Seasonal soil freeze-thaw events may enhance soil nitrogen transformation and thus stimulate nitrous oxide (N₂O) emissions in cold regions.  However, the mechanisms of soil N₂O emission during the freeze-thaw cycling in the field remain unclear.  We evaluated N₂O emissions and soil biotic and abiotic factors in maize and paddy fields over 20 months in Northeast China, and the structural equation model (SEM) was used to determine which factors affected N₂O production during non-growing season.  Our results verified that the seasonal freeze-thaw cycles mitigated the available soil nitrogen and carbon limitation during spring thawing period, but simultaneously increased the gaseous N₂O-N losses at the annual time scale under field condition.  The N₂O-N cumulative losses during the non-growing season amounted to 0.71 and 0.55 kg N ha^–1 for the paddy and maize fields, respectively, and contributed to 66 and 18% of the annual total.  The highest emission rates (199.2–257.4 μg m^–2 h^–1) were observed during soil thawing for both fields, but we did not observe an emission peak during soil freezing in early winter.  Although the pulses of N₂O emission in spring were short-lived (18 d), it resulted in approximately 80% of the non-growing season N₂O-N loss.  The N₂O burst during the spring thawing was triggered by the combined impact of high soil moisture, flush available nitrogen and carbon, and rapid recovery of microbial biomass.  SEM analysis indicated that the soil moisture, available substrates including NH₄⁺ and dissolved organic carbon (DOC), and microbial biomass nitrogen (MBN) explained 32, 36, 16 and 51% of the N₂O flux variation, respectively, during the non-growing season.  Our results suggested that N₂O emission during the spring thawing make a vital contribution of the annual nitrogen budget, and the vast seasonally frozen and snow-covered croplands will have high potential to exert a positive feedback on climate change considering the sensitive response of nitrogen biogeochemical cycling to the freeze-thaw disturbance.   

   Leaves play a key role in photosynthesis in rice plants. The premature senescence of such plants directly reduces the accumulation of photosynthetic products and also affects yield and grain quality significantly and negatively. A novel premature senescence mutant, mps1 (mid-late stage premature senescence 1), was identified from a mutant library consisting of ethyl methane sulfonate (EMS) induced descendants of Jinhui 10, an elite indica restorer line of rice. The mutant allele, mps1, caused no phenotypic differences from the wild type (WT), Jinhui 10, but drove the leaves to turn yellow when mutant plants grew to the tillering stage, and accelerated leaf senescence from the filling stage to final maturation. We characterized the agronomic traits, content of photosynthetic pigments and photosynthetic efficiency of mps1 and WT, and fine-mapped MPS1. The results showed that the MPS1-drove premature phenotype appeared initially on the leaf tips at the late tillering stage and extended to the middle of leaves during the maturing stage. Compared to the WT, significant differences were observed among traits of the number of grains per panicle (–31.7%) and effective number of grains per panicle (–38.5%) of mps1 individuals. Chlorophyll contents among the first leaf from the top (Top 1st), the second leaf from the top (Top 2nd) and the third leaf from the top (Top 3rd) of mps1 were significantly lower than those of WT (P<0.05), and the levels of photosynthetic efficiency from Top 1st to the forth leaf from the top (Top 4th) of mps1 were significantly lower than those of WT (P<0.01). Results from the genetic analysis indicated that the premature senescence of mps1 is controlled by a recessive nuclear gene, and this locus, MPS1 is located in a 37.4-kb physical interval between the markers Indel145 and Indel149 on chromosome 6. Genomic annotation suggested eight open reading frames (ORFs) within this physical region. All of these results will provide informative references for the further researches involving functional analyses and molecular mechanism exploring of MPS1 in rice.

The excessive nitrogen (N) fertilizer input coupled with flood irrigation might result in higher N leaching and lower nitrogen recovery efficiency (NRE). Under an intensive rice system in the Ningxia irrigation region, China, environmental friendly N management practices are heavily needed to balance the amount of N input for optimum crop production while minimize the nitrogen loss. The objective of this study was to determine the influences of side-dressing (SD) technique in mechanical transplanting systems on the NRE, N leaching losses and rice yield in anthropogenic-alluvial soil during two rice growing seasons (2010-2011). Four fertilizer N treatments were established, including conventional urea rate (CU, 300 kg ha–1 yr–1); higher SD of controlled-release N fertilizer rate (SD1, 176 kg ha–1 yr–1); lower SD of controlled-release N fertilizer rate (SD2, 125 kg ha–1 yr–1); and control (CK, no N fertilizer). Field lysimeters were used to quantify drainage from undisturbed soil during six rice growing stages. Meanwhile, the temporal variations of total nitrigen (TN), NO3 –-N, and NH4 +-N concentrations in percolation water were examined. The results showed that SD1 substantially improved NRE and reduced N leaching losses while maintaining rice yields. Across two years, the averaged NRE under SD1 treatment increased by 25.5% as relative to CU, but yet the rice yield was similar between two treatments. On average, the nitrogen loss defined as TN, NH4 +-N, and NO3 –-N under the SD1 treatment reduced by 27.4, 37.2 and 24.1%, respectively, when compared with CU during the study periods. Although the SD2 treatment could further reduce N leaching loss to some extent, this technique would sharply decline rice yield, with the magnitude of as high as 21.0% relative to CU treatment. Additionally, the average NRE under SD2 was 11.2% lower than that under SD1 treatment. Overall, the present study concluded that the SD technique is an effective strategy to reduce N leaching and increase NRE, thus potentially mitigate local environmental threat. We propose SD1 as a novel alternative fertilizer technique under an irrigated rice-based system in Ningxia irrigation region when higher yields are under consideration.

A total of 479 bacterial strains were isolated from brine (Bohai, Qinhuangdao City, Hebei Province, China). Bioassay results indicated that 4 strains named Ha1, Ha17, Ha38, and Ha384 had herbicidal activity. And strain Ha1 had the highest effective herbicidal activity. As a result, this study aims to identify strain Ha1, characterize its physiological and biological activities, evaluate the herbicidal activity of its metabolites, and develop a ‘pesta’ formulation and assess its effectiveness on Digitaria sanguinalis. Ha1 was identified as Serratia marcescens based on 16S rDNA sequencing. This strain has a flagellum, a diameter of 0.5 to 0.8 μm, and a length of 0.9 to 2.0 μm. The indole test shows positive results, and the catalase enzyme exhibits strong positive reactions. Results further showed that the inhibitory concentration (IC50) of the crude extracts to D. sanguinalis radicula and coleoptile were 3.332 and 2.828 mg mL–1, respectively. Both the suppression of D. sanguinalis and the cell viability of the Ha1 formulation in ‘pesta’ were higher when stored at 4°C than at (25±2)°C. These results indicated that S. marcescens Ha1 can potentially be used as a biocontrol agent against D. sanguinalis.