水氮耦合对荒漠草原植物物种多样性及生物量的影响

Effect of water and nitrogen interaction on plant species diversity and biomass in a desert grassland

为了研究大气氮沉降和降水变化对荒漠草原物种多样性及地上、地下生物量的影响,设置自然降雨(CK)、增雨30%(W)和减雨30%(R)3个水分处理及0(N0)、30(N30)、50(N50)和100 kg·(hm2·a)-1(N100)4个氮素(NH4NO3)水平(其中不包括大气氮沉降),进行水氮交互试验。结果表明,1)CK×N和R×N处理下荒漠草原物种多样性随着施氮量增加,整体呈现先上升后下降的趋势,N30水平达到最大,W×N处理下随着施氮量增加物种多样性显著降低(P<0.05)。2)对比W×N0处理,CK×N0和R×N0处理地上生物量显著增加(P<0.05)。水氮交互作用下,随着施氮量增加,CK×N和W×N处理有助于地上生物量显著增加(P<0.05),R×N处理地上生物量有增加的趋势。水氮交互作用对一、二年生植物有显著影响(P<0.05),地上生物量整体呈现(W×N)>(CK×N)>(R×N)。3)不同水氮交互作用下,地下生物量随土层增加逐渐减少,主要集中在0-30 cm土层,W×N处理可促进根系向深层土壤生长。在CK×N和R×N处理下,随着施氮量增加,荒漠草原物种地下生物量整体呈现先上升后下降的趋势,W×N处理随着施氮量增加地下总生物量显著增加(P<0.05)。4)CK×N30和R×N30处理下,根冠比显著降低(P<0.05)。以上结果说明,荒漠草原植物物种多样性及生物量与水分及养分有密切关系。

To demonstrate the effects of atmospheric nitrogen deposition and precipitation on species diversity and biomass in desert grassland,we examined water and nitrogen interactions,using three levels of water treatment [natural precipitation( CK),increased precipitation 30%( W) and reduced precipitation 30%( R) ] and four nitrogen( NH4NO3) levels: 0( N0),30( N30),50( N50),and 100( N100) kg·( hm2·a)-1( which does not include atmospheric nitrogen deposition). The following results were obtained: 1) The species diversity of desert grassland under CK× N and R × N treatments increased with an increase in nitrogen application rate,showing an initial increase trend and a subsequent decrease,with maximum diversity being attained with the N30 treatment. Under the W × N treatment,the species diversity was significantly reduced( P < 0. 05) with an increase of nitrogen application rate. 2) The aboveground biomass obtained with CK × N0 and R × N0 treatments was significantly increased( P < 0. 05) compared with the W × N0 treatment. Under the water and nitrogen interaction,the aboveground biomass of CK × N and W × N treatments was significantly increased( P < 0. 05) with an increase in nitrogen application rate. The water and nitrogen interaction had a significant effect on annual and biennial plants. The overall aboveground biomass trend was as follows:( W × N) >( CK × N) >( R × N). 3) Under the water and nitrogen interactions,the underground biomass decreased gradually with the depth of soil,and was mainly concentrated in the 0-30 cm. The W × N treatment promoted root extension into deeper soil. The biomass of desert grassland under CK × N and R × N treatments showed an initial increase trend and then a subsequent decrease with an increase of nitrogen application rate,and the underground biomass obtained with the W × N treatment showed a significant increase( P < 0. 05). 4) The treatments of CK × N30 and R × N30 significantly reduced the root/shoot ratio( P < 0. 05). Collectively,the results of this study showed that the plant species diversity and biomass in desert grassland are closely related to water and nutrients.