Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon, 97331, USA.
Arts and Sciences Division, University of Maine at Fort Kent, Fort Kent, Maine, 04743, USA.
Am J Bot. 2018 Feb;105(2):266-274. doi: 10.1002/ajb2.1022. Epub 2018 Feb 26.
Changing climates are expected to affect the abundance and distribution of global vegetation, especially plants and lichens with an epiphytic lifestyle and direct exposure to atmospheric variation. The study of epiphytes could improve understanding of biological responses to climatic changes, but only if the conditions that elicit physiological performance changes are clearly defined.
We evaluated individual growth performance of the epiphytic lichen Evernia mesomorpha, an iconic boreal forest indicator species, in the first year of a decade-long experiment featuring whole-ecosystem warming and drying. Field experimental enclosures were located near the southern edge of the species' range.
Mean annual biomass growth of Evernia significantly declined 6 percentage points for every +1°C of experimental warming after accounting for interactions with atmospheric drying. Mean annual biomass growth was 14% in ambient treatments, 2% in unheated control treatments, and -9% to -19% (decreases) in energy-added treatments ranging from +2.25 to +9.00°C above ambient temperatures. Warming-induced biomass losses among persistent individuals were suggestive evidence of an extinction debt that could precede further local mortality events.
Changing patterns of warming and drying would decrease or reverse Evernia growth at its southern range margins, with potential consequences for the maintenance of local and regional populations. Negative carbon balances among persisting individuals could physiologically commit these epiphytes to local extinction. Our findings illuminate the processes underlying local extinctions of epiphytes and suggest broader consequences for range shrinkage if dispersal and recruitment rates cannot keep pace.
预计气候变化将影响全球植被的丰度和分布，特别是具有附生生活方式和直接暴露于大气变化的植物和地衣。对附生植物的研究可以提高对气候变化的生物响应的理解，但前提是必须明确引起生理性能变化的条件。
我们在一个长达十年的实验的第一年评估了附生地衣 Evernia mesomorpha 的个体生长表现，该实验具有整个生态系统的增温和干燥。野外实验围封区位于该物种分布范围的南部边缘附近。
在考虑到与大气干燥相互作用的情况下，Evernia 的平均年生物量生长在实验增温每增加 1°C 的情况下显著下降了 6 个百分点。在环境处理中，平均年生物量生长为 14%，在未加热对照处理中为 2%，在能量添加处理中为-9%至-19%（减少），温度比环境温度高出 2.25 至 9.00°C。持久个体中变暖引起的生物量损失是灭绝债务的迹象，这可能会导致进一步的局部死亡事件。
变暖和干燥模式的变化将减少或逆转 Evernia 在其南部分布范围的生长，这可能对维持当地和区域种群产生潜在影响。在持续存在的个体中出现负碳平衡可能会在生理上使这些附生植物面临局部灭绝的风险。我们的研究结果阐明了附生植物局部灭绝的过程，并表明如果扩散和招募率跟不上，对范围缩小会产生更广泛的影响。
