巴西橡胶树排胶机制研究进展

橡胶树是世界上商业用天然橡胶最主要的来源,排胶是天然橡胶生产的最后关键环节,为了安全高效的获取胶乳产量,橡胶树排胶机制的研究一直受到人们的重视。橡胶树中的乳管是天然橡胶合成和储存的组织,人们通过割胶收集从乳管中流出的胶乳用作提炼天然橡胶。胶乳的排出速度及排胶持续时间是决定天然橡胶产量的重要因素,是排胶动力和排胶阻力共同作用的结果。笔者对与排胶相关的乳管细胞学基础、排胶主要初动力的乳管膨压、排胶继动力的乳管胶乳水分稀释效应以及乳管排胶阻力的形成及其调控机制等研究进行了归纳,主要分析了乳管伤口堵塞物的形成和影响排胶阻力的多种因素,指出乳管堵塞在胶乳的停排中起重要作用。针对目前排胶机制的研究进展缓慢这一现状,我们提出有必要从以下几点展开深入研究：（1）乳管膨压形成相关的树皮木质素合成和调控;（2）水分运输相关的水通道蛋白基因表达和活性分析;（3）停排相关的乳管伤口末端堵塞物的形成和调节。这些研究将为全面解析橡胶树排胶机制奠定基础,也可为分子辅助育种-选育排胶通畅的种质提供依据。     

Annual shoot length of temperate broadleaf species responses to drought

In recent years, Central European forests and trees have been severely suffered from drought events in the growing season. To examine the tree growth response to drought stress, measurements of annual shoot lengths (ASL) of various tree species with distinct ages and habitats were taken in southeast Germany. The index of relative ASL increase (RAI), which is a standardized ASL increase, was calculated to indicate the growth rate of various tree species between the non-drought (2015–2017) and the drought period (2018–2020). The results showed the ASLs of most early-young trees (< 10 years) significantly showed a decreasing tendency in the drought period, whereas the middle-young (11–15 years) and late-young trees (> 16 years) presented a relatively stable trend. The ring-porous species with anisohydric behavior were likely to have higher RAIs associated with higher drought tolerance than diffuse-porous species with isohydric behavior. However, tree growth rate did not correlate with drought tolerance (resistance) of tree species indicated by leaf turgor loss point (Ψ_tlp, MPa). Therefore, this study suggested parameters, such as growth rate, age phases, and microhabitats, should be considered to predict tree species’ drought tolerance other than Ψ_tlp. Finally, we emphasized tree shoot growth responses to drought were affected by multiple internal and external factors, and strongly depended on species- and site-specific characteristics, such as age phases, xylem structure, hydraulic strategy, microhabitat, grafting effect, and competition. ASL measurement can be recommended to be an easy, fast, and effective method to detect tree growth rate and response to environmental stress.