The influence of moisture and temperature on the number of bacteria in the soil

Прямым флюоресцентным микроскопическим методом исследовали зависимость между числом бактерий в почве и температурой почвы и содержанием почвенной влаги. Исследовали 20 расличных образпов почвы, принадлежавших к подзолистым почвам, бурозему, чернозему и садовым почвам. Число бактерий в различных видах почвы колебалось, и разница между максимальным и минимальным их содержанием в почве варьировала (рис. 1). Во всех случаях мы убеждались, что главным фактором, влияюшим на число бактерий в почве, является влажность. Роль температуры отступлает на второй план. Мы нигде не наблюдали отношений, которые отвечали бы зависимостям, установленным Fehér (R-фактор). Для большей части образцов почв зависимость между содержанием почвенной влаги и числом бактерий такова, что с повышением влажности количество бактерий возрастает почти линейно, достигая максимума при приблизительно 60% влажности. При приблизительно 80% влажности начинается выразительное падение числа бактерий (рис. 2). Для небольшого числа образцов среды мы установили наличие определенной аномалии, которая заклучается в том, что повышение содержания влаги больше чем на 80% полной влагоемкости почвы не вызывает понижения числа бактерий, однако несколько повышает дисперсию установленных величин (рис-3).     

The influence of the soil structure and moisture content on the number of bacteria and the degree of nitrification

ИзгчалоAЬ одноврeмeнноe дeйствиe сBрCкСC@ы поGвKi и Aодeрeа влаBи на количe бактeрий и интeнсивноAтЬ нитрифика. ции в гумуA-карбонаBной почвe. Путeм просeиваниHя образцоCпочвы чeрeз сиBа были в044B;цeлeны слeдующиe фракции: I — агрeгaаты мeнЬшe 1 мм; II — агрeгаты размe@ами в 1—2; мм; III — аг@eгаты размeрами в 2—3 мм; IV — агтeгаBы размeрами в 3—4 мм; V — агрeгаBы размeрами в 4—5 мм. Образцы брали три @аза а год. Для опрeДeлeния количeства бактeрий полЬзовалисЬ прямым мeтодeм флуорeсцeнтной м0438;H043A;H0440;H043E;скопии по Strugger в модификации по Seifert. Пeрeд опрeдeлeниeм биогeнности образцы насыщли влагой до заранee установлeнного уровня и инкCбировали 48 час. при тeмпeратгрe 20° С Нитрификацию опрeдeлOли послe 14-днeвной ?нкгбации образFов, насKщeнных влвгой до опрeдeлeнного уровня и хранившихся в тeрмостатe пр? 20° А. Бы;ло установлeно, что количeство бактeрий зависит от содeржания влаги и 043F;очти нe зависит оB размeров агрeгатов (рис. 1). ИнтeнсивностЬ нитрификации зависит как от содeржаниO влаги, так ? оB размeров агр;eгатов. НаиболЬHая интeнсивностЬ наблюдаласЬ в слу чаe агрeгатов пe@вой фракции, т. e. при диамeтрах мeнЬHe 1 мм. С гвeличeниeм диамeтров агрeгатов интeнсивностЬ нитрификации постeпeнно поннжаласЬ (@ис. 2). Понижeниe интeнсивности нитрификации отличалосЬ опрeдeлCнной правилЬностЬю, инаосновании ee анализа мы пришли к выводу, что инBeнсивностЬ нитрификаFии прямо пропорFионадЬна вeдиGинe спeцифичeAкой повeрхносBи агрeгатов. ДоказатdдЬство зтого привeдeно на рис. З. Для протeрки того, как на интeнсивносBЬ нитрификации дeйствуeт радмeлЬчeниe агрeгатов, мы поставнди опыт, при котором апрeгаBы V фракции были размeлЬчeны до размeров I фракции. Послe измeлЬчeниO интeнсивностЬ ниBририкаFии знаGиBeлЬно повысиласЬ (рис. 4).     

The influence of moisture and temperature on the number of microorganisms in the soil

Folia Microbiologica - The influence of moisture and temperature on the number of bacteria in the soil was studied by means of Strugger’s microscopic fluorescence method. Field and laboratory...     

