Systems Ecology, Department of Ecological Science, VU University De Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands ; State Museum of Natural History Karlsruhe Erbprinzenstr. 13, 76133, Karlsruhe, Germany.
Systems Ecology, Department of Ecological Science, VU University De Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands.
Ecol Evol. 2014 Jun;4(11):2217-27. doi: 10.1002/ece3.1079. Epub 2014 May 7.
Nutrient resorption from senescing photosynthetic organs is a powerful mechanism for conserving nitrogen (N) and phosphorus (P) in infertile environments. Evolution has resulted in enhanced differentiation of conducting tissues to facilitate transport of photosynthate to other plant parts, ultimately leading to phloem. Such tissues may also serve to translocate N and P to other plant parts upon their senescence. Therefore, we hypothesize that nutrient resorption efficiency (RE, % of nutrient pool exported) should correspond with the degree of specialization of these conducting tissues across the autotrophic branches of the Tree of Life. To test this hypothesis, we had to compare members of different plant clades and lichens within a climatic region, to minimize confounding effects of climatic drivers on nutrient resorption. Thus, we compared RE among wide-ranging basal clades from the principally N-limited subarctic region, employing a novel method to correct for mass loss during senescence. Even with the limited numbers of species available for certain clades in this region, we found some consistent patterns. Mosses, lichens, and lycophytes generally showed low REN (<20%), liverworts and conifers intermediate (40%) and monilophytes, eudicots, and monocots high (>70%). REP appeared higher in eudicots and liverworts than in mosses. Within mosses, taxa with more efficient conductance also showed higher REN. The differences in REN among clades broadly matched the degree of specialization of conducting tissues. This novel mapping of a physiological process onto the Tree of Life broadly supports the idea that the evolution of conducting tissues toward specialized phloem has aided land plants to optimize their internal nitrogen recycling. The generality of evolutionary lines in conducting tissues and nutrient resorption efficiency needs to be tested across different floras in different climatic regions with different levels of N versus P availability.
衰老光合器官中养分的再吸收是在贫瘠环境中保存氮（N）和磷（P）的强大机制。进化导致了传导组织的分化增强，以促进光合产物向其他植物部位的运输，最终导致韧皮部。这些组织也可能在衰老时将 N 和 P 转移到其他植物部位。因此，我们假设养分再吸收效率（RE，输出养分库的%）应该与这些传导组织在生命之树自养分支中的特化程度相对应。为了验证这一假设，我们必须在同一气候区域内比较不同植物类群和地衣的成员，以最大限度地减少气候驱动因素对养分再吸收的影响。因此，我们比较了主要受 N 限制的亚北极地区广泛分布的基础类群之间的 RE，采用了一种新的方法来纠正衰老过程中的质量损失。即使在该地区某些类群的物种数量有限的情况下，我们也发现了一些一致的模式。苔藓、地衣和石松通常表现出低的 REN（<20%），而蕨类植物、裸子植物居中（40%），而 monilophytes、真双子叶植物和单子叶植物则较高（>70%）。REP 在真双子叶植物和蕨类植物中比在苔藓中更高。在苔藓中，具有更高传导效率的类群也表现出更高的 REN。不同类群之间的 REN 差异与传导组织的特化程度大致相符。这种将生理过程映射到生命之树上的新方法广泛支持这样一种观点，即传导组织向专门的韧皮部的进化帮助了陆地植物优化其内部氮循环。需要在不同气候区域的不同植物群中，用不同的 N 与 P 供应水平来测试进化线在传导组织和养分再吸收效率方面的普遍性。
