Effects Of Altered Carbon Input On Carbon Emissions Of The Marshy Wetlands And The Microbiological Mechanisms

Plant litter?including standing litter?modification may play a vital role in wetland carbon balance,which can be greatly altered by global change.Our knowledge of the fundamental function of plant litter in ecosystem respiration is crucial for evaluating the C exchange between the atmosphere and biosphere.However,it is not well understood how plant litter manipulation could affect the dynamics of ecosystem respiration?Re?and temperature sensitivity(Q₁₀)in wetland ecosystems.In the present study,we conducted a field manipulation experiment in a seasonal flooded marsh to study the effects of wetland plant litter on carbon emissions and the possible underlying mechanisms for these effects in northeastern China.The results showed that:1)varied wetland plant litter input manipulation treatments had significant effects on CH₄ and CO₂ emissions.The accretion of CH₄ emissions in vegetation removal treatment was significantly higher than that of litter double treatment and the treatment effects were more obvious in the second year than the first year,specific performance for the order of CK<double litter<aboveground standing litter removal<aboveground all litter removal treatments.The CH₄ efflux was also increased in the double litter treatment,but the increment strength was significantly lower than litter removal treatment,suggesting that the changes in CH₄ emission was more sensitive to litter removal treatment.The quantity of methanogens in the soil surface 10 cm under different treatments were analyzed and we found that methanogens of the aboveground all litter removal treatments were obvious higher than other treatments,which was similar with CH₄ emission characteristics;2)the CO₂ emissions was increased in the double litter treatment,whereas it was decreased in the litter removal treatments with the order of aboveground all litter removal treatment<aboveground standing litter removal<CK<double litter treatment,which was different from CH₄ emissions.We also found that Re was more susceptible to litter removal treatments compared to the controls;3)the concentrations of NH₄⁺and DOC,as microbes directly used carbon and nitrogen sources in soil pore water,were significantly affected by the litter input manipulation treatments suggesting that there are varied carbon and nitrogen sources within and outside the plant litter;4)the Q₁₀0 value of Re under each litter input manipulation treatment varied,and the highest value occurred in the all plant-derived litter input removal treatments indicating that the wetland soil was vulnerable to disturbance that prone to carbon losses in the context of global warming.Our results also demonstrated that the Q₁₀0 values of the deeper soil?below 15 cm?with vegetation present were lower than that for the other litter removal treatments implying the important function of the carbon sink in this wetland ecosystem;5)the microbial community structure was analyzed by PLFAs in varied treatments and found that the contents of total biomass,bacteria,fungi,AMF,SF,Gm+and Gm-were followed by the order of aboveground standing litter removal<aboveground all litter removal treatment<CK<double litter treatment.The biomass of bacteria group was significantly higher than other microbial groups.The ratios of fungi/bacteria and AMF/SF were not significantly affected by varied litter input treatments.Overall,we recommend that the role of altered wetland plant litter inputs to the soil system should be seriously considered when predicting biosphere-atmosphere C exchange under global climate change.Soil organic carbon?SOC?mineralization is an important process of carbon?C?cycling and budgeting associated with litter decomposition in terrestrial ecosystems.Research on altered plant-derived C input on soil C stability due to climate change is controversial and there remains considerable uncertainty in predicting soil C dynamics with the techniques currently available.In this study,we conducted a laboratory incubation experiment to test the effects of single-and mixed-Deyeuxia angustifolia?DA?and Carex lasiocarpa?CL?leaf litter addition on cumulative marshland soil CO₂ emission under waterlogged and non-waterlogged conditions in Sanjiang Plain,Northeast China.Results showed that 1)the cumulative CO₂ emissions were significantly increased after leaf litter addition in both water conditions,and that the effect was more pronounced for DA amendment than CL regardless of water condition.The cumulative CO₂ efflux differed considerably between water conditions after DA addition,whereas no significant differences were found after CL addition;2)remarkably impact of leaf litter types on cumulative CO₂ evolution was observed overall,water condition and interactions between leaf litter types and water conditions had no significant effect on CO₂ emissions,however;3)there were no non-additive effects of individual leaf litter type on total CO₂ efflux of the mixed-leaf litter addition treatments.The results of this study indicate that plant litter input to the C-rich marshy soil can induce rapid changes in SOC decomposition regardless of water conditions and that plant residue effects should be taken into consideration when assessing the dynamics of wetland soil system to the future climate scenarios.We conducted a laboratory incubation experiment with ¹³C-glucose and N single and mixture addition to test the priming effect?PE?of wetland soil organic carbon decomposition.Our result revealed that:1)¹³C-glucose addition level?0,4%MBC and 40%MBC?,temperature,time and the interactive effects between time and ¹³C-glucose addition level had significant effects on native wetland SOC decomposition.The cumulative CO₂ emission with varied C addition level incubated at different temperature changed significantly;2)the strength of PE changed with time and the positive PE was higher than negative PE under different temperature and C addition level during incubation.The native C emission was enhanced by 10.63%with low C?4%MBC?addition incubated at 10?,while it was increased by17.96%with high C?40%MBC?addition;and the corresponding values increased by1.47%and 8.83%incubated at 20?;3)the PE with N addition treatment was stronger than C addition,but significantly lower than C,N addition together.There were no significant differences of cumulative native CO₂ emission between high and low C additions;4)there were positive and negative PE after C and N addition,inducing the cumulative primed CO₂changed with time.Compared with N addition alone treatment,the cumulative primed CO₂of native SOC in the low C and N added together treatment was increased by 5.93%,while it was 2.47%in the high C and N added together treatment.Based on the results obtained above,there's evidence that the stability of wetland soil organic carbon was greatly affected by the addition level of exogenous carbon and nitrogen that is the microbial availability of soil carbon and nitrogen.