Microbial carbon mineralization in tropical lowland and montane forest soils of Peru

Climate change is affecting the amount and complexity of plant inputs to tropical forest soils. This is likely to influence the carbon (C) balance of these ecosystems by altering decomposition processes e.g., "positive priming effects" that accelerate soil organic matter mineralization. However, the mechanisms determining the magnitude of priming effects are poorly understood. We investigated potential mechanisms by adding (13)C labeled substrates, as surrogates of plant inputs, to soils from an elevation gradient of tropical lowland and montane forests. We hypothesized that priming effects would increase with elevation due to increasing microbial nitrogen limitation, and that microbial community composition would strongly influence the magnitude of priming effects. Quantifying the sources of respired C (substrate or soil organic matter) in response to substrate addition revealed no consistent patterns in priming effects with elevation. Instead we found that substrate quality (complexity and nitrogen content) was the dominant factor controlling priming effects. For example a nitrogenous substrate induced a large increase in soil organic matter mineralization whilst a complex C substrate caused negligible change. Differences in the functional capacity of specific microbial groups, rather than microbial community composition per se, were responsible for these substrate-driven differences in priming effects. Our findings suggest that the microbial pathways by which plant inputs and soil organic matter are mineralized are determined primarily by the quality of plant inputs and the functional capacity of microbial taxa, rather than the abiotic properties of the soil. Changes in the complexity and stoichiometry of plant inputs to soil in response to climate change may therefore be important in regulating soil C dynamics in tropical forest soils.This study was financed by the UK Natural Environment Research Council (NERC) grant NE/G018278/1 and is a product of the Andes Biodiversity and Ecosystem Research Group consortium (www.andesconservation.org); Patrick Meir was also supported by ARC FT110100457

Grassland biodiversity restoration increases resistance of carbon fluxes to drought

Evidence suggests that the restoration of plant diversity in grasslands not only brings benefits for biodiversity conservation, but also the delivery of ecosystem services. While biodiversity-function experiments show that greater plant diversity increases resistance of plant productivity to climate extremes, it is not known whether real-world management options for grassland restoration likewise stabilize ecosystem responses to extreme climate events. We used a long-term (23 year) field experiment in northern England to test the hypothesis that management aimed at biodiversity restoration increases the resistance and recovery of ecosystem carbon (C) fluxes to short-term summer drought. This was tested by measuring plant, soil and microbial responses to a simulated drought in experimental grassland plots where fertilizer application and seed addition have been managed to enhance plant species diversity. The cessation of fertilizer application brought about small increases in plant species richness. Additionally, cessation of fertilizer application reduced overall plant productivity and promoted hemi-parasitic plants at the expense of grasses and forbs. Resistance of CO 2 fluxes to drought, measured as ecosystem respiration, was greater in non-fertilized plots, as lower plant biomass reduced water demand, likely aided by proportionally more hemi-parasitic plants further reducing plant biomass. Additionally, legumes increased under drought, thereby contributing to overall resistance of plant productivity. Recovery of soil microbial C and nitrogen was more rapid after rewetting than soil microbial community composition, irrespective of restoration treatment, suggesting high resilience of soil microbial communities to drought. Synthesis and applications. This study shows that while grassland diversity restoration management increases the resistance of carbon fluxes to drought, it also reduces agricultural yields, revealing a trade-off for land managers. Furthermore legumes, promoted through long-term restoration treatments, can help to maintain plant community productivity under drought by increasing their biomass. As such, grassland management strategies not only have consequences for ecosystem processes, but also the capacity to withstand extreme weather events

Biological Interactions in Grassland Soils and Productivity

This paper describes research on interactions between grassland plant species and soil microorganisms. Both parasitic and symbiotic microorganisms modify nutrient transfers between plants and soil. Experiments are described in which nematode infection of clover increased nitrogen transfer to companion ryegrass plants. Infection of clover enhanced activity of soil bacterial and fungal communities. Legume genotypes differing only in responses to symbionts (rhizobium and arbuscular mycorrhizal fungi) and pathogens are being developed for studies of gene expression during establishing and functional symbioses. Such plants can be used in experiments as defined perturbations that will provide information on the interactions and functions of symbiotic and pathogenic microorganisms. Such studies, related to field observations, may have value for defining biological attributes of sustainable grassland soil systems

