Abstract
Dalbergia cochinchinensis and D. oliveri are classified as vulnerable and endangered, respectively, in the IUCN Red List and under continued threat from deforestation and illegal harvesting for rosewood. Despite emerging efforts to conserve and restore these species, little is known of their responses to drought and heat stress, which are expected to increase in the Greater Mekong Subregion where the species co‐occur and are endemic. In this study of isolated and combined drought and heat effects, we found that D. oliveri had an earlier stomatal closure and more constant midday water potential in response to increasing drought level, suggesting that D. oliveri is relatively isohydric while D. cochinchinensis is relatively anisohydric. Heat shock and drought had synergistic effects on stomatal closure. Our results indicate contrasting relationships in water relations, photosynthetic pigment levels, and total soluble sugars. An increase in chlorophyll a was observed in D. cochinchinensis during drought, and a concomitant increase in carotenoid content likely afforded protection against photo‐oxidation. These physiological changes correlated with higher total soluble sugars in D. cochinchinensis. By contrast, D. oliveri avoided drought by reducing chlorophyll content and compromising productivity. Anisohydry and drought tolerance in D. cochinchinensis are adaptations which fit well with its ecological niche as a pioneering species with faster growth in young trees. We believe this understanding of the stress responses of both species will be crucial to their effective regeneration and conservation in degraded habitats and in the face of climate change.
Highlights
The pantropical genus Dalbergia Linn. f. (Fabaceae: Faboideae) contains around 250 species (Vatanparast, 2013), many of which produce valuable heartwood timber known as rosewood (Winfield, Scott, & Graysn, 2016), which is used to manufacture luxury furniture, boats, and musical instruments (Bhagwat, Dholakia, Kadoo, Balasundaran, & Gupta, 2015)
We found that the critical Soil water content (SWC) of D. cochinchinensis (32.65%, p = 4.65e−11) was lower than D. oliveri (47.23%, p < 2e−16), suggesting that D. cochinchinensis closed its stomata later than D. oliveri in response to decreasing SWC
We found that levels of chlorophyll a and carotenoids increased in D. cochinchinensis in response to drought and decreased in D. oliveri
Summary
The pantropical genus Dalbergia Linn. f. (Fabaceae: Faboideae) contains around 250 species (Vatanparast, 2013), many of which produce valuable heartwood timber known as rosewood (Winfield, Scott, & Graysn, 2016), which is used to manufacture luxury furniture, boats, and musical instruments (Bhagwat, Dholakia, Kadoo, Balasundaran, & Gupta, 2015). Growing demand and diminishing supply have drastically increased the economic value of rosewood, resulting in much illegal harvesting and poorly regulated exploitation of natural populations Among these are Dalbergia cochinchinensis Pierre and D. oliveri Gamble ex Prain (Figure 1), both of which are endemic to Cambodia, Laos, Thailand, and Vietnam within the Greater Mekong Subregion (GMS). D. cochinchinensis was once the most sought-after rosewood species globally, but it is virtually commercially extinct, as is D. oliveri (EIA, 2017) They were classified as vulnerable and endangered, respectively, in the IUCN Red List in 1998, with international trade strictly regulated since 2017 under CITES Appendix II. We have little understanding of the physiological adaptations of D. cochinchinensis and D. oliveri, which hinders informed decision-making in both conservation and forest restoration initiatives
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