Pearl River Delta is experiencing increased acid deposition and heavy metal pollution coupled with other anthropogenic activities during the rapid urbanlization course, which has threatened human life, natural communities, and the environment. Dr. WEN Dazhi and his research team (Environmental Ecology Group) of South China Botanical Garden selected representative forest ecosystems located in urban and suburban industrial areas as the polluted sites and that in remote rural region as the clean one. They determined the temporal trends and spatial patterns of selected pollution indicator elements and their relationships with multiple environmental indicators through systematic and synthesized analyses of annual radial growth, xylem wood chemistry, stable carbon and nitrogen isotopes of masson pine trees and chemistry of the rooting soils at each site, and obtained some important research progress recently.

Major findings are summarized as follows. (1) Masson pine trees grown at the polluted sites had suffered a prolonged recession since the late 1980s, and atmospheric acid deposition and the subsequent soil acidification, base-cations leaching and aluminum activation were the important contributors responsible for the growth recession; (2) Sulfur and heavy metal concentrations in pine needles and rooting soils revealed the spatial varieties of pollutants and the changes of environmental quality along the urban-rural transect, which suggested potential risks of pollutants and forest decline occurred over larger scales; (3) The historical scenario of atmospheric pollution was re-established by analyzing the tree-ring sulfur content with specific economic indicators; (4) Soil acidification at the study sites were successfully retrospected by using single indicator or mole ratios of elemental concentration(s) in tree-rings, and the mole ratios were particularly resonable and efficient；(5) Heavy metals(Pb,Cu,Cr) concentrations and the concentration index in Masson pine rings rose fastest since the late 1980s, coincided with the episodes of increased acid deposition and heavy metals in soils as the reform and opening-up policy was implemented in early 1980s; (6) Sampling and biomonitoring methods have been improved, when the whole needle was divided into apex, mid, base sections, and sheath, and the bark into inner and outer parts devided as separate samples for chemical assay. These results provide both scientific basis and empirical rationales for ecosystem health assessment, particularly under polluted stresses, and give insights for further study into the underlying mechanisms on forest recession. The study also provides large sets of original data on regional environmental changes that are difficult to be acquired by conventional ways of environmental monitoring.

Relevant results have been published in Environ Sci Pollut Res, 2007, 14: 270-275；For Ecol Manag, 2008, 255: 3534-3540; Ann For Sci, 2008, doi:10.1051 forest: 2008070；Environ Monit Assess, 2008, doi:10. 1007/s10661-008-0394-3; Front For Chin, 2009, 4(1): 1-6.