ISSN:0012-9658    

DOI:10.2307/1943153

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

Endophytes are fungi that form inapparent infections within leaves and stems of healthy plants. Closely related to virulent pathogens but with limited, if any, pathogenic effects themselves, many endophytes protect host plants from natural enemies. Animal herbivores and, in some cases, pathogenic microbes are poisoned by the mycotoxins produced by endophytes. "Constitutive mutualism" is the relatively faithful association, usually with grasses, of endophytes that infect host ovules and are propagated in host seed; substantial fungal biomass with probable high metabolic cost develops throughout the aerial parts of the host plant. "Inducible mutualist" endophytes are not involved with host seed and disseminate independently through air or in water. Infecting only vegetative parts of the host and remaining metabolically inactive for long periods with relatively little fungal biomass, inducible mutualists grow rapidly and produce toxins against herbivores when damaged host tissues provide new sites for infection. I surmise that endophytes may be as common among plants as are mycorrhyzae.

ISSN:0012-9658    

DOI:10.2307/1943154

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

Many grasses are infected by systemic fungal endophytes (family Clavicipitaceae, Ascomycetes) that produce pysiologically active alkaloids in the tissues of their hosts. Infection makes grasses toxic to domestic mammals and increases resistance to insect herbivores. Some grasses are sterilized by endophyte infection while remaining vegetatively vigorous; other infected grasses remain completely fertile. Experiments demonstrate that plant growth and seed production can be increased by infection. This symbiotic association may be a defensive mutualism in which the fungi defend their hosts against herbivory, thereby defending their own resources. Recent studies suggest that defensive mutualism of endophytes with grasses may be widespread.

ISSN:0012-9658    

DOI:10.2307/1943155

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

ISSN:0012-9658    

DOI:10.2307/1943156

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

The biochemistry of the weathering, landscape movements, and chemical transformations of phosphorus and its availability of plants were examined in a chronosequence of soils developed from quartz monzonite alluvium in southern New Mexico. Total P in the soil profile decreased with increasing soil age and was removed from the ecosystem as readily as the most leachable base cations. Although Ca—bound forms of P decreased with increasing soil age, Ca—P remained the singlee largest fraction of total P in all soils. In contrast, Fe— and Al—bound P was a very small percent of total P in all soils. There was little evidence for the stabilization of P by soil organic matter within this ecosystem; both soil organic P and microbial P represented very small pools of total soil P. Phosphorus availability, measured by in situ resin bags, was not well correlated with soil age or total soil P, and P concentrations in shrub tissues did not reflect changes in forms or total amounts of soil P. The biogeochemical cycle of P in this system differs sharply from that in a more mesic, forested system, where fixation by iron and aluminium oxides and biologic activity play more dominant roles in the conservation of P within the ecosystem.

ISSN:0012-9658    

DOI:10.2307/1943157

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

Aboveground net primary production of grasslands is strongly influenced by the amount and distribution of annual precipitation. Analysis of data collected at 9500 sites throughout the central United States confirmed the overwhelming importance of water availability as a control of production. The regional spatial pattern of production reflected the east—west gradient in annual precipitation. Lowest values of aboveground net primary production were observed in the west and highest values in the east. This spatial pattern was shifted eastward during unfavorable years and westward during favorable years. Variability in production among years was maximum in northern New Mexico and southwestern Kansas and decreased towards the north and south. The regional pattern of production was largely accounted for by annual precipitation. Production at the site level was explained by annual precipitation, soil water—holding capacity, and an interaction term. Our results support the inverse texture hypothesis. When precipitation is370 mm/yr.

ISSN:0012-9658    

DOI:10.2307/1943158

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

Eleven experimental treatments were applied to 2 x 2 m plots over 2 yr at Konza Prairie Research Natural Area, Riley County, Kansas, to ascertain why burning tallgrass prairie causes increased production and flowering. Warming of the soil in unburned plots resulted in an increase in both total production and flower stalk production of dominant tall grasses, primarily big bluestem (Andropogon gerardii) and Indian grass (Sorgastrum nutans), but the increase was small (34% increase in biomass; 78% increase in number of flower stalks) compared with that in burned plots (151% increase in biomass; 435% increase in flower stalks). Increased surface light intensity also appears to be a factor affecting changes in productivity following burning as suggested by the combined responses of increased productivity with removal of standing dead, whether by clipping or burning, and decreased productivity with shading. Further, the addition of ammonium nitrate increased yield 41% and flowering 168% for the dominant grasses, suggesting that any factor increasing nitrogen availability would affect these vegetative parameters. Neither ash left from burning nor heating of the soil surface during burning produced detectable effects on subsequent vegetative growth. Different results for some parameters between years and between species suggest that many complex interactions operate to affect the grassland's response to burning, but surface light, soil surface temperature, and nitrogen appear to be particularly important factors.

