Persistence of soil microbial function at the rock-soil interface in degraded karst topsoils

Abstract

Extensive and progressive rock emergence in karst ecosystems may cause localized variations in soil biogeochemical and microbial properties, and thus produce nutrient cycling 'hot spots' that could alter functional responses to perturbation. Here, we investigated the differences between microbial compositions and functions in topsoils at the rock-soil interface (RSI) compared with adjacent bulk soil along a gradient of increasing human perturbation in the Chinese Karst Critical Zone Observatory. Microbial abundance decreased with increasing perturbation and was higher at the RSI compared to bulk soil. Compared with the bulk soil, C-cycling and N cycling enzyme activities at the RSI were 72–427% higher, respectively, and those related to N cycling were 72–98% higher, and were greatest in primary forest and abandoned land. Mineral contents explained the large variances in enzyme activities suggesting that mineral availability modified microbial functions for nutrients acquisition in nutrient-poor karst system. The significantly larger nutrient contents of RSI soil in the primary forest suggest that weathering of the karst rocks in unperturbed environments is the primary source of nutrients, which is driven by microbial enzyme production. The enzyme activities related to C and N cycling were highest in abandoned land, which suggests a rapid switch in microbial function caused by nutrient limitation when cultivation ceased. In conclusion, soil microbial abundance and function next to karst rocks is higher than bulk soils and persists after recovery. This suggests that the potential for long-term recovery of very degraded karst landscapes is possible after abandonment because microbial functions for C and nutrient cycling persist in RSI 'hot spots'.