干旱区荒漠植被丙二醛及保护酶活性对地下水位的响应

塔里木河下游的乔木、灌木、草本植被的主要建群种为胡杨、柽柳和罗布麻,对其中丙二醛(MDA)含量以及保护酶活性对地下水位的研究表明:1)MDA含量以及SOD、POD活性均呈增加趋势,而且均与地下水位呈正相关关系;2)对同一断面相同地下水位条件下胡杨、柽柳和罗布麻的SOD活性和POD活性比较,可以反映出SOD和POD作用的互补性;3)根据不同地下水位条件下胡杨、柽柳和罗布麻的MDA含量和SOD活性所反映出的适宜植物生存的合理生态水位、(严重)胁迫水位,并将其进行综合比较与分析,初步推断在塔里木河下游地下水埋深超过3.12 m时,胡杨和柽柳的生长即开始受到抑制,6 m左右的地下水位即对胡杨造成严重胁迫,≥8.83 m的地下水位则会危及胡杨的生存;而柽柳的严重胁迫地下水位以及临界地下水位分别为5 m左右和≥8.83 m.相比之下,罗布麻所能承受的胁迫地下水位比较高,超过3.12 m的地下水位即会对其生长造成严重水分胁迫,地下水位低于4.42 m则危及其生存.

Responses of Malondialdehyde and Protecting Enzymes of Desert Vegetation to the Variation of Water Table in Arid District

At different sections of the lower reaches of Tarim River,the MDA contents of the main constructive species of the arbor,bush,herbaceous vegetation-Populus euphratica,Tamarix ramosissima and Apocynum venetumas show an increasing tendency and a positive correlation with the water table along with the constant increase of the groundwater depth and the distance from river.Among them,the Tamarix ramosissima MDA contents of almost every section occupy the first place in the three,which proves that under the condition of moisture coercing at lower reaches of Tarim River,the oxidizing degree of the cell membrane fat of Tamarix ramosissima is relatively high and it is coerced heavy by the aridity;SOD activity of them also rises gradually with the decline of the water table and presents a positive correlation with the water table.However,POD activity keeps dropping with the gradual increase of groundwater depth and presents a negative correlation with the water table.These results indicate that the membrane fats of Populus euphratica,Tamarix ramosissima and Apocynum venetumas have a strong oxidation under the condition of serious water stress,which results in a large amount of MDA accumulation,activates the protection enzyme system in the body of Tamarix ramosissima at the same time and improves its ability of fighting drought through strengthening SOD activity.The reason why POD activity declines may be that arid environment causes POD control system in plant cell obtuseness or protein formatting ability drop,or there are many ways of removing H₂O₂ in plant,the concrete reason awaits to be studied further.The comparison of SOD and POD activity of Populus euphratica,Tamarix ramosissima and Apocynum venetumas under the same water table at the same section in the lower reaches of Tarim River reflects the complement of SOD and POD functions,namely they cooperate with each other while the plant cell defends active oxygen and other peroxide free radicals,which makes plant adapt to the arid environment better.The rational ecological water level and(serious) coercing water level suitable for the plant survival,which are reflected by the MDA content and SOD activity under different water table conditions,are compared and analyzed,and then a preliminary inference is gotten.When the groundwater depth in the lower reaches of Tarim River is over 3.12 meters,the growth of Populus euphratica and Tamarix ramosissima begins to be suppressed promptly,about 6 meters of water table will cause serious coercion to Populus euphratica,and ≥8.83 meters of water table can jeopardize Populus euphratica’s existence.And the serious coercing water table and critical water table of Tamarix ramosissima are about 5 meters and ≥8.83 meters,respectively.By contrast,the coercing water table to which Apocynum venetumas can bear is relatively high: more than 3.12 meters water table will cause serious coercion to its growth and lower than 4.42 meters water table will endanger its survival.