The Effects of Soil Type,Particle Size, Temperature,and Moisture on Reproduction of Belonolaimus longicaudatus

Effects of soil type, particle size, temperature, and moisture on the reproduction of Belonolaimus longicaudatus were investigated under greenhouse conditions. Nematode increases occurred only in soils with a minimum of 80% sand and a maximum of 10% clay. Optimum soil particle size for reproduction of the Tarboro, N.C. and Tifton, Ga. populations of the nematode was near that of 120-370 μm (65-mesh) silica sand. Reproduction was greatest at 25-30 C. Some reproduction by the Tifton, Ga. population occurred at 35 C, whereas the Tarboro, N.C. population declined, as compared to the initial inoculum. Both populations reproduced slightly at 20 C. Nematode reproduction was greater at a moisture level of 7% than at a high of 30% or a low of 2%. Reproduction occurred at the high moisture level only when the nutrient solution was aerated.     

Photosynthesis and Transpiration in Rice as Influenced by Soil Moisture and Air Humidity

The paper describes the effect of soil moisture content andair humidity on CO₂ exchange (P_N), CO₂ diffusion resistance(Cr) and transpiration (E) in four varieties of japonica rice(Oryza sativa L.). A decrease in soil moisture content reducedthe rate of photosynthesis to a varying degree in the varieties.Reduction in photosynthesis was attributed to increase in Cr.The effect of low soil moisture on photosynthesis and CO₂ diffusionwas further intensified by decrease in air humidity. By maintaininga high humidity in the air around the leaves however, the effectof soil moisture deficiency was reduced considerably, exceptin Rikuto Norin 21 which was very sensitive to soil-moisturedeficiency alone. Dryness of the air enhanced the transpirationrate, although the increase was relatively less in the plantsfacing a simultaneous water crisis at the root surface. In plantsgrowing under flooded conditions, a decrease in air humiditycaused a slight depression in P_N despite the simultaneous decreasein Cr. Oryza sativa L., rice, photosynthesis, transpiration, diffusion resistance, soil moisture, air humidity     

Influence of Precipitation and Soil on Transport of Fecal Enterococci in Fractured Limestone Aquifers

Limestone aquifers provide the main drinking water resources of southern Italy. The groundwater is often contaminated by fecal bacteria because of the interaction between rocks having high permeability and microbial pollutants introduced into the environment by grazing and/or manure spreading. The microbial contamination of springwater in picnic areas located in high mountains can cause gastrointestinal illness. This study was carried out in order to analyze the interaction between Enterococcus faecalis and the soil of a limestone aquifer and to verify the influence of this interaction on the time dependence of groundwater contamination. E. faecalis was chosen because, in the study area involved, it represents a better indicator than Escherichia coli. The research was carried out through field (springwater monitoring) and laboratory experiments (column tests with intact soil blocks). The transport of bacterial cells through soil samples was analyzed by simulating an infiltration event that was monitored in the study area. Comparison of laboratory results with data acquired in the field showed that discontinuous precipitation caused an intermittent migration of microorganisms through the soil and produced, together with dispersion in the fractured medium (unsaturated and saturated zones), an articulated breakthrough at the spring. The short distances of bacterial transport in the study area produced a significant daily variability of bacterial contamination at the field scale.     

