Pathogen-Induced Tree Mortality Modifies Key Components of the C and N Cycles with No Changes on Microbial Functional Diversity

An increase in tree mortality rates as a consequence of biotic disturbances has been detected worldwide. Biotic disturbances in forests might cause significant impacts at ecosystem-level, with strong effects on soil biological activity and organic matter transformation. However, very few empirical studies have explored to date the consequences of biotic disturbances for soil microbial communities and C and N cycles. Here, we assessed the effects ofQuercus suberdieback, caused by the exotic root pathogenPhytophthora cinnamomi,on the soil microbial community and key components of the C and N cycle. We used a spatially explicit neighborhood approach to analyze the effects ofQ. subertrees with different health status and non-declining coexistent species on soil variables. The study was replicated in the two mainQ. suberforest types of the region (closed forests and open woodlands) with contrasting soil texture characteristics. Pathogen-induced tree dieback did not affect microbial functional diversity or biomass, but translated into lower soil microbial respiration. Tree mortality induced changes in several variables of the C and N cycle, but the sign and magnitude of these effects varied depending on the local characteristics of soil texture. Coexistent species differed strongly fromQ. suberin their effects on the C and N cycle. Overall, our results show that tree dieback due to invasive pathogens translates into complex short- and long-term effects on different components of the C and N cycles, despite no effects on microbial functional diversity and biomass.

Automated summary

The study assessed the effects of tree dieback caused by an exotic root pathogen on soil microbial community and key components of the C and N cycle. The results showed that tree mortality induced changes in variables of the C and N cycle, with effects varying depending on soil texture characteristics. Coexistent species had different effects on the C and N cycle compared to the main species affected by the pathogen.