Department of Botany, Dolphin (PG) Institute of Bio-Medical and Natural Sciences, Dehradun, Uttarakhand, 248007, India.
Central Himalayan Environment Association (CHEA), Dehradun, Uttarakhand, 248007, India.
Environ Monit Assess. 2023 Jan 3;195(2):258. doi: 10.1007/s10661-022-10860-9.
The difference in maintaining a safety margin with regard to hydraulic conductance between pine and oak species influences their distribution in a region. Chir pine (Pinus roxburghii) and banj oak (Quercus leucotrichophora) are the principal species of Central Himalayan forests between 1000 and 2000 m elevations. Nearly 80% of annual precipitation of ~ 1400 mm in the region occurs during monsoon, from mid-June to September, whereafter droughts of varying length and intensity are common. The main objective of the study is to find out the responses of these two evergreen tree species to pre-monsoon (March to mid-June) water stress and topographical heterogeneity that occur in Central Himalaya. We measured soil and tree water potential and osmotic adjustment across five seasons on three slope positions, namely, hill base, mid-slope, and hill top, on north and south slope aspects. Chir pine showed an early response to pre-monsoon drought by restraining daily change in Ψ to 0.89 MPa, while predawn Ψ (Ψ) was still moderate (isohydric tendency). In contrast, the daily reduction in Ψ of banj oak kept on increasing up to 1.49 MPa, despite severely low Ψ (anisohydric tendency). In both tree species, Ψ was invariably lower on south aspect than north aspect and declined from hill base to hill top. Such responses to slope aspect and position, however, were relatively less apparent in chir pine, which tended to maintain a wide safety margin when under stress. As for soil Ψ, banj oak site retained monsoon rainwater more effectively than chir pine.
松科和壳斗科树种在维持水力传导率安全裕度方面的差异影响着它们在一个地区的分布。华山松（Pinus roxburghii）和巴东栎（Quercus leucotrichophora）是喜马拉中央山脉海拔 1000 至 2000 米之间森林的主要树种。该地区近 80%的年降水量约为 1400 毫米，主要集中在季风期（6 月中旬至 9 月），此后旱季的长短和强度各不相同。本研究的主要目的是找出这两个常绿树种对喜玛拉中央山脉预季风（3 月至 6 月中旬）水胁迫和地形异质性的响应。我们在北坡和南坡的三个坡面位置（山脚、坡面中部和山顶），横跨五个季节，测量了土壤和树木水势和渗透调节。华山松对预季风干旱的反应较早，通过将每日 Ψ 变化限制在 0.89 MPa，而黎明前 Ψ（Ψ）仍适中（等水倾向）。相比之下，尽管巴东栎的每日 Ψ 减少仍在继续增加，达到 1.49 MPa，但仍保持较高水平（异水倾向）。在这两个树种中，南坡的 Ψ 始终低于北坡，从山脚到山顶呈下降趋势。然而，这种对坡面方位和位置的响应在华山松中相对不太明显，因为华山松在受到胁迫时倾向于保持较大的安全裕度。至于土壤 Ψ，巴东栎的生境比华山松更有效地保留了季风降雨。
