Study of plant water relations

Abstract

Study on plant water relations and phenology of Castanopsis tribuloides and Quercus leucotrichophora was performed in Shivapuri Nagarjun National Park, Kathmandu, Nepal. Monthly variation in water relation parameters and phenological processes such as leaf emergence, senescence, flowering, fruiting, etc. of C. tribuloides and Q. leucotrichophora were studied. The measurements were carried out from February 2019 to January 2020 at monthly interval. Water relation parameters like soil moisture content at 15 cm and 30 cm depth, Pressure Volume (P-V) curve analysis, Huber value (Hv), specific conductivity (Ks), leaf specific conductivity (Kl), hydraulic conductivity (Kh), specific leaf mass (SLM), twig starch content and phenological changes were recorded. Soil moisture content showed significant variation among sampled months and was lowest in the month of February. Relative water content at zero turgor (RWCz) showed lowest value during March in both species. Both osmotic potential at zero and full turgor (ψsz and ψsf respectively) showed lowest value during November in C. tribuloides and during January in Q. leucotrichophora when post monsoon rain was negligible. High elasticity in C. tribuloides was found in April and showed a synchrony with the ongoing phenological activities. Phenological activities such as bud break, leaf emergence, twig emergence and shoot elongation in both species started with the onset of dry months (February-May) while flowering in Q. leucotrichophora started in dry months but in C. tribuloides flowering took place in the month of September. Low values in Relative Water Content at zero turgor (RWCz), osmotic potential at zero turgor (ψsz), xylem conductance and index of elasticity (ε) were found during dry months in both species in spite of high IDT. Xylem conductance had a strong effect on phenological activities. Some patterns of xylem conductance were related to leaf emergence as Kh, Kl and Hv increased in February. Starch0 and starch1 in both species showed high seasonal variation and had a strong effect of phenological activities. SLM decreased at the time of senescence and increased when leaves were fully