Precipitation is a key driver of litter decomposition in arid/semiarid regions; where soils are poor in organic matter, and thus re-incorporation of litter is key for soil nutrient accumulation and soil structure. It remains unclear, though, whether litter decomposition responds symmetrically to precipitation variation (e.g., if precipitation surpluses produce a stimulatory effect of a similar magnitude, but opposite direction to inhibitory effects of precipitation deficits), and whether litter decomposition and litter nutrient dynamics in arid and semiarid ecosystems that differ in climate show similar responses to precipitation. We set up a 5-and-a-half-year experiment that manipulated rainfall along a gradient (7 treatments): increases by 20%, 40%, and 60%, background precipitation, and reductions by the same 3 percentages. We applied such experiment in two sites with different pattens of precipitation (Urat: arid; and Naiman: semiarid) in Inner Mongolia to elucidate our questions. Litter mass loss and all nutrients that we measured (carbon, nitrogen, phosphorous, potassium, plus lignin) decomposed faster at the highest level of surplus precipitation, and more slowly in the two largest precipitation reductions. This indicates that these levels of precipitation constitute thresholds (value of precipitation beyond which ecosystem function is critically altered). Litter decomposition in the semiarid site was faster and more complete, but decomposition in the direr Urat was more efficient per unit cumulative rainfall. Thus, site specific effects played an important role in decomposition. Reductions in precipitation decreased the loss of C, N, P, K, and lignin from litter; and clear precipitation thresholds in the dynamic of these nutrients in litter were observed. Overall, this indicated the importance of precipitation limitation at controlling nutrient release. Our study highlights the importance of long-term studies on litter decomposition in environments with slow decomposition rates, and the importance of taking into account mechanistic effects of water availability on decomposition.

The scientific concepts of soil threats (STs) and soil‐related ecosystem services (SESs) are gaining importance and are fueling the debate on natural resources management and decision‐making within the EU. The literature reports numerous assessments of individual STs and SESs at the European scale. However, a comprehensive overview of the patterns emerging from the relationships between STs and SESs is still lacking, which restricts the ability to limit soil degradation and its impact on SESs. In this article, we provide an in‐depth analysis of existing European maps for three STs (soil organic carbon loss, erosion, and compaction) and four SESs (climate regulation and carbon sequestration, hydrological control, biomass production, and erosion control) and the feasibility of combining them to study their relationships. At the EU‐level, 37 maps for these STs and 17 for these SESs were encountered. With the notable exception of erosion, these maps differ considerably in their conceptualization of STs and SESs, and in the indicators, methods, and databases used to assess them. In the current situation, the combination of individual maps of STs and SESs to study their relationships is rarely possible. Besides these limitations, we identify possible combinations and provide recommendations aimed at improving the compatibility between different STs/SESs maps. We conclude that there is a need for a more robust framework for conceptualizing STs/SESs and for systematically and precisely specifying the chosen indicators.

Evidence that plants differ in their ability to take up both organic (ON) and inorganic (IN) forms of nitrogen (N) has increased ecologists’ interest on resource-based plant competition. However, whether plant uptake of IN and ON responds to differences in soil microbial community composition and/or functioning has not yet been explored, despite soil microbes playing a key role in N cycling. Here, we report results from a competition experiment testing the hypothesis that soil microbial communities differing in metabolic activity as a result of long-term differences to grazing exposure could modify N uptake of Eriophorum vaginatum L. and Nardus stricta L. These graminoids co-occur on nutrient-poor, mountain grasslands where E. vaginatum decreases and N. stricta increases in response to long-term grazing. We inoculated sterilised soil with soil microbial communities from continuously grazed and ungrazed grasslands and planted soils with both E. vaginatum and N. stricta, and then tracked uptake of isotopically labelled NH₄⁺ (IN) and glycine (ON) into plant tissues. The metabolically different microbial communities had no effect on N uptake by either of the graminoids, which might suggest functional equivalence of soil microbes in their impacts on plant N uptake. Consistent with its dominance in soils with greater concentrations of ON relative to IN in the soluble N pool, Eriophorum vaginatum took up more glycine than N. stricta. Nardus stricta reduced the glycine proportion taken up by E. vaginatum, thus increasing niche overlap in N usage between these species. Local abundances of these species in mountain grasslands are principally controlled by grazing and soil moisture, although our results suggest that changes in the relative availability of ON to IN can also play a role. Our results also suggest that coexistence of these species in mountain grasslands is likely based on non-equilibrium mechanisms such as disturbance and/or soil heterogeneity.

Soil nutrient buildup is a key process in nutrient-poor arid and semiarid regions. However, our knowledge of the factors that control soil nutrient buildup in these systems is still limited. An experiment was set up and carried out for five and a half years in order to investigate how precipitation and other site factors control soil nutrient buildup. Topsoil carbon (C), nitrogen (N), phosphorus (P), and potassium (K) derived from litter (soil nutrient buildup) were tracked twice a year at two sites differing in terms of climate and soils (Urat: arid and Naiman: semiarid, both in Inner Mongolia). Precipitation was manipulated at both sites to include seven precipitation levels: three reduced levels (−20, −40, and −60% with respect to the background), background (control), and three enhanced levels (+20, +40, and +60% with respect to the background). The dynamic buildup (i.e., amount of nutrients released among consecutive samplings) for all nutrients was controlled by precipitation (nonlinearly), site effects (lower buildup at the site dominated by aeolian pedogenesis), and seasonality (higher under warm conditions). However, the considered nutrients differed in the factor that most determined their buildup. Through studying the concurrent dynamics of litter decomposition and soil nutrient buildup, we can foresee that changes in precipitation and land degradation are most likely to affect the soil nutrient pools in these ecosystems.