东北稻田水体噬藻体psbA基因多样性

【目的】揭示东北稻田噬藻体psbA基因多样性,分析其系统进化地位,为噬藻体生态学研究提供数据支持。【方法】采用滤膜分离并浓缩噬体、PCR-克隆测序技术对我国东北稻田水体中噬藻体psbA基因进行调查。【结果】在东北稻田水体中共得到17条来自于噬藻体的psbA基因,经系统进化分析表明,我国东北稻田具有新的噬藻体的类群,与日本稻田生态系统中psbA基因类群相比,两地间噬藻体类群存在显著的差异,稻田水体中噬藻体psbA基因类群有别于海洋、湖泊类群。【结论】采用PCR-克隆测序技术以psbA基因为分子标记首次对我国东北稻田水体噬藻体类群进行调查,发现有新的噬藻体类群。     

Ability of a Microbial Consortium to Remove Pesticide,Carbendazim and 2,4-Dichlorophenoxyacetic Acid

A bacterial consortium capable of simultaneously degrading the fungicide, carbendazim, and the herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D) was obtained by enrichment of soil samples collected from paddy fields in Japan. This consortium was acclimated in a continuously fed culture with 20 M carbendazim and 2 mM 2,4-D as sole carbon sources using a glass column reactor. By denaturing gradient gel electrophoresis, we observed changes in the bacterial population following the degradation of the both pesticides. This acclimated consortium completely degraded up to 100 M carbendazim and 3 mM 2,4-D within 36 and 24 h, respectively, in batch culture, but a lag time was observed after precultivation in a rich medium. The immobilization of the consortium on a polyester support enhanced the degradation ability of this consortium compared with the use of free cells. This microbial consortium could be useful for bioremediation at sites contaminated with these pesticides.     

自然条件下福寿螺繁殖特性

为了弄清福寿螺在自然条件下的繁殖特性,在湖南省资兴市水稻田内进行了为期3年的人工养殖试验.结果表明:福寿螺在湘南自然条件下1年可发生不完全3代.第1代、第2代和第3代(越冬代)雌螺的平均性成熟期分别为59.3、45.4和213.0 d.雄螺的平均性成熟期比雌螺早4.3d.福寿螺的自然性比(♀∶♂)为1.54:1.每次交配持续时间平均为19.2h,但并非每次交配后都会产卵.田间福寿螺月产卵块数与月平均气温呈显著正相关(r=0.756).福寿螺卵块的平均孵化期(d)与日平均气温(℃)呈显著负相关(r=-0.980),其线性回归方程为y=-0.726x+23.064.福寿螺卵块的平均孵化期为20.7d,平均孵化率为44.1％.雌螺与雄螺的平均寿命分别为2.40和1.98 a.平均每头雌螺一生可产卵13764粒,可繁殖幼螺6070头.     

Occupational strategy of runner reed (Phragmites japonica): Change of growth patterns with developmental aging

The characteristics of P. japonica stands growing along ten transect in an AFP were assessed. Especially those of the reproductive organs in terms of developmental stages were focused. Four consecutive stages were observed based on the existence of reproductive organs (flowers and stolons). Plants in the ‘stolon’ and ‘flower and stolon’ stages played a role as a colonizer by stolonization (the longest length of stolon was more than 9 m) while those in the ‘flower’ stage played a role as an occupant via forming tall and dense shoots on tussocks (more than 2 m and about 20 shoots per tussock including dead standing shoots). Consecutive developmental stages according to changes in growth patterns, particularly in the conversion of reproductive organ from asexual (stolon) to sexual (flower), was the critical strategy of P. japonica for efficient monotypic occupation. This occupational strategy of P. japonica also resulted in a sharp decrease of the plant species richness (two to three including P. japonica) growing in the same area with P. japonica in the mature (‘flower’) stage.     

Host searching behavior and potential of an aquatic ichneumonid pupal parasitoid of rice caseworm (Parapoynx stagnalis) in an upland rice paddy agro-ecosystem of the Western Ghats,India

Parapoynx stagnalis (Zeller) (=Nymphula depunctalis (Guenée), is a sporadic rice paddy pest of south and southeast Asian rice paddy fields, and widely known as rice caseworm. A recent outbreak of the pest was observed in the upland rice paddy agro-ecosystem of the central Western Ghats, India. No potential natural enemies of this pest have so far been reported, mainly due to the semi-aquatic behavior of the larvae and pupae. However, an undescribed aquatic ichneumonid wasp species (belonging to a genus near Litochila) is reported as a potentially useful early stage pupal parasitoid of this pest in our study. The host searching behavior and potential of the parasitoid wasp was studied in detail using both field and laboratory experiments. The adult female wasps usually dive into the water in search of the host pupae, remaining under water for a maximum of 90.2s, while searching for rice caseworm pupae. In field and laboratory experiments, we found 73% of the parasitized pupae of P. stagnalis kept under water yielded adult parasitic wasps. However, no parasitoids emerged from parasitized host pupae maintained in dry terrariums. Sex ratio was 2.8:1. The present discovery of the semi-aquatic parasitoid wasp could aid in better management of the rice caseworm population in rice paddy fields.     

