Six alfalfa varities in manual climatic chamber were used as samples to study the drought and heat resitance of alfalfa.The soil relative water content,leaf length,leaf width,plant relative height,plant absolute height,stem diameter of these morphological characteristics,and carotenoid and chlorophyll contents were measured.The results showed that with the increase of drought and hot stress,the soil relative water content, leaf length,leaf width,stem diameter,chlorophyll content in leaf were declined.However,the relative height, absolute height,carotenoid content showed an increasing trend.The impacts of drought and hot stress on the relative water content of soil,plant height,chlorophyll content and carotenoid content were significant.

为了解紫花苜蓿(Medicago sativa L.)在干热胁迫条件下光合特性的变化规律,对其6个品种的叶片净光合速率(Pn)、蒸腾速率(Tr)、胞间二氧化碳浓度(Ci)、气孔导度(Gs)、水分利用效率(WUE)进行测定.结果表明,随着干热胁迫强度的增加,各紫花苜蓿品种叶片的净光合速率、蒸腾速率、气孔导度、水分利用效率整体呈下降趋势;而胞间二氧化碳浓度整体呈上升趋势(P＜0.05).且经过一定时间的复水处理,WL525的蒸腾速率和气孔导度得到了明显的恢复(P＜0.05),与胁迫前的状态接近,且其他品种的蒸腾速率和气孔导度也得到一定程度的恢复;而供试品种的净光合速率、胞间CO2浓度及水分利用效率均没有得到明显改善.相关分析表明,在干热胁迫条件下,净光合速率与蒸腾速率、气孔导度、水分利用效率均成极显著正相关(P＜0.01),而与胞间二氧化碳浓度成极显著负相关(P＜0.01).

The leaf epidermal structure and stomata size of Deqin alfalfa and Algonguin alfalfa were studied by scanning electron microscopy under drought and heat stress in order to investigate its change of stomata size.The result showed that length and width of epicuticle and exocuticle of alfalfa leaf were firstly increased with the stress deepened and then decreased.The stomatal aperture of alfalfa leaf was firstly increased with the stress time and then decreased and increased by rewatering.Under the same treatment conditions,the mostly same indicators of Deqin and Algonguin showed significant differences(P <0.05).

Alfalfa(Medicago sativa L.) is very important forage in the development of farming and live stock industry in the world.Alfalfa has strong tolerance to drought,but drought is the mainly adversity factor to restrict alfalfa production.In recent years,greenhouse effect is continuously strengthening,and global temperature becomes warm,so it is very important to study crops and pasture tolerance to drought and heat.Six alfalfa were cultivated in the Jianshui County,Honghe,Yunnan Province and their photosynthetic characteristics and response to dry-hot environment were studied.The results showed that net photosynthetic rate of alfalfa No.24 was significantly higher than those of other alfalfa(P0.05).The transpiration rates of alfalfa No.14 and No.15 were significantly higher than those of other alfalfa(P0.05).The stomatal conductances of alfalfa No.15 and No.16 were significantly higher than those of other alfalfa(P0.05).The Internal CO2 of alfalfa No.14 and No.24 were significantly higher than those of other alfalfa(P0.05).Net photosynthetic rate was positively correlated with photosynthetic active radiation,transpiration rate,intercellular CO2 concentration,but it was negatively correlated with stomatal conductance.

Leaf chlorophyll content,relative conductivity and water saturation deficit were determined in six gernplasms of alfalfa when subjected to heat stress and rehydrated condition.The results showed that as heat stress prolonged: 1) the water saturation deficit increased in all gernplasms;2) the relative conductivity increased except accession 16 and 15 decreased in the eighth day;3) leaf chlorophyll content decreased except accession 15 increased in the eighth day.Based on the results,present study suggested that accession 28 performed better than the other varieties in heat resistance,while accession 26 was relative worse.Correlation analysis showed that water saturation deficit significantly negatively correlated with chlorophyll content but positively correlated with relative conductivity.This implied that water deficit severely affected the integrity of cell membrane and lead to chlorophyll content inhibition.