| This experiments was conducted on the young-growth Eucalyptus sp. forest (ASYS(4a)), old-growth Eucalyptus spp. forest (ASYs(20a)), Pinus massoniana forest (MWSYS(22a)) in Yaoshan mountain of Guilin, and on the Eucalyptus sp. forest (ASLC(4a)), Pinus massoniana forest (MWSLC(30a)), Cunninghamia lanceolata forest (SMLC(25a)), Phyllostachys heterocycla forest (MZLC), the broadleaf forest (KYLLC) in Lingchuan of Guilin, and on the Eucalyptus sp. forest (ASBH(4a)) in Beihai. From July2012to December2013, the soil respiration and its components, the soil temperature and the soil moisture content of the nine forests had been observed. We analyzed the characteristics on soil respiration and its components in diurnal dynamics, in each month and in each seasons, and analyzed the relationships between main environmental factors and soil respiration. Finally, annual soil respiration carbon flux of each forests had been estimated. The main study results were as follows:(1) In Yaoshan mountain of Guilin. the characteristic on soil respiration in each month of the three forests were similar, the maximum value of soil respiration rate occured in July, the minimum value of soil respiration rate occured in December or January. Overall, soil respiration rate and its components could be expressed as a single-peak curve. Analyze the relationships between environmental factors and month changes of soil respiration shows that:Soil respiration rate and its components had significant exponential correlation with soil moisture content in the three forests. Soil respiration rate and their soil moisture content were not significant in ASYS (4a) and MWSLC (30a), ASYS (20a) has notable positive correlations between soil respiration rate and soil moisture content. In terms of respiratory components and soil moisture content, the autotrophic respiration and their soil moisture content were not significant in the three forests; It was notable positive correlations between heterotrophic respiration rate and soil moisture content in ASYs(20a), and It was notable negative correlations between heterotrophic respiration rate and soil moisture content in MWSLC (30a).(2) Soil respiration has obvious seasonal characteristic. The soil respiration rate of all forests showed that soil respiration rate were highest in summer, and there were lowest in winter, soil respiration rate could be expressed as a single-peak curve. Soil respiration rate were as following order:MZLC>ASBH (4a)>KYLLC>ASYS(4a)>MWSYS(22a)>ASYS(20a)>MWSLC(30a)>SMLC(25a)> ASLC(4a). In different latitudes of the study area (Beihai, Yaoshan mountain of Guilin and Lingchuan), Eucalyptus sp. forest’s soil respiration rate showed that:Eucalyptus sp. forests at low latitudes (Beihai), Soil respiration rate is greater than the high-latitude regions Eucalyptus sp. forests (Yaoshan mountain of Guilin and Lingchuan); In the same study area (Lingchuan), different forest’s soil respiration rate showed that:the soil respiration rate of the native broadleaf forests(MZLC, KYLLC) were greater than native coniferous forests (MWSLC(30a), SMLC(25a)); Soil respiration characteristics of different forest age of Eucalyptus sp.(Yaoshan mountain of Guilin)showed that: young-growth forest soil respiration rate is more than old-growth forests.In this study, case study of the three forests in Yaoshan mountain of Guilin showed that:There were not significant difference on the soil respiration rate among the three forests in Yaoshan mountain of Guilin. But in autumn and winter, Soil respiration rate of the ASYS(4a) and the MWSys(22a) were notable higher than the ASys(20a), There were not significant difference between the ASys(4a) and the MWSys(22a); In terms of autotrophic respiration, each season were showed that:the autotrophic respiration rate of the ASys(4a) was higher than the ASYS(20a) and the MWSYS(22a), and the MWSYS(22a) was higher than the ASys(20a) in spring and summer; In terms of heterotrophic respiration, The heterotrophic respiration rate of the ASys(20a) was higher than the ASYS(4a) and the MWSys(22a) in spring and summer, but the heterotrophic respiration rate of the MWSys(22a) was higher than the ASys(4a) and the ASys(20a) in autumn and winter; According to correlation analysis, There existed exponential relationships between the soil temperature and the soil respiration rate in all seasons. In terms of temperature sensitivity, The value of the ASYS(4a) was the highest, and the MWSys(22a) was the lowest in spring and summer, but in autumn and winter, the value of the MWSys(22a) was the highest, and the ASys(4a) was the lowest; In spring and summer, soil moisture content didn’t have a significant influence on the soil respiration rate in the ASys(4a).There was notable positive correlations between soil respiration rate and soil moisture content in the ASys(20a), and there was notable negative correlations between soil respiration rate and soil moisture content in the MWSys(22a), but in autumn and winter, there was notable negative correlations between soil respiration rate and soil moisture content in the three forests.