Quantifying leaf-trait co-variation and strategies for ecosystem functioning of Quercus leucotrichophora (Ban Oak) forest in Himalaya

Leaf functional traits determine a plant’s survival and growth. Variation in leaf traits control the functioning of forest ecosystem. The study examines the variation in 18 leaf traits (4 morphological, 6 physiological, 6 biochemical, and 2 stoichiometry) of 3 dominant evergreen broadleaved tree species (Quercus leucotrichophora, Rhododendron arboreum, and Myrica esculenta) of Ban Oak forests (BOF) of Garhwal Himalaya. The aim of the study is to understand the resource utilization plant strategy of major tree species of BOF and determining the impact of seasonality and elevation on leaf traits. Leaf traits data were collected during three seasons (winter, summer and monsoon) within two altitudes (1400–1700 amsl and 1701–1980 amsl) for two years (2019–2021). Thirty-six individuals from each of the three major tree species were selected for measurement on leaf traits for the three seasons of two years. Results showed that specific leaf area, leaf mass per area, photosynthesis rate, stomatal conductance, intercellular CO2, transpiration rate, leaf phosphorus, potassium concentration, and photosynthetic nitrogen use efficiency were higher during monsoon season. However, intrinsic water use efficiency and leaf nitrogen concentration were higher during summer season, and leaf dry matter content, water use efficiency, and leaf C/N were higher in winter season. Structural Equation Modelling (SEM) was used to established the relationship between plant strategies, i.e. resource capture and defense (RCD), gas exchange (GE), photosynthetic and resource utilization (PRU), and nutrient cycle and limitation strategy (NCL). Among the morphological, physiological, biochemical and stoichiometry traits, specific leaf area, transpiration rate, leaf nitrogen concentration, and leaf C/N ratio, were having positive relationship with RCD, GE, PRU and NCL, respectively. Result demonstrates that all the three major species of BOF had resource conservative strategies. Q. leucotrichophora was major species for forest functioning, whereas M. esculenta had higher resource uptake efficiency. Overall, leaf traits were varied with different species and seasonal changes facilitate an adaptive role in a plant's survival under the existing microclimatic condition. The findings of the study provides insight into changes in leaf traits and the plant strategies at the temperate forests of the Himalayas and provide inputs for projection of future changes in leaf attributes and the environment's adaptation at Himalaya and regional level.