Jinsong Zhao

Nitrous oxide emission from two acidic soils as affected by dolomite application

The effect of dolomite (CaMg(CO3)2) application on nitrous oxide (N2O) emission was examined in a laboratory study with soil from a rice paddy–rapeseed rotation (PR soil, pH 5.25) and from a rice paddy–fallow–flooded rotation soil (PF soil, pH 5.52). The soils were treated with 0, 0.5 (L) and 1.5 (H) g dolomite 100 g–1 soil. Results showed that N2O emissions were higher in control treatments (untreated dolomite) in both soils. Application of dolomite decreased N2O emissions significantly (P ≤ 0.001) as soil pH increased in both soils. The H treatment was more effective than the L treatment for the reduction of N2O emissions. The H treatment decreased the cumulative N2O emissions by up to 73.77% in PR soil and 64.07% in PF soil compared with the control. The application of dolomite also affected concentrations of dissolved organic carbon, microbial biomass carbon, ammonium and nitrate in soils, which related to N2O emission. The results suggest that dolomite not only counteracts soil acidification but also has the potential to mitigate N2O emissions in acidic soils.

Assessing soil nitrous oxide emission as affected by phosphorus and nitrogen addition under two moisture levels

Abstract Agricultural soils are deficient of phosphorus (P) worldwide. Phosphatic fertilizers are therefore applied to agricultural soils to improve the fertility and to increase the crop yield. However, the effect of phosphorus application on soil N 2 O emissions has rarely been studied. Therefore, we conducted a laboratory study to investigate the effects P addition on soil N 2 O emissions from P deficient alluvial soil under two levels of nitrogen (N) fertilizer and soil moisture. Treatments were arranged as follows: P (0 and 20 mg P kg −1 ) was applied to soil under two moisture levels of 60 and 90% water filled pore space (WFPS). Each P and moisture treatment was further treated with two levels of N fertilizer (0 and 200 mg N kg −1 as urea). Soil variables including mineral nitrogen (NH 4 +-N and NO 3 − -N), available P, dissolved organic carbon (DOC), and soil N 2 O emissions were measured throughout the study period of 50 days. Results showed that addition of P increased N 2 O emissions either under 60% WFPS or 90% WFPS conditions. Higher N 2 O emissions were observed under 90% WFPS when compared to 60% WFPS. Application of N fertilizer also enhanced N 2 O emissions and the highest emissions were 141 μg N 2 O kg −1 h −1 in P+N treatment under 90% WFPS. The results of the present study suggest that P application markedly increases soil N 2 O emissions under both low and high soil moisture levels, and either with or without N fertilizer application.

Carbon budget and greenhouse gas balance during the initial years after rice paddy conversion to vegetable cultivation

Rice paddy conversion to vegetable production is a common agricultural practice driven by economic benefits and shifting diets. However, little is known on the initial effects of this land-use conversion on net ecosystem carbon budget (NECB) and greenhouse gas (GHG) balance. Annual NECB and emissions of CH4 and N2O were measured from a native double rice cropping system (Rice) and a vegetable field recently converted from rice paddy (Veg) under no nitrogen (N) fertilization (Rice-N0 and Veg-N0) and conventional N fertilization (Rice-N+ and Veg-N+) during the initial four years upon conversion in subtropical China. Land-use conversion from rice to vegetable cultivation led to substantial C losses (2.6 to 4.5 Mg C ha-1 yr-1), resulting from strongly reduced C input by 44-52% and increased soil organic matter mineralization by 46-59% relative to Rice. The magnitude of C losses from Veg was highest in the first year upon conversion, and showed a decreasing trend over time. N fertilization shifted rice paddy from a slight C source in Rice-N0 (-1.0 Mg C ha-1 yr-1) to a significant C sink in Rice-N+ (1.1 Mg C ha-1 yr-1) and alleviated the impact of land-use conversion on C loss via increased C input from higher crop productivity. Land-use conversion greatly increased the global warming potential (GWP) from Veg by 116-395% relative to Rice in the first year, primarily due to increased C losses and N2O emission outweighing the decreased CH4 emission. However, the GWP did not show obvious difference between Rice and Veg in the following years. N fertilization and land-use conversion interactively increased GWP in the first year via increased N2O production. Concluding, NECB and GHG emissions in the first year after conversion are crucial and should be considered when evaluating the environmental consequences of land-use conversion.

Mosses Are Better than Leaves of Vascular Plants in Monitoring Atmospheric Heavy Metal Pollution in Urban Areas

Mosses and leaves of vascular plants have been used as bioindicators of environmental contamination by heavy metals originating from various sources. This study aims to compare the metal accumulation capabilities of mosses and vascular species in urban areas and quantify the suitability of different taxa for monitoring airborne heavy metals. One pleurocarpous feather moss species, Haplocladium angustifolium, and two evergreen tree species, Cinnamomum bodinieri Osmanthus fragrans, and substrate soil were sampled in the urban area of different land use types in Wuhan City in China. The concentrations of Ag, As, Cd, Co, Cr, Cu, Mn, Mo, Ni, V, Pb, and Zn in these samples were analyzed by inductively coupled plasma mass spectrometry. The differences of heavy metals concentration in the three species showed that the moss species was considerably more capable of accumulating heavy metals than tree leaves (3 times to 51 times). The accumulated concentration of heavy metals in the moss species depended on the metal species and land use type. The enrichment factors of metals for plants and the correlations of metals in plants with corresponding metals in soil reflected that the accumulated metals in plants stemmed mostly from atmospheric deposition, rather than the substrate soil. Anthropogenic factors, such as traffic emissions from automobile transportation and manufacturing industries, were primarily responsible for the variations in metal pollutants in the atmosphere and subsequently influenced the metal accumulation in the mosses. This study elucidated that the moss species H. angustifolium is relatively more suitable than tree leaves of C. bodinieri and O. fragrans in monitoring heavy metal pollution in urban areas, and currently Wuhan is at a lower contamination level of atmospheric heavy metals than some other cities in China.