Study on the monthly dynamic change of soil respiration rate of plum trees with different planting ages in rocky desertification area

Soil respiration is the main process of soil carbon emission and an important factor affecting the dynamic change of soil carbon pool and atmospheric carbon pool. The amount of soil respiration determines the source and sink of soil carbon pool to a certain extent. It is of great significance to understand the mechanism of soil organic carbon accumulation, via studying the dynamic changes of soil respiration in fruit trees with different planting ages in karst areas. In this study, the soils samples of plum trees with different planting ages (i.e. 2 a, 5 a and 20 a, respectively) in the process of rocky desertification control in Gongcheng county, Guilin were selected as the research objects. The soil respiration rates were monitored on a monthly basis by using alkali absorption method from which the influencing factors were investigated and the data were analyzed by one-way analysis of variance (ANOVA) method. The results show that， (1) In a year time, the soil temperature and soil water content show a completely opposite seasonal trend, the change of soil respiration rate of the plum trees with different ages is basically consistent with the change of month, showing a multi-peak shape. On a seasonal scale, the soil respiration rate decreased gradually with the alternation of spring, summer, autumn and winter; (2) The planting ages of the plum trees have influence on soil respiration rate to different extents. The soil respiration rates of 2 a, 5 a and 20 a are 48.56 mgC·(m2·h)-1,45.63 mgC·(m2·h)-1 and 41.64 mgC·(m2·h)-1, respectively. This may be attributed to the higher soil respiration rate of the trees in their young stages (2 a) and full fruiting period (5 a), who require more carbon sources and nutrients for plant growth than the older ones（20 a）. The higher respiration rate reflects higher organic metabolism and material circulation. Compared the plum trees of 2 a and 5 a, the underground ecosystem of the 20 a tree is relatively stable; and the soil respiration rate of the latter slightly decreases； (3) In the same period of high soil heat and high rainfall from April to August, there is a significant negative correlation between soil temperature and soil water content (P < 0.01), a significant negative correlation between soil temperature and soil respiration rate (P < 0.01), and a significant positive correlation between soil water content and soil respiration rate (P < 0.01), which are mainly caused by the lag effect of soil respiration on time scale.