Family- and population-level responses to atmospheric CO2 concentration: gas exchange and the allocation of C, N, and biomass in Plantago lanceolata (Plantaginaceae).

To ascertain the inheritance of responses to changing atmospheric CO(2) content, we partitioned response to elevated CO(2) in Plantago lanceolata between families and populations in 18 families in two populations. Plants were grown in 35 Pa and 71 Pa partial pressure of CO(2) (pCO(2)) in open-top chambers. We measured above- and belowground mass, carbon (C), nitrogen (N), hexose sugar, and gas exchange properties in both CO(2) treatments. Families within populations differed in mass, mass allocation, root : shoot ratios, aboveground percentage N, C : N ratio, and gas exchange properties. The CO(2) × family interaction is the main indicator of potential evolutionary responses to changing CO(2). Significant CO(2) × family interactions were observed for N content, C : N ratio, and photosynthetic rate (A: instantaneous light-saturated carbon assimilation capacity), intercellular CO(2) concentration, transpiration rate (E), and water use efficiency (WUE = A/E), but not for stomatal conductance. Families differed significantly in acclimation across time. The ratio of A in elevated vs. ambient growth CO(2), when measured at a common internal CO(2) partial pressure was 0.79, indicating down-regulation of A under CO(2) enrichment. Mass, C : N ratio, percentage, C (%C), and soluble sugar all increased significantly but overall %N did not change. Increases in %C and sugar were significant and were coincident with redistribution of N aboveground. The observed variation among populations and families in response to CO(2) is evidence of genetic variation in response and therefore of the potential for novel evolutionary trajectories with rising atmospheric CO(2).

Interaction of temperature and other environmental variables influencing plant distribution.

Statistical analyses of the relationships between the patterns of distribution of plants with C4 photosynthesis and Crassulacean acid metabolism (CAM) have revealed a variety of correlations with environmental variables. The worldwide abundance of C4 grasses, relative to C3 grasses, is highly positively correlated with growing season temperature. However, microscale analyses have revealed that C4 grasses are more abundant than C3 grasses in habitats with high levels of solar irradiance and low moisture availability. There are numerous exceptions to these generalizations. C4 dicots generally are more abundant in habitats characterized by high rates of evaporation. Species possessing CAM occur in habitats having low levels of soil moisture store. In the Cactaceae such habitats also have very high potential rates of evaporation and the CAM pathway is the primary mechanism of the uptake of atmospheric CO2. In contrast many species of the Crassulaceae grow in habitats with lower potential rates of evaporation and the CAM pathway is less important or not used at all in the uptake of atmospheric CO2.

Carbon-isotope discrimination by leaves of Flaveria species exhibiting different amounts of C3-and C 4-cycle co-function.

Carbon-isotope ratios were examined as δ(13)C values in several C3, C4, and C3-C4 Flaveria species, and compared to predicted δ(13)C, values generated from theoretical models. The measured δ(13)C values were within 4‰ of those predicted from the models. The models were used to identify factors that contribute to C3-like δ(13)C values in C3-C4 species that exhibit considerable C4-cycle activity. Two of the factors contributing to C3-like δ(13)C values are high CO2 leakiness from the C4 pathway and pi/pa values that were higher than C4 congeners. A marked break occurred in the relationship between the percentage of atmospheric CO2 assimilated through the C4 cycle and the δ(13)C value. Below 50% C4-cycle assimialtion there was no significant relationship between the variables, but above 50% the δ(13)C values became less negative. These results demonstrate that the level of C4-cycle expression can increase from, 0 to 50% with little integration of carbon transfer from the C4 to the C3 cycle. As expression increaces above 50%, however, increased integration of C3- and C4-cycle co-function occurs.

Seasonal variation in crassulacean acid metabolism in Dudleya blochmanae (Crassulaceae).

