Soil microbial populations in deep floodplain soils are adapted to infrequent but regular carbon substrate addition

This is the final version of the article. Available from Elsevier via the DOI in this record.Floodplain soils provide an important link in the land-ocean aquatic continuum. Understanding microbial activity in these soils, which can be many metres deep, is a key component in our understanding of the role of floodplains in the carbon (C) cycle. We sampled the mineral soil profile to 3 m depth from two floodplain sites under long-term pasture adjacent to the river Culm in SW England, UK. Soil chemistry (C, nitrogen (N), phosphorus (P), soil microbial biomass (SMB), moisture content) and soil solution (pH, dissolved organic C (DOC) and N, nitrate, ammonium, water extractable P) were analysed over the 3 m depth in 6 increments: 0.0–0.2, 0.2–0.7, 1.0–1.5, 1.5–2.0, 2.0–2.5, and 2.5–3.0 m. 14 C-glucose was added to the soil and the evolution of 14 CO 2 measured during a 29 d incubation. From soil properties and 14 C-glucose mineralisation, three depth groups emerged, with distinct turnover times extrapolated from initial k 1 mineralisation rate constants of 2 h (topsoil 0.0–0.2 m), 4 h (subsoil 0.2–0.7 m), and 11 h (deep subsoil 1.0–3.0 m). However, when normalised by SMB, k 1 rate constants had no significant differences across all depths. Deep subsoil had a 2 h lag to reach maximal 14 CO 2 production whereas the topsoil and subsoil (0.2–0.7 m) achieved maximum mineralisation rates immediately. SMB decreased with depth, but only to half of the surface population, with the proportion of SMB-C to total C increasing from 1% in topsoil to 15% in deep subsoil ( > 1.0 m). The relatively large SMB concentration and rapid mineralisation of 14 C-glucose suggests that DOC turnover in deep soil horizons in floodplains is limited by access to biologically available C and not the size of the microbial population.Natural Environment Research Council (NERC)Biotechnology and Biological Sciences Research Council (BBSRC

Woody plant encroachment into grasslands leads to accelerated erosion of previously stable organic carbon from dryland soils

Journal ArticleDrylands worldwide are experiencing rapid and extensive environmental change, concomitant with the encroachment of woody vegetation into grasslands. Woody encroachment leads to changes in both the structure and function of dryland ecosystems and has been shown to result in accelerated soil erosion and loss of soil nutrients. Covering 40% of the terrestrial land surface, dryland environments are of global importance, both as a habitat and a soil carbon store. Relationships between environmental change, soil erosion, and the carbon cycle are uncertain. There is a clear need to further our understanding of dryland vegetation change and impacts on carbon dynamics. Here two grass-to-woody ecotones that occur across large areas of the southwestern United States are investigated. This study takes a multidisciplinary approach, combining ecohydrological monitoring of structure and function and a dual-proxy biogeochemical tracing approach using the unique natural biochemical signatures of the vegetation. Results show that following woody encroachment, not only do these drylands lose significantly more soil and organic carbon via erosion but that this includes significant amounts of legacy organic carbon which would previously have been stable under grass cover. Results suggest that these dryland soils may not act as a stable organic carbon pool, following encroachment and that accelerated erosion of carbon, driven by vegetation change, has important implications for carbon dynamics.University of ExeterRothamsted Research North Wyk

Long-term nitrogen addition modifies microbial composition and functions for slow carbon cycling and increased sequestration in tropical forest soil.

