Can a previous drought help forest soil bacteria withstand another dry spell?

Details

Global climate models project a decrease in precipitation amounts in tropical regions. Changes in rainfall patterns have important implications for tropical soil moisture and redox status, but little is known about their effects on microbial community structure. This study asked whether exposure to earlier stress increases resistance to a later disturbance.

Researchers conducted a field experiment reducing precipitation throughfall—the rain reaching the soil through the canopy—in tropical forest soils in the Luquillo Mountains, Puerto Rico. They compared newly established throughfall exclusion plots (de novo excluded), plots undergoing throughfall reduction for a second time (pre-excluded), and ambient control plots.

Ten months of throughfall exclusion produced a small but statistically significant decline in soil water potential, and bacterial populations clearly adapted to increased osmotic stress. Although the water potential decline was small and microbial biomass did not change, bacterial phylogenetic diversity in the de novo-excluded plots decreased by approximately 40% compared with control plots. Pre-excluded plots, however, showed no significant change in phylogenetic diversity.

Nevertheless, the relative abundances of bacterial taxa changed significantly in both de novo-excluded and pre-excluded plots compared with control plots. Changes in bacterial community structure could be explained by changes in soil pore water chemistry and suggested changes in soil redox status.

Soluble iron declined in treatment plots, and this decline was correlated with decreased soluble phosphorus concentrations. The authors suggest this may have significant implications for microbial productivity in these phosphorus-limited systems.