Plants of Dudleya blochmanae were studied over a growing season (December-June) in their native habitat on the central California coast. During the season soil water potential fluctuatdd widely, becoming unmeasurably negative (<-5.0 MPa) by early May. In contrast, leaf water potential did not fluctuate greatly with the most negative value of-0.56 MPa occurring in June. The leaves exhibited nocturnal accumulation of titratable acidity at all sampling periods, with the greatest magnitudes of accumulation occurring late in the growing season. The fruits also exhibited nocturnal accumulation of titratable acidity. The biomass δ13C values of all organs were most negative in December and least negative in June. The findings confirmed earlier suggestions that there may be biologically important differences in carbon isotope content among the various organs of a single plant of D. blochmanae. The water potential of thephotosynthetic organs was highly correlated (r2=0.84) with the biomas δ13C value. A greenhouse study demonstrated that the fruits exhibit an, apical dominance with regard to maintenance of plant water potential during drought.

Photosynthetic adaptation of Solanum dulcamara L. to sun and shade Environments : IV. A comparison of North American and European genotypes.

Clonal replicates of six genotypes of Solanum dulcamara L. grown in eight different environments were compared for photosynthesis and growth. Four of the genotypes were native to shaded habitats, two to sun habitats. The experimental growth environments differed in light level, daily temperature amplitude and substrate moisture availability. Treatments elicited large differences in lightsaturated photosynthetic rates and growth. Genotypic differences in response to the treatments were identified. However, when genotypes native to sun and shade habitats were compared, there were no consistent differences in photosynthesis or total plant dry weight. It was concluded that previously reported differences in the photosynthetic response of genotypes native to sun and shade habitats to treatment light level may have been the result of the persistent after-effects to changes in leaf water potential and not an adaptive response to growth light level.

Leaf thickness and carbon isotope composition in the Crassulaceae.

Measurements of leaf thickness and δ13C value were obtained for twenty species and three intergeneric hybrids of the Crassulaceae. The data include plants growing in their native habitats and also in greenhouse cultivation. There is a strong relationship between leaf thickness and leaf δ13C values. The plants with the thickest leaves of ca. 7 to 11 mm had δ13C values ranging from -11.5‰ to -13.8‰. Plants with leaves that were thinner than 2.0 mm all had δ13C values that were more negative than -23‰. Plants having intermediate leaf thickness possessed intermediate δ13C values. The leaf tissue of four genotypes spanning the range of leaf thicknesses all exhibited a two-fold or greater nocturnal increase in titratable acidity. It appears that the differences in leaf thickness and δ13C values among the tested species are genetically determined.

The distribution of C4 species of the Cyperaceae in North America in relation to climate.

The percent of species of the Cyperaceae possessing the C4 pathway was calculated for twenty-five regions of North America. A stepwise multiple regression analysis was used to determine which climatic variables were most highly correlated with the percent C4 species among the various regions. The square of the mean July minimum daily temperature exhibited the strongest correlation with the transformed percentage of C4 species. It appears that the relationship to climatic variables of the C4 species of the Cyperaceae is similar, but not identical to the relationship previously reported for C4 species of the Gramineae.

Photosynthetic adaptation ofSolanum dulcamara L. to sun and shade environments. III. Characterization of genotypes with differing photosynthetic performance.

Clone mal9, a genotype ofSolanum dulcamara L. having photosynthetic characteristics similar to previously hypothesized shade ecotypes, is compared to five other genotypes having photosynthetic characteristics similar to previously hypothesized sun ecotypes. The primary differences are a 35% reduction in total leaf conductance and a 15% reduction in leaf chlorophyll content in mal9. Both factors contribute to a 44% reduction in lightsaturated photosynthetic rate in mal9. In relation to the 5 other genotypes, mal9 appears to be poorly adapted for growth in the normal range of natural habitats.

Photosynthetic Adaptation of Solanum dulcamara L. to Sun and Shade Environments: II. Physiological Characterization of Phenotypic Response to Environment.

Photosynthetic and growth properties of Solanum dulcamara L. were studied under controlled environments. The 200 experimentally tested plants were clonal replicates of five field-collected individuals, three from fully exposed habitats and two from deeply shaded habitats. After 4 weeks of growth in one of eight environmental treatments, each plant was measured for leaf adaxial and abaxial conductance to water vapor, specific leaf weight, chlorophyll per square decimeter of leaf, photosynthetic unit size, light-saturated photosynthetic rate, total leaf area, and total leaf, stem, and root dry weights. Changes in light level influenced photosynthesis and growth of each plant more than changes in water availability or temperature. It is strongly suggested that the primary adaptive response of the tested individuals to changes in levels of light involves the regulation of leaf thickness.

