青藏高原东部乔灌交错带地被物和土壤碳氮磷化学计量特征

Carbon,nitrogen,and phosphorus stoichiometric characteristics of ground cover and soil in a forest-shrub ecotone in the eastern Tibetan Plateau

为深入了解青藏高原东部高寒灌丛群落扩张对生态系统地表地被物和土壤C、N和P生态化学计量学特征的影响,以青藏高原东部岷江源头区典型的高寒针叶林—乔灌—灌丛垂直分布带为研究对象,分析乔灌交错带地表地被物(枯落物和苔藓层)和土壤(0-10 cm、10-20 cm和20-30 cm)全C、全N和全P含量及生态化学计量学特征.结果表明:针叶林和和灌丛枯落物全C含量和C/P显著大于乔灌(P<0.05);针叶林和乔灌枯落物全N、全P含量、N/P和C/N显著大于灌丛(P<0.05).针叶林苔藓层全C含量、C/N和C/P显著大于乔灌,而全N、全P含量和N/P显著小于乔灌(P<0.05).乔灌0-30 cm土壤全C、全N和全P含量显著大于针叶林和灌丛(P<0.05).不同植被类型土壤C/N、N/P和C/P随土层深度具有显著差异,但没有表现出一致的变化规律.Pearson相关分析结果表明,交错带枯落物和苔藓层全C含量与0-30 cm土壤全C、全N和全P含量呈显著负相关(P<0.05),全N含量与0-30 cm土壤全C含量呈显著正相关(P<0.05),全P含量与0-30 cm土壤全C、全N和全P含量呈显著正相关(P<0.05).枯落物和苔藓层C/N和C/P与0-30 cm土壤全C和全P含量呈显著负相关(P<0.05),N/P与0-30 cm土壤C/N和C/P呈显著正相关(P<0.05),与0-30 cm土壤N/P呈显著负相关(P<0.05).以上结果表明,青藏高原东部高寒灌丛群落扩张能够促进地表地被物和土壤对C、N和P的固存,进而影响区域森林地表C、N和P物质周转和循环等生态过程.

This study was undertaken to understand the effects of alpine shrubland expansion on the carbon(C),nitrogen(N),and phosphorus(P)stoichiometric characteristics of ground cover and soils on the eastern Qinghai-Tibet Plateau.The ground cover(i.e.,litter and moss)and soils from different layers(0-10 cm,10-20 cm,and 20-30 cm)were collected from three vegetation types of a typical alpine forest-shrub ecotone in the source area of the Minjiang River.The vegetation types were dominated by Picea likiangensis(coniferous forest),Picea likiangensis-Salix oritrepha(forest-shrub),and Sibiraea angustata(shrub).We analyzed the total C,total N,total P,and C/N,C/P,and N/P ratios of litter,moss,and soils,as well as their relationships.The results showed that the total C content and C/P ratio of litter in the coniferous forest and the shrubland were significantly higher(P<0.05)than those in the forest-shrub.The total C,total P,and N/P and C/N ratios of litter in coniferous forest and forest-shrub were significantly higher(P<0.05)than those in shrubland.The total C content,and C/N and C/P ratios of moss in coniferous forest were significantly higher(P<0.05)than those in forest-shrub,while the total N,total P,and N/P ratio of moss in coniferous forest were significantly lower(P<0.05)than those in forest-shrub.The total C,total N,and total P contents of 0-30 cm soils in forest-shrub were significantly higher(P<0.05)than those in coniferous forest and shrubland.Moreover,the C/N,N/P,and C/P ratios varied with soil layer and vegetation type,and there were no consistent patterns of the ratios in soils.Furthermore,the Pearson correlation analysis indicated that the total C content of litter and moss in the forest-shrub ecotone were significantly(P<0.05)and negatively correlated with total C,total N,and total P contents in the 0-30 cm soils.The total N content of litter and moss was significantly(P<0.05)and positively correlated with total C contents in the 0-30 cm soils.The total P content of litter and moss was significantly(P<0.05)and positively correlated with total C,total N,and total P contents in the 0-30 cm soils.The C/N and C/P ratios of litter and moss were both significantly(P<0.05)and negatively correlated with total C and total P contents of 0-30 cm soils,while N/P ratio was significantly(P<0.05)and positively correlated with C/N and C/P ratios,and significantly(P<0.05)and negatively correlated with N/P ratio of 0-30 cm soils.These results imply that the expansion of alpine scrubland could accelerate the sequestration of C,N,and P in ground cover and soil,and further affect the ecological processes of C,N,and P returning and cycling on the forest floor of the eastern Qinghai-Tibet Plateau.