Effects Of Conversion From Paddy Fields To Lei Bamboo(Phyllostachyspraecox) Stands On The Soil Carbon Pool And Soil Respiration

Land use change has a very significant impact on the carbon cycling in ecosystemsand global climate change. Soil carbon storage has the2-3times capacity of theatmospheric carbon pools, and the process of soil respiration is regarded as the mainpathway to the emission of pedosphere carbon into the atmosphere. Study on the effectsof land use change on soil carbon pools and soil respiration rate would have a veryimportant significance for revealing the response of ecosystems to land-use change andassociated mechanisms, and scientific estimates of regional ecosystem carbonsequestration. Lei bamboo （Phyllostachys praecox C.D. Chu et C.S. Chao） is a bamboospecies widely distributed in southern China. The shoot of his bamboo species isdelicious and nutrient-rich, and its production has a higher economic value. In the recentyears, more and more paddy fields have been transformed into Lei bamboo stand.Intensive management measures including fertilizer application and mulching of organicmaterials was mostly applied in the production of Lei bamboo, which will probably havea have a significant impact on the soil carbon pools and soil respiration rate. In thepresent study, soils from replicated adjacent paddy fields and bamboo forests with aknown land-use history were sampled. Soil different labile carbon pools, nutrients poolsand other basic soil properties were determined. Soil organic carbon functionalcompositions were determined by the13C-NMR （nuclear magnetic resonance） technique.Additionally, one-year location test was carry out to study the dynamic change in soilrespiration and environmental factors （including temperature, moisture and water-solubleand dynamic changes of today）, and the relationships between soil respiration rate andenvironmental factors in the above-mentioned two land-use types were discussed. Themain results obtained are as follows:1. Conversion of paddy fields to bamboo stands significantly increased the differentcontents of nitrogen forms （including total nitrogen, water-soluble organic nitrogen,NH4+-N content, and NO3--N）, available phosphorus and potassium contents （P <0.05）,but different soil layers （0-20cm,20-40cm and40-60cm） showed the increase ratedifferently in some extent. The WSOC content was not different between the twoland-use types in the0-20cm soil layer, but was lower in the bamboo forest soils in theother two soil layers. Hot water soluble organic C （HWSOC） and microbial biomass C （MBC） contents were not different between the two land-use types in any soil layerstudied （Fig.4B and4C）. The readily oxidizable C （ROC） content in the0-20cm soillayer was higher in bamboo forest than in the paddy soil （P <0.05）.2. Solid state NMR spectroscopy of soil samples showed that All four NMR spectraof soils in both paddy fields and bamboo stands included four significant resonance areasor organic carbon forms: alkyl C （0–50ppm）, O-alkyl C （50–110ppm）, aromatic C（110–160ppm）, and carbonyl C （160–220ppm）. Significant differences in the signalintensity of different carbon forms were observed between the two land-use types insome soil layers.The soil organic C was dominated by O-alkyl C in both paddy fields andbamboo stands. The contents of O-alkyl C significantly increased （P <0.05） while that ofaromatic C, alkyl C to O-alkyl C ratio （A/O-A）, and aromaticity of organic mattersignificantly decreased （P <0.05）, indicating that the stability of organic C decreasedafter the above-mentioned land-use change.3. The one-year experiment results showed that the soil respirations of rice fieldsand lei bamboo forests had significant seasonal variations. However, the trends of thetwo showed significant difference. The soil respiration rate changes of lei bamboo forestswas correspondent with the temperature changes in soil, while the seasonal changes insoil respiration were more complex due to the impact of dramatic changes in soilmoisture. The cumulative total CO₂emissions of the yearly soil respiration of rice fieldsand lei bamboo forests were45.4t CO₂ha^-1yr^-1and34.7t CO₂ha^-1yr^-1, respectively.The daily variation of soil respiration of rice fields and the lei bamboo forests showedcertain regularity: being high during the day and low the night. But there were somechanges in the time period of the appearance of maximum soil respiration in differentdates.4. The relationship between the soil respiration rate of lei bamboo forests of and thelayers of soil temperature （including the surface temperature, the temperature of the soilsurface of5cm,10cm of the soil surface temperature at20cm of the soil surfacetemperature） were highly significant （P <0.01）, while the relationship between the soilrespiration rate of rice field and the different layers of soil temperature were insignificant. However, the relationship between the soil respiration rate of rice field and the differentlayers of soil temperature were significant （P <0.01）, discounting the eight measuredpoints in the rice fields during the flood. This suggested that the dramatic changes of thesoil water content in the rice field impact the relationship between temperature and soilrespiration significantly. The related analysis showed that: the relationship between the ricesoil respiration rate and soil volumetric water content was significantly negatively related,while the relationship between the lei bamboo soil respiration rate and soil volumetricwater content was insignificant. In addition, the relationship between the soil respirationrate of those two land uses and water-soluble organic carbon content of the soil wasinsignificant.