Nutrient availability controls the impact of mammalian herbivores on soil carbon and nitrogen pools in grasslands

Grasslands are subject to considerable alteration due to human activities globally, including widespread changes in populations and composition of large mammalian herbivores and elevated supply of nutrients. Grassland soils remain important reservoirs of carbon (C) and nitrogen (N). Herbivores may affect both C and N pools and these changes likely interact with increases in soil nutrient availability. Given the scale of grassland soil fluxes, such changes can have striking consequences for atmospheric C concentrations and the climate. Here, we use the Nutrient Network experiment to examine the responses of soil C and N pools to mammalian herbivore exclusion across 22 grasslands, under ambient and elevated nutrient availabilities (fertilized with NPK + micronutrients). We show that the impact of herbivore exclusion on soil C and N pools depends on fertilization. Under ambient nutrient conditions, we observed no effect of herbivore exclusion, but under elevated nutrient supply, pools are smaller upon herbivore exclusion. The highest mean soil C and N pools were found in grazed and fertilized plots. The decrease in soil C and N upon herbivore exclusion in combination with fertilization correlated with a decrease in aboveground plant biomass and microbial activity, indicating a reduced storage of organic matter and microbial residues as soil C and N. The response of soil C and N pools to herbivore exclusion was contingent on temperature – herbivores likely cause losses of C and N in colder sites and increases in warmer sites. Additionally, grasslands that contain mammalian herbivores have the potential to sequester more N under increased temperature variability and nutrient enrichment than ungrazed grasslands. Our study highlights the importance of conserving mammalian herbivore populations in grasslands worldwide. We need to incorporate local-scale herbivory, and its interaction with nutrient enrichment and climate, within global-scale models to better predict land–atmosphere interactions under future climate change.National Science Foundation Research Coordination Network, Long Term Ecological Research, Institute on the Environment, Strategic Resources of the Netherlands Institute of Ecology, Research Foundation Flanders, VENI grant, NWO-RUBICON grant, NWO-VENI grant, German Centre for Integrative Biodiversity Research, German Research Foundation (FZT 118).http://wileyonlinelibrary.com/journal/gcbpm2021Mammal Research InstituteZoology and Entomolog

Nonlinear responses of soil nematode community composition to increasing aridity

Aim: Increasing aridity under global change is predicted to have a profound impact on the structure and functioning of terrestrial ecosystems, yet we have a poor understanding of how belowground communities respond. In order to understand the longer term responses of different trophic levels in the soil food web to increasing aridity, we investigated the abundance, richness and community similarity of the soil nematode community along a 3,200 km aridity gradient. Location: A transect across semi-arid and arid grasslands in Northern China, where the aridity ranges from.43 to.97. Time period: July and August 2012. Major taxa studied: Soil-borne Nematoda. Methods: We used generalized additive (mixed) models to analyse the abundance, richness and community similarity patterns of soil nematodes. We used structural equation modelling (SEM) to disentangle the direct and indirect environmental drivers (aridity, soil and plant variables) of the nematode community. Results: The abundance, richness and similarity of nematode communities declined nonlinearly with increasing aridity. The most pronounced decline in nematode richness and community similarity occurred in arid conditions (aridity >.80). However, the shape of the response to aridity differed among nematode feeding groups. In arid conditions, the abundance and richness of bacterial feeders were less sensitive to changes in aridity than for fungal feeders. The SEM analysis revealed that nematode community responses to aridity were not mediated via changes in plant and soil variables, but instead were affected directly by aridity. Main conclusions: Our results showed that in mesic grasslands, increasing aridity primarily caused a decline in nematode abundance, whereas increasing aridity in xeric grasslands led to a loss of nematode diversity. The nonlinear responses of nematodes to aridity could also result in nonlinear shifts in ecosystem functioning, because soil nematodes operate at various trophic levels in the soil food web, thereby influencing the performance of plants, soil biodiversity and biogeochemical cycling.</p

