Temporal shifts in diversity and quantity of nirS and nirK in a rice paddy field soil

Denitrification is an important part of the nitrogen cycle in the environment, and diverse bacteria, archaea, and fungi are known to have denitrifying ability. Rice paddy field soils have been known to have strong denitrifying activity, but the microbes responsible for denitrification in rice paddy field soils are not well known. Present study analyzed the diversity and quantity of the nitrite reductase genes (nirS and nirK) in a rice paddy field soil, sampled four times in one rice-growing season. Clone library analyses suggested that the denitrifier community composition varied over sampling time. Although many clones were distantly related to the known NirS or NirK, some clones were related to the NirS from Burkholderiales and Rhodocyclales bacteria, and some were related to the NirK from Rhizobiales bacteria. These denitrifiers may play an important role in denitrification in the rice paddy field soil. The quantitative PCR results showed that nirK was more abundant than nirS in all soil samples, but the nirK/nirS ratio decreased after water logging. These results suggest that both diversity and quantity changed over time in the rice paddy field soil, in response to the soil condition.     

黄土丘陵区生物结皮对土壤磷素有效性及碱性磷酸酶活性的影响

黄土丘陵区生物结皮广泛发育,可影响土壤磷素有效性。目前鲜见生物结皮对土壤磷素有效性的研究报道。本文以该区不同年限退耕地的生物结皮为研究对象,通过野外调查和室内分析,研究了生物结皮对土壤全磷、有效磷及碱性磷酸酶活性的影响。结果表明,1）生物结皮的形成可显著提高结皮层土壤全磷含量,而下层(010 cm)全磷含量差异不显著; 2）生物结皮的形成可显著提高结皮层土壤有效磷含量,研究区生物结皮层土壤有效磷含量为3.27~5.87 mg/kg,占到同层土壤全磷含量的0.57%~0.95%,生物结皮层磷酸酶活性高于下层(010 cm) 381倍; 3）生物结皮对土壤磷素有效性及碱性磷酸酶活性的影响与生物结皮发育阶段有关; 4）生物结皮主要通过提高结皮层土壤碱性磷酸酶活性和有机质含量,降低土壤pH,进而提高了土壤磷素有效性。本文研究结果表明,生物结皮的形成有助于提高黄土丘陵区退耕地土壤磷素有效性。     

纳米Fe^0／Fe_3O_4复合体系对溶液中PCB77的降解研究

研究了纳米Fe^0与纳米Fe_3O_4。单一与复合体系对溶液中PCB77的降解动力学,以及影响降解效率的不同因素。结果表明,投加纳米Fe^0对PCB77有显著的降解效果,反应240min后PCB77残留率为8．94％;投加纳米Feo同时配以不同比例的纳米Fe_3O_4。能明显影响PCB77的降解速率,纳米Fe^0／Fe_3O_4投加比例为1：0．1、1：0．2和1：1时,PCB77的残留率分别为6．46％、10．23％和38．20％。溶液pH对纳米FFe^0／Fe_3O_4复合体系降解PCB77具有较大的影响,当溶液pH为6．8时,纳米Fe^0／Fe_3O_4复合体系降解PCB77的效果最好。纳米Fe^0／Fe_3O_4复合体系对PCB77的降解是一个还原脱氯的过程,随着PCB77残留率的减小,氯离子浓度不断增大,同时反应体系中氧化还原电位不断降低。研究结果将为环境中残留PCBs提供一种高效去除方法,并为PCBs污染水体和土壤的修复提供理论依据。     

坡耕地保护性耕作冬小麦增产机理的研究

利用长期定位试验在豫西旱区坡耕地上对不同保护性耕作下冬小麦主要生育期的土壤温度、土壤养分、水分动态、干物质积累和小麦产量进行研究。结果表明:深松和免耕覆盖土壤含水量较高,深松与免耕覆盖技术能够提高土壤肥力,越冬期保护性耕作5 cm地温较低,而0~30 cm地温相差不大。深松覆盖在灌浆期土壤日均地温较低,有利于防御干热风对小麦的危害。小麦中后期深松覆盖和免耕干物质积累量较多,能延缓小麦植株衰老。     

