Salinity decreases the contribution of microbial necromass to soil organic carbon pool in arid regions

Bin Jia; Han Mao; Yanmei Liang; Jie Chen; Li Jia; Meilan Zhang; Xiao Gang Li

doi:10.1016/j.scitotenv.2024.172786

Salinity decreases the contribution of microbial necromass to soil organic carbon pool in arid regions

Sci Total Environ. 2024 Apr 25:930:172786. doi: 10.1016/j.scitotenv.2024.172786. Online ahead of print.

Authors

Bin Jia¹, Han Mao¹, Yanmei Liang¹, Jie Chen¹, Li Jia¹, Meilan Zhang², Xiao Gang Li³

Affiliations

¹ College of Ecology, Lanzhou University, 222 South Tianshui Road, Lanzhou 730000, China.
² General Station of Gansu Cultivated Land Quality Construction and Protection, Lanzhou, Gansu 730000, China.
³ College of Ecology, Lanzhou University, 222 South Tianshui Road, Lanzhou 730000, China. Electronic address: lixiaogang@lzu.edu.cn.

PMID: 38677417
DOI: 10.1016/j.scitotenv.2024.172786

Abstract

Saline soils are widely distributed in arid areas but there is a lack of mechanistic understanding on the effect of salinity on the formation and biochemical composition of soil organic carbon (SOC). We investigated the effects of salinity on the accumulation of microbial necromass under natural vegetation and in cropland in salt-affected arid areas stretching over a 1200-km transect in northwest China. Under both natural vegetation and cropland, microbial physiological activity (indicated by microbial biomass carbon normalized enzymatic activity) decreased sharply where the electrical conductivity approached 4 ds m^-1 (a threshold to distinguish between saline and non-saline soils), but microbial biomass was only slightly affected by salinity. These indicated that a larger proportion of microbes could be inactive or dormant in saline soils. The contribution of fungal necromass C to SOC decreased but the contribution of bacterial necromass C to the SOC increased with increasing soil salinity. Adding fungal and bacterial necromass C together, the contribution of microbial necromass C to SOC in saline soils was 32-39 % smaller compared with non-saline soils. Fungal necromass C took up 85-86 % of microbial necromass C in non-saline soils but this proportion dropped to 60-66 % in saline soils. We suggested that the activity, growth, and turnover rate of microbes slowed by salinity was responsible for the decreased accumulation of fungal necromass in saline compared with non-saline soils, while the increased accumulation of bacterial residue in saline soils could be induced mainly by its slower decomposition. Soil microbial biomass was a poor predictor for the accumulation of microbial necromass in saline soils. We demonstrated a reduced contribution of microbial necromass to SOC and a shift in its composition towards the increase in bacterial origin in saline relative to non-saline soils. We concluded that salinity profoundly changes the biochemistry of SOC in arid regions.

Keywords: Arid areas; Microbial necromass carbon; Salt-affected soils; Soil organic matter biochemistry.