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1.
Soil-to-plant abiotic transport of a recombinant nucleopolyhedrovirus (HzSNPV.LqhIT2) was studied to quantify the proportion
of different concentrations of soil virus transported to specific parts of cotton plants under controlled greenhouse conditions;
these results were related to transport in the field where wind, rain, and soil type were not controlled. Under conducive
precipitation conditions in the greenhouse, the estimated number of viral occlusion bodies (OB) transported ranged from 7 OB
(to the top third of the plant, 40–60 cm above the soil, at the low virus concentration, 250 OB/g soil) to 629 OB (to the
bottom third of the plant, 0–20 cm, at the high virus concentration, 12,500 OB/g soil). Under conducive wind conditions in
the greenhouse, the estimated number of OB transported ranged from 8 OB (to the top third of the plant at the low concentration)
to 94 OB (to the bottom third of the plant at the high concentration). The overall proportion of OB transported from soil
to plant was greatest, ranging from 2.1–6.2 × 10−6, from the lowest soil concentration to the lowest 40 cm of the plant. Only 5 × 10−8 of the soil OB were transported from the high-concentration soil to a height of 40–60 cm on the plants. In the field experiment,
the estimated number of OB on each cotton plant depended on the concentration of OB in soil in June and July, but this effect
was no longer significant in August. There were significantly more OB on the lower third of plants than on the top third in
July, but not in June or August. Significantly more OB were detected on cotton leaves than on buds or squares in July, and
there were more OB on leaves than on buds, squares, bracts, or bolls in August. The amount of HzSNPV.LqhIT2 naturally transported
from soil to cotton plants was sufficient to infect 6–11% (low to high soil concentration) of first instar Heliothis virescens (Fabricius) (Lepidoptera: Noctuidae) in June, 2–6% in July, and 1–3% in August. These results fill gaps in understanding
NPV epizootiology that are important to biological control and risk assessment. 相似文献
2.
Quantification of Soil-to-Plant Transport of Recombinant Nucleopolyhedrovirus: Effects of Soil Type and Moisture, Air Currents, and Precipitation 总被引:3,自引:1,他引:2
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Significantly more occlusion bodies (OB) of DuPont viral construct HzSNPV-LqhIT2, expressing a scorpion toxin, were transported by artificial rainfall to cotton plants from sandy soil (70:15:15 sand-silt-clay) than from silt (15:70:15) and significantly more from silt than from clay (15:15:70). The amounts transported by 5 versus 50 mm of precipitation were the same, and transport was zero when there was no precipitation. In treatments that included precipitation, the mean number of viable OB transported to entire, 25- to 35-cm-tall cotton plants ranged from 56 (clay soil, 5 mm of rain) to 226 (sandy soil, 50 mm of rain) OB/plant. In a second experiment, viral transport increased with increasing wind velocity (0, 16, and 31 km/h) and was greater in dry (−1.0 bar of matric potential) than in moist (−0.5 bar) soil. Wind transport was greater for virus in a clay soil than in silt or sand. Only 3.3 × 10−7 (clay soil, 5 mm rain) to 1.3 × 10−6 (sandy soil, 50 mm rain) of the OB in surrounding soil in experiment 1 or 1.1 × 10−7 (−0.5 bar sandy soil, 16-km/h wind) to 1.3 × 10−6 (−1.0 bar clay soil, 31-km/h wind) in experiment 2 were transported by rainfall or wind to cotton plants. This reduces the risk of environmental release of a recombinant nucleopolyhedrovirus (NPV), because only a very small proportion of recombinant virus in the soil reservoir is transported to vegetation, where it can be ingested by and replicate in new host insects. 相似文献
3.
