Leaf toughness increases with tree height and is associated with internal leaf structure and photosynthetic traits in a tropical rain forest

Although leaf toughness is an essential plant adaptation to herbivore pressure and environmental stress, the relationships of with anatomy photosynthetic traits, its spatial variations within tropical rainforests, remain poorly understood. We measured these traits in 103 tree species belonging 27 families from canopy understory using a crane system rainforest Sarawak, Malaysia. focused on anatomical trait bundle-sheath extensions (BSEs) around vascular bundle due their diverse ecophysiological functions. divided trees into heterobaric BSEs homobaric lacking BSEs, investigate height, functional such as carbon (C) nitrogen (N) content, thickness, mass per area (LMA) maximum rate ( P max ). Leaf toughness, LMA, thickness C N contents increased height regardless BSE presence. Heterobaric leaves had greater than leaves, whereas LMA were similar between two types throughout gradient. found that standardized or was species, consist mainly fibrous tissue. higher for upper presumably functions including water conductivity, but did not differ type lower layers. In other words, efficiently exploit advantages tougher by having BSEs. The proportion , consistent physically stressful conditions canopy, high strong light.