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Geology topics

Jon E. Keeley

Publications and source records attributed to Jon E. Keeley.

At least 235 records · Page 13Linked to original sources
USGS1983

Crassulacean acid metabolism in the seasonally submerged aquatic Isoetes howellii

Evidence to date is consistent with the hypothesis that the submerged aquatic Isoetes howellii Engelmann possesses crassulacean acid metabolism. Quantitative 14 C uptake studies indicate that CO 2 assimilation in both the light and dark are functions of pH and total inorganic carbon level. In both the light and dark, maximum uptake rates in 0.6 mM NaHCO 3 were double the rates in 0.3 mM NaHCO 3 . At both carbon levels there was a large drop in carbon assimilation rate between pH 6 and 8. In nature water pH and inorganic carbon level fluctuated diurnally thus complicating the determination of the contribution of light vs dark CO 2 uptake to the total carbon gain. On a sunny day between 0600 and 1200 h water chemistry changed markedly with ∼40% reduction in total carbon, ∼2 pH unit rise resulting from ∼100% depletion of free CO 2 . Under such conditions daytime deacidification in Isoetes leaves was 88% complete by noon. In contrast, on an overcast day, reduction of carbon in the water was much slower, deacidification was only 46% complete by noon and substantial malic acid levels remained in the leaves at the end of the day. Upon emergence crassulacean acid metabolism was largely lost in Isoetes leaves. Preliminary estimates suggest that under natural submerged conditions, early morning photosynthetic rates may be substantially higher than dark CO 2 uptake rates, though uptake rates throughout much of the day could be substantially lower than nightime CO 2 assimilation.

Oecologia↗
USGS1983

Crassulacean acid metabolism in Isoetes bolanderi in high elevation oligotrophic lakes

Isoetes bolanderi dominates the littoral flora of Siesta (elevation 2,440 m) and Ellery (2,905 m) lakes in the Sierra Nevada Range of California, USA. Both lakes are sparsely vegetated and I. bolanderi maintained aboveground oven dry weight of 30–50 m −22 through most of the 1981 summer growing season. Plants at the higher elevation Ellery Lake were half as large as plants at Siesta Lake and had substantially more biomass in corms. Titratable acidity levels in Isoetes leaves showed a diurnal fluctuation <50 μeq g 1 fresh weight early in the season at the highest elevation site but this increased to ∼300 μeq g 1 FW by mid-summer; starch and chlorophyll levels likewise increased in the leaves over this time. Throughout the season the magnitude of the diurnal acid change was comparable in Isoetes from both lakes but the dynamics of daytime deacidification were not. Averaged over the season, total daytime deacidification at Ellery Lake was 65% complete by noon whereas at Siesta Lake it was only 22% complete by noon. It is suggested that this may be related to the fact that Siesta Lake was more acidic and thus more carbon was in the form of free CO 2 . In both lakes water chemistry showed no consistent diurnal fluctuation in pH or free CO 2 though total inorganic carbon levels were at the extreme low end for aquatic habitats. The studies reported here suggest that under extremely low inorganic carbon levels there may be selection for nighttime CO 2 assimilation. Consistent with this hypothesis is the observation that emergent I. bolanderi plants, resulting from fluctuating water levels, initiated leaves with stomata (unlike adjacent submerged plants) and, although these leaves had substantially higher chlorophyll levels, they showed an order of magnitude less acid fluctuation than submerged leaves.

California↗
USGS1982

Gas exchange characteristics of the submerged aquatic Crassulacean acid metabolism plant, Isoetes howellii

The submerged aquatic plant Isoetes howellii Engelmann possesses Crassulacean acid metabolism (CAM) comparable to that known from terrestrial CAM plants. Infrared gas analysis of submerged leaves showed Isoetes was capable of net CO 2 uptake in both light and dark. CO 2 uptake rates were a function of CO 2 levels in the medium. At 2,500 microliters CO 2 per liter (gas phase, equivalent to 1.79 milligrams per liter aqueous phase), Isoetes leaves showed continuous uptake in both the light and dark. At this CO 2 level, photosynthetic rates were light saturated at about 10% full sunlight and were about 3-fold greater than dark CO 2 uptake rates. In the dark, CO 2 uptake rates were also a function of length of time in the night period. Measurements of dark CO 2 uptake showed that, at both 2,500 and 500 microliters CO 2 per liter, rates declined during the night period. At the higher CO 2 level, dark CO 2 uptake rates at 0600 h were 75% less than at 1800 h. At 500 microliters CO 2 per liter, net CO 2 uptake in the dark at 1800 h was replaced by net CO 2 evolution in the dark at 0600 h. At both CO 2 levels, the overnight decline in net CO 2 uptake was marked by periodic bursts of accelerated CO 2 uptake. CO 2 uptake in the light was similar at 1% and 21% O 2 , and this held for leaves intact as well as leaves split longitudinally. Estimating the contribution of light versus dark CO 2 uptake to the total carbon gain is complicated by the diurnal flux in CO 2 availability under field conditions.

