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1.
Differences in plant growth arising from differences in aggregate size in the seedbed are normally atributed to limitations
in nutrient or water supply during the early growth period. This study was initiated to determine if these were the only mechanisms
by which aggregate size influences plant response.
Four different aggregate size fractions (less than 1.6 mm, 1.6 to 3.2 mm, 3.2 to 6.4 mm and 6.4 to 12.8 mm diameter) were
sieved from a silt loam soil. Nutrients were added to the soil and maize was grown in the aggregates for eighteen days after
seedling emergence. Soil matric potential was maintained between — 3 and −20 kPa.
Shoot dry weight declined by 18% as aggregate size increased from less than 1.6 mm to 1.6–3.2 mm. There was little further
decline as aggregate size increased to 6.4–12.8 mm. Final leaf area showed a similar decline. The availability of nutrients
or water were not limiting.
Total root length in the coarsest aggregate system was less than 60% of that in the finest system. Main axes of seminal and
nodal roots were longer in the coarser aggregate systems, the length of primary laterals was not affected, and length of secondary
laterals was lower in the coarser systems. A greater proportion of the roots penetrated the larger aggregates than the smaller
aggregates; however, the larger aggregates offered greater resistance to penetration by a rigid micropenetrometer (150 μ diameter
probe). Diameter of the main axes roots were greatest in the largest two aggregate fractions. it is speculated that a combination
of increased endogenous ethylene in roots in the finest aggregate system due to entrapment by water and increased mechanical
resistance in the coarsest aggregate system accounts for the observed effects on root norphology. 相似文献
2.
Land use impacts on physical properties of 28 years old reclaimed mine soils in Ohio 总被引:1,自引:0,他引:1
Reclamation enhances soil quality by improving physical and chemical properties, which helps in restoration of mine soils.
Evaluation of the effects of post-reclamation land uses on physical and chemical properties of mine soils helps to identify
suitable land uses for mining companies. The objectives of this study were to evaluate the effects of post-reclamation land
uses (e.g., forest, hay and pasture) on selected physical properties of soil in relation to undisturbed forest and agricultural
land use. Soil samples were collected from the 0- to 5-, 5- to 15- and 15- to 30-cm depths in order to determine particle
size distribution, bulk density, water-stable aggregates, mean-weight diameter and soil moisture retention. Cone index and
infiltration rate were determined at soil surface. After 28 years of reclamation, bulk density in the surface layer of all
land uses in the reclaimed mine soil (RMS) was similar to that of undisturbed forest (1.1 Mg m−3) but lower than that of agricultural soils (1.3 Mg m−3). However, soil bulk density at lower depths was not affected. The cone index was higher in the RMS-pasture (2.6 MPa) than
the RMS-forest (1.4 MPa) and RMS-hay (1.5 MPa) due to the trampling effect of grazing animals. The water-stable aggregates
(>2 mm), of 5–8 mm aggregates, were higher in RMS-forest by 24%, 90%, 66%, and under RMS-hay by 13%, 74%, 43% for the 0- to
5-, 5- to 15-, and 15- to 30-cm depths, respectively, than that under undisturbed forest. The mean-weight diameter (0- to
30-cm) of aggregates under RMS-forest and RMS-hay were higher than that under undisturbed forest by 41% and 27%, respectively.
The initial infiltration rates at 5 min in RMS under forest, hay and pasture were less by 20%, 53% and 85%, respectively,
than that under undisturbed forest (19.3 cm min−1). The reclamation of mine soils with forest and hay improved surface soil bulk density and cone index, and enhanced water
infiltration capacity and water-stable aggregates at the lower depths. Therefore, establishment of forest and hay should be
encouraged in the RMS. 相似文献
3.
Görres Josef H. Savin Mary C. Neher Deborah A. Weicht Thomas R. Amador José A. 《Plant and Soil》1999,212(1):75-83
The porous soil environment constrains grazing of microorganisms by microbivorous nematodes. In particular, at matric potentials
at which water-filled pore spaces have capillary diameters less than nematode body diameters the effect of grazing, e.g. enhanced
mineralization, should be reduced ('exclusion hypothesis') because nematodes cannot access their microbial forage. We examined
C and N mineralization, microbial biomass C (by fumigation-extraction), the metabolic quotient (C mineralization per unit
biomass C), nematode abundance, and soil water content in intact soil cores from an old field as a function of soil matric
potential (−3 to −50 kPa). We expected, in accordance with the exclusion hypothesis, that nematode abundance, N and C mineralization
would be reduced as matric potential decreased, i.e. as soils became drier. N mineralization was significantly greater than
zero for −3 kPa but not for −10, −20 and −50 kPa. Microbial biomass C was less at −50 kPa than at −10 kPa, but not significantly
different from biomass C at −3 and −20 kPa. The metabolic quotient was greatest at −50 kPa than any of the other matric potentials.
