[Effect of seasonal distribution in precipitation on soil nitrogen mineralization in a subtropical forest]

Soil N mineralization is a key process of nutrient cycling in ecosystems. The mechanism of the seasonal distribution of precipitation on soil N mineralization remains unclear. We conducted a precipitation manipulation experiment in a subtropical forest in the middle and lower reaches of the Yangtze River in China from 2020 to 2022, with three treatments, including control (CK), decreased precipitation in the dry season with extremely increased precipitation in the wet season (T1), and decreased precipitation in the dry season with proportionally increased precipitation in the wet season (T2). With in situ resin core method, we explored the effect of seasonal distribution of precipitation on soil N mineralization. The results showed that T1 and T2 significantly decreased dry season net nitrification rate by 57.9% and 72.5% and the net N mineralization rate by 82.5% and 89.6%, respectively, and significantly increased wet season net nitrification rate by 64.3% and 79.5% and net N mineralization rate by 64.2% and 81.1%, respectively. Proportionally increased precipitation in the wet season was more conducive to soil N mine-ralization process than extremely increased precipitation in the wet season. Results of the structural equation model showed that change in seasonal distribution of precipitation could significantly affect soil N mineralization processes in the subtropical forest by changing soil water content, ammonium nitrogen, microbial biomass nitrogen, and soil C:N. Our results had important reference for understanding soil nitrogen cycling and other ecological processes, and were conducive to more accurate assessment on the impacts of future changes in seasonal precipitation pattern on subtropical forest ecosystems.

Responses of terrestrial ecosystem productivity and community structure to intra-annual precipitation patterns: A meta-analysis

INTRODUCTION

The productivity and community structures of terrestrial ecosystems are regulated by total precipitation amount and intra-annual precipitation patterns, which have been altered by climate change. The timing and sizes of precipitation events are the two key factors of intra-annual precipitation patterns and potentially drive ecosystem function by influencing soil moisture. However, the generalizable patterns of how intra-annual precipitation patterns affect the productivity and community structures of ecosystems remain unclear.

METHODS

We synthesized 633 observations from 17 studies and conducted a global meta-analysis to investigate the influences of intra-annual precipitation patterns on the productivity and community structures of terrestrial ecosystems. By classifying intra-annual precipitation patterns, we also assess the importance of the magnitude and timing of precipitation events on plant productivity.

RESULTS

Our results showed that the intra-annual precipitation patterns decreased diversity by 6.3% but increased belowground net primary productivity, richness, and relative abundance by 16.8%, 10.5%, and 45.0%, respectively. Notably, we found that the timing uniformity of precipitation events was more important for plant productivity, while the plant community structure benefited from the increased precipitation variability. In addition, the relationship between plant productivity and community structure and soil moisture dynamic response was more consistent with the nonlinear model.

COMCLUSIONS

The patterns of the responses of plant productivity and community structure to altered intra-annual precipitation patterns were revealed, and the importance of the timing uniformity of precipitation events to the functioning of production systems was highlighted, which is essential to enhancing understanding of the structures and functions of ecosystems subjected to altered precipitation patterns and predicting their changes.

[Effect of long-term fertilization on winter wheat yield from the dry land under different precipitation patterns]

Based on 30 years long-term fertilization experiment on the semiarid Loess Plateau in China, we studied the effect of different fertilizer treatments on the winter wheat yield, fertilizer contribution rate (FCR) and precipitation use efficiency (PUE) in different precipitation years (drought, normal and wet years). The result showed that the wheat yield, FCR and PUE were significantly higher in nitrogen + phosphorus (NP) and nitrogen + phosphorus +potassium (NPK) treatments than in control (CK) and phosphorus (P) treatments when winter wheat was planted for 30 consecutive years. The wheat yield, FCR and PUE in NPK treatment were highest, with values of 3480 kg·hm^-2, 61.45 kg·kg^-1 and 6.13 kg·mm^-1·hm^-2, respectively, and those in the wet years were higher than in drought and normal years. The stepwise regression analysis showed that wheat yield was mainly influenced by the amount of nitrogen, phosphorus input and precipitation during fallow period and wintering period. Accordingly, increasing nitrogen and phosphorus input accompanying with potassium and water conservation practices during the fallow period could improve the wheat yield on the semiarid Loess Plateau in China.

Nitrogen supply modulates the effect of changes in drying-rewetting frequency on soil C and N cycling and greenhouse gas exchange

Climate change and atmospheric nitrogen (N) deposition are two of the most important global change drivers. However, the interactions of these drivers have not been well studied. We aimed to assess how the combined effect of soil N additions and more frequent soil drying-rewetting events affects carbon (C) and N cycling, soil:atmosphere greenhouse gas (GHG) exchange, and functional microbial diversity. We manipulated the frequency of soil drying-rewetting events in soils from ambient and N-treated plots in a temperate forest and calculated the Orwin & Wardle Resistance index to compare the response of the different treatments. Increases in drying-rewetting cycles led to reductions in soil NO3- levels, potential net nitrification rate, and soil : atmosphere GHG exchange, and increases in NH4+ and total soil inorganic N levels. N-treated soils were more resistant to changes in the frequency of drying-rewetting cycles, and this resistance was stronger for C- than for N-related variables. Both the long-term N addition and the drying-rewetting treatment altered the functionality of the soil microbial population and its functional diversity. Our results suggest that increasing the frequency of drying-rewetting cycles can affect the ability of soil to cycle C and N and soil : atmosphere GHG exchange and that the response to this increase is modulated by soil N enrichment.

Contrasting above- and belowground sensitivity of three Great Plains grasslands to altered rainfall regimes

Intensification of the global hydrological cycle with atmospheric warming is expected to increase interannual variation in precipitation amount and the frequency of extreme precipitation events. Although studies in grasslands have shown sensitivity of aboveground net primary productivity (ANPP) to both precipitation amount and event size, we lack equivalent knowledge for responses of belowground net primary productivity (BNPP) and NPP. We conducted a 2-year experiment in three US Great Plains grasslands--the C4-dominated shortgrass prairie (SGP; low ANPP) and tallgrass prairie (TGP; high ANPP), and the C3-dominated northern mixed grass prairie (NMP; intermediate ANPP)--to test three predictions: (i) both ANPP and BNPP responses to increased precipitation amount would vary inversely with mean annual precipitation (MAP) and site productivity; (ii) increased numbers of extreme rainfall events during high-rainfall years would affect high and low MAP sites differently; and (iii) responses belowground would mirror those aboveground. We increased growing season precipitation by as much as 50% by augmenting natural rainfall via (i) many (11-13) small or (ii) fewer (3-5) large watering events, with the latter coinciding with naturally occurring large storms. Both ANPP and BNPP increased with water addition in the two C4 grasslands, with greater ANPP sensitivity in TGP, but greater BNPP and NPP sensitivity in SGP. ANPP and BNPP did not respond to any rainfall manipulations in the C3 -dominated NMP. Consistent with previous studies, fewer larger (extreme) rainfall events increased ANPP relative to many small events in SGP, but event size had no effect in TGP. Neither system responded consistently above- and belowground to event size; consequently, total NPP was insensitive to event size. The diversity of responses observed in these three grassland types underscores the challenge of predicting responses relevant to C cycling to forecast changes in precipitation regimes even within relatively homogeneous biomes such as grasslands.