However, the number of invasive plants with horticultural origin is high, making it critically important to natural resource managers, ecologists and policymakers to predict which newly introduced species pose the greatest risk of escape and invasion.California has approximately 3,400 species of native plants, of which 24% are found only in the state . However, California is also some thing of a hotspot for nonnative plants, with over 1,500 nonnative species naturalized, weedy in agricultural systems or invasive in natural areas . As a result, California not only faces a high risk of escape, establishment and invasion of introduced ornamental plants, but also has a high proportion of native species threatened by invasive plants. Within California, there are two lists that identify invasive plants. First, based on 13 questions that assess impacts, invasiveness and distribution, the California Invasive Plant Council’s list includes 214 species that cause ecological harm in the state’s wildlands . Approximately 63% of these species were deliberately introduced to California, mostly as ornamental plants . Second, the California Department of Food and Agriculture Noxious Weed List primarily lists plants that cause, or have the potential to cause, economic damage to the state’s agricultural industry; CDFA has legal authority to regulate plants on this list through Section 4500 of the California Code of Regulations .
Because the criteria for these lists have a different focus,gutter berries the listed species overlap but are not the same. Few species derived from the horticultural trade are included on the state Noxious Weed List. The horticultural trade is one of the major pathways for invasive plants in California and elsewhere . For example, higher market frequency and lower prices were shown to be good predictors of a plant’s probability of invasion in Britain . Horticulture is also a major agricultural sector in California, accounting for $2.5 billion in sales in 2011 . The ability to predict potential invasiveness is important both for species that have already been introduced to a region but are not yet invasive and for species that may be introduced through the horticultural industry in the future. In both cases, prediction of invasiveness before it occurs can, through collaborative efforts with the nursery industry, lead to voluntary restrictions in sales, preventing the potential for damage should the species escape cultivation. Knowing that a plant is invasive in one region can give insight into whether it might be problematic in another region, particularly if the two regions have similar climates. For woody or namental species, for example, being invasive elsewhere was the single best predictor of potential invasiveness in a new region of introduction . In addition, Caley and Kuhnert showed that four variables were most important for screening potential invasive plants: human dispersal, naturalized elsewhere, invasiveness elsewhere and a high degree of domestication.
Two of these variables, human dispersal and high degree of domestication, are characteristics of horticultural species. California is one of five Mediterranean climate regions in the world, along with the Mediterranean Basin of Europe and northern Africa, central Chile, the Cape Region of South Africa and western Australia. All these regions are characterized by a winter rainy season and a summer dry season and are likely to share invasive species due to their similar climates. The primary objective of this study was to identify ornamental species at high risk of becoming newly invasive in California. To develop this list, we considered the single most important factor to be a species’ invasiveness in other areas of the world with a similar Mediterranean climate or in a state neigh boring California. While we recognize that this list is not comprehensive, we believe that it provides a good starting point for subsequently conducting risk assessments that could reduce the threat of introducing new invasive ornamentals to the state. This approach might also help determine which naturalized species should be monitored to see if they will become truly invasive. Invasive plant data were collected through online databases and published lists from other regions with Mediterranean climates. We also used established invasive plants reported from states neighboring California, including Arizona , Nevada and Oregon . We included spe cies on the California Noxious Weed List as well as those that have been shown to invade wildlands . Of the plants that have invaded other Mediterranean regions, we first removed species native to California and those already known to be invasive in wildland areas within the state.
Then for each of the remaining plant species, we evaluated the Mediterranean-type region invaded, location of origin, human uses and whether the species was native, cultivated, naturalized or invasive in California . For species already naturalized but not yet invasive in California, we determined the year they were first re ported as naturalized based on the online Consortium of California Herbaria data base . In addition, we determined if plants are currently sold in the horticultural and ornamental trade in California using the Sunset Western Garden Book and the Plant Locator , a directory of nurseries stocking particular species. While these references do not include all of the species available by mail order or via the Internet, they represent plants most commonly available in nurseries.Based on our criteria, we found 774 plants listed as invasive in other Mediterranean regions or adjacent states . Of these, 366 are not natural ized in California and therefore fit our focus on potential new invaders. Of the remaining 408 species , we eliminated 318 species that did not fit our focus on new invaders: they were either native to California or al ready invasive in California , or had naturalized in the state before 1940 without becoming invasive . This left us with 90 species that naturalized after 1940. We assumed that species that naturalized before 1940 and that have not yet be come invasive in California are unlikely to become invasive in the future. Many of the naturalized species have been present in the state for over a century, with 20 recorded in the 1860s and 144 recorded before 1900. While we believe that 70 years of naturalization without significant spread and harm is sufficient to consider a species as having low potential for invasion, this may not be true for all species. There may be some instances where longer lag periods — a length of time when a species is present in natural areas before beginning to spread and cause ecological harm — could occur prior to rapid expansion of a species. Furthermore, the movement of ornamental plants is facilitated by humans, thus increasing the opportunity for introduction to suitable habitats. In addition to possibly increasing the potential for invasion by introduced plants,strawberry gutter system this facilitation could also reduce the time between introduction and invasion. Next, we subdivided the 90 species that became naturalized after 1940 and the 366 species that are not naturalized in California based on whether they are sold as ornamentals. We also noted whether they are sold in California . Of the 90 naturalized species, 70 are currently sold as ornamentals some where in the world, with 60 sold in California. Of the 366 non-naturalized species in California, only 32% were ornamentals.
