Zhenghua Hu

Interannual variability in soil respiration from terrestrial ecosystems in China and its response to climate change

Soil respiration is an important process in terrestrial carbon cycle. Concerning terrestrial ecosystems in China, quantifying the spatiotemporal pattern of soil respiration at the regional scale is critical in providing a theoretical basis for evaluating carbon budget. In this study, we used an empirically based, semi-mechanistic model including climate and soil properties to estimate annual soil respiration from terrestrial ecosystems in China from 1970 to 2009. We further analyzed the relationship between interannual variability in soil respiration and climatic factors (air temperature and precipitation). Results indicated that the distribution of annual soil respiration showed clear spatial patterns. The highest and lowest annual soil respiration rates appeared in southeastern China and northwestern China, respectively, which was in accordance with the spatial patterns of mean annual air temperature and annual precipitation. Although the mean annual air temperature in northwestern China was higher than that in some regions of northeastern china, a greater topsoil organic carbon storage in northeastern China might result in the higher annual soil respiration in this region. By contrast, lower temperature, less precipitation and smaller topsoil organic carbon pool incurred the lowest annual soil respiration in northwestern China. Annual soil respiration from terrestrial ecosystems in China varied from 4.58 to 5.19 Pg C a−1 between 1970 and 2009. During this time period, on average, annual soil respiration was estimated to be 4.83 Pg C a−1. Annual soil respiration in China accounted for 4.93%–6.01% of the global annual soil CO2 emission. The interannual variability in soil respiration depended on the interannual variability in precipitation and mean air temperature. In order to reduce the uncertainty in estimating annual soil respiration at regional scale, more in situ measurements of soil respiration and relevant factors (e.g. climate, soil and vegetation) should be made simultaneously and historical soil property data sets should also be established.

Sulfate formation and extraction from Red soil treated with micronized elemental sulfur fertilizer and incubated in closed and open systems

Two extractants, 0.01 M CaCl2 and 0.01 M Ca(H2PO4)2, and two incubation systems, closed and open, were used to investigate the influence of granule dispersion and granule size on formation in a Red soil treated with a new micronized, granular S0 fertilizer at rates of 500 and 3000 mg kg−1 of S0. Sulfate production was significantly greater with dispersed micronized particles than for either the 1 to 2 mm or 2 to 4 mm intact granule size fractions. Increasing the dosage of S0 resulted in much greater formation from all particle sizes of S0. Quantities of extracted by 0.01 M Ca(H2PO4)2 generally exceeded those removed by 0.01 M CaCl2 in both the closed and open incubation systems. Levels of extractable recovered in the open incubation procedure were consistently much greater than those in closed incubation. In open incubation, extractable varied from 0.66 to 36.79 mg S/100 g soil and 1.35 to 65.02 mg S/100 g soil, respectively, for the 0.01 M CaCl2 and 0.01 M Ca(H2PO4)2 leaching solutions. With closed incubation, recoveries ranged from 0.15 to 12.08 mg S/100 g soil and 0.21 to 31.74 mg S/100 g soil in the 0.01 M CaCl2 and 0.01 M Ca(H2PO4)2 extracts, respectively. The average oxidation percentages measured by 0.01 M Ca(H2PO4)2 extraction were 27.9%, and 36.7% greater than those occurring with 0.01 M CaCl2 extraction, in closed and open incubation, respectively. Oxidation percentages for the dispersed S0 particles were significantly higher than for intact fertilizer S0 granules, which increased significantly with decreasing granule size. Oxidation percentages were significantly greater at the lower dosage rate of S0 fertilizer. Highly significant linear function relationships between cumulative formed by oxidation of S0 and the time of open incubation were found.

Effects of elevated O3 on soil respiration in a winter wheat–soybean rotation cropland

The increasing tropospheric ozone (O3) concentration has been reported to have negative effects on ecosystems. However, few investigations have focussed on the impacts of elevated O3 on soil respiration in cropland. This study aimed to examine the responses of soil respiration to elevated O3 with open-top chambers (OTCs) in a winter wheat (Triticum aestivum L.)–soybean (Glycine max (L.) Merr) rotation. The experiment was performed in the cropland near Nanjing city, south-east China. Seasonal changes in soil respiration rates, soil CO2 production rates, and nitrification and denitrification rates in ambient air (control) and elevated O3 (100 ppb) treatments were investigated in the 2009–10 winter wheat and 2010 soybean growing seasons. Seasonal mean soil respiration rates for the control and 100 ppb treatments were 3.16 and 2.66 μmol/m2.s, respectively, in the winter wheat growing season, and they were 3.59 and 2.51 μmol/m2.s, respectively, in the soybean growing season. Mean soil respiration rate in the control was ~29% higher than that in the 100 ppb treatment across the whole winter wheat–soybean rotation season. Elevated O3 significantly decreased soil respiration in both crops, with a larger effect observed in soybean. Mean soil CO2 production rates were reduced by ~42% in the 100 ppb O3 treatment compared with the control. No O3 effects were observed on soil nitrification and denitrification during the period monitored. A further analysis of covariance showed that soil respiration was significantly correlated with both soil temperature and moisture, and no interaction effects of O3 treatment and covariate (temperature or moisture) were observed.

Experimental Warming Effects on Soil Respiration, Nitrification, and Denitrification in a Winter Wheat-Soybean Rotation Cropland

ABSTRACT A field experiment was conducted to examine responses of soil respiration, nitrification, and denitrification to warming in a winter wheat (Triticum aestivum L.)–soybean (Glycine max (L.) Merr) rotation cropland. The results showed that seasonal variations in soil respiration were positively related to seasonal fluctuations in soil temperature. Seasonal mean soil respiration rates for the experimental warming (EW) and control (CK) plots were 3.98 ± 0.43 and 2.54 ± 0.45 μmol m−2 s−1, respectively, in the winter wheat growing season, and they were 4.59 ± 0.16 and 4.36 ± 0.08 μmol m−2 s−1, respectively, in the soybean growing season. There was a marginally significant level (p = 0.097) for mean nitrification rates between EW and CK plots. Soil temperature and moisture accounted for 58.2% and 58.1% of the seasonal variations observed in the winter wheat and soybean plots, respectively.

Ultraviolet-A Radiation Accelerated N2O Emission in Winter-Wheat Ecosystem

Extensive research has been done to find the effect of enhanced UV-B (280-320nm) radiation on ecosystem, however, the available information related to the effect of UV-A (320-400nm) on ecosystem is limited. It merits further studies due to the facts that UV-A constitutes a major portion of the solar radiation and passes through the stratospheric ozone layer almost unattenuated. To investigate the impact of UV-A radiation on trace gases N2O emission from winter-wheat ecosystem, outdoor pot experiments with simulating 0%(CK) and 20% (T) supplemental of UV-A were conducted, and static dark chamber-gas chromatograph method were used to measure N2O fluxes. Results indicated that enhanced UV-A radiation increased N2O fluxes in bare soil, which N2O fluxes of T were 2.86 times larger than that of CK (p=0.059), also accelerated significantly N2O emission from winter-wheat ecosystem, which N2O fluxes of T were 1.33 times larger than that of CK (p=0.012).