Hydrothermal conditions determine soil potential net N mineralization

 rates in arid and semi-arid grasslands

作者：Shuya Hu1,2, Changhui Wang1,3*, Anita C Risch4, Yuan Liu5, Yang Li1,2, Lei Li1,2, Xiaohui Xu1,2, Nianpeng He2, 5, Xingguo Han1,2, Jianhui Huang1,2*

期刊：Functional Ecology

出版年份：2022

Abstract：

1. Soil net nitrogen (N) mineralization is a key biogeochemical process influencing plant available N and net primary productivity (NPP) in terrestrial ecosystems. However, the spatial variations and controlling factors of soil net N mineralization (RPNM) in arid and semi-arid grasslands are less studied and unclear.

2. In this study, we investigated the soil RPNM by performing a laboratory incubation experiment. Soil samples were collected from 30 sites in three east-west transects on the Inner Mongolia Plateau (MP), Loess Plateau (LP), and Tibetan Plateau (TP) along a 3,200 km arid and semi-arid grassland gradient, with each transect containing three different grassland types (meadow steppe, typical steppe, and desert steppe, respectively).

3. Results showed that the average RPNM values ranged from -0.37 to 1.29 mg N kg–1 d– 1, with a significantly lower RPNM found in the desert steppe (0.08 ± 0.01 mg N kg–1 d–1) compared with those in the meadow steppe (0.30 ± 0.03 mg N kg–1 d–1) and in the typical steppe (0.33 ± 0.03 mg N kg–1 d–1) in the MP and LP transects (p < 0.05). This difference could be explained by variations in climatic and soil factors, such as hydrothermal index (HT), the soil pH, soil organic matter (SOM) and precipitation. However, no significant differences in RPNM were found among different grassland types in the TP transect, possibly due to the similarly low microbial activity, as indicated by the MBC values. Across all three grassland transects, HT, SOM, and microbial variables were the major factors controlling RPNM, which together explained 20.7% of the variation in RPNM. Further SEM analysis indicated HT was an ntegral predictor of RPNM, directly or indirectly via SOM, under different conditions of precipitation and temperature.

4. Our findings provide field evidence and parameters for biogeochemical cycling to better predict future N transformation processes under changing precipitation and temperature regimes across a wide range of arid and semi-arid grassland ecosystems.

Conclusions：

This is the first study to quantify the net N mineralization (RPNM) from different grassland transects across a large range of arid- and semi-arid grasslands of the Eurasian steppe. RPNM showed significant differences among different grassland types and transects, mainly due to the differences in the major ecological factors that singly orjointly affect the N transformation processes. Specifically, HT was found to be a key index that explained the majority of variance of RPNM across the arid and semi-arid grasslands while soil physical and chemical properties directly explained the RPNM at local scales. Taken together, our findings imply that the HT index that incorporates both MAT and MAT can be applied to biogeochemical models to more accurately forecast the future N dynamics under the scenario of a warmer and drier climate in arid and semi-arid regions.

  全文链接：doi:10.1111/1365-2435.14167