Available soil moisture as a basis for land capability assessment in semi arid regions

Rangelands are extensive areas in arid or semi arid regions. They have many uses (e.g. grazing, dry land farming, wildlife habitat, recreation and mining). Generally vegetation is sparse and the principal plant species are adapted to erratic rainfall events. Rainfall use efficiency (RUE) is the quotient of annual primary production divided by annual rainfall i.e. the number of kilograms aerial dry matter produced by 1 ha in 1 year per millimetre of rain. It decreases with increasing aridity. Reasonably well managed arid and semi arid grazing lands are usually in the 3.0–6.0 value range. Available soil moisture is the principal determinant of productivity. The role and significance of the major parameters (rainfall, soil depth, slope and salinity, texture, cover, erosion etc) are considered. Available moisture can be predicted if the appropriate relative productivity indices (RPI) are used in a parametric way. The predictions can be used to classify land according to its capability to support plant growth. Equations have been derived which enable land to be classified on the basis of its potential productivity. Links between land capability and vegetation cover are given.     

The influence of soil moisture on water potential,transpiration and photosynthesis of conifer seedlings

Summary The influence of soil moisture content and soil water potential on plant water potential, transpiration and net-photosynthesis of potted larch (Larix decidua), spruce (Picea abies) and pine (Pinus cembra) was studied under constant and close to optimum conditions in a laboratory.The equilibrium plant water potential measured under non-transpiring conditions came close to soil water potential, but in moist soil the equilibrium potential was slightly lower, particularly in larch where transpiration was not fully arrested. In very dry soil, plants had higher water potential than soil, presumably due to roots exploiting the wettest points within the soil.Pine, spruce and larch utilised a large part of soil moisture (down to 25wt.% soil water content or –1.5 bars potential) while maintaining plant water potential near –8, –9.5 and –12.5 bars respectively. A similar pattern occurred in dry soil. The differences between species are explained by differing stomatal sensitivity to water potential.Pine began a gradual reduction in gas-exchange below a soil water potential of –0.4 bars. Larch showed no marked reduction until the soil potential fell to –3.5 bars but below this the shut-down in gas-exchange was rapid. Spruce lay in between.In spite of the early and sensitive gas-exchange reduction with decreasing soil moisture, pine maintained the highest net photosynthesis/transpiration ratio and thus used limited soil water more slowly and economically than the other species.Seedlings maintained a higher rate of gas-exchange in strong light than in weak light, especially at low soil water potentials.     

Intensity of nitrification in soil as a function of time and soil moisture

Proceeding from three previously derived expressions for the intensity of nitrification in soil as a function of time (logΣN=K.logt+q), as a function of incubation moisture (logΣN=A.pF _i+B), as a function of initial moisture (logΣN=C.pF _v+D), it was shown that the nitrification intensity as a function of time and of moisture can be expressed by the bilinear function log ΣN=a.pF _i.logT+b.pF _i+c.logt+d; as a function of time and of initial moisture by the bilinear function logΣ=N=a.pF _v.logt+b.pF _v+c.logt+d; as a function of initial and incubation moisture by the bilinear function log ΣN=a.pF _ipF _v+b.pF _i+c.pF _v+d. The intensity of nitrification as a function of time, incubation moisture and initial moisture may be expressed by the multilinear function log ΣN=a.pF _i.pF _v.logt+b.pF _i.pF _v+c.pF _i.logt+d.pF _v.logt+e .pF _i+f.pF _v=g.logt+h. This function is valid for all the incubation moistures lying between pF _i 3.0 and 4.0 and for all initial moistures between 3.5 and 5.9 provided that the incubation temperature remains constant.     

The influence of moisture regimes on the population and activity of soil microorganisms

This paper deals with the influence of soil moisture on the fungal population, bacterial population, CO₂-evolution and dehydrogenase activity. Correlation coefficients of various parameters of the soil with different moisture regimes are given. It is demonstrated that soil moisture significantly alters the microbial population, its activity and the relationships between various parameters.     

Calibration of Watermark soil moisture sensors for soil matric potential and temperature

Rapid, accurate, and automated measurement of soil matric potential is desirable. Evidence suggested that the Watermark resistance block might be an appropriate and inexpensive tool, so we conducted an evaluation of its relevant characteristics. A number of these blocks were calibrated under laboratory conditions to determine their individual and aggregate responses to soil matric potential, soil type, and temperature. We found that the temperature response could be expressed as a single equation, valid for all tested blocks, but comparison against matric potential revealed that each block had a characteristic response. Furthermore, block responses were different in two soils and, for a given soil, not necessarily reproducible. Given these limitations, these sensors are probably useful only as relative indicators of soil water status.     

Suction force variation in double-hybrid maize as a function of soil moisture

In experiments with double-hybrid maize grown in the field and in a greenhouse, we analysed the value of the suction force as related to the regime of irrigation. The results showed that the level of water supply to the plants is in good connection with the value of the suction force and the coefficient H (the relative degree of water saturation of the cells) analysed at the same time. In the case of the 2 hybrids under investigation the highest value of coefficient H was found to be between 35–48. The data indicate that the use of these two indices should take part in a physiological method for the settlement and the application of water rules in irrigation.     

