This article presents a new instrument with which to assess the effects of opiate treatment. The Opiate Treatment Index (OTI) is multi-dimensional in structure, with scales measuring six independently measured outcome domains: drug use; HIV risk-taking behaviour; social functioning; criminality; health; and psychological adjustment. Psychometric properties of the Index are excellent, suggesting that the OTI is a relatively quick, efficient means of obtaining reliable and valid data on opiate users undergoing treatment over a range of relevant outcome domains.
Atmospheric CO partial pressure (pCO) was as low as 18 Pa during the Pleistocene and is projected to increase from 36 to 70 Pa CO before the end of the 21st century. High pCO often increases the growth and reproduction of C annuals, whereas low pCO decreases growth and may reduce or prevent reproduction. Previous predictions regarding the effects of high and low pCO on C plants have rarely considered the effects of evolution. Knowledge of the potential for evolution of C plants in response to CO is important for predicting the degree to which plants may sequester atmospheric CO in the future, and for understanding how plants may have functioned in response to low pCO during the Pleistocene. Therefore, three studies using Arabidopsis thaliana as a model system for C annuals were conducted: (1) a selection experiment to measure responses to selection for high seed number (a major component of fitness) at Pleistocene (20 Pa) and future (70 Pa) pCO and to determine changes in development rate and biomass production during selection, (2) a growth experiment to determine if the effects of selection on final biomass were evident prior to reproduction, and (3) a reciprocal transplant experiment to test if pCO was a selective agent on Arabidopsis. Arabidopsis showed significant positive responses to selection for high seed number at both 20 and 70 Pa CO during the selection process. Furthermore, plants selected at 20 Pa CO performed better than plants selected at 70 Pa CO under low CO conditions, indicating that low CO acted as a selective agent on these annuals. However, plants selected at 70 Pa CO did not have significantly higher seed production than plants selected at 20 Pa CO when grown at high pCO. Nevertheless, there was some evidence that high CO may also be a selective agent because changes in development rate and biomass production during selection occurred in opposite directions at low and high pCO. Plants selected at high pCO showed no change or reductions in biomass relative to control plants due to a decrease in the length of the life cycle, as indicated by earlier initiation of flowering and senescence. In contrast, selection at low CO resulted in an average 35% increase in biomass production, due to an increase in the length of the life cycle that resulted in a longer period for biomass accumulation before senescence. From the Arabidopsis model system we conclude that some C annuals may have produced greater biomass in response to low pCO during the Pleistocene relative to what has been predicted from studies exposing a single generation of C plants to low pCO. Furthermore, C annuals may exhibit evolutionary responses to high pCO in the future that may result in developmental changes, but these are unlikely to increase biomass production. This series of studies shows that CO may potentially act as a selective agent on C annuals, producing changes in development rate and carbon accumulation that could not have been predicted from single-generation studies.
Summary Interactive effects of CO2 and water availability have been predicted to alter the competitive relationships between C3 and C4 species over geological and contemporary time scales. We tested the effects of drought and CO2 partial pressures (pCO2) ranging from values of the Pleistocene to those predicted for the future on the physiology and growth of model C3 and C4 species. We grew co‐occurring Abutilon theophrasti (C3) and Amaranthus retroflexus (C4) in monoculture at 18 (Pleistocene), 27 (preindustrial), 35 (current), and 70 (future) Pa CO2 under conditions of high light and nutrient availability. After 27 days of growth, water was withheld from randomly chosen plants of each species until visible wilting occurred. Under well‐watered conditions, low pCO2 that occurred during the Pleistocene was highly limiting to C3 photosynthesis and growth, and C3 plants showed increased photosynthesis and growth with increasing pCO2 between the Pleistocene and future CO2 values. Well‐watered C4 plants exhibited increased photosynthesis in response to increasing pCO2, but total mass and leaf area were unaffected by pCO2. In response to drought, C3 plants dropped a large amount of leaf area and maintained relatively high leaf water potential in remaining leaves, whereas C4 plants retained greater leaf area, but at a lower leaf water potential. Furthermore, drought‐treated C3 plants grown at 18 Pa CO2 retained relatively greater leaf area than C3 plants grown at higher pCO2 and exhibited a delay in the reduction of stomatal conductance that may have occurred in response to severe carbon limitations. The C4 plants grown at 70 Pa CO2 showed lower relative reductions in net photosynthesis by the end of the drought compared to plants at lower pCO2, indicating that CO2 enrichment may alleviate drought effects in C4 plants. At the Pleistocene pCO2, C3 and C4 plants showed similar relative recovery from drought for leaf area and biomass production, whereas C4 plants showed higher recovery than C3 plants at current and elevated pCO2. Based on these model systems, we conclude that C3 species may not have been at a disadvantage relative to C4 species in response to low CO2 and severe drought during the Pleistocene. Furthermore, C4 species may have an advantage over C3 species in response to increasing atmospheric CO2 and more frequent and severe droughts.
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