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.  Nitrogen (N) deposition is a component of global change that has considerable impact on belowground carbon (C) dynamics. Plant growth stimulation and alterations of fungal community composition and functions are the main mechanisms driving soil C gains following N deposition in N-limited temperate forests. In N-rich tropical forests, however, N deposition generally has minor effects on plant growth; consequently, C storage in soil may strongly depend on the microbial processes that drive litter and soil organic matter decomposition. Here, we investigated how microbial functions in old-growth tropical forest soil responded to 13 years of N addition at four rates: 0 (Control), 50 (Low-N), 100 (Medium-N), and 150 (High-N) kg N ha-1 yr-1 . Soil organic carbon (SOC) content increased under High-N, corresponding to a 33% decrease in CO2 efflux, and reductions in relative abundances of bacteria as well as genes responsible for cellulose and chitin degradation. A 113% increase in N2 O emission was positively correlated with soil acidification and an increase in the relative abundances of denitrification genes (narG and norB). Soil acidification induced by N addition decreased available P concentrations, and was associated with reductions in the relative abundance of phytase. The decreased relative abundance of bacteria and key functional gene groups for C degradation were related to slower SOC decomposition, indicating the key mechanisms driving SOC accumulation in the tropical forest soil subjected to High-N addition. However, changes in microbial functional groups associated with N and P cycling led to coincidentally large increases in N2 O emissions, and exacerbated soil P deficiency. These two factors partially offset the perceived beneficial effects of N addition on SOC storage in tropical forest soils. These findings suggest a potential to incorporate microbial community and functions into Earth system models considering their effects on greenhouse gas emission, biogeochemical processes and biodiversity of tropical ecosystems. This article is protected by copyright. All rights reserved.National Natural Science Foundation of ChinaNational Key R&D Program of ChinaYouth Innovation Research Team Projec

Effect of farm management on topsoil organic carbon and aggregate stability in water: A case study from Southwest England, UK

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordThere are few reliable data sets to inspire confidence in policymakers that soil organic carbon (SOC) can be measured on farms. We worked with farmers in the Tamar Valley region of southwest England to select sampling sites under similar conditions (soil type, aspect and slope) and management types. Topsoils (2–15 cm) were sampled in autumn 2015, and percentage soil organic matter (%SOM) was determined by loss on ignition and used to calculate %SOC. We also used the stability of macroaggregates in cold water (WSA) (‘soil slaking’) as a measure of ‘soil health’ and investigated its relationship with SOC in the clay-rich soils. %SOM was significantly different between management types in the order woodland (11.1%) = permanent pasture (9.5%) > ley-arable rotation (7.7%) = arable (7.3%). This related directly to SOC stocks that were larger in fields under permanent pasture and woodland compared with those under arable or ley-arable rotation whether corrected for clay content (F = 8.500, p <.0001) or not (F = 8.516, p <.0001). WSA scores were strongly correlated with SOC content whether corrected for clay content (SOCadj R2 =.571, p <.0001) or not (SOCunadj R2 = 0.490, p =.002). Time since tillage controlled SOC stocks and WSA scores, accounting for 75.5% and 51.3% of the total variation, respectively. We conclude that (1) SOC can be reliably measured in farmed soils using accepted protocols and related to land management and (2) WSA scores can be rapidly measured in clay soils and related to SOC stocks and soil management.Biotechnology and Biological Sciences Research Council (BBSRC)National Institute of Food and Agriculture, U.S. Department of AgricultureGlobal Farm PlatformWestcountry Rivers Trus

Geomorphically mediated carbon dynamics of floodplain soils and implications for net effect of carbon erosion

