Warm Temperature Regimes Research Articles

The RustPuccinia abruptavar.partheniicola,a Potential Biocontrol Agent of Parthenium Weed: Environmental Requirements for Disease Progress

The rust fungus Puccinia abrupta var. partheniicola, a potential biological control agent of parthenium weed (Parthenium hysterophorus), was evaluated under controlled environmental conditions. A range of spore germination temperatures as well as dew period durations and temperatures were investigated to determine some of the environmental requirements for disease establishment and disease progress. Plants were inoculated with urediniospores and exposed to dew periods between 3 to 12 h at temperatures of 10, 15, or 20 degrees C. For disease expression, the inoculated plants were then grown in a glasshouse at one of two temperature regimes (30/26 degrees C or 18/13 degrees C; day/night). Urediniospores germinated best at 12 +/- 1 degrees C, with lower germination rates at 5 degrees C or above 20 degrees C. No infection occurred when the plants were exposed to dew periods of less than or equal to 3 h, regardless of the incubation temperature. The disease progressed most rapidly when plants were inoculated and incubated for a dew period of at least 12 h at a temperature of 15 +/- 1 degrees C. The disease progressed most slowly following inoculation at dew periods of 6 h or less. Disease progress was more rapid when the plants were exposed to a cool-temperature regime (18/13 degrees C) than when exposed to a warm-temperature regime (30/26 degrees C). This suggests that good infection of parthenium weed could be obtained when the urediniospores arrive on the plants during the afternoon in the cooler months of the central Queensland autumn when relatively long dew periods are expected. (C) 1999 Academic Press.

The effect of temperature on inflorescence initiation and subsequent development in chrysanthemum cv. Snowdon ( Chrysanthemum× morifolium Ramat.)

The relationships between temperature and time to inflorescence initiation and subsequent development in chrysanthemum cv. Snowdon ( Chrysanthemum× morifolium Ramat.) were investigated. From pinching, flowering occurred most rapidly in plants grown at a mean temperature of 20.4°C, whilst those grown at 10.9°C had the lowest leaf number at flowering. The final leaf number, from the pinch to the inflorescence, increased with increasing temperature above 10.9°C. This could be attributed to a marked sigmoidal increase in the rate of leaf initiation with temperature, not delayed initiation. Above 20°C temperature had little effect on the time of floral initiation (plants initiating after 8–9 days), although temperatures below this led to a considerable delay in floral initiation (20.5 days at 9.6°C). Once initiated the inflorescences developed most rapidly at 20.2°C, however, unlike the process of flower initiation, subsequent flower development was delayed by both warmer and cooler temperature regimes.

Latitudinal compensation in oyster ciliary activity

1. Theories of latitudinal compensation predict that individuals living in colder temperature regimes should physiologically compensate for the slowing of standard physiological rates, owing to the relatively low temperature of their local environments, by increasing their metabolic rate in colder water temperatures relative to individuals living in warmer water temperature regimes. 2. This hypothesis was tested with oyster strains originally from geographically separated populations that were raised in a common environment for seven generations. The physiological parameter measured was ciliary activity across a temperature gradient. 3. Support for the latitudinal compensation hypothesis was found: the strain originally from the colder temperature regime had more active cilia at lower experimental temperatures than individuals originally from the warmer temperature regime. Ciliary activity of the more northern Long Island Sound oysters was significantly greater than activity in the more southern Delaware Bay oysters at temperatures of –1, 2 and 6 °C. 4. These results suggest that there is genetically based physiological differentiation between these populations of oysters consistent with the latitudinal compensation for local temperature regime.

Is Seedling Root Morphology Predictive of Seasonal Accumulation of Shoot Dry Matter in Maize?

