Soil Respiration And Carbon Balance Study Of Casuarina Equisetifolia Plantation Ecosystem On Coastal Sand

AbstractThe carbon cycle of forest ecosystem plays an important role in the global carbon cycle,which has been a focus in the last decades. With the reduce of natural forest resource and thegradually increase of plantation these years, the proportion and status of plantation is more andmore larger and important. But there are few data on the carbon cycle of plantation ecosystem inChina, especially in sub-tropical zone, China, which limited the exact estimation on the carbonsink or source of the forest ecosystem of China. Soil respiration has the critical status in the carboncycle. In china, especially in southeast coastal, Casuarina equisetifolia protection plantation is themain tree species and has an very important status as the windbreak, and with the graduallyconsummate of nation's coastal protection forest system, the status of Casuarina equisetifoliaplantation will be more and more important.So this thesis studied the soil respiration especially the soil heterotrophic respiration and thecarbon balance in 5 plots (1 young-forest,3 mid-forest and 1 mature-forest) of Casuarinaequisetifolia plantation ecosystem on coastal sandy in Quanzhou city Fujian province with thestatic chamber-infra-red CO₂ gas analyzer method and LICOR-8100 Automated Soil CO₂ FluxSystem. The results were showed as follows:1．Soil carbon content rates were at a low level in the 5 plots, the mean value was about 5g/kg,and which was generally decreased with the increase of the soil depth. With the increase of the soildepth, the difference between the two borders upon soil layer of soil carbon content rate was lessand less distinct. In 100cm depth, the soil carbon content of the young-forest(6 years) was 13．61t/hm², the soil carbon content of mid-forest plot (18 years) and the mature-forest (31 years) were23．37 and 56．17t/hm²ï¼Ž2．The DOC (Dissolved organic carbon) and MBC (Microbial biomass carbon) content wereat a lower level in the soil surface layer (0～20cm) of the 5 Casuarina equisetifolia plantationplots. The DOC content was gradually larger but the MBC content was gradually smaller with thegrowth of the forest. With the growth of the forest, the difference between the two borders uponsoil layer of MBC content was less and less distinct. The ratio value of MBC/organic carbon insoil (0～20cm) were also at a lower level, which was about only 0．75%.3．The diurnal variation of air temperature,the surface temperature and the soil temperatureat 5cm depth in the 5 forest types could all be expressed as a one-humped curve. The peak values appeared at about 12:00～15:00 pm. The diurnal variation of water volume content in the 5 plotscould be expressed as a not two-humped curve, the highest value appeared at about 7:00～8:00 am,and the secondary highest value appeared at about 16:00～18:00 pm. So The diurnal variation ofsoil respiration could be expressed as a two-humped curve, the peak value appeared at 8:00 pmand 14:00～16:00 pm, the lowest value appeared at about 20:00～22:00 pm4．The monthly variation of soil respiration rate in the 5 forest types could all be expressed asa one-humped curve. The peak values appeared at about June or July, and the lowest valuesappeared at about November or December. The soil total respiration had a same change rule withthe soil heterotrophic respiration, which was similar to the change of the soil temperature of 5cmdepth and water volume content in soil. The results showed that there was a significant differencein monthly ranges of soil respiration rates among the various forests and the mid-forest had abigger monthly change than that of young and mature forest. The monthly ranges of soilheterotrophic respiration rates among the various forests were 1．41,3．37,4．14,2．27 and2．53μmol m^-2·s^-1 . The monthly ranges of soil total respiration among the various forests were1．21,4．37,5．44,3．09 and 3．52μmol m^-2·s^-1 .5．The relationship beweeen soil heterotrophic respiration and temperature and soil watervolume content was analyzed with the regression analysis of the SPSS and the results showed:there was a good exponent correlation (R =ae (bT) ) beween soil respiration and temperature(including air temperature,the soil surface temperature and the soil temperature of 5cm depth),especially the soil temperature of 5cm depth, the R² values beweeen soil heterotrophic respirationrate and the soil temperature of 5cm depth in 5 forests were 0．6343,0．5437,0．6773,0．5552 and0．6677．the Q₁₀ of the soil temperature of 5cm depth in the 5 forests were 1．385,1．438,1．533,1．831 and 1．948．There was a good liner correlation beween soil respiration and the soil watervolume cotent in the upper 20cm (Y＝aX +b) , the R² values in the 5 forests were 0．5713,0．7839,0．7511,0．8165 and 0．8207．The relationship beween soil respiration rate and the twovariables of soil temperature at 5cm depth and the soil water volumn content in the upper 20cmcould be described in this regression equation-R = a×e^bT×W^c , which had much morepredictive power than that using temperature or water cotent as single independent variable, andthe R² values were 0．690,0．919,0．801,0．868 and 0．902 in the 5 forests.6．The soil respiration was divided into autotrophic respiration (root respiration) andheterotrophic respiration (microbe respiration) through the trenching method. The results showedthat the proportion of heterotrophic respiration to the soil total respiration ranged from 68．59%～76．87% in the 5plots, with a average of 72．73%. There was no distinct difference of the proportionamong the 5 plots and 12 monthes. 7．The differences of soil respiration among the 5 plots were studied. The soil heterotrophicrespiration mean rates in one year were 2．05,2．70,2．90,2．01 and 2．20μmol m^-2·s^-1 and the soiltotal respiration mean rates in one year were 2．62,3．72,4．02,2．67 and 3．10μmol m^-2 ?s^-1 . Thediurnal variation rules of soil respiration were almost among the 5 plots.8．The results by the static chamber-infra-red CO₂ gas analyzer method and LICOR-8100Automated Soil CO₂ Flux System were highly liner correlated (R² =0．8258) . The average value ofthe soil respiration rate measured by the static method was about 1．327 tines and had a biggervariance that by the dynamic method.9．The net flux beween the 5-forest ecosystem and the atmosphere were 11．165,15．628,10．204,7．986 and 0．479t·hm^-2·a^-1 ; which indicated that the Casuarina equisetifolia plantationecosystem on coastal sandy in south subtropical acted as a carbon sink when exchanged with theatmosphere. So, it is high time for us to protect and manage the Casuarina equisetifolia plantationecosystem on coastal sandy because it helped to not only break wind but also reduce theatmosphere carbon dioxide concentration and amend the climate in the future.Subject words: Soil respiration, LI-8100, Casuarina equisetifolia...