Mechanisms for Soil Moisture Effects on Activity of Nitrifying Bacteria

Moisture may limit microbial activity in a wide range of environments including salt water, food, wood, biofilms, and soils. Low water availability can inhibit microbial activity by lowering intracellular water potential and thus reducing hydration and activity of enzymes. In solid matrices, low water content may also reduce microbial activity by restricting substrate supply. As pores within solid matrices drain and water films coating surfaces become thinner, diffusion path lengths become more tortuous, and the rate of substrate diffusion to microbial cells declines. We used two independent techniques to evaluate the relative importance of cytoplasmic dehydration versus diffusional limitations in controlling rates of nitrification in soil. Nitrification rates in shaken soil slurries, in which NH(inf4)(sup+) was maintained at high concentrations and osmotic potential was controlled by the addition of K(inf2)SO(inf4), were compared with rates in moist soil incubations, in which substrate supply was controlled by the addition of NH(inf3) gas. Comparison of results from these techniques demonstrated that diffusional limitation of substrate supply and adverse physiologic effects associated with cell dehydration can explain all of the decline in activity of nitrifying bacteria at low soil water content. However, the relative importance of substrate limitation and dehydration changes at different water potentials. For the soil-microbial system we worked with, substrate limitation was the major inhibiting factor when soil water potentials were greater than -0.6 MPa, whereas adverse physiological effects associated with cell dehydration were more inhibiting at water potentials of less than -0.6 MPa.     

Determinants of Soil Microbial Communities: Effects of Agricultural Management, Season, and Soil Type on Phospholipid Fatty Acid Profiles

Abstract Phospholipid fatty acid (PLFA) profiles were measured in soils from organic, low-input, and conventional farming systems that are part of the long term Sustainable Agriculture Farming Systems (SAFS) Project. The farming systems differ in whether their source of fertilizer is mineral or organic, and in whether a winter cover crop is grown. Sustained increases in microbial biomass resulting from high organic matter inputs have been observed in the organic and low-input systems. PLFA profiles were compared to ascertain whether previously observed changes in biomass were accompanied by a change in the composition of the microbial community. In addition, the relative importance of environmental variables on PLFA profiles was determined. Redundancy analysis ordination showed that PLFA profiles from organic and conventional systems were significantly different from April to July. On ordination plots, PLFA profiles from the low-input system fell between organic and conventional systems on most sample dates. A group of fatty acids (i14:0, a15:0, 16:1ω7c, 16:1ω5c, 14:0, and 18:2ω6c) was enriched in the organic plots throughout the sampling period, and another group (10Me16:0, 2OH 16:1 and 10Me17:0) was consistently lower in relative abundance in the organic system. In addition, another group (15:0, a17:0, i16:0, 17:0, and 10Me18:0) was enriched over the short term in the organic plots after compost incorporation. The relative importance of various environmental variables in governing the composition of microbial communities could be ranked in the order: soil type > time > specific farming operation (e.g., cover crop incorporation or sidedressing with mineral fertilizer) > management system > spatial variation in the field. Measures of the microbial community and soil properties (including microbial biomass carbon and nitrogen, substrate induced respiration, basal respiration, potentially mineralizable nitrogen, soil nitrate and ammonium, and soil moisture) were seldom associated with the variation in the PLFA profiles. Received: 3 February 1997; Accepted: 7 August 1997     

Confounding Effects of Soil Moisture on the Relationship Between Ecosystem Respiration and Soil Temperature in Switchgrass

Understanding the response of ecosystem respiration (ER) to major environmental drivers is critical for estimating carbon sequestration and large-scale modeling research. Temperature effect on ER is modified by other environmental factors, mainly soil moisture, and such information is lacking for switchgrass (Panicum virgatum L.) ecosystems. The objective of this study was to examine seasonal variation in ER and its relationship with soil temperature (T _s) and moisture in a switchgrass field. ER from the nighttime net ecosystem CO₂ exchange measurements by eddy covariance system during the 2011 and 2012 growing seasons was analyzed. Nighttime ER ranged from about 2 (early growing season) to as high as 13 μmol m^?2 s^?1 (peak growing period) and showed a clear seasonality, with low rates during warm (>30 °C) and dry periods (<0.20 m³ m^?3 of soil water content). No single temperature or moisture function described variability in ER on the seasonal scale. However, an exponential temperature–respiration function explained over 50 % of seasonal variation in ER at adequate soil moisture (>0.20 m³ m^?3), indicating that soil moisture <0.20 m³ m^?3 started to limit ER. Due to the limitation of soil–atmosphere gas exchange, ER rates declined markedly in wet soil conditions (>0.35 m³ m^?3) as well. Consequently, both dry and wet conditions lowered temperature sensitivity of respiration (Q ₁₀). Stronger ER–T _s relationships were observed at higher soil moisture levels. These results demonstrate that soil moisture greatly influences the dynamics of ER and its relationship with T _s in drought prone switchgrass ecosystems.     

