Evolutionary tradeoffs can select against nitrogen fixation and thereby maintain nitrogen limitation
Evolutionary tradeoffs can select against nitrogen fixation and thereby maintain nitrogen limitation
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DOI：
10.1073/pnas.0711411105
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发表时间：
2008-02-05
影响因子：
11.1
通讯作者：
Hedin, Lars O.
中科院分区：
文献类型：
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作者：
Menge, Duncan N. L.;Levin, Simon A.;Hedin, Lars O.
共生固氮树在古老的温带和北方生态系统中是不存在的，尽管其中许多是氮限制的。为了探索在氮有限的古老生态系统中选择反对氮固定的机制，我们开发了一个简单的基于资源的氮固定进化模型。当不存在固氮成本时，将选择增加固氮量，直到N不再限制生产。然而，氮固定和植物死亡率或营业额之间的权衡，植物吸收土壤有效氮，或氮利用效率（NUE）可以选择对氮固定在氮有限的生态系统，从而可以无限期地保持氮限制（假设有植物无效氮的损失）。三个关键性状影响阈值，决定了这些权衡必须有多大，以选择对N固定。一个低的NUE，高死亡率（或营业额）率和低损失的植物不可用的N都增加的可能性，N固定将被选择反对，并对这些参数发表的数据的初步研究表明，这些机制，特别是与NUE的权衡，在某些系统中是相当可行的。虽然这些结果是有希望的，更好地表征这些参数在多个生态系统是必要的，以确定这些机制是否解释了缺乏共生固氮，从而维持氮限制，在古老的森林。
Symbiotic nitrogen (N) fixing trees are absent from old-growth temperate and boreal ecosystems, even though many of these are N-limited. To explore mechanisms that could select against N fixation in N-limited, old-growth ecosystems, we developed a simple resource-based evolutionary model of N fixation. When there are no costs of N fixation, increasing amounts of N fixation will be selected for until N no longer limits production. However, tradeoffs between N fixation and plant mortality or turnover, plant uptake of available soil N, or N use efficiency (NUE) can select against N fixation in N-limited ecosystems and can thereby maintain N limitation indefinitely (provided that there are losses of plant-unavailable N). Three key traits influence the threshold that determines how large these tradeoffs must be to select against N fixation. A low NUE, high mortality (or turnover) rate and low losses of plant-unavailable N all increase the likelihood that N fixation will be selected against, and a preliminary examination of published data on these parameters shows that these mechanisms, particularly the tradeoff with NUE, are quite feasible in some systems. Although these results are promising, a better characterization of these parameters in multiple ecosystems is necessary to determine whether these mechanisms explain the lack of symbiotic N fixers-and thus the maintenance of N limitation-in old-growth forests.