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[Non-structural carbohydrate content of trees and its influencing factors at multiple spatial-temporal scales: A review].

Non-structural carbohydrates (NSC) are essential substances for the tree growth and metabolism, and play an important role in environmental adaptation of trees. At temporal scale, NSC contents in trees have limited inter-annual variation, which could be attributed to the strategy of tree growth and carbon storage. Different factors influence NSC contents of trees in various climatic regions, which change substantially at the seasonal scale. At spatial scale, the variations of NSC content in trees show an insignificantly decreasing trend with the decreases of latitude at global and continental scales, which are mainly related to the hydrothermal gradients. The trend at regional scale is opposite because of the decrease of hydrothermal gradients and lower sample frequency. More sophisticated relations exist between the variations of NSC content in trees and altitudes, which are caused by species-specific characteristics and the variations of micro-habitat conditions. The variations of NSC content in trees at multiple spatial-temporal scales are generally determined by both biotic and abiotic factors, which are mainly dependent on the tradeoff among photosynthate production, respiratory depletion, and tree growth. Furthermore, the methods used for the determination of NSC content are different, which results in great uncertainties in comparing conclusions from different studies. The methods used for sample collection and measurement of NSC should be improved and unified to enhance the comparison among different studies. The NSC contents of trees in different age classes should be measured with all organs collected at multiple spatial-temporal scales. The underlying mechanisms, significance of NSC storage, transformation and allocation on tree growth and survival should be further discussed.