Variation in grazing tolerance among three tallgrass prairie plant species.
Variation in grazing tolerance among three tallgrass prairie plant species.
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DOI：
10.3732/ajb.89.10.1634
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发表时间：
2002-10
影响因子：
3
通讯作者：
S. Damhoureyeh;D. Hartnett
中科院分区：
文献类型：
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作者：
S. Damhoureyeh;D. Hartnett
以三种高草草原植物、两种常见的多年生草本植物（黄花蒿和紫菀[Asteraceae]）和一种优势的C(4)多年生草本植物（Sorghastrum nutans）为研究对象，在田间和温室条件下评价了其放牧耐受性（补偿生长能力）的种间变化。通过比较25年无放牧和适度有蹄动物放牧的种群中植物的落叶反应，还评估了对有蹄动物放牧的适应性。在野外条件下，随着落叶的发生，3种植物的茎部相对生长率、生物量和繁殖率均显著降低。在两种牧草中，剪枝均导致地上部RGR为负，每分株的地上部分枝数和分枝长度均减少。由于叶片产量的补偿性增加，在落叶条件下高粱保持正的RGR。去叶减少了金针花和金针花的根茎产量，但没有减少金针花的根茎产量。剪枝明显减少了这三个物种的有性生殖分配，尽管胡桃树的减少幅度小于forbs。所有三种植物在燃烧和未燃烧的地点对落叶的反应相似。在温室条件下，类似的修剪方案导致的生长和繁殖的减少比在田间观察到的要小。3种植物在自然条件下的放牧耐受性指数均显著低于温室条件下的放牧耐受性指数，且种间格局存在差异。在温室条件下，紫菀的总体耐落叶性最高，其次是紫菀。黄花蒿（Artemisia ludoviciana）是唯一一种在野外不被有蹄类动物放牧的研究物种，其放牧耐受性最低。在田间试验中，花生表现出最高的放牧耐受性，两种牧草的低耐指数相似。这些模式表明，尽管草原植物具有较高的补偿生长潜力，但有限的资源可利用性和野外竞争显著降低了补偿程度，并改变了草原植物种间的放牧耐受性差异。在这三个物种中，落叶对有性生殖的抑制大于生长或营养生殖。在一些响应变量（根冠比、根茎芽形成和生殖分配）上，植物对落叶的响应与原生地（历史放牧或未放牧地）之间存在显著的交互作用，表明在相对较短的有蹄类放牧压力下，植物的种群分化和遗传适应存在一定程度的差异。本研究结果表明，高草草原的放牧耐受性模式既有遗传基础，也有环境依赖。
Three tallgrass prairie plant species, two common perennial forbs (Artemisia ludoviciana and Aster ericoides [Asteraceae]) and a dominant C(4) perennial grass (Sorghastrum nutans) were studied under field and greenhouse conditions to evaluate interspecific variation in grazing tolerance (compensatory growth capacity). Adaptation to ungulate grazing was also assessed by comparing defoliation responses of plants from populations with a 25-yr history of no grazing or moderate ungulate grazing. Under field conditions, all three species showed significant reductions in shoot relative growth rates (RGR), biomass, and reproduction with defoliation. In the two forbs, clipping resulted in negative shoot RGR and reductions in both number and length of shoot branches per ramet. Sorghastrum nutans maintained positive RGR under defoliation due to a compensatory increase in leaf production. Defoliation reduced rhizome production in A. ericoides and S. nutans, but not in A. ludoviciana. Clipping significantly reduced sexual reproductive allocation in all three species, although S. nutans showed a smaller reduction than the forbs. All three species showed similar responses to defoliation in burned and unburned sites. Under greenhouse conditions, a similar clipping regimen resulted in smaller reductions in growth and reproduction than those observed in the field. For all three species, the grazing tolerance indices calculated under natural field conditions were significantly lower than those estimated from greenhouse-grown plants, and the interspecific patterns of grazing tolerance were different. Aster ericoides exhibited the highest overall defoliation tolerance under greenhouse conditions, followed by S. nutans. Artemisia ludoviciana, the only study species that is typically not grazed by ungulates in the field, showed the lowest grazing tolerance. In the field experiment S. nutans showed the highest grazing tolerance and the two forbs had similar low tolerance indices. These patterns indicate that, despite high compensatory growth potential, limited resource availability and competition in the field significantly reduce the degree of compensation and alter interspecific differences in grazing tolerance among prairie plants. In all three species, defoliation suppressed sexual reproduction more than growth or vegetative reproduction. Significant interactions between plant responses to defoliation and site of origin (historically grazed or ungrazed sites) for some response variables (root/shoot ratios, rhizome bud initiation, and reproductive allocation) indicated some degree of population differentiation and genetic adaptation in response to a relatively short history of ungulate grazing pressure. The results of this study indicate that patterns of grazing tolerance in tallgrass prairie are both genetically based and also environmentally dependent.