Browsing by Author "Sands, David C."

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Biological ice nucleation initiates hailstone formation
(2014-11) Michaud, Alexander B.; Dore, John E.; Priscu, John C.; Leslie, Deborah; Lyons, W. Berry; Sands, David C.
Cloud condensation and ice nuclei in the troposphere are required precursors to cloud and precipitation formation, both of which influence the radiative balance of Earth. The initial stage of hailstone formation (i.e., the embryo) and the subsequent layered growth allow hail to be used as a model for the study of nucleation processes in precipitation. By virtue of the preserved particle and isotopic record captured by hailstones, they represent a unique form of precipitation that allows direct characterization of the particles present during atmospheric ice nucleation. Despite the ecological and economic consequences of hail storms, the dynamics of hailstone nucleation, and thus their formation, are not well understood. Our experiments show that hailstone embryos from three Rocky Mountain storms contained biological ice nuclei capable of freezing water at warm, subzero (°C) temperatures, indicating that biological particles can act as nucleation sites for hailstone formation. These results are corroborated by analysis of δD and δ18O from melted hailstone embryos, which show that the hailstones formed at similarly warm temperatures in situ. Low densities of ice nucleation active abiotic particles were also present in hailstone embryos, but their low concentration indicates they were not likely to have catalyzed ice formation at the warm temperatures determined from water stable isotope analysis. Our study provides new data on ice nucleation occurring at the bottom of clouds, an atmospheric region whose processes are critical to global climate models but which has challenged instrument-based measurements.
Geographic, seasonal, and precipitation chemistry influence on the abundance and activity of biological ice nucleators in rain and snow
(2008-11) Christner, Brent C.; Cai, Rongman; Morris, Cindy E.; McCarter, Kevin S.; Foreman, Christine M.; Skidmore, Mark L.; Montross, Scott N.; Sands, David C.
Biological ice nucleators (IN) function as catalysts for freezing at relatively warm temperatures (warmer than −10 °C). We examined the concentration (per volume of liquid) and nature of IN in precipitation collected from Montana and Louisiana, the Alps and Pyrenees (France), Ross Island (Antarctica), and Yukon (Canada). The temperature of detectable ice-nucleating activity for more than half of the samples was ≥ −5 °C based on immersion freezing testing. Digestion of the samples with lysozyme (i.e., to hydrolyze bacterial cell walls) led to reductions in the frequency of freezing (0–100%); heat treatment greatly reduced (95% average) or completely eliminated ice nucleation at the measured conditions in every sample. These behaviors were consistent with the activity being bacterial and/or proteinaceous in origin. Statistical analysis revealed seasonal similarities between warm-temperature ice-nucleating activities in snow samples collected over 7 months in Montana. Multiple regression was used to construct models with biogeochemical data [major ions, total organic carbon (TOC), particle, and cell concentration] that were accurate in predicting the concentration of microbial cells and biological IN in precipitation based on the concentration of TOC, Ca2+, and NH4+, or TOC, cells, Ca2+, NH4+, K+, PO43−, SO42−, Cl−, and HCO3−. Our results indicate that biological IN are ubiquitous in precipitation and that for some geographic locations the activity and concentration of these particles is related to the season and precipitation chemistry. Thus, our research suggests that biological IN are widespread in the atmosphere and may affect meteorological processes that lead to precipitation.
Striga Biocontrol on a Toothpick: A Readily Deployable and Inexpensive Method for Smallholder Farmers
(2016-08) Nzioki, Henry S.; Oyosi, Florence; Morris, Cindy E.; Kaya, Eylul; Pilgeram, Alice L.; Baker, Clair S.; Sands, David C.
Striga hermonthica (witchweed) is a parasitic weed that attacks and significantly reduces the yields of maize, sorghum, millet, and sugarcane throughout sub-Saharan Africa. Low cost management methods such as hand weeding, short crop rotations, trap cropping, or conventional biocontrol have not been effective. Likewise, Striga-tolerant or herbicide resistant maize cultivars are higher yielding, but are often beyond the economic means of sustenance farmers. The fungal pathogen. Fusanum oxysporum f.sp. strigae, has been the object of numerous studies to develop Striga biocontrol. Under experimental conditions this pathogen can reduce the incidence of Striga infestation but field use is not extensive, perhaps because it has not been sufficiently effective in restoring crop yield and reducing the soil Striga seed bank. Here we brought together Kenyan and US crop scientists with smallholder farmers to develop and validate an effective biocontrol strategy for management of Striga on smallholder farms. Key components of this research project were the following: (1) Development of a two-step method of fungal delivery, including laboratory coating of primary inoculum on toothpicks, followed by on-farm production of secondary field inoculum in boiled rice enabling delivery of vigorous, fresh inoculum directly to the seedbed; (2) Training of smallholder farmers (85% women), to produce the biocontrol agent and incorporate it into their maize plantings in Striga-infested soils and collect agronomic data. The field tests expanded from 30 smallholder farmers to a two-season, 500-farmer plot trial including paired plus and minus biocontrol plots with fertilizer and hybrid seed in both plots and; (3) Concerted selection of variants of the pathogen identified for enhanced virulence, as has been demonstrated in other host parasite systems were employed here on Striga via pathogen excretion of the amino acids L-leucine and L-tyrosine that are toxic to Striga but innocuous to maize. This overall strategy resulted in an average of >50% increased maize yield in the March to June rains season and >40% in the September to December rains season. Integration of this enhanced plant pathogen to Striga management in maize can significantly increase the maize yield of smallholder farmers in Kenya.
