Dataset Information

Soil net nitrogen mineralisation across global grasslands.

ABSTRACT: Soil nitrogen mineralisation (N_min), the conversion of organic into inorganic N, is important for productivity and nutrient cycling. The balance between mineralisation and immobilisation (net N_min) varies with soil properties and climate. However, because most global-scale assessments of net N_min are laboratory-based, its regulation under field-conditions and implications for real-world soil functioning remain uncertain. Here, we explore the drivers of realised (field) and potential (laboratory) soil net N_min across 30 grasslands worldwide. We find that realised N_min is largely explained by temperature of the wettest quarter, microbial biomass, clay content and bulk density. Potential N_min only weakly correlates with realised N_min, but contributes to explain realised net N_min when combined with soil and climatic variables. We provide novel insights of global realised soil net N_min and show that potential soil net N_min data available in the literature could be parameterised with soil and climate data to better predict realised N_min.

SUBMITTER: Risch AC

PROVIDER: S-EPMC6823350 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Soil net nitrogen mineralisation across global grasslands.

Risch A C AC Zimmermann S S Ochoa-Hueso R R Schütz M M Frey B B Firn J L JL Fay P A PA Hagedorn F F Borer E T ET Seabloom E W EW Harpole W S WS Knops J M H JMH McCulley R L RL Broadbent A A D AAD Stevens C J CJ Silveira M L ML Adler P B PB Báez S S Biederman L A LA Blair J M JM Brown C S CS Caldeira M C MC Collins S L SL Daleo P P di Virgilio A A Ebeling A A Eisenhauer N N Esch E E Eskelinen A A Hagenah N N Hautier Y Y Kirkman K P KP MacDougall A S AS Moore J L JL Power S A SA Prober S M SM Roscher C C Sankaran M M Siebert J J Speziale K L KL Tognetti P M PM Virtanen R R Yahdjian L L Moser B B

Nature communications 20191031 1

Soil nitrogen mineralisation (Nmin), the conversion of organic into inorganic N, is important for productivity and nutrient cycling. The balance between mineralisation and immobilisation (net Nmin) varies with soil properties and climate. However, because most global-scale assessments of net Nmin are laboratory-based, its regulation under field-conditions and implications for real-world soil functioning remain uncertain. Here, we explore the drivers of realised ( ...[more]

PMID: 31672992

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Project description: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.

Project description:The sustainable use of grasslands in intensive farming systems aims to optimize nitrogen (N) inputs to increase crop yields and decrease harmful losses to the environment at the same time. To achieve this, simple optical sensors may provide a non-destructive, time- and cost-effective tool for estimating plant biomass in the field, considering spatial and temporal variability. However, the plant growth and related N uptake is affected by the available N in the soil, and therefore, N mineralization and N losses. These soil N dynamics and N losses are affected by the N input and environmental conditions, and cannot easily be determined non-destructively. Therefore, the question arises: whether a relationship can be depicted between N fertilizer levels, plant biomass and N dynamics as indicated by nitrous oxide (N₂O) losses and inorganic N levels. We conducted a standardized greenhouse experiment to explore the potential of spectral measurements for analyzing yield response, N mineralization and N₂O emissions in a permanent grassland. Ryegrass was subjected to four mineral fertilizer input levels over 100 days (four harvests) under controlled environmental conditions. The soil temperature and moisture content were automatically monitored, and the emission rates of N₂O and carbon dioxide (CO₂) were detected frequently. Spectral measurements of the swards were performed directly before harvesting. The normalized difference vegetation index (NDVI) and simple ratio (SR) were moderately correlated with an increasing biomass as affected by fertilization level. Furthermore, we found a non-linear response of increasing N₂O emissions to elevated fertilizer levels. Moreover, inorganic N and extractable organic N levels at the end of the experiment tended to increase with the increasing N fertilizer addition. However, microbial biomass C and CO₂ efflux showed no significant differences among fertilizer treatments, reflecting no substantial changes in the soil biological pool size and the extent of the C mineralization. Neither the NDVI nor SR, nor the plant biomass, were related to cumulative N₂O emissions or inorganic N at harvesting. Our results verify the usefulness of optical sensors for biomass detection, and show the difficulty in linking spectral measurements of plant traits to N processes in the soil, despite that the latter affects the former.

Dataset Information

Soil net nitrogen mineralisation across global grasslands.

Publications

Soil net nitrogen mineralisation across global grasslands.

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