From the exclusion hypothesis we expected significantly fewer nematodes to be present at −50 and −20 kPa representing water-filled
capillary pore sizes less than 6 and 15 μm, respectively, than at −3 and −10 kPa. Microbivorous (fungivorous+bacterivorous)
nematode abundance per unit mass of soil was not significantly different among matric potentials. Body diameters of nematodes
ranged from 9 μm to 40 μm. We discuss several alternatives to the exclusion hypothesis, such as the 'enclosure hypothesis'
which states that nematodes may become trapped in large water-filled pore spaces even when capillary pore diameters (as computed
from matric potential) are smaller than body diameters. One of the expected outcomes of grazing in enclosures is the acceleration
of nutrient cycling.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
4.
A system was designed, constructed, tested, and used to growBrassica rapa L. seedling roots which were exposed to O2 concentrations from 0 to 0.21 mol mol−1, water potentials from 0 to −80 kPa, temperatures from 10 to 34°C, and mechanical impedance from 0 to 20.8 kPa. The experimental
design was a central composite rotatable design with seven replications of the center point. Measurements were taken of taproot
length, taproot diameter at the point of initiation of root hairs (diameter 1), and one cm above the first measurement (diameter
2), and total length and number of first-order laterals.
Temperature had the greatest effect on seedling root growth, with linear and quadratic temperature effects significant for
all root measurements except taproot diameter 2 which just had a significant linear effect. Water potential had a significant
linear effect on lateral length and number of laterals and a significant quadratic effect on taproot diameter 1. Mechanical
impedance had a significant effect only on taproot diameter 2. Oxygen was not significant for any root measurement. The mechanical
impedance by water potential interaction was significant for taproot length and taproot diameter 1.
A temperature optimum was found for taproot length, taproot diameter 1, lateral length, and lateral number, at 26.0, 42.5,
26.5, and 26.4°C, respectively. Taproot diameter 1 had a water potential optimum at −36.5 kPa, whereas taproot diameter 2
had a mechanical impedance optimum at 12.5 kPa.
A growth cell designed for this study allows independent control of soil strength, water potential, oxygen concentration,
and temperature. Thus, the cell provides the capability which was demonstrated forBrassica rapa L. to grow seedling roots under complete control of the soil physical properties. 相似文献
5.
Neher Deborah A. Weicht Thomas R. Savin Mary Görres Josef H. Amador José A. 《Plant and Soil》1999,212(1):85-99
The influence of soil matric potential on nematode community composition and grazing associations were examined. Undisturbed
cores (5 cm diameter, 10 cm depth) were collected in an old field dominated by perennial grasses on a Hinckley sandy loam
at Peckham Farm near Kingston, Rhode Island. Ten pairs of cores were incubated at −3, −10, −20 and −50 kPa matric potential
after saturation for 21–28 or 42–58 days. Nematodes were extracted using Cobb's decanting and sieving method followed by sucrose
centrifugal-flotation and identified to family or genus. Collembola and enchytraeids present were also enumerated because
they are grazers that reside in air-filled spaces. Direct counts of bacteria and fungi were made to estimate biovolume using
fluorescein isothiocyanate and fluorescein diacetate stains, respectively. Trophic diversity and maturity indices were calculated
for nematode communities. Three patterns of matric potential effect were observed for nematode taxa. One, there was a consistent
effect of matric potential for all seasons for Alaimus, Monhysteridae, Prismatolaimus, Paraxonchium and Dorylaimoides. Two,
some effects of matric potential were consistent among seasons and other effects were inconsistent for Aphelenchoides, Aphelenchus,
Cephalobidae, Coomansus, Eudorylaimus, Huntaphelenchoides, Panagrolaimidae, Paraphelenchus, Sectonema, and Tripyla. Third,
effects of matric potential were always inconsistent among seasons for Aphanolaimus, Aporcelaimellus, Bunonema, Rhabditidae,
and Tylencholaimus. As predicted, fungal and bacterial biomass responded oppositely to matric potential. Total bacterial biomass
was greater at −3 kPa than −10, −20 and −50 kPa (P=0.0095). Total fungal biomass was greater at −50, −20 and −10 kPa than
−3 kPa (P=0.0095). Neither bacterial-feeding, fungal-feeding nor predacious nematodes correlated significantly with bacterial
or fungal biomass. Omnivorous and predacious nematodes correlated positively with number of bacterial-feeding nematodes; predacious
nematodes also correlated positively with fungal-feeding nematodes. Numbers of Collembola and enchytraeids were more often
correlated positively with microbial-grazing nematode numbers in drier than moist soils. From this study, we propose two mechanisms
that may explain nematode community structure changes with matric potential: differential anhydrobiosis and/or enclosure hypotheses.