Significantly more occlusion bodies (OB) of DuPont viral construct HzSNPV-LqhIT2, expressing a scorpion toxin, were transported by artificial rainfall to cotton plants from sandy soil (70:15:15 sand-silt-clay) than from silt (15:70:15) and significantly more from silt than from clay (15:15:70). The amounts transported by 5 versus 50 mm of precipitation were the same, and transport was zero when there was no precipitation. In treatments that included precipitation, the mean number of viable OB transported to entire, 25- to 35-cm-tall cotton plants ranged from 56 (clay soil, 5 mm of rain) to 226 (sandy soil, 50 mm of rain) OB/plant. In a second experiment, viral transport increased with increasing wind velocity (0, 16, and 31 km/h) and was greater in dry (-1.0 bar of matric potential) than in moist (-0.5 bar) soil. Wind transport was greater for virus in a clay soil than in silt or sand. Only 3.3 x 10(-7) (clay soil, 5 mm rain) to 1.3 x 10(-6) (sandy soil, 50 mm rain) of the OB in surrounding soil in experiment 1 or 1.1 x 10(-7) (-0.5 bar sandy soil, 16-km/h wind) to 1.3 x 10(-6) (-1.0 bar clay soil, 31-km/h wind) in experiment 2 were transported by rainfall or wind to cotton plants. This reduces the risk of environmental release of a recombinant nucleopolyhedrovirus (NPV), because only a very small proportion of recombinant virus in the soil reservoir is transported to vegetation, where it can be ingested by and replicate in new host insects. 相似文献
4.
Pulvinus activity of Phaseolus species in response to environmental stimuli plays an essential role in heliotropic leaf movement. The aims of this study
were to monitor the continuous daily pulvinus movement and pulvinus temperature, and to evaluate the effects of leaf movements,
on a hot day, on instantaneous leaf water-use efficiency (WUEi), leaf gas exchange, and leaf temperature. Potted plants of Phaseolus vulgaris L. var. Provider were grown in Chicot sandy loam soil under well-watered conditions in a greenhouse. When the second trifoliate
leaf was completely extended, one plant was selected to measure pulvinus movement using a beta-ray gauging (BRG) meter with
a point source of thallium-204 (204Tl). Leaf gas exchange measurements took place on similar leaflets of three plants at an air temperature interval of 33–42°C
by a steady-state LI-6200 photosynthesis system. A copper-constantan thermocouple was used to monitor pulvinus temperature.
Pulvinus bending followed the daily diurnal rhythm. Significant correlations were found between the leaf-incident angle and
the stomatal conductance (R
2 = 0.54; P < 0.01), and photosynthesis rate (R
2 = 0.84; P < 0.01). With a reduction in leaf-incidence angle and increase in air temperature, WUEi was reduced. During the measurements, leaf temperature remained below air temperature and was a significant function of air
temperature (r = 0.92; P < 0.01). In conclusion, pulvinus bending followed both light intensity and air temperature and influenced leaf gas exchange. 相似文献
5.
Long-term exposure of native vegetation to elevated atmospheric CO2 concentrations is expected to increase C inputs to the soil and, in ecosystems with seasonally dry periods, to increase soil
moisture. We tested the hypothesis that these indirect effects of elevated CO2 (600 μl l−1 vs 350 μl l−1) would improve conditions for microbial activity and stimulate emissions of nitrous oxide (N2O), a very potent and long-lived greenhouse gas. After two growing seasons, the mean N2O efflux from monoliths of calcareous grassland maintained at elevated CO2 was twice as high as that measured from monoliths maintained at current ambient CO2 (70 ± 9 vs 37 ± 4 μg N2O m−2 h−1 in October, 27 ± 5 vs 13 ± 3 μg N2O m−2 h−1 in November after aboveground harvest). The higher N2O emission rates at elevated CO2 were associated with increases in soil moisture, soil heterotrophic respiration, and plant biomass production, but appear
to be mainly attributable to higher soil moisture. Our results suggest that rising atmospheric CO2 may contribute more to the total greenhouse effect than is currently estimated because of its plant-mediated effects on soil
processes which may ultimately lead to increased N2O emissions from native grasslands.
Received: 11 September 1997 / Accepted: 20 March 1998 相似文献
6.
