Biogenic volatile organic compounds (BVOCs) play an essential role in biosphere-atmosphere interactions, and their impacts on global climate have received increasing attention. Tropical rainforest is regarded as the biggest BVOCs source among terrestrial ecosystems, but the emission of BVOCs from tropical forests in South-East Asia, is still unclear in terms of both its amount and physiological functions. Model studies suggest that this region may contribute more than half of the global BVOCs emission, but flux measurements indicate much less emission as compared with Amazon tropical forests. Since BVOCs emission varies highly with biological and environmental factors, detailed field assessments are necessary to clarify the magnitude and ecology in BVOCs emission from the vast South-East Asian tropical forests.
Isoprene is one of the key identified BVOCs. In this study, we were to address isoprene emission in some typical species in the South-East Asian tropical forests, and its relation to light environment and photosynthetic physiology. We measured CO2 gas exchange, fluorescence and isoprene emissions (Is) in 10 species (including 4 families and 7 genera) with different light tolerance under 4 different light environments. The measurements were conducted using a portable Li-6400 system in combination with an air sampling system modified ourselves. Natural plants are used from a secondary rainforest in the Pasoh Forest Reserve in the west Malaysia.
Results/Conclusions
Major results are as follows:
Isoprene emission rate measured under a PAR (photosynthetic active radiation) of 1000 μmol m-2 s-1 and leaf temperature (30℃) differed considerably among different species. Significant isoprene emission was observed only in two shade-intolerant species (Macaranga gigantia and Macaranga hypoleuca), while the other shade-intolerant and all shade-tolerant species show little isoprene emission.
- Isoprene emission rate in seedlings of the above two shade-intolerant species increased with the decrease of the maximum assimilation rate (A), stomatal conductance (gs) and intercellular CO2 concentration (Ci).
- In juveniles of the two species, however, isoprene emission rate increased with the increase of gs and A.
- Fluorescence data suggests that emission of isoprene is correlated with the capability of heat loss.
Our study indicates that the isoprene emission is species- and age-dependent in the South-East Asian tropical forests. Shade-tolerant species or plants under low light environments may have less contribution to the emission of BVOCs.