Phenology and water relations of eight woody species in the Coronation Garden of Kirtipur, central Nepal

Abstract

Phenological activities of eight woody species planted in Kirtipur (central Nepal) were examined, each for one dry season between September 2001 and June 2003. From Pressure Volume (P-V) analysis, we determined relative water content at zero turgor (RWC_z), osmotic potential at zero turgor (Ψ_sz) and full turgor (Ψ_sf ), and bulk modulus of elasticity (ε) once a month through the course of dry season. Both evergreen species (Cotoneaster bacillaris Wall., Quercus lanata Sm., Ligustrum confusum Decne., Woodfordia fruticosa (L.) Kurz.) and deciduous species (Celtis australis Linn., Alnus nepalensis D.Don., Bauhinia variegata Linn. and Lagerstroemia indica Linn.) put out their new leaves during the dry summer when day length and temperature were increasing. Generally, bud break coincided with concentrated leaf fall during the dry summer and the leaf fall reduced total leaf area to its lowest value. The deciduous species were leafless for one to three months, followed by a prolonged period of leaf production and shoot elongation. Evergreen and deciduous species manifested distinct adaptive strategies to water deficit. Evergreens can reduce osmotic potential (Ψ_s) to its low value and maintain proper water potential (Ψ) gradient from soil to plant, which facilitates absorption of water during dry season. Elastic tissue in deciduous species is coupled with leaf shedding during the dry season; both factors may help maintain proper Ψ_s for new growth during dry period. One evergreen species (Woodfordia fruticosa) and three deciduous species (Celtis australis, Bauhinia variegata and Lagerstroemia indica) have inherently high dehydration tolerance due to their elastic tissue. During drought there has been osmotic adjustment in Quercus lanata, and elastic adjustment in Ligustrum confusum, Celtis australis and Lagerstroemia indica. Key words: Himalayas, Pressure Volume (P-V) curve, relative water content (RWC), osmotic adjustment, elastic adjustment Himalayan Journal of Sciences Vol.4(6) 2007 p.49-56