The Preliminary Study On Through-fall & Litter-fall Of Subtropical Forest Under Acidic Deposition Condition, South China

The study in this paper was supported by the Integrated Monitoring Program on Acidification of Chinese Terrestrial Systems (IMPACTS ). It carried out at three cites located in south of China. The main research contents including three parts: the relationship of canopy and rainfall, the temporal and spatial variability of forest litterfall and the influence of O₃ & weather factors on litterfall mass. The main results are summarized as following: (1) The temporal variation of canopy throughfall of four plots at each studied site has the same trend. The unitary linear regression equation can well show the relationship of CTF and WO at every studied plots and sites. (2) The analysis results of pH value of WO at three studied sites showed that the sequence of pH value for three studied cites was: LXH> LGS> CJT. All WO of three sites belong to serious acid deposition. The further analysis results of the ratio [SO₄^2-] / [NO₃^-] of WO showed the wet deposition of LXH is SO42-acid deposition, while that of LGS and CJT are SO₄^2- & NO₃^-mixed acid deposition. (3) [Ca²⁺], [Mg²⁺] of throughfall rooted in the washout action of the atmosphere deposition and the secretion of canopy when raining. The analysis result of radio Ca plus Mg to Al suggested that little Al element was carried to soil through throughfall at three studied cites. (4) The analysis results showed that there resisted the prominently relative relationship between the SO₂ and NO₂ of atmosphere to [SO₄^2-], [NO₃^-] of throughfall at CJT, while there were not the closely relationship between dry deposition to the elements of throughfall at LGS and LXH. The study result also suggested that the influence of SO₂ at CJT was more power than that of NO₂. (5) The curves of Monthly Variation of Litterfall Mass is different among 3 study sites. The curves of LGS forests and bamboo at CJT are single-peak, while the curve of LXH forests and the broadleaves forests at CJT are double-peak. The X-coordinate and value of peak at studied sites is related with atmospheric temperature and RH closely. (6) There are not the prominent linear relationship between the average litterfall mass and O₃ & weather factors at each plots. However, O₃ is a important factor for litterfall Mass at all studied plots. Under some special conditions, the factors of temperature, WO and wind maybe become the main influence factors for forest litterfall Mass. (7) The ( Ca+ Mg)/Al ratio of litterfall at LXH is higher than 3, which was more lower than the other two studied cites. It's maybe the reason why the buffer ability of litterfall to prevent the soil acidification at LXH is lower than other two studied cites. So the soil at LXH would more easily be acidified.