Elevation Effects on Growth Pattern and Resource Allocation of <i>Picea crassifolia</i> in Qilian Mountains, Northwest China

Abstract

Environmental variances in temperature, moisture, and soil fertility caused by elevation gradients affect tree growth. However, the variability in regional climate and differences in tree physiology give rise to much uncertainty regarding the effects of elevation on tree growth patterns and resource allocation. In order to clarify the growth-limiting factors and physiological mechanisms of trees at different elevations, we selected Picea crassifolia (Qinghai spruce) at high (3300 m), middle (2850 m) and low (2585 m) elevations to analyze the interannual trends of tree radial growth and the resource allocation trade-offs involving nonstructural carbohydrates (NSC). The results were as follows: 1) the limiting factor for the growth of Qinghai spruce changed from growth limitation to carbon limitation with an increase in elevation; this was supported by the higher concentrations of NSC and its components in the whole plant and all tissues at middle and low elevations compared to high elevation, while the basal area increment (BAI) showed a decreasing trend at middle and low elevations and an increasing trend at high elevation. 2) The greatest concentrations of NSC were found in the leaves and thick roots at all three elevations, but soluble sugar (SS) and starch (ST) mainly accumulated in overground tissues (leaves and trunks) and underground tissues (fine and thick roots), respectively. 3) The ratios of soluble sugar to starch (SS/ST) at high elevations were significantly greater than those at middle and low elevations, indicating that more carbon was used for growth at high elevations, while more carbon was used for long-term energy storage at middle and low elevations. The results elucidate the growth constraints of Qinghai spruce at different elevations and the resource allocation trade-off mechanism, and offer reference points for ecological adaptation theory and conservation measures for trees at different elevations.