Seedling vigor at suboptimal temperatures is an important characteristic in maize (Zea mays L.) growth in cool regions. Selection for improved vegetative growth and seasonal dry matter accumulation at suboptimal temperatures would be more efficient if seedling traits related to field performance could be identified under controlled conditions. This study evaluated if root traits of seedlings grown at cool or warm temperature regimes are predictive of early growth and silage yield in the field. Twenty early‐ to medium‐late maturing European hybrids (FAO maturity ratings 200–280) were grown in a solid substrate until the third leaf stage under two controlled temperature regimes (25/22.5°C and 15/12.5°C, day/night) and until silage maturity in three field environments on a Orthic Luvisol soil in Central Germany. The closest relationships with early field growth were found for the total length of the main roots (r = 0.65, P < 0.01) and total length (r = 0.60, P < 0.01) and number (r = 0.68, P < 0.01) of firstorder laterals of the seminal roots at 25122.5°C. Silage yield was best correlated with the branching density of the seminal roots (r= 0.66, P < 0.01) at 15112.5°C and the total root surface area (r = 0.58, P < 0.01) at 25122.5°C. These root traits could potentially be used only in combination with other secondary characters for the indirect selection for shoot performance because individual root traits explained less than 50% of the variation in shoot weight in the field. Negative correlations between the chilling stability of most seedling traits, as expressed by the relative difference of trait means at 15/12.5°C and 25122.5°C, and silage yield indicated that chilling‐tolerant genotypes may be less capable of benefiting from the warmer temperatures during later growth stages.

Flowering in Pigeonpea (Cajanus cajan) in Kenya: Responses of Medium- and Late-maturing Genotypes to Location and Date of Sowing

SUMMARYThe effects of temperature and photoperiod on times from sowing to flowering (f) were investigated in medium-and late-maturing pigeonpea (Cajanus cajan). Twelve genotypes were sown in two seasons at seven sites in Kenya, covering latitudes 0–4°S and a wide range of altitudes (50–2000 m), as well as under polythene enclosures constructed at six sites to create warmer temperature regimes (a total of 26 environments). The same genotypes were also sown at monthly intervals and in an artificially extended photoperiod (in the open as well as under polythene) created by incandescent lamps suspended above the plots at Katumani (1°30′S).Times from sowing to flowering varied from 70 to more than 300 days and were associated with variations in mean pre-flowering values of temperature and photoperiod which ranged from 15.2° to 32.7°C and from 12.6 to 15.0 h d−1. Genotypic variation in f in the most inductive regimes (a mean pre-flowering temperature of 24.3°C for the medium- and 20.8°C for the late-maturing genotypes, combined with a mean pre-flowering photoperiod of 12.6 and 12.8 h d−1) ranged from 70 and 76 days and from 85 to 112 days, respectively. There were no photoperiodic effects on f over the range from 12.6 to 13.1 h d−1, but the artificially extended day delayed flowering, especially in the late-maturing genotypes.The relation between l/f and the mean pre-flowering temperature was linear below and above an optimum temperature, To. The genotype-specific parameters derived from these thermal linear rate models based on flowering responses in 26 environments closely predicted l/f and therefore f in an independent sequence of monthly sowings. It was thus responses to temperature below and above To and not responses to daylength which modulated flowering throughout the wide range of natural environments tested within this vast country, even in the late-maturing and most photoperiod-sensitive genotypes.

Effects of Host Resistance on Germination of Cercospora arachidicola on Peanut Leaf Surfaces1

Abstract Conidial germination by a North Carolina field-isolate of Cercospora arachidicola Hori was studied on leaf surfaces of two highly resistant and two susceptible peanut (Arachis hypogaea L.) genotypes under 5 day/night temperature regimes. Conidia germinated at all temperature regimes, but a greater percentage germinated at the coolest temperature regimes of 26 C day/20 C night and constant 24 C than in warmer temperature regimes. Percentage germination differed significantly with respect to time and genotype in each temperature regime. Fewer conidia germinated on resistant compared to susceptible genotypes, with lowest germination on the resistant genotype 91 PA 150 (a Virginia type derived from a cross of A. hypogaea and A. cardenasii Krapov. and W. C. Gregory). Conidia germinated more quickly and more conidia germinated overall on the susceptible NC 7 than on the other genotypes tested.

