Effects Of Tree Species Diversity On Litter Amount And Nutrient Return

There are various types of subtropical vegetation and complex community structure in China,and the zonal vegetation is evergreen broad-leaved forest.Nutrient restoration of litters is an important process of nutrient cycling in forest ecosystem,and it is an important guarantee and link to maintain soil nutrient and forest sustainable productivity.At present,mixed forest planting has become the main method of forest cultivation because of the more advantages than pure forest in the process of forest cultivation after years of practice and theoretical exploration.Studies have shown that biodiversity can improve the productivity and stability of the ecosystem,so as to increase the amount of litters and nutrient return.However,within the range of natural ecosystem,studies on the amount of litters and nutrient return by species diversity are rare.In this study,we selected the climax forest—L.glaber-C.glauca evergreen broadleaved forest in subtropical.They play an important role in water conservation,wood supply,regional sustainable development,ecosystem balance,material circulation and energy flow.In the 1hm-2 stand,we set the combination of tree species clusters in gradient of tree species diversity,ranging from one to four species in February 2017 to January 2018.The dynamic characteristics of litter amount and nutrient restitution in different species diversity combinations were studied,which provided theoretical basis for the cultivation of trees in subtropical areas,the establishment of mixed forests and the improvement of ecosystem productivity.The research results are as follows:(1)In different species diversity combination,the amount of litters in each component of litters showed three peaks or irregular pattern.The leaf is the main component of litter,accounting for 69.35%?77.27%of the total litter,and the branch accounted for 9.11%?12.56%of the total litter.The proportion of chippings in total litters ranged from 8.74%to 11.39%.The fruit with the smallest proportion ranged from 1.68%to 8.72%.The order of litter biomass was:leaf>branch>chippings>fruit.With the increase of species diversity,the litter biomass in each month showed a decreasing trend,and the litters in January and February were the least in the whole experimental year.The annual litters of 1-4 species diversity combinations were 432.12 g·m-2,410.45 g·m-2,404.52 g·m-2,290.99 g·m-2,and the order of diversity combination was:Tree species diversity 1(TSD1)>Tree species diversity 2(TSD2)>Tree species diversity 3(TSD3)>Tree species diversity 4(TSD4).(2)The nutrient content of litter in the combination of different species diversity was basically expressed as C>N>Ca>K>Mg>P.The nutrient contents were different in different tree combinations and different tree species.In general,with the increase of species diversity,the contents of C,N,K and Mg tended to increase,while the contents of P and Ca tended to decrease.The effects of tree species diversity on nutrient elements in different tree combinations were not consistent and the mechanisms were different.(3)The annual total amount of nutrient elements returned showed the order was:TSD1(2041.58 kg·hm-2)>TSD2(1869.45 kg·hm-2)>TSD3(1838.09 kg·hm-2)>TSD4(1529.32 kg·hm-2);The nutrient return amount of was:1459.97 kg·hm-2?1946.45 kg·hm-2(C),43.47 kg·hm-2?58.14 kg·hm-2(N),3.15 kg·hm-2?5,02 kg·hm-2(P),3.86 kg·hm-2?5.92 kg·hm-2(K),15.90 kg·hm-2?24.56 kg·hm-2(Ca)and 2.95kg·hm-2?5.31kg·hm-2(Mg).Overall,with the increase of tree species diversity,the total amount of nutrients returned to litters,C,K,Ca and Mg all showed a trend of decline.