The later suggests that drying of soil generates pockets of moisture in aggregates that become isolated from one another enclosing
nematodes and their food in relatively high concentrations creating patches of activity separated by larger areas of inactivity.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
B. Shrestha S. Lipe K. A. Johnson T. Q. Zhang W. Retzlaff Z.-Q. Lin 《Plant and Soil》2006,288(1-2):189-196
Biological volatilization of selenium (Se) in contaminated areas represents an environmentally friendly phytoremediation approach. Implementation of phytovolatilization technology for the remediation of Se-contaminated soils or sediments is oftentimes limited by its low remediation efficiency under field conditions. This greenhouse study determined the feasibility of manipulating soil organic content and hydraulic conditions in a soil–pickleweed (Salicornia bigelovii) system for the enhancement of Se volatilization. Based on annual shoot biomass production rate under field conditions (approximately 1.5 kg m−2), the addition of pickleweed shoot tissues to the soil surface resulted in 2.2-fold more biogenic volatile Se than the control, up to 251.6 ± 140.5 μg m−2 d−1. Selenium volatilization was significantly reduced at a soil water potential of −25 kPa, but substantially increased after re-irrigation to 0 kPa. In a 42-day experiment, the rate of Se volatilization was significantly correlated with soil water potential (P < 0.0001). Findings from this study demonstrate that Se volatilization be substantially enhanced by amending soil with pickleweed residues and by creating wetting and drying cycles that can be monitored with soil water potential probes in the field. 相似文献
7.
An experiment was conducted to determine soil and plant resistance to water flow in faba bean under field conditions during
the growing season. During each sampling period transpiration flux and leaf water potential measured hourly were used with
daily measurements of root and soil water potential to calculate total resistance using Ohm's law analogy. Plant growth, root
density and soil water content distributions with depth were measured. Leaf area and root length per plant reached their maximum
value during flowering and pod setting (0.31 m2 and 2200 m, respectively), then decreasing until the end of the growing period. Root distribution decreased with depth ranging,
on average, between 34.2% (in the 0–0.25 m soil layer) and 18.1% (in the 0.75–1.0 m soil layer). Mean root diameter was 0.6
mm but most of the roots were less than 0.7 mm in diameter. Changes in plant and soil water potentials reflected plant growth
characteristics and climatic patterns. The overall relationship between the difference in water potential between soil and
leaf and transpiration was linear, with the slope equal to average plant resistance (0.0165 MPa/(cm3 m-1 h-1 10-3). Different regression parameters were obtained for the various measurement days. The water potential difference was inversely
related to transpiration at high leaf stomatal resistance and at high values of VPD. Total resistance decreased with transpiration
flux in a linear relationship (r=−0.68). Different slope values were obtained for the different measurement days. Estimated
soil resistance was much lower than the observed total resistance to water flow. The change from vegetative growth to pod
filling was accompanied by an increase in plant resistance. The experimental results support previous findings that resistance
to water flow through plants is not constant but is influenced by plant age, growth stage and environmental conditions. A
more complex model than Ohm's law analogy may be necessary for describing the dynamic flow system under field conditions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
M. Drążkiewicz 《Folia microbiologica》1996,41(1):76-80
Nitrification was measured in fractions of chernozemic rendzina and lessivē soil differing in aggregate size. In both soils
the maximum rates occurred in aggregates between 1 and 3 mm in diameter. The effects of structural and other properties (particle
composition, pore-size distribution, surface area, organic C and total N content, ratio of air volume to water volume in aggregates)
proved to be insignificant except for the nitrification rate in the lessivē soil, which positively correlated with the fraction
of particles between 20 and 50 μm in diameter. 相似文献
9.