ISSN:0012-9658    

DOI:10.2307/1943159

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

Mass nitrogen, and phosphorus of litterfall were measured for 4 yr on annually burned and unburned tallgrass prairie near Manhattan, Kansas. Decomposition and minearilization rates of foliage, flowering stem, and roots were concurrently studied with a series of litterbag and tethered litter experiments. Amounts of nitrogen and phosphorus in living and dead foilage and roots were measured for 2—yr on an annually burned site. Litterfall exhibited seasonal peaks on all sites, with most of the annual litter decompsition occurring in autumn. An average of 52 g°m—2°yr—1of litter was deposited on the soil of the annually burned watersheds, while 142 g°m—2°—1was collected on unburned sites. Nitrogen and phosphorus amounts were 0.53 and 0.07 g°m—2°yr—1, respectively, from burned sites and 1.94 and 0.19 g°m—2°yr—1, on unburned sites. Litterfall on unburned sites averaged °35% of aboveground maximum biomass estimates. Litter decay rates varied from a minimum of °10% yr for flowering stems in the canopy to a maximum of °50%/ yr for roots. Foilage and stems act as nitrogen and phosphorus sinks during the first 2 yr of decomposition. Dead roots and rhizomes also act as temporary nitrogen sinks, but unlike foilage, roots appear to minearlize significant amounts of phosphorus during the 1st yr of decay. Root nitrogen to phosphorus ratios may provide a proximate explanation for nitrogen limitation in tallgrass prairies.

ISSN:0012-9658    

DOI:10.2307/1943160

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

The stratigraphic, seddimentary pigment, loss—on—ignition, pollen, and radiocarbon data of a sedimentary record from Anangucocha, in the Ecuadorian Amazon, define three environmental episodes during the last 3100 yr. A swamp episode (<3100—1300 BP) was followed by regional flooding (1300—800 BP) and an open lake period (since 800 BP). Pollen data show that a Mauritia palm forest occupied the early blackwater swamp and was replaced by a riparian community dominated by Cecropia during the flooding episode. The pollen of Urticaceae—Moraceae taxa, especially Urtica, has increased in abundance since the flood. Past flooding was an important disturbance agent, which influenced the history of the plant community around Anangucocha. In the Amazon forest, such episodic flooding may be an important type of disturbance that promotes and maintains high species diversity. The Anangucocha record indicates that Amazonia experienced climatic fluctuation during the late Holocene.

ISSN:0012-9658    

DOI:10.2307/1943161

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

The ability of nest predation to explain patterns of covariation in species numbers with area and habitat was examined for forest birds. Numbers of individuals and species of birds were counted in 23 drainages in high elevation (2300 m) forest in central Arizona for 3 yr. Variation in bird species numbers was compared to variation in area and habitat structure among drainages. Birds were grouped into foraging (bark, understory foliage, canopy foliage, aerial) and nesting (cavity, understory foliage, canopy foliage) guilds based on heights and substrates used. Numbers of species increased with area for all guilds, but species—area slopes differed among nesting guilds. Differences in slopes cannot be explained by passive sampling because source pool size was the same or similar between guilds compared. Differences in slopes are consistent with a prediction that slopes should be greater for guilds that are more susceptible to nest predation. Variation in numbers of species among drainages was positively correlated with variation in the density of foraging and nesting substrates. However, correlations were greater when based on nesting than foraging heights and substrates. The results are consistent with a prediction that birds are selecting habitat sites based in part on the availability of nest sites that minimize risk of nest predation, and that these nest sites increase with density of foliage at nest height. These results ar also consistent with a hypothesis that availability of suitable nest sites is one of the bases for the relationship between species numbers and foliage density for foliage—nesting species. This conclusion is supported by a re—analysis of the data of Willson (1974), where foliage—nesting birds were grouped into nest—height guilds using data from the Cornell Nest Record Program; more of the birds that were added with vegetation layers tended to nest in those layers than forage in them. In short, multiple activities (foraging and nesting) can allow multiple processes to act simultaneously.

ISSN:0012-9658    

DOI:10.2307/1943162

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY