title: 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).
authors.affiliation: Amrit Science Campus, Tribhuvan University, Kathmandu, Nepal.
authors.forename: K
authors.initials: K
authors.lastname: Poudyal
authors.forename: P K
authors.initials: PK
authors.lastname: Jha
authors.forename: D B
authors.initials: DB
authors.lastname: Zobel
authors.forename: C B
authors.initials: CB
authors.lastname: Thapa
mesh_terms: D003681:Dehydration / Q000503:physiopathology; D029962:Fagaceae / Q000502:physiology; D019684:Magnoliopsida / Q000502:physiology; D009390:Nepal; D018515:Plant Leaves / Q000502:physiology*; D018526:Plant Transpiration / Q000502:physiology*; D029963:Quercus / Q000502:physiology; D029793:Rhododendron / Q000502:physiology; D012987:Soil; D014197:Trees / Q000502:physiology*; D014867:Water / Q000502:physiology
chemical_list: D012987:Soil; D014867:Water