Changes in Hg fractionation in soil induced by willow 总被引:1,自引:0,他引:1
This study investigated the effect of willow (Salix viminalis × S. schwerinii) on soil characteristics, including changes in Hg fractionation in the soil solid phase, and Hg accumulation and distribution
in pot-grown plants cultivated for 32 and 76 days in aged Hg-contaminated soil (30 mg Hg kg−1DW). Changes in soil pH and organic carbon content as well as in Hg fractionation were monitored in both rhizospheric soil
and in soil without plants. Mercury fractionation was performed by a 5-step sequential soil extraction procedure. Organic
carbon content increased while pH decreased in the rhizospheric soil. Both chemically defined exchangeable Hg (0.1) and Hg
bound to humic and fulvic acids (1.1) decreased in the rhizospheric soil, whereas plant accumulation of Hg increased with
cultivation time. The sum of the decrease of these two soil Hg fractions after 76 days of cultivation was approximately equal
to the amount of Hg accumulated in plants. Furthermore, the major Hg fractions (Hg bound to residual organic matter (53),
sulphides (43), and the residual fraction (2.5)) remained stable. Neither whole plant accumulation of Hg from the soil, approximately
0.2 of total Hg in soil after 76 days cultivation, nor the fraction of total plant Hg in the shoots, which accounted for about
3 of the total plant Hg pool regardless of the cultivation time, were high. The overall results suggest that plants might
be suitable for phytostabilization of aged Hg-contaminated soil, where root systems trap bioavailable Hg and help to control
both leaching of Hg and re-entrainment of Hg-containing particulates from a contaminated site. 相似文献
7.
Two field experiments were conducted using three dominant perennial species of the Chihuahuan Desert: Hilaria mutica (a tussock grass), Larrea tridentata (a microphyllous shrub) and Opuntia rastrera (a flat-stemmed succulent cactus). Two hypotheses concerning competition in arid plant communities were tested. (1) Marked
resource partitioning with no interspecific competition could be expected since the three species belong to different life-forms,
and that plant growth in deserts is basically limited by harsh environmental conditions. (2) Alternatively, resource scarcity
(particularly water) will result in strong plant competition. In a 1-year removal experiment, water status and plant growth
of the three species were monitored in twelve 10 m × 10 m plots randomized in three blocks and assigned to the following treatments:
(a) removal of all species, except H. mutica; (b) removal of all species, except L. tridentata; (c) removal of all species, except O. rastrera, and (d) control without any manipulation. In a watering experiment, under two neighbourhood conditions (growing isolated
or in associations of plants of the three species in plots of 20 m2), the water status of the three species and the growth of H.mutica and L.tridentata were studied for 32 days after an irrigation equivalent to 30 mm of rain, similar to a strong storm event at the site. In
the removal experiment, where plants were free to capture water, no evidence of competition was observed. However, during
the watering experiment, in which water was forced into the soil, competitive effects were observed. Associated individuals
of L. tridentata had lower xylem water potentials and osmotic potentials (OPs) and produced shorter twigs and less leaves and nodes. Although
less pronounced, neighbours also had a negative effect on the OP in O. rastrera. According to these results, the intensity of the interspecific competition for water seems to depend on the level of resource
availability in the soil. Thus, the validity of the two hypotheses tested in this study also depends on the level of resources.
Competition could be absent or very low in years of low precipitation, as in the year of this study (173 mm against a 25-year
average of 264 mm). However, when soil water availability is high, e.g. following heavy rain, the negative interactions between
species could be more intense.
Received: 3 October 1997 / Accepted: 23 March 1998 相似文献
8.
Daniela Soares dos Santos Vívian Tamaki Catarina Carvalho Nievola 《In vitro cellular & developmental biology. Plant》2010,46(6):524-529
Acanthostachys strobilacea (Schult. f.) Klotzsch is an ornamental species of Bromeliaceae that may show an elongated stem when cultivated in vitro. This work reports a micropropagation protocol for A. strobilacea using nodal segments. Seeds were placed in Murashige and Skoog’s medium with macronutrients diluted to 1/5. Nodal segments
isolated from the stems of in vitro elongated plants were subcultured in the same medium and kept in different light intensities (14, 41, and 50 μmol m−2 s−1) or continuous darkness. Another group of nodes was subcultured according to the position in the mother seedling. The plants
that showed the most stem elongation were those that were cultured in 14 μmol m−2 s−1 or that came from isolated nodal segments in the median and basal regions of the mother plant. After 2 mo, all of the plants
originating from the development of lateral buds were transferred to a greenhouse. Only those that were not elongated survived
ex vitro and flowered after 1 yr. 相似文献
9.
