| In nutrient cycling in plant—litter—forest soil ecosystem,plant community as the initiative factor absorbs nutrients from soil and establishes its organic body.The nutrients absorbed can be returned to the soil by litter.As the basic carrier of nutrients,litter acts as the ligament between the plant and soil in the nutrient cycling.Therefore,litter plays very important role in maintaining soil fertility,facilitating the normal cycling and balance of nutrients in forest ecosystems.Litterfall is an important component of productivity of forest ecosystem and an important part in biochemical cycling as well.Thus,it is necessary to conduct litterfall study for understanding the function of forest ecosystems.This study was conducted to observe the dynamic patterns of litterfall and related nutrients in a subtropical evergreen broad-leaved forest in Xiaoken forested watershed,southern Anhui. The purpose of the study is to determine litterfall production and its chemical composition, which would be helpful for the retoration and sustainable management of subtropical forest. The result from the study are shown below.1.Forest structure and species diversityA total of 26 tree species(DBH≥3.0 cm) appeared within the 5 sampling plots in the forest,which belong to 15 families and 21 genera.Fagaceae and Hamamelidaceae were dominant family for this forest.The vertical structure of the forest was simple without obvious shrub and herb layers.The stand density ranged from 4152(18-yr) to 2492(65-yr) stems hm-2.The trees with DBH≥20 cm contributed about 3%of the total number in the young stands(18-and 36-yr) and 30%in the old stands(over 40-yr),while the basal area of those large trees contributed,respectively,6.7%～20.6%and 61.9%～70.7%of the total basal area for different successional phases of young(18-and 36-yr) and old(over 40-yr) stands.The diversity index and equality of tree species in old stands averaged 1.79 and 0.53.Based on the importance value,the dominant family for the forest was Fagaceae, and the dominant tree species were Castanopsis eyrei,C.sclerophlla,Lithocarpus harlandii,and Cyclobalanopsis glauca.In the view of successional trend,C.sclerophlla and L.harlandii were development type and successional mid-phase species,while C.eyrei and C.glauca were growing type and climax phase species.2.Litterfall productionAnnual litterfall production of the 36-yr stand ranged from 6.91 to 9.07 t hm-2,and for 48-yr stand from 7.86 to 9.05 t hm-2.The average annual litterfall productions of the stands mentioned above were 9.07 t hm-2 and 8.45 t hm-2.3.Litter componentsThe different components of litter showed a consistent annual temporal sequence in the following order:leaves＞flowers and fruits＞raffle＞branches.The amount of leaf litter was the absolute dominance in this subtropical evergreen broad-leaved forest in Xiaokeng, which controlled the annual variation in litterfall.4.Litterfall patternThe annual temporal pattern of total litterfall of the forest showed two peaks,one in April to May and another in November to December.5.Leaf litter of the dominant treesIn the 36-yr stand,the total leaf litter of Castanopsis eyrei(Champ.) Tutch.,Castanopsis sclerophlla(Lindl.) Schott.,Cyclobalanopsis glauca Oerst.and Lithocarpus glaber (Thumb.) Nakai.contributed 56.41%to the annual total litterfall.In the 48-yr stand,the total leaf litter of Castanopsis eyrei(Champ.) Tutch.,Castanopsis sclerophlla(Lindl.) Schott.,Pinus masoniana Lamb.and Lipuidamba formosana hance contributed 51.64%. Leaf litter of the dominant trees greatly determined the annual temporal pattem of total litterfall to some degree.6.Nutrient of litterfallThe contents of the nutrients measured ranked as follows:Ca＞N＞Fe＞K＞Na＞Mg＞P.The nutrient retum by litterfall in 36-yr stand was low with the annual rate of 117.39 kg hm-2 a-1,while great in the 48-yr stand with the annual rate of 138.72 kg hm-2 a-1.The content of all nutrient elements showed strong seasonal change.However,there existed significant differenced in temporal patterns amongst the bio-elements.In 36-yr stand,the mean annual nutrient returns by litterfall over two years were:N 29.10,P 1.58,K 14.88,Ca 37.11,Na 10.49,Mg 12.19 and Fe 16.42 kg hm-2 a-1.In 48-yr stand,they were:N 34.14,P 1.58,K 14.88,Ca 37.11,Na 10.486k,Mg 12.19 and Fe 16.42 kg hm-2 a-1.Of the total nutrient retumed,the dominant tree,Castanopsis eyrei made the greatest contribution to the annual total.Reproductive and miscellaneous materials ranked the second.
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