Effect of salinity, temperature, and growth regulators on the germination and early seedling growth of Atriplex griffithii var. stocksii

Seed germination and early seedling growth of Atriplex griffithii var. stocksii from seeds collected from a saline desert habitat in Karachi, Pakistan, were studied. The seeds of A. griffithii did not germinate under high salt stress (516 mM NaCl). Best germination percentages were obtained in distilled water. Seed germination was stimulated in light at cooler alternating temperature (25:10 °C) and inhibited at warmer temperature (30:15, 30:20, and 35:25 °C) regimes. Early seedling growth showed responses towards salinity and temperature that were similar to the germination responses. Both GA3 and kinetin alleviated salinity-induced germination inhibition, and in most cases germination was stimulated by growth regulator treatments. A low concentration of kinetin (0.46 μM) and a high concentration of GA3 (28.9 μM) significantly promoted early seedling growth at all salinity treatments. Key words: Atriplex griffithii var. stocksii, seed germination, early seedling growth, salinity, temperature, growth regulators.

Response of Soybean to Combinations of Clomazone, Metribuzin, Linuron, Alachlor, and Atrazine

Field observations in 1986 indicated that increased injury to soybean could occur from clomazone plus metribuzin and clomazone plus linuron compared with metribuzin or linuron alone. Field experiments to measure this response were conducted in 1988, 1989, and 1990 at two locations in Michigan. Atrazine at 0, 1120, 2240, and 3360 g ha-1was applied the year previous to soybean planting to determine if atrazine residues in the soil influenced soybean response. Herbicide treatments in soybean included clomazone, metribuzin, linuron, alachlor, clomazone plus metribuzin or linuron, alachlor plus metribuzin or linuron, and an untreated control. Additive and synergistic responses in soybean to clomazone plus linuron and clomazone plus metribuzin, regardless of atrazine application rate, occurred in some field environments. Experiments in the greenhouse demonstrated that soybean shoot weight was reduced synergistically from clomazone plus metribuzin compared with either herbicide alone, and the response was greater on a soil with 2.5% organic matter compared with a soil with 4.4% organic matter. Clomazone plus metribuzin reduced leaf area and shoot dry weight, regardless of placement, while leaf area and shoot dry weight were reduced more when clomazone plus linuron- and atrazine plus metribuzin-treated soil was placed in the same zone as the soybean seed. The synergistic interaction in soybean to clomazone plus metribuzin occurred under both cool and warm temperature regimes in growth chamber studies.

Quality and morphological characteristics of alfalfa as affected by soil moisture, pH and phosphorus fertilization

Alfalfa (Medicago sativa L. ’Saranac’) was grown in a greenhouse on Ste-Rosalie clay and Danby gravelly sandy loam to determine the effects of phosphorus fertilization, air temperature, soil moisture regime and soil pH on chemical composition and plant morphology. The following treatments were applied in factorial combination: three moisture regimes (1, semi-dry, with soil moisture between field capacity or 100% of available water and wilting point or 0% of available water; 2, optimal, between field capacity and 70% of available water; 3, wet, between saturation point and field capacity), three rates of phosphorus in the form of disodium phosphate (0, 12.5 and 25.0 P kg−1 of dry soil) and three soil pH levels (natural, near 5.4, 6.5 and 7.5). Half the alfalfa was grown in a warm greenhouse section with a minimum daytime temperature of 25 °C and 19 °C at night and the other half was grown in a cool section with a daytime minimum of 15 °C and 9 °C at night. Quality of alfalfa was generally improved by water deficit as shown by decreased concentrations of acid detergent fiber (ADF) and acid detergent lignin (ADL) and increased concentrations of crude protein (CP). Cold temperatures decreased ADF content which indicates that quality of alfalfa grown under cold compared to warm temperature regimes is better. Phosphorus fertilization seemed to have more effects on plant morphology and quality under cold than warm temperature regimes. In general, concentrations of CP, ADF and ADL, stem length, leaf area and the number of stems increased in parallel with soil pH. The data indicate that low temperature and low soil moisture regimes were generally associated with higher quality alfalfa than were high temperature and wet soil moisture regimes.Key words: Alfalfa, soil moisture regime, air temperature, phosphorus fertilization, soil pH