This study investigated the nitrogen (N) acquisition from soil and insect capture during the growth of three species of pitcher
plants, Nepenthes mirabilis, Cephalotus follicularis and Darlingtonia californica. 15N/14N natural abundance ratios (δ15N) of plants and pitchers of different age, non-carnivorous reference plants, and insect prey were used to estimate proportional
contributions of insects to the N content of leaves and whole plants. Young Nepenthes leaves (phyllodes) carrying closed pitchers comprised major sinks for N and developed mainly from insect N captured elsewhere
on the plant. Their δ15N values of up to 7.2‰ were higher than the average δ15N value of captured insects (mean δ15N value = 5.3‰). In leaves carrying old pitchers that are acting as a N source, the δ15N decreased to 3.0‰ indicating either an increasing contribution of soil N to those plant parts which in fact captured the
insects or N gain from N2 fixation by microorganisms which may exist in old pitchers. The δ15N value of N in water collected from old pitchers was 1.2‰ and contained free amino acids. The fraction of insect N in young
and old pitchers and their associated leaves decreased from 1.0 to 0.3 mg g−1. This fraction decreased further with the size of the investigated tiller. Nepenthes contained on average 61.5 ± 7.6% (mean ± SD, range 50–71%) insect N based on the N content of a whole tiller. In the absence
of suitable non-carnivorous reference plants for Cephalotus, δ15N values were assessed across a developmental sequence from young plants lacking pitchers to large adults with up to 38 pitchers.
The data indicated dependence on soil N until 4 pitchers had opened. Beyond that stage, plant size increased with the number
of catching pitchers but the fraction of soil N remained high. Large Cephalotus plants were estimated to derive 26 ± 5.9% (mean ± SD of the three largest plants; range: 19–30%) of the N from insects. In
Cephalotus we observed an increased δ15N value in sink versus source pitchers of about 1.2‰ on average. Source and sink pitchers of Darlingtonia had a similar δ15N value, but plant N in this species showed δ15N signals closer to that of insect N than in either Cephalotus or Nepenthes. Insect N contributed 76.4 ± 8.4% (range 57–90%) to total pitcher N content. The data suggest complex patterns of partitioning
of insect and soil-derived N between source and sink regions in pitcher plants and possibly higher dependence on insect N
than recorded elsewhere for Drosera species.
Received: 14 April 1997 / Accepted: 18 August 1997 相似文献
10.
Pulses of soil phosphorus availability in a Mexican tropical dry forest: effects of seasonality and level of wetting 总被引:3,自引:0,他引:3
Intact cores from the upper soil profile and surface litter were collected at the peak of the dry season and during the rainy
period in the tropical deciduous forest of the Chamela region, Jalisco, México, to (1) analyze upper soil phosphorus (P) movement
and retention, (2) compare soil P dynamic pools (soluble, bicarbonate, and microbial) in dry and rainy seasons, and (3) determine
the response of these P pools to wetting. Unperturbed litter-soil cores were treated in the laboratory with either 10 mm or
30 mm of simulated rain with carrier-free 32P and compared to a control (no water addition) to determine the fate and retention of added P. 31P concentrations and pools in most litter and soil fractions were higher in the dry than in the rainy season. Soluble P was
0.306 g/m2 and microbial P was 0.923 g/m2 in the dry season (litter plus soil) versus 0.041 (soluble) and 0.526 (microbial) g P/m2 in the rainy season. After water addition, rainy-season cores retained 99.9 and 94% of 32P in the 10- and 30-mm treatments, respectively. Dry-season samples retained 98.9 and 80% of inputs in the same treatments.
Retention after wetting occurred mostly in soil (bicarbonate and microbial fractions). Simulated rainfall on rainy-season
soils increased P immobilization. On the other hand, simulated rainfall on dry-season soils released P through mineralization.
The P release represents between 46 and 99% of the annual litterfall return. Our results suggest that both soluble and microbial
P constitute important sources for initiation of plant growth at the onset of the rainy season in tropical dry forest.
Received: 23 September 1997 / Accepted: 2 February 1998 相似文献
11.
