长期不同施氮水平对草原植物群落结构的影响

为探讨施氮对贝加尔针茅草原植物群落结构的影响,该研究于内蒙古贝加尔针茅草原设置不同施氮水平0(N0)、15(N15)、30(N30)、50(N50)、100(N100)、150(N150)、200(N200)和300(N300)kg·hm-2·a-1,研究连续施氮9年后贝加尔针茅草原群落物种组成、重要值、多样性及生物量等指标对不同施氮水平的响应。结果表明:(1)长期施氮导致植物群落物种组成发生了明显的变化,在高浓度氮素添加量下群落物种数最低,但可显著提高优势种在群落中的重要值(P<0.05)。(2)长期施氮使贝加尔针茅草原植物多样性指数不同程度地降低,使优势度指数增加,其中N300添加水平效果最为明显(P<0.05)。(3)长期施氮使草原植被生产力(地上、地下生物量)整体呈先上升后下降的趋势,地上生物量在N100水平时出现峰值,地下生物量在N50水平时出现最大值(P<0.05),且根系分布具有明显的表聚特征(0~10 cm)。(4)RDA分析表明,寸草苔和狭叶柴胡地上生物量与土壤pH呈显著正相关关系(P<0.05);展枝唐松草和二裂委陵菜地上生物量与土壤有机质含量呈显著正相关关系(P<0.05)。研究认为,长期不同施氮水平均可改变贝加尔针茅草原群落物种组成,降低物种多样性,对植物群落结构有着明显的影响。

Effects of Long term Different Nitrogen Addition Levels on Plant Community Structure

We conducted an experiment on 9 years of continuous nitrogen application to explore the effect of nitrogen addition on plant community structure in Stipa baicalensis steppe, with different nitrogen addition levels of 0(N0), 15(N15), 30(N30), 50(N50), 100(N100), 150(N150), 200(N200) and 300(N300) kg·hm^-2·a^-1. The responses of community structure and important value, diversity as well as biomass to different nitrogen addition in 9 years of continuous nitrogen application were explored. The results showed that: (1) community structure was significantly responded to long term nitrogen addition with the lowest species number in high nitrogen application rate, while the highest important value in dominant species under high nitrogen application rate was observed. (2) Plant diversity index in S. baicalensis steppe was reduced with varying degrees in long term nitrogen addition. The dominance index was increased with long term nitrogen addition with the most prominent value in N300 level addition (P<0.05). (3) The productivity of grassland vegetation (aboveground and belowground biomass) increased firstly and then decreased after long term nitrogen addition. The peak value of aboveground biomass was observed under N100 level addition, while the maximum value of belowground biomass was appeared at N50 level (P<0.05). Root was characterized at 0-10 cm distribution. (4) RDA analysis showed that aboveground biomass of Carex duriuscula and Bupleurum scorzonerifolium were significantly positively correlated with soil pH (P<0.05), and Thalictrum sguarrosum and Potentilla bifurca were significantly positively correlated with soil organic matter (P<0.05). The community structure in S. baicalensis steppe was greatly responded to long term nitrogen addition composition with diversity decreased and changes in community composition.