内蒙古科尔沁沙地两种沙生植物冷蒿和差不嘎蒿竞争策略的生理生态学依据

研究了中国内蒙古科尔沁沙地两种优势灌木冷蒿(Artemisiafrigida Willd)和差不嘎蒿(Artemisia halodendronTurcz.ex Bess)在不同土壤水分状况条件下的气体交换、水分关系和叶片的化学特性.测定设置了5个土壤水分梯度:土壤最大含水量(体积含水量,30%)、田间持水量(对照,20%)、轻度水分胁迫(10%)、极端干旱(＜4%)和旱后复水(20%).冷蒿的净光合速率(Pn)、蒸腾速率(TR)和水势(ψw低于差不嘎蒿,相对水分亏缺(RWD)、束缚水含量(BWC)、束缚水与自由水的比值(BWC/FWC)和综合抗旱性指数(DI)高于差不嘎蒿.两种灌木对不同土壤含水量的响应不同,随着土壤含水量的逐渐下降,差不嘎蒿的ψw、BWC和BWC/FWC出现大幅度的波动,波动幅度远远的大于冷蒿,冷蒿则显示了一个较差不嘎蒿高的持水能力和抗旱能力.冷蒿和差不嘎蒿的脯氨酸和总可溶性糖含量随土壤含水量的降低均呈增加的趋势,冷蒿增加的幅度大于差不嘎蒿,说明冷蒿的渗透调节能力在干旱过程中有较大提高.在长期极端干旱条件下,两种灌木的ψw,RWD,BWC和BWC/FWC的终极值相近;有机物、脯氨酸和总可溶性糖含量大量累积;冷蒿的脯氨酸和总可溶性糖含量增加的幅度和可溶性蛋白质降解的幅度远远超过差不嘎蒿;我们认为此时累积的物质主要作为营养物质,以供植物的旱后恢复,此时冷蒿的恢复能力超过差不嘎蒿,这是极端干旱条件下差不嘎蒿死亡而冷蒿存活的主要原因之一.我们的研究结果显示,相对于差不嘎蒿而言,冷蒿在水分胁迫条件下的生理生态学特性更有利于其在固定沙地的生长,差不嘎蒿则由于对水资源微弱的竞争丧失了生存优势,是引起科尔沁沙地植被演替过程中冷蒿替代差不嘎蒿的主要原因.

Ecophysiological Evidence for the Competition Strategy of Two Psammophytes Artemisia halodendron and A.frigida in Horqin Sandy Land, Nei Mongol

Gas exchange, water relations and leaf chemical characteristics were examined of two dominant psammophytes: Artemisia frigida Willd and A. halodendron Turcz. ex Bess in Horqin sandy land, Nei Mongol, China under different water regimes. The measurements were conducted by submitting the plants to five different irrigation levels. A. frigida was characterized by lower photosynthetic rate (P_n), lower transpiration rate (TR) and lower shoot water potential (Y_w) relative to A. halodendron. Foliage of A. frigida had higher values of relative water deficit (RWD), bound water content (BWC), ratio of bound water content to free water content (BWC/FWC) and integrated drought-resistant index (DI) than that of A. halodendron. Water relations differed significantly between two species in response to soil water availability. Yw, BWC and BWC/FWC ratio of A. halodendron exhibited large variation with gradual decrease of soil moisture. However, in terms of these parameters, A. frigida was characterized by higher capacity of water holding and drought tolerance relative to A. halodendron. Proline and total soluble sugar contents of A. frigida and A. halodendron tended to increase with decrease of soil moisture and the former had a larger increase amplitude than the latter. This shows that A. frigida has a higher osmotic regulation ability than A. halodendron. Under the extreme drought conditions, Yw, RWD, BWC and BWC/FWC of two species were approximate, but soluble proteins degraded largely. A large amount of accumulation of organic matter, proline and total soluble sugars were observed in both A. halodendron and A. frigida. The increase in proline and total soluble sugar contents and soluble protein degradation of A. frigida far exceeded those of A. halodendron. We believe that the accumulated materials at this moment are mostly of nutrient substances available for the recovery of plants after the drought. This is one of the reasons why A. halodendron plants died while A. frigida plants survived under extremely drought condition. Our results suggest that these ecophysiological features of A. frigida are favorable to its growth in the fixed sandy land compared with A. halodendron, which often lost its dominance due to weak competition for water sources under lower soil water availability and are major factors resulting in replacement of A. halodendron by A. frigida in the later stage of sandy vegetation succession in Horqin.