Photosynthetic adaptation of Solanum dulcamara L. to sun and shade environments : I. A Comparison of Sun and Shade Populations.

The photosynthetic response properties of individuals of Solanum dulcamara L. collected from sun and shade habitats were compared in controlled environments. Light-saturated photosynthetic rates and seven additional parameters associated with photosynthetic and growth performance were measured over a range of 12 environmental conditions that simulated natural habitat differences in light intensity, moisture availability and daily temperature amplitude. In contrast to previous studies, the results suggest there is no ecotypic differentiation with respect to the sun and shade environments from which the individuals were collected. It appears that all but one of the field-collected individuals are capable of successfully inhabiting the full range of light environments from which the species was collected.

δ13C values of an herbivore and the ratio of C3 to C4 plant carbon in its diet.

The δ13C values of whole body samples of the beetle Tribolium castaneum are closely correlated with the δ13C values of the plant carbon in its diet. The correlation is always high for diets ranging from 100% C4 to 100% C3 plant material. The degree of correlation is independent of the growth rate of the animals.

Environmental and genetic control of phenotypic adaptation to drought in Potentilla glandulosa Lindl.

Two populations of Potentilla glandulosa (Rosaceae) have strongly contrasting abilities to seasonally modify their phenotypic sensitivity to drought by low temperature-induced changes in leaf morphology. One population is native to an inland continental climate with unpredictable droughts occurring at any time during the year. The second population is native to a coastal mediterranean climate with a highly predictable annual cycle of winter rain and summer drought. In response to low temperatures in the autumn, the inland plants produce a compact rosette of small leaves and shed their large summer leaves, thereby reducing the total plant leaf area. The inland plants begin growth in the spring in the compact rosette phenotype and are much less sensitive to drought, maintaining higher values of stomatal conductance and leaf water potential, than when in the largeleaved summer phenotype. The coastal plants do not exhibit the low temperature-induced change in leaf morphology and are relatively sensitive to drought when grown at high or low temperatures. The F1 hybrids of a coastal x inland cross exhibit an intermediate response to low temperature and drought. In the F2 generation the inland parental class of individuals fully responding to low temperature segregates in a 1:63 ratio.

Changes in the photosynthetic apparatus of maize in response to simulated natural temperature fluctuations.

The response of the photosynthetic apparatus to low temperature periods differed among three hybrids of maize (Zea mays L.) grown in a phytotron. Light-saturated photosynthetic rates, leaf chlorophyll content, and mesophyll cell photosynthetic unit density all declined with increasing duration of low temperature. No single metabolic or physiological parameter appeared to control the response of the three hybrids to low temperature stress. Among all temperature treatments, net photosynthetic rate on a leaf area basis was more closely correlated with leaf chlorophyll content than with any other measured parameter. Final shoot dry weight was most highly correlated with stomatal conductance to CO(2).

Climatic patterns and the distribution of C4 grasses in North America.

A stepwise multiple regression analysis was used in an attempt to correlate statistically the geographic patterns in the abundance of C4 grasses with patterns in climatic variables. The percent of grasses having the C4 pathway was computed for the total grass flora in twenty-seven widely spaced regions of North America. From long-term climatic records seasonal and annual values for solar irradiance, water supply, heat availability, and combinations of these variables were assigned to each of the twentyseven regions. The results of the analysis suggest that high minimum temperatures during the growing season have the strongest correlation with the relative abundance of C4 grass species in a regional flora. It appears that the deleterious effects of low temperatures during growth negate the advantages of possessing the C4 pathway in cooler habitats.

Polar desert adaptations of a high arctic plant species.

Plants of Saxifraga oppositifolia (Saxifragaceae) possess metabolic adaptations that allow them to grow successfully in polar desert microenvironments. Net photosynthesis (net carbon uptake) continues to be positive during drought until the leaf water stress declines to the range of -21 to -29 bars, which is considerably below the nonstress range of 0 to -10 bars. The plants can survive leaf water stresses of at least -44 bars in the field and leaf water stresses of -55 bars in a growth chamber.