Anderson M D, Taylor D L, Olson K, Ruess R W
Biology Department Macalester College Saint Paul Minnesota USA.
Institute of Arctic Biology University of Alaska Fairbanks Alaska USA.
Ecol Evol. 2024 Jul 8;14(7):e11458. doi: 10.1002/ece3.11458. eCollection 2024 Jul.
In root nodule symbioses (RNS) between nitrogen (N)-fixing bacteria and plants, bacterial symbionts cycle between nodule-inhabiting and soil-inhabiting niches that exert differential selection pressures on bacterial traits. Little is known about how the resulting evolutionary tension between host plants and symbiotic bacteria structures naturally occurring bacterial assemblages in soils. We used DNA cloning to examine soil-dwelling assemblages of the actinorhizal symbiont in sites with long-term stable assemblages in ssp. nodules. We compared: (1) phylogenetic diversity of in soil versus nodules, (2) change in assemblages in soil versus nodules in response to environmental variation: both across succession, and in response to long-term fertilization with N and phosphorus, and (3) soil assemblages in the presence and absence of host plants. Phylogenetic diversity was much greater in soil-dwelling than nodule-dwelling assemblages and fell into two large clades not previously observed. The presence of host plants was associated with enhanced representation of genotypes specific to , and decreased representation of genotypes specific to a second species. The relative proportion of symbiotic sequence groups across a primary chronosequence was similar in both soil and nodule assemblages. Contrary to expectations, both N and P enhanced symbiotic genotypes relative to non-symbiotic ones. Our results provide a rare set of field observations against which predictions from theoretical and experimental work in the evolutionary ecology of RNS can be compared.
在固氮细菌与植物之间的根瘤共生关系（RNS）中，细菌共生体在根瘤内和土壤中的生态位之间循环，这对细菌性状施加了不同的选择压力。关于宿主植物与共生细菌之间由此产生的进化张力如何构建土壤中自然存在的细菌群落，我们所知甚少。我们利用DNA克隆技术，在刺槐共生体长期稳定群落的地点，研究其土壤栖息群落。我们比较了：（1）土壤和根瘤中刺槐共生体的系统发育多样性；（2）土壤和根瘤中刺槐共生体群落在响应环境变化时的变化，包括演替过程中的变化以及对氮和磷长期施肥的响应；（3）有宿主植物和无宿主植物情况下的土壤群落。土壤栖息群落的系统发育多样性远高于根瘤栖息群落，且分为两个此前未观察到的大分支。宿主植物的存在与刺槐共生体特定基因型的丰度增加以及第二种刺槐共生体特定基因型的丰度降低有关。在土壤和根瘤群落中，共生序列组在初级时间序列中的相对比例相似。与预期相反，相对于非共生基因型，氮和磷都增加了共生基因型。我们的研究结果提供了一组罕见的实地观察结果，可用于比较RNS进化生态学理论和实验工作的预测。
