塔克拉玛干沙漠南缘3种荒漠植物光合特性的比较

在2008年6、7和8月中旬，以塔克拉玛干沙漠南缘固氮植物骆驼刺（Alhagi sparsiftia Shap．）和非固氮植物柽柳（Tamarx ramossimaLedeb．）、花花柴（Karelinia caspica Less．）为研究对象，研究了两种类型植物的净光合速率、光响应、CO：响应模型参数、叶绿素和叶氮...

Comparison of photosynthetic characteristics of three species growing at the southern fringe of the Taklimakan Desert

Indigenous vegetation in the foreland of river oases at the extremely arid southern margin of the Taklimakan Desert in Xinjiang,NW China,is dominated by a few perennial phreatophytes,primarily Alhagi sparsifolia Shap.,Tamarix ramosissima Ledeb.and Karelinia caspica Less.Water is well known as a limiting factor for plant growth in deserts,availability of nutrients has also been determined as a critical factor limiting plant growth in arid regions.Water source for plants is groundwater at the southern fringe of the Taklimakan Desert.So nutrients are the most important resource for plant growth in the same groundwater depth.When the soil N content or the nitrogen validity are low,plants with the ability to fix N2 might have an advantage and be capable of taking in more N than plants without this ability.Leaf N content correlates strongly with photosynthesis as most of the leaf N is allocated to photosynthesis.So some people considered that the nitrogen fixing plants might have higher Pmax than the nitrogen non-fixing ones living in the same habitat.However,in our previous research,we found that nitrogen non-fixing species had higher photosynthetica capacity.In order to answer this question,nitrogen fixing species A.sparsifolia and nitrogen non-fixing species K.caspica and T.ramosissima were compared in their typical habitat at the southern fringe of the Taklimakan Desert.The diurnal variations of net photosynthetic rate,indexs of light and CO2 to net photosynthetic rate(Pn),Chl content,leaf nitrogen content of nitrogen fixing and non-fixing species were investigated in June,July and August 2008.The results showed that from 08∶00 to 20∶00 the diurnal variations of Pn showed double peak curve both nitrogen fixing and non-fixing species in June and July.In August,the curve changed into a single peak.The order of average photosynthetic rate of three months: K.caspica>T.ramosissima>A.sparsifolia.It also showed that nitrogen non-fixing species had higher Pn than nitrogen fixing species.The maximum net photosynthetic rate(Pmax),apparent quantum requirement(AQY),CO2 saturation point(CSP),dark respiration rate(Rday) of nitrogen non-fixing species were higher than nitrogen fixing species,the difference was significant(P<0.05),respectively.Carboxylation efficiency(Vcmax) and electron transport rate(Jmax) were not significantly different between nitrogen fixing and non-fixing species(P>0.05).The nitrogen fixing species had significantly higher light compensation point(LCP),light saturation point(LSP),CO2 compensation point(CCP),Chl content and leaf nitrogen content than nitrogen non-fixing species(P<0.05).Through correlative analysis,we found that there was no obviously relationship between Pmax and Chl,leaf nitrogen content in A.sparsifolia.There was no obviously relationship between Pmax and Chl in K.caspica and T.ramosissima.Pmax of T.ramosissima was negatively correlated with leaf nitrogen content.But Pmax of K.caspica was positively correlated with leaf nitrogen content.In despite of higher leaf nitrogen content in nitrogen fixing species,nitrogen non-fixing species had higher photosynthetic capacity.The higher leaf nitrogen content not always bring higher photosynthetic rate in nitrogen fixing and non-fixing species.