Influence of soil properties on the vertical movement of genetically-marked Pseudomonas fluorescens through large soil microcosms

Summary Vertical translocation of the introduced transposon Tn5-tagged Pseudomonas fluorescens cells was studies after irrigation of 50-cm long soil columns of loamy sand. The soil in the columns was slowly brought to saturation using groundwater, and enough water was then slowly added to permit collection of the percolated water. Introduced bacteria were transported to lower soil layers to a significantly higher degree in undisturbed soil cores than in repacked cores; water transport was hampered in both core types due to high soil bulk densities. Soil bulk density affected the degree of transport of the introduced cells; progressively more cells were translocated to deeper soil layers and into the percolation water at decreasing soil bulk densities. Repeated percolation of soil at a bulk density of 1.25 caused an increase in Tn5-tagged cell numbers in the lower soil layers and in the percolated water. Further, cells initially introduced into a dry (5.3% moisture) soil were translocated to a lesser extent than cells introduced into a wetter (13% moisture) soil. Finally, wheat roots enhanced the water-induced transport of introduced cells to the 40- and 50-cm deep soil layers and into the effluent, but not to the remaining soil layers. Large soil columns such as those used in the present study are useful in assessing the transport and survival of introduced bacterial cells in soils under a variety of simulated environmental conditions.     

Potassium Dynamics in US Coastal Plain Soils

ABSTRACT

Potassium (K) deficiency in crops in southern US Coastal Plain soils has been documented since the l880s. Long-term soil fertility studies such as Alabama’s “Cullars Rotation” experiment (circa 1911) have been conducted with K since 1911. Other Alabama long-term experiments on several Coastal Plain and related Hapludults, Paleudults, and Kandiudults also contain K variable treatments which have been monitored since 1929. Soil test data from these long-term experiments have allowed us to answer some practical questions regarding K dynamics in Coastal Plain soils. Potassium movement through the soil profile is dependent on the soil’s cation exchange capacity (CEC) but relative accumulation is greater in the plow layer regardless of soil CEC. While subsoil K testing may be useful for identifying situations where subsoil K has been depleted, this extra effort and expense is not necessary for most cropping situations. A crop will remove most of its K from the plow layer if it is present in sufficient quantity based on soil test. Crop depletion of plow-layer K to the point where yield may be reduced is gradual and may take 10–15 years or more depending upon soil CEC and initial soil K concentration. Depletion is most rapid in low CEC soils as would be expected. However, soil test K can vary considerably during the course of a crop season with the lowest soil test K concentrations occurring immediately after harvest.     

覆膜开孔土壤蒸发的水盐分布特征及运移规律研究

在干旱半干旱的新疆地区,覆膜灌溉面积在逐年增加。但由于田间地膜覆盖率无法达到100%,同时出苗孔和灌水孔的存在使得研究覆膜灌后地表覆膜开孔率不同时蒸发的水盐运动很有必要。为获得覆膜开孔蒸发的土壤水盐分布特征,采用垂直一维入渗蒸发双层有机玻璃土柱实验系统进行蒸发试验。以概化的覆膜开孔率为上边界条件,针对初始水盐均匀和入渗结束后的蒸发两种处理,研究了覆膜开孔率影响下,蒸发土壤含盐量剖面和盐分浓度剖面的分布特征。结果表明,对水盐均匀处理,剖面盐分浓度可采用含水率及开孔率的函数关系表达;而对入渗蒸发处理,剖面盐分浓度随覆膜开孔率的范围不同可采用不同的指数形式表达。表土10cm返盐量随覆膜开孔率的增大而逐渐增加。单位膜孔面积的返盐量随覆膜开孔率的增加而减小,呈幂函数关系。此外,相同开孔率条件下,单位膜孔面积上蒸发量(ER)与土表10cm返盐量(Wsm,10)之间呈良好的线性关系。     

水分淋洗下菜园土壤各形态锌的迁移转化特征

采用室内模拟降雨淋溶土柱的方法，研究了经过1年降雨的淋溶后，菜园土壤垂直方向上各形态锌的迁移转化规律。结果表明：锌的大多数形态很难随水分运动发生迁移，～年的降雨至多能使占总量0．57％的水溶态锌发生淋溶损失。水分淋洗和施磷锌平均能使分别占总量3％和4％的难溶态RES—Zn和OX-Zn向易被植物利用的EX—Zn、CABS—Zn和OM—Zn形态转化。随施锌量的增加，土壤锌的有效性指数增加30％～78％．有效锌总量增加3．12～10．07mg／kg。当施磷50mg／kg时，土壤Zn的有效性指数增加3％～28％，有效锌总量增加0．04～0．28mg／kg，磷锌在土壤中表现为协同作用。     

