Laboratory of Plant Ecology, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium.
Medical Imaging and Signal Processing - Innovative Flemish In-vivo Imaging Technology, Department of Electronics and Information Systems, Faculty of Engineering and Architecture, Ghent University, Ghent, Belgium.
Tree Physiol. 2019 Feb 1;39(2):211-221. doi: 10.1093/treephys/tpy131.
Phloem transport is of great importance in trees to distribute assimilated carbon across the entire tree. Nevertheless, knowledge of phloem is incomplete, because of the complexity of measuring its transport and characteristics. Only few studies have addressed how phloem transport might alter under climatic changes, with most data originating from theoretical studies. We measured phloem characteristics in leaves of young Populus tremula L. trees grown during 5 months under ambient (TA, 404 ppm ± 5) and elevated (TE, 659 ppm ± 3) atmospheric CO2 concentration ([CO2]) using a combination of positron emission tomography (PET) and compartmental modelling. Short-term phloem dynamics were measured in vivo and non-invasively using the short-lived isotope of carbon, 11C (half-life 20.4 min). Trees were scanned in well-watered and dry conditions to assess changes in phloem characteristics induced by drought. Reliability of the PET-derived results was verified with reported observations in the literature. Phloem speed was highest in well-watered TE trees and strongly reduced by 81% under drought, whereas phloem speed reduced by 61% in TA trees at the same level of drought. These findings led us to speculate that phloem transport in TE trees might be more vulnerable to drought. We discuss how a higher phloem vulnerability to drought in a changing climate could impact tree hydraulic functioning. Taken together our results suggest that trees grown for 5 months under elevated [CO2] seem to be less well-acclimated to face projected hotter droughts in a changing climate.
韧皮部运输对于树木在整个树体中分配同化碳具有重要意义。然而，由于测量其运输和特性的复杂性，人们对韧皮部的了解并不完全。只有少数研究探讨了在气候变化下韧皮部运输可能会如何改变，而且大多数数据都来自理论研究。我们使用正电子发射断层扫描（PET）和分区建模相结合的方法，在 5 个月的时间里，测量了在环境（TA，404 ppm±5）和升高（TE，659 ppm±3）大气 CO2浓度（[CO2]）下生长的年轻欧洲山杨（Populus tremula L.）叶片的韧皮部特性。使用短寿命碳同位素 11C（半衰期 20.4 分钟），在活体和非侵入性条件下测量了短期韧皮部动态。在充分供水和干旱条件下对树木进行扫描，以评估干旱引起的韧皮部特性变化。使用文献中报道的观察结果验证了 PET 衍生结果的可靠性。在充分供水的 TE 树木中，韧皮部速度最高，干旱条件下降低了 81%，而在相同干旱水平下 TA 树木中的韧皮部速度降低了 61%。这些发现使我们推测，在不断变化的气候中，TE 树木中的韧皮部运输可能更容易受到干旱的影响。我们讨论了在不断变化的气候中，韧皮部对干旱的脆弱性增加如何影响树木的水力功能。总之，我们的研究结果表明，在升高的[CO2]下生长 5 个月的树木似乎对面临气候变化下预计更炎热干旱的适应能力较差。
