放牧对天山北坡山地草原生态系统土壤δ^(15)N的影响

Impact of grazing on soil δ^(15)N of mountainous grassland ecosystems over the northern Tianshan Mountains,China

测定了天山北坡山地草原优势植物种针茅(Stipa capillata)、羊茅(Festuca ovina)、短柱苔草(Carex turkestanica)、博乐绢蒿(Seriphidium borotalense)根际0-10 cm土壤和非根际10-20、20-30 cm土层土壤稳定性N同位素和全氮含量,通过对比放牧和围封草地优势植物根际土壤δ^(15)N的变化,分析不同利用方式对不同植物根际土壤和不同土层深度土壤δ^(15)N的影响。结果表明,天山北坡山地草原生态系统土壤δ^(15)N值在2.25‰~16.03‰变化,放牧显著降低了表层0-10 cm土壤δ^(15)N值;放牧草地0-30 cm土壤δ^(15)N值(7.14‰±0.67‰)整体上比围封(6.95‰±0.34‰)增加了2.8%,但差异不显著(P>0.05)。放牧和围封条件下天山北坡山地草原土壤δ^(15)N值均随着土层深度的加深而显著增加(P<0.05),且土壤δ^(15)N值与土壤全氮含量呈显著的负相关(P<0.05)。放牧对天山北坡山地草原不同植物种根际土壤δ^(15)N的影响程度不同,放牧草地的针茅和羊茅0-30 cm土壤δ^(15)N分别比围封草地的高17%和53%,但放牧降低了短柱苔草和博乐绢蒿0-30 cm土壤δ^(15)N,且对短柱苔草的降低作用显著。

The total N and δ^（15）N of rhizosphere soil 0- 10 and 10- 20,20- 30 cm of Stipa capillata,Festuca ovina,Carex turkestanica and Seriphidium borotalense in the mountainous grassland ecosystems over the northern Tianshan Mountains were measured. δ^（15）N of dominant plants＇ rhizosphere soil in grazing and fencing grassland was compared to reveal the impacts of different usage patterns on δ^（15）N of rhizosphere soil in different plants and different soil layer. The results indicated that the range of soil δ^（15）N of mountainous grassland ecosystems over the northern Tianshan Mountains were from 2. 25‰ to 16. 03‰. Grazing significantly decreased δ^（15）N in 0- 10 cm soil. The δ^（15）N in 0- 30 cm soil of grazing grassland（ 7. 14‰ ± 0. 67‰） increased by 2. 8% than that of fencing grassland（ 6. 95‰ ± 0. 34‰） although there was no significant difference between them. The δ^（15）N in soil significantly increased with the increasing of soil depth in both grazing and fencing grassland and it had significantly negative correlation with soil total N. The impacts of grazing on δ^（15）N in rhizosphere soil of different plants were different. The δ^（15）N in the 0- 30 cm rhizosphere soils of Stipa capillata and Festuca ovina in the grazing grassland were 17% and 53% higher than that in fenced grassland respectively.However,the δ^（15）N in the 0- 30 cm rhizosphere soils of Carex turkestanica and Seriphidium borotalense were lower than that in fenced grassland. The measurement of δ^（15）N supported an aggregative indicator of N cyclic process in a typical area for the ecosystem and showed that grazing changed the N cycle of grassland ecosystem.