Abstract:

Forests are large and persistent carbon (C) sink mainly through the C sequestration of tree growth, which can mitigate the rising rate of CO₂ concentration in the atmosphere. According to C availability in trees, two mechanisms involved in controlling tree growth are attributed to limitations to C input and C utilities. Since many environmental factors influence the activities of C-source and C-sink of trees interdependently, it is difficult to quantify how the sensitivity of C-source or C-sink activity to environmental changes affects tree growth. Therefore, it is of significance to understand physiological mechanisms underlying potential limitations to tree growth in order to predict tree growth and forest C sink under global change scenarios. In this review, the debates on the C-source and C-sink limitations to tree growth were firstly introduced. Second, we discussed responses of tree growth to biotic and abiotic stresses, such as defoliation, drought and low temperature from the perspective of C-source/sink limitations. Finally, we proposed three priorities for future studies in this field: (1) to explore the regulating mechanisms on the allocation of non-structural carbohydrates (NSC) in trees, and to determine what conditions and what extent trees actively allocate the photosynthates to NSC storage at the expense of growth; (2) to strengthen studies on the tree C-sink, and determine the photosynthates allocated to all components of tree C-sink, especially the missing C-sinks such as the activities of roots and related microorganisms; and (3) to implement studies on interactions among C metabolism, mineral nutrition and hydraulics physiology, and fully understand the C-water-nutrient coupling and its effects on tree growth.

Key words: carbon sink, carbon source, non-structural carbohydrates, stress, tree growth