Timing of Drought Affected the Growth, Physiology, and Mortality of Mongolian Pine Saplings

Hui Qian,Ai-Fang Wang,Di-Ying Xiang,Ai-Mei Dong,Tapani Repo,Gang Zhang,Marja Roitto

doi:10.3390/f12111491

Hui Qian, Ai-Fang Wang + Show 5 more

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https://doi.org/10.3390/f12111491

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Abstract

Background and Objectives: More frequent and severe droughts are occurring due to climate change in northern China. In addition to intensity and duration, the timing of droughts may be decisive for its impacts on tree growth, mortality, and the whole forest ecosystem. The aim of this study was to compare the effect of drought occurring in the early- and mid-growing season on the growth and physiology of Mongolian pine (Pinus sylvestris var. mongolica Litv.) saplings. Materials and Methods: Four-year-old container saplings that were about to sprout were exposed to three treatments: (i) regular irrigation throughout the growing season (CTRL), (ii) no irrigation in the early growing season (weeks 1–5) followed by regular irrigation (EGD), (iii) no irrigation in the mid growing season (weeks 5–10), and regular irrigation in the early and late growing season (MGD). We measured the root and shoot growth, sapling mortality, and the physiological changes in the roots and needles periodically. Results: Drought in the mid growing season was more harmful than in the early growing season in terms of chlorophyll fluorescence, electrolyte leakage of needles, needle length, stem diameter increment, and sapling mortality. The high mortality in the mid growing season might be attributed to the joint effect of drought and high temperature. Drought in the early growing season decreased root growth, and the starch and soluble sugars in roots as much as the drought in the mid growing season. Abscisic acid concentration increased in fine roots, but decreased in old needles after drought. Conclusions: Special attention should be paid on forest sites susceptible to drought during afforestation in the face of ongoing climate change.

Highlights

The global land areas exposed to drought have remarkably increased over the past decades [1]
We aimed to explore the impact of the timing of drought, when occurring in the beginning and middle of the growing season, on the above- and below-ground physiology and growth of Mongolian pine saplings
We studied the physiological and growth response of Mongolian pine saplings to We studied the physiological and growth response of Mongolian pine saplings to drought during the early and middle drought during the early and middle of the growing season

Summary

Introduction

The global land areas exposed to drought have remarkably increased over the past decades [1]. Frequent and severe droughts have occurred in different parts of the world [2]. Severe droughts are expected to strongly impact forest ecosystems through affecting the growth, mortality, and regeneration of many tree species. In addition to intensity and duration, the timing of droughts has impacted plant productivity [3]. Found that legacies from extreme drought events during the dry season lasted longer and impacted stronger on tree growth than those from extreme drought events during the wet season, suggesting that the timing of drought is a crucial factor in determining the impact on tree recovery [4]. Timing of drought may affect the mode, direction, and magnitude of the impact on terrestrial ecosystems [5,6]

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