Chen, Xiaopeng;Zhang, Tao;Guo, Ruiying;Li, Haiyan;Zhang, Rui;Degen, A. Allan;Huang, Kewei;Wang, Ximing;Bai, Yanfu;Shang, Zhanhuan
Chinese Acad Sci, Northwest Inst Ecoenvironm & Resources, Lanzhou 730000, Peoples R China.
Chinese Acad Sci, Inst Mt Hazards & Environm, Key Lab Mt Surface Proc & Ecol Regulat, Chengdu 610041, Peoples R China.
Lanzhou Univ, Sch Life Sci, State Key Lab Grassland Agroecosyst, Lanzhou 730000, Peoples R China.
Chinese Acad Sci, Northwest Inst Plateau Biol, Qinghai Prov Key Lab Restorat Ecol Cold Area, Xining 810008, Peoples R China.
Northeast Normal Univ, Inst Grassland Sci, Key Lab Vegetat Ecol, Minist Educ, Changchun 130024, Jilin, Peoples R China.
Ben Gurion Univ Negev, Blaustein Inst Desert Res, Wyler Dept Dryland Agr, Desert Anim Adaptat & Husb, IL-8410500 Beer Sheva, Israel.
Shanxi Agr Univ, Coll Grassland Sci, Taigu 030801, Peoples R China.
N-15 tracing;Grazing exclusion;Nutrition strategy;Alpine meadow
The grasslands of Qinghai-Tibetan Plateau have become extremely degraded, resulting in widespread deficiency of soil N. In efforts to restore degraded lands, fencing enclosure has been used extensively. However, the effect of fencing on N allocation patterns and nutritional strategy of alpine plants are equivocal. In this study, we used N-15 tracer (CO ((NH2)-N-15)(2), 10 g N m(-2)) to examine the allocation and distribution of N in plants and soil in grasslands either grazed heavily by livestock or fenced for three years in an alpine meadow of Northern Tibet. The N-15 recovery (N-15(rec)) in shoots of the fenced enclosure increased by 207% in grasses, decreased by 103% in forbs, and did not change in sedges when compared to the grazed meadow. The N-15(rec) in shoots accounted for only 1.97% and 4.65% of the total N in the grazed and fenced meadows, respectively. Fencing increased soil N-15 content at 0-5 cm depth by 6.9%, but decreased the content at 5-10 cm depth by 11.7%. The results demonstrated that fencing altered the soil N distribution by increasing N-15 rec in top soil and by decreasing N-15(rec) in subsurface soil. In addition, fencing had no impact on root N-15 storage (33%-39%), N-15 losses (9.6%-12.5%) and soil available N-15(rec) (NH4+ -N, NO3--N and light fraction organic N), but decreased root:shoot N-15(rec) ratio by 49.8% (16.9:1 in grazed and 8.4:1 in fenced grassland). Fencing increased soil organic carbon, total N and NO3--N concentrations, which indicated that the strategy of the plants was to allocate relatively more N to roots in nutrient-poor soil (grazed) but relatively more N to shoots in nutrient-rich soil (fenced).