| The forest-stream continuum,as an important component of forest watersheds,is a key hub linking terrestrial and aquatic ecosystems.As the source of many rivers,lakes and other large inland water bodies,the dynamics of the forest-stream continuum significantly affects the material cycle and microbial community composition and diversity of downstream water.Microbial communities,as important taxa in the integrated forest-stream system,are key element in the biogeochemical cycle.Previous studies on microbial communities have mainly focused on glacial streams,rivers,rivers and oceans,and fewer studies have been conducted on microbial community composition and diversity in forest streams.Therefore,in this study,microbial communities in a typical subtropical forest-stream continuum in Wuyi Mountain were studied in two seasons: the dry season(November-December)and the rainy season(July-August),combining stream classification,real-time measurement of environmental indicators,indoor experiments and microbial sequencing methods.Main findings:(1)In the forest-stream continuum,the structure and diversity of soil microbial communities differed significantly(P < 0.05)under different seasonal conditions.Microbial diversity and richness were significantly different(P < 0.05)in dry-season soils at different distances from streams,while they were highly similar in wet-season soils.The structure and diversity of soil microbial communities in different soil layers were highly similar in both dry and wet seasons.The environmental factors affecting soil microbial communities were mainly: nitrate nitrogen content in soil,soil water content,ammonium nitrogen content in soil,soil p H,and soluble organic carbon in soil;among them,the effect of nitrate nitrogen content in soil in dry season on the diversity of bacterial communities was positive with an importance of 68.55%,and the effect of ammonium nitrogen content on the diversity of soil fungal communities was positive with an importance of 37.73%;Soil p H had a positive effect on bacterial community with an importance of 50.99% and a negative effect on bacterial richness with an importance of 84.10% during the rainy season,while p H had a positive effect on fungal community diversity with an importance of 53.34% and phosphorus content in the soil had a negative effect on fungal richness with an importance of 78.87%.Our results emphasize that different seasons contribute significantly to the variation in soil microbial community composition and diversity in the system;that horizontal differences in distance from streams are drivers of variation in microbial community composition and diversity at spatial scales;and those different environmental factors also explain the complexity and diversity of microbial community composition,respectively.(2)In the forest-stream continuum,the structure and diversity of stream microbial communities showed significant heterogeneity(P < 0.05)under different seasonal conditions.In dry-season streams,microbial richness differed significantly in different stream gradients,respectively,and the composition of microbial communities differed significantly(P < 0.05)in low-order streams(1st,2nd-order streams)and high-order streams(3rd,4th,and 5th-order streams);in wet-season streams,the diversity and richness of microbial communities were similar in different stream gradients,and the composition of bacterial communities was heterogeneous,while fungal communities exhibited high similarity.The environmental factors affecting the microbial communities in streams were mainly: water temperature,p H,resistivity,dissolved oxygen concentration,and soluble organic carbon concentration.In dry season waters,the increase in bacterial community diversity was mainly influenced by the increase in water temperature(28.70% relative importance),the increase in bacterial community richness was mainly influenced by the increase in TDS in water(67.29%),and the decrease in fungal community diversity was mainly caused by the TDS in water(47.29%)and the increase in fungal community richness was caused by the increase in water temperature(56.08%);in rainy season water bodies,the increase in bacterial community diversity was mainly influenced by the increase in water temperature(34.62%relative importance),the decrease in bacterial community richness was mainly influenced by the increase in TDS in water(58.05%)and the decrease in fungal community diversity was mainly was caused by an increase in DOC in the water(35.03%),and the increase in fungal community richness was caused by an increase in p H(68.58%).Our study indicates that the diversity of bacterial and fungal community composition is heterogeneous among streams of different terraces in an integrated forest-stream system,with higher temperature water showing high community diversity and complexity,and that seasonal changes make the p H of rainy season water bodies an important environmental factor driving changes in fungal community diversity and abundance,demonstrating an important role in triggering changes in the microbial community dynamics of water bodies in the watershed.(3)In the forest-stream continuum in the dry season,the diversity and richness of bacterial communities in streams were significantly higher than those in soil,and the diversity and richness of fungal communities in streams were significantly lower than those in soil(P < 0.05);the composition of bacterial communities in streams differed from those in riparian zone soils,and the composition of fungal communities in streams was similar to that in riparian zone soils.In the integrated forest-stream system during the rainy season,the diversity and richness of bacterial communities in streams were significantly higher than those in soil,and the diversity and richness of fungal communities in streams were significantly higher than those in soil(P < 0.05);the composition of bacterial communities in streams differed from those in riparian zone soils,and the composition of fungal communities in streams was similar to that of fungal communities in riparian zone soils.Our study suggests that the microbial community in soil may be a source of microbial community in streams,and there is a correlation between the two,while the dynamic change pattern of microbial community in the integrated forest-stream system in the watershed has some similarity between streams and soils,and the process cannot be separated between streams and soils.This provides new insights for subsequent studies on biogeochemical cycling processes and elemental transport mechanisms in the watershed.In summary,there was a high degree of heterogeneity in the diversity and richness of microorganisms in the forest-stream continuum,with significant variability in the structure of bacterial communities and similarity in the structure of fungal communities.With increasing precipitation,the diversity and richness of bacterial communities in the integrated forest-stream system decreased significantly;the diversity of fungal communities increased significantly;and the richness decreased significantly.Changes in precipitation resulted in significant changes in the structure of the microbial communities in the system.Soil water content in forest-stream continuums provided the driving force for variation in soil microbial communities;in streams,water temperature was the key environmental factor shaping microbial community dynamics.Changes in microbial community structure and diversity demonstrate their resilience to environmental change,and differences in microbial community structure and diversity in different habitats demonstrate the complexity of the integrated forest-stream system. |
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