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

干旱对植物适应度、生理和健康的深刻影响已经在广泛的条件下进行了研究。然而，非生物胁迫与性之间的联系，特别是在长寿的克隆树种中，尚未被探索。该项目的长期目标是：1)了解性别在白杨（Populus tremuloides Michx.）无性系在景观中的抗逆性和分布中的作用；2)评估生态生理、生长和木材品质性状作为抵抗非生物胁迫（如干旱）机制的潜在权衡。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，我将调查干旱胁迫对不同年龄雄性和雌性的影响是否存在差异，并通过测量自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成本之间是否存在权衡。一种性别与另一种性别的差异扩张可能导致雄性和雌性在景观上的分离，并最终导致该物种分布的转变。随着最近（2015年）一种简单的基于dna的白杨性别标记的发现，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，雄性会比雌性表现得更好，因为雌性繁殖的成本更高。迄今为止在阿斯彭的证据并不令人信服。影响无性系大小的因素包括再定植率、回火间隔和开花和种子传播期间的水分有效性。例如，在北方，无性系往往较小，那里最近发生了再殖民化，水分对幼苗再生的限制较少。由于性别以前是在树木开花的时候确定的，所以目前的性别比例在整个景观中是未知的。然而，最近北美大部分地区的白杨健康状况下降，主要是由于南部北方森林边缘的干旱，这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。****在这个发现基金中，我将测试一个假设，即在干旱条件下，雄性的表现优于雌性，因为雄性在繁殖过程中消耗的能量减少了，这扭曲了雄性和雌性在景观上的分布。另一种与之竞争的假设是，由于白杨种子生产的成本很小（没有胚乳），雌性在景观上的代表性是平等的，没有额外的繁殖成本和母性投资。该计划的第二个组成部分将测试假设，即具有较高木材密度的无性系将表现出更高的水利用效率，对水运系统的破坏有更大的抵抗力，最终更能抵抗干旱胁迫。******

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.******