Plant Physiology↗
USGS1981

Dark CO2-fixation and diurnal malic acid fluctuations in the submerged-aquatic Isoetes storkii

In the leaves (but not corms) of the submerged aquatic Isoetes storkii malic acid concentration fluctuated from 22 μeg g FW -1 in the evening to 171 μeg g FW -1 in the morning. Associated with this was a change in titratable acidity of 152 μeg g FW -1 between morning and evening. 14 C carbon was fixed in both the light and the dark, though the amount of carbon fixed in the light was more than that fixed in the dark. Autoradiographs show 88% of 14 CO 2 fixed in the dark is recovered after 1 h, in malic acid and the remainder in one other unidentified product, whereas these two products contain less than 15% of the 14 C fixed after 1 h exposure to 14 CO 2 in the light. It is suggested that CAM metabolism in this aquatic species may be related to the low availability of CO 2 for photosynthesis during the day in its aquatic environment and that this metabolic pathway may prove common in the genus Isoetes .

Oecologia↗
USGS1981

Post-fire succession of the herbaceous flora in southern California chaparral

Postfire succesion of the temporary herbaceous and suffrutescent cover was studied after chaparral fires in San Diego County, California, USA. Four categories of species make up the temporary cover. (1) "Generalized herbaceous perennials" are present before and after fire. Populations of these herbs are sparse under the shrub canopy. They resprout after fire from bulbs or other underground parts and postfire populations are sparse. (2) "Generalized annuals" are present in openings before fire but produce their peak population size in the first few years after fire. (3) Specialized "fire—annuals" are more or less restricted to the 1st postfire yr. (4) Specialized "fire—perennials" (subshrubs) are uncommon before fire, establish from seed in the 1st postfire yr and reach maximum cover in the 3rd and 4th yr. Community—level changes in cover and diversity are interpreted in light of differences in population dynamics of the four groups. Specis richness was highest in the 1st yr after fire because this was the only time all four groups were present together. Throughout succession herbaceous species richness was positively related to herb cover, negatively related to elevation and unrelated to slope aspect. The number of annual species fluctuated greatly through succession at all sites, but the number of herbaceous perennials did not. Herb cover fluctuated markedly from year to year and was positively related to amount of annual precipitation and negatively related to subshrub or "fire—perennial" cover. Artificial seeding with annual rye grass Lolium multiflorum had not apparent effect on total herb cover since sites with poor Lolium establishment had as high or higher herb cover as sites with high Lolium establishment. Lolium success was at the expense of the native cover and this negative effect was greatest on the "fire annuals."

Ecology↗
USGS1979

Alcoholic fermentation in swamp and upland populations of Nyssa sylvatica: Temporal changes in adaptive strategy

Both the upland and swamp varieties of Nyssa sylvatica respond initially to flooding with an acceleration of ethanol production. Under continued flooding the roots of the upland variety sylvatica have decreased rates of ethanol production, very likely a result of the progressively worsening necrosis of the root system. Few of these plants survive a full year of flooding. The swamp variety biflora survives and grows well under flooded conditions due to sequential metabolic and anatomical changes in the roots. Within a month after flooding, var. biflora initiates new roots with greatly accelerated rates of ethanol production, perhaps providing for a short-term compensatory energy source. Long-term acclimation to flooding involves a replacement of these roots and increased oxygen transport to the roots. The hypoxic conditions of the soil environment are avoided, and these rates of ethanol production are similar to those of drained plants.

American Naturalist↗
USGS1979

Population differentiation along a flood frequency gradient: Physiological adaptations to flooding in Nyssa sylvatica

