Institute of Ecology and Earth Sciences, University of Tartu, Liivi 2, 50409, Tartu, Estonia.
Institute of Veterinary Medicine and Animal Sciences, Estonian University of Life Sciences, Kreutzwaldi 62, 51006, Tartu, Estonia.
Oecologia. 2023 Jun;202(2):193-210. doi: 10.1007/s00442-023-05388-9. Epub 2023 May 29.
Plant secondary metabolites (PSMs) defend plants against abiotic stresses, including those caused by climate change and against biotic stresses, such as herbivory and competition. There is a trade-off between allocating available carbon to growth and defence in stressful environments. However, our knowledge about trade-off is limited, especially when abiotic and biotic stresses co-occur. We aimed to understand the combined effect of increasing precipitation and humidity, the tree's competitive status, and canopy position on leaf secondary metabolites (LSMs) and fine root secondary metabolites (RSMs) in Betula pendula. We sampled 8-year-old B. pendula trees growing in the free air humidity manipulation (FAHM) experimental site, where treatments included elevated relative air humidity and elevated soil moisture. A high-performance liquid chromatography-quadrupole-time of flight mass spectrometer (HPLC-qTOF-MS) was used to analyse secondary metabolites. Our results showed accumulation of LSM depends on the canopy position and competitive status. Flavonoids (FLA), dihydroxybenzoic acids (HBA), jasmonates (JA) and terpene glucosides (TG) were higher in the upper canopy, and FLA, monoaryl compounds (MAR) and sesquiterpenoids (ST) were higher in dominant trees. The FAHM treatments had a more distinct effect on RSM than on LSM. The RSMs were lower in elevated air humidity and soil moisture conditions than in control conditions. The RSM content depended on the competitive status and was higher in suppressed trees. Our study suggests that young B. pendula will allocate similar amounts of carbon to constitutive chemical leaf defence, but a lower amount to root defence (per fine root biomass) under higher humidity.
植物次生代谢物（PSM）可以帮助植物抵御非生物胁迫，包括气候变化引起的胁迫以及生物胁迫，如草食和竞争。在有压力的环境中，植物在将可用碳分配给生长和防御之间存在权衡。然而，我们对这种权衡的了解是有限的，尤其是当非生物和生物胁迫同时发生时。我们的目的是了解增加降水和湿度、树木的竞争地位以及冠层位置对桦树叶片次生代谢物（LSM）和细根次生代谢物（RSM）的综合影响。我们对在自由空气湿度操纵（FAHM）实验区生长的 8 年生桦树（Betula pendula）进行了采样，该实验区的处理包括增加相对空气湿度和增加土壤水分。我们使用高效液相色谱-四极杆飞行时间质谱（HPLC-qTOF-MS）来分析次生代谢物。结果表明，LSM 的积累取决于冠层位置和竞争地位。类黄酮（FLA）、二羟基苯甲酸（HBA）、茉莉酸（JA）和三萜糖苷（TG）在上层冠层中含量较高，而 FLA、单芳基化合物（MAR）和倍半萜烯（ST）在优势树上含量较高。FAHM 处理对 RSM 的影响比对 LSM 的影响更为明显。在空气湿度和土壤水分升高的条件下，RSM 含量低于对照条件。RSM 含量取决于竞争地位，在被抑制的树木中含量较高。我们的研究表明，年轻的桦树在高湿度条件下，将相似数量的碳分配给组成性的叶片化学防御，但分配给根防御（每根细根生物量）的碳数量较低。
