Litter-fall Characters And Hydrological Influences Of Pinus Massoniana Forests Damaged By Acid Rain In Chongqing Southwest China

A study was carried out in the typical acid rain region of Tieshanping in Chongqing during growing season (March-November) of 2009, to investigate the quantity, composition and monthly variation of litter-fall of Pinus massoniana forests which had been damaged by the long-term acid rain; meanwhile, the dynamics of soil moisture in different layers of root zone was monitored. It showed that, the total litter-fall in the growing season was 4704.27 kg·hm^-2, of which, 53.68% was needles and 25.69% was twigs; the weight ratio of inflorescences, barks, cones and other-litters accounted for 8.29%, 5.12%, 1.71% and 5.51%, respectively.As a result of decreased root quantity and topsoil concentrating of root distribution caused by long-term soil acidification, the monthly variation of litter-fall was more obviously influenced by the lower soil moisture. The monthly distribution of litter-fall was different from that of healthy forests, with a low period in May and June and a high period from July to November. The high period of needle litter-fall appeared from July to November, and the high period of twig litter-fall appeared from September to October.There was a significant negative correlation between the monthly total litter-fall and soil moisture of 0-40 cm layers in previous month, but there was no significant correlation with the soil layers below 40 cm. Among the components of monthly litter-fall, only the needle and twig were significantly correlated with soil moisture, with the most related layer of 0-10 cm and 30-40 cm, respectively. This indicated that the needle-litter was most sensitive to soil moisture, the twig-litter as the second sensitive one, but other components were not sensitive to soil moisture. Preliminary analysis showed a time lag of about one month for the response of litter-fall to soil water condition. Statistic relations among litter-fall, weather conditions and soil moisture in previous month were derived as follows: y1=2004.750-6686.992x1+185.067x₂ (R²=0.89) among the monthly total litter-fall (y1), soil moisture of 10-20 cm layer (x1) and monthly mean wind speed (x₂); y₂=1252.392-3304.796x₃ (R²=0.73) between monthly needle litter-fall (y₂) and soil moisture of 0-10 cm layer (x₃); y₃=1662.136-5452.943x₄ (R²=0.79) between monthly twig litter-fall (y₃) and soil moisture of 30-40 cm layer (x₄); y₄=-6.949+0.237x₅ (R²=0.81) between monthly bark litter-fall (y₄) and monthly evaporation (x₅); y₅=-202.310+11.247x6 (R²=0.79) between monthly inflorescence litter-fall (y₅) and monthly maximum wind speed (x6); y6=4.041+0.034x₇ (R²=0.61) between monthly cone litter-fall (y6) and monthly precipitation (x₇); y₇=-838.669+29.049x₈ (R²=0.64) between monthly other litter-fall (y₇) and monthly mean air pressure (x₈).With decreasing soil moisture in the 0-10 cm layer, the monthly needle litter-fall increased linearly, until the soil moisture lowered to 28%, thereafter it remained less changed. For the monthly twig litter-fall, it increased just after the soil moisture in the 30-40 cm layer decreased below 28%. The different response of needle and twig litter-fall to soil moisture made an integrated result of fast linearly increase of monthly total litter-fall with decreasing soil moisture in the 10-20 cm layer.