The Research Of Soil And Fine Root Respiration Of Forest Mode In Converting Farmlands To Forest

The IRGA(infrared gas analyzer) research methods were carried out to measure soil respiration and fine root respiration in three different complex ecosystems ((Betula luminifera+ Hemarthria compressa, Betula luminifer + Pleioblastus amarus, Betula luminifer) in converting farmlands to forest in Sichuan basin in Hong-Ya county (29°24′N, 102°49′E) in this article. Some influenced factors as air and soil temperature, soil water content, soil SOM and total N contents, free root biomass, fine root N concentration were measured to analyze the relationship with soil respiration and fine root respiration. From this study these results were gained:There were significant seasonal dynamic during the research period (April 2006 and August to December 2006) of the different complex ecosystems. The maximum values were obtained in August (the mean values in three sites were 8.25, 6.69, 4.95μmol·m^-2·s^-1), and then decreased in October, the minimum values were measured in December (1.49, 1.17, 0.96μmol·m^-2·s^-1). The same as controlled treatment, the soil respiration in trenched treatment were also showed a clearly seasonal dynamic, the maximum values were appeared in August (2.10, 1.83, 1.49μmol·m^-2·s^-1), then decreased, there was a sharply reduction in October, the minimum soil respiration rate were obtained in December (0.86, 0.72, 0.57μmol·m^-2·s^-1).There were significant correlation between soil respiration and temperature (air and soil temperature) , and the soil respiration increased exponentially with air and soil temperature respectively(Rair temperature=0.512, 0.628, 0.204, P＜0.01, Rsoil temperature=0.528, 0.645, 0.192, P＜0.01). Compared to air temperature, the correlation between soil temperature and respiration was higher. This was because soil temperature could give better description of soil condition to roots and soil microbe.Soil water content and soil nutrient condition also affected soil respiration rate. There was a linear correction between soil respiration and soil water content in different forest mode (R=0.884, 0.906, 0.850, P＜0.01). A significant correction between soil respiration and soil organic matter content and total nitrogen content were obtained. The correction decreased with soil depths in SOM and total N.The respiration of excised fine roots were measured with a LI-COR 6400 at three sites of complex ecosystem of converting farmlands to forest in Sichuan basin in Hong-Ya county (29°24′N, 102°49′E) from March to December 2006. The air temperature, soil temperature of upper layer (5cm), soil water content, biomass of the fine-roots and fine-roots N concentration were analyzed at the three sites.Fine-root CO₂ efflux were 0.4—2.1μmol·m^-2s^-1, differed between sites, but fine-root respiration at three study forest types showed a clearly seasonal variation. Maximum values were obtained in August (the mean values in three sites were 1.83±0.12, 2.03±0.15, 1.88±0.14μmol·m^-2·s^-1), and then decreased in October, the minimum values were measured in December(0.39±0.18, 0.56±0.20, 0.48±0.17μmol·m^-2·s^-1). There were a significant correlation between free-roots respiration and temperature (Rair=0.643, 0.72, 0.676, Rsoil=0.66, 0.75, 0.722, P＜0.01), and the respiration of fine-roots increased exponentially with air and soil temperature respectively. Compared to air temperature, the correlation between soil temperature and respiration was higher.Contrary to our prediction, soil water content did not appear fine-root respiration at three sites; this phenomenon may be caused by the research error. In the study, a clearly relationship between fine roots respiration and free root biomass were found across sites and soil depths, the correlation was significant, and the Correlation between fine root respiration and fine root biomass was decreased with soil depths. The relationship was the most in the upper layer, the least in the lower layer. A positive relationship between tissue N concentration and fine root respiration was reported in this research, which was significant (P＜0.01), since the variation in free root N concentration between plants and times of year was small.