Md Habibullah Bahar John Stanley David Backhouse Robert Mensah Alice Del Socorro Peter Gregg 《Entomologia Experimentalis et Applicata》2019,167(5):415-423
There is no conclusive evidence that Helicoverpa spp. (Lepidoptera: Noctuidae) in Australia have evolved significant levels of resistance to Bollgard II® cotton (which expresses two Bt toxin genes, cry1Ac and cry2Ab). However, there is evidence of surviving larvae on Bollgard II cotton in the field. The distribution and survival of early‐instar Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae were examined on whole Bollgard II and non‐Bt cotton plants in greenhouse bioassays. The expression of Cry toxins in various parts of Bollgard II plants was compared to the survival of larvae in those locations. Only 1% of larvae survived after 6 days on greenhouse‐grown Bollgard II plants compared to 31% on non‐Bt cotton plants. Overall, and across all time intervals, more larvae survived on reproductive parts (squares, flowers, and bolls) than on vegetative parts (leaves, stems, and petioles) on Bollgard II plants. The concentration of Cry1Ac toxin did not differ between plant structures, whereas Cry2Ab toxin differed significantly, but there was no relationship between the level of expression and the location of larvae. This study provides no evidence that lower expression of Cry toxins in the reproductive parts of plants explains the survival of H. armigera larvae on Bollgard II cotton. 相似文献
12.
Plant nutrient responses to 4 years of CO2 enrichment were investigated in situ in calcareous grassland. Beginning in year 2, plant aboveground C:N ratios were increased
by 9% to 22% at elevated CO2 (P < 0.01), depending on year. Total amounts of N removed in biomass harvests during the first 4 years were not affected by
elevated CO2 (19.9 ± 1.3 and 21.1 ± 1.3 g N m−2 at ambient and elevated CO2), indicating that the observed plant biomass increases were solely attained by dilution of nutrients. Total aboveground P
and tissue N:P ratios also were not altered by CO2 enrichment (12.5 ± 2 g N g−1 P in both treatments). In contrast to non-legumes (>98% of community aboveground biomass), legume C/N was not reduced at
elevated CO2 and legume N:P was slightly increased. We attribute the less reduced N concentration in legumes at elevated CO2 to the fact that virtually all legume N originated from symbiotic N2 fixation (%Ndfa ≈ 90%), and thus legume growth was not limited by soil N. While total plant N was not affected by elevated CO2, microbial N pools increased by +18% under CO2 enrichment (P = 0.04) and plant available soil N decreased. Hence, there was a net increase in the overall biotic N pool, largely due increases
in the microbial N pool. In order to assess the effects of legumes for ecosystem CO2 responses and to estimate the degree to which plant growth was P-limited, two greenhouse experiments were conducted, using
firstly undisturbed grassland monoliths from the field site, and secondly designed `microcosm' communities on natural soil.
Half the microcosms were planted with legumes and half were planted without. Both monoliths and microcosms were exposed to
elevated CO2 and P fertilization in a factored design. After two seasons, plant N pools in both unfertilized monoliths and microcosm communities
were unaffected by CO2 enrichment, similar to what was found in the field. However, when P was added total plant N pools increased at elevated CO2. This community-level effect originated almost solely from legume stimulation. The results suggest a complex interaction
between atmospheric CO2 concentrations, N and P supply. Overall ecosystem productivity is N-limited, whereas CO2 effects on legume growth and their N2 fixation are limited by P.
Received: 12 July 1997 / Accepted: 15 April 1998 相似文献
13.
Wang Xi-Ling Zhou Jin-Xing Yu Mao-De Li Zhen-Gang Jin Xiao-Yun Li Qi-You 《In vitro cellular & developmental biology. Plant》2011,47(3):434-440
Efficient plant regeneration is essential for successful transformation and in vitro polyploidy induction in mulberry. A high frequency (80%) of plant regeneration from hypocotyls occurred under in vitro conditions in mulberry (Morus multicaulis Poir.). We identified three key factors for enhancing successful regeneration based on earlier work: (1) hypocotyl position,
(2) the combination and concentration of growth regulators, and (3) the addition of AgNO3. The highest frequency of shoot regeneration was achieved using hypocotyl segments, which are proximal to apical meristems,
and the optimal culture conditions were Murashige and Skoog’s (MS) (Murashige and Skoog, 1962) basal medium supplemented with 3.0 mg l−1 6-benzylamino purine, 0.3 mg l−1 indole-3-acetic acid, 0.1% polyvinypyrrolidone, and 1.0 mg/l silver nitrate (AgNO3) under subdued light at 25 ± 2°C. Treating the shoots with 0.2% colchicine (dipping for 72 h) resulted in a 14% tetraploid
frequency, whereas a 20% tetraploid frequency resulted from using a 0.25% colchicine (dripping for 5 d) treatment, as determined
by chromosome number counts. The diploid plant chromosome number was 28 (2n = 2x = 28) and that of tetraploid plants was 56 (2n = 4x = 56). Regenerated shoots rooted easily in 8–10 d using half-strength basal MS medium with 0.5 mg l−1 indole-3-butyric acid and were successfully established in the soil. 相似文献
14.
