Evergreen Quercus aquifolioides remobilizes more soluble carbon components but less N and P from leaves to shoots than deciduous Betula ermanii at the end-season

Abstract

Remobilization is an important mechanism of resource conservation in plants. However, our understanding of whether the responses of resource remobilization to global warming differ between deciduous and evergreen trees remains unclear. We assessed resource remobilization from leaves to 1-year-old shoots in a deciduous (Betula ermanii) and an evergreen (Quercus aquifolioides) species along elevational gradients (i.e., temperature gradient) at the end of growing season. We aimed to test the hypotheses that the reallocation rate increased with increasing elevation and that more resources were reallocated from leaves to storage tissues in deciduous species than in evergreen species. We analyzed the concentrations of non-structural carbohydrates (NSC), nitrogen (N) and phosphorus (P), and compared the differences in remobilization efficiency of NSC, N, and P between leaves and shoots within each species and between the two species along the elevational gradients. Due to the different strategies of evergreen and deciduous species in nutrients use, the deciduous species had higher N and P remobilization rate, but lower remobilization rate of sugars, starch, and NSC than the evergreen species at the end of growing season. The remobilization rate of NSC, N, and P was significantly higher in trees at their upper limits compared to lower elevations. Our results suggest that trees reallocate resources from leaves to storage tissues before leaf senescence or at the end of growing season, to increase the resource use efficiency and to adapt to the harsh alpine environments. These results contribute to better understanding of the alpine treeline phenomenon in a changing world.

Keywords

• Altitudinal Gradient
• Non-structural Carbohydrates
• Sugars
• Starch
• Nutrients
• Reallocation