Although prevention is the most costeffective way to avoid the enormous expenses associated with plant invasions, invasive plants continue to be imported as trade commodities for horticultural use. With very little government regulation of horticultural imports of invasive plants, efforts have turned toward fostering voluntary initiatives to encourage self-regulation by the horticulture trade. Our study takes the first step toward evaluating the potential success of these voluntary initiatives. We conducted a survey of nursery professionals to gauge their perceptions of invasive species, the role of the horticulture trade in invasive plant introductions, and their participation-potential and actual-in preventive measures outlined in the St Louis Voluntary Codes of Conduct for nursery professionals. We found nursery professionals to be highly aware of invasive plants and to accept responsibility as a trade for horticultural introductions. Although only 7% of respondents had heard of the St Louis Voluntary Codes of Conduct, the majority (57%) reported having participated in at least two of seven preventive measures, and most (78%) reported willingness to engage in the majority of preventive measures. We found that several factors significantly predict increased participation in preventive measures, particularly awareness of invasive plants and involvement in trade associations. We also identified incentives and obstacles to participating in preventive behaviors, including ''concern for the environment'' and ''lack of information,'' respectively. Our results suggest that participation in voluntary initiatives will improve through increased outreach, and we provide specific recommendations for improving participation in voluntary programs in the horticulture trade.

Root plasticity, a trait that can respond to selective pressure, may help plants forage for nutrients in heterogeneous soils. Agricultural breeding programs have artificially selected for increased yield under comparatively homogeneous soil conditions, potentially decreasing the capacity for plasticity in crop plants like barley (Hordeum vulgare). However, the effects of domestication on the evolution of root plasticity are essentially unknown. Using a split container approach, we examined the differences in root plasticity among three domestication levels of barley germplasm (wild, landrace, and cultivar) grown under different concentrations and distribution patterns of soil nutrients. Domestication level, nutrient concentration, and nutrient distribution interactively affected average root diameter; differential root allocation (within-plant plasticity) was greatest in wild barley (Hordeum spontaneum), especially under low nutrient levels. Correlations of within-plant root plasticity and plant size were most pronounced in modern cultivars under low-nutrient conditions. Barley plants invested more resources to root systems when grown in low-nutrient soils and allocated more roots to higher-nutrient locations. Root plasticity in barley is scale dependent and varies with domestication level. Although wild barley harbors a greater capacity for within-plant root plasticity than domesticated barley, cultivars exhibited the greatest capacity to translate within-plant plasticity into increased plant size.

The aquarium trade is an important and rapidly growing vector for introduced species in the United States. We examined this vector by surveying pet stores in the San Francisco Bay-Delta region to compile a list of aquarium fish species commonly stocked. We identified which of these species might be able to survive in the Bay-Delta, and investigated store representatives' knowledge and attitudes about biological invasions. A restrictive analysis using conservative estimates of fish temperature tolerances and environmental conditions found that the local aquarium trade includes 5 fish species that can survive in a temperate system such as the Bay-Delta. Under more inclusive parameters, up to 27 fish species met the criteria for survival in the Bay-Delta. We further explored these results by comparing potential invader incidence between different types of stores. In the more restrictive analysis, three national retail chains stocked significantly more potentially invasive species than independent aquarium stores, but there was no difference in the more inclusive analysis. A significantly higher percentage of fish taxa were easily identifiable and well-labeled in chain stores than in independent stores. Most aquarium store representatives indicated willingness to take action to reduce the threat of traderelated introductions, although chain store employees were more willing to assign responsibility for reducing this threat to the aquarium industry than were independent store employees. Management efforts for this vector should focus on (a) improving labeling and identification of fish species in stores, (b) expanding the often spotty data on fish physiological tolerances, especially for saltwater species, (c) educating customers and store employees about the risks posed by pet release, and (d) providing better options for responsible disposal of unwanted fish.