四川盆地西部漂洗土壤区水体铁元素的分布特征

铁是水质监测的重要指标。为了弄清四川盆地西部漂洗土壤区不同水环境中铁的形态和含量、浅层潜水的季节动态及其形成原因,为该区土、水资源合理利用提供一定参考,于不同时期在四川省名山县漂洗土壤区采集潜水、池塘水、稻田和茶园沟渠地表水、土壤孔隙水及相应的土壤样品,分析了其铁的形态和含量及相应的理化性质。结果表明,从潜水和土壤孔隙水来看,潜水总铁和亚铁含量（分别为0.30、0.08mg·L^-1）均为最低,稻田孔隙水总铁和亚铁含量（分别为2.92、1.13mg·L^-1）均为最高,茶园孔隙水总铁和亚铁含量（3a生以下茶园分别为1.25、0.92mg·L^-1,6a生以上茶园分别为2.66、0.65mg·L^-1）居中;就稻田和茶园的土壤孔隙水与沟渠地表水比较而言,孔隙水总铁和亚铁含量总体上高于沟渠地表水相应的总铁和亚铁含量;潜水总铁和亚铁含量分别变动在0~0.86mg·L^-1和0~0.36mg·L^-1之间,其季节动态在不同区域间存在一定差异,与其所处地形部位及地表径流条件、离居民房屋和畜禽圈舍远近、土壤pH、有机质和铁元素的形态和含量、土地利用方式及作物种植年限、天气状况及水井自身氧化还原电位等条件有关。     

Film fully-mulched ridge-furrow cropping affects soil biochemical properties and maize nutrient uptake in a rainfed semi-arid environment

Abstract

This study evaluated the effects of plastic mulched ridge-furrow cropping on soil biochemical properties and maize (Zea mays L.) nutrient uptake in a semi-arid environment. Three treatments were evaluated from 2008 to 2010: no mulch (narrow ridges with crop seeded next to ridges), half mulch (as per no mulch, except narrow ridges were mulched), and full mulch (alternate narrow and wide ridges, all mulched with maize seeded in furrows). Compared to the no mulch treatment, full mulch increased maize grain yield by 50% in 2008 and 25% in 2010, but reduced yield by 21% in 2009 after low precipitation in early growth. Half mulch had a similar grain yield to no mulch in the three cropping years, suggesting half mulch is not an effective pattern for maize cropping in the area. Mulch treatments increased aboveground nitrogen (N) uptake by 21?34% and phosphorus (P) uptake by 21?42% in 2008, and by 16?32% and 14?29%, respectively, in 2010; but in 2009 mulching did not affect N uptake and decreased P uptake. Soil microbial biomass and activities of urease, β-glucosidase and phosphatase at the 0?15 cm depth were generally higher during vegetative growth but lower during reproductive growth under mulch treatments than no mulch. Mulching treatments increased carbon (C) loss of buried maize residues (marginally by 5?9%), and decreased light soil organic C (15?27%) and carbohydrate C (12?23%) concentrations and mineralizable C and N (8?36%) at harvest in the 0?20 cm depth compared with no mulch, indicating that mulching promotes mineralization and nutrient release in soil during cropping seasons. As a result of these biological changes, mineral N concentration under mulch was markedly increased after sowing in upper soil layers compared with no mulch. Therefore, our results suggest that mulched cropping stimulated soil microbial activity and N availability, and thus contributed to increasing maize grain yield and nutrient uptake compared with no mulch.     

基于CFD的养殖污水净化内循环流化床反应器结构优化

针对水产养殖污水净化对内循环流化床反应器的相关要求及流化状态下反应器结构、操作参数与相流体力学行为的密切关系,该文利用构建的描述不同结构、操作参数反应器气液两相流动的计算流体力学数学模型,分析了不同结构、操作参数下反应器液体流场、液体循环流量、气含率的变化规律,得到了对于内径200 mm、底部采用均孔布气盘的反应器,在表观气速为0.5~2.5 cm/s时,导流筒与反应器的内径比0.5,导流筒高度与反应器内径比6,导流筒下端到反应器底部距离50 mm,导流筒上端到液面距离100 mm为最优值;针对液体循环流量,使用相关数学模型求解理论值并与试验值进行比对,通过偏差分析探究了数学模型应用的局限性;使用MATLAB最小二乘法拟合了反应器在最优结构参数下表观气速与液体循环流量、气含率的关系,验证了拟合公式的精确性。该研究为内循环流化床反应器在水产养殖污水处理中的设计应用提供理论和技术参考。     

