Soil Respiration Of Larix Gmelinii And Its Response To Letter In The North Of Daxing'an Mountains

Forest soil respiration is an important part of terrestrial ecosystemin carbon cycle,its dynamic change plays an important role in global carbon cycle.The Daxing'anling Mountains is located in the cold temperate zone of China.The zonal vegetation is a bright coniferous forest dominated by Larix gmelinii as the constructive species.In this study,the LI-6400 chamber was used to measure soil respiration(Rs),respiration components including root respiration(Rr),heterotrophic respiration(Rh)and soil mineral respiration(Rm)and soil litterfall respiration(Ri),which were belong to heterotrophic respiration(Rh)and their impacting factors of five typical forest types,which were Larix gmelini forest,Rhododendron simsii-Larix gmelini forest,Ledum palustre var.decunbens-Larix gmelini forest,Betula platyphylla-Larix gmelini forest,Pinus sylvestris var.mongolica-Larix gmelini.The temperature of top 10 cm soil(T10),the humidity of top 10 cm soil(W10)and letter which were regarded as impacting factors were measured at the same time.The seasonal dynamics of soil respiration and its components,the contributions to total soil respiration of different soil respiration components and the effects of W10,T10 and the letterfall to soil respiration were analysed,in order to provide scientific basis for further research of carbon release and its influence on the regional climate in cold temperate region of China.The results were as follows:(1)The soil respiration(Rs),root respiration(Rr)and heterotrophic respiration(Rh)all presented a single-peak curve in growing season,and the peak values all appeared in August for the five kinds of larch forests.The average soil respiration rates of the five communities ranged from 4.71 ?mol/(m2·s)to 7.41?mol/(m2·s),and their rank was Pinus sylvestris var.mongolica-Larix gmelini>Ledum palustre var.decunbens-Larix gmelini>Betula platyphylla-Larix gmelini>Larch gmelini>Rhododendron simsii-Larix gmelini.The average Rr ranked as Ledum palustre var.decunbens-Larix gmelini>Pinus sylvestris var.mongolica-Larix gmelini>Betula platyphylla-Larix gmelini>Rhododendron simsii-Larix gmelini>Larch gmelini,ranged from 1.97 ?mol/(m2 s)to 3.15 ?mol/(m2·s).The average Rh ranged from 3.80?mol/(m2·s)tp 5.56 ?mol/(m2.S),the Rh of Pinus sylvestris var.mongolica-Larix gmelini was maximum and the minimum Rh was in Rhododendron simsii-Larix gmelini.The soil mineral respiration(Rm)was the main component of Rh,the average Rh ranked as Pinus sylvestris var.mongolica-Larix gmelin>Betula platyphylla-Larix gmelini>Larch gmelini>Ledum palustre var.decunbens-Larix gmelini>Rhododendron simsii-Larix gmelini in observing period,ranged from 2.98 ?mol/(m2·s)to 4.85 ?mol/(m2·s),the rate of letterfall respiration was small,the average R1 ranked as Ledum palustre var.decunbens-Larix gmelini>Larch gmelini>Betula platyphylla-Larix gmelini>Rhododendron simsii-Larix gmelini>Pinus sylvestris var.mongolica-Larix gmelili,ranged from 0.70 ?mol/(m2·s)to 1.22 ?mol/(m2·s).(2)There were differences between soil respiration and its components in different types of five Larix gmelinii forests.During the observation period,the Rs of Rhododendron simsii-Larix gmelini was significantly smaller than that of other types of Larix gmelini forests(P<0.05),with Rs of Pinus sylvestris var.mongolica-Larix gmelini achieving extremely significant(P<0.01).Rs of Pinus sylvestris var.mongolica-Larix gmelini was also significantly greater than that of Larch gmelini(P<0.05),but there was no significant difference in Rs between other types of Larix gmelinii forests(P>0.05);There were significant differences between Larch gmelini and Pinus sylvestris var.mongolica-Larix gmelini and Ledum palustre var.decunbens-Larix gmelini for Rr(P<0.05);During the observation period,the Rh of Rhododendron simsii-Larix gmelini was significantly smaller than that of other types of Larix gmelini forests(P<0.05),with Rs of Pinus sylvestris var.mongolica-Larix gmelini achieving extremely significant(P<0.01);Rm of Pinus sylvestris var.mongolica-Larix gmelini was significantly greater than that of Rhododendron simsii-Larix gmelini and Ledum palustre var.decunbens-Larix gmelini(P<0.05).However there was no significant difference in R1 between the five types of Larix gmelinii forests(P>0.05).