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21.
Contrary to our expectations, soil salinity and moisture explained little of the spatial variation in plant establishment in the upper intertidal marsh of three southern California wetlands, but did explain the timing of germination. Seedlings of 27 species were identified in 1996 and 1997. The seedlings were abundant (maximum densities of 2143/m2 in 1996 and 1819/m2 in 1997) and predominantly annual species. CCAs quantified the spatial variation in seedling density that could be explained by three groups of predictor variables: (1) perennial plant cover, elevation and soil texture (16% of variation), (2) wetland identity (14% of variation) and (3) surface soil salinity and moisture (2% of variation). Increasing the spatial scale of analysis changed the variables that best predicted patterns of species densities. Timing of germination depended on surface soil salinity and, to a lesser extent, soil moisture. Germination occurred after salinity had dropped below a threshold or, in some cases, after moisture had increased above a critical level. Between 32% and 92% of the seedlings were exotic and most of these occurred at lower soil salinity than native species. However, Parapholis incurva and Mesembryanthemum nodiflorum were found in the same environments as the native species. In 1997, the year of a strong El Niño/Southern Oscillation event with high rainfall and sea levels, the elevation distribution of species narrowed and densities of P. incurva and other exotic species decreased but densities of native and rare species did not change. The ‘regeneration niche’ of wetland plant communities includes the effects of multiple abiotic and biotic factors on both the spatial and temporal variations in plant establishment. 相似文献
22.
Enumeration of denitrifying microbial populations in turf 总被引:2,自引:0,他引:2
Summary Denitrifer populations of a silt and silt loam soil under a Kentucky bluegrass turf were enumerated using the most probable
number (MPN) procedure. The influence of soil texture, soil depth, soil moisture, and additions of nitrate fertilizer on denitrifier
populations were determined.
Saturated soil conditions increased denitrifier populations 87-fold in the silt soil and 121-fold in the silt loam soil. Denitrifier
populations did not differ significantly between soil depths and additions of fertilizer nitrate did not influence populations. 相似文献
23.
Nitrogen fertigation of greenhouse-grown cucumber 总被引:2,自引:0,他引:2
I. Papadopoulos 《Plant and Soil》1986,93(1):87-93
Summary This greenhouse study investigated the response of trickle-irrigated cucumber (Cucumis sativa cv. ‘Petita’) to three N levels applied with every irrigation via the irrigation stream. The plants were grown in pots filled
with 12 kg of soil. Water containing 5.8, 11.8, or 17.8 mmol N/l, and uniformly supplied with 2.0 and 3.9 mmol/l of P and
K, respectively, was applied two to three times daily. In all treatments of 0.3 leaching fraction was allowed.
The resulting total N applications were 15.7, 31., and 47.2 g N/plant. The total amount of water applied was 1851/plant. Total
N and NO3-N, in lajinae and petioles, increased with increasing N level whereas P and K in generated decreased. Although different
NO3/NH4 ratios in the treatments may have influeced the response to N, it could be concluded that the highest yield was obtained
with 11.8 mmol N/1 due to increased number of fruit. In the root volume of this treatment the NO3-N concentration in the soil solution was aroun 7 mmol/1 for most of the growing season. The dry matter concentration of fruits
was not affected by the N levels.
It was concluded that 11.8 mmol N/1 applied with every irrigation via the irrigation stream is adequate to cover the needs
of greenhous-grown cucumber for higher yield (9.42 kg/plant over a harvesting period of 93 days). 相似文献
24.
Summary Amylase, dehydrogenase, arylsulphatase and phosphatases activities were measured in a clay-loam soil amended with seven different
crop residues. All enzyme activities, except phosphomonoesterase, were generally higher in the derived soil samples than in
the original soil. Addition of tobacco and sunflower residues caused an increase on most of the enzyme activities while tomato
residues increased only the amylase and phosphodiesterase activities.
As the enzyme activities were positively correlated to each other, a common source of the enzymes is suggested even though
the coefficients of correlation demonstrate that only a low percentage of the variability can be ascribed to the interactions
among enzyme activities. 相似文献
25.
Gamze Gülez 《Journal of microbiological methods》2010,82(3):324-326
To study bacterial behavior under varying hydration conditions similar to surface soil, we have developed a system called the Pressurized Porous Surface Model (PPSM). Thin liquid films created by imposing a matric potential of − 0.4 MPa impact gene expression and colony development in Pseudomonas putida. 相似文献
26.
27.
Summary The effect of cropping systems of wheat-maize (WM), wheat-rice (WR), wheat-groundnut (WG), gram-bajra (GrB), potato-guara
(PGu), and raya-mash (RaMa) in combination with treatments of dummy (uncultivated area) and applied Zn 0.0 (Zn0), 2.8 (Zn1), 5.6 (Zn2) 11.2 (Zn3) kg/ha was studied on the transformation of labile Zn fractions: exchangeable (Exch.), adsorbed (TAd) [weakly (WAd), moderately
(MAd), strongly (SAd)], and organic matter (OM) in different layers of sandy loam soil. The added Zn stayed largely in the
0–30 cm layer and was associated with the WAd- and OM-Zn fractions. About 70% of the total labile Zn (PAv) remained in the
WAd- and OM-Zn, that is, 33 and 39% in 0–15 cm layer, and 33–39% and 31–36% in 16–150 cm layer. All the Zn fractions in 0–15
cm layer, and only of WAd in 16–30 cm layer, significantly increased with rates of Zn addition. These were also significantly
higher in Zn1–3 than Zn0 and dummy treatments because of the residual Zn.
