The karst forests have great plant species diversity and are rich in endemic species; however, there is little knowledge about the hydraulic traits of the tree species therein. The severe water deficit of the karst habitats could put a great selective pressure on the water-use strategies of tree species; hence the co-occurring evergreen and deciduous trees may differ in their stem hydraulic traits and leaf water relationships.
Prof. Cao Kunfang and his research team of Xishuangbanna Tropical Botanical Garden (XTBG) carried out a study in a karst forest that was located approx. 3 km from XTBG (21°54′N, 101°46′E, 580 m a.s.l.), southern Yunnan, China. They compared the stem hydraulic conductivity, xylem-cavitation resistance, wood anatomy, leaf life span, leaf pressure–volume characteristics and gas exchange of six evergreen and six deciduous tree species co-occurring in a tropical dry karst forest in south-west China.
The researchers hypothesized that different leaf habits represent different water-use strategies that the co-occurring evergreen and deciduous species differ in stem hydraulic traits and leaf water relationships; specifically, the deciduous tree species have higher stem hydraulic efficiency, and the evergreen tree species have greater xylem-cavitation resistance and greater water-stress tolerance.
They usedphylogenetic independent contraststo test the correlated evolution between leaf life span and hydraulic traits as well as the evolutionary relationships between leaf water-stress tolerance and stem traits.
The study found that there were clear distinctions in stem hydraulic traits and leaf water-stress tolerance between the co-occurring evergreen and deciduous angiosperm trees in Xishuangbanna dry karst forest. The evergreen tree species had higher cavitation resistance and greater leaf water-stress tolerance so that could maintain their stem and leaf function in the dry season, while the deciduous species had greater hydraulic efficiency and higher photosynthetic capacity in the wet season.
They also found thatthere was correlated evolution between leaf life span and xylem water transport capacity, leaf photosynthetic capacity and leaf water-stress tolerance.
The researchers concluded that different hydraulic strategies between the co-occurring evergreen and deciduous trees may contribute to the maintenance of water balance of a dry karst forest ecosystem and, consequently, species co-existence and diversity.
The study entitled “Stem hydraulic traits and leaf water-stress tolerance are co-ordinated with the leaf phenology of angiosperm trees in an Asian tropical dry karst forest” has been published online in Annals of Botany, doi: 10.1093/aob/mcs092