Recipient Organization
VIRGINIA POLYTECHNIC INSTITUTE
(N/A)
BLACKSBURG,VA 24061
Performing Department
School of Plant and Environmental Sciences
Non Technical Summary
Weeds continue to be the most costly and labor-intensive management challenge for agricultural producers globally. Weeds reduce crop productivity primarily by direct competition for growth-limiting resources, but may also serve as a host or reservoir for pathogens and pests, particularly in cases of weeds closely related to crops. Despite tremendous advances in crop development, herbicide chemistry and precision application, and alternative management technologies (e.g., flame weeders), both small and large-scale growers continue to face weed management challenges. Widespread adoption of herbicide resistant crops has been associated with a dramatic increase in herbicide resistant weeds (Heap 2018), forcing growers to apply additional herbicides or resort to mechanical or manual removal (Vencill et al. 2012). This has led to increased farm costs and unintended environmental impacts as less-safe chemistries are applied to address herbicide resistant weeds.Understanding the processes and limitations to how invasive and agricultural weeds spread can be used to mitigate future invasions,is especially important as climate change alters weed distributions (Dukes & Mooney 1999). Weeds continue to be the primary threat to agricultural yield, and invasive plants damage native ecosystems, therein reducing ecosystem functioning. Thus, we strive to understand what underlies the spread of invasive weeds to protect our human and natural systems.Johnsongrass (JG, Sorghum halepense) has the rare distinction of being both an invasive species and one of the world's worst agricultural weeds (Holm et al. 1997) [herein we use weed in the agricultural context, and invasive in the context of natural or minimally managed habitats]. JG costs US farmers tens of millions of dollars annually in management costs and yield losses (Burke, Wilcut & Cranmer 2006). Johnsongrass is a globally distributed, highly damaging weed and invader of natural areas (Warwick, Phillips & Andrews 1986), whose range is projected to expand northward with a warming climate (McDonald et al. 2009). With 26 herbicide-resistant biotypes now known (Heap 2018) it will only become more problematic in the future. For example, a glyphosate-resistant JG biotype discovered in Argentina in 2002 had covered 10,000 ha by 2009 (Binimelis, Pengue & Monterroso 2009). Listed as a noxious weed in 20 U.S. states, JG is also labeled an invasive species in 16 states (Quinn et al. 2013). This tremendous 'success' of JG can be partially attributed to its "invasive syndrome", with a complement of advantageous traits: robust spreading rhizomes, shattering inflorescences, rapid growth, seed dormancy, large and extensive annual seed production, tremendous disturbance tolerance, allelochemicals, and associations with nitrogen-fixing bacterial endophytes (Monaghan 1979; Paterson et al. 1995; Rout & Chrzanowski 2009; Liu et al. 2011).Our group has already generated a wealth of publicly available genetic and ecological data using microsatellite markers. We identified genetic clusters to reconstruct the expansion of founding populations (Sezen et al. 2016), which are centered in the Southeastern US. Across the introduced range of the US, JG exhibits extremely high genetic (Sezen et al. 2016) and phenotypic variability (Atwater et al. 2016b) and some level of habitat specialization (Atwater et al. 2016a). Importantly, our recent evidence suggests that the climate niche of edge populations is considerably wider than that of core (i.e., near founding locations) populations (Atwater et al. 2016b). Additionally, others have shown that JG lacks winter rhizome survival in some northern locations (Warwick, Phillips & Andrews 1986), thus exhibiting an annual life history. Finally, we have demonstrated that JG has differentiated in response to both climatic variation and habitat. Thus, there is evidence that edge populations are differentiating from core populations, and that climate may be playing an important role in limiting their range. While our previous work reveals the existence of considerable genetic and phenotypic differentiation in JG, it was not designed to thoroughly sample the edge and expanding front, nor to parse the ecological and genetic factors influencing range expansion in the species.
Animal Health Component
10%
Research Effort Categories
Basic
90%
Applied
10%
Developmental
(N/A)
Goals / Objectives
Objectives1) To understand if Johnsongrass performs best when grown where it originated.2) To determine if Johnsongrass changes how it allocates resources in response to climate and competition.3) To elucidate whether Johnsongrass alters its physiology, photosynthetic rates, and rhizome growth in response to cold and dry growing conditions.
Project Methods
ProceduresThe goal of this study is to characterize the nature and mechanisms of range limits in a globally important invasive plant, and to identify the extent of life history trade-offs, and local adaptation among core, edge, and peripheral populations. We propose both field and growth chamber experiments to address these questions. The field experiment will allow us to assess Johnsongrass survival and growth in ecologically realistic conditions across both temperature and precipitation gradients, directly addressing Objectives 1 and 2. The growth chamber experiments will allow us to isolate the effects of important climatic drivers, from the field experiment (e.g., cold), on competition, and performance, which will be used to directly address Objective 3.