Characteristics Of Coarse Woody Debris Decomposition And Respiration Of Two Tree Species At Liuxihe

Coarse woody debris(CWD)is the sinks of carbon(C)and nutrients in forest ecosystem.CO2 released by CWD respiration is the main route for the loss of C,which has a significant influence on the global C cycle.Based on the analyses of density loss and infrared gas,we observed the characteristics of decomposition process and respiration rate of Pinus massoniana and Lithocarpus glaber CWD in Liuxihe.In particular,we described the decomposition rate and release of nutrient elements,analyzed the seasonal dynamics characteristics of CWD respiration and the response of respiration rate to temperature and discussed the effects of temperature and elemental composition on CWD respiration(RCWD)of the two tree species.The results were summarized as follows:(1)With the progress of the decomposition,the density of two tree species decreased,and chemical properties of CWD had changed.The density of L.glaber was significantly greater than that of P.massoniana,and the decomposition rate was also greater than that of P.massoniana.The decomposition constants of P.massoniana and L.glaber are about 0.056~0.148 and 0.105~0.161,and the time for the decomposition amount of 95% are 20~53 a and 18~28 a respectively.During the process of decomposition,the C content of L.glaber decreased significantly,while the N and P contents of 2 tree species did not change significantly.From short-term observation of 1 year,C content decreased to some extent,and N and P contents increased with varying degrees.(2)The dynamics of RCWD of P.massoniana and L.glaber were consistent with the trend of seasonal temperature,which showed a unimodal curve pattern.The temperature has a good explanation for the RCWD.There is a significant positive correlation between RCWD and temperature(p<0.01),and the temperature can explain the 64.0%~75.6% and 69.3%~86.2% of the respiration of P.massoniana and L.glaber respectively.The difference of RCWD for the 2 tree species was significant,and the RCWD of the L.glaber was higher than that of P.massoniana.But annual variation in RCWD of P.massoniana was smaller than that of L.glaber.The chemical element content of CWD affects its respiration rate.N,P,C/N,C/P and N/P between P.massoniana and L.glaber were significantly different(p<0.05),but C content had no significant difference.RCWD and C content had a strong negative correlation,the correlation coefficient R2 was 0.318.There are strong positive correlations among RCWD N and P content(p<0.05).The correlation coefficient R2 are 0.638 and 0.471.The most significant negative correlation among RCWD,C/N and C/P(p<0.01),the correlation coefficient R2 are 0.746 and 0.633.but there is no significant correlation between RCWD and N/P.(3)Under the laboratory conditions,the respiration rate of P.massoniana and L.glaber was consistent with the temperature dynamic,and the respiration rate of the L.glaber at all temperatures was greater than that of P.massoniana.At 5~25℃,RCWD increased along with the rise of temperature,and the RCWD have a significant positive correlation with temperature(p<0.01).RCWD showed a trend of decreasing along with the change of temperature between 35~45℃.The range of Q10 values at different temperature ranges for P.massoniana and L.glaber was 0.40~6.50 and 0.47~3.17,respectively.There was no significant correlation between Q10 values and decay classes,but a significant correlation between Q10 value and temperature range.The RCWD of the two tree species are most sensitive to temperature in the range of 15~25℃.When the temperature exceeds 35℃,the respiraton rate will be less sensitive to temperature.CWD has a long decomposition time,and the decomposition process is complex.There are many factors affecting its decomposition and respiration.The temperature,chemical properties and water content of tree species have a great influence on CWD decomposition.To further understand the process and control factors of CWD decomposition,it is necessary to establish a Long-term plots for observations,meanwhile it requires the integration of multiple disciplines to carry out more research(especially microbiology).