两种措施下施氮肥对狼毒型退化草地群落及营养品质的影响

施肥是退化草地恢复常用的管理措施。以狼毒型退化天然草地为对象,研究了禁牧和刈割两种措施下不同施氮量10(N₁)、20(N₂)、30(N₃)、40(N₄) kg·hm^-2对狼毒型退化草地群落结构、功能及牧草品质的影响。结果表明:两种措施下狼毒密度及地上生物量均显著低于对照区(P<0.05),且禁牧+施肥处理下狼毒种群下降最明显。在禁牧区,N₄处理的丰富度指数具有最高值,但与CK处理差异不显著(P>0.05),N₁的Alatalo指数最高;而在刈割区,Shannon-Wiener指数最高的为N₄,刈割后不施肥的Alatalo指数显著高于N₄(P<0.05),且其物种数最多。不同施氮水平的草地群落功能群地上生物量均显著高于CK,莎草科的地上生物量均高于禾本科,不同施肥水平间的总地上生物量和各个功能群的生物量差异均不显著(P>0.05),禁牧+N₃的总生物量和莎草科的增产比率均为最高,分别为47.21%和48.24%,禁牧+N₄的禾本科的增产比率最高,为119.35%。不同施肥水平牧草营养物质含量除粗蛋白含量禁牧显著高于禁牧+N₁(P<0.05)、粗灰分含量刈割+N₂显著高于CK(P<0.05)和中性洗涤纤维含量刈割显著高于刈割+N₂(P<0.05)外差异均不显著(P>0.05)。通过分析单位面积的粗蛋白和粗脂肪的含量得到粗蛋白含量在各施肥样区差异不显著(P>0.05),但与CK差异显著(P<0.05),粗脂肪含量为禁牧+N₄显著高于禁牧和CK(P<0.05),刈割+N₁显著高于刈割和CK(P<0.05)。

Effects of nitrogen fertilizer on community structure and nutritional quality of degraded grassland of Stellera chamaejasme under two different management measures

Fertilization is an effective management measure for the recovery of degraded grasslands. The aim of this study was to determine the effects of nitrogen fertilization on the community structure and nutritional quality of degraded alpine meadows of Stellera chamaejasme. We conducted a fertilization experiment with different amounts of nitrogen fertilizer [10 (N₁), 20 (N₂), 30 (N₃), 40 (N₄) kg·ha^-1], under two different management measures, clipping and prohibition of grazing. The density and above-ground biomass of S. chamaejasme were significantly lower under the two different management measures than in the control (P<0.05), and were decreased in the fertilization+prohibition of grazing treatments. In the area in which grazing was prohibited, the richness index was highest in N₄, but was not significantly different from that in CK (P>0.05). The Alatalo index was highest in N₁, and the Shannon-Wiener index was highest in the clipping+N₄ area. The Alatalo index was significantly higher in the clipping area than in the clipping+N₄ treatment (P<0.05), and the highest number of species was in the clipping area. The above-ground biomass was significantly higher in all the N-fertilization treatments than in CK (P<0.05). The above-ground biomass of the Cyperaceae was higher than that of the Gramineae. The total aboveground biomass and the biomass of functional groups did not differ significantly among the different fertilization treatments (P>0.05). Total biomass and the biomass of the Cyperaceae showed high rates of increase (47.21% and 48.24%, respectively). The highest rate of increase of the Gramineae was in the grazing-prohibition+N₄ treatment (119.35%). Overall, the nutrient contents of grass did not differ significantly (P>0.05) among the different fertilization treatments. However, the crude protein content was significantly higher in the grazing treatment than in the grazing+N₁ treatment. The crude ash content was significantly higher in the clipping+N₂ treatment than in CK, and the neutral detergent fiber content was significantly higher in the clipping treatment than in the clipping+N₂ treatment (P<0.05). The crude protein content per unit area did not differ significantly among the different fertilization treatments (P>0.05). The crude fat content per unit area was significantly higher in the grazing+N₄ treatment than in the grazing treatments and CK (P<0.05), and significantly higher in the clipping+N₁ treatment than in CK (P<0.05).