Moler E R V, Page G, Flores-Rentería L, Garms C G, Hull J B, Cooper H F, Swenson J, Perks S, Waring K M, Whipple A V
Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ, 86011, USA.
College of Natural Resources, Center for Forest Nursery and Seedling Research, University of Idaho, Moscow, ID, 83843, USA.
Plant Methods. 2021 Jan 6;17(1):1. doi: 10.1186/s13007-020-00700-7.
Forest dieback driven by rapid climate warming threatens ecosystems worldwide. The health of forested ecosystems depends on how tree species respond to warming during all life history stages. While it is known that seed development is temperature-sensitive, little is known about possible effects of climate warming on seed development and subsequent seedling performance. Exposure of seeds to high air temperatures may influence subsequent seedling performance negatively, though conversely, warming during seed development may aid acclimation of seedlings to subsequent thermal stress. Technical challenges associated with in-situ warming of developing tree seeds limit understanding of how tree species may respond to seed development in a warmer climate.
We developed and validated a simple method for passively warming seeds as they develop in tree canopies to enable controlled study of climate warming on seedling performance. We quantified thermal effects of the cone-warming method across individual pine trees and stands by measuring the air temperature surrounding seed cones using thermal loggers and the temperature of seed cone tissue using thermocouples. We then investigated seedling phenotypes in relation to the warming method through a common garden study. We assessed seedling morphology, physiology, and mycorrhizal nodulation in response to experimental cone-warming in 20 seed-source-tree canopies on the San Francisco Peaks in northern Arizona, USA. The warming method increased air temperature surrounding developing seed cones by 2.1 °C, a plausible increase in mean air temperature by 2050 under current climate projections. Notable effect sizes of cone-warming were detected for seedling root length, shoot length, and diameter at root collar using Cohen's Local f. Root length was affected most by cone-warming, but effect sizes of cone-warming on root length and diameter at root collar became negligible after the first year of growth. Cone-warming had small but significant effects on mycorrhizal fungal richness and seedling multispectral near-infrared indices indicative of plant health.
The method was shown to reliably elevate the temperature surrounding seed cones and thereby facilitate experimental in-situ climate warming research on forest trees. The method was furthermore shown to influence plant traits that may affect seedling performance under climate warming.
快速的气候变暖导致的森林衰退威胁着全球生态系统。森林生态系统的健康状况取决于树种在其整个生命历史阶段对变暖的反应方式。虽然已知种子发育对温度敏感，但对于气候变暖对种子发育及后续幼苗表现可能产生的影响却知之甚少。将种子暴露于高气温下可能会对后续幼苗表现产生负面影响，不过相反的是，种子发育期间的变暖可能有助于幼苗适应随后的热胁迫。与正在发育的树木种子原位变暖相关的技术挑战限制了我们对树种在气候变暖情况下如何应对种子发育的理解。
我们开发并验证了一种简单的方法，可在种子在树冠中发育时对其进行被动加热，从而能够对气候变暖对幼苗表现的影响进行可控研究。我们通过使用热记录仪测量球果周围的气温，并使用热电偶测量球果组织的温度，对单个松树和林分中球果加热方法的热效应进行了量化。然后，我们通过一项共同园圃研究，调查了与加热方法相关的幼苗表型。我们在美国亚利桑那州北部旧金山峰的20个种子源树的树冠中，评估了实验性球果加热对幼苗形态、生理和菌根结瘤的影响。这种加热方法使正在发育的球果周围的气温升高了2.1°C，这在当前气候预测下到2050年平均气温可能出现的升幅范围内。使用科恩局部f检验，在幼苗根长、苗高和根茎直径方面检测到了球果加热的显著效应量。根长受球果加热的影响最大，但在生长的第一年之后，球果加热对根长和根茎直径的效应量变得可以忽略不计。球果加热对菌根真菌丰富度和指示植物健康状况的幼苗多光谱近红外指数有微小但显著的影响。
该方法被证明能够可靠地提高球果周围的温度，从而便于对森林树木进行实验性原位气候变暖研究。此外，该方法还被证明会影响可能在气候变暖情况下影响幼苗表现的植物性状。
