High CO2 concentration increases relative leaf carbon gain under dynamic light in Dipterocarpus sublamellatus seedlings in a tropical rain forest, Malaysia

Understory plants in tropical forests often experience a low-light environment combined with high CO2 concentration. We hypothesized that the high CO2 concentration may compensate for leaf carbon loss caused by the low light, through increasing light-use efficiency of both steady-state and dynamic photosynthetic properties. To test the hypothesis, we examined CO2 gas exchange in response to an artificial lightfleck in Dipterocarpus sublamellatus Foxw. seedlings under contrasting CO2 conditions: 350 and 700 μmol CO2 mol(-1) air in a tropical rain forest, Pasoh, Malaysia. Total photosynthetic carbon gain from the lightfleck was about double when subjected to the high CO2 when compared with the low CO2 concentration. The increase of light-use efficiency in dynamic photosynthesis contributed 7% of the increased carbon gain, most of which was due to reduction of photosynthetic induction to light increase under the high CO2. The light compensation point of photosynthesis decreased by 58% and the apparent quantum yield increased by 26% at the high CO2 compared with those at the low CO2. The study suggests that high CO2 increases photosynthetic light-use efficiency under both steady-state and fluctuating light conditions, which should be considered in assessing the leaf carbon gain of understory plants in low-light environments.

Population genetics of Intsia palembanica (Leguminosae) and genetic conservation of Virgin Jungle Reserves in Peninsular Malaysia

A field survey of Virgin Jungle Reserve (VJR) compartments in Peninsular Malaysia allowed us to identify six populations of Intsia palembanica for this study. These were Pasoh Forest Reserve (FR) (Pasoh), Sungai Lalang FR (Lalang), Bukit Lagong FR (Lagong), Bubu FR (Bubu), Bukit Kinta FR (Kinta), and Bukit Perangin FR (Perangin). About 40 adult individuals were sampled in each population. In addition, progeny arrays were collected from nine mother plants at Lagong for a mating system study. A total of nine allozymes, encoded by 14 putative gene loci, were consistently resolved in I. palembanica. The mating system study showed that the species exhibited a mixed-mating system, with multilocus outcrossing rate of 0.766. The levels of diversity were comparably high (mean number of alleles per polymorphic locus = 2.4, mean effective number of alleles per polymorphic locus = 1.64, and mean expected heterozygosity (H(e)) = 0.242), and the majority of the diversity was partitioned within population (G(ST) = 0.040 and F(ST) = 0.048). Significant levels of inbreeding were detected in Bubu and Perangin. Probability tests of recent effective population size reduction using the Infinite Allele Model showed the occurrence of genetic bottlenecks on Lalang and Kinta. Two genetically unique populations (Pasoh and Perangin) were inferred using jackknife analysis. By using the neutral mutation rates, effective population size (N(e)) to maintain the H(e) was 80-800 000 individuals. A simulation study based on pooled samples, however, circumscribed the N(e) to 200 and 210 individuals. Implications of the study for managing the species and the VJRs are discussed.