| With increasing atmospheric CO2concentration in recent years, studies of stem respiration have become popular. As one of the key physiological processes, stem respiration play an important role in controlling the annual carbon balance of forest ecosystem. The influencing factors of stem respiration and its respone to management measures play an important role in studying the carbon balance of global ecosystem and its effects on global change has important scientific significance. This paper takes larix principis-rupprechtii of different age groups (young forest, mid-maturation forest, nearly cooked) as the researeh object in Sihanba mechanical forest farms. Spatio-temporal variations of stem respiration rates for larix principis-rupprechtii were studied in this paper by using Li-8100carbon flux auto-system, relationships between stem respiration rates and environmental factors were analyzed. The results showed that:1. The temporal variations of stem respiration rates of larix principis-rupprechtii:The diurnal variation of stem respiration rate of larix principis-rupprechtii showed single peak curve model, which was consistented with the temperature. The peak located at14:00to18:00, and low peak located at2:00to6:00the next day. Daily average in each month respectively:stem respiration rate of13-year-old rang from3.24to7.83μmol·m-2·s-1, stem respiration rate of22-year-old rang from2.61to3.61μmol·m-2·s-1, stem respiration rate of38-year-old rang from2.16to3.49μmol·m-2·s-1. The seasonal variation of stem respiration rate of larix principis-rupprechtii showed unimodal curve model, and peak in July (young forest) and August(mid-maturation forest and nearly cooked), then stem respiration rates declined. The stem respiration average rates of different age were4.35,2.65and2.41μmol·m-2·s-1.2.The spatial variations of stem respiration rate of larix principis-rupprechtii:The stem temperature difference between the south side and the north side of larix principis-rupprechtii in different age stand were0.07,0.06and0.30℃. The south stem respiration rate is higher than the north in all ages, each acount for13.52%、8.87%、37.32%. The order of stem respiration rate with height of the trunk was H3.5m>H0.1m>H1.3m>H2.5m.The stem respiration rate of all stand, but from13-year-old stand, decreased with the increase of thinning intensity. There was no significant difference in stem respiration with thinning intensity in all ages.3.Stem respiration rates of larix principis-rupprechtii in different ages:Stem respiration rate of the young larch stand was significantly higher than the other larch stand, they were13-year-old (4.35μmol·m-2·s-1)>22-year-old(2.65μmol·m-2·s-1)>38-year-old(2.41μmol·m-2·s-1). 4. Relationships between stem respiration rate of larix principis-rupprechtii and main environmental factors:Temperature is the main influence factor to stem respiration rate of larix principis-rupprechtii. The Q10values of stem respiration rate of13-year-old stand was1.59,2.15,6.07, for air temperature, soil temperature and stem temperature respectively. In addition, the22-year-old stand was1.7,2.12,6.45; the38-year-old stand was1.6,1.7,2.61. The stem perature can explain83.9%to96.6%monthly variation of stem respiration. There was no significant difference between stem respiration rate and soil moisture content. A significant negative correlation was found between stem respiration and air humidity t(P<0.05).5. To distinguish between maintain respiration and growth respiration:The maintain respiration rate and growth respiration rate of13-year-old stand was0.28,4.17μmol·m-2·s-1,and the13-year-old stand was0.34,2.65umol·m-2·s-1; the13-year-old stand was0.39,2.41μmol·m-2·s-1. Each maintain respiration account for an annual average total stem respiration6.47%,13.02%and16.46%.6. Estimation of the total amount of stem respiration of larix principis-rupprechtii with different ages:The diurnal release of CO2generated from stem respiration showed unimodal curve model, and peak in July (young forest) and August(mid-maturation forest and nearly cooked),13-year-old (109.39kgCO2·hm-2·d-1),22-year-old (79.71kgCO2·hm-2·d-1),38-year-old (89.89kgCO2·hm-2·d-1). The annual CO2emission of stem respiration of larix principis-rupprechtii in different ages were24.41,15.76,16.08tCO2·hm-2·y-1. |
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