Landuse determines soil microbial community resistance and resilience to climate change in the lowland tropics
Productivity of tropical forests depends on key functions performed by soil microbial communities. Warming temperatures and declining precipitation may push tropical ecosystems beyond their native climate envelope, but how and to what degree soil microbial communities will respond to such altered climate conditions is not fully understood. Further, it is unknown if microbial communities will respond consistently among undisturbed and disturbed tropical ecosystems. The objective of our study was to determine how land-use regulates the resistance and resilience of soil microbial community structure and function to altered climate conditions. To address this, we collected soil from three land-use types in Costa Rica: active pasture, secondary forest, and diverse primary forest. To measure the resistance and resilience of soil communities to disturbance, we exposed soils to experimental heating (+H), drought (+D), and combined treatments (+H+D). We used 16S rRNA gene sequencing to determine changes in bacterial community composition and a catabolic response profiling technique that measured short-term respiration responses to eight different organic carbon substrates to assess changes in microbial function. We predicted that resistance and resilience of microbial structure and function would vary by land-use type, but that changes in structure and function would be coupled across treatments.
Microbial community structure shifted dynamically in response to experimental heat and drought treatments, while changes in community function were subtle. The response of community composition to heat and drought differed across land-use types. Pasture soils were relatively unchanged due to disturbance (P = 0.64), while primary (P = 0.001) and secondary (P = 0.02) forest soils were significantly altered. Likewise, pasture communities showed high resilience (P = 0.39) to altered climate treatments whereas both primary (P =0.001) and secondary (P = 0.001) forests had low resilience. In forests, soil communities were more resilient to the effects of drought than heat or heat and drought combined. Microbial function was significantly reduced by drought and to a lesser degree by drought and heat combined across all land-use types (P = 0.003). For all land-use types and treatments, we observed a high degree of functional resilience. Despite dramatic shifts in soil microbial composition, the relatively subtle changes in decomposer function suggest that tropical soil communities have a high degree of functional redundancy for carbon decomposition. Together, our results suggest that soil microbial structure and function are decoupled in their resistance and resilience responses to both climate and land use change.