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Browsing by Author "Lakoba, Vasiliy T."

Now showing 1 - 5 of 5
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    Ecotypic Variation in Johnsongrass in Its Invaded U.S. Range
    Lakoba, Vasiliy T. (Virginia Tech, 2021-05-28)
    Biological invasions have been observed throughout the world for centuries, often with major consequences to biodiversity and food security. Tying invasion to species identity and associated traits has led to numerous hypotheses on why, and where, some species are invasive. In recent decades, attention to intraspecific variation among invaders has produced questions about their adaptation to climate, land use, and environmental change. I examined the intraspecific variation of invasive Johnsongrass's (Sorghum halepense (L.) Pers.) seedling stress response, propagule cold tolerance, and large-scale niche dynamics for correlation with populations' climatic and ecotypic (i.e., agricultural vs. non-agricultural) origin. Overall, I found a greater number of home climate effects than ecotypic effects on various traits. Non-agricultural seed from cold climates and agricultural seed from warm climates germinated more and faster, while non-agricultural seedlings showed uniform chlorophyll production regardless of home soil carbon origin, unlike their agricultural counterparts. Neither seedling stress response nor propagule cold tolerance interacted with ecotype identity; however, drought stress varied with population origins' aridity and soil fertility, and seed from warm/humid and cold/dry climates was most germinable. Comparison of seed and rhizome cold tolerance also suggested that the latter is a conserved trait that may be limiting S. halepense poleward range expansion. This physiological limit, an unchanged cold temperature niche boundary between continents and ecotypes, and a narrowed niche following transition to non-agricultural lands all imply low likelihood of spread based on climatic niche shift. Instead, evidence points to range expansion driven primarily by climate change and highlights agriculture's role in facilitating invasibility. This tandem approach to climate and land use as drivers of intraspecific variation is transferable to other taxa and can help refine our conception of and response to invasion in the Anthropocene.
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    A global invader's niche dynamics with intercontinental introduction, novel habitats, and climate change
    Lakoba, Vasiliy T.; Atwater, Daniel Z.; Thomas, Valerie E.; Strahm, Brian D.; Barney, Jacob (2021-11)
    Species niches have been defined in different ways, variably encompassing abiotic and biotic parameters limiting an organism's spatial distribution. Climate is often the primary component of the abiotic (fundamental) niche, especially among terrestrial plants. In invasion biology, there is an ongoing debate on the prevalence of niche shifts, which may be linked to divergent traits in a species' native and invaded ranges, as well as dispersal limitations and invasion lag phases. Using a global dataset, we tested whether shifts occurred in the invader Johnsongrass (Sorghum hale-pense), which has undergone intercontinental spread as well as habitat-switching within its invaded range in North America. Climate space ordination showed that North America is, on average, colder than Afro-Eurasia, and North American Johnsongrass occupies wetter environ-ments than in its native range. Within North America, both agricultural and non-agricultural ecotypes shifted slightly toward colder climates. Notably, while non-agricultural populations far outnumber agricultural ones, the former occupy a narrower niche (DM = 42.7 +/- 0.8) than the latter (DM = 59.3 +/- 1.1), implying agriculture's role in providing suitable environments in otherwise suboptimal climates. Maximum entropy models of agricultural and non-agricultural North American populations showed limited ecotypic differences in current suitability and range expansion under climate change through the rest of this century. We also predicted climatic suitability for Johnsongrass to increase most in the Upper Midwest and Great Plains by 2100. Our results help contextualize the empirical evidence for ecotypic differentiation in Johnsongrass, as well predict future range expansion and damage niches.
