[Response of non-structural carbohydrates in leaves of different life-form plants to altitude in secondary Betula platyphylla forests in mountainous area of northern Hebei, China].

secondary forests across an altitude gradient (950, 1150, 1350, 1550, and 1750 m) in the northern Hebei mountainous region and analyzed their relationships with environmental factors. The results showed that both trees and shrubs exhibited significantly higher soluble sugar and NSC contents than herbaceous plants, while the starch-to-soluble sugar ratio (SC/SSC) was significantly lower in woody species, indicating a tendency to maintain higher carbon storage levels. With increasing altitude, NSC contents in trees first decreased and then increased, shifting from carbon limitation to growth limitation as a response to environmental stress, demonstrating a flexible trade-off strategy between 'growth' and 'energy storage'. In contrast, NSC in shrubs and herbaceous plants increased significantly with altitude, dominated by growth limitation, reflecting a conservative strategy focused on carbon accumulation under low-temperature stress. The mixed-effects model revealed that altitude was the key driver of NSC variation, with interspecific differences being the primary source of leaf NSC variation. Redundancy analysis indicated that the first two principal components explained 87.6%, 79.9%, and 93.1% of the cumulative variance for trees, shrubs, and herbaceous plants, respectively. The main influencing factors were soil moisture and total nitrogen for trees; soil pH, available phosphorus, and mean temperature of the growing season for shrubs; and, mean temperature of the growing season, soil moisture, and pH for herbaceous plants. This study revealed the differential regulation of hydrothermal conditions and nutrient supply on carbon balance of different plant life forms, and clarified that life form is a key dimension to explain the diversity of plant adaptation strategies to altitude gradient.