蒸发条件下夹砂层土壤盐离子的迁移特性研究

针对新疆地区大面积盐碱地垦区土壤剖面多呈层状且砂质夹层较多的特点,通过室内土柱模拟试验,研究了蒸发条件下不同层位夹砂层土壤剖面盐离子的动态变化情况。结果表明,砂质夹层对离子运动有较大影响。与均质土相比,层位较低的砂层可以促进盐离子向土表迁移;层位较高的砂层能有效延缓盐离子向土表迁移的速度,并可降低土表盐离子的含量,使得更多的盐离子滞留于砂层以下土壤及土、砂界面处,尤其N a+更是如此;砂层层位越高,其对离子向上迁移的抑制作用越强。最后用回归分析法求得了砂层对C l-和N a+起抑制作用的相对临界层位。     

Rooted in grass: Challenging patterns of knowledge exchange as a means of fostering social change in a southeast Minnesota farm community

By convening a multidisciplinary team(the Monitoring Team) that included farmers,university and agency researchers, andnon-profit staff; a small group of farmers insoutheast Minnesota, U.S.A., bolstered thelegitimacy of the sustainable agriculturemovement. Through the experience of forming ateam and working with individuals who operatedwithin the mainstream knowledge paradigm,farmers gained validation of their knowledgeabout farming, while researchers came to valuealternative knowledge systems. In the contextof a socially embedded movement, farmers wereempowered by sharing their knowledge withresearchers, and ultimately contributed to thesustainable agriculture movement by challengingtraditional patterns of knowledge exchange.     

外源NO和ABA对杨树气孔运动和SOD及POD活性的影响

研究了外源NO和脱落酸(ABA)对杨树气孔运动和SOD、POD活性的影响。结果表明：NO和ABA均可诱导杨树叶片气孔关闭，且NO有加强ABA诱导气孔关闭的作用。NO清除剂(C—PTIO)能显抑制NO和ABA对气孔关闭的诱导效应。不同浓度硝普钠(SNP)和ABA处理杨树离体叶片，SOD活性变化不明显，POD活性受到显抑制。粗酶液的体外实验结果表明，不同浓度SNP对POD活性的抑制呈明显的浓度及时间效应；而ABA对POD活性则几乎没有影响。说明在ABA调控气孔运动的过程中需要NO的参与，由此推测ABA对杨树叶片气孔运动的调节与NO对POD的抑制有关。     

木材真空-浮压干燥过程中自由水迁移特性

该文以马尾松为试验材料 ,通过对真空 浮压干燥中木材内部温度场、湿度场随压力浮动频率变化的试验研究 ,总结出木材在真空 浮压干燥过程中内部自由水迁移的基本规律 ,并对水分迁移的机制与驱动势进行了分析 .试验结果和理论分析显示 ,在真空 浮压干燥过程中自由水的输运由两部分完成 ,一部分为毛细管压力下液体的团块迁移 ;另一部分为在压力梯度下 ,由于压力波动而引起自由水的蒸发或沸腾后所产生的水蒸气的迁移 ,且后者在自由水的迁移过程中占主导地位 .     

农村社区发展的资金问题──Ⅰ．农村社区资金的新特点

资金是经济发展的一个重要条件．农村社区的社会主义新农村的建设需要大量资金的投入，但是农村社区却最缺乏资金，因此要加强农村资金问题的研究．首先，农村金融组织需改革深化，挖掘农村资金的潜力，着重使农民的资金的“资产”投入转向“生产”投入．其次，农村资金运动已呈现了新特点，这些特点有：分散化及结构复杂化；总量增大，周期时间延长；资金运动的盲目性和不稳定性．再次，农村社区资金的需求与供应呈现的新特点，这些特点有：要求合理地引导资金的流动；不可忽视的社区经济要求；常年性需求；供给和积累的加速．最后，还必须注意到在市场化下产生的与社区发展相矛盾的资金的逆向运动．     

保卫细胞液泡内pH调节的可逆解聚聚合颗粒物性质初探

为研究保卫细胞液泡(GCV)的pH在气孔保卫细胞渗透调节中的作用及蚕豆(Vicia faba)叶片气孔GCV中的颗粒物的性质,本实验采用激光共聚焦显微术配合pH荧光探针BCECF AM的荧光比值法对ABA诱导的气孔关闭过程进行观测,发现:蚕豆气孔关闭过程中GCV的pH升高约0.5(pH5.3→5.8)。分别用pH5.3和5.8的Mes/Tris缓冲液调控离体开放态GCV的pH,透射电镜(4×104倍)观察负染片说明:pH 5.3对开放态GCV液所含颗粒物的线度及分布密度无实质影响;而pH 5.8的处理使取自开放态GCV液所含颗粒物的线度明显增大、分布密度显著减小;非特异性蛋白酶Proteinase K处理可使GCV中的颗粒物消失。基于GCV内颗粒物的线度、形状及对pH调控和对Proteinase K处理的响应,推测此种颗粒物是蛋白质。