Saikat Gantait Nirmal Mandal Somnath Bhattacharyya Prakash Kanti Das 《In vitro cellular & developmental biology. Plant》2010,46(6):537-548
A novel, efficient, and simple protocol was developed on in vitro mass propagation and acclimatization of Gerbera jamesonii Bolus cv. Sciella, an ornamental plant with attractive flowers. Shoot tip was used as the primary explant for in vitro establishment in which Murashige and Skoog (MS) medium supplemented with a low level of NAA (0.5 mg l−1) and BAP (1.5 mg l−1) promoted earliest axillary bud initiation within 5 d in 91.6% of the inoculants. Five axillary buds were initiated from
a single explant within 13 d after inoculation. A very high rate of shoot multiplication (14 shoots per inoculated axillary
bud) and proliferation was achieved when MS medium was fortified with a relatively higher level of BAP (2 mg l−1) and 60 mg l−1 ADS within 27 d of multiple shoot culture. A maximum number of well-developed roots per plant was observed in MS medium with
0.5 mg l−1 IAA in the next 26 d. In the easy low-cost acclimatization process of 20 d, a combination of sand, soil, cow urine, and tea
leaves extract (1:1:1:1; v/v) ensured 95% survival rate. Sixty-one well-acclimatized plants were obtained from a single shoot tip within 86 d. The sustained
multiple shoot culture for 15 mo paved the way toward the conservation of genetic resources as well as beneficial economics.
The clonal fidelity study of micropropagated and sustained cultured clones using ISSR primers ensured the continuous supply
of quality propagules retaining genetic uniformity. The in vitro-generated plants performed better over conventionally propagated plants in the field condition. 相似文献
15.
The effect of the fungicide, chlorothalonil, on vesicular-arbuscular mycorrhizal (VAM) symbiosis was studied in a greenhouse
using Leucaena leucocephala as test plant. Chlorothalonil was applied to soil at 0, 50, 100 and 200 μg g−1. The initial soil solution P levels were 0.003 μg mL−1 (sub-optimal) and 0.026 μg mL−1 (optimal). After 4 weeks, the sub-optimal P level was raised to 0.6 μg mL−1 (high). The soil was either uninoculated or inoculated with the VAM fungus, Glomus aggregatum. The fungicide reduced mycorrhizal colonization of roots, development of mycorrhizal effectiveness, shoot P concentration
and uptake and dry matter yields at all concentrations tested, although the highest inhibitory effect was noted as the concentration
of the fungicide was increased from 50 to 100 μg g−1. Phosphorus applied after four weeks tended to partially offset the deleterious effects of chlorothalonil in plants grown
in the inoculated and uninoculated soil which suggests that the fungicide was interfering with plant P uptake. The results
suggest that the use of chlorothalonil should be restricted to levels below 50 μg g−1 if the benefits of mycorrhizal symbiosis are to be expected.
Contribution from Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No. 3464.
Contribution from Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No. 3464. 相似文献
16.
Differential water resource use by herbaceous and woody plant life-forms in a shortgrass steppe community 总被引:11,自引:0,他引:11
We conducted a study to test the predictions of Walter's two-layer model in the shortgrass steppe of northeastern Colorado.