长期秸秆还田对水稻土团聚体及氮磷钾分配的影响

为了探究秸秆还田配施化肥条件下水稻土团聚体组成及其稳定性,以及土壤团聚体氮、磷、钾养分特征,本研究进行了34年定位试验,设置无肥(CK)、化肥(NPK)、秸秆还田+化肥(NPKS)3个处理。采用湿筛法测定0～20、20～40 cm土层水稳性团聚体组成,量化分析氮、磷、钾养分分配特征、贡献率和活化度。结果表明: 水稻土水稳性团聚体以>2 mm和0.25～1 mm粒级为主,<0.053 mm粒级含量最低。与CK相比,在0～20 cm和20～40 cm土层,NPKS处理增加了>2 mm和1～2 mm团聚体含量,降低了0.053～0.25 mm和<0.053 mm团聚体含量;NPK处理在0～20 cm土层也表现出与NPKS类似的规律。NPKS较NPK处理0～20 cm和20～40 cm土层团聚体平均重量直径(MWD)提高3.9%～15.5%,几何平均直径(GMD)提高6.3%～41.7%,不稳定团粒指数(E_LT)降低5.7%～28.7%。NPKS处理显著提高了团聚体全氮、有效磷和速效钾含量,尤其是直径>0.25 mm部分,但对碱解氮和全钾的提升效果与NPK处理差异不显著。水稻土团聚体养分贡献率受到其团聚体组成的影响,NPKS处理明显增大了>1 mm团聚体氮、磷、钾养分贡献率。秸秆还田配施化肥可提高0～20 cm和20～40 cm土层团聚体稳定性,并增加团聚体氮、磷、钾养分含量,尤其是大团聚体(>1 mm)。该研究结果为调节土壤碳氮比来保障稻田土壤质量和资源可持续发展提供了科学依据。     

短期落干对水稻土反硝化微生物丰度和N2O释放的影响

为了探明水稻土落干过程对温室气体排放和反硝化微生物的影响,通过模拟水稻土淹水落干过程,系统监测了落干开始后24 h内N2O的释放和氧化还原电位(Eh)的变化,并利用实时PCR(qPCR)方法测定了反硝化功能基因narG和nosZ的丰度.结果表明：落干开始后4 h N₂O释放量就明显增加,在24 h时N₂O的释放量比淹水对照增加了5倍多;narG和nosZ基因丰度也随着落干过程的推移而快速增加;而且N₂O排放通量与narG基因呈极显著相关(P<0.01).表明水稻土短期淹水落干过程中,含narG基因反硝化微生物是驱动N₂O释放的主要功能微生物.     

Early responses of vegetation and soil organic carbon to waterlogging and winter wildfire on abandoned red paddy soils

为了探明积水和冬季火烧对弃耕红壤稻田地表植被和土壤有机碳的影响, 该实验设置了对照(无人为干扰)、积水、冬季火烧和积水-冬季火烧4个不同处理, 采用样方法对样地植物的高度、密度、盖度及物种组成进行了调查。地上部分生物量采用收获法进行测定, 根系采用土柱法获取, 弃耕前后土壤有机碳含量的测定采用K₂Cr₂O₇外加热法。结果表明: 1)积水和冬季火烧对红壤稻田弃耕早期物种组成、丰富度、均匀度及多样性具有重要的影响。双穗雀稗(Paspalum paspaloides)和水竹叶(Murdannia triquetra)是积水条件下的优势种, 而柔枝莠竹(Microstegium vimineum)是冬季火烧条件下的优势种, 大狼杷草(Bidens frondosa)是积水和冬季火烧条件下的共优种。2)分布在0-5 cm表层土壤中的根系占0-20 cm深度土壤中根系的66.50%-80.34%。样地在积水条件下, 2011-2013年0-20 cm深度的土壤根系生物量分别高出对照样地的49.84%、73.34%和28.94%。3)冬季火烧可以提高样地的物种多样性和增加地上部分生物量, 2011-2013年冬季火烧样地分别高出对照样地的25.74%、64.30%和50.24%。4)与稻田弃耕前土壤有机碳含量逐渐上升趋势相反, 稻田弃耕6年后, 对照、积水、冬季火烧和积水-冬季火烧样地中土壤有机碳含量分别降低11.16%、18.99%、9.17%和19.12%, 并且在积水条件下土壤有机碳含量降低更明显(p < 0.05)。研究结果表明, 红壤稻田弃耕后地表植被物种组成、地上和地下生物量、土壤有机碳含量与积水和冬季火烧关系密切(p < 0.05)。     

Elevated methane emissions from a paddy field in southeast China occur after applying anaerobic digestion slurry

One hundred million tons of farm stalk waste and livestock and poultry excrement are used every year in China for the production of clean energy (biogas) by anaerobic digestion. Consequently, a large amount of fermented liquid is produced, and if disposed of improperly, it will result in secondary pollution. Agricultural application of this anaerobic slurry as a liquid fertilizer would reduce possible eutrophication of water sources from random slurry discharge and supply a superior organic fertilizer for farming. This study investigated the effect of applying anaerobic digestion slurry as a liquid fertilizer on the methane emitted from a paddy field. A two‐year (2008–2009) field experiment replacing chemical fertilizer with liquid fertilizer from anaerobically digested pig manure slurry was conducted in a paddy field in Yixing, Jiangsu, China. A static closed chamber method was used to measure methane fluxes over the period from June 2008 to October 2009. All fertilizer treatments increased methane emissions relative to untreated controls, with increases in methane ranging from 40–70% in 2008 to 48–84% in 2009. Paddy fields treated with anaerobically digested pig manure slurry had greater methane emissions (8–84% in 2008 and 3–26% in 2009) than those treated with chemical fertilizer. This suggests that the anaerobic digestion slurry would increase methane emission and so is unsuitable as a liquid fertilizer in paddy fields without development of cultivation practices to limit these emissions.