Dissertation Research: Life History Responses to Fire in a Clonal Herb, Pityopsis graminifolia

目前尚不清楚诸如频繁的低强度（如亚致死）火灾等干扰如何影响植物的生活史进化。谷草松是一种适应火的无性系多年生草本植物，常见于东南部长叶松稀树草原的被烧过的沙丘。该物种的生殖生物学在两个已被研究的沙丘群落中有所不同，尽管火灾在两个群落中导致很少的成虫死亡或幼苗建立。拟议的研究有两个主要目标。本文将首先研究低强度火灾如何改变这两个沙地禾本科种群的有利环境条件。具体来说，我们将研究火灾是否以及在多大程度上通过增加这些群落中营养物质的可用性来降低这种耐受性物种的开花和营养繁殖（例如克隆生长）的成本。还将研究这些地点火灾后植物食草性和种子捕食性的影响。根据这些沙丘群落中该物种在火灾后表现出的生殖行为的表型变异，评估其影响的重要性。结果可能表明，在植物的生命周期波动的环境条件如何影响生命史的进化。该研究的第二个目标是解决开花和克隆生长的动态如何对其历史和进化重要性不同的火灾（例如生长季节与休眠季节火灾）做出反应。特别是，在历史上重要的生长季节火灾之后，更丰富的开花和更短的持续时间是否会减少该物种的花食草性和/或种子捕食的影响，将进行评估。这类证据可以为长叶松稀树草原生长季节与休眠季节亚致死火灾的适应意义提供见解。

It is not well understood how disturbances such as frequent, low- intensity (e.g. sublethal) fire have influenced life history evolution in plants. Pityopsis graminifolia is a fire-adapted, clonal perennial herb that inhabits frequently burned sandhills in Southeastern longleaf pine savannas. The reproductive biology of this species differs in two sandhill communities in which it has been studied despite the fact that fire results in little adult mortality or seedling establishment in either community. The proposed study has two major objectives. It will first examine how low intensity fires change the favorability of environmental conditions in these two sandhill populations of P. graminifolia. Specifically, if and to what extent fire reduces the cost of flowering and vegetative reproduction (e.g. clonal growth) in this stress-tolerant species by increasing the availability of nutrients in each of these communities will be examined. The impact of floral herbivory and seed predation following fire in each of these sites will also be examined. The significance of their impact in light of the phenotypic variation in reproductive behavior exhibited by this species following fires in each of these sandhill communities will be assessed. Results may indicate how fluctuating environmental conditions during the life of a plant influence life history evolution. The second goal of the study is to address how the dynamics of flowering and clonal growth respond to fires that differ in their historical, evolutionary importance (e.g. growing season vs. dormant season fires). In particular, whether the more profuse flowering and fruiting of shorter duration following historically important growing season fires reduces the impact of floral herbivory and/or seed predation in this species will be assessed. Evidence of this kind could provide insight regarding the adaptive significance of growing season vs. dormant season sublethal fires in longleaf pine savannas.