Keith R. J. Smettem 《Biologia》2009,64(3):470-473
During rainfall events, macropores are generally considered to play a dominant role in infiltration after matrix ponding has
occurred. Once ponding has been initiated on the soil matrix, surface runoff may be generated at rainfall intensities less
than the saturated hydraulic conductivity of the soil. The amount of runoff will depend on detention storage and how efficiently
the surface flow is captured by soil macropores. The efficiency of surface water removal by macropores is diminished if surface
vents become clogged sealed by washed-in sediment during the runoff event.
Post-event opening of surface vents by the animals that created them can remove evidence of the sealing process and so it
is particularly important to examine the temporal stability of the soil surface during rainfall events.
In this paper evidence of macropore clogging and post-event clearing of the surface vents is presented. A fine sandy loam
passed through a 2 mm diameter sieve was packed into two boxes, each with a surface area of 0.5 m2. The boxes were irrigated at 28 mm h−1 using a low energy rainfall sprinkler. This application rate exceeded the saturated hydraulic conductivity of the soil matrix.
After measuring runoff and infiltration from the boxes, one box was held as a control and the second was inoculated with earthworms.
After four weeks the inoculated box had a burrow density at the soil surface of 380 m−2, with an average diameter of 5 mm.
Macropore sealing occurred immediately after ponding and runoff from the macroporous soil was only 10.7% less than a control
with no macropores. Within 24 h after cessation of simulated rainfall the earthworms had cleared washed in material from over
95% of burrow vents. Time to matrix ponding was well predicted using hydraulic parameters characteristic of the soil matrix,
indicating that matrix sealing was not significant under the experimental conditions. 相似文献
10.
Poor crop stand is a common problem in saline areas. Germination and seedling emergence may be depressed as a result of impeded
aeration, saline or dry conditions. In this study, we examined the effects of salinity and moisture stress and their interactions
on seed germination and seedling growth of carrots. Variable soil matric and osmotic potentials were either obtained by equilibrating
soil salinized to different degrees on a 0.5 MPa ceramic plate soil moisture extractor or by adding different amounts of salt
solutions to the same mass of air-dried soil, based on a previously determined soil moisture release curve, and allowing to
equilibrate for 1 week.
Germination decreased significantly in the investigated silty soil (Aquic Ustifluvent) at soil moisture potentials higher
than −0.01 MPa, whereas osmotic potentials as low as −0.5 MPa did not influence germination. Matric potentials of −0.3 and
−0.4 MPa, respectively, resulted in a strong decrease (35–95%) of germination and delayed germination by 2 to 5 days in the
silty soil to which different amounts (18 and 36%, respectively) and sizes (0.8–1.2 mm and 1.5–2.2 mm, respectively) of sand
particles had been added. No effect of sand and grain diameter was detected. Germination was not affected by comparable osmotic
potentials.
Seedling growth showed a much higher sensitivity than germination to decreasing matric potentials, but was not affected by
osmotic potentials ranging from −0.05 to −0.5 MPa. Optimum shoot growth occurred at matric potentials between −0.025 and −0.1
MPa. Shoot and root growth decreased markedly at matric potentials higher than −0.01 MPa. Fresh weight of shoots decreased
gradually at matric potentials lower than −0.2 MPa. Root growth was significantly increased at matric potentials of −0.1 to
−0.3 MPa, whereas comparable osmotic potentials did not have equivalent effects.
It is concluded that germination and seedling growth are differently affected by comparable matric and osmotic stresses and
that water stress exerts a more negative effect than salt stress. 相似文献
11.
The rates of emergence of wheat and lupin were measured in 13 field experiments on water repellent sands. Conventional sowing
was compared with furrow sowing either with or without the use of a press wheel and several rates of banded wetting agent.
