Agropyron smithii (a C3 species) and Bouteloua gracilis (a C4 species) occur in the same habitat of the shortgrass prairie ecosystem in northeastern Colorado. The hypothesis tested in this study was that the two species differ in their fundamental niches partly as a function of their different physiological responses to temperature and moisture gradients. Growth and gas exchange patterns were measured on plants grown in controlled—environment chambers at cool (20°/15°C) and warm (35°/15°C) temperatures. Total dry mass growth of A. smithii was approximately two times greater when grown at cool compared to warm temperatures, whereas total dry mass of B. gracilis was 2.7 times greater when grown at warm compared to cool temperatures. The temperature for maximal growth was correlated with the temperature response patterns for gas exchange of leaves and roots. A smithii had maximal rates of net photosynthesis when grown at cool temperatures, while B. gracilis had maximal rates when grown at warm temperatures. In plants not water stressed, net photosynthesis was limited primarily by stomatal aperture in B. gracilis and internal leaf factors in A. smithii. Rates of net photosynthesis of both species from both growth temperatures were very sensitive to leaf water potential and decreased exponentially with decreasing leaf water potential. Root respiration, measured simultaneously with leaf gas exchange in hydroponically grown plants, was greater in A. smithii grown at 20°/15°C and in B. gracilis grown at 35°/15°C, and decreased with decreasing solution water potential. Root respiration of warm—grown A. smithii and cool—grown B. gracilis was lower than that of plants grown at more nearly optimal temperatures and did not decrease with decreasing solution water potential. These finding suggest that the temporal displacement of growth between A. smithii and B. gracilis in their native habitat is partly a function of the differential temperature responses of photosynthesis and related metabolic processes. The differences in the temperature responses of photosynthesis appear to be a consequence of the species having different photosynthetic pathways. The similarities between the species in their physiological responses to water stress suggest that seasonal moisture gradients are not as important a parameter along which niche separation has occurred as are seasonal temperature gradients.

Ash from Mount St. Helens has fallen over a diverse agricultural area, with deposits of up to 30 kilograms per square meter. Crop losses in eastern Washington are estimated at about $100 million in 1980-about 7 percent of the normal crop value in the affected area and less than was expected initially. Production of wheat, potatoes, and apples will be normal or above normal because the favorable conditions for growth of these crops since the ashfall helped offset the losses. Alfalfa hay was severely lodged under the weight of the ash, but ash-contaminated hay is apparently nontoxic when eaten by livestock. The ash as an abrasive is lethal to certain insects, such as bees and grasshoppers, but populations are recovering. The ash has increased crop production costs by necessitating machinery repairs and increased tillage. On soil, the ash reduces water infiltration, increases surface albedo, and may continue to affect water runoff, erosion, evaporation, and soil temperature even when tilled into the soil. Ash on plant leaves reduced photosynthesis by up to 90 percent. Most plants have tended to shed the ash. With the possible exception of sulfur, the elements in the ash are either unavailable or present in very low concentrations; and no significant contribution to the nutrient status of soils is expected.

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 (C), 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 (C) and Buchloe dactyloides (C), exhibited higher photosynthetic capacities when grown in the warmer temperature regime. The sedge, Carex eleocharis (C), 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 CO appeared to have a greater regulatory role in these responses for the two C species, relative to stomatal conductance or photorespiration (O inhibition of photosynthesis). In the two C 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 CO 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 CO 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.

ABSTRACTof photosynthesis observed at above-optimum temperatures (3).Temperature has also been shown to affect both the Km (CO2) and V,= of RuBP carboxylase in vitro (2,24). Weis (35) has suggested that a temperature-dependent inactivation of RuBP carboxylase occurs at above-optimal temperatures in intact spinach chloroplasts. Such temperature effects may be partly responsible for the reversible temperature limitations on net photosynthesis observed for intact leaves. However, difficulties arise in interpreting these data due to the uncertainties encountered in using in vitro studies to describe processes in vivo.Photosynthetic inhibition at analysis temperatures beyond the point of reversibility is due in part to irreversible inhibition of the quantum yield for CO2 fixation, and decreased activity of certain enzyme reactions (4). An irreversible reduction in the quantum yield has been used as an indication of heat damage to the photosynthetic apparatus (29), and is presumably related to the integrity of the thylakoid membranes (1).Agropyron smithii is a C3 perennial grass which constitutes a major biomass producer of the short-and mixed-grass prairie ecosystems. Plants of this species initiate growth during the early spring months when seasonal temperatures are relatively cool (6). (P2%0-P21%0,/P2%0,) 100(1)Leaf transmittance and reflectance measurements were conducted on freshly cut leaf discs, at 5-nm wavelength intervals between 400 and 700 nm, with the integrating sphere described by Robberecht and Caldwell (28 min prior to initiating each assay, a 2-to 3-ml aliquot of the frozen extract was removed from the mortar and allowed to thaw at room temperature. The thawed extract was pressed through a 40-,um nylon net attached to a 20-ml syringe and irnmediately assayed.The assays were conducted in small glass vials which were half immersed in a temperature-controlled water bath. The assay buffer (100 mM C02-free Tricine, pH 8.0), which contained 5 mm DTT and 20 mm MgCl2, was added to each reaction vial approximately 2 min prior to each assay in order to insure temperature equilibration. N2 was bubbled through the assay medium for the entire 2-min equilibration period. Carbonic anhydrase (100 units) and RuBP (0.4 mm) were added to the assay medium at 60 and 45 s prior to initiating each assay, respectively. The appropriate concentration of NaH4C03-(7.0 mCi mm-) was added 5 s before initiating the reaction, thus minimizing losses of 14CO2 to the atmosphere above the reaction medium. The reaction was initiated by the addition of 20 IAl of crude extract. The final volume of the reaction mixture was 1 ml. The reaction was terminated after 30 s (1 min at 10 and 15°C) by the addition of 200 ,ul of 6 N HCI. The contents of each reaction vial were transferred to a scintillation

Governments around the world are deploying automation tools in making decisions that affect rights and entitlements. The interests affected are very broad, ranging from time spent in detention to the receipt of social security benefits. This article focusses on the impact on rule of law values of automation using: (1) pre-programmed rules (for example, expert systems); and (2) predictive inferencing whereby rules are derived from historic data (such by applying supervised machine learning). The article examines the use of these systems across a range of nations. It explores the tension between the rule of law and rapid technological change and concludes with observations on how the automation of government decision-making can both enhance and detract from rule of law values.