Microbial Carbon Use Efficiency in Coastal Soils Along a Salinity Gradient Revealed by Ecoenzymatic Stoichiometry

Abstract

AbstractSoil salinity affects the microbial carbon use efficiency (CUE) that in turn regulates soil‐atmosphere gas exchange and soil C sequestration. So far, little is known about CUE in salt‐affected soils. Hereby, CUE across coastal soils with electric conductivity (EC) ranging from 0.14 dS m−1 to 13.65 dS m−1 was investigated using stoichiometric modeling. Contrary to the belief that CUE decreases with salinity increase, this present study showed that CUE follows a unimodal pattern along the saline gradient with the highest CUE observed at EC = 2 dS m−1. When EC > 2 dS m−1, both CUE and soil microbial growth rate significantly decrease with salinity indicating that microorganisms sacrifice growth for survival/adaptation to high salt stress. When EC < 2 dS m−1, CUE shows a significant positive correlation with EC, but microbial community growth rates remain stable. We also observed that microbial growth becomes limited by carbon scarcity and that the degree of carbon constraint is significantly aggravated with EC. This implies that elevating CUE can be the preferred mechanism for microorganisms to stabilize elemental stoichiometry and maintain growth rate. Our results revealed that along the saline gradient, the dominant factor of CUE shifted from the ecological stoichiometry to salinity, which provides an insight into the microbial‐driven carbon cycling in salt‐affected soils.