(3) The diurnal variation of soil respiration could be expressed as a single-peak curve in the ASys(20a). In four seasons, the maximum value of soil respiration appeared at17:00-19:00, and the minimum value of soil respiration appeared at5:00～9:00. The soil respiration was high and changed by a large margin during the day, but low and fluctuation within a narrow range in the night; There were significant differences between the four seasons Carbon emissions of soil respiration, the results showed that:summer> spring> autumn> winter; There existed positive correlation index exponential relationships between the soil temperature and the soil respiration rate in spring and autumn, But in summer and winter; the soil temperature didn’t have a significant influence on the soil respiration rate; Soil moisture content didn’t have a significant influence on the soil respiration rate and its components in four seasons.(4) The soil temperature was the main environmental factor influencing the soil respiration rate. All forests, except ASLc(4a) autotrophic respiration excessive interferenced by human factors, performanced no significant relationship between soil temperature outside, There existed significant or highly exponential relationships between the soil temperature and the soil respiration rate. In terms of temperature sensitivity, In different latitudes of the study areas of Eucalyptus sp. plantations soil temperature sensitivity showed that: Eucalyptus sp. plantations at high latitudes ASYS(4a), Soil temperature sensitivity coefficient was greater than ASBH(4a), the low-latitude regions Eucalyptus sp. plantations; In the same study area, different forest’s temperature sensitivity coefficient showed that:the evergreen coniferous forest was larger than evergreen broadleaf forest; Eucalyptus spp. plantations’ soil temperature sensibility of different forest age showed that, old-growth plantation’s Q10value was greater than young-growth plantation.(5)The soil moisture content was also an environmental factor influencing the soil respiration rate. In this study, in addition to ASYS(4a), MWSYS(22a) and ASLC(4a), the three forests’ soil respiration rate and their soil moisture content were not significant. And in the remaining forests, there were notable positive correlations between soil respiration rate and soil moisture content. Analysis of the relationship between the soil respiration rate and soil moisture content showed that:soil moisture content had a huge impact on the soil heterotrophic respiration rate. In the study, in addition to ASYS (4a), soil heterotrophic respiration rate had significant or highly significant correlation with soil moisture content in the remaining forests. But in terms of the soil autotrophic respiration, only KYLLC, MWSLC(30a) and ASBH(4a) which had notable relationship between the autotrophic respiration rate and the soil moisture.(6)The annual soil respiration rate and carbon emissions for each study area of three stands were the same. The annual soil respiration carbon emissions of MZLC was the maximum, the ASLC (4a) was the minmum. From Lingchuan research points to broadleaved forest (KYLLC) the annual soil respiration and carbon emissions were higher than native conifer species forests (MWSLC (30a), SMLC (25a)); seen from Guilin Yaoshan study, the young-growth plantation, ASYS (4a) of the annual carbon emissions were greater than the old-growth plantation (ASYS (20a)), while the annual soil respiration and carbon emissions of the age-grade Pinus massoniana forest (MWSYS (22a)) were higher than the old-growth Eucalyptus spp. plantation (ASYS (20a)); the annual carbon emissions from soil respiration of the young-growth Eucalyptus sp. plantation (ASBH (4a), ASYS (4a), ASLC (4a)) showed a decreasing trend with the increased latitude; In tending management measures, clearing understory shrub and grass (eg:ASLC (4a) the annual carbon emissions were lower than the ASYS (4a) which was not tended), maked for the less carbon emissions of soil respiration. |
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