Precipitation Patterns Impact Soil Aggregates and Organic Carbon of an Alpine Wetland on the Qinghai-Tibetan Plateau

Abstract

Precipitation amount decrease and precipitation interval extend in alpine wetland on the Qinghai-Tibetan Plateau is occurring. However, little is known about how precipitation changes affect soil aggregates and SOC in alpine wetlands. Plots of an alpine wetland on the Qinghai-Tibetan Plateau were subjected to two precipitation frequencies (high vs. low, i.e., 1 and 3 times of nature rainfall intervals) crossed with two precipitation amounts (high vs. low, i.e., 100% and 70% of the amount of natural rainfall). Two years later, we investigated changes of soil aggregates (silt + clay, < 53 μm; microaggregates, 53~250 μm; and macroaggregates, >250 μm) and SOC in three soil depths, i.e., 0-15 cm, 15-30 cm and 30-50 cm. The low frequency high amount and low amount high frequency treatment led to a 19.6% and 26.2% increase in SOC compared with the high frequency high amount treatment. Furthermore, the macroaggregate fraction in the 0-15 cm soil depth decreased by 21.9% and 18.6% in the low frequency high amount and low amount high frequency treatment than that in the high frequency high amount treatment. However, none of the three soil aggregate fractions in the 15-30 cm soil depth responded to the changes in the precipitation patterns. The structural equation models showed that SOC was regulated by soil aggregate composition and microbial biomass carbon. Reduced precipitation frequency and amount shifted macroaggregate-associated organic carbon to microaggregate-associated organic carbon in the 0-15 cm soil depth. The results indicate that the reduction in precipitation frequency and amount decreased the mean weight diameter of the surface soil, weakening the physical protection of soil aggregates for SOC. Therefore, changes in precipitation patterns may produce a predominant impact on SOC storage and stability in alpine wetlands via their impacts on soil aggregate composition.

Keywords: alpine wetland, soil aggregate, aggregate associated organic carbon, precipitation, soil organic carbon