Measurements included, severity of water repellence, plant emergence, rainfall, soil temperature at sowing and, at one site,
the area of wet soil after sowing. All ameliorative techniques improved emergence, with responses being greatest when seeds
were sown into dry soil. Compared with conventional sowing, furrow sowing increased wheat and lupin emergence by an overall
average of 16 and 41%, respectively. The benefits were greater at the drier sites. Increases in emergence due to the use of
a press wheel were sometimes small, although they always occurred (1–19%). It was visually observed that press wheel use gave
more uniform seeding depth, reduced clods and ensured more accurate placement of banded wetting agent. Banded wetting agent
consistently improved wheat and lupin emergence, particularly where early rains were light and press wheels were used. The
wetting agent increased the cross-sectional area of wet topsoil (0–10 cm) which was positively related with increased wheat
emergence (R2 = 0.91). At 0.5 L ha−1 of banded wetting agent, the soil along the furrow was four times wetter than without wetting agent. Wetting agent at 0.5
and 1 L ha−1 (with press wheels) increased wheat emergence by 6 and 11% and lupin emergence by 13 and 11%, respectively. The high rates
of banded wetting agent gave highest plant densities. Grain yield was only measured at three sites. Furrow sowing did not
increase grain yield, however, press wheels use with furrow sowing increased grain yield by 30%. Banded wetting agent increased
grain yield and they were positively correlated. The highest rate increased grain yields by a further 9% above press wheels
and furrow sowing.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
12.
Life history aspects of Ephemera orientalis, a common lowland burrowing mayfly that resides in temperate East Asia, were studied in terms of voltinism, secondary production,
and accumulated degree days for larval development. From March 1998 to June 1999, larvae were sampled monthly (weekly or biweekly
during the emergence period) from a lower reach of the Gapyeong stream in Korea, a stream typical of temperate East Asia,
using a Surber sampler (0.25 m2, mesh 0.25 mm). As a result, the mean density of E. orientalis was 47.21 ± 13.58 indiv. m−2 during the study period. Very small larvae less than 2 mm in body length were sampled on three separate occasions, and emergence
was observed between late April and early October, except during late May. Based on the larval body length distribution and
emergence time, two different developmental groups could be distinguished: the slow developmental group (S-group) and the
fast developmental group (F-group). The F-group completed its life cycle within 4 months, whereas the S-group had a one-year
life cycle. The S-group could be divided into two subgroups, dubbed the S1 and S2-groups, based on larval development. The
developmental groups alternate their life cycles in the order: S1→F→S2→S1. Estimated annual production of the larvae was 68.81 mg DW m−2 y−1; mean biomass was 8.43 mg DW m−2; the annual production to mean biomass ratio was 8.16. The annual mean water temperature of the study year was 14.76 ± 6.63°C.
The total accumulated degree days for larval development was 1396°C for the F-group, 2,055°C for the S1-group, and 1,975°C
for the S2-group. Two different adult body size groups were distinguished (P < 0.001 by t-test): larger adults, which belonged to the S-group, were present throughout the emergence period, whereas smaller adults,
which belonged to the F-group, were mainly present later in the emergence period (August–October). The difference in the accumulated
degree days between the developmental groups may explain the size differences of adults. 相似文献
13.
Summary Ammonium nitrate fertilizer, labelled with15N, was applied in spring to winter wheat growing in undisturbed monoliths of clay and sandy loam soil in lysimeters; the rates
of application were respectively 95 and 102 kg N ha−1 in the spring of 1976 and 1975. Crops of winter wheat, oilseed rape, peas and barley grown in the following 5 or 6 years
were treated with unlabelled nitrogen fertilizer at rates recommended for maximum yields. During each year of the experiments
the lysimeters were divided into treatments which were either freelydrained or subjected to periods of waterlogging. Another
labelled nitrogen application was made in 1980 to a separate group of lysimeters with a clay soil and a winter wheat crop
to study further the uptake of nitrogen fertilizer in relation to waterlogging.
In the first growing season, shoots of the winter wheat at harvest contained 46 and 58% of the fertilizer nitrogen applied
to the clay and sandy loam soils respectively. In the following year the crops contained a further 1–2% of the labelled fertilizer,
and after 5 and 6 years the total recoveries of labelled fertilizer in the crops were 49 and 62% on the clay and sandy loam
soils respectively.
In the first winter after the labelled fertilizer was applied, less than 1% of the fertilizer was lost in the drainage water,
and only about 2% of the total nitrogen (mainly nitrate) in the drainage water from both soils was derived from the fertilizer.
