Effects Of Soil Warming On Specific Respiration Rates Of Fine Roots In Chinese Fir (Cunninghamia Lanceolata) Seedlings

In order to reveal the belowground responses and the adaptability of Chinese fir(Cunninghamia lanceolata)plantation to global warming,a field mesocosm experiment consistsing of the soil warming(W,ambient+4 ℃ carble warming)and the control(CT),each with 6 replicate 2.5×2.5 m mini-plots,was conducted in Chenda State-Own Forest Farm,Sanming,Fujian Province,which based on the forecast in the IPCC fourth assessment report by the end of the century that the global mean surface warming would increase 0.3-4.8 ℃(IPCC,2013).According to the growing season,the fine root metabolism characteristics(specific respiration rates of fine roots and nonstructural carbohydrates),fine root morphological characteristics(specific root length,specific surface area,root tissue density),stoichiometry(C,N,C/N)of two varieties(three generations seedlings and short side branches)were determined by destructive sampling.In order to explore the effect of warming on the respiration of Chinese fir,and the mechanism.The results showed that:(1)Soil warming cause different effect on the morphology of Chinese fir seedlings depending on different seasons.For the three generations of seedling,soil warming had no significant effect on the specific root length and specific surface area,and the root tissue density decreased significantly in the winter and spring.During summer,soil warming increased the specific root length,reduced the specific surface area and increased the root tissue density significantly.The specific root length,specific surface area and root tissue density of the short lateral branch were not significantly affected by soiling warming in summer.After soil warming,the specific root length,the specific surface area significantly decreased in winter,the root tissue density increased significantly.In spring,the specific root length and the specific surface area increased significantly,and the root tissue density did not change significantly.In autumn,the specific root length and the root tissue density increased significantly,and the specific surface area did not change significantly.The effect of soil warming on the morphological characteristics of short lateral branches was more significant.(2)The interaction between the seasons,soil warming,season and soil warming had significant effects on the carbon,nitrogen and carbon nitrogen ratios of three generations of seedlings and short lateral branches.Among winter,spring,autumn,soil warming makes fine root nitrogen content of the three generations of seedlings and the short lateral branch increased significantly,however during the summer,the nitrogen of the three generations of seedling instead dropped significantly after soil warming,short lateral branch did not differ significantly between the two treatment.Because of the increase of fine roots N concentration,which reduces the carbon concentration of fine root.After soil warming,the carbon concentration of fine root of the three generations of seedling reduced significantly in winter and spring and autumn,the content of fine root carbon decreased significantly,and no significant influence was found in other season.(3)The four samples showed no significant influence on the concentration of fine root NSC and the ratio of soluble sugar to starch of Chinese fir seedlings.In summer and autumn,there was no significant effect on the concentration of soluble sugar and starch.During the winter,the starch content of fine root was significantly reduced,and the soluble sugar of three generations of seedlings did not change significantly,but the short side branches increased significantly.In spring,after soil warming,three generations of seedlings and short lateral branch were significantly reduced in soluble sugars,and there was no significant difference in the content of starch content.(4)The season,soil warming,variety and the interaction of soil warming and variety has a significant effect on the respiration of three generations of seedlings and short lateral branches.In the cold winter,soil warming had no significant influence on fine root respiration of Chinese fir seedling,and in spring and autumn,soil warming significantly promoted the fine root respiration,but in summer,root respiration of the three generations acclimated partly.For fine root respiration of the short lateral branch,there were no significant differences between the two treatment.Correlation analysis results show that the sampling time,fine root nitrogen content and soluble sugar concentration has remarkable effect on the specific root respiration rate.The specific root respiration rate of short lateral branch seedlings was less than three generations on the whole.Among four sampling time,The specific root respiration rate of the third time is the highest in summer.In contrast,the specific root respiration rate of the control treatments was less than warming,and the specific root respiration rate was positively correlated with the nitrogen concentration of fine root,which was negatively correlated with the soluble sugar content.In conclusion,soil warming can improved the nitrogen availability of topsoil,and enhances the nitrogen concentration of fine root,thus promote the fine root respiration;but decreased soil moisture availability which limited fine root respiration.In summer,due to the combined effects of soil warming and ambient temperature,fine root reduce per unit mass root maintenance by reducing nitrogen,causing fine root respiration domesticated.Because of there were significant differences about aboveground growth,the difference between varieties had significant effect on the fine root respiration of Chinese fir seedlings,Thus,the underground carbon distribution is affected.The difference of SRR between different varieties of Chinese fir was mainly related to the concentration of fine root N and the concentration of soluble sugar.Three generations of seedlings are more temperature-sensitive to global warming.