Contrasting Impacts of Grazing on Soil Properties and Plant Communities between Semiarid and Temperate Rangeland Ecosystems

We discuss how grazing by large herbivores as a land use option does not necessarily involve a trade-off in terms of soil carbon (C) storage, by presenting results from field grazing gradient experiments from rangeland ecosystems under different climatic conditions in semiarid grasslands from Central Mexico and temperate ecosystems from Northern England. In general, moderate grazing pressure did not reduce soil C in both ecosystems after comparisons with long-term grazing exclusions, and moderate grazing even showed higher soil C in the semiarid area. In the semiarid area, our results are likely explained by grazing tolerance of plant species in moderate grazing pressure, and by effects of herbivores on plant community structure and proportion of bare soil in heavy grazing pressure. In the temperate area, C losses might be more linked to temperature-limitation on heterotrophic soil C respiration. Our results indicate that moderate grazing is compatible with soil C storage, although we also provide warnings against this generalisation under scenarios of climate warming

Contrasting environmental preferences of photosynthetic and non‐photosynthetic soil cyanobacteria across the globe

Aim: Cyanobacteria have shaped the history of life on Earth and continue to play important roles as carbon and nitrogen fixers in terrestrial ecosystems. However, their global distribution and ecological preferences remain poorly understood, particularly for two recently discovered non‐photosynthetic cyanobacterial classes (Sericytochromatia and Melainabacteria). Location: Two hundred and thirty‐seven locations across six continents encompassing multiple climates (arid, temperate, tropical, continental and polar) and vegetation types (forests, grasslands and shrublands). Time period: Sampling was carried out between 2003 and 2015. Major taxa studied: Photosynthetic and non‐photosynthetic cyanobacterial taxa. Methods: We conducted a field survey and used co‐occurrence network analysis and structural equation modelling to evaluate the distribution and environmental preferences of soil cyanobacteria across the globe. These ecological preferences were used to create a global atlas (predictive distribution maps) of soil cyanobacteria. Results: Network analyses identified three major groups of cyanobacterial taxa, which resembled the three main cyanobacterial classes: the photosynthetic Oxyphotobacteria‐dominated cluster, which were prevalent in arid and semi‐arid areas, and the non‐photosynthetic Sericytochromatia‐ and Melainabacteria‐dominated clusters, which preferred hyper‐arid oligotrophic and acidic/humid environments, respectively. Main conclusions: This study provides new insights into the environmental preferences of non‐photosynthetic cyanobacteria in soils globally. Our findings highlight the contrasting environmental preferences among the three clusters of cyanobacteria and suggest that alterations in environmental conditions linked to climate change might result in important changes in the ecology and biogeography of these functionally important microorganisms.M.D.-B. is supported by a Ramón y Cajal grant from the Spanish Ministry of Science and Innovation (RYC2018-025483-I), and by the BES grant agreement No LRB17\1019 (MUSGONET). The work of C.C.-D. and F.T.M. and the global drylands database were supported by the European Research Council [ERC Grant Agreements 242658 (BIOCOM) and 647038 (BIODESERT)] and by the Spanish Ministry of Economy and Competitiveness (BIOMOD project, ref. CGL2013-44661-R). F.T.M. acknowledges support from Generalitat Valenciana (BIOMORES project, ref. CIDEGENT/2018/041). Research on biodiversity by B.K.S. is supported by the Australian Research Council (DP170104634). R.D.B. was supported by the U.K. Department of Environment, Food and Rural Affairs (DEFRA) project no. BD5003 and a Biotechnology and Biological Sciences Research Council (BBSRC) International Exchange Grant (BB/L026406/1)