Effects of CGA-154281 and Temperature on Metolachlor Absorption and Metabolism, Glutathione Content, and Glutathione-S-Transferase Activity in Corn (Zea mays)

CGA-154281 and temperature effects on metolachlor absorption and metabolism were studied in corn seedlings grown in untreated soil or soil treated with metolachlor, CGA-154281, or both. Seedlings were grown under a cool (21/13 C, 16-h day) or warm (30/21 C, 16-h day) temperature regime and exposed to14C-metolachlor for 10 min at either 21 or 30 C. Corn grown under the cool temperature regime absorbed slightly more14C-metolachlor than corn grown under the warm temperature regime. Corn held at 21 C during a 10-min14C-metolachlor exposure period metabolized metolachlor more slowly than corn held at 30 C. Decreased corn tolerance to metolachlor observed at lower temperatures may be due in part to slower metolachlor metabolism. Corn grown in the presence of metolachlor plus CGA-154281 metabolized14C-metolachlor to the glutathione conjugate twice as fast as corn grown in the presence of metolachlor alone. The increase in metabolism rate was due to a fivefold increase in glutathione-S-transferase (GST, EC 2.5.1.18) activity and not to an increase in glutathione (GSH) content. Results are consistent with the hypothesis that CGA-154281 protects corn from metolachlor injury by enhancing GST activity, which accelerates metolachlor detoxification via GSH conjugation.

Seasonal Ozone Levels and Control by Seasonal Meteorology

Meteorological data, particularly 850-MB level temperatures, for Fort Totten, New York (1980) and Atlantic City, New Jersey (1981-1988) were examined for any relationship to seasonal ozone levels. Other radiosonde stations in the Northeast were utilized for 1983 and 1986, years of widely differing ozone levels. Statistics for selected parameters and years are presented. Emphasis is placed on recurring warm temperature regimes in high ozone years. Successive occurrences or episodes of high temperatures characterize seasonally high ozone years. Seasonally persistent high temperatures are related to seasonally chronic high ozone. An example is presented relating the broad-scale climatologlcally anomalous pattern of high temperatures to anomalous circulation patterns at the 700-MB level.

Pedogenic Factors Affecting Magnetic Susceptibility of Northern California Soils

AbstractMass magnetic susceptibility (χ) was measured on samples taken from horizons from 27 northern California soils to determine the amount and vertical distribution of χ, and if the observed χ distribution could be related to parent material, climate, topography and time. In most of the soils with vertical morphological distinctions, eluvial horizon χ was greater than illuvial, R or CR χ. This susceptibility enhancement was interpreted as being due to pedogenic processes. Soils formed on parent material rich in Fe‐bearing minerals (e.g. basalt) had higher absolute χ and greater χ enhancement than did soils formed on Fe‐poor parent material (e.g. siltstone). Enhancement was greater in soils from areas of high (>1000 mm) mean annual precipitation compared with areas of low (<500 mm) mean annual precipitation, and soils formed under mean annual temperature ≤6 °C had less distinct enhancement than soils formed in warmer temperature regimes provided the precipitation was the same. Two soils with poor and somewhat‐poor drainage classes had distinctly lower absolute χ than associated well‐drained soils. Both absolute χ in eluvial horizons and susceptibility enhancement of eluvial over illuvial, and eluvial over C horizons increased as soils became older. Older soils were enhanced to a greater depth than younger soils. Eluvial and illuvial χ was greater than parent material χ in most profiles because non‐ or weakly magnetic minerals were converted to maghemite, which accumulated in eluvial horizons. In young soils with little morphological differentiation formed on transported parent material, χ measurements help to locate lithologic discontinuities.

