Pramsohler Manuel, Lichtenberger Edith, Neuner Gilbert
Laimburg Research Centre, Laimburg 6, Pfatten/Vadena, 39040 Auer/Ora, Italy.
Unit of Functional Plant Biology, Department of Botany, University of Innsbruck, Sternwartestraße 15, 6020 Innsbruck, Austria.
Plants (Basel). 2022 Aug 6;11(15):2058. doi: 10.3390/plants11152058.
pH of xylem sap (pHx) was determined in three trees (Malus domestica (apple tree), Picea abies and Pinus cembra) in response to seasonal changes. Conifer trees from lowland (600 m) were compared to trees growing at the alpine timberline (1950 m a.s.l.). Xylem sap was extracted with a Scholander pressure bomb and pHx was measured with a pH microsensor. In all species, pHx changed markedly with season. In spring, pHx was acidic; during winter, the pHx was more alkaline. In apple trees, the pHx did not show a significant correlation with temperature but was rather affected by developmental stage. During flushing in spring, xylem sap acidification took place concomitant to the developmental stage “tight cluster”, when foliar development enables a significant transpiration and a consequent movement of water in the xylem. The xylem sap of the two studied conifers showed a significantly larger seasonal alkalinisation (+2.1) than found in apple trees (+1.2) and was significantly more pronounced at the timberline. Xylem sap acidification took place before bud break. pHx had a significant negative correlation with soil temperatures and corresponded to already reported pHx of angiosperms. Overall, pHx appears to be a sensitive stress marker and indicator of activity status in tree xylem.
为了研究季节性变化对木质部汁液pH值（pHx）的影响，我们测定了三种树木（苹果（Malus domestica）、欧洲云杉（Picea abies）和瑞士石松（Pinus cembra））的木质部汁液pH值。我们将低地（600米）的针叶树与生长在高山林线（海拔1950米）的树木进行了比较。使用Scholander压力室提取木质部汁液，并用pH微传感器测量pHx。在所有物种中，pHx都随季节发生显著变化。春季时，pHx呈酸性；冬季时，pHx则更偏碱性。在苹果树上，pHx与温度没有显著相关性，而是受发育阶段的影响更大。在春季新梢生长期间，木质部汁液酸化与“紧密叶簇”发育阶段同步发生，此时叶片发育使得蒸腾作用显著增强，进而导致木质部中的水分流动。研究的两种针叶树的木质部汁液季节性碱化幅度（+2.1）明显大于苹果树（+1.2），且在林线处更为显著。木质部汁液酸化发生在芽萌动之前。pHx与土壤温度呈显著负相关，且与已报道的被子植物的pHx相符。总体而言，pHx似乎是树木木质部中一个敏感的胁迫指标和活性状态指标。