Historical context modifies plant diversity–community productivity relationships in alpine grassland

While most studies yield positive relationships between biodiversity (B) and ecosystem functioning (EF), awareness is growing that BEF relationships can vary with ecological context. The awareness has led to increased efforts to understand how contemporary environmental context modifies BEF relationships, but the role of historical context, and the mechanisms by which it may influence biodiversity effects, remains poorly understood. We examined how historical context alters plant diversity–community productivity relationships via plant species interactions in alpine grassland. We also tested how historical context modifies interactions between plants and arbuscular mycorrhizal (AM) fungi, which can potentially mediate the above processes. We studied biodiversity effects on plant community productivity at two grassland sites with different histories related to grazing intensity—heavy versus light livestock grazing—but similar current management. We assembled experimental communities of identical species composition with plants from each of the two sites in disturbed soil from a contemporary heavily grazed grassland, ranging in species richness from one to two, three and six species. Moreover, we carried out a mycorrhizal hyphae-exclusion experiment to test how plant interactions with AM fungi influence plant responses to historical context. We detected a significantly positive diversity–productivity relationship that was driven by complementarity effects in communities composed of plants from the site without heavy-grazing history, but no such relationship in plant communities composed of plants from the site with heavy-grazing history. Plants from the site with heavy-grazing history had increased competitive ability and increased yields in low-diversity communities but disrupted complementarity effects in high-diversity communities. Moreover, plants of one species from the site with heavy-grazing history benefitted more from AM fungal communities than did plants from the site without such history. Synthesis. Using the same experimental design and species, communities assembled by plants from two sites with different historical contexts showed different plant diversity–community productivity relationships. Our results suggest that historical context can alter plant diversity–community productivity relationships via plant species interactions and potentially plant–soil interactions. Therefore, considering historical contexts of ecological communities is of importance for advancing our understanding of long-term impacts of anthropogenic disturbance on ecosystem functioning

Relationships between plant traits, soil properties and carbon fluxes differ between monocultures and mixed communities in temperate grassland

1. The use of plant traits to predict ecosystem functions has been gaining growing attention. Above‐ground plant traits, such as leaf nitrogen (N) content and specific leaf area (SLA), have been shown to strongly relate to ecosystem productivity, respiration and nutrient cycling. Furthermore, increasing plant functional trait diversity has been suggested as a possible mechanism to increase ecosystem carbon (C) storage. However, it is uncertain whether below‐ground plant traits can be predicted by above‐ground traits, and if both above‐ and below‐ground traits can be used to predict soil properties and ecosystem‐level functions. 2. Here, we used two adjacent field experiments in temperate grassland to investigate if above‐ and below‐ground plant traits are related, and whether relationships between plant traits, soil properties and ecosystem C fluxes (i.e. ecosystem respiration and net ecosystem exchange) measured in potted monocultures could be detected in mixed field communities. 3. We found that certain shoot traits (e.g. shoot N and C, and leaf dry matter content) were related to root traits (e.g. root N, root C:N and root dry matter content) in monocultures, but such relationships were either weak or not detected in mixed communities. Some relationships between plant traits (i.e. shoot N, root N and/or shoot C:N) and soil properties (i.e. inorganic N availability and microbial community structure) were similar in monocultures and mixed communities, but they were more strongly linked to shoot traits in monocultures and root traits in mixed communities. Structural equation modelling showed that above‐ and below‐ground traits and soil properties improved predictions of ecosystem C fluxes in monocultures, but not in mixed communities on the basis of community‐weighted mean traits. 4. Synthesis. Our results from a single grassland habitat detected relationships in monocultures between above‐ and below‐ground plant traits, and between plant traits, soil properties and ecosystem C fluxes. However, these relationships were generally weaker or different in mixed communities. Our results demonstrate that while plant traits can be used to predict certain soil properties and ecosystem functions in monocultures, they are less effective for predicting how changes in plant species composition influence ecosystem functions in mixed communities