Comparative physiology of plant adaptation: resource acquisition and constraints of growing season length in balsam poplar from temperate, boreal and arctic environments

在北方的几种被子植物种群中，有一种光合速率更高的趋势，这可能有助于补偿短暂的夏季。 我们最近报道了高纬度香脂白杨光合作用的增强是由于叶重和单位面积氮的增加，并得到叶肉导度（gm）增强的支持。 叶肉传导率是衡量CO2通过叶片的难易程度的一个指标，但其估计值非常不确定，必须加以验证。 一名硕士学生将使用在线同位素鉴别技术来确认和扩展这些观察结果，在控制北南杂交的香脂杨树。 我们将比较香脂白杨和黑棉白杨，黑杨在北方基因型中也表现出增强的光合作用，但得到更高的气孔导度（gs）的支持。 增加gs可以提高氮的利用效率，但降低水的利用效率。 相比之下，gm的增加应该会改善这两个方面。 这些不同的策略可能反映了水供应的差异，这是较少限制黑棉白杨从西北海岸比香脂白杨从大陆内部。 沿着其他路线，我们在温哥华和萨斯喀彻温省的类似纬度建立了一个广泛收集香脂白杨的共同花园。 无论起源如何，所有基因型在温哥华开花、生长和出芽的时间都提前了约5周。 因此，虽然北方树木可以利用较早的春天，他们可能会捕捉较少的夏天。 在高纬度地区，如果气候变暖足以在冬至前几周诱发潮红，这些固有的反应可能会对树木生长产生强烈的负面影响。 我们将从现场和室内实验中获取数据，以模拟这些关系。 最后，一个博士生将测试假设，允许氮吸收效率，同化和离子通量的网站从N同位素歧视数据提取的信息。 他将研究植物地理学模式的来源偏好，歧视和转录丰度（硝酸盐和铵同化和运输基因家族）在香脂白杨从温暖，高pH值，硝酸盐为主的土壤与树木从寒冷，低pH值，铵为主的土壤。

There is a trend toward higher photosynthetic rates in northern populations of several angiosperm tree species that may help compensate for short summers. We recently reported that greater photosynthesis in high latitude balsam poplar results from increased leaf mass and nitrogen per area, supported by an enhanced mesophyll conductance (gm). Mesophyll conductance is a measure of the ease with which CO2 travels through leaves, but its estimation is very uncertain and must be verified. An MSc student will use an on-line isotope discrimination technique to confirm and extend these observations in controlled north-south crosses of balsam poplar. We will compare balsam poplar with black cottonwood, which also shows enhanced photosynthesis in northern genotypes, but supported by a higher stomatal conductance (gs). Increased gs can improve nitrogen-use efficiency but reduces water-use efficiency. In contrast, increased gm should improve both. These different strategies may reflect differences in water supply, which is less limiting for black cottonwood from the northwest coast than for balsam poplar from the continental interior. Along other lines, we have established common gardens of a range-wide collection of balsam poplar at Vancouver and at similar latitude in Saskatchewan. Regardless of origin, all genotypes flush, grow and set bud ~5 weeks earlier in Vancouver. Consequently, although boreal trees can take advantage of earlier springs, they may capture less of the summer. At very high latitudes, these inherent responses could lead to strong negative impacts on tree growth if climate warming is sufficient to induce flushing a few extra weeks before the solstice. We will acquire data from field and chamber experiments to model these relationships. Finally, a PhD student will test assumptions that allow information on nitrogen uptake efficiency, sites of assimilation and ion flux to be extracted from N isotope discrimination data. He will examine phytogeographic patterns in source preference, discrimination and transcript abundance (nitrate and ammonium assimilation and transport gene families) in balsam poplar from warmer, high pH, nitrate-dominated soils vs. trees from colder, low pH, ammonium-dominated soils.