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Climate change and disturbance can alter invasion success of clonal plants by differentially affecting the clonal traits influencing their establishment as young plants. Clonal traits related to the vegetative reproduction of native Pascopyrum smithii and non-native Bromus inermis grass seedlings were evaluated under altered precipitation frequencies and a single grazing event. Pascopyrum smithii maintained similar vegetative reproduction under three simulated precipitation frequencies whereas B. inermis vegetative reproduction declined as precipitation became more intermittent. Vegetative reproduction of the non-native B. inermis was greater than the native P. smithii under all simulated precipitation frequencies except the most intermittent scenario. A single grazing event did not affect either species’ response to intra-annual precipitation variability but did slightly reduce their clonal growth and increase their bud dormancy. In young plants, clonal traits of the invasive grass favored its superior expansion and population growth compared to the native grass except under the most severe climate change scenario. Grassland restoration using native P. smithii seeds would be successful in most years due to its resilient clonal growth in a changing climate. Clonal infrastructure development in young plants is critical to clonal plant establishment and persistence in a changing climate and under disturbed conditions.

Invasive clonal species may exhibit different growth strategies than their native clonal competitors. In this study, we examined the spatial distribution of tiller outgrowth and the bud bank by comparing the investment in phalanx versus guerilla growth of a native and invasive perennial grass in North America. We also examined the effect of altered precipitation frequency, clipping, and competition on their clonal growth strategies. Investment in phalanx and guerilla growth was assessed by examining live propagule and tiller production from the plant crown versus its rhizomes. Although invasive Bromus inermis and native Pascopyrum smithii exhibited similar clonal growth strategies as young seedlings, their clonal growth strategies significantly differed by the end of their first growing season. Pascopyrum smithii invested in dual phalanx and guerilla tiller outgrowth and bud placement, and B. inermis primarily invested in phalanx tiller outgrowth and bud placement. Competition rather than intra-annual precipitation variability and clipping altered the clonal growth strategy of these species. Intra- and inter- specific competition did not alter tiller outgrowth for either species. However, inter-specific competition caused both species to alter their bud placement. Bromus inermis shifted more buds from phalanx to guerilla positions while P. smithii shifted in the opposite direction. This may enable invasive B. inermis to expand while confining native P. smithii to more localized areas in the future. Clonal growth strategies appear to be species specific and responsive to inter-specific competition. Investigating the belowground bud aspect of clonal growth can reveal the mechanism driving the future aboveground clonal growth strategy of native and invasive rhizomatous grasses and help inform the patterns of invasion within a plant community.

Linked Article: https://doi.org/10.1002/ece3.3964

Leafy spurge (Euphorbia esula), a native perennial weed introduced from Eurasia around the turn of the century, disrupts natural and agroecosystems across much of the Northern Great Plains. While leafy spurge displaces many native plant species, it has been demonstrated that small everlasting (Antennaria microphylla), a native perennial, is allelopathic to leafy spurge. Caffeic acid (CA), one of three compounds isolated from small everlasting, inhibits leafy spurge seed germination, root elongation, and callus culture growth. This study investigated the mechanism of this interference at the whole-plant level. Results indicate that inhibition of growth in leafy spurge after exposure to CA is primarily due to a disruption of plant-water relations. Leafy spurge cuttings were propagated in 0.5 strength Hoagland's nutrient solution for 30 days. For treatments, six plants were transferred into nutrient medium amended with either 0.1 or 0.25 mM CA for a period of 30 days. To determine the effect of pH, two additional groups of six plants were grown in nutrient medium adjusted with HCl corresponding to pH levels of plants treated with CA (pH 5.5-5.8 for 0.1 mM CA and pH 4.5-4.8 for 0.25 mM CA). By day 12 of the treatment period, plants treated with both levels of CA had significantly higher leaf diffusive resistances than control plants. Plants grown at the corresponding pH levels experienced higher diffusive resistances later in the treatment period (day 21). Transpiration was similarly affected with treated plants showing relatively higher transpiration rates compared to controls. Chlorophyll fluorescence was significantly lower than controls in all treated plants by end of the treatment period. The stable carbon isotope ratio (^sup 13^C:^sup 12^C) in these plants was higher than controls. These data show that a disruption of plant water relations is the primary mechanism of plant growth inhibition.[PUBLICATION ABSTRACT]

