沙木蓼和沙枣对地下水位变化的生理生态响应Ⅱ.叶片光合作用及其对温度和光的反应

 在甘肃民勤沙生植物园内，研究了两种优势旱生植物沙木蓼(Atraphaxis frutescens)和沙枣(Elaeagnus angustifolia)的光合生理等特性对不同地下水深度(1.4～3.4 m)的响应。结果表明：1)地下水深度的变化导致了这两种旱生植物净光合速率(Pn)、蒸腾速率(E)、气孔导度（Gs）、叶绿素a、叶绿素b、叶绿素总量、叶绿素a与叶绿素b的比值、光量子效率、CO2羧化效率等的显著变化；2)两种植物均能较好地适应地下水深度为3.4 m的水分胁迫；3)两种植物对地下水深度变化的适应方式略有不同，沙木蓼主要通过一定程度地净光合速率的降低、并保持一定的水分利用率来适应干旱，而沙枣则通过净光合速率的较大幅度降低以增加其水分利用率来适应干旱；4)地下水深度的变化并未导致两种植物光合作用适宜温度的明显变化，但却引起了在适宜温度下净光合速率的显著下降。沙枣是非豆科固氮植物，两者的差异是否与固氮作用相关还有待进一步研究。

ECOPHYSIOLOGICAL RESPONSES OF TWO XEROPHYTES ATRAPHAXIS FRUTESCENS AND ELAEAGNUS ANGUSTIFOLIA TO THE CHANGE OF GROUNDWATER DEPTH IN ARID AREA Ⅱ. LEAF PHOTOSYNTHESIS AND PHOTOSYNTHETIC RESPONSE TO LIGHT AND TEMPERATURE

The eco_physiological responses of dominant trees (Atraphaxis frutescens and Elaeagnus angustifolia) to ground water availability were investigated in a controlled environment at the Plant Transpiration Consume Water Observation S tation in Minqin Desert Botanical Garden, Gansu province. In this experiment, th e depths of groundwater (DGW) were designed as 1.4 m, 2.4 m and 3.4 m. In each t rea tment, the two desert species were transplanted to the observation sites with di fferent DGW after growing naturally for 3 or 4 years. The results showed that: 1 ) the changes of DGW resulted in the significant changes of net photosynthetic r ate (Pn), the transpiration rate (E), stomatal conductance (Gs), lea f contents o f chlorophyll a (Chl a), chlorophyll b (Chl b) and the total chlorophyll (Chl a + Chl b), the ratio of Chl a and Chl b (Chl a/Chl b), the quantum yield efficien cy and the CO 2 carboxylation efficiency; 2) although these two desert species were well adapted to the water stress environment at 3.4 m DGW, their adaptive s trategies were different. In response to the water stress environment, A. fru tescens reduced its photosynthetic rate and maintained the level of water use efficiency, while E. angustifolia largely decreased the transpiration rat e and thus increased the water use efficiency; 3) in different DGW, the optimal temperature of photosynthesis in these two desert species did not change signif icantly, but the net photosynthetic rate under the optimal temperature range dec lined markedly. Since E. angustifolia is a nitrogen fixation species, fur ther studies are needed to verify whether or not the differences of drought adap tation between these two species are related to the nitrogen fixation.