Particulate organic carbon is more vulnerable to nitrogen addition than mineral-associated organic carbon in soil of an alpine meadow
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Background and aims
Long-term nitrogen (N) addition can affect soil organic carbon (SOC) pool within different soil fractions with different turnover rates. However, the mechanisms of these effects, particularly in alpine grassland ecosystems, are not clear.
We studied the responses of SOC content in different soil fractions to N addition based on a six-year N addition field experiment in an alpine meadow ecosystem on the Tibetan Plateau. We measured soil chemical and microbial properties, and SOC content in bulk soil, particular organic matter (POM) and mineral-associated organic matter (MAOM) fractions in response to N addition.
N addition increased soil N availability, decreased soil pH and microbial biomass, but had minimal effect on plant biomass, soil enzyme activity, and SOC content in bulk soil. With increasing levels of N addition, SOC in the POM fraction (POC) showed a significant negative trend, while SOC in the MAOM fraction (MAOC) did not change significantly.
As plant biomass input and soil enzyme activity were not significantly altered with N addition, the decline in POC was likely caused by changes in microbial physiology (carbon use efficiency), while the insignificant change in MAOC may be determined by the balance between input (from microbial necromass) and output (from microbial decomposition). Taken together, our study showed that the less-protected POC fraction is more vulnerable to N addition than the more-protected MAOC fraction in the alpine grassland. This finding may improve the prediction of soil C dynamics in response to N deposition in alpine grassland ecosystems on the Tibetan Plateau.
KeywordsNitrogen addition Soil organic carbon Soil fractions Particulate organic matter Mineral-associated organic matter Alpine meadow
soil organic carbon
particulate organic carbon
mineral-associated organic carbon
particulate organic matter
mineral-associated organic matter
microbial biomass carbon
microbial biomass nitrogen
extractable organic carbon
extractable total nitrogen
This study was financially supported by the National Natural Science Foundation of China (Grant numbers 31622013, 31621091 and 31830009). This work was done at the Alpine Meadow and Wetland Ecosystems Research Station of Lanzhou University. We also sincerely thank two anonymous reviewers and the Editor (Dr. Ingrid Kögel-Knabner) for their helpful comments and suggestions that greatly improved the manuscript.
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