Study On Soil Respiration In Phyllostachvs Edulis Forest In The North Of Subtropical Area

Soil respiration is the main output pathways for soil carbon storage,the important sourceof atmospheric CO₂and the hot issues of the global carbon cycle and climate changerearch.Phyllostachys edulis forest is an important forest resources in south of China. With theglobal forest area dropped sharply today,Phyllostachys edulis forest area increased in annual3%speed, which means Phyllostachys edulis forest will be an increasing carbon sink. Oursubject is to learn characteristics of soil respiration in typical Phyllostachys edulis forest in thenorth subtropic of China. By using closed dynamic chamber Automated Soil CO₂Flux System,we have measured the temporal variation of soil respiration, variation characteristics alongwith elevation gradient,effection of nitrogen fertilization and the components of soilrespiration in Phyllostachys edulis forest.We have also estimated the annual soil respirationflux. The study results will help for the further study of the characteristics of the regional soilcarbon cycling and provide theoretical guidance for the reasonable management ofPhyllostachys edulis forest. At the same time, we also provide the microscopic experimentdata for the global CO₂concentration changes and the scientific basis for all levels ofgovernment to develop forestry development planning and environmental protection policiesfor national environmental climate negotiations. The main fingdings and resutls are as follows:(1) The soil respiration in Phyllostachys edulis forest has obvitous temporal variationThe daily variation of soil respiration rate in the forest presents a peak curve inspring,summer and autumn.But in winter it has no obvious daily variation.Daily maximumvalue appeares in20:30,21:30,6:00, the maximum value respectively is4.71,7.93,4.44μmolCO₂·m^-2·s^-1; minimum value appeares in11:00,11:00,14:30, corresponding to theminimum value is3.29,5.69,2.6μmolCO₂·m^-2·s^-1.The soil temperature at5and10cm depthhas obvious diurnal variation; while the soil temperature at5and10cm depth has small dailyfluctuations.Soil respiration in spring, summer and autumn 's daily peak time is latter3.5,5.5,6.5hours than the peak time of the soil temperature at5cm depth.Soil moisture has no obvious diurnal variation in all the year.The soil respiration in Phyllostachys edulis forest has obviousseasonal variation, variation curve thus showes that a single-peak type, in August reaches themaximal value,8.54μmolCO₂·m^-2·s^-1, from September to January second year, graduallydecreasing, second year in January for the annual minimum value of soil respiration,0.62μmolCO₂·m^-2·s^-1.Different depth of the soil temperature has obvious seasonal variation, butfor soil moisture,it has no clear seasonal variation.Seasonal variation of soil respiration andsoil temperature has seasonal variation of synchronization.(2)The soil respiration components contribution rate is different.The soil respiration in Phyllostachys edulis forest has three components: root respiration,litter respiration, heterotrophic respiration. The three components has obvious seasonalvariation, and the change trend is similar with the soil respiration, present apparent single-peakcurve. And this change is also according with the soil temperature seasonal variation, thelowest is appeared in January and the highest is appeared in August. The soil respirationcontribution rate of different components is different., root respiration, litter respiration,heterotrophic respiration's annual contribution rates are25.7%,57%and17.3%respectively.All contribution rates have seasonal variations, root respiration and litterrespiration showed single peak curve, the highest values are appeared in June and April,heterotrophic respiration contribution rate variation of seasons double peak curve, maximumvalues occurres in October and January respectively.(3)Model fitting the relationship between soil respiration with soil temperature and soilmoistureWe have used the van 't Hoff exponential equation to fit soil respiration and soiltemperature, the results are that they have good exponential regression, and the R²of theequation is relatively high, varies from0.937to0.977.Q₁0is slightly different in differentdepth, varies from2.97to4.52.Soil respiration components (root respiration, litter respiration,heterotrophic respiration) for the different depth soil temperature, regression equation R²isalso relatively high, varies from0.84to0.95.The Q₁0of Soil respiration components variesfrom3.77,4.03,4.7.We have used the linear model, logarithmic model and exponential model to fit the soil moisture and soil respiration.The relationship between soil respiration and thesoil moisture at5,20,40cm depth is very significant, but it is not significant with the soilmoisture at10cm depth. The power exponent model equation R²is the highest one of threemodels. The relationship between soil respiration components with different soil moisture isdifferent. The root respiration, heterotrophic respiration have a significant relationship with thesoil moisture at5,20,40cm depth, litter respiration has a very significant relationship with thesoil moisture at5,20,40cm depth.All respiration components have no significant relationshipwith the soil moisture at10cm.We also used the linear double factor model and exponentialpower double factor model to fit the relationship between soil respiration and soil temperatureand soil moisture, the results showed that index-power exponent model could well fit therelationship. The equation R²is varied from0.956to0.981.We only can use linear doublefactor mode to fit soil respiration components with soil temperature and moisture.It hasshown that the double factor model is better than single factor model for soil respiration.(4) The soil respiration is different significantly along with elevation gradientFrom120m to640m elevation gradient, the soil respiration is very significant, along withthe altitude increasing, respiration rate is decreasing gradually. Based on the mainenvironmental factors and soil respiration response analysis, it has shown that there is asignificant correlation among the air temperature, the soil temperature with the soil respiration;the soil bulk density, the soil water content with the soil respiration has shown a significantnegative correlation; the atmospheric CO₂concentration with soil between breaths exhibitesextremely significant positive correlation. Through principal component analysis, the airtemperature, the soil temperature, the soil available phosphorus content, the soil bulk density,the soil organic carbon and the soil available potassium content have a cumulative contributionrate with92.27%.Q₁0is deferent in different elevation.(5)The soil respiration is different significance in the different fertilization treatmentIn different fertilization, the soil respiration of using organic fertilization is the highest,reached at5.62μmolCO₂·m^-2·s^-1; followed by the application of organic fertilizer andinorganic fertilizer treatment, the respiration flux is5.03μmolCO₂·m^-2·s^-1.The the direct cause of significant differences of soil respiration is that fertilization leading to soil organic carboncontent has very significant difference.(6)Estimation of the annual soil respiration flux in study areaIn the study area, the annual root respiration flux is404.76g C·m^-2·a^-1, the annualheterotrophic respiration flux is246.214g C·m^-2·a^-1,the annual litter respiration flux is726.789g C·m^-2·a^-1.The annual total soil respiration flux varies from526.83-1377.763g C·m^-2·a^-1alongelevation gradient.