J. A. Teeri

The Distribution of C4 Species of the Cyperaceae in North America in Relation to Climate

SummaryThe 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.

Leaf thickness and carbon isotope composition in the Crassulaceae

SummaryMeasurements 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.

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

SummaryClone 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.

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

SummaryPlants 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.