Impact of sex on aspen distribution and response to abiotic drought stress

干旱对植物物种的适应性、生理学和健康的深刻影响已经在广泛的条件下进行了研究。然而，非生物胁迫和性别之间的联系，特别是在长寿的克隆树种中，还有待探索。该计划的长期目标是：1)了解性别在杨树抗逆性和分布中的作用。2)评估生态生理、生长和木材质量性状的潜在权衡，以此作为抵抗非生物胁迫(如干旱)的机制。通过研究发生非生物胁迫的天然林系统和使用幼苗的人工温室实验，我将调查干旱胁迫是否对不同年龄的雄性和雌性产生不同的影响，并通过测量天然林分中的克隆大小，确定在非生物胁迫下繁殖成本与克隆扩张和生长是否存在权衡。一种性别与另一种性别的不同扩张可能导致景观上的雄性和雌性的分离，并最终导致这种物种的分布发生变化。随着最近(2015年)在杨树上发现了一种简单的基于DNA的性别标记，我们可以开始深入探索这些问题。 文献告诉我们，在雄性和雌性在不同植物上的物种中，雄性会比雌性表现更好，因为雌性的繁殖成本更高。到目前为止，阿斯彭的证据并不令人信服。有几个因素似乎影响克隆的大小，包括重新定殖率、火返回间隔和开花和种子传播期间的水分可用性。例如，在北方，无性系往往较小，那里发生了较新的重新定居，水分对幼苗再生的限制较小。由于之前已经确定了树木何时开花，目前尚不清楚目前整个景观的性别比例是多少。然而，最近北美大部分地区杨树健康状况的下降，主要是由于南部北方森林边缘的干旱，似乎对物种范围产生了深远的影响，并可能对该物种在景观上的性别分布和最终持久性产生严重影响。 在这份探索基金中，我将测试一种假设，即在干旱条件下，雄性比雌性表现更好，这是因为繁殖所需的能量减少，从而扭曲了雄性和雌性在景观上的分布。一个相互竞争的假说是，由于杨树的种子生产成本很低(没有胚乳)，雌性在景观上的比例是平等的，不会增加繁殖和母体投资的成本。该计划的第二部分将检验这样的假设，即木材密度较高的无性系将表现出更高的水分利用效率，对水分运输系统的破坏具有更强的抵抗力，最终将更耐干旱。

The profound impact of drought on the fitness, physiology and health of plant species has been studied across a wide range of conditions. However, the linkage between abiotic stress and sex, particularly in long-lived clonal tree species has yet to be explored. The long-term objectives of this program are to: 1) understand the role of sex in stress resistance and distribution of aspen (Populus tremuloides Michx.) clones on the landscape, and 2) assess potential trade-offs in ecophysiology, growth and wood quality traits as mechanisms to resist abiotic stress (ie: drought). By studying both a natural forest system where abiotic stress is occurring and through artificial greenhouse experiments using seedlings, I will investigate if drought stress differentially affects males and females at different ages and by measuring clone size in natural stands, determine if there is a trade-off in the cost of reproduction vs clonal expansion and growth under abiotic stress. Differential expansion of one sex vs the other, could lead to a separation of males and females on the landscape and ultimately cause a shift in the distribution of this species. With the recent discovery (2015) of a simple DNA-based marker for sex now available for aspen, we can begin to explore these questions in depth. The literature tells us that males will outperform females in species where males and females are on different plants, because of a higher cost of reproduction in the female. The evidence to date in aspen is not convincing. Several factors appear to affect clone size including recolonization rates, fire return interval and moisture availability during flowering and seed dispersal. For example, clones tend to be smaller in the north where more recent recolonization has occurred and moisture is less limiting to seedling regeneration. Since sex has previously been determined when trees were flowering, it is unknown what the current sex ratio is across the landscape. A recent decline in aspen health across much of North America, due primarily to drought at the southern boreal forest fringe however, appears to be having a profound impact on the species range and may be having a serious impact on the sex distribution and ultimate persistence of this species on the landscape. In this Discovery Grant, I will test the hypothesis that males are out-performing females under drought conditions due to a reduced need to expend energy in reproduction, skewing the distribution of males and females on the landscape. A competing hypothesis is that females are equally represented on the landscape with no added cost to reproduction and maternal investment due to the small cost of seed production in aspen (no endosperm). A second component of the program will test the hypothesis that clones with higher wood density, will exhibit greater water use efficiency, greater resistance to damage of the water transport system and ultimately be more drought stress resistant.