滴头流道结构对悬浮颗粒分布影响的数值分析

迷宫滴头内部结构复杂尺寸微小,研究流道结构对悬浮颗粒浓度分布的影响对于流道优化有重要意义。该文采用正交试验方法设计齿形流道,根据两相流理论,利用计算流体动力学软件对设计滴头进行了液固两相流数值分析。模拟得到入流浓度及颗粒大小不同时滴头内的速度及颗粒浓度分布,分析了结构参数、颗粒大小及入流浓度对悬浮颗粒浓度分布的影响。研究结果表明：流道结构参数对颗粒分布均有影响,程度从大到小顺序为：齿角度－齿间距－流道深度－齿高;入流颗粒大小为流道最小尺寸的1/10～1/6时滴头不易堵塞;齿高与齿间距的比值小于0.5时有利于提高滴头的抗堵塞性。研究为滴头结构优化提供参考。     

氮肥运筹、配施有机肥和坐水种对春玉米产量与养分吸收转运的影响

采用田间试验方法,研究了氮肥运筹、配施有机肥和坐水种对春玉米产量与养分吸收转运的影响。结果表明,适宜氮肥运筹方式、配施有机肥和坐水种均能显著增加春玉米产量,氮肥两次追肥处理的产量较一次追肥处理的产量增加10.6%～17.0%,配施有机肥增产10.3%～18.0%,坐水种增产9.1%,配施有机肥并坐水种增产20.4%。氮肥两次追施、配施有机肥及配施有机肥并坐水种均能显著提高春玉米干物质最大积累速率和积累总量,分别提高干物质最大积累速率11.1%～29.5%、28.0%～28.8%和32.1%,依次提高干物质积累总量11.9%～15.5%、21.2%～24.4%和26.9%。氮肥两次追施、配施有机肥和坐水种均可提高N、P、K养分最大吸收速率和吸收总量,养分最大吸收速率以K最高,N居中,P最低;养分吸收总量以N最高,K居中,P最低;养分最大吸收速率出现的时间以K最早（57.2～60.4 d）,N居中（65.3～68.5 d）,P最晚（71.4～74.8 d）,三者均早于干物质积累最大速率出现的时间（82.5～89.3 d）。氮肥两次追施、配施有机肥和坐水种均有利于N、P、K养分由营养体向籽粒的转运量、转运效率、籽粒中养分含量以及氮肥利用率的提高,养分转运效率以P最高（59.3%～66.1%）,其次是N（41.5%～55.1%）,K最低（35.9%～38.0%）。在本实验条件下,施氮量为225 kg/hm2,基肥:拔节肥比1:3,配施有机肥结合坐水种,为最佳施肥处理。     

我国低温冷冻害的发生规律分析

本研究简要介绍了低温冷冻害的类型及影响,重点分析了我国冷冻害的时空格局,探讨了全国范围内冷冻害的发生情况.我国受低温冷冻害影响的范围非常广,其中东北和黄淮海地区是影响最大的两个区域,并且近十几年来我国黄淮平原及华中部分地区有加重趋势.云南和广东等华南和西南地区也经常出现不同程度的冷害.个别年份强度非常大.近20年来,我国低温冷冻害经历了减弱-增强-减弱的过程.1992～1999年是冷冻害影响最严重的时段,其中1998年全国总受灾面积867万hm-2,仅江苏、安徽两省就超过了500万hm-2.2000年及以后的几年强度有所降低,但平均每年的受灾面积仍高于370万hm-2.1986～1991年、1992～1999年、2000～2005年3个时段内各省区冷冻害发展变化趋势的分析表明,我国大部分省区冷冻害强度在不断加大,其中有8个省区年平均受灾面积上升辐度超过lO万hm-2.