Aquatic Hyphomycete Species are Screened by the 1 Hyporheic Zone of Woodland Streams

48 Aquatic hyphomycetes strongly contribute to organic matter dynamics in streams but their 49 abilities to colonize leaf litter buried in streambed sediments remain unexplored. Here, we 50 conducted field and laboratory experiments (slow-filtration columns and stream-simulating 51 microcosms) to test the following hypotheses: (a) that the hyporheic habitat acting as a 52 physical sieve for spores filters out unsuccessful strategists from a potential species pool, (b) 53 that decreased pore size in sediments reduces species dispersal efficiency in the interstitial 54 water, and (c) that the physicochemical conditions prevailing in the hyporheic habitat will 55 influence fungal community structure. Our field study showed that spore abundance and 56 species diversity were consistently reduced in the interstitial water compared with surface 57 water within three differing streams. Significant differences occurred among aquatic 58 hyphomycetes, with dispersal efficiency of filiform-spore species being much higher than 59 those with compact or branched/tetraradiate spores. This pattern was remarkably consistent 60 with laboratory experiments that tested the influence of sediment pore size on spore dispersal 61 in microcosms. Furthermore, leaves inoculated in a stream and incubated in slow filtration 62 columns exhibited a fungal assemblage dominated by only two species while five species 63 were co-dominant on leaves from the stream-simulating microcosms. Results of this study 64 highlight that the hyporheic zone exerts two types of selection pressure on the aquatic 65 hyphomycete community, a physiological stress and a physical screening of the benthic spore 66 pool, both leading to drastic changes in the structure of fungal community. 67 68 on O cber 2, 2017 by gest ht://aem .sm .rg/ D ow nladed fom