Divergent responses of belowground carbon investment in Quercus spp. and Acer saccharum to reduced precipitation

With global change already enhancing drought frequency and severity, there is a critical need to determine if temperate forests will continue to act as carbon (C) sinks. The degree to which belowground strategies sustain tree growth under water stress remains uncertain. We examined differences between two temperate forest tree species in their belowground response to experimentally reduced precipitation over three years. We chose trees that are dominant in temperate forests and have different belowground resource acquisition strategies. We tested our hypothesis that in response to reduced precipitation, sugar maple trees would reduce belowground C investment while oak trees would show resiliency belowground. We found that oak trees maintained belowground C investment at the same level, likely reflecting an ability to leverage a higher baseline level of investment to enhance water and nutrient uptake. By contrast, sugar maple trees initially responded with increased investment in roots and mycorrhizae, but mycorrhizal colonization faded over time. Moreover, the treatment reduced rhizodeposition belowground by sugar maple trees, suggesting that the belowground C investment we observed does not lead to increased mobilization of nutrients. Our findings indicate that there are species specific responses of C investment in roots, mycorrhizae, and rhizodeposits to reduced precipitation.