施肥和降水对生土熟化的影响

农业生产中常采用深耕、秸秆还田和施用土壤改良剂等措施促进生土熟化。本研究旨在探索施肥与降水配合对生土棉花根、苗、土及微生物间的相互影响机制,为不同降水年型下生土作物合理施肥提供科学依据。试验连续3年以黄土母质生土为供试土壤,探讨施肥深度在0～20 cm,施氮肥(N)、磷肥(P)、氮磷钾复合肥(NPK)、有机肥(ORG)以及干旱、平水、丰水三个降水年型下在40～60 cm施ORG和ORG+NPK分别对生土熟化的效果。研究结果表明,生土地0～20 cm施有机肥显著增加棉花杆重、棉桃总重和地上部总重量,施有机肥或含磷肥对生土棉花根际土壤养分、根系养分含量和酶活性有明显促进作用。施有机肥明显改善了土壤微生物多样性和丰富度;相同施肥条件下,降水对土壤熟化的效果至关重要。其中,干旱年和丰水年施有机肥均显著增加棉花产量,在平水年施有机肥和氮磷钾复合肥,干旱年或丰水年单施有机肥能更有效的提高土壤微生物多样性。综合分析得出,生土地快速改良熟化土壤的施肥措施为有机肥加磷肥。结合降水的条件下,加快生土熟化、提高土壤微生物多样性的最佳施肥方式为:平水年配施有机肥和氮磷钾复合肥,干旱年和丰水年单施有机肥。     

The Effects of Temperature, Daylength, Soil Fertility and Soil Moisture on Leaf Number and Duration to Tassel Emergence in Zea mays L.

The studies reported were conducted in controlled environmentgrowth cabinets, using three hybrids: Warwick SL209, DekalbXL45A, and Funk's G4384. Leaf number decreased with decreasingday temperature, and was lower in the 26/26 than the 26/10 ?Ctemperature regime. Fewer leaves were developed in 12-h thanin 16-h daylength in the same temperature regime. Fewer leaveswere developed, compared with the control treatments, when theplants were subjected to conditions of soil fertility stressand soil moisture stress. Duration to tassel emergence was slowat low day temperatures, under conditions of soil fertilitystress and soil moisture stress, and at the 16-h daylength atconstant 26 ?C temperature. In field experiments, all threehybrids developed more leaves and attained mid-silk later atLa Pocatiere, Quebec (48? N) than at Beltsville, Maryland (38?N).     

Total C and N Pools and Fluxes Vary with Time,Soil Temperature,and Moisture Along an Elevation,Precipitation, and Vegetation Gradient in Southern Appalachian Forests

The interactions of terrestrial C pools and fluxes with spatial and temporal variation in climate are not well understood. We conducted this study in the southern Appalachian Mountains where complex topography provides variability in temperature, precipitation, and forest communities. In 1990, we established five large plots across an elevation gradient allowing us to study the regulation of C and N pools and cycling by temperature and water, in reference watersheds in Coweeta Hydrologic Laboratory, a USDA Forest Service Experimental Forest, in western NC, USA. Communities included mixed-oak pine, mixed-oak, cove hardwood, and northern hardwood. We examined 20-year changes in overstory productivity and biomass, leaf litterfall C and N fluxes, and total C and N pools in organic and surface mineral soil horizons, and coarse wood, and relationships with growing season soil temperature and precipitation. Productivity increased over time and with precipitation. Litterfall C and N flux increased over time and with increasing temperature and precipitation, respectively. Organic horizon C and N did not change over time and were not correlated to litterfall inputs. Mineral soil C and N did not change over time, and the negative effect of temperature on soil pools was evident across the gradient. Our data show that increasing temperature and variability in precipitation will result in altered aboveground productivity. Variation in surface soil C and N is related to topographic variation in temperature which is confounded with vegetation community. Data suggest that climatic changes will result in altered aboveground and soil C and N sequestration and fluxes.     

