| The Yellow River Delta wetland is the most extensive, complete and youngest wetlandecosystem in warm temperate. It plays an important role in the maintaining the biodiversityand regional eco-safety and has become a hot spot area. Nowadays, it is the national strategy toexploitation its ecological resources rationally. However, the role of the wetland ecosystem inmaintaining the global carbon balance has not been taken into attention enough. Therefore, inthis paper,4plantations, i.e. mixed plantation of black locust and tree of heaven, black locustand white elm, and black locust and chinese ash, pure black locust, and barelandwere selected in the Yellow River Delta. The ACE automatic detection system made inEngland was used to measure soil respiration rate and soil temperature and humidity, andmeantime microclimate of forests, soil physi-chemical properties, microbes and root biomasswere investigated by conventional methods. The spatial and temporal dynamic characteristicsof soil respiration and their influencing factors were analyzed. Its aim is to understandcarbon cycle of the different afforestations in the region, and provide with scientificguidances for the vegetation restoration, ecological reconstruction in the region. The mainresults are as follows:1. Temporal and spatial variation of soil respiration rate(1) The daily dynamic showed a single peak curve (in12:00to14:00) in the studyarea, and increased with temperature increasing; soil respiration of plantation and its dailyrange were higher than that of bareland at the same time significantly; there were slightdifferencies between stands. The daily soil respiration was smaller in April ranging from0.24μmol·m-2·s-1to0.95μmol·m-2·s-1, while bigger in August ranging from3.27μmol·m-2·s-1to6.51μmol·m-2·s-1, and they ranged from0.16μmol·m-2·s-1to0.32μmol·m-2·s-1and2.61μmol·m-2·s-1to2.93μmol·m-2·s-1. It showed that soil respiration rate was improved afterplanting respectively.(2) Soil respiration rate in summer was significantly bigger than that of the spring, andthere were significant differences among5stands (P<0.05). The average daily soil respirationrates in April were pure black locust (0.69μmol·m-2·s-1)> mixed black locust and chinese ash(0.59μmol·m-2·s-1)> mixed black locust and white elm (0.48μmol·m-2·s-1)> mixed black locust and tree of heaven (0.43μmol·m-2·s-1)> bareland (0.26μmol·m-2·s-1), while in Augustwere mixed black locust and white elm (4.65μmol·m-2·s-1)> mixed black locust and chineseash (4.43μmol·m-2·s-1)> pure black locust (4.13μmol·m-2·s-1)> mixed black locust and treeof heaven (3.99μmol·m-2·s-1)> bareland (2.74μmol·m-2·s-1); their CO2flux of soil respirationin August were7.37g·m-2·d-1,7.01g·m-2·d-1,6.54g·m-2·d-1,6.32g·m-2·d-1,4.34g·m-2·d-1respectively, and they were bigger than that in April. CO2flux of soil respiration in summerwere9.64times,7.45times,5.89times,9.24times and10.54times to the spring respectively.(3) There were similar variationof soil respiration rates in vertical soil layers amongstands, and showed litter layer>0-10cm>10-20cm. Their daily soil respiration rates weresingle peak curve too, but the deeper soil, the less diurnal range of soil respiration rate; soilrespiration rate in four stands in summer was higher than that of the spring significantly. TheQ10value increased with the soil depth increasing because of soil temperature decreased,which enhanced the sensitivity to temperature of mixed lands.2. The correlations between soil respiration and environmental factorsSoil respirations of different lands were due to the integral effects by environmentalfactors, including micro-climate and soil environmental factors. The soil respiration rateswere smaller in April ranging from0.24μmol·m-2·s-1to0.95μmol·m-2·s-1, and no obviouscorrelation to the environmental factors, so the correlations between soil respiration andenvironmental factors in summer were taken into account.(1) The air temperature and humidity had the different impacts on soil respirationrate in August in4lands. Mixed black locust and tree of heaven, mixed black locust and whiteelm had highly significant positive correlation with temperature (P<0.01), bareland asignificant positive correlation (P<0.05); soil respiration rate in4lands had a significantnegative correlation with air relative humidity, while the air relative humidity in the barelandwas instability, the correlation was not obvious.(2) The impacts of soil physical and chemical on soil respiration rate were different in5stands. Nonlinear regression analysis derived that the correlation between soil respiration andsoil temperature in different layers could be described by exponential equation, and therewere significant or highly significant correlations in4lands; the correlation between soilrespiration rate and the daily soil volumetric water content could be described by linearequation in five stands, and there were significant positive correlation in4lands, bareland nosignificant correlation; there were no significant correlation between between soil respirationrate and the seasonal soil volumetric water content. Soil porosity, pH and salt content wereimportant influencing factors of soil respiration in the region. There was a highly significant positive correlation which could be described by exponential equation between soilrespiration rate and its porosity three kinds of mixed black locust, their R2were more than0.90, the R2of pure black locust was more than0.80. The negative correlation could bedescribed by linear equation between soil respiration rate and soil pH and salt content.(3) Soil microbe biomass was not an important influencing factorof soil respiration rate;root biomass affected soil respiration rate in some degree, the more the root biomass, the moresignificant the correlation.(4) Q10increased with the depth of soil and had different sensitivity of soil temperature.Results as follows: mixed balck locust and white elm> mixed black locust and chinese ash>mixed black locust and tree of heaven> pure black locust.3. The rate of release CO2by buried litterThe rate of release CO2by buried litter determined in August showed that in each land,the daily dynamic variation of release CO2rate by litter showed single a peak curve by fourtreatments, and the value of release CO2was Va>Vb>Vc>Vd, but multiple relationshipsbetween the release CO2flux and amount of the corresponding litter was not a geometric. Therate of mass loss increased after burring litter, which resulted in the increasing of the rate ofrelease CO2. The contribution of soil respiration rate was respectively increased23.26%,4.23%,7.22%,28.26%, and12.86%, and black locust and tree of heaven, pure black locustwith relatively large accumulation of litter increased the largest magnitude. The release CO2rate of litter was mainly influenced by0-5cm soil temperature, volumetric moisture content,and litter storage.In summary, the temporal and spatial variation of soil respiration of mixed black locustwas due to the integral effects by environmental factors in the Yellow River Delta. Therefore,future research needs to increase observation density, and in combination with otherenvironmental factors, such as soil nutrients, near-surface atmospheric pressure, CO2concentration, nitrogen deposition, and so on. Further in-depth study of soil respiration inautotrophic and heterotrophic respiration components need to be done in order to enrich andperfect the mechanism of temporal and spatial variation of soil respiration rate in the region. |
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