毛乌素沙地南缘柠条固沙恢复区植物多样性及生物量对水氮添加的响应

Responses of plant species diversity and biomass to water and nitrogen addition in sand-fixing restoration area of Caragana korshinskii in southern Mu Us Sandy Land

为研究大气氮沉降和降水变化对毛乌素沙地南缘柠条(Caragana korshinskii)固沙恢复区草本植物多样性及地上生物量的影响,采用随机区组设计,设置不增水(W_(0))、增水量分别为年均降水量的33%(W_(1))、66%(W_(2))和100%(W_(3))4个水分添加处理,及4个氮添加处理,分别为添加纯氮含量为0(N_(0))、5(N_(5))、10(N_(10))、20(N_(20)) g/(m^(2)·a)的(NH_(4))_(2)SO_(4),共16个处理组合,计4个区组,进行水氮添加试验。结果表明:1)水氮添加对植物群落组成、重要值产生显著影响(P<0.05),一、二年生植物比多年生植物对增水和施氮的反应更敏感,但半灌木、小半灌木所受影响最小;2)水分处理对植物群落物种丰富度和多样性指数有显著影响(P<0.05),二者都随水分添加呈先增加后减小的趋势,在添加量为W_(1)处理时达到水分阙值;3)氮素处理显著影响物种丰富度、优势度指数和多样性指数(P<0.01),研究发现增水在一定程度上会抵消氮沉降增加对植物物种多样性的负面影响,进而改变植物群落组成与结构;4)水氮耦合处理对植物群落盖度和群落地上生物量有显著影响(P<0.05);5)植物群落地上生物量与Shannon-Wienner多样性指数呈正相关,与物种丰富度、Simpson优势度指数和Pielou均匀度指数呈负相关关系。主成分分析表明,W_(3)-N_(1)0水氮添加方案对柠条固沙恢复区的草本植被生产力恢复效果最好,而W_(1)-N_(5)水氮添加方案对该区草本植物群落多样性恢复效果最好。

In order to study the effects of atmospheric nitrogen deposition and precipitation changes on herbaceous plant diversity and above-ground biomass in sand-fixing restoration area of Caragana korshinskii in southern Mu Us Sandy Land,a randomized group design experiment was used to conduct a water and nitrogen addition experiment. The experimental scheme was designed in the following way. Four water addition treatments were set: no water addition(W_(0)),33% of average annual precipitation(W_(1)),66% of average annual precipitation(W_(2)),100% of average annual precipitation(W_(3));Four nitrogen addition treatments were set up,and ammonium sulfate with pure nitrogen content of 0 g/(m^(2)·a)(N_(0)),5 g//(m^(2)·a)(N_(5)),10 g/(m^(2)·a)(N_(10)),20 g/(m^(2)·a)(N_(20)) were added respectively. and a total of 4 groups were tested for water and nitrogen addition. A combination of one water addition treatment and one nitrogen addition treatment which were both randomly selected from the above described four treatments to form a combined water and nitrogen treatment for each experiment plot. A total of 16 experiment plots in each block and 4 blocks in total were performed in this study. The results showed as follows: 1) Plant community composition and the importance value were significantly affected by water and nitrogen addition(P<0. 05). Annual and biennial plants were more sensitive to water and nitrogen application than perennial plants,whereas,semishrubs and undershrubs were least affected. 2) Indices of species richness and Shannon-Wiener of the Plant community were significantly affected by water treatment(P<0. 05),and both of them increased first and then decreased with water addition,and reached the water threshold at W_(1)treatment;3) Indices including species richness,Simpson index,and Shannon-Wiener index were all significantly influenced by nitrogen addition(P<0. 01),it was found that water addition could compensate the negative effects of increased nitrogen deposition on plant species diversity to some extent,and thus change the composition and structure of plant community;4) Plant community coverage and aboveground biomass were significantly affected by coupling treatments of water and nitrogen(P<0. 05);5) The aboveground biomass of the plant community was positively correlated with Shannon-Wiener diversity index,but negatively correlated with species richness,Simpson dominance index,and Pielou evenness index. Further more,principal component analysis showed that the W_(3)-N_(1)0treatment had the best effect on the recovery of herbaceous vegetation productivity in sand-fixing restoration area of Caragana korshinskii,while the W_(1)-N_(5)treatment had the best effect on restoring the species diversity of herbaceous plant community in this area.