Interactive Effects of Soil Nutrients, Moisture and Sand Burial on the Development, Physiology, Biomass and Fitness of Cakile edentula

The relative importance and interactive effects of nutrientsupply, soil moisture content and sand burial on the development,physiology, biomass allocation and fitness ofCakile edentulawere examined under controlled greenhouse conditions. Planttraits were more frequently affected by nutrient supply thanby soil moisture content or sand burial. Measurements on mostplant traits also varied depending on the two or three way interactionsamong the three environmental factors. Plants partially buriedby sand had higher leaf chlorophyll concentration than thoseunburied at the early stages of development, especially underlow soil moisture content. High nutrient supply tended to lowerthe leaf chlorophyll concentration of mature plants, and thiseffect was more pronounced under high as compared to low soilmoisture content. High nutrient supply enhanced the photosyntheticcapacity of plants when they were water stressed. With adequatesoil moisture, high nutrient supply increased/decreased thephotosynthetic capacity of plants with/without previous experienceof water stress. High nutrient supply increased the biomassallocation to the root system of plants, especially at low soilmoisture content. Partial sand burial also promoted biomassallocation to the root system of plants grown at low soil moisturecontent. Soil nutrition; water supply; sand accretion; multiple stresses; biomass allocation; Cakile edentula     

Identification of Enzymes and Quantification of Metabolic Fluxes in the Wild Type and in a Recombinant Aspergillus oryzae Strain

Two α-amylase-producing strains of Aspergillus oryzae, a wild-type strain and a recombinant containing additional copies of the α-amylase gene, were characterized with respect to enzyme activities, localization of enzymes to the mitochondria or cytosol, macromolecular composition, and metabolic fluxes through the central metabolism during glucose-limited chemostat cultivations. Citrate synthase and isocitrate dehydrogenase (NAD) activities were found only in the mitochondria, glucose-6-phosphate dehydrogenase and glutamate dehydrogenase (NADP) activities were found only in the cytosol, and isocitrate dehydrogenase (NADP), glutamate oxaloacetate transaminase, malate dehydrogenase, and glutamate dehydrogenase (NAD) activities were found in both the mitochondria and the cytosol. The measured biomass components and ash could account for 95% (wt/wt) of the biomass. The protein and RNA contents increased linearly with increasing specific growth rate, but the carbohydrate and chitin contents decreased. A metabolic model consisting of 69 fluxes and 59 intracellular metabolites was used to calculate the metabolic fluxes through the central metabolism at several specific growth rates, with ammonia or nitrate as the nitrogen source. The flux through the pentose phosphate pathway increased with increasing specific growth rate. The fluxes through the pentose phosphate pathway were 15 to 26% higher for the recombinant strain than for the wild-type strain.     

温度、土壤水分和NaCl对黄顶菊种子萌以的影响

光照和黑暗条件下的黄顶菊种子萌发无显著差异;种子萌发的适宜温度为25～35℃:种子萌发率随着NaCl浓度的升高而下降;种子萌发的最佳土壤含水量为35%～45%.在最适温度下,种子萌发耐受NaCI的临界值为89.919 mmol·L-1,极限值为218.92 mm01.L-1;不同温度和NaCl以及二者共同作用使黄顶菊种子萌发受到的抑制都极显著.     

