The Responses of Extracellular Enzyme Activities to Saline Conditions: A Data Synthesis

ABSTRACT Soil extracellular enzymes are crucial for mediating microbial turnover of soil C and nutrients; however, the effects of soil salinity on enzyme activities remain poorly understood. Here, a pioneering data synthesis was conducted to investigate the associations between soil salinity levels and the activities of enzymes, using a dataset compiled from 150 peer‐reviewed articles. Results showed that enzyme activities assayed by spectrophotometric methods were generally greater than those assayed by fluorometric methods. The activities of most soil enzymes were either insensitive to or negatively correlated with soil salinity levels. However, PHOX activities increased with elevating soil salinity levels. Spectrophotometrically assayed BG and CBH activities exhibited positive relationships with soil pH, whereas fluorometrically assayed BG, CBH, NAG, and ALP activities showed negative correlations with soil pH. Changes in soil salinity primarily accounted for the decreases in enzyme activities. Therefore, salt inputs introduced through amendment applications may attenuate the positive effects of exogenous organic materials and nutrients on enzyme activities. Our study reveals that soil enzyme activity is an unreliable metric for assessing soil health in saline environments, as highly saline soils may exhibit similar enzyme activity levels to slightly saline or even non‐saline soils. Future studies should investigate how soil soluble ions influence enzyme activities to illuminate the responses of biochemical processes to salinity.