Land Change Science, Swiss Federal Research Institute WSL, Birmensdorf, Switzerland.
Biodiversity and Conservation Biology, Swiss Federal Research Institute WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland.
Tree Physiol. 2022 Feb 9;42(2):273-288. doi: 10.1093/treephys/tpab105.
Abies alba (Mill.) has a high potential for mitigating climate change in European mountain forests; yet, its natural regeneration is severely limited by ungulate browsing. Here, we simulated browsing in a common garden experiment to study growth and physiological traits, measured from bulk needles, using a randomized block design with two levels of browsing severity and seedlings originating from 19 populations across Switzerland. Genetic factors explained most variation in growth (on average, 51.5%) and physiological traits (10.2%) under control conditions, while heavy browsing considerably reduced the genetic effects on growth (to 30%), but doubled those on physiological traits related to carbon storage. While browsing reduced seedling height, it also lowered seedling water-use efficiency (decreased $\delta ^{13}$C) and increased their $\delta ^{15}$N. Different populations reacted differently to browsing stress, and for seedling height, starch concentration and $\delta ^{15}$N, population differences appeared to be the result of natural selection. First, we found that populations originating from the warmest regions recovered the fastest from browsing stress, and they did so by mobilizing starch from their needles, which suggests a genetic underpinning for a growth-storage trade-off across populations. Second, we found that seedlings originating from mountain populations growing on steep slopes had a higher $\delta ^{15}$N in the common garden than those originating from flat areas, indicating that they have been selected to grow on N-poor, potentially drained, soils. This finding was corroborated by the fact that nitrogen concentration in adult needles was lower on steep slopes than on flat ground, strongly indicating that steep slopes are the most N-poor environments. These results suggest that adaptation to climate and soil nitrogen availability, as well as ungulate browsing pressure, co-determine the regeneration and range limit of silver fir.
银冷杉（Abies alba (Mill.)）具有在欧洲高山森林中缓解气候变化的巨大潜力；然而，其天然更新受到食草动物啃食的严重限制。在这里，我们通过使用随机区组设计的两水平啃食严重程度和来自瑞士 19 个种群的幼苗，在一个普通花园实验中模拟啃食，研究了使用整株针叶测量的生长和生理特征。在对照条件下，遗传因素解释了生长（平均 51.5%）和生理特征（10.2%）的大部分变异，而重度啃食大大降低了生长的遗传效应（至 30%），但与碳储存相关的生理特征的遗传效应增加了一倍。虽然啃食降低了幼苗的高度，但也降低了幼苗的水分利用效率（降低了$\delta ^{13}$C）并增加了它们的$\delta ^{15}$N。不同种群对啃食压力的反应不同，而对于幼苗的高度、淀粉浓度和$\delta ^{15}$N，种群差异似乎是自然选择的结果。首先，我们发现来自最温暖地区的种群从啃食压力中恢复得最快，它们通过从针叶中动员淀粉来实现这一点，这表明在不同种群中存在生长-储存权衡的遗传基础。其次，我们发现来自生长在陡峭山坡上的山地种群的幼苗在普通花园中的$\delta ^{15}$N 比来自平地的幼苗高，这表明它们已经被选择在氮贫、潜在排水良好的土壤上生长。这一发现得到了一个事实的证实，即在陡峭的山坡上，成年针叶中的氮浓度比在平坦的地面上低，这强烈表明陡峭的山坡是最缺氮的环境。这些结果表明，对气候和土壤氮供应的适应，以及食草动物的啃食压力，共同决定了银冷杉的更新和分布范围的限制。