Maximum annual loss occurred the following year but the proportion of tracer nitrogen in drainage was nevertheless smaller.
Leaching losses over the 5 and 6 years from the clay and sandy loam soil were respectively 1.3 and 3.9% of the original application.
On both soils the percentage of labelled nitrogen to the total crop nitrogen content was greater after a period of winter
waterlogging than for freely-drained treatments. This was most marked on the clay soil; evidence points to winter waterlogging
promoting denitrification and the consequent loss of soil nitrogen making the crop more dependent on spring fertilizer applications. 相似文献
14.
Christopher J. Kucharik Kristofor R. Brye John M. Norman Jonathan A. Foley Stith T. Gower Larry G. Bundy 《Ecosystems》2001,4(3):237-258
Landmanagement practices such as no-tillage agriculture and tallgrass prairie restoration have been proposed as a possible
means to sequester atmospheric carbon, helping to refurbish soil fertility and replenish organic matter lost as a result of
previous agricultural management practices. However, the relationship between land-use changes and ecosystem structure and
functioning is not yet understood. We studied soil and vegetation properties over a 4-year period (1995–98), and assembled
measurements of microbial biomass, soil organic carbon (SOC) and nitrogen (N), N-mineralization, soil surface carbon dioxide
(CO2) flux, and leached C and N in managed (maize; Zea mays L.) and natural (prairie) ecosystems near the University of Wisconsin Agricultural Research Station at Arlington. Field data
show that different management practices (tillage and fertilization) and ecosystem type (prairie vs maize) have a profound
influence on biogeochemistry and water budgets between sites. These measurements were used in conjunction with a dynamic terrestrial
ecosystem model, called IBIS (the Integrated Biosphere Simulator), to examine the long-term effects of land-use changes on
biogeochemical cycling. Field data and modeling suggest that agricultural land management near Arlington between 1860 and
1950 caused SOC to be depleted by as much as 63% (native SOC approximately 25.1 kg C m−2). Reductions in N-mineralization and microbial biomass were also observed. Although IBIS simulations depict SOC recovery
in no-tillage maize since the 1950s and also in the Arlington prairie since its restoration was initiated in 1976, field data
suggest otherwise for the prairie. This restoration appears to have done little to increase SOC over the past 24 years. Measurements
show that this prairie contained between 28% and 42% less SOC (in the top 1 m) than the no-tillage maize plots and 40%–47%
less than simulated potential SOC for the site in 1999. Because IBIS simulates competition between C3 and C4 grass species,
we hypothesized that current restored prairies, which include many forbs not characterized by the model, could be less capable
of sequestering C than agricultural land planted entirely in monocultural grass in this region. Model output and field measurements
show a potential 0.4 kg C m−2 y−1 difference in prairie net primary production (NPP). This study indicates that high-productivity C4 grasslands (NPP = 0.63
kg C m−2 y−1) and high-yield maize agroecosystems (10 Mg ha−1) have the potential to sequester C at a rate of 74.5 g C m−2 y−1 and 86.3 g C m−2 y−1, respectively, during the next 50 years across southern Wisconsin.
Received 28 December 1999; accepted 11 December 2000. 相似文献
15.
Soybean is an important agricultural crop and has, among its genotypes, a relatively wide variation in salt tolerance. As
measured by vegetative growth and yield, however, the achievement or failure of a high emergence ratio and seedling establishment
in saline soils can have significant economic implications in areas where soil salinity is a potential problem for soybean.
This study was conducted to determine the effects of salinity, variety and maturation rate on soybean emergence and seedling
growth. Included in the study were the variety ‘Manokin’; four near-isogenic sibling lines of the variety ‘Lee’ belonging
to maturity groups IV, V, VI and VII; and the variety ‘Essex’ and two of its near-isogenic related lines representing maturity
groups V, VI and VII, respectively. Field plots were salinized with sodium chloride and calcium chloride salts prior to planting.
The soybeans were irrigated with furrow irrigation which redistributed the salts towards the tail ends of the field plots.
Elevated soil salinity near the tail ends of the field significantly reduced soybean emergence rate, shoot height and root
length. No significant reduction was found for emergence or seedling growth of variety ‘Manokin’ when the electrical conductivity
of soil solution extract (ECe) was less than 3 dS m−1. Soybean emergence and seedling growth was significantly reduced when soil ECe reached about 11 dS m−1. Maturity groups V and VII of variety ‘Lee’ or V and VI of ‘Essex’ appeared to be more sensitive to salinity stress than
other maturity groups. Salt tolerance of different genotypes and maturity groups should be considered, among other limiting
factors, in minimizing salinity effects on soybean growth.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
16.
