Wet and dry season ecosystem level fluxes of isoprene and monoterpenes from a southeast Asian secondary forest and rubber tree plantation

Abstract

Canopy scale fluxes of isoprene and monoterpenes were investigated in both wet and dry seasons above a rubber tree (Hevea brasiliensis)/secondary tropical forest in the Yunnan province of southwestern China. Drought conditions were unusually high during the dry season experiment. The eddy covariance measurement technique was used to measure isoprene fluxes, while monoterpene fluxes were modeled based on leaf level emission measurements. Maximum observed isoprene fluxes occurred during the wet season and daytime average fluxes were about 1 mg C m À2 h À1. Dry season fluxes were much lower with a daytime average of 0.15 mg C m À2 h À1. Wet season isoprene fluxes compare quite well with isoprene fluxes observed from other tropical forests. Monoterpene fluxes came, almost entirely, from Hevea brasiliensis, which is a light-dependent monoterpene emitter. Modeled wet season total monoterpene fluxes were about 2 mg C m À2 h À1 (average for the daytime), and in the dry season were undetectable. Extreme drought conditions, and the drought deciduous nature of Hevea brasiliensis may be the cause of the low dry season fluxes. r

Volatile organic compounds from vegetation in southern Yunnan Province, China: Emission rates and some potential regional implications

“…This is consistent with other studies in the tropics . It is possible that isoprene emissions increase during the dry season due to higher cumulative radiation exposure as observed by Sharkey et al (1999), Geron et al (2000), and Pe´tron et al (2001), although the cooler nighttime temperatures observed during the dry season at this site (Baker et al, 2005) have been found to reduce isoprene emission potential in these same studies.…”

“…In 1983 Hevea plantations occupied 50,200 ha in Xishuangbanna Prefecture, or 2.6% of the total land area. This increased to 118,000 ha (6.2%) in 2000, and further increased to 170,000 (9.0%) ha by 2003 (Baker et al, 2005). Baker et al (2005) estimates that typical wet season daytime average monoterpene fluxes from H. brasiliensis plantations are approximately 10 times higher (2.0 vs. 0.2 mg C m À2 h À1 ) than typical mixed tropical forest (or non-forest) landscapes.…”

“…A Baccaurea ramiflora tree near a flux tower (Baker et al, 2005) emitted no isoprene and exhibited negligible CO 2 assimilation (A) and stomatal conductance (g s ) rates upon initial enclosure. However, we induced it to emit isoprene at a rate of 10 mg C g À1 h À1 by removing moisture from the purge air, elevating vapor pressure deficit and temporarily opening the stomata.…”

Biogenic emissions of isoprenoids and NO in China and comparison to anthropogenic emissions

“…Baker et al (2005) have recently demonstrated that monoterpene emissions from subtropical Chinese vegetation can be light-dependent but it is not known if this behavior is widespread in China. We have used Eq.…”

“…However, the emission inventory described by that study does not include biogenic emissions. There are a few measurements of biogenic VOC emissions, including grasslands in northern China (He et al, 2004), and tropical forest in southern China (Wang et al, 2005a, b;Baker et al, 2005;Geron et al, 2006). To fully understand the chemistry in China and to model the distributions of air pollutants, the biogenic emissions of VOCs and NO need to be estimated.…”