| It was important and significance to partitioning root-derived respiration to autotrophic and heterotrophic respiration in the soil respiration evaluation of terrestrial ecosystem carbon balance quantitatively. Although in recent years studies on rhizosphere priming effect has achieved a certain degree of cognition, but little knowledge about the priming effect of forest plantation soil respiration of North China play a role and its ecological significance in the global carbon cycle has been known. The nature 813C abundance method of microbial biomass is a suitable way that can be applied under field conditions to partition rhizosphere respiration. But it is difficult to be applied in the field practice. In this study, the Robini.a pseudoacacia plantation in the Yellow River Xiaolangdi Ecology Research Station was chosen as the research object, the nature δ13C abundance method for partitioning plantation soil respiration to root respiration, rhizomicrobial respiration and basal microorganism respiration was proposed and demonstrated under the field condition; and analyzed the variations in different months and different depth of root respiration, rhizomicrobial respiration and basal microorganism respiration; discussed about the influence of autotrophic and heterotrophic respiration to soil temperature, moisture content and soil depth. The results showed:(1) In this study, a suitable method for partitioning plantation soil respiration to root respiration, rhizomicrobial respiration and basal microorganism respiration in North China were deduced. The method according to the principles of natural 13C fractionation, combined with the linear two components mixing model distinguish method suitable for application in artificial forest derived, was verified successfully.(2) The soil organic matter (SOM) δ13C values did not change significantly with soil depth, but there was a significant positive correlation between the rootless SOM δ13C values and depth (R2=0.970, p<0.001). And the δ13C values fractionation of Robinia pseudoacacia roots decreased linearly with depth (R2=0.793,p<0.001). It was indicated that the influence of SOM decomposition decreasing with soil depth.(3) The proportion of each parts of soil respiration components at the same depth and different locations remained invariable. The proportion of rhizosphere respiration to the total soil respiration increased and the proportion of basal respiration decreased with soil depth significantly. It was showed that the more deep the soil, more effects on the release of carbon.(4) Both the root respiration and rhizomicrobial respiration were varied as fold lines. There were priming effect existed in deeper soil of the plantation, and the proportion of autotrophic respiration and heterotrophic respiration derived by priming effect varied with depth and month. The priming effect in deeper soil was too large to ignore. Such phenomenon may be related to the "Nitrogen mineralization" mechanism of priming effect.(5) The relationship between basal respiration, rhizosphere respiration, rhizom icrobial respiration and soil temperature was not significant. The first half of the growing season (April, May, June) of root respiration was significant increased with temperature linearly and the other half of the growing season (July, August, September) was showed binomial relationship significantly. This shows that in the different stages of the plant growth, plant root can adjust the temperature sensitivity of the respiration which direct controlled by root (root respiration). No significant variation of rhizomicrobial respiration and basal respiration with soil temperature, but their combination (microbial respiration) was positive correlated with soil temperature significantly.(6) No significant relationship was shown between root respiration and soil moisture content, also between rhizosphere respiration and soil moisture content. The basal respiration was positive correlated with soil water content (R2=0.946, P<0.001) in May to September, rhizomicrobial respiration had exponential negative correlation (R2=0.868,p<0.001) with soil water content significantly.(7) Root respiration, rhizomicrobial respiration and basal microorganism respiration are three different biological processes. Therefore, their responses to soil temperature and soil moisture content variations were not the same. Separating root respiration and rhizomicrobial respiration was necessary to the study about the soil respiration response to the environment factors. "Nitrogen mineralization" is the main mechanism to control the rhizosphere priming effect in the plantation. |
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