Comparison in phytoplankton diversity-productivity-community stability between river-type reservoir and lake-type reservoir

Relationship between biodiversity and ecosystem function is one of the core issues in ecological research.Phytoplankton,as the main producer of aquatic ecosystem,its diversity,productivity,and community stability are of great signifi cance to reveal ecosystem function.There are signifi cant diff erences in hydrodynamics,water retention time,and phytoplankton community structure between river-type reservoir and newly built lake-type reservoir.The comparative analysis of phytoplankton community stability between the two types of reservoir has not been reported.Jiuquwan Reservoir(river-type)and Taihu Reservoir(lake-type),the two reservoirs in the Dongjiang River source area of Zhujiang(Pearl)River Basin,were selected for comparison in terms of multi-year operation vs.new impoundment,river-type vs.lake-type,and shallow water vs.sub-deep water reservoirs.Samples were collected in dry season(December 2019),normal season(March 2020),and wet season(August 2020),on which the phytoplankton diversity and productivity of the two reservoirs,and the relationship and diff erence of community stability were examined.Results show that(1)the number of phytoplankton species in Jiuquwan Reservoir decreased comparing that before algal bloom and the restoration treatment,while that in Taihu Reservoir increased compared with that before the impoundment of the reservoir.There was no signifi cant diff erence in functional groups and species number between the two reservoirs(P>0.05);(2)the biological stability,diversity,productivity,and resource utilization effi ciency of newly built lake-type reservoir were higher than those of multi-year river-type reservoir.In addition,the utilization effi ciency of phytoplankton resources was the highest in wet season in both reservoirs.The increases in biodiversity,richness,and evenness promoted the stability of the community,while increases in productivity and resource utilization effi ciency weakened the stability of the community;(3)community stability was aff ected by both biotic and abiotic factors,and hydrodynamic index was the main factor.This study is helpful to understand the relationship and diff erences in phytoplankton diversity,productivity and community stability in diff erent types of reservoirs,and provides a guidance for maintaining the stability of reservoir water ecosystem and protecting the biodiversity.The relationships between phytoplankton diversity,productivity,and community stability will be investigated in depth,for which a long-term observation will be conducted on the impact of environmental factors and diversity on the local biostability in diff erent types of reservoirs.

Species diversity and stability of natural secondary communities with different cutting intensities after ten years

Species diversity and stability of natural secondary communities in different layers with different cutting intensities 10 years later were investigated by calculating Marglef Richness index（R）,Shannon-Wiener diversity index（H）,Simpson diversity index（P）,and Pielou Evenness index（J）.Results show that the values of R,H and P among different layers are listed in a decreasing order：the shrub layer the arbor layer the herb layer,all the three indices values reach the maximum under medium selective cutting intensity after 10 years.The J value of the shrub layer shows a concave parabolic change with the increase in cutting intensity;it shows a linear increase for the arbor layer,whereas the J value of the herb layer shows an opposite change pattern.The values of R at different cutting intensities had high significant difference,but other indices had not significant difference.The stability of communities at different cutting intensities after 10 years is non-cutting low selective cutting intensity medium selective cutting intensity high selective cutting intensity extra-high intensity clear cutting.The stability of communities at different cutting intensities after 10 years shows that the greater cutting intensities,the worse the stability is.

Soil salinization increases the stability of fungal not bacterial communities in the Taklamakan desert

●Bacterial richness declined but fungal richness increased under salinization.●Bacteria did not become interactively compact or facilitative under salinization.●Fungi exhibited more compartmentalized and competitive patterns under salinization.●Fungal stability showed steeper increases under salinization than bacterial stability.Soil salinization is a typical environmental challenge in arid regions worldwide.Salinity stress increases plant convergent adaptations and facilitative interactions and thus destabilizes communities.Soil bacteria and fungi have smaller body mass than plants and are often efficient against soil salinization,but how the stability of bacterial and fungal communities change with a wide range of soil salinity gradient remains unclear.Here,we assessed the interactions within both bacterial and fungal communities along a soil salinity gradient in the Taklamakan desert to examine(i)whether the stability of bacterial and fungal communities decreased with soil salinity,and(ii)the stability of which community decreased more with soil salinity,bacteria or fungi.Our results showed that the species richness of soil fungi increased but that of soil bacteria decreased with increasing salinity in topsoils.Fungal communities became more stable under soil salinization,with increasing compartmentalization(i.e.,modularity)and proportion of competitions(i.e.,negative:positive cohesion)as salinity increased.Bacterial communities exhibited no changes in modularity with increasing salinity and smaller increases in negative:positive cohesion under soil salinization compared to fungal communities.Our results suggest that,by altering interspecific interactions,soil salinization increases the stability of fungal not bacterial communities in extreme environments.

