent soil moisture conditions to alter pore-scale, core-scale, and field-scale C dynamics. Drought legacy and wetting direction are perhaps more important determinants of short-term C mineralization than current soil moisture content in these soils. Our results highlight that microbial access to C is not solely limited by physical protection, but also by drought or wetting-induced shifts in hydrologic connectivity. We argue that models should treat soil moisture within a three-dimensional framework emphasizing hydrologic conduits for C and resource diffusion.
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Katerina Georgiou,Rose Z. Abramoff,John Harte,William J. Riley & Margaret S. Torn. Microbial community-level regulation explains soil carbon responses to long-term litter manipulations. Nature Communications 8, Article number: 1223 (2017) doi:10.1038/s41467-017-01116-z
Abstract
Climatic, atmospheric, and land-use changes all have the potential to alter soil microbial activity, mediated by changes in plant inputs. Many microbial models of soil organic carbon (SOC) decomposition have been proposed recently to advance prediction of climate and carbon (C) feedbacks. Most of these models, however, exhibit unrealistic oscillatory behavior and SOC insensitivity to long-term changes in C inputs. Here we diagnose the source of these problems in four archetypal models and propose a density-dependent formulation of microbial turnover, motivated by community-level interactions, that limits population sizes and reduces oscillations. We compare model predictions to 24 long-term C-input field manipulations and identify key benchmarks. The proposed formulation reproduces soil C responses to long-term C-input changes and implies greater SOC storage associated with CO2-fertilization-driven increases in C inputs over the coming century compared to recent microbial models. This study provides a simple modification to improve microbial models for inclusion in Earth System Models.
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Javier H. Segura, Mats B. Nilsson, Mahsa Haei, Tobias Sparrman, Jyri-Pekka Mikkola, John Gräsvik, Jürgen Schleucher & Mats G. Öquist. Microbial mineralization of cellulose in frozen soils. Nature Communications 8, Article number: 1154 (2017) doi:10.1038/s41467-017-01230-y
Abstract
High-latitude soils store ~40% of the global soil carbon and experience winters of up to 6 months or more. The winter soil CO2 efflux importantly contributes to the annual CO2 budget. Microorganisms can metabolize short chain carbon compounds in frozen soils. However, soil organic matter (SOM) is dominated by biopolymers, requiring exoenzymatic hydrolysis prior to mineralization. For winter SOM decomposition to have a substantial influence on soil carbon balances it is crucial whether or not biopolymers can be metabolized in frozen soils. We added 13C-labeled cellulose to frozen (−4 °C) mesocosms of boreal forest soil and followed its decomposition. Here we show that cellulose biopolymers are hydrolyzed under frozen conditions sustaining both CO2 production and microbial growth contributing to slow, but persistent, SOM mineralization. Given the long periods with frozen soils at high latitudes these findings are essential for understanding the contribution from winter to the global carbon balance.
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Nikolas Hagemann, Stephen Joseph, Hans-Peter Schmidt, Claudia I. Kammann, Johannes Harter, Thomas Borch, Robert B. Young, Krisztina Varga, Sarasadat Taherymoosavi, K. Wade Elliott, Amy McKenna, Mihaela Albu, Claudia Mayrhofer, Martin Obst, Pellegrino Conte, Alba Dieguez-Alonso, Silvia Orsetti, Edisson Subdiaga, Sebastian Behrens & Andreas Kappler. Organic coating on biochar explains its nutrient retention and stimulation of soil fertility. Nature Communications 8, Article number: 1089 (2017) doi:10.1038/s41467-017-01123-0
Abstract
Amending soil with biochar (pyrolized biomass) is suggested as a globally applicable approach to address climate change and soil degradation by carbon sequestration, reducing soil-borne greenhouse-gas emissions and increasing soil nutrient retention. Biochar was shown to promote plant growth, especially when combined with nutrient-rich organic matter, e.g., co-composted biochar. Plant growth promotion was explained by slow release of nutrients, although a mechanistic understanding of nutrient storage in biochar is missing. Here we identify a complex, nutrient-rich organic coating on co-composted biochar that covers the outer and inner (pore) surfaces of biochar particles using high-resolution spectro(micro)scopy and mass spectrometry. Fast field cycling nuclear magnetic resonance, electrochemical analysis and gas adsorption demonstrated that this coating adds hydrophilicity, redox-active moieties, and additional mesoporosity, which strengthens biochar-water interactions and thus enhances nutrient retention. This implies that the functioning of biochar in soil is determined by the formation of an organic coating, rather than biochar surface oxidation, as previously suggested.
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Etienne Laliberte et al. Soil fertility shapes belowground food webs across a regional climate gradient. Ecology Letters, Volume 20, Issue 10 October 2017 Pages 1273–1284
Abstract
Changes in soil fertility during pedogenesis affect the quantity and quality of resources entering the belowground subsystem. Climate governs pedogenesis, yet how climate modulates responses of soil food webs to soil ageing remains unexplored because of the paucity of appropriate model systems. We characterised soil food webs along each of four retrogressive soil chronosequences situated across a strong regional climate gradient to show that belowground communities are predominantly shaped by changes in fertility rather than climate. Basal consumers showed hump-shaped responses to soil ageing, which were propagated to higher-order consumers. There was a shift in dominance from bacterial to fungal energy channels with increasing soil age, while the root energy channel was most important in intermediate-aged soils. Our study highlights the overarching importance of soil fertility in regulating soil food webs, and indicates that belowground food webs will respond more strongly to shifts in soil resources than climate change.
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Manuel Delgado-Baquerizo, et al. Soil microbial communities drive the resistance of ecosystem multifunctionality to global change in drylands across the globe. Volume 20, Issue 10
October 2017 Pages 1295–1305
Abstract
The relationship between soil microbial communities and the resistance of multiple ecosystem functions linked to C, N and P cycling (multifunctionality resistance) to global change has never been assessed globally in natural ecosystems. We collected soils from 59 dryland ecosystems worldwide to investigate the importance of microbial communities as predictor of multifunctionality resistance to climate change and nitrogen fertilisation. Multifunctionality had a lower resistance to wetting–drying cycles than to warming or N deposition. Multifunctionality resistance was regulated by changes in microbial composition (relative abundance of phylotypes) but not by richness, total abundance of fungi and bacteria or the fungal: bacterial ratio. Our results suggest that positive effects of particular microbial taxa on multifunctionality resistance could potentially be controlled by altering soil pH. Together, our work demonstrates strong links between microbial community composition and multifunctionality resistance in dryland soils from six continents, and provides insights into the importance of microbial community composition for buffering effects of global change in drylands worldwide.
