Sun-Shade Plasticity in Leaf Traits of Early and Late-Successional Tree Species in a Low Land Rain Forest South West Sri Lanka

Light is one of the most limiting resources for plant growth and survival in lowland rainforests. Leaf morphology and leaf chemical characteristics have proven to be importantfeatures that adjust continuously to the changing light environment. The objective of thestudy was to investigate the plasticity of leaf traits of early and late-successional species, andto compare the plasticity differences in leaf traits of sun and shade leaves of these twogroups. Ten species were selected for the study: five early-successional species; Alastoniamacrophylla, Trema orientalis, Macaranga peltata, Wendlandia bicuspidate andSchumacheria castaneifolia and five late-successional species; Shorea congestiflora, Mesuanagassarium, Dipterocarpus zeylanicus, Shorea disticha and Shorea cordifolia.Sun and shade leaves of fully matured trees were collected from three sample locations.Measured chemical attributes are leaf nutrients (leaf Nitrogen and Phosphorus) and leafchlorophyll content. Chlorophyll: Nitrogen ratio was calculated using these values. Measuredmorphological attributes are leaf length, leaf width, leaf area, and leaf dry /fresh weight andderived parameters are leaf dry matter content and specific leaf area. Leaf trait plasticity wascalculated for each species based on the mean leaf trait values in the sun and shade.Most of the leaf chemical and morphological characteristics varied between sun and shadeleaves of early and late successional groups. Specific leaf area was higher in shade leavesthan sun leaves (p > 0.05). In early- successional species, leaf trait plasticity was higher inspecific leaf area (19%), Nitrogen content (23%), Phosphorus content (31%) and it wasrelatively low in leaf area (5.7%), leaf length (4.2%) and leaf width (4.6%). In latesuccessionalspecies, leaf trait plasticity was higher in specific leaf area (10.3%), Nitrogencontent (16.4%) and Phosphorus content (21%) and plasticity was relatively low in leaf area(3.5%) and leaf length (4%).Early -successional species have shown a higher plasticity thanlate-successional species.