Tomomi Nakamoto 《Journal of plant research》1995,108(1):71-75
The growth of the primary seminal root of maize (Zea mays L.) is characterized by an initial negative gravitropic reaction and a later positive one that attains a plagiotropic liminal
angle. The effects of temperature and water potential of the surrounding soil on these gravitropic reactions were studied.
Temperatures of 32, 25, and 18C and soil water potentials of −5,−38, and −67 kPa were imposed and the direction of growth
was measured for every 1 cm length of the root. The initial negative gravitropic reaction extended to a distance of about
10cm from the graln. Higher temperatures reduced the initial negative gravitropic reaction. Lower soil water potential induced
a downward growth at root emergence. A mathematical model, in which it was assumed that the rate of the directional change
of root growth was a sum of a time-dependent negative gravitropic reaction and an establishment of the liminal angle, adequately
fitted the distance-angle relations. It was suggested that higher temperatures and/or a lower water potential accelerated
the diminution of the intitial negative gravitropic reaction. 相似文献
17.
Aspects of denitrification and benzoate degradation were studied in two estuarine microbial mat communities on the California
coast by measuring the depth distributions of potential denitrification rates, genetic potential for denitrification, nitrate
concentration, benzoate mineralization rates, total bacterial abundance, and abundance of a denitrifying strain (TBD-8b) isolated
from one of the sites. Potential denitrification was detected in microbial mat cores from both Elkhorn Slough and Tomales
Bay. Maximum denitrification rates were more than two orders of magnitude higher at Elkhorn Slough (3.14 mmol N m−2 d−1) than at Tomales Bay (0.02 mmol N m−2 d−1), and at both sites, the maximum rates occurred in the 0–2 mm depth interval. Ambient pore [NO3+NO2] was substantially higher at Elkhorn Slough than at Tomales Bay. Incorporation and mineralization of benzoate was maximal
near the mat surface at Elkhorn Slough. The areal rate of benzoate utilization was 1045 nmol C m−2 d−1, which represented utilization of 70% of the added substrate in 24 h. Total bacterial and TBD-8b abundances were greatest
near the surface at both Tomales Bay and Elkhorn Slough, and TBD-8b represented less than 0.2% of the total. Genetic potential
for denitrification, quantified by hybridization with a nitrite reductase gene fragment, was present below the mat surface
at average levels representing presence of the gene in approximately 10% of the total cells. 相似文献
18.
Restoring soil C pools by reducing land use intensity is a potentially high impact, rapidly deployable strategy for partially
offsetting atmospheric CO2 increases. However, rates of C accumulation and underlying mechanisms have rarely been determined for a range of managed
and successional ecosystems on the same soil type. We determined soil organic matter (SOM) fractions with the highest potential
for sequestering C in ten ecosystems on the same soil series using both density- and incubation-based fractionation methods.
Ecosystems included four annual row-crop systems (conventional, low input, organic and no-till), two perennial cropping systems
(alfalfa and poplar), and four native ecosystems (early successional, midsuccessional historically tilled, midsuccessional
never-tilled, and late successional forest). Enhanced C storage to 5 cm relative to conventional agriculture ranged from 8.9 g C m−2 y−1 in low input row crops to 31.6 g C m−2 y−1 in the early successional ecosystem. Carbon sequestration across all ecosystems occurred in aggregate-associated pools larger
than 53 μm. The density-based fractionation scheme identified heavy-fraction C pools (SOM > 1.6 g cm−3 plus SOM < 53 μm), particularly those in macroaggregates (>250 μm), as having the highest potential C accumulation rates,
ranging from 8.79 g C m−2 y−1 in low input row crops to 29.22 g C m−2 y−1 in the alfalfa ecosystem. Intra-aggregate light fraction pools accumulated C at slower rates, but generally faster than in
inter-aggregate LF pools. Incubation-based methods that fractionated soil into active, slow and passive pools showed that
C accumulated primarily in slow and resistant pools. However, crushing aggregates in a manner that simulates tillage resulted
in a substantial transfer of C from slow pools with field mean residence times of decades to active pools with mean residence
times of only weeks. Our results demonstrate that soil C accumulates almost entirely in soil aggregates, mostly in macroaggregates,
following reductions in land use intensity. The potentially rapid destruction of macroaggregates following tillage, however,
raises concerns about the long-term persistence of these C pools. 相似文献
19.
