Soil net nitrogen mineralisation across global grasslands

Abstract

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 (field) and potential (laboratory) soil net Nmin across 30 grasslands worldwide. We find that realised Nmin is largely explained by temperature of the wettest quarter, microbial biomass, clay content and bulk density. Potential Nmin only weakly correlates with realised Nmin, but contributes to explain realised net Nmin when combined with soil and climatic variables. We provide novel insights of global realised soil net Nmin and show that potential soil net Nmin data available in the literature could be parameterised with soil and climate data to better predict realised Nmin.

Global impacts of fertilization and herbivore removal on soil net nitrogen mineralization are modulated by local climate and soil properties

“…Each site participating in the study received a package containing identical material from the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) to be used for sampling and on-site N incubations. For the field incubation, we followed the protocol by Risch et al (2015Risch et al ( , 2019. Briefly, we drove a 5 × 15 cm (diameter × depth) steel cylinder 13.5 cm deep into the soil after clipping the vegetation at randomized locations in each plot.…”

“…values were scaled to represent daily mineralization rates (mg N kg −1 soil day −1 ; Risch et al, 2015). Realized soil net N min values represent an average period of 42 days prior to peak biomass, typically the highest period of biological activity, and not the entire year (Risch et al, 2019).…”

“…Similarly, fertilization and herbivore removal individually or in combination did not affect microbial extracellular enzyme activities in a Californian grassland (Esch et al, 2013), further emphasizing the variability of results found across studies. (Arnold et al, 2008;Risch et al, 2019). Hence, to predict and estimate how global change drivers such as biodiversity loss, fertilization and climate change, alter the rates of N mineralization in grassland ecosystems, it is important to measure soil N processes in the field and not in the laboratory.…”

“…Reliably estimating soil net N min is not straightforward, and methodological constraints can limit, or even misguide, our understanding of this key process under real-world, field conditions (Arnold, Corre, & Veldkamp, 2008;Makarov, Kuznetsova, Malysheva, Maslov, & Menyailo, 2017;Pinto, Brito, & Coutinho, 2020;Risch et al, 2019).…”

“…Soil N availability is largely determined by the breakdown and depolymerization of organic material to monomers and inorganic N for which plants and microbes compete (Butterbach‐Bahl & Gundersen, 2011; Kuzyakov & Xu, 2013; Mooshammer, Wanek, Zechmeister‐Boltenstern, & Richter, 2014; Schimel & Bennett, 2004). The net balance between N mineralization and immobilization, further referred to as soil net N mineralization (soil net N min ), is largely controlled by soil physical and chemical properties (e.g., clay content, bulk density, pH, carbon (C) and N content), the type and amount of above‐ and belowground organic matter inputs (e.g., plant production), plant and soil microbial composition and activity (release of enzymes, nutrient uptake), and climatic factors (Booth, Stark, & Rastetter, 2005; Conant et al., 2011; Craine, Fierer, & McLauchlan, 2010; Dessureault‐Rompré et al., 2010; Giardina, Ryan, Hubbard, & Binkley, 2001; Giese, Gao, Lin, & Lin, 2011; Risch et al., 2019; Schimel & Bennett, 2004).…”