Diverse effects of cropping systems on soil properties, residual Zn, and labile Zn fractions were found. The influence was
strong in 0–15 cm layer decreasing gradually with soil depth due largely to differences in Zn requirement, crop intake of
various Zn fractions and the cultural practices of the systems. All the crops and rotations appreciabilly responded to Zn
application. Uptake of Zn by crops markedly and successively increased with increasing rates of Zn application. The WR caused
a significant increase in soil organic matter whereas WR and WM in CaCO3. The WR, WM and GrB resulted in a decrease in pH while WG and GrB in CaCO3. The RaMa and PGu maintained much higher residual Zn than other systems. The systems which caused the maximum decrease in
Zn fractions were: cereal-cereal (WM) in Exch. legume-millet (GrB) in all the adsorbed, PAv and the Zn associated with CaCO3, vegetable-legume (PGu) also in MAd and SAd; and cereal-legume (WG) in OM and PAv. Hence GrB, WG and WM in that order will
cause the deficiency of Zn much earlier than the other systems due to greater use and or transformation of WAd- andOM-Zn.
Such effects were least under RaMa because it increased the WAd-, MAd- and OM-Zn. 相似文献
28.
Maria João Feio Trefor B. Reynoldson Verónica Ferreira Manuel Augusto S. Graça 《Hydrobiologia》2007,579(1):55-68
We sampled macroinvertebrates at 75 locations in the Mondego river catchment, Central Portugal, and developed a predictive
model for water quality assessment of this basin, based on the Reference Condition Approach. Sampling was done from June to
September 2001. Fifty-five sites were identified as “Reference sites” and 20 sites were used as “Test sites” to test the model.
At each site we also measured 40 habitat variables to characterize water physics and chemistry, habitat type, land use, stream
hydrology and geographic location. Macroinvertebrates were generally identified to species or genus level; a total of 207
taxa were found. By Unweighted Pair Group Method with Arithmetic mean (UPGMA) clustering and analysis of species contribution
to similarities percentage (SIMPER), two groups of reference sites were established. Using Discriminant Analysis (stepwise
forward), four variables correctly predicted 78% of the reference sites to the appropriate group: stream order, pool quality,
substrate quality and current velocity. Test sites’ environmental quality was established from their relative distance to
reference sites, in MDS ordination space, using a series of bands (BEAST methodology). The model performed well at upstream
sites, but at downstream sites it was compromised by the lack of reference sites. As with the English RIVPACS predictive model,
the Mondego model should be continually improved with the addition of new reference sites. The adaptation of the Mondego model
methodology to the Water Framework Directive is possible and would consist mainly of the integration of the WFD typology and
increasing the number of ellipses that define quality bands.
Handling editor: K. Martens 相似文献
29.
The estimation of soil moisture by using the backscattering coefficient of radar in a mountainous region is a challenging task due to the complex topography, which impacts the distribution of soil moisture and changes the backscattering coefficient. Complicated terrain can disturb empirical moisture estimation models, thereby, the resulting estimates of soil moisture are very unlikely reliable. This article proposed an innovative way of integration of the topographic wetness index (TWI) and the backscattering coefficient of soil obtained from the TerraSAR-X image, which improves the accuracy of measurement of the soil moisture. The standard estimation error and the coefficient of determination from the model were used to evaluate the performance of TWI. Our results show that the standard estimation error was decreased from: (1) 4.0% to 3.3% cm3 cm−3 at a depth of 5 cm and (2) 4.5% to 3.9% cm3 cm−3 at a depth of 10 cm. The most reliable estimation was observed at a depth of 5 cm, when it was compared with those of 0–5 cm, 10 cm and 15 cm. The TWI from the digital elevation model (DEM) is useful as a constraint condition for modeling work. This article concludes that the integration of the backscattering coefficient of soil with TWI can significantly reduce the uncertainty in the estimation of soil moisture in a mountainous region. 相似文献
30.
Previous studies have demonstrated that higher nitrogen (N) and water availability affect both above- and below-ground communities, soil carbon and N pools, and microbial activity in semi-arid grasslands of Inner Mongolia. However, how soil phosphorus (P) and sulfur (S) pools, and related soil enzyme activities (as indicators of P and S cycles) respond to long-term N and water addition has still remained unclear. Since 2005, a field experiment with urea and water amendments has been conducted to examine their effects on total and available P and S concentrations and alkaline phosphomonoesterase (PME) and aryl-sulfatase (ArS) activities in three soil aggregate fractions: large macroaggregates (>2 mm), small macroaggregates (0.25–2 mm), and microaggregates (<0.25 mm) in an Inner Mongolia semi-arid grassland. Normalized to aggregate mass, microaggregates retained the highest total P and S concentrations. Both N and water additions increased the available P (by up to 84.5%) and the available S (by up to 150%) in the soil aggregate fractions. Soil acidification, as a result of the N addition, decreased both alkaline PME and ArS activities by up to 62.9% and 39.6%, respectively, while the water addition increased their activities. Our observations revealed that soil acidification (under the N addition) and elevated enzyme activity (under the water addition) played important roles in the levels of soil available P and S. The depression of P- and S-acquiring enzymes with soil acidification may decrease P and S availability, potentially impacting ecosystem processes and limiting the restoration of these grassland systems. The water addition was shown to be a more effective practice than the urea amendment for improving soil structure, supplying available P and S, and maintaining the sustainability of this semi-arid grassland. 相似文献