Zhaohai Zeng

Effects of Nitrogen Application on Chlorophyll Fluorescence Parameters and Leaf Gas Exchange in Naked Oat

Naked oat (＂Avena nuda＂ L.) was originated from China, where soil nitrogen (N) is low availability. The responses of chlorophyll (Chl.) fluorescence parameters and leaf gas exchange to N application were analysed in this study. After the N application rate ranged from 60 to 120 kg ha^(-1), variable fluorescence (F_v), the maximal fluorescence (F_m), the maximal photochemical efficiency (F_v/F_m), quantum yield (Φ_(PS II)) of the photosynthetic system II (PS II), electron transport rate (ETR), and photochemical quenching coefficient (qP) increased with N application level, however, non-photochemical quenching coefficient (qN) decreased. Moreover, there was no difference in initial fluorescence (F_o) with further more N enhancement. The maximum net photosynthetic rate (P_(max)), apparent dark respiration rate (R_d) and light saturation point (LSP) were improved with 40-56 kg N ha^(-1) as basal fertilizer and 24-40 kg N ha^(-1) as top dressing fertilizer applied at jointing stage. Initial quantum yield (α) was decreased with 24 kg N ha^(-1) as basal fertilizer and 56 kg N ha^(-1) as top dressing fertilizer. Flag-leaf net photosynthetic rate (P_n) was significantly enhanced at the jointing and heading stages with 40-56 kg N ha^(-1) as basal fertilizer; in addition, increased at grain filling stage of naked oat with 40-56 kg N ha^(-1) as top dressing fertilizer. 90 kg N ha^(-1) (50-70% as basal fertilizer and 30-50% as top dressing fertilizer) application is recommended to alleviate photodamage of photosystem and improve the photosynthetic rate in naked oat.

Effects of Chinese Milk Vetch (Astragalus sinicus L.) Residue Incorporation on CH4 and N2O Emission from a Double-Rice Paddy Soil

Abstract Methane (CH4) and nitrous oxide (N2O) emissions from paddy soils have seldom been estimated when leguminous green manure is applied as a nitrogen source. In this paper, gas fluxes were measured by using a pot sampling device combined with a static chamber method to estimate the effects of Chinese milk vetch (Astragalus sinicus L., CMV) on CH4 and N2O emissions and their integrated global warming potentials (GWP) in a double-rice cropping system. Four treatments (no nitrogen fertilizer, NF; urea as chemical fertilizer, CF; CMV incorporation, MV; 50% CMV incorporation and 50% urea, MVCF) were established. CH4 flux peaked on the 15th d after treatment application. Total season CH4 emission was increased by MV and MVCF by 370 and 209%, 152 and 66%, when compared with NF and CF, respectively. Most of the increased CH4 was emitted in the first two months after incorporation of CMV. N2O emission from CF was 17- and 5.6-fold higher than that from MV and MVCF, respectively. Application of CMV restricted N2O emission caused by the application of urea. Improved CMV residue management was needed to minify CH4 emission induced by the input of organic material. Despite the highest GWP being found in MV, we recommend CMV, when applied as an N source in paddy fields, as a potential mitigation tool for greenhouse gas emissions.

Methane Emissions and Microbial Communities as Influenced by Dual Cropping of Azolla along with Early Rice

Azolla caroliniana Willd. is widely used as a green manure accompanying rice, but its ecological importance remains unclear, except for its ability to fix nitrogen in association with cyanobacteria. To investigate the impacts of Azolla cultivation on methane emissions and environmental variables in paddy fields, we performed this study on the plain of Dongting Lake, China, in 2014. The results showed that the dual cropping of Azolla significantly suppressed the methane emissions from paddies, likely due to the increase in redox potential in the root region and dissolved oxygen concentration at the soil-water interface. Furthermore, the floodwater pH decreased in association with Azolla cultivation, which is also a factor significantly correlated with the decrease in methane emissions. An increase in methanotrophic bacteria population (pmoA gene copies) and a reduction in methanogenic archaea (16S rRNA gene copies) were observed in association with Azolla growth. During rice cultivation period, dual cropping of Azolla also intensified increasing trend of 1/Simpson of methanogens and significantly decreased species richness (Chao 1) and species diversity (1/Simpson, 1/D) of methanotrophs. These results clearly demonstrate the suppression of CH4 emissions by culturing Azolla and show the environmental and microbial responses in paddy soil under Azolla cultivation.

