Effects Of Clonal Integration On Soil Microbial Communities And Greenhouse Gas Emissions Of A Phragmites Australis Wetland Under Disturbance

Connected asexual individuals(ramets)of clonal plants can transport and share resources such as water,nutrients,and photosynthates.Such clonal integration can enhance net productivity and the capacity of ramets to tolerate environmental stresses,thus may further influence net emissions of greenhouse gasses and the composition and biomass of soil microbial communities.Although a large number of studies have examined the effects of clonal integration on the capacities of clonal plants to withstand stresses,very few have tested its influence on net emissions of greenhouse gasses and soil microbial communities associated with increases in environmental stress.In a Phragmites australis wetland in the Yellow River Delta in China,we added 0,5,and 10 mm crude oil per year or applied four different intensities of shoot clipping(i.e.simulated grazing by animals;0%,30%,60%and 90%)to circular plots of 60 cm in diameter.In half of the plots,we severed the rhizome connections between the ramets of P.australis inside and outside the plots to prevent clonal integration,whereas the rhizome connections were kept intact in the other half to allow integration.The experiment lasted for two years from 2014 to 2015.We sampled soil in each plot in August,and measured the phospholipid fatty acids(PLFA)of soil microbes and the carbon and nitrogen concentrations of the soil microbial biomass.Net emissions of CO2,CH4 and N2O were measured twice a month from June to October 2015.All aboveground mass in each plot was harvested and measured in late October in each year.Sampling time had a significant effect on the total soil microbial PLFA,carbon,and nitrogen,and these three variables were all higher in 2015 than in 2014.Crude oil addition significantly increased the total PLFA content of soil microbes in 2015,but had little effect in 2014.Furthermore,crude oil addition resulted in a decrease in soil microbial carbon and nitrogen in 2014,but an increase in 2015.Clonal integration had no significant effect on soil microbial PLFA,carbon,or nitrogen in either 2014 or 2015.Total soil microbial PLFA was significantly positively related to soil microbial carbon and nitrogen.When rhizomes were severed,plots with no oil absorbed about 300 g CO2 equivalents m-2 over three months in the second year,while plots with 10 mm oil a-1 emitted about 800 g CO2 equivalents m-2.Leaving rhizomes connected decreased total emissions by about half and increased mass per shoot and total aboveground dry biomass by about half in the plots with 10 mm oil a-1.Connection had no effect on either measure in the plots with no oil.Shoot clipping significantly decreased the aboveground mass,productivity and shoot density of P.australis and the whole community.Leaving rhizomes connected significantly increased the aboveground mass and productivity of P.australis in 2015,but had little effect in 2014.The total soil microbial PLFA and soil PLFAs of the total bacteria,gram-positive bacteria and gram-negative bacteria were all greater in 2015 than in 2014,and clonal integration markedly increased these four variables as well as soil microbial concentrations of carbon and nitrogen.Thus,physiological integration of clonal plants may have a cascading effect on soil microbial communities.Shoot clipping increased the greenhouse gas emissions from about-300 g CO2 equivalents with no shoot clipping to about 300 g CO2 equivalents when 90%of the plant aboveground mass was removed.Meanwhile,clonal integration could also contribute to the cumulative emissions of CO2 and CO2 equivalents,and this effect tended to be greater with intensification of shoot clipping.The greenhouse gas fluxes of wetland ecosystems are regulated by plant and soil microbial activities associated with CO2 production and consumption processes.Greenhouse gas emissions of ecosystems are closely related to plant net production and soil microbial dynamics.These results indicate that environmental stresses may aggravate the global warming effect of wetlands via stimulating CO2 productions and/or reducing CO2 consumptions.Clonal integration with unstressed plants can enhance the capacity of ramets to tolerate environmental stresses and thus have a cascading positive effect on plant net productivity and soil microbial biomass and activities.An increase in plant productivity induced by clonal integration could decrease the emissions of greenhouse gasses.On the other hand,clonal integration may also stimulate greenhouse gas emission by increasing soil microbial biomass.Thus,physiological integration may have a complicated effect on greenhouse gas emissions of wetland ecosystems dominated by clonal plants.