The influence of soil moisture on losses of buried seeds to fungi

Although soil fungi are likely to be a major cause of mortality for buried seeds, few ecological studies have examined the role these pathogens play in natural systems. In particular, few studies have investigated whether losses of seeds to soil fungi are habitat-dependent. We used fungicide treatments to investigate whether losses of buried seeds of four grasses (Bromus inermis, Danthonia spicata, Glyceria striata, and Poa pratensis) to soil fungi differed among meadows differing in soil moisture. We also applied water to some treatments, to determine whether this increased losses of seeds to fungi. For all four grasses, fungicide additions improved one or more measures of seed viability, though this effect was small. For Danthonia and Glyceria, fungicide was less likely to improve viability in dry meadows than in wet and/or mesic meadows. Adding water reduced some measures of viability of seeds of Danthonia and Poa in dry meadows, but fungicide partly counteracted these negative effects, suggesting that adding water reduced performance by increasing fungal attack. These results indicate that fungi represent a hazard for buried seeds of these species, particularly in wetter soils, and potentially may contribute to the reduction of populations of vulnerable species in wetter sites.     

Phosphorus depletion in the rhizosphere as influenced by soil moisture

To study the influence of soil moisture on phosphorus (P) depletion in the rhizosphere, maize (Zea mays cv. Trak) was pre-grown in vermiculite filled-PVC tubes for 9 days and then the plants with the tubes were transplanted into soil columns maintained at two soil moisture levels () of 0.14 and 0.20 cm³ cm^–3 for 10 days. The soil columns were separated at 1 cm depth by a nylon screen of 53 m inner mesh size, into 1 cm soil layer above and 3 cm soil column below screen. A root mat developed over the screen, but root hairs only could penetrate it. Regardless of the soil moisture level in the columns, and adequate and equal water and nutrients supply was maintained via wicks from an external nutrient solution to the plant roots in vermiculite. After 10 days, the soil columns were separated from the root mats, quickly frozen in liquid nitrogen and sliced into thin layers (0.2mm) using a refrigerated microtome to give soil samples at defined distances from the root mats for analyses. Lower soil moisture (=0.14) resulted in narrower and steeper depletion profile of 0.5 M NaHCO₃ extractable P (NaHCO₃-P_i) as compared to higher soil moisture (=0.20). Depletion of P in soil solution in the immediate vicinity of root mats did not differ much but the extension of the depletion zones was 0.10 cm at =0.14 and 0.20 cm at =0.20. The depletion up to 0.05cm with =0.14 and up to 0.07 cm with =0.20 was uniform, and may be attributed to the depletion in the root hair zone. Beyond the root hair zones, the theory of diffusion and mass flow was able to explain the observed differences in shape and extent of the P depletion profiles at the two soil moisture levels.     

Leaf gas exchange in a clonal eucalypt plantation as related to soil moisture, leaf water potential and microclimate variables

In order to determine how environmental and physiological factors affect leaf gas exchange in a 9-year-old clonal eucalypt plantation (Eucalyptus grandis Hill ex. Maiden hybrids) in the State of Espirito Santo, Brazil, the diurnal patterns of predawn leaf water potential (Ψ_pd), and leaf gas exchange were monitored from November 1995 to August 1996. Soil water content (Θ) and microclimatic variables were also recorded. Most of the rainfall during the experimental period occurred from October to December 1995 and from March to April 1996, causing a significant variation in Θ and Ψ_pd. A high positive correlation (r ²=0.92) was observed between Ψ_pd and Θ measured at 0.3 m depth from the soil surface. During conditions of high soil water availability, the maximum values of stomatal conductance for water vapor (g _s) and net photosynthetic rate (A) were over 0.4 mol m^–2 s^–2 and l5 μmol m^–2 s^–1, respectively. The results showed that Ψ_pd and leaf gas exchange of the examined trees were susceptible to changes in the water content of the upper soil layers, where the major concentration of active roots occur. Multiple linear regression analysis indicated that photosynthetic active radiation (Q), vapor pressure deficit (VPD), atmospheric CO₂ molar fraction (C _a), and Ψ_pd were the most important factors controlling g _s whereas Q and VPD were the main microclimatic variables controlling A. Received: 5 November 1998 / Accepted: 10 November 1999     

Intraspecific competition as a regulating factor limiting the number of transconjugants in soil

A laboratory study was carried out to determine survival of transconjugant cells ofPseudomonas fluorescens intro duced into sterile soil. The transconjugant survived significantly better when it was the only strain inoculated into the soil; when introduced into soil pre-colonized by the recipient strain, the transconjugant was undetectable. These results indicate that intraspecific competition is a regulating factor limiting the number of transconjugants in soil.     