M. B. Kirkham 《Plant and Soil》1988,105(1):19-24
Genotypes of sorghum [Sorghum bicolor (L.) Moench] vary in drought resistance. Yet it is not known if their hydraulic resistances vary. The objective of this study
was to determine if the hydraulic resistance of a drought-resistant sorghum was the same as that of a drought-sensitive sorghum.
Leaf water and osmotic potentials were measured daily, during a 14-d period, in leaves of a drought-resistant (‘KS9’) and
a drought-sensitive (‘IA25’) sorghum, which had the roots in pots with a commercial potting soil that was either well watered
or allowed to dry. Soil water potential, adaxial stomatal resistance, and transpiration rate were determined daily. Hydraulic
resistance of the plants was calculated from the slope of the line relating soil water potential minus leaf water potential
versus transpiration rate. When the soil was not watered, the drought-sensitive sorghum had a water potential that averaged
−0.50 MPa lower and an osmotic potential that averaged −0.57 MPa lower, but a similar adaxial stomatal resistance (1.19 s
mm−1), compared with the drought-resistant sorghum. Seven days after the beginning of the experiment, the water potential of the
soil with the drought-sensitive sorghum was −0.25 MPa lower than that of the soil with the drought-resistant sorghum. With
the water-limited conditions, the drought-sensitive sorghum depleted the soil-water reserve more quickly and died 2 d before
the drought-resistant sorghum. Under well watered conditions, the two sorghums had similar water potentials (−1.64 MPa), osmotic
potentials (−2.83 MPa), and adaxial stomatal resistances (0.78 s mm−1). The calculated hydraulic resistance of the two sorghums did not differ and averaged 3.4 × 107 MPa s m−1. The results suggested that the variation in susceptibility to drought between the two genotypes was due to differences in
rate of soil-water extraction.
Contribution No. 86-249-J from the Kansas Agricultural Experiment Station. The paper is dedicated to the memory of Dr Dan
M Rodgers. 相似文献
20.
Frans J. M. Maathuis 《Plant and Soil》2007,299(1-2):1-15
Toxic aluminum (Al) ion is a major constraint to plant growth in acid soils. Aluminum tolerance in wheat (Triticum aestivum L.) is strongly related to the Al-triggered efflux of malate from root apices. A role of the secreted malate has been postulated
to be in chelating Al and thus excluding it from root apices (malate hypothesis), but the actual process has yet to be fully
elucidated. We measured Al content and root growth during and after Al exposure using seedlings of near-isogenic lines [ET8
(Al tolerant) and ES8 (Al sensitive)] differing in the capacity to induce Al-triggered malate efflux. Aluminum doses that
caused 50% root growth inhibition during 24-h exposure to Al in calcium (Ca) solution (0.5 mM CaCl2, pH 4.5) were 50 μM in ET8 and 5 μM in ES8. Under such conditions, the amount of Al accumulated in root apices was approximately
2-fold higher in ET8 than ES8. Al-treated seedlings were then transferred to the Al-free Ca solution for 24 h. Compared to
control roots (no Al pretreatment), root regrowth of Al-treated roots was about 100% in ET8 and about 25% in ES8. The impaired
regrowth in ES8 was observed even after 24-h exposure to 2.5 μM Al which had caused only 20% root growth inhibition. The addition
of malate (100 μM) during exposure to 50 μM Al in ES8 enhanced root growth 1.6 times and regrowth in Al-free solution 7 times,
resulting in similar root growth and regrowth as in ET8. Short-term Al treatments of ES8 for up to 5 h indicated that the
Al-caused inhibition of root regrowth started after 1-h exposure to Al. The stimulating effect of malate on root regrowth
was observed when malate was present during Al exposure, but not when roots previously exposed to Al were rinsed with malate,
although Al accumulation in root apices was similar under these malate treatments. We conclude that the malate secreted from
root apices under Al exposure is essential for the apices to commence regrowth in Al-free medium, the trait that is not related
to the exclusion of Al from the apices. 相似文献