(3)In the five types of Larix gmelinii forest,the rates of contribution each respiratory components of soil to total respiration varied.Among them,Rh contributes the most to Rs,during the observation period,the average of rates of contribution of Rh to Rs ranged from 61.84%to 71.76%;Rm,is the main part of Rh,the average of rates of contribution of Rmto Rs ranged from 46.28%to 58.18%;But the average of rates of contribution of R1to Rs ranged from 8.34%to 15.57%.The rates of contribution of Rr to Rs was small,the average of rates of contribution of Rrto Rs ranged from 28.24%to 38.16%during the observation period.The rates of contribution of Rh is two times that of Rr.Therefore,heterotrophic respiration is the main part of soil respiration.During the observation period,although the contribution rates of soil respiration components of different types of Larix gmelini forests were different,but the differences were not significant(P>0.05).(4)The regression relation between total soil respiration(Rs)and soil temperature(T10)and soil humidity(W10)of top 10 cm in five typical larch forest types indicated that There was a significantly positive correlation(P<0.05)between soil respiration rate and the temperature of top 10 cm soil(T10).T10 could explain 43.6%-57.0%of seasonal variation for soil respiration.The Rs is sensitive to the change of T10 in the five types of Larix gmelini,the temperature sensitivity index(Q10)ranged from 2.29 to 3.29.But the correlations between the soil respiration rate and the soil humidity were different among the five types of larch forests.There were significant negative correlations between soil respiration and soil W10 in Betula platyphylla-Larix gmelini forest,Pinus sylvestris var.mongolica-Larix gmelini forest,and Ledum palustre var.decunbens-Larix gmelini(P<0.05)),but the correlation coefficients were very small,W10 could only explain 10.6%,11.6%and 24.3%of the seasonal changes in soil respiration of the three types of Larix gmelini forests,far below the influence of temperature on the respiration;There was no significant correlation between soil respiration and Wio in Rhododendron szimsii-Larix gmelini and Lach gmelini forest(P>0.05).This result showed that temperature was the main influence factor of soil respiration,while humidity had less effect on soil respiration.(5)The effects of letterfall on soil respiration in five types of Larix gmelinii forests were complex.The removal of letter did not affect the seasonal dynamics of soil respiration.However,after the letter-removal,soil respiration would be reduced,but the total soil respiration It would increase by 10.49%-17.94%,and the removal of letter could increase the T10 of five types of Larix gmelinii forests by 0.11?-0.53?,and it could increase the W10 of Betula platyphylla-Larix gmelini,Rhododendron simsii-Larix gmelini and Larch gmelini by 4.01%,22.55%,and 3.29%,respectively,while W10 of Pinus sylvestris var.mongolica-Larix gmelini and Ledum palustre var.decunbens-Larix gmelini forest decreased by 16.00%and 9.03%,respectively.After letter removal,there was higher correlations between soil respiration and Tio,at this time,T10 could explain 56.2%-62.4%of the seasonal dynamics of soil respiration of five types of Larix gmelini forests,but the temperature sensitivity index of soil respiration would be reduced.The Q10 of five types of Larix gmelinii forests was between 2.15?3.03.Whether the letter removal or not,W10 had weak effect on soil respiration.This showed that soil moisture is not a major factor affecting soil respiration in this area.