施肥和围栏封育对退化高寒草甸植被恢复的影响

Effects of Fertilization and Grazing Exclosure on Vegetation Recovery in a Degraded Alpine Meadow on the Tibetan Plateau

施肥和围栏封育是改良退化草地常用的有效管理措施.在藏北高寒草甸区测试了氮肥单施(N 50 kg hm-2 a-1,LN;N 100 kg hm-2 a-1,HN)、与磷肥配施[(50 kg N+50 kg P)hm-2 a-1,LN+P;(100 kg N+50 kg P)hm-2 a-1,HN+P]对植物群落特征和生产力的影响,并比较了辅以围栏封育的效果.结果显示,施氮未显著改变群落盖度,而氮磷配施显著提高了群落盖度,在自由放牧样地LN+P、HN+P处理群落盖度的提高比例分别为86%和63%,而在围栏封育样地LN+P、HN+P处理群落盖度的提高比例分别为107%和248%,在相同施肥水平下围栏封育能显著提高群落盖度.施氮处理有利于提高禾草类植物优势度,而氮磷配施有利于莎草科植物和蔷薇科植物的生长,围栏封育后施氮肥更有利于禾草植物的恢复.在自由放牧样地,施氮对群落植物地上生产无显著影响,而氮磷配施显著促进植物生产,其中LN+P处理提高了137%的地上生物量.在围栏封育样地,施氮对莎草植物无显著影响,而HN处理的禾草地上生物量是对照处理的8.4倍;氮磷配施对禾草、莎草及杂类草植物均有促进作用,LN+P和HN+P处理比对照分别提高了杂草植物98%和86%的地上生物量.研究表明,施加氮肥结合围栏封育对退化高寒草甸群落的恢复有促进作用;氮磷配施,不论围栏与否均有利于高寒草甸的恢复,但结合围栏封育恢复效果更显著.

Both fertilization and grazing exclosure are effective management measures for recovery of degraded grasslands. To better understand the effects of both measures and their interaction on restoration of degraded alpine grasslands, a long-term experiment of exclosure and addition of nitrogen （50 kg N hm-2 a-1, LN; 100 kg N hm-2 a-1, HN） combined with phosphorus （（50 kg N ＋ 50 kg P） hm-2 a-1, LN ＋ P; （100 kg N ＋ 50 kg P） hm-2 a-1, HN ＋ P） was carried out in a degraded Kobresia pygeama alpine meadow on the Tibetan Plateau since 2008. The results showed that nitrogen （N） addition did not affect plant community coverage, while in grazing plots LN ＋ P and HN ＋ P treatments significantly increased plant community coverage by 86% and 63%, respectively. Moreover, in grazing exclosure plots LN ＋ P and HN ＋ P treatments significantly increased 107% and 248% of plant community coverage respectively, compared with grazing plots under the same fertilization levels. N addition alone contributed to enhancing importance values （IV） of grass, and this effect was specifically improved by exclosure. However, sedge and Potentilla were much more responsive to combination of N and P addition. N addition alone under free grazing did not affect aboveground biomass for grass, sedge or herbs of Potentilla, while LN ＋ P treatment significantly enhanced community aboveground biomass by 137%. Under exclosure conditions, N addition did not significantly change the aboveground biomass of sedge, but increased the aboveground biomass of grass by 8.4 times. However, N combined with P addition in fencing plots significantly promoted aboveground biomass of grass, sedge and Potentilla herbs. For example, LN ＋ P and HN ＋ P treatments enhanced the aboveground biomass of herbs by 98% and 86%, respectively. Our results suggested that though N addition alone could not improve the condition of degraded alpine meadow, N combined with P fertilization and/or exclosure will contribute greatly to the restoration of degraded alpine meadow.