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    Home climate and habitat drive ecotypic stress response differences in an invasive grass
    Lakoba, Vasiliy T.; Barney, Jacob (Oxford University Press, 2020-11-24)
    Invasive plants and agricultural weeds are a ubiquitous and ever-expanding threat to biosecurity, biodiversity and ecosystem services. Many of these species are known to succeed through rapid adaptation to biotic and abiotic stress regimes, often in highly disturbed systems. Given the current state of evidence for selection of weedy genotypes via primary physiological stresses like drought, flooding, heat, cold and nutrient deficiency, we posit that adaptation to land management regimes which comprise suites of these stresses can also be expected. To establish this link, we tested adaptation to water and nutrient stresses in five non-agricultural and five agricultural populations of the invader Johnsongrass (Sorghum halepense) sampled across a broad range of climates in the USA. We subjected seedlings from each population to factorial drought and nutrient stresses in a common garden greenhouse experiment. Agricultural and non-agricultural ecotypes did not respond differently to experimentally applied stresses. However, non-agricultural populations from more drought-prone and nutrient-poor locations outperformed their agricultural counterparts in shoot allocation and chlorophyll production, respectively. We also found evidence for root allocation adaptation to hotter climates, in line with other C4 grasses, while greater adaptation to drought treatment was associated with soil organic carbon (SOC)-rich habitats. These findings imply that adaptation to land-use types can interact with other macrohabitat parameters, which will be fluctuating in a changing climate and resource-needy world. We see that invasive plants are poised to take on novel habitats within their introduced ranges, leading to complications in the prevention and management of their spread.
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    A perennial invader's seed and rhizome differ in cold tolerance and apparent local adaptation
    Lakoba, Vasiliy T.; Welbaum, Gregory E.; Seiler, John R.; Barney, Jacob (2021-11-16)
    Extreme cold plays a key role in the range boundaries of plants. Winter survival is central to their persistence, but not all structures are equally susceptible to frost kill and, therefore, limiting to distributions. Furthermore, we expect intraspecific variation in cold tolerance both within and among tissue types. In a laboratory setting, we determined freezing tolerances of two overwintering propagule types - seeds and rhizomes - of the globally invasive Johnsongrass (Sorghum halepense), testing apparent emergence and electrolyte leakage as a proxy for cell death. We used 18 genotypes from agricultural and non-agricultural habitats spanning the climatic extremes occupied by Johnsongrass in the US. Single node rhizome fragments had an average LT90 of-5.1 degrees C with no significant variation based on home climate or ecotype. Seeds frozen at-85 degrees C suffered a decline in germinability to 10% from 25% at 22 degrees C. Population origin did not affect seed response to any temperature. However, non-agricultural seeds germinated more and faster than agricultural seeds from the coldest climates, with a reversed relationship among warmest origin seeds. Regardless of ecotype, seeds from the cold/dry and wet/warm sectors of Johnsongrass's range germinated more and faster. Drastic differences in cold tolerance between seeds and rhizome and evidence for seeds' local adaptation to land use and climate suggest that its spread is likely limited by winter rhizome survival, as well as adaptability of germination behavior to longer winters. These findings shed light on Johnsongrass' dispersal dynamics and help identify future avenues for mechanistically understanding its range limitation.
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    Salt dilution and flushing dynamics of an impaired agricultural−urban stream
    Lakoba, Vasiliy T.; Wind, Lauren L.; DeVilbiss, Stephen; Lofton, Mary E.; Bretz, Kristen; Weinheimer, Alaina R.; Moore, Chloe; Baciocco, Colin; Hotchkiss, Erin R.; Hession, W. Cully (2020-11-09)
    Anthropogenic freshwater salinization is increasing with global change. Rising freshwater salinity threatens ecosystem biodiversity, health, and services via toxicity to organisms and mobilization of nutrients and metals. Brining roads is one major source of freshwater salinization that continues to grow with rising urbanization. While the detrimental effects of salinization in streams are well-documented, high-frequency, temporal patterns in salt transport, particularly during winter road de-icing in mixed land use landscapes, are less understood. To address this knowledge gap, we analyzed high-frequency specific conductance as a proxy for salinity across 114 high-flow events from 2013 to 2018 in an impaired stream draining mixed agriculture−urban land use. The specific conductance was highest in winter (median = 947 μS cm−1) and decreased with first-order kinetics up to 90 days after brining (β1 = −0.003), suggesting lasting impacts of road de-icing on water quality. Although hysteresis patterns suggested a transition from distal to proximal salt sources, they showed no clear correlation of flushing versus dilution to brining events. While seasonal brining increased salinity in receiving streams, unpredictable transport dynamics reduced the efficacy of hysteresis in characterizing salt transport dynamics. Thus, the complexity of mixed land use watersheds requires more spatially and temporally explicit monitoring to characterize stream salinization dynamics.