The Toothpick Project: commercialization of a virulence-selected fungal bioherbicide for Striga hermonthica (witchweed) biocontrol in Kenya
(Wiley, 2023-09) Baker, Claire S.; Sands, David C.; Nzioki, Henry Sila
The high-level view of global food systems identifies three all-encompassing barriers to the adoption of food systems solutions: knowledge, policy, and finance. These barriers, and the siloed characteristics of each of these, have hindered the development and adoption of microbial herbicides. How knowledge, policy, and finance are related to the Toothpick Project's path of commercializing a new bioherbicide, early in the scope of the industry, is discussed here. The Toothpick Project's innovation, developed over four decades and commercialized in 2021, uses strains of Fusarium oxysporum f.sp. strigae selected for overproduction and excretion of specific amino acids, killing the parasitic weed Striga hermonthica (Striga or witchweed), Africa's worst pest threat to food security. Historically, bioherbicides have not been a sufficient alternative to the dominant use of synthetic chemical herbicides. To be used safely as bioherbicides, plant pathogens need to be host specific, non-toxic, and yet sufficiently virulent to control a specific weed. For commercialization, bioherbicides must be affordable and require a sufficient shelf life for distribution. Given the current triple storm encountered by the chemical herbicide industry (herbicide-resistant weeds, lawsuits, and consumer pushback), there exists an opportunity to use certain plant pathogens as bioherbicides by enhancing their virulence. By discussing barriers in the scope of knowledge, policy, and finance in the development of the Toothpick Project's new microbial bioherbicide, we hope to help others to anticipate the challenges and provide change-leaders, particularly in policy and finance, a ground level perspective of bioherbicide development. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
Trees, forests and water: Cool insights for a hot world
(2017-03) Ellison, David; Morris, Cindy E.; Locatelli, Bruno; Sheil, Douglas; Cohen, Jane; Murdiyarso, Daniel; Gutierrez, Victoria; van Noordwijk, Meine; Creed, Irena F.; Pokorny, Jan; Gaveau, David; Spracklen, Dominick V.; Tobella, Aida Bargues; Ilstedt, Ulrik; Teuling, Adriaan J.; Gebrehiwot, Solomon Gebreyohannis; Sands, David C.; Muys, Bart; Verbist, Bruno; Springgay, Elaine; Sugandi, Yulia; Sullivan, Caroline A.
Forest-driven water and energy cycles are poorly integrated into regional, national, continental and global decision-making on climate change adaptation, mitigation, land use and water management. This constrains humanity's ability to protect our planet's climate and life-sustaining functions. The substantial body of research we review reveals that forest, water and energy interactions provide the foundations for carbon storage, for cooling terrestrial surfaces and for distributing water resources. Forests and trees must be recognized as prime regulators within the water, energy and carbon cycles. If these functions are ignored, planners will be unable to assess, adapt to or mitigate the impacts of changing land cover and climate. Our call to action targets a reversal of paradigms, from a carbon-centric model to one that treats the hydrologic and climate-cooling effects of trees and forests as the first order of priority. For reasons of sustainability, carbon storage must remain a secondary, though valuable, by-product. The effects of tree cover on climate at local, regional and continental scales offer benefits that demand wider recognition. The forest- and tree-centered research insights we review and analyze provide a knowledge-base for improving plans, policies and actions. Our understanding of how trees and forests influence water, energy and carbon cycles has important implications, both for the structure of planning, management and governance institutions, as well as for how trees and forests might be used to improve sustainability, adaptation and mitigation efforts.
Ubiquity of biological ice nucleators in snowfall
(2008-02) Christner, Brent C.; Morris, Cindy E.; Foreman, Christine M.; Cai, Rongman; Sands, David C.
Despite the integral role of ice nucleators (IN) in atmospheric processes leading to precipitation, their sources and distributions have not been well established. We examined IN in snowfall from mid- and high-latitude locations and found that the most active were biological in origin. Of the IN larger than 0.2 micrometer that were active at temperatures warmer than -7°C, 69 to 100% were biological, and a substantial fraction were bacteria. Our results indicate that the biosphere is a source of highly active IN and suggest that these biological particles may affect the precipitation cycle and/or their own precipitation during atmospheric transport.