4种荒漠植物气体交换特征的研究

A STUDY OF THE GAS EXCHANGE CHARACTERISTICS OF FOUR DESERT PLANTS

在自然条件下我们对塔克拉玛干沙漠南缘策勒绿洲边缘 4种主要荒漠植物胡杨 (PopuluseuphraticaOliv.)、沙拐枣 (Calligonumcaput_medusaeSchrenk .)、骆驼刺 (AlhagisparsifoliaB .KelleretShap)和柽柳 (TamarixramosissimaLbd .)的气体交换、水势及其δ13 C的季节变化特征进行了比较研究。结果表明胡杨和沙拐枣气体交换日变化为单峰曲线 ,骆驼刺和柽柳为双峰曲线 ;其中骆驼刺属低光合低蒸腾型 ,WUEph最低 ,胡杨和柽柳为高光合高蒸腾型 ,而沙拐枣则属高光合低蒸腾型 ,WUEph最高 ;骆驼刺 (9:0 0～ 13:0 0 )和柽柳 (10 :0 0～ 14:0 0 )An 的“午降”主要取决于气孔导度 ,而柽柳午后 (15 :0 0～ 18:0 0 )的An 降低则主要取决于非气孔因子 ;耐旱机理上 ,沙拐枣和骆驼刺同属高水势延迟脱水类型 ,但是二者又有区别 ,沙拐枣通过减少水分丧失 ,而骆驼刺则通过发达的根和强大吸水输导系统来维持高水势 ,胡杨和柽柳属于低水势忍耐脱水类型 ;在试图建立起用δ13 C表现植物WUEph的关系时我们发现有δ13

Populus euphratic, Calligonum caput-medusae, Alhagi sparsifolia and Tamarix ramosissima, are four very important species of desert plants in the frangible desert-oasis ecosystem in the southern margin of the Taklimakan Desert. They are used for preventing drift-sand and sand storms. The desert vegetation is being severely decreased use for firewood by the local populace and by the low level of the underground water. This decrease brings on many problems such as sand storms and dust-floating weather. It is vital task to restore the vegetation, and choosing good plant species that could acclimate to the local environment is a very urgent issue. Little research into the photosynthetic characteristics of these plants in natural conditions has been done in China. To understand the growing features of the desert plants and how these plants adapt themselves to extreme drought, it is necessary to study their gas exchange mechanisms and water potential. We did this hoping to get information on the eco-physiologic characteristics of three aspects of the four desert plants: 1) the photosynthesis and transpiration diurnal courses of the four desert plants, the seasonal changes of the same species and the different features of different species 2) the mechanisms applied by different species to adapt to the desert environment, especially to water stress 3) the relationships of stable carbon isotope (δ 13C) and the water use efficiency (WUE ph) of the plants with different photosynthetic pathways. If we have a good understanding of these three aspects, it will provide a sound foundation for local people to make a scientific plan to select appropriate plants for the conservation of the desert vegetation and the establishment of windbreaks. We measured the diurnal courses of photosynthesis using Li-cor 6400 (LICOR, USA) once every hour from 6:00 to 19:00 in different seasons, and got data on PPFD (photosynthetic photon flux density), T a (air temperature),VPD (vapor pressure deficit), A n (net assimilation rate), E (transpiration rate), G s (stomatal conductance) and C i (intercellular CO 2 concentration). WUE ph was calculated by A n/E. The A n and E diurnal courses of P. euphratic, C. caput-medusae displayed a unimodal pattern, while those of A. sparsifolia, T. ramosissima were bimodal. In the four plants, C. caput-medusae displayed the highest WUE ph because of its higher A n and lower E, A .sparsifolia displayed a low A n and E and the lowest WUE ph, P. euphratic and T. ramosissima had high A n and E. The first A n decline of A. sparsifolia, T. ramossima was due to the effect of G s, and the low carboxylation capacity of the leaf mesophyll contributed much to the second decline in the afternoon (15:00～18:00).In the interval between of gas exchange measurements, we measured the water potential (Ψ) once every two hours. Different plants had different mechanisms to adapt to drought stress. C. caput-medusae and A. sparsifolia maintained a high water potential to delay dehydration. A. sparsifolia did this through reducing transpiration and depended on its powerful water-absorbing system and widely-expanded roots. P. euphratic and T. ramosissima had the ability to endure drought with a very low (more negative) water potential (Ψ). We sampled the sunny, mature and healthy leaves of the four desert plants in different months, and then analyzed the stable carbon isotope discrimination (δ 13C) of the samples. The δ 13C showed a lag effect, when trying to establish the relationships of WUE ph and δ 13C of the four plants in different months. This phenomenon requires further study.