Figure 5.

Physiological constraints may limit the size of the effective seed bank. The degree of rareness of a given bacterial taxon may itself impose constrains on whether it can effectively recruit and become part of the effective seed bank (i.e., the seed bank that we can identify as such because it is expressed at some point within the network). (a) This may be particularly relevant in the aquatic portion of these complex boreal networks, where, depending on the water residence time of the ecosystem (horizontal axis) and the initial cell densities of potentially recruiting taxa (different lines), the bacterial growth rates (vertical axis) required for a taxon to attain a certain dominance in a community will vary largely: for example, taxa that are extremely rare (initial theoretical density of 1) would need to have unrealistically high growth rates to overcome extreme rarity and attain high abundances within the ecosystem water residence time. This implies that a taxon will only be able to behave as a seed within a limited set of combinations of realistic growth rates and water residence times (shaded area in a), and that its probability to recruit will thus be dependant on its initial degree of rareness (orange line in b). Even if the conditions for its activation and growth are favourable, a taxon will only be able to recruit above a threshold initial abundance (shaded area in b). Below this threshold, unreactive taxa (green line in b) and potentially reactive taxa (orange line in b) behave essentially as unreactive and do not make part of the seed bank (non-shaded area), at least within the time frame dictated by the movement of water in the landscape.