Guangdong Provincial Key Laboratory of Applied Botany & Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, 723 Xingke Road, Guangzhou 510650, China.
Center for Ecological Research, College of Forestry, Northeast Forestry University, 26 Hexing Road, Harbin 150040, China.
Tree Physiol. 2024 Nov 5;44(11). doi: 10.1093/treephys/tpae132.
Freeze-thaw cycles (FTCs) are the major seasonal environment stress in the temperate and boreal forests, inducing hydraulic dysfunction and limiting tree growth and distribution. There are two types of FTCs in the field: FTCs with increasing temperature from winter to spring (spring FTCs); and FTCs with decreasing temperature from autumn to winter (autumn FTCs). While previous studies have evaluated the hydraulic function during the growing season, its seasonal changes and how it adapts to different types of FTCs remain unverified. To fill this knowledge gap, the eight tree species from three wood types (ring- and diffuse-porous, tracheid) were selected in a temperate forest undergoing seasonal FTCs. We measured the branch hydraulic traits in spring, summer, autumn, and early, middle and late winter. Ring-porous trees always showed low native hydraulic conductance (Kbranch), and high percentage loss of maximum Kbranch (PLCB) and water potential that loss of 50% maximum Kbranch (P50B) in non-growing seasons (except summer). Kbranch decreased, and PLCB and P50B increased in diffuse-porous trees after several spring FTCs. In tracheid trees, Kbranch decreased after spring FTCs while the P50B did not change. All sampled trees gradually recovered their hydraulic functions from spring to summer. Kbranch, PLCB and P50B of diffuse-porous and tracheid trees were relatively constant after autumn FTCs, indicating almost no effect of autumn FTCs on hydraulic functions. These results suggested that hydraulic functions of temperate trees showed significant seasonal changes, and spring FTCs induced more hydraulic damage (except ring-porous trees) than autumn FTCs, which should be determined by the number of FTCs and trees' vitality before FTCs. These findings advance our understanding of seasonal changes in hydraulic functions and how they cope with different types of FTC in temperate forests.
冻融循环（FTCs）是温带和北方森林主要的季节性环境胁迫因素，会导致水力功能障碍，并限制树木的生长和分布。野外存在两种类型的 FTCs：从冬季到春季升温的 FTCs（春季 FTCs）；以及从秋季到冬季降温的 FTCs（秋季 FTCs）。虽然先前的研究已经评估了生长季的水力功能，但它的季节性变化以及如何适应不同类型的 FTCs 仍未得到验证。为了填补这一知识空白，选择了经历季节性 FTCs 的温带森林中的三种木材类型（环孔材、散孔材和导管材）的 8 个树种。我们在春季、夏季、秋季以及初冬、仲冬和隆冬测量了树枝的水力特性。环孔材树木在非生长季始终表现出较低的原生水力传导度（Kbranch）、较高的最大水力传导度损失百分比（PLCB）和水势，除夏季外，最大水力传导度损失 50%时的水势（P50B）。在经历了几个春季 FTCs 后，散孔材树木的 Kbranch 降低，而 PLCB 和 P50B 增加。在导管材树木中，Kbranch 在春季 FTCs 后降低，而 P50B 不变。所有采样树木的水力功能从春季到夏季逐渐恢复。散孔材和导管材树木的 Kbranch、PLCB 和 P50B 在秋季 FTCs 后相对稳定，表明秋季 FTCs 对水力功能几乎没有影响。这些结果表明，温带树木的水力功能表现出显著的季节性变化，而春季 FTCs（除环孔材树木外）比秋季 FTCs 造成更大的水力损伤，这应取决于 FTCs 的数量和 FTCs 前树木的活力。这些发现提高了我们对水力功能季节性变化以及树木如何应对温带森林中不同类型 FTCs 的理解。
