Mass loss and nutrient release during litter decomposition drive biogeochemical cycling in terrestrial ecosystems. However, the relationship between the litter decomposition process and the decomposition stage, precipitation, and litter quality has rarely been addressed, precluding our understanding of how litter decomposition regulates nutrient cycling in various ecosystems and their responses to climate change. In this study, we measured mass loss as well as carbon and nutrient releases during the decomposition of 16 types of leaf litter under three precipitation treatments over 12 months in a common garden experiment (i.e., using standardized soil and climatic conditions). Sixteen types of leaves were divided into three functional groups (evergreen, deciduous, and herbaceous). The objectives were to understand the effects of decomposition stages and precipitation regimes on litter decomposition and to examine the relationship between this effect and chemical properties. The mass loss and release of nitrogen and potassium were significantly higher in the 6‐ to 12‐month stage of decomposition (high temperature and humidity) than in the 0‐ to 6‐month stage. Phosphorus was relatively enriched in evergreen leaves after 6 months of decomposition. The rates of mass loss and nutrient release were significantly greater in herbaceous than in deciduous and evergreen leaves. Increasing precipitation from 400 to 800 mm accelerated mass loss and potassium release but decreased phosphorus release in the 0‐ to 6‐month stage of decomposition. These results highlighted the contribution to and complexity of litter chemical properties in litter decomposition.

The distribution and turnover of organic carbon (OC) and nitrogen (N) associated with aggregates in soils is critical for understanding the behaviour of C and N in soils. We collected soil samples from aspen (Populus simonii Carr.) woodland in the semi-arid Loess Plateau of China to investigate the distribution of aggregate-associated OC and N. The distribution of aggregates and aggregate-associated OC and N were measured, and OC and N stocks in each aggregate fraction were calculated. Across the sites and soil depths, microaggregates and the silt + clay fraction dominated the distribution of soil aggregates, which varied with site. Organic C and N accumulated mainly in the macro- and micro-aggregate fractions in loamy soils but in the silt + clay fractions in sandy soils. The OC and N stocks in the bulk soil of aspen woodland were determined by the OC and N stocks associated with silt + clay fraction. The results of this study indicate that soil texture may play an important role in assessing the distributions of soil OC and N in both bulk soils and aggregate size fractions in aspen woodland, especially in semi-arid regions. Furthermore, the establishment of aspen woodland would result in greater accumulation of OC and N in loam soils than in sandy soils.

Carbon dioxide (CO₂) flux provides feedback between C cycling and the climatic system. There is considerable uncertainty regarding the direction and magnitude of the responses of this process to precipitation changes, hindering accurate prediction of C cycling in a changing world. We examined the responses of ecosystem CO₂ flux to ambient precipitation and experimentally decreased (−35%) and increased precipitation (+20%) in a semiarid grassland in China between July 2013 and September 2015. The measured CO₂ flux components included the gross ecosystem productivity (GEP), net ecosystem CO₂ exchange (NEE), ecosystem respiration (Re), and soil respiration (Rs). The results showed that the seasonal and diurnal patterns of most components of ecosystem CO₂ flux were minimally affected by precipitation treatments, with less than 4% changes averaged across the three growing seasons. GEP and NEE had a quadratic relationship, while Re and Rs increased exponentially with soil temperature. GEP, RE, and Rs, however, decreased with soil moisture. Decreased precipitation reduced the dependence of CO₂ flux on soil temperature but partly increased the dependence on soil moisture; in contrast, increased precipitation had the opposite influence. Our results suggested a relatively stable CO₂ flux in this semiarid grassland across the tested precipitation regimes.

Currently, we lack a clear understanding of how climate influences the responses of soil organic carbon (OC) and nitrogen (N) to land-use changes in semiarid regions. Thus, to clarify the mechanisms involved, we measured the soil OC and total N (TN) concentrations and stocks in the 0–100 cm soil layer in adjacent grassland, farmland, and woodland at five sites on the Loess Plateau in China, which varied in terms of the mean annual precipitation (MAP) and mean annual temperature (MAT). The farmland or woodland was converted from grassland at each site. Conversion of grassland to farmland significantly reduced the soil OC and TN, with greater decreases in sites with relatively lower MAP and MAT (–0.60 Mg OC ha⁻¹yr⁻¹ and –0.22 Mg TN ha⁻¹yr⁻¹, respectively) than sites with relatively higher MAP and MAT (–0.35 Mg OC ha⁻¹yr⁻¹ and –0.04 Mg TN ha⁻¹yr⁻¹). Conversion of grassland to woodland increased OC and TN at sites with higher MAP and MAT, but decreased them at sites with lower MAP and MAT. OC and TN increased to a depth of 100 cm with MAP and MAT after this land-use change. OC and TN decreased at relatively drier and colder sites, but increased at relatively wetter and warmer sites. These findings provide insights into the effects of land-use changes on the soil OC and TN under different climate conditions, thereby facilitating the sustainable management of grasslands in semiarid regions.

Plant litter decomposition figures importantly in the cycling of C and N pools in terrestrial ecosystems. We investigated how C and N fluxes changed during the decomposition of leguminous and non-leguminous leaf litters, and how these processes responded to different precipitation regimes. We used the dual-isotope tracing method to investigate differences in leaf and soil C and N, along with δ¹³C and δ¹⁵N, in the soil of the Loess Plateau in China. The δ¹⁵N and δ¹³C values were 3604‰ and 56‰ for Robinia pseudoacacia (Leguminosae) and 8115‰ and 452‰ for Populus tomentosa (Salicaceae) leaf litters. Through decomposition, δ¹³C decreased in all litters, and δ¹⁵N in the leguminous litter increased while it decreased in the non-leguminous litter. In the surface soil, the fraction of litter-derived N (14%) from the leguminous litter was significantly higher than that of the non-leguminous litter after 16 months. The C and N concentrations of both litters and soil always had a positive correlation during decomposition, and the responses of N to C changes in soil were reduced by the litter cover. Increased precipitation enhanced the litters’ C and N correlation. The 600 mm precipitation treatment most benefited litter C’s transformation to SOC, and drought conditions promoted the transformation of legume litter N to soil TN, but inhibited non-legume litter N. In the soil and both litters, C and N changes always had a positive correlation. After 16 months, the proportion of soil N from legumes was higher than that from non-legumes. Reduced precipitation could promote leguminous N in soil. Our results provide a scientific basis for accurately predicting the C and N cycles in terrestrial ecosystems.