Soil amendments alter plant biomass and soil microbial activity in a semi-desert grassland

Abstract

We tested the effects of soil biotic disturbance and biochar or woodchip amendments on plant growth, soil microbial biomass and activity, and soil physiochemical parameters in response to disturbance in a semi-desert grassland. In a 78-day growth chamber experiment using six grass species native to the Southwest U.S., we compared the effects of autoclave heatshock, which mimics soil stockpiling in hot drylands, and amendments on plant and microbial biomass, potential extracellular enzyme activity, and soil moisture and nutrient availability. Plant biomass was lowest in woodchip-amended soils, and highest in autoclaved and biochar-amended soils (p < 0.05). Root:shoot ratios were higher in the autoclaved and woodchip-amended soils (p < 0.05). Biochar addition improved soil water-holding capacity resulting in higher dissolved organic carbon (p < 0.001) and nitrogen (p < 0.001). Soil microbial activity and plant biomass were not correlated. Amendment-induced changes in activity could be partially explained by nutrient availability. Neither microbial biomass nor activity recovered to pre-disturbance values. In this study, biochar and woodchip amendment and autoclave-induced changes to moisture and nutrient availability influenced plant biomass allocation and soil microbial activity. Amendments increased carbon, nitrogen, and phosphorus mineralizing enzyme activities with no significant change in microbial biomass, indicating that soil recovery in drylands is a long-term process. Understanding plant-soil feedbacks in drylands is critically important to mitigating climate and anthropogenic-driven changes and retaining or reestablishing native plant communities.