Top Sara M, Preston Caroline M, Dukes Jeffrey S, Tharayil Nishanth
Plant and Environmental Sciences, Clemson UniversityClemson, SC, USA.
Natural Resources Canada, Pacific Forestry CentreVictoria, BC, Canada.
Front Plant Sci. 2017 May 16;8:423. doi: 10.3389/fpls.2017.00423. eCollection 2017.
Environmental stresses not only influence production of plant metabolites but could also modify their resorption during leaf senescence. The production-resorption dynamics of polyphenolic tannins, a class of defense compound whose ecological role extends beyond tissue senescence, could amplify the influence of climate on ecosystem processes. We studied the quantity, chemical composition, and tissue-association of tannins in green and freshly-senesced leaves of exposed to different temperature ( and ) and precipitation treatments () at the Boston-Area Climate Experiment (BACE) in Massachusetts, USA. Climate influenced not only the quantity of tannins, but also their molecular composition and cell-wall associations. Irrespective of climatic treatments, tannin composition in was dominated by condensed tannins (CTs, proanthocyanidins). When exposed to and conditions, produced higher quantities of tannins that were less polymerized. In contrast, under favorable conditions (), tannins were produced in lower quantities, but the CTs were more polymerized. Further, even as the overall tissue tannin content declined, the content of hydrolysable tannins (HTs) increased under treatments. The molecular composition of tannins influenced their content in senesced litter. Compared to the green leaves, the content of HTs decreased in senesced leaves across treatments, whereas the CT content was similar between green and senesced leaves in treatments that produced more polymerized tannins. The content of total tannins in senesced leaves was higher in treatments under both and precipitation treatments. Our results suggest that, though climate directly influenced the production of tannins in green tissues (and similar patterns were observed in the senesced tissue), the influence of climate on tannin content of senesced tissue was partly mediated by the effect on the chemical composition of tannins. These different climatic impacts on leaves over the course of a growing season may alter forest dynamics, not only in decomposition and nutrient cycling dynamics, but also in herbivory dynamics.
环境胁迫不仅会影响植物代谢物的产生，还可能改变其在叶片衰老过程中的再吸收。多酚单宁是一类防御化合物，其生态作用不仅限于组织衰老，其产生 - 再吸收动态可能会放大气候对生态系统过程的影响。我们在美国马萨诸塞州的波士顿地区气候实验（BACE）中，研究了暴露于不同温度（ 和 ）和降水处理（ ）下的 绿色和刚衰老叶片中单宁的含量、化学组成及组织关联。气候不仅影响单宁的含量，还影响其分子组成和细胞壁关联。无论气候处理如何， 中的单宁组成均以缩合单宁（CTs，原花青素）为主。当暴露于 和 条件下时， 产生的单宁量更高，但聚合程度较低。相反，在有利条件下（ ），单宁产量较低，但CTs聚合程度更高。此外，即使总体组织单宁含量下降，在 处理下可水解单宁（HTs）的含量仍会增加。单宁的分子组成影响其在衰老凋落物中的含量。与绿叶相比，各处理下衰老叶片中HTs的含量均下降，而在产生更多聚合单宁的 处理中，绿叶和衰老叶片中的CT含量相似。在 和 降水处理下， 处理中衰老叶片的总单宁含量更高。我们的研究结果表明，尽管气候直接影响绿色组织中单宁的产生（衰老组织中也观察到类似模式），但气候对衰老组织中单宁含量的影响部分是由对单宁化学组成的影响介导的。在生长季节中，这些不同的气候对叶片的影响可能会改变森林动态，不仅在分解和养分循环动态方面，而且在食草动物动态方面。
