[Multi-year measurement of soil respiration components in a subtropical secondary forest].

A four-year field experiment was performed from March 2010 to February 2014 in order to investigate the contribution of different respiratory components to soil respiration and the temperature sensitivity of different respiratory components. Four blocks were arranged in field, and there were trenched and un-trenched plots in each block. Trenching, which can exclude roots, was performed around the trenched plots. A portable soil CO2 fluxes system ( Li-8100) was used to measure soil respiration rates. Soil temperature and soil moisture were simultaneously observed when measuring soil respiration rates. The results showed that the heterotrophic respiration rate in the trenched plots and the soil respiration rate in the un-trenched plots had the same seasonal pattern. Soil respiration rate in the un-trenched plots was significantly (P < 0.001) higher than that in the trenched plots. Mean soil respiration rates in untrenched plots and mean heterotrophic respiration rate in trenched plots were (2.59 ± 0.48 ) and (1.74 ± 0.28) µmol x (M2 x s)(-1), respectively. There was no significant (P > 0.05) difference in the mean soil respiration rate or mean heterotrophic respiration rate between measurement years. The relationship between heterotrophic respiration and soil respiration could be fitted with a proportion function. Heterotrophic and autotrophic respiration contributed 65.9% and 34.1% to the soil respiration, respectively. The main contributor to soil respiration was heterotrophic respiration. The relationship between the ratio of heterotrophic respiration to soil respiration and measurement date could be fitted with a linear function. An exponential function could be used to fit the relationship between heterotrophic respiration and soil temperature, and between autotrophic respiration and soil temperature. The temperature sensitivity coefficient (Q10) for heterotrophic respiration was lower than that for autotrophic respiration.

[Effects of simulated warming on soil respiration in a cropland under winter wheat-soybean rotation].

This study was aimed to investigate the effects of simulated warming on soil respiration in a cropland under winter wheat-soybean rotation. Randomized experiments were carried out in the cropland. 6 Plots were arranged and there were 2 treatments, simulated warming and control. A portable soil CO2 fluxes system (LI-8100) was used to measure soil respiration rates. Soil CO2 production rates were determined by using a Barometric Process Separation (BaPS) method. Soil temperature and soil moisture were simultaneously determined when measuring soil respiration rates. Results indicated that soil respiration rates in different treatments showed similar seasonal variability, in accordance with the variability in soil temperature. Seasonal mean soil respiration rates for simulated warming and control treatments were 3.54 and 2.49 micromol x (m2 x s)(-1), respectively, during the winter wheat growth season, while they were 4.80 and 4.14 micromol x (m2 x s)(-1), respectively, during the soybean growth season. Simulated warming significantly (P < 0.05) enhanced soil respiration during both the winter wheat and soybean growth seasons. The impact of simulated warming on soil respiration was particularly obvious during the later growth stages of winter wheat (from heading to maturity stages) and soybean (from flowing to maturity stages). Further investigations suggested that, for both the winter wheat and soybean growth seasons, the relationship between soil respiration and soil temperature could be well explained (P < 0.01) by exponential functions. The temperature sensitivity (Q10) of soil respiration in the simulated warming treatments was significantly higher than that in the control treatments. The Q10 values for the simulated warming and control treatments were 1.83 and 1.26, respectively, during the winter wheat growth season, while they were 2.85 and 1.70, respectively, during the soybean growth season. This study showed that simulated warming significantly increased soil respiration in the cropland.

[Review of the factors influencing the temporal and spatial variability of soil respiration in terrestrial ecosystem].

