Physiological mechanisms of drought-induced tree die-off in relation to carbon, hydraulic and respiratory stress in a drought-tolerant woody plant

Shin-Taro Saiki,Kenichi Yoshimura,Kenichi Yazaki,Atsushi Ishida

doi:10.1038/s41598-017-03162-5

Shin-Taro Saiki, Kenichi Yoshimura + Show 2 more

Open Access

https://doi.org/10.1038/s41598-017-03162-5

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Abstract

Drought-induced tree die-off related to climate change is occurring worldwide and affects the carbon stocks and biodiversity in forest ecosystems. Hydraulic failure and carbon starvation are two commonly proposed mechanisms for drought-induced tree die-off. Here, we show that inhibited branchlet respiration and soil-to-leaf hydraulic conductance, likely caused by cell damage, occur prior to hydraulic failure (xylem embolism) and carbon starvation (exhaustion of stored carbon in sapwood) in a drought-tolerant woody species, Rhaphiolepis wrightiana Maxim. The ratio of the total leaf area to the twig sap area was used as a health indicator after drought damage. Six adult trees with different levels of tree health and one dead adult tree were selected. Two individuals having the worst and second worst health among the six live trees died three months after our study was conducted. Soil-to-leaf hydraulic conductance and leaf gas exchange rates decreased linearly as tree health declined, whereas xylem cavitation and total non-structural carbon remained unchanged in the branchlets except in the dead and most unhealthy trees. Respiration rates and the number of living cells in the sapwood decreased linearly as tree health declined. This study is the first report on the importance of dehydration tolerance and respiration maintenance in living cells.

Highlights

Global climate change has altered the annual patterns and seasonal distribution of rainfall[1], which greatly affects forest ecosystems through drought-induced tree die-off 2–4
Two major hypotheses have been proposed to explain non-pathogenic, drought-induced tree die-off: the hydraulic failure hypothesis, which postulates that die-off is largely a result of dysfunctional water transport systems caused by embolisms in the xylem[6]; and the carbon starvation hypothesis, which suggests that die-off is caused by shortages of stored carbohydrates resulting from a decline in photosynthetic activity because of stomatal closure[5]
The results showed that the hydraulic conductance decreases between the middle stem and the root system before xylem dysfunction occurs in the branchlets

Summary

Introduction

Global climate change has altered the annual patterns and seasonal distribution of rainfall[1], which greatly affects forest ecosystems through drought-induced tree die-off 2–4. We demonstrate that inhibited respiration related to dehydration-induced cell damage and decreased soil-to-leaf hydraulic conductance (Ksoil-to-leaf) occur before carbon starvation and hydraulic failure in the branchlets of drought-tolerant woody plants. To evaluate this tripartite relationship (hydraulic failure, carbon starvation and metabolic failure), we measured Ksoil-to-leaf, the percent loss of conductivity (PLC) in the branchlets, the non-structural carbon (NSC) and the respiration rates in the branchlets and at the middle and base of the stems, along with the leaf water potential, leaf gas exchange and the living cell ratio (the number of living cells/ the number of total cells in parenchyma) of the branchlets. The evaluating of metabolic tolerance among tree species will help to increase our knowledge about future forest degradation caused by the forecasted drier climate

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