The majority of these species are currently sold in California, while the other 22 are ornamentals not sold in the state. Thus, in total, we listed 186 species of ornamentals as the greatest concern for introduction and/or invasiveness to California through the horticultural pathway. This total includes both those species currently sold and those that could be sold in the future . This study, however, did not take into consideration the potential effects of climate change on habitat suitability and plant invasions within California. It is possible that warmer temperatures or modified precipitation patterns due to climate change will allow some currently noninvasive ornamentals to spread and become invasive. However, predictions of the spread of invasive plants in the western United States indicate that while some will likely spread, others may contract their ranges . Thus, it was not possible to determine the impact of climate change on all the species evaluated in this study.To reduce the sale of invasive plants in California, environmental groups, scientists, government agencies and the horticulture industry are participating in the Plant Right partnership, a coalition that works with retail nurseries and grow ers on voluntary measures to reduce the sale of invasive plants and promote non invasive alternatives ; the authors serve on its steering committee. Specific guidelines or recommendations could be established for the high-risk species we identified in tables 1 to 4 to minimize future introduction, establishment and invasion. Cooperative efforts can discourage the introduction of ornamental plants in other regions that are neither naturalized nor sold in California , and these plants also could be included in a cautionary list that would require full prescreening risk assessment before introduction to the state. Plants that are not naturalized in California but that are sold here should be reviewed by the nursery industry to reduce their sale and also watched for any spread into wild lands. In addition, noninvasive ornamentals that serve the same purpose in a landscape should be promoted as alter native options. Species that are naturalized but not yet sold in California should be restricted from sale, and land managers should watch for their further spread. Finally, species that are both naturalized and also sold in California may be considered for removal from the trade and also watched by land managers for further spread into wild lands. This list provides a good starting point for identifying plants, especially ornamental species, that are invasive in regions with similar climates to California and could become problematic here. However, additional steps are required to further understand the potential risk of invasion. In particular, a more detailed risk assessment should be conducted for each of the species we identified as being at high risk for future invasion. Several risk assessment protocols are available to prioritize the greatest potential threats to wild land systems. Implementing these preventative approaches and establishing an early detection program to eradicate incipient populations of these targeted species are far less costly than attempting to manage or contain large well-established populations of invasive plants. The use of copper-based nanoparticles in agriculture as fungicides and bactericides is increasing rapidly due to their relatively low toxicity and higher efficiency in delivering the active component . There are numerous copper containing pesticides on the market, e.g. copper sulfate , cuprous oxide , copper hydrox ide , and nano copper . The U.S. Department of Agriculture maintains an official list of synthetic substances that can be used for organic farming. According to this list, copper-based materials are allowed for use in organic crop production.However, more and more evidence indicates that copper-based nanoparticles induce phytotoxicity in various plants, such as bean,lettuce,alfalfa,cilantro,cucumber.The adverse impact in clude decreased root and shoot elongation, disturbed mineral nutrients homeostasis, decreased photosynthesis rate, inhibited antioxidant enzyme activities.So far the molecular mechanism underlying those physiological changes is not well understood. In recently years, “omics” have become a promising meth odology for studying plant responses to abiotic and biotic stress.Transcriptomics-based gene expression and proteomics-based protein production have been applied to evaluate the changes of plants to external stressors at the mo lecular level.Unlike transcriptomics and proteomics, which reveal what might be happening in plant tissues, meta bolomics profiling can tell what already happened. Metabo lites are the end product of gene expression,16 and the changes of metabolites are regarded as ultimate responses of plant to stress. Thus, environmental metabolomics is be coming a powerful tool to investigate the response of plants to various stressors, e.g., water, light, temperature, and high levels of metals.18 Recently, Pidatala et al. employed LC-MS/ MS based metabolomics to elucidate the stress response mechanism of lettuce to lead. They observed several key metabolic pathways, including sugar and amino acid metabolism, that were disturbed by lead.Our recent study,apply ing GC-TOF-MS based metabolomics and PLS-DA multivariate analysis, also revealed the profile of metabolites in root exudates was significantly altered by nCu. A number of amino acids were up-regulated to defend against an excess of copper. More recently, we determined that nCu altered the nutritional supply of cucumber fruit,21 using 1 H NMR and GC-MS based metabolomics.