Respiration Of Soil, Root And Soil Microbial In Larix Gmelinii And Fraxinus Mandshurica Plantaions

Soil respiration(Rs) is the process that soil releases CO₂ to atmosphere(also called soil surface CO₂ flux),and is the important part of carbon cycling in terrestrial ecosystems.Soil microbial respiration and root respiration showed different response to soil basal physical and chemical properties,and intensity of root exudates directly influenced rhizosphere C flux,so measurement the different components(root respiration and soil microbial respiraion) of soil respiration is critical to learn the carbon cycling of forest ecosystem.Excepisally to make further know the fine root turnover,carbon cost and cycling at stand level.In this study,we measured soil respiration,root respiration,soil microbial(bulk soil and rhizosphere) respiration using infrared gas exchange analyzer(Li-Cor-6400) at fertilized and unfertilized plot of Larix gmelinii and Fraxinus mandshurica plantations which are the same site.At the same time,soil temperature,moisture,organic matter and available nitrogen were measured,main objective was to estimate the contribution of root respiration,soil microbial respiration to soil respiration, so as to learn seasonal dynamic pattern of soil respiration,root respiration,and microbial respiration,as well as to investigate the effect of soil properties and N fertilization on those. The results as follow:(1) Fine root respiration rate were closely related to fine root morphology,anatomy,and tissue nitrogen concentration in L.gmelinii and F.mandshurica plantation.Fine root respiration decreased with the increase of root order,first-order roots showed lowest diameter and highest respiration,while fifth order was opposite to first-order root.Because first-order roots exhibited primary development with an intact cortex,highest tissue N concentration,while higher order(fifth) showed mostly secondary development with lowest tissue N concentration. Fine root respiration rate were closely related to temperature,the range of Q₁₀ in root respiration at two plantations were 1.66～2.21,and Q₁₀ at different branch orders in fertilized plot and control plot were not significantly different.Fine root respiration exhibited seasonal dynamical pattern,which was same to the pattern of soil temperature.N fertilization increased average fine root respiration and that at first third order per month during growth season (because N fertilizer increased root tissue N concenation).Fine root respiration was negative related to while positive correlation to.(2) Soil rhizosphere respiration was higher 11%and 5%than soil bulk respiration in L. gmelinii and F.mandshurica plantations respectively,for the priming effect of rhizosphere soil. The average rhizosphere effect was 10%in L.gmelinii and F.mandshurica plantations.Soil microbial respiration in L.gmelinii was higher than that of F.mandshurica,main reason was different soil microbial biomass and the number of colony forming units of soil microbes between two plantations.Soil bulk and rhizosphere respiration showed same seasonal dynamical with soil temperature.N fertilizer decreased soil microbial(rhizosphere and bulk soil) respiration.The reduction of soil bulk respiration in L.gmelinii and F.mandshurica plantations were 13.3%and 17.2%,while that of rhizosphere respiration were 16.4%and 17.5%respectively,because N fertilization decreased the average soil microbial biomass and number of colony forming units in two plantations significantly,the reductions of C_mic and N_mic in L.gmelinii plantation were 24%and 63%,and that in F.mandshurica plantation were 51% and 68%respectively,reductions of bacteria,actinomyces and fungi in L.gmelinii plantation were 98%,63%,and 61%,and that in F.mandshurica plantation were 43%,70%,and 72%..(3) Soil respiration was different in L.gmelinii and F.mandshurica plantations.Main reason was the different of fine root repiration,biomass and soil microbial biomass,and respiration between two plantations.Soil respiration showed same seasonal dynamical pattern with soil microbial and root respiration,because soil respiration positive related to soil temperature,Q₁₀ of soil respiration in L.gmelinii(2.34～2.67) was higher than that in F. mandshurica(2.73～3.75).soil microbial(bulk and rhizosphere) respiration,and soil respiration in surface layer(0～10 cm) were higher than subsurface layer(10-20 cm),for C_mic and N_mic in surface were higher 23.0%and 28.0%than subsurface in L.gmelinii plantation,and 34.0%and 39.5%in F.mandshurica plantation.N fertilization decreased soil respiration too,soil respiration of fertilized plot was lower than control plot in L.gmelinii plantation(29.6%) and F. mandshurica plantation(23.8%),main reason were the reduction of root biomass,respiration, soil microbial biomass and respiration.However,the N fertilization did not significantly change the Q₁₀ in two plantations.(4)Contribution of root respiration and soil microbial repiration to soil respiration were nearly same in two plantations.Contribution of root respiration and soil microbial respiration to soil respiration in L.gmelinii plantation was 30.1%and 30.8%,and that in F.mandshurica was 31.1%and 29.2%respectively.N fertilization decreased the ratio of root respiration to soil respiration,contrast to control plot,the ratio in fertilized plot was 27.6%(L.gmelinii) and 28.4%(F.mandshurica) respectively.While N fertilizer increased the contribution of soil microbial respiration to soil respiration in L.gmelinii(38.9%) and F.mandshurica(33.2%) plantations.Overall,root respiration,soil microbial respiration,and soil respiration in L.gmelinii plantation was lower than that in F.mandshurica plantation.While soil respiration,root respiration and soil microbial respiration showed same seasonal dynamical pattern in fertilized and control plot,and contribution of root respiration to soil respiration was about 30%in two plantations,although N fertilization reduced them,contribution of soil microbial respiration was close to 30%and others 40%of soil respiration may be the respiration of fine root growth, corse root and soil fauna which did not measured in our study.The study on root respiration, soil microbial respiration and soil respiration was critical to learn C allociation pattern and process in two plantaions.