Autumn nitrogen enrichment destabilizes ecosystem biomass production in a semiarid grassland

Nitrogen(N)deposition decreases the temporal stability of ecosystem aboveground biomass production(ecosystem stability).However,little is known about how the responses of ecosystem stability differ based on seasonal N enrichment.By adding N in autumn,winter,or growing season,from October 2014 to May 2020,in a temperate grassland in northern China,we found that only N addition in autumn resulted in a significantly positive correlation between ecosystem mean aboveground net primary productivity(ANPP)and its standard deviation and significantly reduced ecosystem stability.Autumn N-induced reduction in ecosystem stability was associated with the vanished negative effect of community-wide species asynchrony(asynchronous dynamics among populations to environmental perturbations)on the standard deviation of ecosystem ANPP in combination with the emerged positive effect of dominance(Simpson's dominance index that indicates the relative weight of dominant species in a community).Our findings indicate that autumn N addition might overestimate the negative effect of annual atmospheric N deposition on ecosystem stability,suggesting that to better evaluate the influence of N deposition in temperate grasslands,both field experiments and global modeling should consider not only the annual N load but also its seasonal dynamics.Moreover,further studies should pay more attention to the alteration in the ecosystem temporal deviations,which might be more sensitive to human-induced environmental changes.

Unbalanced diets enhance the complexity of gut microbial network but destabilize its stability and resistance

Stability is a fundamental ecological property of the gut microbiota and is associated with host health.Numerous studies have shown that unbalanced dietary components disturb the gut microbial composition and thereby contribute to the onset and progression of disease.However,the impact of unbalanced diets on the stability of the gut microbiota is poorly understood.In the present study,four-week-old mice were fed a plant-based diet high in refined carbohydrates or a high-fat diet for four weeks to simulate a persistent unbalanced diet.We found that persistent unbalanced diets significantly reduced the gut bacterial richness and increased the complexity of bacterial co-occurrence networks.Furthermore,the gut bacterial response to unbalanced diets was phylogenetically conserved,which reduced network modularity and enhanced the proportion of positive associations between community taxon,thereby amplifying the co-oscillation of perturbations among community species to destabilize gut microbial communities.The disturbance test revealed that the gut microbiota of mice fed with unbalanced diets was less resistant to antibiotic perturbation and pathogenic bacteria invasion.This study may fill a gap in the mechanistic understanding of the gut microbiota stability in response to diet and provide new insights into the gut microbial ecology.

Impact of rewilding,species introductions and climate change on the structure and function of the Yukon boreal forest ecosystem

Community and ecosystem changes are happening in the pristine boreal forest ecosystem of the Yukon for 2 reasons.First,climate change is affecting the abiotic environment(temperature,rainfall and growing season)and driving changes in plant productivity and predator-prey interactions.Second,simultaneously change is occurring because of mammal species reintroductions and rewilding.The key ecological question is the impact these faunal changes will have on trophic dynamics.Primary productivity in the boreal forest is increasing because of climatic warming,but plant species composition is unlikely to change significantly during the next 50-100 years.The 9-10-year population cycle of snowshoe hares will persist but could be reduced in amplitude if winter weather increases predator hunting efficiency.Small rodents have increased in abundance because of increased vegetation growth.Arctic ground squirrels have disappeared from the forest because of increased predator hunting efficiency associated with shrub growth.Reintroductions have occurred for 2 reasons:human reintroductions of large ungulates and natural recolonization of mammals and birds extending their geographic ranges.The deliberate rewilding of wood bison(Bison bison)and elk(Cervus canadensis)has changed the trophic structure of this boreal ecosystem very little.The natural range expansion of mountain lions(Puma concolor),mule deer(Odocoileus hemionus)and American marten(Martes americana)should have few ecosystem effects.Understanding potential changes will require long-term monitoring studies and experiments on a scale we rarely deem possible.Ecosystems affected by climate change,species reintroductions and human alteration of habitats cannot remain stable and changes will be critically dependent on food web interactions.