Paljakka Teemu, Rissanen Kaisa, Vanhatalo Anni, Salmon Yann, Jyske Tuula, Prisle Nønne L, Linnakoski Riikka, Lin Jack J, Laakso Tapio, Kasanen Risto, Bäck Jaana, Hölttä Teemu
Faculty of Agriculture and Forestry, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Helsinki, Finland.
Faculty of Science, Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, Helsinki, Finland.
Front Plant Sci. 2020 Jul 16;11:1090. doi: 10.3389/fpls.2020.01090. eCollection 2020.
Increased abiotic stress along with increasing temperatures, dry periods and forest disturbances may favor biotic stressors such as simultaneous invasion of bark beetle and ophiostomatoid fungi. It is not fully understood how tree desiccation is associated with colonization of sapwood by fungi. A decrease in xylem sap surface tension (σ) as a result of infection has been hypothesized to cause xylem embolism by lowering the threshold for air-seeding at the pits between conduits and disruptions in tree water transport. However, this hypothesis has not yet been tested. We investigated tree water relations by measuring the stem xylem hydraulic conductivity (K), σ, stem relative water content (RWC), and water potential (Ψ), and canopy conductance (g), as well as the compound composition in xylem sap in Norway spruce () saplings. We conducted our measurements at the later stage of infection when visible symptoms had occurred in xylem. Saplings of two clones (44 trees altogether) were allocated to treatments of inoculated, wounded control and intact control trees in a greenhouse. The saplings were destructively sampled every second week during summer 2016. σ, K and RWC decreased following the inoculation, which may indicate that decreased σ resulted in increased embolism. g did not differ between treatments indicating that stomata responded to Ψ rather than to embolism formation. Concentrations of quinic acid, myo-inositol, sucrose and alkylphenol increased in the xylem sap of inoculated trees. Myo-inositol concentrations also correlated negatively with σ and K. Our study is a preliminary investigation of the role of σ in infected trees based on previous hypotheses. The results suggest that infection can lead to a simultaneous decrease in xylem sap surface tension and a decline in tree hydraulic conductivity, thus hampering tree water transport.
随着气温升高、干旱期延长以及森林干扰增加，非生物胁迫加剧，这可能有利于生物胁迫因子的滋生，比如小蠹虫和长喙壳菌同时入侵。目前尚不完全清楚树木干燥与边材被真菌定殖之间的关联。有假说认为，感染导致木质部树液表面张力（σ）降低，会通过降低导管间纹孔处的气穴形成阈值以及破坏树木水分运输，从而引发木质部栓塞。然而，这一假说尚未得到验证。我们通过测量挪威云杉（）树苗的树干木质部水力传导率（K）、σ、树干相对含水量（RWC）、水势（Ψ）、冠层导度（g）以及木质部树液中的化合物成分，来研究树木的水分关系。我们在感染后期出现木质部可见症状时进行测量。将两个克隆的树苗（共44棵）分配到温室中的接种处理、创伤对照处理和完整对照处理组。在2016年夏季，每隔一周对树苗进行一次破坏性采样。接种后，σ、K和RWC均下降，这可能表明σ降低导致栓塞增加。各处理组之间的g没有差异，这表明气孔对Ψ作出反应，而非对栓塞形成作出反应。接种树木的木质部树液中奎尼酸、肌醇、蔗糖和烷基酚的浓度增加。肌醇浓度也与σ和K呈负相关。我们的研究是基于先前的假说对σ在感染树木中的作用进行的初步调查。结果表明，感染会导致木质部树液表面张力同时降低以及树木水力传导率下降，从而阻碍树木水分运输。