A comparison of organic and inorganic nitrogen fertilizers: Their nitrate-N and ammonium-N release characteristics and effects on the growth response of lettuce (Lactuca sativa L. cv. Fortune)

The response of pot grown lettuce to inorganic (ammonium nitrate) and organic (dried blood and Protox) N fertilizers was determined at two temperature regimes (15°C day/10°C night and 20°C day/15°C night) and related to the NH4−N and NO3−N release characteristics of each material. The N release characteristics of the organic materials matched the N requirements of lettuce more closely than the inorganic fertilizer. However, was rapidly released from the protein based materials such that composts were depleted of available fertilizer N at the same time irrespective of the form supplied. The warmer temperature regimes resulted in a more rapid depletion of the fertilizers due to biological immobilization such that N recoveries in shoots, roots and leachates were reduced. Approximately 20% of the N present in Protox (a material derived from activated sewage sludge, processed to reduce the heavy metal content to minimal levels) appeared to be resistant to microbial degradation and was unavailable to the plants. Therefore, the growth response of lettuce was slightly reduced with Protox compared to the other materials at similar rates of incorporation. The organic materials did not contribute NO3−N to the plant and small NO3−N concentrations in petioles were derived from the water used for irrigation. However, NO3−N levels in plants receiving inorganic ammonium nitrate were initially high but progressively declined as the fertilizer NO3−N became depleted.

Temperature Effects on Megagametophytic Development in Meadowfoam

Seed yield of meadowfoam (Limnanthes alba Benth.), an open‐pollinated winter annual, is partially determined by the number of seeds per flower. Each flower has the potential for five seeds, but typically an average of two seeds per flower has been measured in the cultivar Mermaid. The causes of less‐than‐maximum seeds per flower are not known. Therefore, an investigation of the effects of temperature on the growth rates of the unfertilized ovule and embryo sac and on megagametophytic structure was conducted. Treatment effects at 0, 48, 96, and 144 h postanthesis (HPA) under the regimes of 15/15, 24/15, and 33/15 °C alternating day/night were measured. Growth rate for embryo sac width, ovule width, embryo sac/ovule width growth rate (ESOWGR), embryo sac length, ovule length, and embryo sac/ovule length growth rate (ESOLGR) was significantly (P < 0.01) lower at 15/15 °C than at higher temperatures. Growth rate for embryo sac width, ESOWGR, and ESOLGR was significantly (P < 0.05) higher at 24/15 than at 33/15 °C. At anthesis, the number of flowers with four or five normal appearing megagametophytes was approximately the same in all temperature regimes. However, over time, with each warmer temperature regime there were increasing numbers of abnormal embryo sacs wherein the egg apparatus pulled away from the micropyle resulting in the megagametophyte appearing to float within the embryo sac. This temperature effect may explain some of the yearly variation in seed yield and suggest the need for timely pollinator management, especially during periods of rapid bloom when temperatures are typically above 24 °C.

Measurement, prediction and interpretation of soil temperature for use in soil taxonomy: Tropical Australian experience

Soil temperature data for use in the application of Soil Taxonomy to soil classification in the Australian tropics is reported for a three year study period at 15 sites. The research indicates that, although there is a paucity of soil temperature data in the tropics and that simple instrumentation and relatively infrequent observation will provide soil temperature data that are suitable for use in Soil Taxonomy, there are a number of problems of interpretation which can have important consequences to classification. Vegetative cover has a significant effect on soil temperature at a depth of 50 cm in both the humid and semi-arid tropics of Australia. This effect is sufficient to cause a shift from iso to non-iso regimes; for a change from vegetated to bare surfaces, as is common with a cropping land use. The relationship between the defined summer and winter periods and the measured hottest and coldest three months is strongly influenced by both the soil moisture regime and vegetative cover. Again these differences in interpretation are sufficient to seriously affect classification. In order to avoid these problems the ‘Trop’ concept could be modified to ‘mesic or warmer temperature regime and an udic moisture regime’ and deletion of the iso requirements. A comparison of two recommended methods for estimating soil temperature from screen temperature showed them both to be unsatisfactory, particularly in the semiarid tropics. The errors produced by each method were sufficient to cause important changes to soil classification when using Soil Taxonomy. The work demonstrates the importance of treating soil temperature and moisture regimes together. In the ustic regimes, mean monthly soil temperature at 50 cm can be adequately predicted by adding 4.0 degrees to the mean monthly screen temperature; whilst in the udic regimes it appears that the same can be achieved by adding 2.0 degrees to the screen temperature.

