© 2004 Heron Publishing—Victoria, Canada
Patterns of leaf conductance and water potential of five Himalayan tree species
K. Poudyal (1), P. K. Jha (2), D. B. Zobel (3, 4) and C. B. Thapa (5)
1. Amrit Science Campus, Tribhuvan University, Kathmandu, Nepal / 2. Central Department of Botany, Tribhuvan University, Kirtipur, Nepal / 3. Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331-2902, USA / 4. Corresponding author (zobeld@science.oregonstate.edu) / 5. P.N. Campus, Tribhuvan University, Pokhara, Nepal / Received May 26, 2003; accepted November 15, 2003; published online April 1, 2004
Summary
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 (Ψs15) and 30 cm (Ψs30) depths, tree water potential at predawn (Ψpd) and midday (Ψmd), and leaf conductance during the morning (gwAM) and afternoon (gwPM) were observed from December 1998 to April 2001, except during the monsoon months. There was significant variation among
sites, species and months in Ψpd, Ψmd, gwAM and gwPM, and among months for all species for Ψs15. Mean Ψpd and Ψmd 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 Ψ 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 Ψpd were related to phenology and leaf damage. During leafing, Ψpd often increased. Mean gwAM and gwPM 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 (Ψ) at 15 cm depth correlated with plant Ψ in all species, but rarely with gwAM and not with gwPM. Plant Ψ declined with increasing elevation, whereas gw increased. As Ψpd declined, so did maximal gw, but overall, gw was correlated with Ψpd only for R. arboreum. Schima wallichii maintained high Ψ, with low stomatal conductance, as did Castanopsis indica, except that C. indica had low Ψ during dry months. Rhododendron arboreum maintained high Ψpd and gw, despite low soil Ψ. Quercus lanata had low gw and low Ψpd in some months, but showed no correlation between tree Ψ and gw. Quercus semecarpifolia, which grows at the highest elevation, had low soil and plant Ψ and high gw.
Keywords:
adaptation, Castanopsis indica, drought, Quercus lanata, Quercus semecarpifolia, Rhododendron arboreum, Schima wallichii, water stress.