This is the final version. Available from Wiley via the DOI in this record. DATA AVAILABILITY: The data that support the findings of this study are openly available in “figshare” at http://doi.org/10.6084/m9.figshare.17263883.v1The fate of organic carbon deposited in floodplain sediments is an important control on the magnitude and direction of the carbon flux from anthropogenically accelerated erosion and channelization of the riverine network. Globally, carbon deposition rates and mean residence time (MRT) within different geomorphic settings remains poorly constrained. We sampled soil profiles to 0.8 m depth from two geomorphic zones: active channel belt (ACB) and lowland floodplain, under long-term pasture adjacent to the river Culm in SW England, UK. We evaluated sedimentation rates and carbon storage using fallout radionuclide 137Cs, particle size and total carbon analyses. Variation in decomposition was assessed via empirical (soil aggregate size, density fractionation combined with natural abundance 13C analysis) and modelling simulation (using the RothC model and catchment implications explored using a floodplain evolution model). Sedimentation and carbon accumulation rates were 5–6 times greater in the ACB than the floodplain. Carbon decomposition rates also varied with geomorphic setting. In floodplain cores, faster decomposition rates were indicated by greater 13C-enrichment and subsoils dominated by mineral-associated soil organic carbon. Whereas, in the ACB, carbon was less processed and 13C-depleted, with light fraction and macroaggregate-carbon throughout the cores, and RothC modelled decomposition rates were 4-fold less than lowland floodplain cores. Including the ACB in floodplain carbon MRT calculations increased overall MRT by 10%. The major differences in the balance of sedimentation and decomposition rates between active and inactive floodplains suggests the relative extent of these contrasting zones is critical to the overall carbon balance. Restoration projects could enhance soil carbon storage by maximizing active floodplain areas by increasing river channel complexity.Natural Environment Research CouncilNatural Environment Research Counci

Contrasting rhizosphere soil nutrient economy of plants associated with arbuscular mycorrhizal and ectomycorrhizal fungi in karst forests

This is the author accepted manuscript. The final version is available from Springer via the DOI in this recordData availability: Requests for data or other materials should be directed to Xinyu Zhang ([email protected]).Purpose Plants growing in the soils of karst forests associate with arbuscular mycorrhizae (AM) or ectomycorrhizae (ECM) to acquire nutrients. We researched how these different mycorrhizal associations affect rhizosphere soil nutrient economy in these calcareous soils. Methods Bulk and rhizosphere soils were sampled beneath 25 AM and 9 ECM plants growing in primary forests at the Puding Karst Critical Zone Observatory. Nutrient contents and potential enzyme activities were analyzed to test the effect of different types of mycorrhizal association on rhizosphere soil nitrogen (N) and phosphorus (P) economies. Results The contents of nitrate-N and available-P were markedly lower in the rhizospheres of ECM plants compared to AM plants. Ectomycorrhizal plants promoted relatively greater investment in N-acquisition enzymes, in contrast, AM plants caused relatively greater investment in P-acquisition enzymes. The decreased pH in the rhizospheres of AM plants likely promoted the greater P availability. Conclusion Our results revealed how plants that form contrasting mycorrhizal associations have fundamentally different effects on rhizospheric nutrient economies in the low fertility karst soils of southwest China. Differentiation in N- and P-acquisition capacity of these plants have implications for species coexistence and the high levels of plant biodiversity observed in these forests.National Natural Science Foundation of ChinaNational Key Research and Development ProgramNatural Environment Research Council (NERC

Microbially mediated mechanisms underlie soil carbon accrual by conservation agriculture under decade-long warming

This is the final version. Available on open access from Nature Research via the DOI in this recordData availability: The DNA sequences of the 16S rRNA gene and ITS amplicons in this study have been deposited in the National Center for Biotechnology Information (NCBI) under project accession numbers PRJNA903096 and PRJNA903090. Raw shotgun metagenomic sequences in this study have been deposited in the National Center for Biotechnology Information (NCBI) under project accession PRJNA1007786. Silva database is available at https://www.arb-silva.de/. UNITE database is available at https://unite.ut.ee/. Source data are provided in this paper. Source data are provided with this paper.Code availability: The analysis code that supports the findings of this study is available at GitHub https://github.com/bio-carbon/code.Increasing soil organic carbon (SOC) in croplands by switching from conventional to conservation management may be hampered by stimulated microbial decomposition under warming. Here, we test the interactive effects of agricultural management and warming on SOC persistence and underlying microbial mechanisms in a decade-long controlled experiment on a wheat-maize cropping system. Warming increased SOC content and accelerated fungal community temporal turnover under conservation agriculture (no tillage, chopped crop residue), but not under conventional agriculture (annual tillage, crop residue removed). Microbial carbon use efficiency (CUE) and growth increased linearly over time, with stronger positive warming effects after 5 years under conservation agriculture. According to structural equation models, these increases arose from greater carbon inputs from the crops, which indirectly controlled microbial CUE via changes in fungal communities. As a result, fungal necromass increased from 28 to 53%, emerging as the strongest predictor of SOC content. Collectively, our results demonstrate how management and climatic factors can interact to alter microbial community composition, physiology and functions and, in turn, SOC formation and accrual in croplands.National Natural Science Foundation of ChinaNational Key R&D Program of China2115 Talent Development Program of China Agricultural UniversityBeijing Advanced Disciplines and Strategic Priority Research Program of the Chinese Academy of Science