TEMPERATURE-SENSITIVE NODULATION AND N2 FIXATION OF Rhizobium leguminosarum BIOVAR Phaseoli STRAINS

Two strains of Rhizobium leguminosarum biovar phaseoli, both previously Nod+Fix+ and efficient in N2 fixation, now have altered symbiotic properties presumably through spontaneous mutation. Rhizobium leguminosarum biovar phaseoli strain RCR 3605 was Nod−Fix− in a cool growth temperature regime (14–23 °C) and Nod+Fix− in a warm regime (17–23 °C) on seven of nine bean cultivars studied. Rhizobium leguminosarum biovar phaseoli strain CIAT 57 was Nod+Fix− in both temperature regimes. CIAT 57 and RCR 3605 are synonyms for strains derived from the same parent strain but housed in different culture collections. The nodulation deficiency in CIAT 57 is presumably genetically predetermined in the bacterium rather than in the plant because no Nod+Fix+ phenotype was identified on nine bean cultivars tested. A control R. leguminosarum biovar phaseoli strain, RCR 3644, was efficient on all cultivars. In the warm temperature regime, the Nod+Fix− phenotype was observed with strain RCR 3605 only on some cultivars, suggesting that the host plant genome played a role in this ineffective symbiosis. It is likely that deleterious genetic mutations during prolonged storage may be altering the N2-fixing ability of these rhizobial strains and that commercial inoculants must be continually monitored for symbiotic performance of strains with a variety of host plant cultivars. Key words: Field bean, Rhizobium leguminosarum biovar phaseoli, N2 fixation

Effects of CO2 enrichment and temperature on growth in two C4 weeds, Echinochloa crus-galli and Eleusine indica

Mathematical growth analyses were carried out on two C4 grasses, Echinochloa crus-galli and Eleusine indica, to test the influence of CO2 enrichment and temperature on growth. Echinochloa populations from Québec, North Carolina, and Mississippi and a single population of Eleusine from Mississippi were grown for 48 days at two CO2 concentrations (350 and 675 μL∙L−1) and three temperature regimes (28:22, 24:18, and 21:15 °C). CO2 enrichment generated an increased root dry weight and induced an earlier development of inflorescences. Net assimilation rate, the only other parameter to respond to CO2 enrichment, was higher for plants grown at high CO2 concentrations during the first harvest interval. Biomass partitioning was affected by temperature. Root dry weight was greater in plants grown at 21:15 °C while more leaf area was produced in warmer temperature regimes. Only plants from Québec maintained normal growth rates under the 21:15 °C regime, suggesting that northern C4 plants are better suited for growth at low temperatures than southern ones.

Growth and development at cold-hardening temperatures. Pigment and benzoquinone accumulation in winter rye

Accumulation of chlorophyll, the carotenoids (β-carotene, lutein, violaxanthin, and neoxanthin), and the benzoquinones (plastoquinone A and α-tocopherol) were monitored in 'Puma' rye as a function of leaf ontogeny at warm and cold-hardening temperatures. Although the kinetics of accumulation differed among the leaves of warm-grown plants, the initial and maximum levels of the pigments and benzoquinones expressed on a leaf area basis did not differ significantly among the first four leaves of the main culm. In contrast, the third and fourth leaf of cold-grown plants, which developed completely at the low temperature, generally exhibited initial and maximum pigment and benzoquinone levels 60–300% greater than was observed for leaf 1 and 2 of cold-grown plants, which were completely or partially developed at the warm temperature regime. This resulted in pigment and benzoquinone levels which were 1.6- to 3-fold greater in the plants grown at cold-hardening temperatures than those grown at the warm temperature, when expressed on a per unit leaf area basis. However, when pigment accumulation was calculated on a chlorophyll basis, the benzoquinone content of leaves that developed solely at cold-hardening temperatures exhibited a 1.7-fold increase over the same leaves developed at warm temperatures. Carotenoids did not exhibit this trend. Calculations based on chlorophyll/carotenoid content and dry weight accumulation indicated that leaves that were developed at cold-hardening temperatures appeared to produce more dry matter per unit of photosynthetic pigments than the same leaves that were developed at nonhardening temperatures.

