Physiological and Growth Responses to Increasing Drought of an Endangered Tree Species in Southwest China

Abstract

Research Highlights: We compared annually resolved records of tree-ring width and stable isotope of dead and surviving Fokienia hodginsii (Dunn) Henry et Thomas trees. We provide new insights into the relationships and sensitivity of tree growth to past and current climate, and explored the underlying mechanism of drought-induced mortality in F. hodginsii. Background and Objectives: Drought-induced tree decline and mortality are increasing in many regions around the world. Despite the high number of studies that have explored drought-induced decline, species-specific responses to drought still makes it difficult to apply general responses to specific species. The endangered conifer species, Fokienia hodginsii, has experienced multiple drought-induced mortality events in recent years. Our objective was to investigate the historical and current responses to drought of this species. Materials and Methods: We used annually resolved ring-width and δ13C chronologies to investigate tree growth and stand physiological responses to climate change and elevated CO2 concentration (Ca) in both dead and living trees between 1960 and 2015. Leaf intercellular CO2 concentration (Ci), Ci/Ca and intrinsic water-use efficiency (iWUE) were derived from δ13C. Results: δ13C were positively correlated with mean vapor pressure deficit and PDSI from previous October to current May, while ring widths were more sensitive to climatic conditions from previous June to September. Moreover, the relationships between iWUE, basal area increment (BAI), and Ci/Ca changed over time. From 1960s to early 1980s, BAI and iWUE maintained a constant relationship with increasing atmospheric CO2 concentration. After the mid-1980s, we observed a decrease in tree growth, increase in the frequency of missing rings, and an unprecedented increase in sensitivity of 13C and radial growth to drought, likely related to increasingly dry conditions. Conclusions: We show that the recent increase in water stress is likely the main trigger for the unprecedented decline in radial growth and spike in mortality of F. hodginsii, which may have resulted from diminished carbon fixation and water availability. Given that the drought severity and frequency in the region is expected to increase in the future, our results call for effective mitigation strategies to maintain this endangered tree species.

Climate change‐induced ecosystem disturbance: a review on sclerophyllous and semi‐deciduous forests in Tunisia

“…In some evergreen tree species, chronic water stress and prolonged stomatal closure will lead to a reduced photosynthesis, resulting in a further decrease in stored carbon as respiration continues (Zheng et al . 2019). Carbohydrate reserves can be then further reduced as are required to drive phloem transport, maintain turgor, and refill embolized xylem during drought (McDowell et al .…”

“…Drought-induced tree decline and mortality are increasing in many regions around the world, which will fundamentally alter forest composition (Engelbrecht et al 2007;Zheng et al 2019), structure (Allen et al 2010), and biogeography (D'Orangeville et al 2016). To develop mitigation strategies and maintain forest sustainability and productivity, it is important to understand how forest species will respond to severe droughts.…”

“…The main physiological mechanisms of trees facing severe drought are capacity to accumulate sufficient carbohydrates (McDowell et al 2011;Breshears et al 2005: Salmon et al 2019, a reduced vulnerability to hydraulic failure (Br eda et al 2006;Meinzer et al 2009Meinzer et al , 2010, or both (McDowell et al 2011;Adams et al 2017). In some evergreen tree species, chronic water stress and prolonged stomatal closure will lead to a reduced photosynthesis, resulting in a further decrease in stored carbon as respiration continues (Zheng et al 2019). Carbohydrate reserves can be then further reduced as are required to drive phloem transport, maintain turgor, and refill embolized xylem during drought (McDowell et al 2011;Torres-Ruiz et al 2015).…”

Chemical and Microbial Differences of Root and Rhizosphere Soil among Different Provenances of Fokienia hodginsii

“…Over 1/2 of the mountainous area in southern China is covered in harsh woodland vegetation, a habitat type that is highly suitable for planting with F. hodginsii given its stronger soil improvement ability than other cultivated tree species in southern China. It was recently documented that both human disturbance [11] and global warming [12] are changing the present status of F. hodginsii by hastening the degradation and fragmentation of its native habitat, which impairs regeneration of F. hodginsii stands in natural forest sites [13]. Thus, establishing seed orchards is imperative for the protection as well as application of F. hodginsii [14].…”

Influence of Climate Change on Tree Growth and Forest Ecosystems: More Than Just Temperature

“…The issue of decreasing growth rates after the 1980s has been reported also in Asia. In this issue, Zheng et al [9] showed how Fokienia hodginsii, an endanger conifer, has decreased its growth, increased the frequency of missing rings, and experimented an unprecedented increase in sensitivity of 13 C and radial growth to drought, likely related to increasingly dry conditions. These researchers linked these negative effects to a spike in tree mortality, which may have resulted from diminished carbon fixation and water availability.…”