模拟N沉降对太岳山油松人工林和天然林草本群落的影响

由于人类活动氮沉降呈逐年增加的趋势,进而增加了陆地生态系统氮的输入,从而影响陆地生态系统多样性、物种组成和功能。为揭示氮沉降增加对油松林草本群落的影响,于2009年7月在太岳山油松人工林和天然林,设计4个施氮水平:对照(CK,0 kg N hm-2a-1),低氮(LN,50 kg N hm-2a-1),中氮(MN,100 kg N hm-2a-1)和高氮(HN,150 kg N hm-2a-1),研究草本群落的生物多样性、生物量以及草本元素含量对模拟N沉降的响应。研究结果表明:模拟N沉降未能显著影响人工林草本群落的生物多样性(P0.05),而中氮、高氮显著降低了天然林草本群落的生物多样性(P0.05);从Jaccard指数和Sorensen指数分析得出人工林不同氮水平之间草本群落差异性较小,而天然林不同氮水平之间草本群落差异性较大。模拟N沉降没有显著改变人工林草本群落生物量(P0.05),而高氮明显促进天然林草本群落生物量的增加(P0.05)。与对照相比,模拟N沉降提高了人工林和天然林羊胡子苔草叶根中的全N含量(P0.05),而降低了全Mg的含量(P0.05),并且根部元素含量变化与土壤养分含量变化较为一致。施氮提高了N/K、N/Ca、N/Mg(P0.05)的比值。说明油松林下草本群落对氮沉降的响应因林分土壤N饱和程度以及林地利用历史的不同而产生差异,其中天然林响应最为敏感。

Effect of simulation N deposition on herbaceous vegetation community in the plantation and natural forests of Pinus tabulaeformis in the Taiyue Mountain

Human activities have significantly altered global and regiona1 cycles of nitrogen (N) in the last several decades due to combustion of fossil fuels, intensive agriculture and stock breeding. The amount of human-made reactive N which is more than the natural production, released into the atmosphere. Nitrogen (N) deposition has been widely considered as an environmental problem that leads to destruction of ecological balance such as biodiversity loss, base cation loss, soil acidification, but increases net primary productivity of N-limited forest ecosystems. Greater N deposition has a significantly effect on productivity, plant diversity and biomass allocation of forest ecosystem. To determine the influence of N deposition on species diversity, biomass and nutrients of herbaceous vegetation community, for this:12, 20 m×20 m plots, respectively, distributed in the plantation and natural forest of Pinus tabulaeformis were established in the Taiyue Mountain, Shanxi Province, since July, 2009. Within each stand, equal numbers of 20 m×20 m plots were treated with four nitrogen fertilization levels: control (CK, 0 kg N hm^-2a^-1), low nitrogen (LN, 50 kg N hm^-2 a^-1), moderate nitrogen (MN, 100 kg N hm^-2 a^-1) and high nitrogen (HN, 150 kg N hm^-2 a^-1), the different levels of N were added at the middle of each month in growing season Since 2009. Herb samples were collected and investigated in August in 2012, and the soil samples were collected in August of 2009 and 2012. The coverage, diversity indices, above-ground biomass, underground biomass, total biomass and element contents of herbaceous vegetation community and soil physical and chemical characteristics of different nitrogen levels were analyzed. Results showed that: Nitrogen additions did not significantly (P > 0.05) affect diversity indices of herbaceous vegetation community in the plantation forest, however, MN and HN treatments significantly decreased the diversity indices (P < 0.05) of herbaceous vegetation community in the natural forest. Jaccard and Sorensen index indicated that there were significant differences in community composition of herbaceous vegetation between different nitrogen levels in the natural forest, while that of plantation forest was not significant. The herb biomass showed no significant (P > 0.05) response to nitrogen deposition in the plantation forest, while HN treatment significantly increased herb biomass (P < 0.05) in the natural forest. The variations of nutrient in root of Carex callitrichos were closely related to soil physical and chemical characteristics. Nitrogen addition increased total N contents (P < 0.05), but decreased total Mg contents (P < 0.05) in leaves and roots of C.callitrichos, and nitrogen deposition significantly increased the ratio of N/K, N/Ca, N/Mg (P < 0.05) when compared to the control in the plantation and natural forest of P. tabulaeformis. It was suggested that external nitrogen addition would affect the species diversity, productivity and elements uptake of herb community in the P. tabulaeformis forests, however, the impact of N enrichment on the herbaceous vegetation community may vary with different soil nitrogen saturation and land-use history, and natural forests may be more sensitive to N deposition.