酸雨和采食模拟胁迫下克隆整合对空心莲子草生长的影响

研究表明克隆整合可以显著提升异质环境中克隆植物的生长,然而当克隆植物遭受均质环境压力时,整合对植物生长影响的研究相对较少。本文以典型入侵克隆植物空心莲子草（Alternanthera philoxeroides）为例,研究均质环境压力酸雨和采食模拟胁迫对空心莲子草生长的影响,以及克隆整合在空心莲子草适应不利环境过程中所起的作用。酸雨设3种浓度梯度：pH值3.5 、pH值4.5和 pH值6.5（对照）;采食设3种水平：不去叶、去叶50%和去叶90%;整合水平：匍匐茎切断和连接。结果表明：无论保持或切断匍匐茎的连接,酸雨处理都不影响空心莲子草生物量。当保持匍匐茎连接时,pH值4.5酸雨处理增加了空心莲子草匍匐茎长度和分株数目,因此,低度酸雨可能对空心莲子草生长有一定的促进作用。同样,无论匍匐茎是否被切断,采食处理都显著降低了空心莲子草克隆片段生物量,而显著增加了叶片数目。当切断匍匐茎连接时,采食处理使空心莲子草分株数目显著增加。本文得出的结论是：空心莲子草能较好地适应酸雨和采食的环境压力,当空心莲子草全部克隆分株遭受均质环境胁迫时,克隆整合并不能显著改善它的生长。

Effects of clonal integration on growth of Alternanthera philoxeroides under simulated acid rain and herbivory

Effects of clonal integration on growth and reproduction of plants in heterogeneous environments have been extensively studied, but relatively little is known about the roles of clonal integration in homogeneous, stressful environments. We conducted a greenhouse experiment to investigate the effects of clonal integration on the stoloniferous invasive plant Alternanthera philoxeroides (alligator weed) under homogeneous, stressful environments, i.e., under simulated acid rain and herbivory. There were three levels of acid rain treatments pH = 6.5 (control), 4.5 (mild acid rain) and 3.5 (severe acid rain)], three levels of herbivory 0 (control), 50% (moderate herbivory) and 90% leaf removal (heavy herbivory)] and two levels of clonal integration (no integration - stolon connection was severed; with integration - stolon connection was intact). In the control (i.e., no acid rain and no herbivory), severing stolon did not affect biomass or biomass allocation of alligator weed, but increased total stolon length, number of ramets and number of leaves. The simulated acid rain treatments did not affect biomass of alligator weed, no matter whether the stolons were intact or severed. When the stolons were left intact, the mild acid rain treatment (pH=4.5) markedly increased total stolons length and number of ramets, suggesting that mild acid rain may improve plant growth. Meanwhile, the acid rain treatments significantly affected biomass allocation to roots and stolons. Under mild acid rain treatment (pH=4.5) biomass allocation to stolons increased significantly, whereas that to roots decreased; however, severe acid rain (pH=3.5) did not affect biomass allocation of alligator weed. When the stolons were severed, the acid rain treatments did not affect growth or biomass allocation of alligator weed. The results suggest that alligator weed can well adapt to acid rain stress and clonal integration play a limited role under acid rain stress. When the stolons were left intact, the simulated herbivory treatments markedly affected biomass and number of leaves of alligator weed, but did not affect total stolon length or number of ramets. With increasing herbivory levels, biomass of alligator weed significantly decreased, but number of leaves increased. When the stolons were severed, effects of the herbivory treatments on biomass, total stolon length and number of leaves were the same as those in the intact clonal fragments. Therefore, despite the status of the stolons, the simulated herbivory treatments markedly decreased growth of alligator weed. The herbivory treatments also modified biomass allocation of alligator weed. With increasing herbivory levels, biomass allocation to leaves significantly increased and that to stolons and roots significantly decreased. The results suggest that alligator weed can also well adapt to herbivory stress and clonal integration also plays a limited role under herbivory stress. These features of alligator weed may be helpful for it to invade into new habitats, and clonal integration plays a limited role under homogeneous stressful, environments.