Dorado-García Irene, Medina-Sánchez Juan Manuel, Herrera Guillermo, Cabrerizo Marco J, Carrillo Presentación
Instituto del Agua, Universidad de Granada, Granada, Spain.
Departamento de Ecología, Facultad de Ciencias, Universidad de Granada, Granada, Spain.
PLoS One. 2014 Jun 11;9(6):e99288. doi: 10.1371/journal.pone.0099288. eCollection 2014.
Because the nature of the main resource that limits bacterioplankton (e.g. organic carbon [C] or phosphorus [P]) has biogeochemical implications concerning organic C accumulation in freshwater ecosystems, empirical knowledge is needed concerning how bacteria respond to these two resources, available alone or together. We performed field experiments of resource manipulation (2×2 factorial design, with the addition of C, P, or both combined) in two Mediterranean freshwater ecosystems with contrasting trophic states (oligotrophy vs. eutrophy) and trophic natures (autotrophy vs. heterotrophy, measured as gross primary production:respiration ratio). Overall, the two resources synergistically co-limited bacterioplankton, i.e. the magnitude of the response of bacterial production and abundance to the two resources combined was higher than the additive response in both ecosystems. However, bacteria also responded positively to single P and C additions in the eutrophic ecosystem, but not to single C in the oligotrophic one, consistent with the value of the ratio between bacterial C demand and algal C supply. Accordingly, the trophic nature rather than the trophic state of the ecosystems proves to be a key feature determining the expected types of resource co-limitation of bacteria, as summarized in a proposed theoretical framework. The actual types of co-limitation shifted over time and partially deviated (a lesser degree of synergism) from the theoretical expectations, particularly in the eutrophic ecosystem. These deviations may be explained by extrinsic ecological forces to physiological limitations of bacteria, such as predation, whose role in our experiments is supported by the relationship between the dynamics of bacteria and bacterivores tested by SEMs (structural equation models). Our study, in line with the increasingly recognized role of freshwater ecosystems in the global C cycle, suggests that further attention should be focussed on the biotic interactions that modulate resource co-limitation of bacteria.
由于限制浮游细菌的主要资源（如有机碳[C]或磷[P]）的性质对淡水生态系统中有机碳的积累具有生物地球化学意义，因此需要关于细菌如何单独或共同响应这两种资源的经验知识。我们在两个具有不同营养状态（贫营养与富营养）和营养性质（自养与异养，以总初级生产：呼吸比衡量）的地中海淡水生态系统中进行了资源操纵的现场实验（2×2析因设计，添加C、P或两者组合）。总体而言，这两种资源协同共同限制浮游细菌，即在两个生态系统中，细菌生产和丰度对两种资源组合的响应幅度高于相加响应。然而，在富营养生态系统中，细菌对单独添加P和C也有正向响应，但在贫营养生态系统中对单独添加C没有响应，这与细菌碳需求与藻类碳供应之间的比值相符。因此，如一个提出的理论框架所总结的，生态系统的营养性质而非营养状态被证明是决定细菌资源共同限制预期类型的关键特征。实际的共同限制类型随时间变化，并部分偏离（协同作用程度较低）理论预期，特别是在富营养生态系统中。这些偏差可能由细菌生理限制之外的外在生态力量来解释，如捕食，结构方程模型（SEMs）测试的细菌与食细菌者动态之间的关系支持了其在我们实验中的作用。我们的研究与淡水生态系统在全球碳循环中日益被认识到的作用一致，表明应进一步关注调节细菌资源共同限制的生物相互作用。
