长期N添加对典型草原几个物种叶片性状的影响

Abstract

Increasing atmospheric nitrogen(N) deposition is one of the hot topics related to global climate change.This change has altered soil N availability and is expected to affect plant N economy.For terrestrial ecosystems where N is a limiting factor,increased N deposition may lead to a shift from N limitation to P limitation,possibly resulting in changes in plant P use strategies.Research into nutrient conservation responses to increased N gradients is important in exploring the effects of global climate change on the nutrient economy of plants and thus on ecosystem-level nutrient cycling.We studied the responses of several leaf traits in relation to nutrient conservation strategies,including specific leaf area(SLA),N and P concentrations in green leaves,and N and P concentrations in senescing leaves.Our objective was to investigate the potential effects of increased N deposition on N and P use strategies for dominant species of temperate grasslands.This study was conducted during 2003—2006 and compared plant responses to N levels of 0,1,2,4,8,16,32,64 g/m2.Five temperate grassland species of Inner Mongolia belonging to three different life-forms were studied: Stipa krylovii Roshev.(grass),Cleistogenes squarrosa(Trin.) Keng.(grass),Artemisia frigida Willd.(semishrub),Potentilla acaulis L.(forb) and Allium bidentatum Fischer ex Prokhanov Ikonnikov-Galitzky(forb).The results show SLAs in A.frigida,P.acaulis and A.bidentatum increased with increasing N availability while no obvious trends were found in the two grasses.N concentrations in green leaves of the five species increased significantly,while the P concentration change in green leaves were species-specific.The P concentration in A.bidentatum initially decreased but increased with higher N levels.The other four species showed insignificant relationships with N addition gradients.In senescing leaves,N concentrations increased significantly for all five species.The response of P concentration to increasing N availability in senescing leaves was also species-specific.P concentrations in A.frigida,P.acaulis and C.squarrosa initially increased and then decreased at high N levels;however,no obvious trends were found in S.krylovii and A.bidentatum.The SLA and nutrient concentrations in A.frigida were higher than the other species but they were lower in the two grasses.These results offer basic data useful in forecasting the potential influences of increasing N deposition and associated changes in P availability on ecosystem nutrient cycling in the temperate grasslands of Inner Mongolia.The generally increasing trends in green leaf SLA and increasing N concentrations in both green and senescing leaves indicate an increase in N deposition enhances N uptake for these species but decreases N reabsorption,therefore decreasing the ability of plants to conserve N.In contrast,the effect of increased N deposition on P use strategy is species-specific,reflecting the flexible adaptation of P strategy of plants in relation to changes in N availability.Consequently,increased N deposition changes a plant′s N and P use strategies,which causes further changes in N and P cycling in plant-soil systems.These species-specific responses will strongly influence community structure.