Abstract
Wet meadows provide opportunities to decrease carbon dioxide (CO2) and methane (CH4) released into the atmosphere by increasing the soil organic carbon (SOC) stored in wetland systems. Although wet meadows serve as the most important and stable C sinks, there has been very few investigations on the seasonal distributions of SOC fractions in high-altitude wet meadows. Here, we studied the effects of four vegetation degradation levels, non-degraded (ND), lightly degraded (LD), moderately degraded (MD), and heavily degraded (HD), on the measured vertical and seasonal changes of SOC and its different fractions. Among these vegetation degradation levels, 0–10 and 10–20 cm soil depths in ND plots had significantly higher SOC contents than the other degradation levels had throughout the year. This is attributed to the relatively greater inputs of aboveground plant litter and richer fine-root biomass in ND plots. Particulate organic carbon (POC) and light fraction organic carbon (LFOC) showed similar vertical and seasonal variations in autumn, reaching a minimum. Moreover, microbial biomass (MBC) and easily oxidizable organic carbon (EOC) contents were highest in summer and the smallest in winter, while dissolved organic carbon (DOC) content was highest in spring and lowest in summer, and were mainly concentrated in the 0–20 cm layer. Pearson correlation analysis indicated that soil properties and aboveground biomass were significantly related to different SOC fractions. The results indicate that vegetation degradation reduces the accumulation of total SOC and its different fractions, which may reduce carbon sink capacity and soil quality of alpine wet meadows, and increase atmospheric environmental pressure. In addition, vegetation biomass and soil characteristics play a key role in the formation and transformation of soil carbon. These results strengthen our understanding of soil C dynamics, specifically related to the different C fractions as affected by vegetation degradation levels and soil depth, in wet meadow systems.
Highlights
Wetlands are important for organic carbon storage, and small changes will affect carbon content in the atmosphere[1]
Little is known about how vegetation degradation in wet meadows of the Qinghai-Tibet Plateau (QTP) affects the seasonal changes of Soil organic carbon (SOC) components in the non-growing season
Our results show that the contents of light fraction organic C (LFOC) and particulate organic C (POC) in the soil surface of the ND treatment were significantly higher than their corresponding contents in the other treatments
Summary
Wetlands are important for organic carbon storage, and small changes will affect carbon content in the atmosphere[1]. Is the growing season important to wet meadows in this region, but the spring–autumn-winter period is critical to their ecosystem function and soil C cycling because plant growth is slow or non-existent, and lower soil temperatures affects microbial activity and the ability to decompose litter[37] During these periods, frequent temperature changes will affect processes of SOC conversion in the C cycle[38,39]. In order to better understand the SOC transformation processes in the Tibetan Plateau, changes in the SOC cycle under different vegetation degradation levels during the non-growing season in the Tibetan wet meadow require further investigation To address these knowledge gaps, this study assessed the seasonal responses of different soil carbon fractions to different degrees of vegetation degradation in a QTP wet meadow. We hypothesized that: (1) with increasing vegetation degradation intensity, the SOC content will decrease because of lower carbon source inputs and higher carbon decomposition after vegetation degradation; and (2) the patterns in seasonal variation of SOC components differ with different intensity of vegetation degradation due to the complexity of various ecological factors (climate, soil, vegetation) and the different dominant position of key factors
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