施肥后青藏高原亚高寒草甸典型物种生态化学计量特征及光合特性的变化

Effects of nutrient addition on ecological stoichiometric characteristics and photosynthesis of representative species in a sub-alpine meadow community

以青藏高原亚高寒草甸为研究对象,通过氮(N)添加试验,研究了群落水平和功能群水平上物种丰富度和生物量对N添加的响应,物种水平上N添加对5种典型物种的叶片w(养分)、化学计量比特征、株高与净光合速率的影响.结果表明:N添加显著降低了物种丰富度而增加了地上净生物量产出.其中N添加对禾本科与莲座状杂类草的物种丰富度影响不显著,而豆科与直立型杂类草的物种丰富度随N添加量的增加而显著减少;N添加显著增加了禾本科物种的地上生物量,显著减少直立型杂类草的地上生物量.随N添加量增加5种典型物种的叶片w(N)、w(N)∶w(P)与株高显著增加,w(C)∶w(N)显著降低.其中垂穗披碱草叶w(N)与株高的平均增幅最大,w(C)∶w(N)平均降幅最大.N添加仅使垂穗披碱草和甘青蒿的净光合速率显著增加,且逐步回归分析表明,仅垂穗披碱草和甘青蒿的净光合速率与叶w(N)正相关,与w(C)∶w(N)负相关.禾本科物种垂穗披碱草相较于其他物种对N更敏感,在富N的生境中,体内w(N)迅速提升用于满足高生长所需的营养物质,表现出高的净光合速率和生物量产出在群落中占据优势.

A field experiment of nitrogen(N)enrichment was conducted in a sub-alpine meadow on the Qinghai-Tibet Plateau.The responses of species richness and biomass to N fertilization were analyzed at the level of community and functional groups.We also tested the effects of N addition on nutrient concentration,ecological stoichiometric patterns,plant height and photosynthesis of five exemplar species.The results showed that N addition significantly decreased species richness and increased aboveground net primary production.N addition had no significant effect on the species richness of grasses and rosette forbs,while the species richness of legumes and upright forbs significantly decreased with increasing N levels.With increasing N addition,significant reduction in the biomass of upright forbs was investigated,and the biomass of grasses increased.Leaf w(N),w(N)∶w(P)and plant height of the exemplar species significant increased with N enrichments,and w(C)∶w(N)decreased.The grass,Elymus nutans,responded positively to fertilization with the biggest increase in leaf w(N),plant height and decrease in w(C)∶w(N).Besides,photosynthetic rate of E.nutans and Artemisia tangutica significantly increased with N addition,and step-wise regression showed a strong positive association of the photosynthetic rate with N concentration was found and there was a negative relationship between the photosynthetic rate and w(C)∶w(N)in E.nutans and A.tangutica.All of the above results suggested that the grass,E.nutans,is more sensitive to nitrogen than others,and presents higher foliar N concentration to satisfy with their faster-growth requirement for nutrient under high nitrogen conditions.Those grasses are an advantage in a fertilized community with a higher photosynthetic rate and aboveground net primary production.