Influência climática no uso e ocupação do solo do município de Poço Verde/SE

Climatic elements such as precipitation and temperature are essential in agriculture, especially in semi-arid, where is specifically the city of Poço Verde/Se, besides other factors such as economic, social, political and technological. Edaphic constraints represented by pedological composition, comprising the Inceptisols, and Entisols Planosols are conducive to farming, though, need to be corrected, using fertilizer. There, in the city, due to inappropriate areas of outcropping rocks as a result of erosion, resulting from human activities and natural processes. The climate is conceived as dynamic qualitative analysis based on reading Monteiro, and Mendonça Pinto and Oliveira. The dynamic environment is scored on the association between nature and society. In this sense, this paper aims to analyze the relationship between climate conditions and anthropogenic lead in the semiarid area of Poço Verde/ SE, proposing understand the behavior climatic variations of precipitation and extreme events likely, specifically drought, not only a natural phenomenon, but its aspects, political and economic, that affect quality of life. This research method is based on the GTP-geosystem, Planning and Landscape, qualitative and quantitative in nature, the idea of having a holistic view of the paid up space. The methodological procedures outlined that this work were: bibliographic and documentary; fieldwork through secondary and primary data through semi-structured interviews and questionnaires with social actors in thematic mapping system Georeferenced Information Processing in ArcGIS version 9.3. Construction of the water balance method of Thornthwaite & Mather (1955). Quantification and data tabulation, analysis, interpretation and description. It is thus understandable that the precipitation variability is striking and irregular, spatially; presents water deficit. ENOS events play a significant role in the dynamics of rain, the genetic character of climatic anomalies producer, overlapping to human actions, wide effect on the local scale. The occupation of agricultural land dominates the local economy, with the agrarian structure of small farms with maize and beans as main crops, directly linked to rainfall distribution and adapted to the small thermal variation of the Poço Verde tropicality itself. The vegetation consists of the savanna biome and amended its origin. The urban population has more than rural, composed of 21,968 inhabitants. The welfare state develops actions, building wells freshwater and brackish water, dams and water distribution pipes for cars. Drought is one of climatic hazards in the city, classified as seasonal and contingent, which interferes with the local farming and has impact on urban life. There are reports of hail. Thus sertanejos poçoverdenses suffer in the dry season and drought, reflected both in the field and in the city, and there are real correlation between the physical, productive, economic, labor relations and social and public policies.Elementos climáticos, como precipitação e temperatura são essenciais na agricultura, sobretudo no semiárido, onde se localiza especificamente o município de Poço Verde, além de outros fatores como o econômico, social, político e tecnológico. Condicionantes edáficos representados pela composição pedológica, constituída pelos Cambissolos, Planossolos e Neossolos, são propícios para o cultivo agrícola, embora, precisem ser corrigidos, utilizando-se adubação. Existem, no município, áreas impróprias devido ao afloramento das rochas em decorrência, da erosão, resultante de atividades antrópicas e de processos naturais. O clima é concebido como dinâmico na análise qualitativa fundada na leitura de Monteiro, Pinto e Mendonça e Oliveira. A dinâmica ambiental é pontuada na associação entre natureza e sociedade. Nesse sentido, esta dissertação tem como objetivo analisar a relação entre os condicionantes climáticos e as derivações antropogênicas no espaço Semiárido de Poço Verde/SE, propondo compreender, o comportamento climático, suas variações de precipitação e os prováveis eventos extremos, especificamente a seca, não somente como fenômeno natural, mas, em seus aspectos, político e econômico, que interferem na qualidade de vida. Esta pesquisa está fundamentada no método GTP- Geossistema, Território e Paisagem, de natureza quali-quantitativa, pela ideia de se ter uma visão holística integralizada do espaço. Os procedimentos metodológicos que delinearam este trabalho foram: levantamento bibliográfico e documental; pesquisa de campo mediante dados secundários e primários, através de entrevistas semi-estruturadas e questionários com atores sociais; elaboração de mapas temáticos no Sistema de Processamento de Informações Georreferenciadas na versão do ArcGis 9.3. Construção do balanço hídrico pelo método de Thornthwaite & Mather (1955). Quantificação e tabulação de dados, análise, interpretação e descrição. Compreende-se assim, que a variabilidade de precipitação é marcante e irregular, espacialmente; apresenta déficit hídrico. Eventos de ENOS exercem papel significativo na dinâmica pluvial, pelo caráter genético produtor de anomalias climáticas, sobrepondo-se às ações antrópicas, de efeito amplo na escala local. A ocupação do solo agrícola domina a economia local, com estrutura fundiária de minifúndios, tendo o milho e o feijão como principais cultivos, vinculados diretamente à distribuição pluvial e adaptados à pequena variação térmica da tropicalidade de Poço Verde-SE. A cobertura vegetal é constituída pelo bioma caatinga, bem alterado em sua origem. O espaço urbano apresenta população superior a rural, composta de 21.968 habitantes. O Estado desenvolve ações assistencialistas, construindo poços tubulares de água doce e de água salobra, barragens e distribuição de água por carros pipas. A seca é um dos azares climáticos no município, classificada como sazonal e contingente, que interfere na agropecuária local e tem repercussão na vida urbana. Há registro de chuva de granizo. Assim, os sertanejos poçoverdenses sofrem no período de estiagem e seca, com reflexos tanto no campo quanto na cidade, sendo que há correlação real entre os elementos físicos, produtivos, econômicos, relações de trabalho e sociais e as políticas públicas

Applying the aboveground-belowground interaction concept in agriculture: Spatio-temporal scales matter

Interactions between aboveground and belowground organisms are important drivers of plant growth and performance in natural ecosystems. Making practical use of such above-belowground biotic interactions offers important opportunities for enhancing the sustainability of agriculture, as it could favor crop growth, nutrient supply, and defense against biotic and abiotic stresses. However, the operation of above-and belowground organisms at different spatial and temporal scales provides important challenges for application in agriculture. Aboveground organisms, such as herbivores and pollinators, operate at spatial scales that exceed individual fields and are highly variable in abundance within growing seasons. In contrast, pathogenic, symbiotic, and decomposer soil biota operate at more localized spatial scales from individual plants to patches of square meters, however, they generate legacy effects on plant performance that may last from single to multiple years. The challenge is to promote pollinators and suppress pests at the landscape and field scale, while creating positive legacy effects of local plant-soil interactions for next generations of plants. Here, we explore the possibilities to improve utilization of above-belowground interactions in agro-ecosystems by considering spatio-temporal scales at which aboveground and belowground organisms operate. We identified that successful integration of above-belowground biotic interactions initially requires developing crop rotations and intercropping systems that create positive local soil legacy effects for neighboring as well subsequent crops. These configurations may then be used as building blocks to design landscapes that accommodate beneficial aboveground communities with respect to their required resources. For successful adoption of above-belowground interactions in agriculture there is a need for context-specific solutions, as well as sound socio-economic embedding.</p