The model suggests that grasses and woody plants use water resources from different layers of the soil profile. Four plant
removal treatments were applied in the spring of 1996 within a plant community codominated by Atriplex canescens (a C4 shrub) and Bouteloua gracilis (a C4 grass). During the subsequent growing season, soil water content was monitored to a depth of 180 cm. In addition, stem and
leaf tissue of Atriplex, Bouteloua and the streamside tree Populus sargentii were collected monthly during the growing seasons of 1995 and 1996 for analysis of the δ18O value of plant stem water (for comparison with potential water sources) and the δ13C value of leaves (as an indicator of plant water status). Selective removal of shrubs did not significantly increase water
storage at any depth in the measured soil profile. Selective removal of the herbaceous understory (mainly grasses) increased
water storage in the top 60 cm of the soil. Some of this water gradually percolated to lower layers, where it was utilized
by the shrubs. Based on stem water δ18O values, grasses were exclusively using spring and summer rain extracted from the uppermost soil layers. In contrast, trees
were exclusively using groundwater, and the consistent δ13C values of tree leaves over the course of the summer indicated no seasonal changes in gas exchange and therefore minimal
water stress in this life-form. Based on anecdotal rooting-depth information and initial measurements of stem water δ18O, shrubs may have also had access to groundwater. However, their overall δ18O values indicated that they mainly used water from spring and summer precipitation events, extracted from subsurface soil
layers. These findings indicate that the diversity of life-forms found in this shortgrass steppe community may be a function
of the spatial partitioning of soil water resources, and their differential use by grasses, shrubs, and trees. Consequently,
our findings support the two-layer model in a broad sense, but indicate a relatively flexible strategy of water acquisition
by shrubs.
Received: 23 December 1997 / Accepted: 16 September 1998 相似文献
17.
Metrosideros polymorpha, a dominant tree species in Hawaiian ecosystems, occupies a wide range of habitats. Complementary field and common-garden
studies of M. polymorpha populations were conducted across an altitudinal gradient at two different substrate ages to ascertain if the large phenotypic
variation of this species is determined by genetic differences or by phenotypic modifications resulting from environmental
conditions. Several characteristics, including ecophysiological behavior and anatomical features, were largely induced by
the environment. However, other characteristics, particularly leaf morphology, appeared to be mainly determined by genetic
background. Common garden plants exhibited higher average rates of net assimilation (5.8 μmol CO2 m−2 s−1) and higher average stomatal conductance (0.18 mol H2O m−2 s−1) than their field counterparts (3.0 μmol CO2 m−2 s−1, and 0.13 mol H2O m−2 s−1 respectively). Foliar δ13C of most common-garden plants was similar among sites of origin with an average value of −26.9‰. In contrast, mean values
of foliar δ13C in field plants increased substantially from −29.5‰ at low elevation to −24.8‰ at high elevation. Leaf mass per unit area
increased significantly as a function of elevation in both field and common garden plants; however, the range of values was
much narrower in common garden plants (211–308 g m−2 for common garden versus 107–407 g m−2 for field plants). Nitrogen content measured on a leaf area basis in common garden plants ranged from 1.4 g m−2 to 2.4 g m−2 and from 0.8 g m−2 to 2.5 g m−2 in field plants. Photosynthetic nitrogen use efficiency (PNUE) decreased 50% with increasing elevation in field plants and
only 20% in plants from young substrates in the common garden. This was a result of higher rates of net CO2 assimilation in the common garden plants. Leaf tissue and cell layer thickness, and degree of leaf pubescence increased significantly
with elevation in field plants, whereas in common garden plants, variation with elevation of origin was much narrower, or
was entirely absent. Morphological characteristics such as leaf size, petiole length, and internode length decreased with
increasing elevation in the field and were retained when grown in the common garden, suggesting a potential genetic basis
for these traits. The combination of environmentally induced variability in physiological and anatomical characteristics and
genetically determined variation in morphological traits allows Hawaiian M. polymorpha to attain and dominate an extremely wide ecological distribution not observed in other tree species.
Received: 12 March 1997 / Accepted: 27 August 1997 相似文献
18.
To improve plant regeneration from oat anther culture, the basic medium, hormonal supplements and genotype effect were studied.
Six of the 14 genotypes tested regenerated plants. Cultivars Kolbu, Katri, Stout and naked oat Lisbeth produced green plants,
cultivars Virma and line OT 257 only albinos. The total number of green plantlets regenerated was 22, of which 13 (11 haploid,
2 doubled haploid) survived into the greenhouse, and 37 albinos. Regenerable-type embryos were induced from heat-pretreated
anthers on media containing 2, 3 or 5 mg l–1 2,4-dichlorophenoxyacetic acid and 0.2 or 0.5 mg l–1 kinetin as hormonal supplements. 6-Benzylaminopurine promoted albino plant regeneration especially in W14 medium. Colchicine treatment was applied successfully to haploid regenerants.
