摘要:

The ultrastructure of the uredinial stage of the rust fungus,Puccinia canaliculata(Schw.) Lagerh., on yellow nutsedge(Cyperus esculentusL.) is described using scanning electron microscopy. This rust has been proposed as a potential biological control agent against this serious weed species. Urediniospores are ellipsoid to ovoid, and echinulate with the spines distributed over the surface except at basal portions. Spines are in circular depressions, encircled by annuli. Germination is through one of two equatorial germ pores. Germ tube growth is primarily perpendicular to the longitudinal orientation of epidermal cells. Appressoria completely cover stomata. Uredinia develop within linearly aligned intercellular cavities in substomatal regions. Uredinia become erumpent, exposing pedicellate urediniospores and smooth paraphyses scattered throughout the sori. Uredinia are nonperidiate.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08583.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Free‐living and lichenized cyanobacterial (cyanolichen) colonies occupy 12–29% of the surface area in the Sand Hills grasslands on the Arapaho Prairie in southwestern Nebraska. During brief periods of favorable conditions (i.e., moderate temperature and high moisture), these diazotrophs are capable of high rates of dinitrogen fixation. Maximum rates of acetylene reduction measured during 1981 and 1982 were 2,237 μg N m‐2hr‐l. The duration of dinitrogen fixation activity is dependent upon moisture conditions; rates of acetylene reduction were shown to decline 90% in as little as three hr. Desiccated colonies resumed acetylene reduction activity within one hr and achieved equilibrium rates within four hr following rehydration.Associative, heterotrophic diazotrophs were isolated from the rhizospheres of several grass species. These bacteria exhibited a range of culturing characteristics which may reflect differing plant‐bacterial interaction potentials important to the establishment and maintenance of the plant species. None of the field assays for heterotrophic dinitrogen fixation performed over the two‐yr period indicated a capacity of this group to provide ecologically significant levels of N in this grassland.Our gross estimate of the annual contribution was 3.5 kg N ha‐1from cyanolichens and 0.8 kg N ha‐1from associative heterotrophs.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08584.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

The type of response the steppe grassAgropyron smithiiRydb. exhibits to mycorrhizal fungi is dependent upon where along the resource gradient the experiment is conducted. At the lower end of a soil‐phosphorus (P) gradient (2 μg P g‐1soil) mycorrhizalA. smithiibiomass was 35% greater than its nonmycorrhizal counterpart; while at the high end of the gradient (20 μg P g‐1soil) no difference in host biomass production was evident. Mycorrhizal plants were shorter in stature (P<0.002) and produced more tillers (P<0.0001) than nonmycorrhizal plants. The stature and tiller response was more pronounced at the high end of the soil‐P gradient. The partitioning of the mycorrhizal fungus was influenced by the soil‐P gradient. At the lower end of the gradient the majority of the fungus was produced extramatrically, where over 5,000 cm of hyphae per plant were encountered after 10 wk growth. While at the high end of the gradient, the majority of fungus was produced internally. The highest mycorrhizal dependency values were measured at the lower end of the soil‐P gradient where cost to the host (as measured by fungus biomass expressed as a percentage of the root system) was also highest. Increasing shoot and root‐P concentrations were correlated with decreasing external fungus biomass. A positive association between tiller production and internal fungus biomass also existed. The significance of these findings, as well as the need to consider characteristics which measure fitness of a host in evaluating the mycorrhizal association of grasses, are discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08585.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

We compile and analyze data on the population genetic structure of broad‐sense clonal plant populations where sexual recruitment is rare or absent. The data from 27 studies show a common theme: multiclonal populations of intermediate diversity and evenness tend to be the rule, most clones are restricted to one or a few populations, and widespread clones are exceptional. While a few studies have demonstrated that ecological differences among sympatric clones do occur, more experimental and theoretical studies are necessary to determine the role of selection and other evolutionary forces in maintaining clonal polymorphism.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08586.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Ten plants ofMimosa pudicaL. were exposed to artificial rain following anesthesia of the leaves of half of the plants. Anesthetized plants, which no longer displayed the seismonastic response of this species, were hypothesized to show greater rates of foliar leaching of nutrients than their unanesthetized counterparts. Leachate was collected and analyzed for levels of K, Na and Ca. Levels were corrected for the amount of leaf area exposed to rainfall. No differences were noted between treatments for rainfall durations of either 6 or 20 min. Leaf surface morphology was examined and lattice‐like extrusions of epicuticular wax were found. We feel that the leaf surface structure may act to keep raindrops from coming in contact with the surface of the leaf thereby minimizing foliar leaching. It appears that the seismonastic response of the leaves plays only a minor role in nutrient conservation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08587.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Morphological and anatomical studies have long utilized qualitative means to reconstruct 3‐dimensional transparent images from serial sections. With the advent of computer graphics systems, more accurate images can be constructed to visualize growing plant parts in transparent 3‐D. We have developed a computer program which allows such reconstruction from stained serial sections. Advantages include 3‐dimensional imaging without the use of stereo pairs and the ability to rotate an image to see all angles.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08588.x

出版商:Wiley    

年代:1987

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08589.x

出版商:Wiley    

年代:1987

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08572.x

出版商:Wiley    

年代:1987

数据来源: WILEY