Non-Structural Carbohydrate Dynamics in Leaves and Branches of Pinus massoniana (Lamb.) Following 3-Year Rainfall Exclusion

Tian Lin,Jinmao Zhu,Huaizhou Zheng,Zhihong Huang,Jian Wang

doi:10.3390/f9060315

Abstract

Drought-induced tree mortality is an increasing and global ecological problem. Stored non-structural carbohydrates (NSCs) may be a key determinant of drought resistance, but most existing studies are temporally limited. In this study, a 3-year 100% rainfall exclusion manipulation experiment was conducted to evaluate the response of NSC dynamics to drought stress in 25-year-old Pinus massoniana leaves and branches. The results showed: (1) compared with the control condition, leaf NSC concentration in the drought treatment increased 90% in the early stage (days 115–542) (p < 0.05), and then decreased 15% in the late stage (days 542–1032), which was attributed to water limitation instead of phenology; (2) the response of leaf NSCs to drought was more significant than branch NSCs, demonstrating a time lag effect; and (3) the response of P. massoniana to mild drought stress was to increase the soluble sugars and starch in the early stage, followed by an increase in soluble sugars caused by decreasing starch in the later stress period. Considering these results, mid-term drought stress had no significant effect on the total NSC concentration in P. massoniana, removing carbon storage as a potential adaptation to drought stress.

Highlights

IntroductionAs an important part of forest ecosystems, increased tree mortality could lead to worldwide large-scale forest die-off [4,5]
The frequency and intensity of tree mortality associated with drought is increasing globally [1,2,3].As an important part of forest ecosystems, increased tree mortality could lead to worldwide large-scale forest die-off [4,5]
We propose three aspects to explain these phenomena: (1) non-structural carbohydrates (NSCs) increased during the growing season because the production of photoassimilates exceeded metabolic and growth demand for carbon; (2) carbohydrates draw down during the dormant season, when photosynthesis decreases and reserves are used to provide the energy required for normal metabolism [23,27]; and (3) during the growing season when water is deficient, the secondary metabolic processes that synthesize structural material were weakened and NSCs increased, resulting in peak NSC concentration during the dry season [36,50,51]

Summary

Introduction

As an important part of forest ecosystems, increased tree mortality could lead to worldwide large-scale forest die-off [4,5]. Such widespread events would have long-term impacts on ecosystem structure and functioning [2,6], as well as forest carbon storage capacity [7]. Despite a growing research interest surrounding the physiology of drought-induced tree mortality [10], our current understanding of the adaptive mechanisms remains poor, limiting our ability to predict widespread mortality events, their feedback in the future climate system, and the impact on ecosystem services provided to humans [11,12,13].

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