Suspended particulate organic material from hydrothermal vent waters at 21° N

Ocean floor spreading centres described recently consist of several sites with chemical and biological features unlike any oceanic sites previously known1–4. The high-pressure and warm-temperature regimes at these sites, coupled with dynamic hydrothermal water circulation, support biological communities that utilize a source of primary production which appears to be non-photosynthetic5. A detailed biochemical analysis of the suspended matter at a biologically-active site has been undertaken, with the goal of describing the relationship between microorganisms, benthic organisms and suspended particulate material within these hydrothermal systems. Suspended particulate matter from warm hydrothermal vent waters (5–38°C) of the East Pacific Rise1–4 (21° N, 106° W) was sampled on the OASIS expedition with an in situ pumping system in April 1982. Particulate organic carbon (POC) and nitrogen (PON) as well as individual organic compound classes from the lipid fraction were analysed to ascertain the sources and composition of the organic matter in this highly productive area. We show here that the particulate organic material (POM) of the vent water was both quantitatively and qualitatively different from the non-vent bottom water. The POC and PON measured within the vent and non-vent waters vary by a factor of 2–5, the higher values being in warm water. The organic matter in the non-vent water was found to be more resistant towards degradation or remineralization than in the vent water, as shown by the C:N ratio and the total lipid:POC ratio. Contributions to the lipid class compounds were assessed using well-known organic compound source biomarkers such as hydrocarbons, fatty alcohols, sterols, triacylglycerols and steryl and wax esters.

Photosynthetic adaptation to temperature in four species from the Colorado shortgrass steppe: a physiological model for coexistence.

Several aspects of photosynthetic adaptation to temperature were examined in four graminoid species from the Colorado shortgrass steppe. The experimental species were chosen to provide examples of a variety of in situ seasonal phenology patterns. The cool season grass, Agropyron smithii (C3), exhibited higher photosynthesis rates when grown in a cool temperature regime (20/15°C), and compared to warm grown plants (35/15°C). The warm season species, Bouteloua gracilis (C4) and Buchloe dactyloides (C4), exhibited higher photosynthetic capacities when grown in the warmer temperature regime. The sedge, Carex eleocharis (C3), which exhibits seasonal growth potential during the cool and warm portions of the growing season, exhibited a marked capacity for photosynthetic temperature acclimation. Differential effects of growth temperature on the intracellular conductance to CO2 appeared to have a greater regulatory role in these responses for the two C3 species, relative to stomatal conductance or photorespiration (O2 inhibition of photosynthesis). In the two C4 species decreases in the intracellular conductance in cool grown plants were correlated with the decreased photosynthetic capacity in normal air for B. gracilis, but not for B. dactyloides. Analysis of the Arrhenius relationship for CO2 saturated net photosynthesis at low leaf temperatures (4.5-17°C) indicated sharp breaks in the apparent energy of activation at 5.8-9.0°C in the warm season species B. gracilis and B. dactyloides. Leaves of A. smithii and C. eleocharis exhibited no significant low temperature limitations according to this analysis. The low temperature limitations in the warm season species were partially reflected in an inhibition of the quantum yield for CO2 uptake after 2 h at 5-6°C in the presence of high photon flux densities. Temperature dependent increases in the chlorophyll fluorescence yield at high temperatures revealed the lowest breakpoint values for A. smithii, and the highest values for B. gracilis. The differential patterns of temperature adaptation among the species further extend the proposal of Kemp and Williams (1980; Ecology 61:846-858) that seasonal temperature gradients in the shortgrass steppe have a regulatory role in maintaining offset patterns of resource utilization and decreasing interspecific competition.