Why the leaves of different plants are of different shape and size? r n rn
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Thin, broad leaves are an adaptation that provide maximum surface to collect sunlight with a minimal distance between the photosynthetic palisade cells and the raw materials for the photosynthetic reaction: CO2, water, sunlight.
In drier climates the leaf surface is reduced to slender blades or even to needles so there is less evaporative surface.
While places with plenty of water support plants with extraordinarily large and broad leaves if sheltered from wind damage. Large leaves with risk from wind damage, like palms, are compound to avoid shredding in the wind.
Compound leaves & lobed simple leaves allow wind to slip through without tearing the leaf. Trees often have simple leaves with variable degrees of lobe (fingers) depending on where the leaf grows on the tree. Canopy leaves will have deep lobes for wind to pass but internal leaves are sheltered so have shallower lobes. Compound leaves or deeply lobed leaves also permit more light to penetrate to interior leaves for photosynthesis.
Leaf margins can be smooth, toothed or serrated. If you lump all the toothed and serrated edges leaves together then they are much more common than smooth edges in temperate forests. Tropical forests have mostly smooth edged leaves.
Climate and leaf margin are closely tied. The presence of a toothed edge seems to offer unfolding leaves maximal photosynthesis as trees open their leaf buds when breaking winter dormancy. The teeth possibly increase transpiration/gas exchange so the plant is maximally photosynthetic when the day's temperature warm enough for photosynthesis to happen and light penetrates to all the young leaves of the canopy. In the higher latitudes temperature is a major rate limiting factor to photosynthesis.
Leaves must continue to transpire even in the rain, in high humidity or in dry air. This has produced ridges and hairs to control how water & air moves over the leaf surface. Hairs, spines, or surface coatings like wax that lower the surface convection can affect this surface boundary air layer. Less convection means less water loss.
Location of stomata is varied depending on the plant’s evolutionary adaptations. Some stomata are sunk in depressions on textured leaves; some are only on one side of leaves. Plants that hold one broad leaf-face flat to the sunlight have stomata only on the sheltered under-face while floating water-plants have stomata only on their exposed upper surfaces.
Yet another strategy is found with the eucalyptus trees. They have leaves that hang vertically to expose less area to the drying sun but allow the leaves to have stomata on both faces of the leaf. They can close the stomata facing the sun but keep the other, sheltered, stomata open.
The red leaf coloration is due to the chromoplasts in the leaves. Chromoplasts contain pigments, just like chloroplasts, but the pigments are not photosynthetic. Plants with more chromoplasts can survive growing in regions of marginal resources because they are better protected from both oxidative and UV stress.
The green leaved sugar maple is more sensitive to nutrient stresses associated with low pH soils than the red maple Acer rubrum. An increase in chromoplast content can offset the negative effects of poor nutrition on red maples by relieving its UV & oxidative stress.
Red maples can out compete other maples for nutrient poor, acidic soils by having more chromoplasts.
In drier climates the leaf surface is reduced to slender blades or even to needles so there is less evaporative surface.
While places with plenty of water support plants with extraordinarily large and broad leaves if sheltered from wind damage. Large leaves with risk from wind damage, like palms, are compound to avoid shredding in the wind.
Compound leaves & lobed simple leaves allow wind to slip through without tearing the leaf. Trees often have simple leaves with variable degrees of lobe (fingers) depending on where the leaf grows on the tree. Canopy leaves will have deep lobes for wind to pass but internal leaves are sheltered so have shallower lobes. Compound leaves or deeply lobed leaves also permit more light to penetrate to interior leaves for photosynthesis.
Leaf margins can be smooth, toothed or serrated. If you lump all the toothed and serrated edges leaves together then they are much more common than smooth edges in temperate forests. Tropical forests have mostly smooth edged leaves.
Climate and leaf margin are closely tied. The presence of a toothed edge seems to offer unfolding leaves maximal photosynthesis as trees open their leaf buds when breaking winter dormancy. The teeth possibly increase transpiration/gas exchange so the plant is maximally photosynthetic when the day's temperature warm enough for photosynthesis to happen and light penetrates to all the young leaves of the canopy. In the higher latitudes temperature is a major rate limiting factor to photosynthesis.
Leaves must continue to transpire even in the rain, in high humidity or in dry air. This has produced ridges and hairs to control how water & air moves over the leaf surface. Hairs, spines, or surface coatings like wax that lower the surface convection can affect this surface boundary air layer. Less convection means less water loss.
Location of stomata is varied depending on the plant’s evolutionary adaptations. Some stomata are sunk in depressions on textured leaves; some are only on one side of leaves. Plants that hold one broad leaf-face flat to the sunlight have stomata only on the sheltered under-face while floating water-plants have stomata only on their exposed upper surfaces.
Yet another strategy is found with the eucalyptus trees. They have leaves that hang vertically to expose less area to the drying sun but allow the leaves to have stomata on both faces of the leaf. They can close the stomata facing the sun but keep the other, sheltered, stomata open.
The red leaf coloration is due to the chromoplasts in the leaves. Chromoplasts contain pigments, just like chloroplasts, but the pigments are not photosynthetic. Plants with more chromoplasts can survive growing in regions of marginal resources because they are better protected from both oxidative and UV stress.
The green leaved sugar maple is more sensitive to nutrient stresses associated with low pH soils than the red maple Acer rubrum. An increase in chromoplast content can offset the negative effects of poor nutrition on red maples by relieving its UV & oxidative stress.
Red maples can out compete other maples for nutrient poor, acidic soils by having more chromoplasts.
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