Optimization of Airborne Endotoxin Exposure Assessment: Effects of Filter Type, Transport Conditions, Extraction Solutions, and Storage of Samples and Extracts

Endotoxin exposure occurs in homes and occupational environments and is known to cause adverse health effects. In order to compare results from different studies and establish standards, airborne endotoxin exposures should be assessed using standardized methods. Although the European Committee for Standardization (CEN) developed guidelines for endotoxin exposure assessment, these leave room for individual interpretation. The influence of methods of sampling, extraction, and analysis has never been investigated in a full experimental design. Thus, we sought to fully elucidate the importance of all facets of endotoxin assessment. Inhalable dust samples collected simultaneously were used to investigate the effects on and interactions with airborne endotoxin concentration in two working environments of filter type (glass fiber or Teflon), transport conditions (with/without desiccant), sample storage (−20 or 4°C), extraction solution (pyrogen-free water [PFW] or PFW plus 0.05% Tween 20), extract storage (−20 or 4°C), and assay solution (PFW or PFW plus 0.05% Tween 20). Four hundred samples were collected and randomly distributed over the 20 combinations of treatments. There were no differences found for transport conditions and storage temperature of extracts. Also, no interactions between study variables existed. Sampling on glass-fiber filters, storage of samples in the freezer, and extraction in PFW plus 0.05% Tween 20 resulted in 1.3-, 1.1-, and 2.1-fold-higher estimated endotoxin concentrations, respectively. Use of PFW plus 0.05% Tween 20 in the assay solution had an additive effect. Thus, this study investigated gaps in the CEN protocol and provides data with which to fully specify a protocol for standardization of endotoxin exposure assessment.     

The Effects of Soil Moisture on Structural and Biomass Characteristics of Four Salt Marsh Plants

In a controlled greenhouse experiment young Deschampsia cespitosa,Grindelia integrifolia, Distichlis spicata and Salicornia virginicaplants were subjected to dry, field capacity, and saturatedsoil conditions. Plant height, stem diameter, stem density,number of leaves, number and length of internodes, and numberof primary and secondary branches varied among the three treatments.The quantity of aerenchyma in S. virginica was greatest in thesaturated treatment. In G. integrifolia the amount of secondaryxylem was greatest in the dry treatment. Maximum above- andbelow-ground biomass occurred under field capacity conditionsfor the four species. Root to shoot ratios of D cespitosa andS. virginica were not affected by changes in soil moisture whilethat of D. spicata was lowest in the saturated treatment andthat of G. integrifolia was lowest in the dry treatment. Key words: Salt marsh, soil moisture, plant structure     

Short and Long-Term Soil Moisture Effects of Liana Removal in a Seasonally Moist Tropical Forest

Lianas (woody vines) are particularly abundant in tropical forests, and their abundance is increasing in the neotropics. Lianas can compete intensely with trees for above- and belowground resources, including water. As tropical forests experience longer and more intense dry seasons, competition for water is likely to intensify. However, we lack an understanding of how liana abundance affects soil moisture and hence competition with trees for water in tropical forests. To address this critical knowledge gap, we conducted a large-scale liana removal experiment in a seasonal tropical moist forest in central Panama. We monitored shallow and deep soil moisture over the course of three years to assess the effects of lianas in eight 0.64 ha removal plots and eight control plots. Liana removal caused short-term effects in surface soils. Surface soils (10 cm depth) in removal plots dried more slowly during dry periods and accumulated water more slowly after rainfall events. These effects disappeared within four months of the removal treatment. In deeper soils (40 cm depth), liana removal resulted in a multi-year trend towards 5–25% higher soil moisture during the dry seasons with the largest significant effects occurring in the dry season of the third year following treatment. Liana removal did not affect surface soil temperature. Multiple and mutually occurring mechanisms may be responsible for the effects of liana removal on soil moisture, including competition with trees, and altered microclimate, and soil structure. These results indicate that lianas influence hydrologic processes, which may affect tree community dynamics and forest carbon cycling.     

