ForestGEO, Smithsonian Tropical Research Institute, Av. Roosevelt 401, Balboa, Ancón, Panama.
Department of Botany, University of Wyoming, Laramie, WY, 82071, USA.
New Phytol. 2018 Aug;219(3):885-899. doi: 10.1111/nph.15071. Epub 2018 Mar 5.
Tropical forests are increasingly being subjected to hotter, drier conditions as a result of global climate change. The effects of drought on forests along successional gradients remain poorly understood. We took advantage of the 2015-2016 El Niño event to test for differences in drought response along a successional gradient by measuring the sap flow in 76 trees, representing 42 different species, in 8-, 25- and 80-yr-old secondary forests in the 15-km 'Agua Salud Project' study area, located in central Panama. Average sap velocities and sapwood-specific hydraulic conductivities were highest in the youngest forest. During the dry season drought, sap velocities increased significantly in the 80-yr-old forest as a result of higher evaporative demand, but not in younger forests. The main drivers of transpiration shifted from radiation to vapor pressure deficit with progressing forest succession. Soil volumetric water content was a limiting factor only in the youngest forest during the dry season, probably as a result of less root exploration in the soil. Trees in early-successional forests displayed stronger signs of regulatory responses to the 2015-2016 El Niño drought, and the limiting physiological processes for transpiration shifted from operating at the plant-soil interface to the plant-atmosphere interface with progressing forest succession.
由于全球气候变化，热带森林正面临越来越炎热和干燥的环境。干旱对演替梯度上森林的影响仍知之甚少。我们利用 2015-2016 年厄尔尼诺事件，通过测量位于巴拿马中部 15 公里的“Agua Salud 项目”研究区中 8 年、25 年和 80 年生次生林内 76 株、代表 42 个不同树种的树木的液流，来检验演替梯度上干旱响应的差异。平均液流速度和边材比水力传导度在最年轻的森林中最高。在旱季干旱期间，由于蒸发需求较高，80 年生森林中的液流速度显著增加，但在较年轻的森林中则没有。随着森林演替的进行，蒸腾的主要驱动因素从辐射转向水汽压亏缺。土壤体积含水量仅在旱季成为限制因素，这可能是由于年轻森林中根系对土壤的探索较少。早期演替森林中的树木对 2015-2016 年厄尔尼诺干旱表现出更强的调节反应迹象，蒸腾的限制生理过程从在植物-土壤界面上运作转变为随着森林演替在植物-大气界面上运作。