Soil respiration is an important process in carbon cycling. Understanding the processes and controlling factors of soil respiration are crucial in investigating the terrestrial carbon cycling. This article reviews the investigations about the factors controlling the temporal and spatial variability of soil respiration. The temporal and spatial variability in soil respiration is linked with climate, vegetation and soil factors. Air temperature and precipitation generally contribute great to the variability of soil respiration. Leaf area index (LAI), litter fall and fine root biomass are three plant-related factors that can be employed to explained the variability of soil respiration, while soil carbon content and texture are two soil factors responsible for the variability of soil respiration. Generally, climate, vegetation and soil factors contribute collectively to the temporal and spatial variability of terrestrial soil respiration. Temperature and precipitation, on the one hand, directly affect the root and microbial respiration rates. On the other hand, temperature and precipitation indirectly affect soil respiration by influencing the plant and microbial growth and soil conditions. In order to understand the controlling factors of the temporal and spatial variability of soil respiration, there are four main issues need to be addressed. The issues include quantitatively partitioning the autotrophic and heterotrophic components of soil respiration, standardizing the method and scale of measuring soil respiration, coupling measurements of soil respiration with environmental factors and performing more measurements of soil respiration in wetland ecosystems.

[Investigation of heterotrophic and autotrophic components of soil respiration in a secondary forest in subtropical China].

Trenched plots were set up in 2010 in a secondary forest in subtropical China, in order to investigate the seasonal variations of soil respiration (R(s)) and heterotrophic respiration (R(h)). Autotrophic respiration (R(a)) was estimated to be the difference between R(s) and R(h). Soil temperature and moisture were simultaneously measured during respiration measurements. Results indicated that R(s) and R(h) showed the similar seasonal variations. Seasonal mean rates for R(s), R(h) and R(a) were 3.42, 2.36 and 1.06 micromol x (m2 x s)(-1), respectively. Regression analysis indicated that R(h) increased with the increase of R(s); an natural logistic equation could be employed to explained the relationship between R(h) (y) and R(s) (x). Approximately 90.5% (R2 = 0.905) variations in R(h) could be explained by the equation. Apparent exponential relationships of R(h) and R(a) with soil temperature existed, but differed from each other and from the relationship for R(s). The exponential equations explained about 78.4%, 76.4% and 65.6% variations in R(s), R(h) and R(a), respectively, with the P values less than 0.01. The Q10 values for R(s), R(h) and R(a) were 1.97, 1.76 and 3.31, respectively. It was indicated that, seasonally, R(h) and R(a) represented 69% and 31% of R(s). R(a) showed significantly higher temperature sensitivity than R(h).

[Effects of elevated ozone concentration on soil respiration, nitrification and denitrification in a winter wheat farmland].

Field experiments were carried out in a winter wheat farmland, in order to investigate the effects of elevated ozone concentration on soil respiration, nitrification and denitrification. Three ozone concentration treatments, which were CK, T1 (100 nL x L(-1)) and T2 (150 nL x L(-1)), were arranged using open top chambers (OTCs). A portable soil CO2 fluxes system was used to measure soil respiration rates. Nitrification and denitrification rates were determined by using a Barometric Process Separation (BaPS) method. Results indicated that there were no significant differences (p > 0.05) in soil respiration rates among CK, T1 and T2 treatments. Mean soil respiration rates for CK, T1 and T2 treatments were (5.36 +/- 0.72), (5.08 +/- 0.04), (4.94 +/- 0.18) micromol x (m2 x s)(-1), respectively. No significant differences (p > 0.05) in mean soil nitrification and denitrification rates were observed between the treatments of CK and T2. During the experimental period, soil respiration showed an exponential relationship with soil temperature for each of the treatment. The Q10 (the respiratory flux at one temperature over the flux at a temperature 10 degrees C lower) values were 1.72, 1.58 and 1.51 for CK, T1 and T2 treatments, respectively. A correlation (Pearson product-momentum correlation) analysis showed that soil water content was correlated significantly (p < 0.05) with soil nitrification (r = 0.828) and denitrification (r = 0.890) rates for CK treatment. Soil water content was correlated significantly (p < 0.05) with soil nitrification rate for T2 treatment, with the correlation coefficient of 0.772. This study indicated that elevated ozone concentration did not significantly affect soil respiration, nitrification and denitrification rates in the winter wheat farmland. Elevated ozone concentration, however, significantly reduced the temperature sensitivity of soil respiration.