Woody shrubs increase soil microbial functions and multifunctionality in a tropical semi-arid grazing ecosystem

Abstract

Woody encroachment is of global concern in arid and semiarid regions around the world. Due to reduction in grass (forage), woody encroachment is viewed as ecosystem disservice and degradation, even though this may not reduce ecosystem functions. Often, management perceptions of degradation remain inadequately informed by knowledge of ecosystem processes. We compared 11 biotic variables related to soil and microbial functions under shrubs against paired-adjacent grassland:- carbon, nitrogen, C:N ratio, organic matter, plant-available N, N-mineralization rate, microbial biomass C and N, basal respiration, and metabolic-quotient. We summarized these as a multifunction-index. We also measured five soil physico-chemical covariates:- pH, conductivity, bulk density, texture and water holding capacity. These 11 biotic variables were 15–48% higher under shrubs than under grass; multifunction-index was also higher (by 366%). After accounting for spatial autocorrelation and background differences in physico-chemical covariates (redundancy analysis), altered ecosystem functions were attributable to shrubs. Overall, shrubs can enhance ecosystem functions, and maintain important ecological processes through concomitant changes in soil physico-chemical properties. While shrubs should not be equated to ecological degradation, they present a challenging triage of ecosystem service, disservice, and function for grasslands. Management strategies could benefit from targeting patterns of nutrient re-distribution under shrubs.