The interaction of carbon and nutrient relations in trees exposed to drought

It is getting more and more clear that the sink activity in trees strongly determines carbon (C) uptake and within-plant C distribution. Here we show that short- and long-term changes in water availability impacted the belowground (mycorrhizosphere) C sink strength, which however, not only affected C transport to the roots but also nitrogen (N) uptake by tree roots and the N allocation to aboveground tissues. The negative drought impact on N uptake might be a result of reduced root growth and the lower availability of recent assimilates for mobilizing inorganic N in the soil as the physiological N uptake capacity of the roots was not clearly affected. On the other hand, we show that increased N availability in the soil can have positive effects on C allocation to the rooting system of trees under drought and consequently can reduce drought induced growth impairment and mortality. Our results show that the strong interaction between nutrients and carbon needs to be taken into account to understand the resilience of trees and forests towards drought events projected to occur more frequently in future.