Precipitation Gradient Drives Divergent Relationship between Non-Structural Carbohydrates and Water Availability in Pinus tabulaeformis of Northern China

Bingyan Hao,Xiuchen Wu,Xiaoyan Li,Craig D Allen,Pei Wang,Yuanqiao Li,Hongyan Liu,Kailiang Yu,Zongshan Li,Fangzhong Shi,Henrik Hartmann

doi:10.3390/f12020133

Abstract

Seasonal non-structural carbohydrate (NSC) dynamics in different organs can indicate the strategies trees use to cope with water stress; however, these dynamics remain poorly understood along a large precipitation gradient. In this study, we hypothesized that the correlation between water availability and NSC concentrations in different organs might be strengthened by decreasing precipitation in Pinus tabulaeformis Carr. forests in temperate China. Our results show that the concentrations of soluble sugars were lower in stems and coarse roots, and starch was higher in branches in the early growing season at drier sites. Throughout the growing season, the concentrations of soluble sugars increased in drier sites, especially for leaves, and remained stable in wetter sites, while starch concentrations were relatively stable in branches and stems at all sites. The NSC concentrations, mainly starch, decreased in coarse roots along the growing season at drier sites. Trees have a faster growth rate with an earlier cessation in active stem growth at drier sites. Interestingly, we also found a divergent relationship between NSCs in different organs and mean growing season water availability, and a stronger correlation was observed in drier sites. These results show that pine forests in arid and semi-arid regions of northern China exhibit different physiological responses to water availability, improving our understanding of the adaptive mechanisms of trees to water limitations in a warmer and drier climate.

Highlights

Widespread tree growth decline and mortality have been widely documented in almost all types of forest ecosystems globally [1,2], attributed mainly to rapid climate change
The TNC concentrations significantly increased by decreasing precipitation and increasing vaporvapor pressure deficitdeficit (VPD), implying that drier conditions lead to higher TNC concentrations in trees
TNC concentrations were significantly increased by decreasing precipitation and increasing VPD, but showed no significant relationship with pre-dawn leaf water potential (Table 1), which means TNC concentrations were more constrained by the long-term environmental conditions than physiological factors during water limitations [21]

Summary

Introduction

Widespread tree growth decline and mortality have been widely documented in almost all types of forest ecosystems globally [1,2], attributed mainly to rapid climate change. Intensified tree mortality was closely associated with increases in both frequency, severity and duration of droughts and pest or pathogen attack in recent years [3,4]. Three interdependent mechanisms have been proposed to explain such drought-induced tree mortality, including (1) hydraulic failure, (2) carbon starvation due to depletion of stored non-structural carbohydrates (NSCs), and (3) the interactions between the inhibiting transport and use of stored NSCs, which are potentially amplified by insect and pathogen attack [5]. Drought-induced tree growth decline might be partially attributed to the imbalance of photosynthesis and plant respiration on non-structural carbohydrate storage, metabolism and allocation [3,5,7,8]. An increasing body of studies indicate that maintaining carbon assimilation and preventing the rapid depletion of NSCs below a certain critical level appears to be a major strategy for tree growth under stress [9], which suggests that NSC storage is a resource crucial for resistance or even survival for trees [3]

Objectives

Methods

Results

Discussion

Conclusion