Spatial patterns and determinants of soil organic carbon component contents and decomposition rate in temperate grasslands of Nei Mongol, China

doi:10.17521/cjpe.2023.0028

Abstract

Abstract:

Aims Grassland is an important component of terrestrial ecosystems around the world and plays an important role in terrestrial carbon cycling. However, large uncertainties still exist in predictions of soil organic carbon (SOC) dynamics in grassland ecosystems using earth system models, partly due to an inadequate understanding of the spatial patterns and drivers of soil carbon components and the rate of decomposition. In this study, we explored the determinants of the contents of total SOC and its components as well as the rate of soil carbon decomposition in the topsoil of temperate grasslands of Nei Mongol.
Methods Soil samples at depths of 0-10 cm were collected during July to August 2015 from field sites on the Nei Mongol Plateau. We measured the contents of total SOC and its partitioning in three soil aggregate size-classes, and the decomposition rate based on laboratory incubation. In addition, we acquired a suite of explanatory factors including climatic, edaphic, vegetation, and mineral variables. Variance partitioning analyses were then used to investigate the relative importance of the four factors in affecting the contents of total SOC, aggregate-classified carbon fractions and soil carbon decomposition rate.
Important findings The contents of total SOC and three carbon fractions displayed an increasing trend from southwest to northeast of the study area, while soil carbon decomposition rate (standardized by SOC) showed a reverse trend. The carbon contents in bulk soil and different aggregate fractions are highest in the meadow steppe, followed by the typical steppe and the desert steppe; whereas soil carbon decomposition rate (standardized by SOC) was highest in the desert steppe, followed by the typical steppe and the meadow steppe. The spatial variations of carbon contents in the three soil aggregate fractions were mainly driven by climatic and mineral factors, with finer soil particles attaching greater relative importance in the effect by the mineral factor. The soil carbon decomposition rate (standardized by SOC) was affected by mineral, edaphic, and climatic factors. These findings highlight the importance of considering the differential influences by minerals in different soil aggregate carbon fractions, particularly the silt- and clay-associated carbon in the Earth system models, so as to improve the accuracy in the prediction of SOC dynamics in grassland ecosystems under changing environment.

Key words: soil organic carbon, carbon fractions, carbon decomposition, mineral, temperate grasslands

CHEN Ying-Jie, FANG Kai, QIN Shu-Qi, GUO Yan-Jun, YANG Yuan-He. Spatial patterns and determinants of soil organic carbon component contents and decomposition rate in temperate grasslands of Nei Mongol, China[J]. Chin J Plant Ecol, 2023, 47(9): 1245-1255.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2023.0028

https://www.plant-ecology.com/EN/Y2023/V47/I9/1245

Figures/Tables 5

Fig. 1 Spatial distributions of total soil organic carbon (C) content (A) and in three fractions content (B-D) in temperate grasslands of Nei Mongol. The vegetation map was obtained from China’s vegetation atlas with a scale of 1:1 000 000 (The Editorial Committee of Vegetation Map of China, Chinese Academy of Sciences, 2001). The lines, lower and upper boundaries, and bars in the boxes show median values, 25th and 75th percentiles, and standard deviations of all data, respectively. Different lowercase letters denote significant differences among different grassland types (p < 0.05). DS, desert steppe; MS, meadow steppe; TS, typical steppe.

Fig. 2 Spatial distribution of soil carbon (C) decomposition rate standardized by soil organic C (OC) in temperate grasslands of Nei Mongol (A), and comparison of soil C decomposition rate among different grassland types (B). The vegetation map was obtained from China’s vegetation atlas with a scale of 1:1 000 000 (The Editorial Committee of Vegetation Map of China, Chinese Academy of Sciences, 2001). The lines, lower and upper boundaries, and bars in the boxes show median values, 25th and 75th percentiles, and standard deviations of all data, respectively. Different lowercase letters denote significant differences among different grassland types (p < 0.05). DS, desert steppe; MS, meadow steppe; TS, typical steppe.

Fig. 3 Comparison of organic carbon (C) contents among different soil aggregate fractions in temperate grasslands of Nei Mongol. The lines, lower and upper boundaries, and bars in the boxes show median values, 25th and 75th percentiles, and standard deviations of all data, respectively. Different lowercase letters denote significant differences of C fractions among different grassland types (p < 0.05).

Fig. 4 Correlations of total soil organic carbon (C) content, C content in different aggregate fractions and C decomposition rate with climatic, edaphic, plant and mineral variables in temperate grasslands of Nei Mongol. Soil organic C, macroaggregate C, microaggregate C, silt and clay C, and C decomposition rate standardized by SOC are lg transformed. The “+” and “-” in parentheses represent positive and negative correlations, respectively. AGB, aboveground biomass; AI, aridity index; CaExch, exchangeable Ca2+; Clay + silt, clay and silt content; Feo + Alo, poorly crystalline Fe/Al oxide; Fep + Alp, organically complexed Fe/Al oxide; MAP, mean annual precipitation; MAT, mean annual air temperature. *, p < 0.05; **, p < 0.01; ***, p < 0.001.

Fig. 5 Relative effects of climatic, edaphic, plant and mineral variables on soil organic carbon (C) content (A), aggregate C fractions content (B-D), and C decomposition rate (E) in temperate grasslands of Nei Mongol. Soil organic C, macroaggregate C, microaggregate C, silt and clay C contents, and C decomposition rate standardized by SOC are lg transformed. AGB, aboveground biomass; AI, aridity index; CaExch, exchangeable Ca2+ content; Clay + silt, clay and silt content; Feo + Alo, poorly crystalline Fe/Al oxide content; MAP, mean annual precipitation; MAT, mean annual air temperature.

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