Water uptake profile response of corn to soil moisture depletion

The effects of soil moisture distribution on water uptake of drip‐irrigated corn were investigated by simultaneously monitoring the diurnal evolution of sap flow rate in stems, of leaf water potential, and of soil moisture, during intervals between successive irrigations. The results invalidate the steady‐state resistive flow model for the continuum. High hydraulic capacitance of wet soil and low hydraulic conductivity of dry soil surrounding the roots damped significantly diurnal fluctuations of water flow from bulk soil to root surface. By contrast, sap flow responded directly to the large diurnal variation of leaf water potential. In wet soil, the relation between the diurnal courses of uptake rates and leaf water potential was linear. Water potential at the root surface remained nearly constant and uniformly distributed. The slope of the lines allowed calculating the resistance of the hydraulic path in the plant. Resistances increased in inverse relation with root length density. Soil desiccation induced a diurnal variation of water potential at the root surface, the minimum occurring in the late afternoon. The increase of root surface water potential with depth was directly linked to the soil desiccation profile. The development of a water potential gradient at the root surface implies the presence of a significant axial resistance in the root hydraulic path that explains why the desiccation of the soil upper layer induces an absolute increase of water uptake rates from the deeper wet layers.     

Improving grasslands: the influence of soil moisture and nitrogen fertilization on the establishment of seedlings

1. In order to investigate the factors influencing the establishment of seedlings in permanent grassland, the influence of soil moisture and nitrogen fertilization on competition between established plants of Lolium perenne and seedlings of Phleum pratense or Trifolium pratense was studied in two experiments under greenhouse conditions using the 'split-box'-technique.
2. There was no difference in the production of plant dry matter of P. pratense or T. pratense between 30% volumetric soil water content (−0·005 MPa) and 22% (−0·04 MPa), but 15% soil moisture (−0·33 MPa) reduced plant growth. L. perenne yields were linearly reduced by reduced soil moisture content.
3. Shoot competition from L. perenne reduced the plant dry matter yield of P. pratense and T. pratense more than did root competition in these experiments. When shoot competition was present, differences between moisture contents were not detected, indicating that light was probably the limiting resource under such conditions. No significant interaction between root competition and soil moisture was observed for plant weight.
4. Root competition was not prevented even though sufficient water and nitrogen were supplied. This indicated either that some other growth factor was limiting or the plants competed for resources at the root hair level even though sufficient resources were supplied at the pot or field scale. Therefore, in the situation of direct drilling of species during grassland renovation, it may be difficult to alleviate competition by adequate provision of water and nitrogen.     

Analysis of ammonia-oxidizing bacteria populations in acid forest soil during conditions of moisture limitation

Ammonia-oxidizer numbers decreased under conditions of moisture limitation in litter, fermentation and humus layers of forest soil in the field, but the extent of regrowth after rehydration varied between layers. Nitrosospira 16S rRNA genes were amplified from all layers, regardless of moisture content or soil pH which varied between 4.1 and 5.2. Nitrosomonas spp. were detected less often, but appeared to exhibit more rapid recovery than the Nitrosospira spp. when drought conditions were relieved by rainfall.     

Indigenous bacteria influence the number of Salmonella typhimurium in the ileum of gnotobiotic mice.

Gnotobiotic BALB/c mice associated with indigenous Lactobacillus, Bacteroides, and two fusiform-shaped Clostridium strains had fewer S. typhimurium present in the ileum 3 days after intragastric challenge with the pathogen than did similarly challenged germfree mice. Acetic and butyric acids were detected in the caecal contents of the gnotobiotic mice, but in smaller concentration than was present in conventionalized mice. No difference in the motility of the small intestine was detected between germfree, gnotobiotic, and conventionalized mice.     

Utilization of the herbicide phosphinothricin as a nitrogen source by soil bacteria

Summary Rhodococcus sp., Pseudomonas paucimobilis and five other bacterial soil isolates were found to be capable of utilizing the l-enantiomer of the herbicide phosphinothricin (2-amino-4-(methylphosphinyl)-butanoic acid) as a nitrogen source. This deamination yielded the structural analogue, 2-oxo-4-(methylphosphinyl)-butanoic acid as the main catabolite of phosphinothricin. On prolonged incubation, slow decarboxylation of the main catabolite occurred with the formation of the stable degradation product 3-methylphosphinico-propanoic acid.