孪花蟛蜞菊凋落物的混合促进西沙群岛优势乔木凋落物的分解

Mixing Wedelia bifloraa litter accelerates litter decomposition of dominant tree species in Xisha Islands

孪花蟛蜞菊(Wedelia biflora)是菊科一种攀援性草本植物,目前在我国西沙群岛呈现出“入侵”态势,已危害岛上原生植被及生态系统的安全。为探究孪花蟛蜞菊扩张后其凋落物混入对本地优势乔木凋落物分解及养分循环的影响,本研究在西沙永兴岛优势乔木抗风桐(Pisonia grandis)和海岸桐(Guettarda speciosa)混交林下,采用凋落物网袋法,设置凋落物分解试验,研究孪花蟛蜞菊凋落物混入后的混合凋落物质量损失和养分循环。结果发现,相比本地优势乔木凋落物,孪花蟛蜞菊凋落物的分解速率更快,这可能是由于孪花蟛蜞菊凋落物质量较高(氮含量为12.1 g·kg^(-1),碳氮比35.0,木质素氮比10.7)所致。本地优势植物凋落物混入孪花蟛蜞菊凋落物后,混合凋落物质量提高,分解过程中的质量损失和碳、氮、磷养分元素释放均增加。结果显示,孪花蟛蜞菊的扩张,使其凋落物混入原生林中,加速了本地优势乔木凋落物的质量分解和养分释放,可能会降低西沙群岛优势乔木凋落物对土壤的减缓侵蚀作用,加速养分的淋失,影响生态平衡。

Wedelia biflora is a climbing herb in family Asteraceae.It has shown an"invasion"trend in the Xisha Islands,endangering the safety of native vegetation and ecosystem.With the expansion of W.biflora,its litter mixes with that of local dominant tree species.To explore this mixture effect on litter decomposition and nutrient release of native dominant tree species,we conducted a litter decomposition experiment in the mixed forest of Pisonia grandis and Guettarda speciosa using litterbag method.We investigated mass loss and nutrient release of mixed litters from native dominant trees(P.grandis and G.speciosa)and W.biflora.The results showed that the decomposition rate of W.biflora litter was faster than that of native dominant trees,due to its higher litter quality[i.e.higher nitrogen content(12.1 g·kg^(-1)),lower carbon-nitrogen ratio(35.0),and lignin-nitrogen ratio(10.7)] than the native dominant trees'litter.When the native dominant trees'litter was mixed with W.biflora litter,the substrate quality of the mixed litter was improved,which resulted in increased mass loss and release of carbon,nitrogen,and phosphorus during litter decomposition.The results indicate that W.biflora expands and mixes its litter into the native forests,accelerating mass loss and nutrient release of dominant trees'liter.Such an effect may reduce soil erosion mitigation effect of dominant trees'litter in Xisha Islands,accelerate nutrient leaching,and ultimately affect ecological balance.