Carbon Sink Limitation Determines the Formation of the Altitudinal Upper Limit of an Evergreen Oak in Eastern China

Temperature is a critical environmental factor determining the upper limits of evergreen broadleaved tree taxa. However, whether carbon source or sink limitation shapes this limit not yet fully understood. We studied subtropical oak (Cyclobalanopsis gracilis) at northern its distributional range. Along an elevational/temperature gradient towards limit, we surveyed variations in non-structural carbohydrate (NSC) concentrations C. gracilis adults for 3 years. Additionally, balance manipulation experiment debudding and defoliation was done to seedlings close aiming investigating changes NSC growth rates different treatment groups. Our results showed that increasing elevation decreasing temperature did affect trends concentration twigs, old branches, trunks adults, nor manipulations (debudding defoliation) have significant effect on growth, while decreased twigs. These suggest key physiological mechanism underlying low shaping dominant species eastern China. Therefore, formation oaks most likely result direct low-temperature restriction meristematic activity tissue instead insufficient supply. More studies with expanded sample sizes are needed other growing their confirm hypothesis reveal detailed mechanisms.