Effect of leaf phenology, and tree age on leaf ecophysiology traits and adaptive strategies of Alnus nepalensis in central Himalaya
The leaf ecophysiological traits are expected to change with the leaf age, and tree age. Leaf phenology and tree age (seedling, sapling, and tree stages) was a stronger driver of changes in ecophysiological traits. In the present study, we measured effect of leaf phenophases (initiation stage, expansion stage, and senescence stages) and tree age (seedling, sapling, and tree stages) on the leaf physiological and morphological traits of nitrogen-fixing Alnus nepalensis (D. Don), a pioneer tree species in the central Himalaya. In fully expanded leaf and seedling stage demonstrate ecophysiological traits consistent with an acquisitive resource-use strategy. Results revealed that net photosynthetic capacity (Aarea and Amass), leaf stomata conductance (gswarea and gswmass), transpiration rate (Earea and Emass), specific leaf area (SLA), pre-dawn and mid-day water potential (Ψ), leaf total chlorophyll concentration, photosynthetic N-, and P-use efficiency (PNUE and PPUE) were highest in seedling stage and sapling than trees. Seedling stage and sapling had significantly higher transpiration rates (Earea and E mass) and stomatal conductance (gswarea and gswmass), therefore showing significantly lower water use efficiency (WUE) and intrinsic water use efficiency (WUEi). Mass-based net photosynthetic capacity (Amass) were positively correlated with PNUE, PPUE, transpiration rate, stomatal conductance, SLA, and chlorophyll concentrations while negatively correlated with WUE and WUEi. However mass-based leaf nitrogen (N), and phosphorus (P) concentrations were higher in fully expended leaf; they did not vary significantly, despite N concentration negatively correlated with SLA. Collectively, our results indicated that seedling A. nepalensis displayed characteristic values associated with a more acquisitive resource-use strategy. Consequently, this may explain their survival and replacement strategies during secondary succession and should be considered for the vegetation restoration model of degraded forest in the central Himalaya.