Patterns of leaf conductance and water potential of five Himalayan tree species

Abstract

We studied variations in water relations and drought response in five Himalayan tree species (Schima wallichii (DC.) Korth. (chilaune) and Castanopsis indica (Roxb.) Miq. (dhale katus) at an elevation of 1400 m, Quercus lanata Smith (banjh) and Rhododendron arboreum Smith (lali gurans) at 2020 m, and Quercus semecarpifolia Smith (khasru) at 2130 m) at Phulchowki Hill, Kathmandu, Nepal. Soil water potential at 15 (Psi(s15)) and 30 cm (Psi(s30)) depths, tree water potential at predawn (Psi(pd)) and midday (Psi(md)), and leaf conductance during the morning (g(wAM)) and afternoon (g(wPM)) were observed from December 1998 to April 2001, except during the monsoon months. There was significant variation among sites, species and months in Psi(pd), Psi(md), g(wAM) and g(wPM), and among months for all species for Psi(s15). Mean Psi(pd) and Psi(md) were lowest in Q. semecarpifolia (-0.40 and -1.18 MPa, respectively) and highest in S. wallichii (-0.20 and -0.63 MPa, respectively). The minimum Psi value for all species (-0.70 to -1.79 MPa) was observed in March 1999, after 4 months of unusually low rainfall. Some patterns of Psi(pd) were related to phenology and leaf damage. During leafing, Psi(pd) often increased. Mean g(wAM) and g(wPM) were highest in Q. semecarpifolia (172 and 190 mmol m(-2) s(-1), respectively) and lowest in C. indica (78 and 74 mmol m(-2) s(-1), respectively). Soil water potential (Psi) at 15 cm depth correlated with plant Psi in all species, but rarely with g(wAM) and not with g(wPM). Plant Psi declined with increasing elevation, whereas g(w) increased. As Psi(pd) declined, so did maximal g(w), but overall, g(w) was correlated with Psi(pd) only for R. arboreum. Schima wallichii maintained high Psi, with low stomatal conductance, as did Castanopsis indica, except that C. indica had low Psi during dry months. Rhododendron arboreum maintained high Psi(pd) and g(w), despite low soil Psi. Quercus lanata had low g(w) and low Psi(pd) in some months, but showed no correlation between tree Psi and g(w). Quercus semecarpifolia, which grows at the highest elevation, had low soil and plant Psi and high g(w).

Leaf and bud demography and shoot growth in evergreen and deciduous trees of central Himalaya, India

“…It is also possible that redistribution of water stored in roots of trees may help in raising the water potential of shoots. Poudyal et al (2004) observed a decrease in wood water content before the onset of leaf flushing, that suggests withdrawal of stored stem water during active phenological development, which may contribute to rehydration of active tissues (Borchert 1994). The establishment of new foliage shortly before the warm and wet rainy season is likely to optimize photosynthetic gain .…”

“…Zobel et al (2001) found lowest water potential at high elevations in this region. Poudyal et al (2004) studied water relations and drought response in five dominant forest tree species in Nepal and found significant variation among sites, species and season in predawn and midday water potential and monthly soil water potential at 15 cm depth for all species. In a subtropical savanna, Nelson et al (2002) found that DS were more deterministic and constrained in their growth responses to increased moisture availability than ES.…”

Influence of tree water potential in inducing flowering in Rhododendron arboreum in the central Himalayan region

“…In an artificial watering experiment in Tabebwa ochracea, a tropical tree species, flower buds' size increased within 2 days of watering and were in full bloom after 5-7 days (Borchert 1994b). Some tree species are able to rehydrate active tissues before leaf flushing by withdrawing stored stem water (Poudyal et al 2004). Significant increase in soil moisture percentage after precipitation is quite obvious and consistent with other studies.…”

“…Water relations of these forests have been investigated by Zobel & Singh (1995), Tewari (1998), Zobel et al (2001, Poudyal et al (2004) and Singh et al (2006), while their phenology was studied by Ralhan et al (1985), Pangtey et al (1990), Rawal et al (1991) and Negi (2006). Rhododendrons (Ericaceae) are under-canopy forest tree species widely distributed around the globe.…”

Plant Water Relations and Phenological Shifts in Response to Drought in Castanopsis Indica at Phulchowki Hill, Kathmandu, Nepal

“…There is little information regarding the role of water in controlling leaf phenology of temperate trees especially central Himalayan trees. Most evergreen tree leaves in the central Himalaya have a life span of more than one year, a period longer than for deciduous leaves [11][12][13] . Phenological processes such as leaf emergence, expansion, flowering and fruiting occur before the onset of monsoon when trees still bear old leaves unlike in deciduous trees where rehydration of leafless twigs becomes a prerequisite for initiation of new leaves 3,14,15 and the loss of leaf dynamics (nitrogen, specific leaf mass, etc.)…”