Leaf hairs may assist in maintaining high leaf water use efficiency in tropical secondary forest tree species. We compared leaf temperature, transpiration, photosynthesis and water use efficiency between hairy and depilated leaves in Mallotus macrostachyus (Euphorbiaceae), to determine the role of leaf hair in leaf water use efficiency (WUE) in tropical degraded secondary forest in Malaysia. Measurements were made on five mature individuals growing in sun-exposed conditions and five in shaded conditions. The hair dry weight per unit leaf area was significantly greater in sun leaves than in shade leaves. The transpiration rate (Tr max ) of depilated leaves in sunexposed conditions was slightly higher than in hairy leaves in both morning and afternoon measurements. In contrast, Tr max in the shade leaves was almost identical in hairy and depilated leaves. Leaf stomatal conductance (g s ) in the morning showed almost the same value among leaf types and light conditions. In the afternoon, g s slightly decreased from the morning values in both sun and shade conditions. In the morning, the leaf water use efficiency (A max /Tr max ) in both conditions did not differ significantly between hairy and depilated leaves. However, in the afternoon, WUE in the depilated leaves was significantly lower than in hairy leaves in sun-exposed conditions. These observations suggest that leaf hairs in M. macrostachyus contribute to the high leaf water use efficiency in drought conditions, such as high vapor pressure deficit experienced at midday in degraded tropical secondary forests.
Degraded secondary forests after burning or other disturbances are widely distributed throughout Southeast Asia 62 . These secondary forests usually show significantly lower above ground biomass, species richness and various forest products such as timber and medicine compared with late successional tropical rainforests 9,10,13,39,42 .Enrichment planting in the secondary forest may be a highly effective method for rehabilitating the forest, using endemic tree species, which provides benefits including timber and medicinal products 1,29,34,35,48 . A better understanding of ecological traits such as strong light tolerance for the target species could improve techniques for enrichment planting in the secondary forest 4,26,32 . Leaf ecophysiological traits should provide valuable ecological information, since leaf photosynthesis is essential to JARQ 42 (4), 299 -306 (2008) AbstractLeaf ecophysiological responses and height growth were studied in four indigenous tree seedlings planted under different size gaps in degraded tropical secondary forest. Dyera costulata, Dipterocarpus baudii, Neobalanocarpus heimii, and Pouteria sp. were selected for study species. The leaf photosynthetic rate at light saturation (A max ), light compensation point (I c ), leaf nitrogen content, and SPAD value were measured at two months after planting. The ratio of variable to the maximum fluorescence (F v /F m ), which represents the maximal photochemical efficiency of photosystem II was also determined at two months after planting. All measurement leaves were old leaves, which had acclimated before the planting light condition. Canopy openness above the seedlings was estimated from a hemispherical photograph, ranged from 6 to 53%. The relationships between canopy openness and A max among species were categorized into two groups. The first group (N. heimii and Pouteria), which had relatively high wood density and late successional status, showed that the maximum A max appeared under relatively low canopy openness such as approximately 10%. A max of the second group (D. costulata and Dip. baudii), which had relatively low wood density and high light demand, maximized from 20 to 40% of canopy openness. Seedling height growth of the first group was lower than the second group. The first group also showed lower F v /F m at high canopy openness than the second group. These responses indicated that the first group may be categorized to less tolerant species for strong light conditions during the early transplanted stage. I c of D. costulata, N. heimii and Pouteria decreased with decreasing canopy openness. These species have high acclimation ability to shade conditions from the early transplanted stage, since these responses contribute to raise the photosynthetic efficiency under shade conditions.
We assessed the variability of chloroplast DNA sequences in populations of the dipterocarp forest tree, Shorea curtisii. This species is widely distributed in hill and coastal hill dipterocarp forests of the Malay Peninsula, whereas isolated populations are found in the coastal hills of north Borneo. Two chloroplast DNA regions (1555 bp of trnH-psbA-trnK and 925 bp of trnL-trnF) were sequenced from 123 individuals collected from six Malay Peninsula and two Bornean populations. There were 15 chloroplast haplotypes derived from 16 polymorphic sites. A haplotype network revealed two distinct haplogroups that correlate with two geographic regions, the Malay Peninsula and Borneo. These two haplogroups differed by a number of mutations, and no haplotypes were shared between populations from the different geographic regions. This suggests an ancient diversification of these haplogroups, and that long-distance seed dispersal was unlikely to have occurred during the Pleistocene when the Sunda Shelf was a contiguous landmass. Phylogenetic analysis of the haplotypes together with those found in other Shorea species showed that two haplogroups in S. curtisii appear in different positions of the phylogenetic tree. This could be explained by the persistence of ancestral polymorphisms or by ancient chloroplast capture. Low levels of genetic differentiation were found between populations within each geographic region. Signature of a bottleneck followed by demographic expansion was detected in the Malay Peninsula haplogroup. The presence of two distinct evolutionary lineages in the different regions suggests that they should be managed independently to conserve the major sources of genetic diversity in S. curtisii.
Sprouting ability is highly variable among different tree species. In many cases, there are trade-offs in carbon allocations between growth and storage in seedlings. However, this trade-off is likely to change with growth stages from seedling to mature plant because carbon investments in reproductive activities and/or risk of disturbance also change by species and growth stage. To examine how sprouting ability and carbohydrate storage change with growth stage, we compared two tropical secondary-forest trees, Macaranga bancana and M. gigantea, which have different ecological traits. Maximum tree size and growth rate are higher in M. gigantea. We monitored sprout growth and stored resources, including total nonstructural carbohydrate (TNC) and nitrogen in the root, among different tree sizes for 12 months following stem-cutting treatment. Sprouting ability (total sprout mass) and TNC concentrations were significantly higher in small individuals than in larger specimens in both species. TNC concentration decreased in all size classes after stem cutting. Macaranga bancana had greater sprout survivorship than M. gigantea, which had higher sprouting ability in larger tree-size classes. Thus, sprouting ability likely depends on root TNC concentration and tree-size class in both Macaranga species. Higher TNC concentration and sprout survival rates in M. bancana may be related to greater carbon allocation in survival than in growth. This hypothesis is consistent with the ecological traits of M. bancana, such as its growth rate, which was lower than that of M. gigantea.
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