The North Wyke Farm Platform: effect of temperate grassland farming systems on soil moisture contents, runoff and associated water quality dynamics

This is the final version of the article. Available from Wiley via the DOI in this record.The North Wyke Farm Platform was established as a United Kingdom national capability for collaborative research, training and knowledge exchange in agro-environmental sciences. Its remit is to research agricultural productivity and ecosystem responses to different management practices for beef and sheep production in lowland grasslands. A system based on permanent pasture was implemented on three 21-ha farmlets to obtain baseline data on hydrology, nutrient cycling and productivity for 2 years. Since then two farmlets have been modified by either (i) planned reseeding with grasses that have been bred for enhanced sugar content or deep-rooting traits or (ii) sowing grass and legume mixtures to reduce nitrogen fertilizer inputs. The quantities of nutrients that enter, cycle within and leave the farmlets were evaluated with data recorded from sensor technologies coupled with more traditional field study methods. We demonstrate the potential of the farm platform approach with a case study in which we investigate the effects of the weather, field topography and farm management activity on surface runoff and associated pollutant or nutrient loss from soil. We have the opportunity to do a full nutrient cycling analysis, taking account of nutrient transformations in soil, and flows to water and losses to air. The NWFP monitoring system is unique in both scale and scope for a managed land-based capability that brings together several technologies that allow the effect of temperate grassland farming systems on soil moisture levels, runoff and associated water quality dynamics to be studied in detail. HIGHLIGHTS: Can meat production systems be developed that are productive yet minimize losses to the environment?The data are from an intensively instrumented capability, which is globally unique and topical.We use sensing technologies and surveys to show the effect of pasture renewal on nutrient losses.Platforms provide evidence of the effect of meteorology, topography and farm activity on nutrient loss.The North Wyke Farm Platform is a UK National Capability supported by the Biotechnology and Biological Sciences Research Council (BBSRC BB/J004308/1)

Roles of instrumented farm-scale trials in trade-off assessments of pasture-based ruminant production systems

For livestock production systems to play a positive role in global food security, the balance between their benefits and disbenefits to society must be appropriately managed. Based on the evidence provided by field-scale randomised controlled trials around the world, this debate has traditionally centred on the concept of economic-environmental trade-offs, of which existence is theoretically assured when resource allocation is perfect on the farm. Recent research conducted on commercial farms indicates, however, that the economic-environmental nexus is not nearly as straightforward in the real world, with environmental performances of enterprises often positively correlated with their economic profitability. Using high-resolution primary data from the North Wyke Farm Platform, an intensively instrumented farm-scale ruminant research facility located in southwest United Kingdom, this paper proposes a novel, information-driven approach to carry out comprehensive assessments of economic-environmental trade-offs inherent within pasture-based cattle and sheep production systems. The results of a data-mining exercise suggest that a potentially systematic interaction exists between 'soil health', ecological surroundings and livestock grazing, whereby a higher level of soil organic carbon (SOC) stock is associated with a better animal performance and less nutrient losses into watercourses, and a higher stocking density with greater botanical diversity and elevated SOC. We contend that a combination of farming system-wide trials and environmental instrumentation provides an ideal setting for enrolling scientifically sound and biologically informative metrics for agricultural sustainability, through which agricultural producers could obtain guidance to manage soils, water, pasture and livestock in an economically and environmentally acceptable manner. Priority areas for future farm-scale research to ensure long-term sustainability are also discussed