Climate change and exotic pathogens have opposite effects on nutrient cycling in a Quercus forest


Abstract: Climate change and exotic pathogens are two main drivers of Quercus forests decline across the globe. However, very little is known about the interactive effects of these drivers on biogeochemical cycles. In this study we addressed empirically for the first time the short-term (after one year) simultaneous impacts of drought (ambient vs. ~30% reduction in rainfall), soil warming (ambient vs. ~ 1 °C increase) and the abundance of the exotic pathogen Phytophthora cinnamomi on nutrient cycling (microbial biomass nitrogen (MB-N), NH4+ and urease, phosphatase and ß-glucosidase activities) in a Mediterranean forest dominated by Quercus suber and affected by P. cinnamomi invasion. The drought treatment caused rapid substantial reductions in MB-N, NH4+ and soil phosphatase activity (49%, 25% and 19%, respectively). Warming also resulted in important changes in nutrient availability, but increased NH4+ concentration by 43%. Moreover, P. cinnamomi abundance in the soil was positively correlated with urease and ß-glucosidase activities. We did not find any short-term interaction between the climate treatments and P. cinnamomi abundance, but a significant interaction between drought and warming for MB-N. Our findings suggest that P. cinnamomi infection and warming might partially buffer the negative impact of drought on nutrient availability in Quercus forests. Climate change and exotic pathogens can have opposite effects on nutrient cycling, highlighting the need for more studies that analyze their simultaneous effect on ecosystem functioning.

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