Sickleweed (Falcaria vulgaris), an introduced species native to Europe and Asia, grows as an aggressive weed in some areas of the upper Midwest in the United States. We are reporting genetic diversity and population structure of sickleweed populations using microsatellite markers and nuclear and chloroplast DNA sequences. Populations showed high genetic differentiation but did not show significant geographic structure, suggesting random establishment of different genotypes at different sites was likely due to human mediated multiple introductions. Three genetic clusters revealed by microsatellite data and presence of six chlorotypes supported our hypothesis of multiple introductions. Chloroplast DNA sequence data revealed six chlorotypes nested into two main lineages suggesting at least two introductions of sickleweed in the upper Midwest. Some individuals exhibited more than two alleles at several microsatellite loci suggesting occurrence of polyploidy, which could be a post-introduction development to mitigate the inbreeding effects. High genetic variation in the introduced range attributable to multiple introductions and polyploidy may be inducing the evolution of invasiveness in sickleweed. Results of this study provide valuable insights into the evolution of sickleweed and baseline data for designing proper management practices for controlling sickleweed in the United States.

Leafy spurge (Euphorbia esula), smooth brome (Bromus inermis), Japanese brome (B. japonicus), and downy brome (B. tectorum) are exotic plant species that dominate and displace native forage species throughout much of central North America. However, information on how exotic plant infestations affect native ungulate use of habitat is limited. We used pellet-group densities to estimate use of habitat by bison (Bos bison), elk (Cervus elaphus), and deer (Odocoileus spp.) during 1992-93 growing seasons within 4 exotic plant-infested and 4 comparable noninfested grassland habitats in Theodore Roosevelt National Park, North Dakota. We used twig count and twig measurement methods to estimate use of browse during summer (1992) and winter (1992-93), respectively, for both leafy spurge-infested and noninfested woodland habitats. Bison use of 2 leafy spurge-infested grassland habitats averaged 83% less than that for noninfested sites (P < 0.001). Deer pellet-group densities, normally highest within creeping juniper (Juniperus horizontalis)-little bluestem (Schizachyrium scoparium) habitat, were reduced ≤70% by infestations of leafy spurge (1992, P = 0.035; 1993, P = 0.002). Use of bromegrass-infested grassland by bison, elk, and deer was similar to that for noninfested sites for 1992 and 1993 (P > 0.05). Use of browse in green ash (Fraxinus pennsylvanica)-chokecherry (Prunus virginiana) habitat during summer and winter was reduced an average of 32% by infestations of leafy spurge (P < 0.05). The reduction in native ungulate use of leafy spurge-infested sites may be attributed to lower forage production in infested sites as well as simple avoidance.

Field observations indicate leafy spurge (Euphorbia esula) is inhibited by the presence of Antennaria microphylla. Hydroquinone (HQ), one of several compounds isolated from A. microphylla has been shown to inhibit leafy spurge seed germination, root elongation, and callus culture growth. The present study was designed to analyze the effects of HQ on water relations and photosynthesis of leafy spurge. Plants grown in 0.25 mM HQ had consistently higher leaf diffusive resistance and lower transpiration rates than control plants (P < 0.05). Chlorophyll fluorescence was significantly lower than controls (P < 0.05) towards the end of the treatment period. At the end of the treatment, tissue from 0.25 mM HQ plants had higher levels of ^sup 13^C, indicating there had been a sustained interference with stomatal function. These data suggest that a disruption of the plant water balance is one mechanism of leafy spurge inhibition by A. microphylla. [PUBLICATION ABSTRACT]

Four sites that varied with respect to grazing history were studied during 1990 and 1991 on an isolated 8,000 ha peninsula in Glen Canyon National Recreation Area. Density and basal area of Oryzopsis hymenoides decreased with increasing grazing intensity while density and foliar cover of Gutierrezia sarothrae increased on grazed sites. Perognathus longimembris was the most abundant rodent species trapped on all sampled sites and demonstrated a 50% decrease in abundance at the heavily grazed site compared to the nongrazed site. Peromyscus maniculatus was the second most abundant rodent species recorded and increased with increasing grazing intensity.