Does microbial habitat or community structure drive the functional stability of microbes to stresses following re-vegetation of a severely degraded soil?

Abstract

Re-vegetation of eroded soil restores organic carbon concentrations and improves the physical stability of the soil, which may then extend the range of microhabitats and influence soil microbial activity and functional stability through its effects on soil bacterial community structure. The objectives of this study were (i) to evaluate the restorative effect of re-vegetation on soil physical stability, microbial activity and bacterial community structure; (ii) to examine the effects of soil physical microhabitats on bacterial community structure and diversity and on soil microbial functional stability. Soil samples were collected from an 18-year-old eroded bare soil restored with either Cinnamomum camphora (“Eroded Cc”) or Lespedeza bicolour (“Eroded Lb”). An uneroded soil planted with Pinus massoniana (“Uneroded Pm”) and an eroded bare soil served as references. The effect of microhabitats was assessed by physical destruction with a wet shaking treatment. Soil bacterial community structure and diversity were measured using a terminal restriction fragment length polymorphism (T-RFLP) approach, while soil microbiological stability (resistance and resilience) was determined by measuring short-term (28 days) decomposition rate of added barley ( Hordeum vulgare) powder following copper and heat perturbations. The results demonstrated that re-vegetation treatment affected the recovery of physical and biological stability, microbial decomposition and the bacterial community structure. Although the restored soils overshot the Uneroded Pm sample in physical stability, they had lower microbial decomposition and less resilience to copper and heat perturbations than the Uneroded Pm samples. Soil physical destruction by shaking had the same effect on soil physical stability, but different effects on soil microbial functional stability. There were significant effects of vegetation treatment and perturbation type, and interactive effects among vegetation treatment, shaking and perturbation type on bacterial community structure. The destruction of aggregate structure increased resilience of the Eroded Lb sample and also altered its bacterial community structure. Both copper and heat perturbations resulted in significantly different community structure from the unperturbed controls, with a larger effect of copper than heat perturbation. Bacterial diversity (Shannon index) increased following the perturbations, with a more profound effect in the Uneroded Pm sample than in the restored soils. The interactive effects of vegetation treatment and shaking on microbial community and stability suggest that soil aggregation may contribute to the generation of bacterial community structure and mediation of biological stability via the protection afforded by soil organic carbon. Differential effects of re-vegetation treatment suggest that the long-term effects are mediated through changes in the quality and quantity of C inputs to soil.