Upscaling Effects of Soil Improvement by Microbially Induced Calcite Precipitation by Surface Percolation

This study has contributed to the technology of soil stabilization via biocementation based on microbially induced calcite precipitation. The newly described method of in situ soil stabilization by surface percolation to dry soil under free draining environment is tested for its up-scaling potential. Then, 2-m columns of one-dimensional trials indicated that repeated treatments of fine sand (<0.3 mm) could lead to clogging closed at the injection end, resulting in limited cementation depth of less than 1 m. This clogging problem was not observed in 2 m coarse (>0.5 mm) sand columns, allowing strength varying between 850 to 2067 kPa along the entire 2 m depth. Three-dimensional fine sand cementation trials indicated that relatively homogenous cementation in the horizontal direction could be achieved with 80% of cemented sand cementing to a strength between 2 to 2.5 MPa and to a depth of 20 cm. A simple mathematical model elucidated that the cementation depth was dependent on the infiltration rate of the cementation solution and the in-situ urease activity. The model also correctly predicted that repeated treatments would enhance clogging close to the injection point. Both experimental and simulated results suggested that the surface percolation technology was more applicable for coarse sand.     

不同土壤水分条件对七叶一枝花光合特性及有效成分皂苷含量的影响

采用盆栽土壤水分胁迫试验方法,分析不同土壤水分含量（5．78％～21．32％）对珍稀濒危药用植物七叶一枝花（Parispolyphylla）光合特性和主要有效成分皂苷积累的影响,以期为人工栽培中水分的管理提供依据。结果表明,随着水分胁迫的加剧,叶绿素含量、最大净光合速率（Amax）和光饱和点（LSP）逐渐下降,而光补偿点（LCP）和暗呼吸速率（Rd）逐渐升高;根茎体内总皂苷含量则随土壤水分含量的降低先增加后降低,当土壤含水量为12．44％时皂苷含量最大（11．95％）。可见水分胁迫不利于七叶一枝花的光合作用,但适度水分胁迫可提高其皂苷含量。因此,人工栽培七叶一枝花时,前期需提供较充足水分以满足其营养生长,后期则可进行适当的水分胁迫,以提高皂苷含量。     

Effects of Local Variations in Soil Moisture on Hydrophobic Deposits and Dye Diffusion in Corn Roots

The effects of local soil water content (SWC) alone on the development of hydrophobic deposits and on diffusivity of root tissues were studied in primary roots of maize seedlings whose top regions were growing at a constant rate in damp soil. Corn primary roots were grown through 30 cm-profiles of soil with pre-set dry (8% SWC), or wet (23% SWC), middle layers, and moist (15% SWC) top and bottom layers. When the root tissues in the soil of variable SWC were maturing (approximately 17% of the total root length), the tips of the roots were in damp soil several centimeters away and growing at the rate characteristic of this environment. Histochemistry and fluorescence microscopy on root sections of similar age showed that in these roots local SWC had no effect on hypodermal and endodermal suberization: both had equally developed Casparian bands and suberized lamellae. However, local SWC did alter the hydrophobic deposits in the walls of the epidermis; they increase in dry soil. To study tissue diffusivity, root portions from dry or wet soil were divided in the transverse direction, and half was dipped in sulphorhodamine G (SRG), sectioned, and observed with fluorescence optics. The other half was studied with a cryo-scanning electron microscope to observe the contents of the cortical intercellular spaces. The rate of SRG diffusion in a portion of root from dry or wet soil was independent of local SWC but was positively correlated with numbers of fluid-filled intercellular spaces. The implications of these observations for the movements of ions through the root cortex are discussed.     

土壤水分含量的理论分析及预测模型

本文应用物理学中的电介质和电磁理论,分析和研究土壤的组成成分,得到了反映土壤水分含量的理论表达式,并在自行研制的测试仪器上,对相关变量进行测量,由此建立了土壤水分含量的预测模型,统计检验和国代结果显示了理论模型和预测模型的合理性．