马尾松与乡土阔叶树种凋落叶分解氮磷释放的混合效应

Effects of mixed leaf litter on nitrogen and phosphorus release in Pinus massoniana and native broad-leaved tree species

为探明乡土阔叶树种与马尾松(Pinus massoniana Lamb.)凋落叶混合分解过程中的养分释放特征,以马尾松、檫木(Sassafras tzumu)、香樟(Cinnamomum camphora)以及香椿(Toona sinensis)凋落叶为实验对象,按照不同树种组合、不同混合比例组合为35个处理后进行野外分解试验研究.结果发现:所有凋落叶的N、P释放率均表现出前期较快、后期较慢的变化趋势.大部分混合凋落叶的N和P释放率在分解过程中表现出非加和效应,且主要表现为协同效应.随分解时间延长协同效应表现出分解前期最强,之后减弱,后期再增强的趋势.31个混合处理中,马尾松+香樟+香椿组合中6:1:3、7:2:1和7:1:2,马尾松+檫木+香椿组合中7:1:2、6:1:3和6:2:2,以及马尾松+檫木+香樟+香椿组合中7:1:1:1和6:1:1:2的N、P释放率在两年的分解时间中有超过一半时期表现出协同效应.可见阔叶占30%-40%时且混合有香椿凋落叶的组合最利于整个混合凋落叶的N、P释放,加快养分归还.因此,在后期马尾松纯林的“混交化”近自然改造中,可根据实际造林需求,选择马尾松+香樟+香椿、马尾松+檫木+香椿或马尾松+檫木+香樟+香椿的树种搭配及合适的混交比例,提高凋落叶分解的养分归还量,有助于维持林下土壤肥力.(图4表4参46)

To investigate characteristics of nutrient release of native broad-leaved tree species and a conifer during mixed decomposition processes,we selected litter from three important native broadleaved tree species(Sassafras tzumu,Cinnamomum camphora,and Toona sinensis)and one coniferous tree(Pinus massoniana)as the focus of mixed decomposition experiments involving 35 treatments(single-species litter,combinations of litter from two and three species,and combinations of P.massoniana,T.sinensis,C.camphora,and S.tzumu litters with different mass proportions).Release rates of nitrogen(N)and phosphorus(P)were found to increase rapidly in early stages but decrease in later stages across all treatments,whereas in mixed litters,N and P release rates exhibited non-additive effects during decomposition and primarily had synergistic effects.As decomposition progressed,the synergistic effect of these mixed treatments was most apparent in the early stages,then weakened and subsequently strengthened again in later stages.Of the 31 mixed treatments,N and P release rates of 6:1:3,7:2:1,and 7:1:2 for the combination of P.massoniana+C.camphora+T.sinensis;7:1:2,6:1:3,and 6:2:2 for the combination of P.massoniana+S.sassafras+T.sinensis;and 7:1:1:1 and 6:1:1:2 for the combination of P.massoniana+S.sassafras+C.camphora+T.sinensis reflected a synergistic effect over half of the two-year decomposition time.The combination of T.sinensis litter and broad-leaved litter accounted for 30%-40%,which was beneficial to the release of N and P of the entire mixed litter and accelerated nutrient return.As such,P.massoniana monocultures could be converted into near-natural states through the use of“mixed”plantings comprised of P.massoniana+C.camphora+T.sinensis,P.massoniana+S.sassafras+T.sinensis,or P.massoniana+S.sassafras+C.camphora+T.sinensis combinations in accordance with afforestation needs to improve forest litter nutrient return and maintain soil fertility.