Winter cover crops alter methanotrophs community structure in a double-rice paddy soil

Abstract Methanotrophs play a vital role in the mitigation of methane emission from soils. However, the influences of cover crops incorporation on paddy soil methanotrophic community structure have not been fully understood. In this study, the impacts of two winter cover crops (Chinese milk vetch (Astragalus sinicus L.) and ryegrass (Lolium multiflorum Lam.), representing leguminous and non-leguminous cover crops, respectively) on community structure and abundance of methanotrophs were evaluated by using PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) and real-time PCR technology in a double-rice cropping system from South China. Four treatments were established in a completely randomized block design: 1) double-rice cropping without nitrogen fertilizer application, CK; 2) double-rice cropping with chemical nitrogen fertilizer application (200 kg ha–1 urea for entire double-rice season), CF; 3) Chinese milk vetch cropping followed by double-rice cultivation with Chinese milk vetch incorporation, MV; 4) ryegrass cropping followed by double-rice cultivation with ryegrass incorporation, RG. Results showed that cultivating Chinese milk vetch and ryegrass in fallow season decreased soil bulk density and increased rice yield in different extents by comparison with CK. Additionally, methanotrophic bacterial abundance and community structure changed significantly with rice growth. Methanotrophic bacterial pmoA gene copies in four treatments were higher during late-rice season (3.18×107 to 10.28×107 copies g–1 dry soil) by comparison with early-rice season (2.1×107 to 9.62×107 copies g–1 dry soil). Type I methanotrophs absolutely predominated during early-rice season. However, the advantage of type I methanotrophs kept narrowing during entire double-rice season and both types I and II methanotrophs dominated at later stage of late-rice.

Contrasting carbon and nitrogen rhizodeposition patterns of soya bean (Glycine max L.) and oat (Avena nuda L.): C and N rhizodeposition of soya bean and oat

H . Z a n g a,c , X . Q i a n a,d, Y . W e n e, Y . H u a, C . R e n b, Z . Z e n g a, L . G u o b & C . W a n g b aCollege of Agronomy and Biotechnology, China Agricultural University, Beijing 100193, China, bNational Oat Improvement Center of China, Baicheng Academy of Agricultural Sciences, Baicheng City 137000, China, cDepartment of Agricultural Soil Science, University of Goettingen, Goettingen 37077, Germany, dNational Engineering Laboratory of Wheat and Maize, Maize Research Institute, Shandong Academy of Agricultural Sciences, Jinan 250100, China, and eSchool of Environment, Natural Resources and Geography, Bangor University, Gwynedd LL57 2UW, UK

Non-leguminous winter cover crop and nitrogen rate in relation to double rice grain yield and nitrogen uptake in Dongting Lake Plain, Hunan Province, China

Abstract Annual ryegrass (Lolium multiflorum Lam.), a non-leguminous winter cover crop, has been adopted to absorb soil native N to minimize N loss from an intensive double rice cropping system in southern China, but a little is known about its effects on rice grain yield and rice N use efficiency. In this study, effects of ryegrass on double rice yield, N uptake and use efficiency were measured under different fertilizer N rates. A 3-year (2009–2011) field experiment arranged in a split-plot design was undertaken. Main plots were ryegrass (RG) as a winter cover crop and winter fallow (WF) without weed. Subplots were three N treatments for each rice season: 0 (N0), 100 (N100) and 200 kg N ha−1 (N200). In the 3-year experiment, RG reduced grain yield and plant N uptake for early rice (0.4–1.7 t ha−1 for grain yield and 4.6–20.3 kg ha−1 for N uptake) and double rice (0.6–2.0 t ha−1 for grain yield and 6.3–27.0 kg ha−1 for N uptake) when compared with WF among different N rates. Yield and N uptake decrease due to RG was smaller in N100 and N200 plots than in N0 plots. The reduction in early rice grain yield in RG plots was associated with decrease number of panicles. Agronomic N use efficiency and fertilizer N recovery efficiency were higher in RG plots than winter fallow for early rice and double rice among different N rates and experimental years. RG tended to have little effect on grain yield, N uptake, agronomic N use efficiency, and fertilizer N recovery efficiency in the late rice season. These results suggest that ryegrass may reduce grain yield while it improves rice N use efficiency in a double rice cropping system.