氮素添加对典型草原区割草场植物群落结构及草场质量指数的影响

Effect of N addition on plant community structure and index of grassland quality of typical steppe mown grassland

养分添加对维持割草场养分平衡具有重要意义,本研究通过不同割草制度下添加氮素试验,探讨了氮素添加对割草地产量、群落物种多样性及草群质量指数的影响。结果表明,1)氮素添加对一年割1次草地的增产效果显著。添加氮素当年N3(64.4kg/hm2)、N4(78.2kg/hm2)较对照显著增产,幅度近50%,且次年也表现出明显的肥料残效;对一年割2次,仅在N4梯度上有显著的增产效果,表现出肥料施用量不足。对不割草处理区,添加氮素未达到显著增产(P<0.05)。2)割草处理下,物种多样性指数随氮素添加梯度的增加呈波动状增长趋势;而均匀性指数呈下降走势。3)添加氮素后羊草和大针茅在一年割1次和不割草处理中都表现出等补偿和超补偿,但在一年割2次中均为不足补偿;糙隐子草则相反,在不割草处理中仅为等补偿而在割草处理后刈割频度越高超补偿现象越明显。添加氮素后3种群的氮含量都明显提高,但在不割草处理中的糙隐子草在N2(50.6kg/hm2)梯度达到最高之后,基本保持该水平。4)氮素添加对不同轮割制度下草地质量有明显的提高作用。施用N4梯度的试验区在2年的综合效果中表现最佳,草地质量维持的最好。

In the grassland region of Inner Mongolia,herdsmen always mow tall grass in autumn in preparation for feeding livestock in winter.The grassland has become increasingly degenerate because of annual mowing so we studied the effects of N addition to mown grassland on standing crops,species composition,community structure,and nitrogen content of the main populations in Stipa grandis grassland of a typical steppe.1） For plots mowed once a year,the community standing crops after adding N were higher than those of control plots,and the plots with more N（N3,64.4 kg/ha,N4,78.2 kg/ha） also had significantly higher productivity in the first two years after adding N.For plots mowed twice a year,only the plots with highest N addition（N4） had significantly higher standing crops than the controls.N addition to non-mowed plots had some effect although this was not significant.2） Community species diversity of the two mown systems increasingly fluctuated with the added N except for the non-mown system,and generally,the evenness decreased with increased N addition.3） For the three main populations,two aspects（crops and nitrogen content） affected by adding N were considered.First,after adding N,S.grandis and Leymus chinensis had equal and super compensation on standing crops in control plots and plots mowed once a year,but in plots mowed twice a year there was no compensation,while with Cleistogenes squarrosa standing crops had equal compensation to control plots,but super compensation in plots mowed after adding N.Second,nitrogen contents in S.grandis and L.chinensis plants were increased with the added N whether in plots mowed once a year or in non-mowed plots.But for C.squarrosa,this phenomenon could only be found in plots mowed once a year,while in non-mowed plots,nitrogen content was highest in the N2（50.6 kg/ha）plots and maintained this level with higher application rates.4） N addition not only ensured productivity of grassland mowed once a year,but also improved the grassland quality to some degree.The N4 treatment had the best effect on grassland.