Throughout the southeastern United States the hardwood Nyssa sylvatica (sensu lato) is distributed along a soil moisture gradient from upland sites, which are never flooded, to floodplains, which are periodically flooded and drained to permanently flooded swamps. Population differentiation with respect to flood tolerance and related physiological attributes was investigated using 1—year—old seedlings grown in a greenhouse from seed collected along this gradient. Upland plants were very intolerant of flooded soils. Their root systems deteriorated, root respiration rates dropped and, after a year under such conditions, survival was poor and those that did remain were greatly stunted and had accumulated large concentrations of many nutrient elements. In contrast swamp plants were quite tolerant of flooded soils. Upon flooding, parts of the orginal root system were lost but new roots were initiated which had an increased capacity for alcoholic fermentation. Many of these new roots were more succulent, larger in diameter, and less branched than drained roots. Such succulent roots however were only a temporary response to short—term flooding; plants flooded for a year did not have such roots, rather the root system superficially resembled drained roots. Concomitant with this return to drained—like roots was an increase in internal oxygen transport to the roots and a drop in alcoholic fermentation. Floodplain plants under drained conditions allocated less biomass to roots than to shoots and had high respiration rates, traits similar to upland plants. Under flooded conditions they initiated new roots with medium respiration rates, allocated less biomass to roots than to shoots, significantly increased oxygen transport to the roots and had high survival, traits similar to swamp plants. Thus, the floodplain population produced a distinctly flood—tolerant phenotype; but not nearly as tolerant of flooded conditions as the swamp phenotype. Floodplain plants differed from swamp plants in transporting less oxygen to the roots under drained conditions, initiating fewer succulent—type roots and not accelerating alcoholic fermentation upon flooding and after a year under flooded conditions having less total biomass, less oxygen transport to the roots and a greater accumulation of Fe and Mn in the roots. The floodplain plants apparently have been selected to be similar to upland plants under drained conditions and swamp plants under flooding and one consequence of this is that their tolerance of flooded conditions is intermediate. It is argued that one of the more important trade—offs in adapting to flooded conditions is that high internal oxygen transport carries with it a ‘cost’ in terms of excessive water loss under water stress conditions.

Ecological Monographs↗
USGS1978

Malic acid accumulation in roots in response to flooding: Evidence contrary to its role as an alternative to ethanol

Across a time course of flooding the malic acid content in roots of the swamp tree Nyssa sylvatica var. biflora increased 5-fold from 1 week to 1 month of flooding and remained at that level through a full year of flooding. Alcoholic fermentation rates accelerated within the first month of flooding but dropped to very low levels under long-term flooding. The theory that, under flooding, malic acid accumulates as an alternative anaerobic end product to ethanol is unlikely in this instance since (1) malate is initially associated with high alcoholic fermentation and (2) the reduction in alcoholic fermentation is accounted for by increased internal aeration of the roots.

Journal of Experimental Botany↗
USGS1977

Seed production, seed populations in the soil and seedling production after fire for two congeneric pairs of sprouting and nonsprouting chaparral shrubs

A study of seed production, seed storage in the soil, and seedling production after fire was undertaken for a sprouting and a nonsprouting congenerica pair of species of Ceanothus and Arctostaphylos. All species exhibited large fluctuations in annual seed production. There was a significant correlation between fruit production and precipitation in the previous year. It is hypothesized that high carbon gain in years of high precipitation results in high numbers of floral primordia which, in these species, remain dominant until the following year. It was also noted that high fruit production was not dependent upon high precipitation the same year; suggesting that the fruits were utilizing carbon stored from the previous year. All 4 species were capable of producing more seeds in a single season than were stored in the soil. Apparently the soil seed pools do not represent a steady accumulation of seeds in the soil but rather are the result of dynamic fluctuations in seed inputs and outputs. Each species also had more seeds in the soil, by several orders of magnitude, than seedlings after fire in an adjacent burned stand. The sprouting and seeding productive strategies are quite different in the two genera. The information from this study coupled with that from other studies indicate 4 reproductive modes: sprouting and seedling production (C. leucodermis), abundant seedling production (C. greggii), low seedling production but better "equipped" seedlings (A. glauca), and predominantly sprouting (A. glandulosa).

Ecology↗
USGS1977

Energy allocation patterns of a sprouting and nonsprouting species of Arctostaphylos in the California chaparral

The r- and K-selection theory was used to generate testable hypotheses about patterns of energy allocation in two chaparral shrubs of different reproductive strategies. Terminal-branchlet vegetative and reproductive biomass of the nonsprouting Arctostaphylos glauca and the sprouting A. glandulosa were sampled in a 23-year-old and a 90-year-old stand of chaparral to test the predictions that: (1) the terminal vegetative growth (g dry weight/m 2 of areal coverage) would be equal in the two species, in both stands; (2) oven dry weight (g) of reproductive parts/m 2 of areal coverage would be greater in A. glauca than in A. glandulosa in both aged populations; (3) allocation to reproductive parts by the shrubs in the 23-year-old stand would be greater than (or equal to) that of the 90-year-old shrubs. The amount of terminal vegetative growth was equal for both species in the 23-year-old and the 90-year-old stands. There was no statistically significant difference in the weight of fruits produced by the two species in the 23-year-old stand. However, fruit production by A. glauca was significantly greater than by A. glandulosa in the 90-year-old stand. Fruit production was also significantly greater for the older A. glauca shrubs than for those in the 23-year-old stand. The relationships of rainfall pattern and age of shrubs to fruit production are discussed.

California↗