Received: 12 April 1999 / Revision received: 19 August 1999 / Accepted: 8 September 1999 相似文献
19.
Grazing and seasonal variation in precipitation and temperature are important controls of soil and plant processes in grasslands.
As these ecosystems store up to 30% of the world’s belowground carbon (C), it is important to understand how this variability
affects mineral soil C pools/fluxes, and how C cycling might be affected by changes in precipitation and temperature, due
to climate change. The aim of this study was to investigate the effects of grazing and differences in soil temperature and
moisture on standard organic matter (OM) decomposition rates (cotton cloth) incubated in the top 10 cm soil of grasslands
with variable topography in Yellowstone National Park (YNP) during the 2004 growing season. Grazing did not affect soil temperature,
moisture, cotton cloth decomposition rates, soil bulk density, soil C and N concentrations, or soil C:N ratios. However, a
large spatio-temporal variability in decomposition was observed: cotton cloth decomposition was positively related to soil
moisture and soil C and N concentrations, and negatively to soil temperature. Highest decomposition rates were found in wetter
slope bottom soils [season averages of decomposition given as rate of decomposition (cotton rotting rate = CRR) = 23–26%]
and lower rates in drier, hill-top soils (season averages, CRR = 20%). Significantly higher decomposition rates were recorded
in spring, early summer and early fall when soils were moist and cool (spring, CRR = 25%; early summer, CRR = 26%; fall, CRR = 20%)
compared to mid-summer (CRR = 18%) when soils were dry and warm. Our findings suggest that climate-change related decreases
in precipitation and increases in temperature predicted for North American grasslands would decrease soil OM decomposition
in YNP, which contrasts the general assumption that increases in temperature would accelerate OM decomposition rates. 相似文献
20.
Coffee beans and tea leaves contain large amounts of potentially metal-chelating substances which could remain in the wastes
after extraction by hot water. The following two experiments have been carried out: a) an incubation experiment with the objective
of verify whether coffee grounds and green tea wastes could be used as an Fe chelating agent to increase Fe availability to
plants in the soil; b) a pot experiment to verify the effect of those composts on the Fe content of the edible part of vegetables.
Japanese leaf radish (Raphanus raphanus sp), whose the leaves are the edible part, was chosen as test plant. Calcareous subsoil (shell fossil soil) with original
pH 9.3 and a B horizon of Andisol (Typic melanudand) with pH adjusted to 7.7 were used. For the incubation experiment, the
treatments included of the direct addition of Fe at rates of 0 (control), 10, 20 and 40 μg g−1 dry soil as ferrous sulfate (FS); coffee waste compost (CWC) and tea waste compost (TWC). Both composts contained approximately
40 g Fe kg−1 dry mass. Thus, the total amounts of CWC and TWC added were of 0, 0.25, 0.5 and 1.0 mg g−1 soil. Considering a soil density of 1 g cm−3 and 10 cm of plow layer, the total amounts of compost applied were of 0, 0.25, 0.5 and 1.0 ton ha−1. Soil samples were collected after 30 and 60 days of incubation and then analyzed for plant available Fe. For the pot experiment,
the doses of 0 (control) and 1 mg g−1 soil of CWC or TWC were used to grow radish. Plants were harvested after 60 days. For samples incubated for 30 days, the
CWC and TWC treatments led to the largest increase in the ammonium bicarbonate diethylene triamine pentaacetic acid (AB-DTPA)
extractable Fe levels of both soils (P < 0.05). After 60 days of incubation the amounts of AB-DTPA-extractable Fe in soil samples treated with both composts were
always higher than in those treated with FS alone. For both soils, the application of 40 μg Fe g−1 dry soil as CWC or TWC enhanced significantly (P < 0.05) the total Fe content of radish shoots compared to the control. We concluded that it has been possible to increase
the plant-available Fe in neutral to alkaline soils using coffee grounds and tea leaf wastes composted with FS. However, more
research on the effectiveness in field conditions are necessary. 相似文献