| Four in-door incubation experiments were performed in order to study the effects of organic matter and nitrogen amendments on the soil microbial respiration. The impacts of different temperature conditions on the microbial respiration of soil from different forests was investigated in the first experiment. In this experiment,5 types of forest soil samples (LS1, LS2, LS3, ZJS, and BHS) were selected and incubated at 5 temperature levels (5℃,10℃,15℃,20℃, and 25℃). The second experiment was conducted to investigate the effects of straw amendments on the soil microbial respiration. In this experiment, the soil samples for the incubation experiment were collected from a farmland. Five types of crop straws (rice, wheat, peanut, corn, and soybean) were added to the soil. In the third experiment, the effects of the straw and nitrogen amendments on the soil microbial respiration were investigated. Two types of straws (SD and XM) and three levels of urea (0.006 g, 0.012 g, and 0.024 g) were added to the farmland soil in this experiment. In the fourth experiment, the soil samples were collected from a mountain (named Long Wang mountain) to investigate the effects of litter amendments on the forest soil. In this experiment, five levels of litter (0 g,0.2 g,0.4 g,0.8 g, and 1.2 g) were added to soil. The activities of soil urease, invertase, and catalase and dissolved organic carbon (DOC) were measured after each round of incubation experiment to investigate the relationship between soil microbial respiration and enzyme activities.(1) Results of the first experiment showed that the variation patterns of the soil microbial respiration under different temperature conditions were similar. With the increase of incubation days, the increasing rate of soil microbial respiration decreased. This indicated that the emission rate of soil microbial respiration was relatively lower during the end of incubation period. At the different ranges of temperature conditions (i.e.,5～15℃,10～20℃,15～25℃), the Qio value of soil microbial respiration decreased with the increase of temperature. Further investigations showed that the relationship between the temperature sensitivity of DOC and Qio value of soil microbial respiration could be simulated by a significant (P= 0.039) linear regression function. The temperature sensitivity of DOC could account for 80.6% variations of Qio value. A very significant (P= 0.003) linear regression f between cumulative soil microbial respiration and DOC was found based on the comprehensive analysis of all the available data. For the individual soil and all soils, the relationship between cumulative soil microbial respiration and invertase activity could be explained by a highly significant (P<0.001) linear regression function, which suggests that invertase is a good indicator of the magnitude of soil microbial respiration.(2) The soil microbial respiration rate for the treatment with HS straw added was higher than that for the treatments with other straws, which may be due to the fact that HS straw had low hemicellulose content and C/N. The Qio value for the 1st day after adding straw was 1.632, and the Qio value for the 27st day was 1.467. With the increase of the incubation time, the Qio value showed a decreasing tendency, and the temperature sensitivity of soil microbial respiration. Soil microbial respiration showed an acclimation to the increase of temperature with the increase of incubation time. There was a highly significant and positive correlation between soil microbial respiration and DOC, and between soil microbial respiration and enzyme activities (P < 0.001), indicating that the DOC content and enzyme activities could be considered as good indicators for soil microbial respiration.(3) With the increase of incubation time, the cumulative soil microbial respiration showed obviously increasing patterns, which indicated that the soil continuously emitted CO2 during the whole incubation time. However, soil CO2 emissions were inhibited due to the nitrogen addition. On the basis of adding the same amount of urea, the cumulative soil microbial respiration for the SD straw added was slightly higher than that for the XM straw added. Soil temperature has a highest explanatory ability for soil microbial respiration with the addition of SD straw. An exponential regression function could be used for fitting the relationship between soil microbial respiration and DOC (P< 0.001). There was a highly significant linear regression relationship between soil microbial respiration and urease and invertase activities (P< 0.05).(4) Further investigations indicated that, under different temperature treatments, the soil cumulative microbial respiration without litter amendments was the lowest. The addition of litter increased soil microbial respiration. The Qio values for different treatments showed small differences. But the Q10 value for the soil without litter added was higher than that for the soils with litter added. The activities of urease, catalase, and invertase increased with the increase of litter amounts. Moreover, CO2 emissions also increased linearly with the increase of enzyme activities. There was a very significant positive correlation between cumulative soil microbial respiration and enzyme (urease, invertase, or catalase) activity (P< 0.001). |
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