Browsing by Author "Strickland, Michael S."

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    Below- and above-ground effects of deadwood and termites in plantation forests
    Ulyshen, Michael D.; Shefferson, Richard; Horn, Scott; Taylor, Melanie K.; Bush, Bryana; Brownie, Cavell; Seibold, Sebastian; Strickland, Michael S. (Ecological Society of America, 2017-08)
    Deadwood is an important legacy structure in managed forests, providing continuity in shelter and resource availability for many organisms and acting as a vehicle by which nutrients can be passed from one stand to the next following a harvest. Despite existing at the interface between below- and above-ground systems, however, much remains unknown about the role woody debris plays in linking these zones. Moreover, it remains untested whether the accelerative effects of wood-feeding insects on wood decomposition influence tree growth or nutritional status in forests. In this study, we added different quantities of pine logs to the bases of saplings in two-year-old loblolly pine (Pinus taeda L.) plantations in Mississippi, USA. We included a treatment in which subterranean termites (Blattodea: Rhinotermitidae: Reticulitermes) were excluded from logs to determine how these insects affect the release of nutrients from wood and, in turn, tree growth. After 51 months of decomposition, we quantified below-ground effects by measuring microbial biomass, plant-available forms of N, and ectomycorrhizal diversity associated with fine tree roots. Meanwhile, above-ground measurements focused on the elemental concentrations in decomposing wood either protected or unprotected from termites and tree metrics related to growth and nutrient status. We found additions of wood to significantly increase nitrate and potential net nitrification relative to reference treatments but detected no significant effects on tree growth, needle nitrogen concentrations, or ectomycorrhizal diversity. Soil nitrate and potential net nitrification were higher under protected vs. unprotected logs, and plant-available forms of N were mostly more abundant short distances away from both protected and unprotected logs than directly under them. The wood of logs protected from termites had significantly lower concentrations of most elements compared to that of unprotected logs, largely due to the large amounts of soil imported into unprotected logs by termites. Termite exclusion had no measurable effect on tree growth, nutritional status, or ectomycorrhizal diversity, however. Our findings indicate that deadwood and termites both contribute to the spatial heterogeneity of soil properties but may have limited short-term local effects on tree growth. Longer-term studies and studies on less fertile sites are needed.
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    Biochemical and physiological responses of Cannabis sativa to an integrated plant nutrition system
    Filho, Jose F. Da Cunha Leme; Thomason, Wade E.; Evanylo, Gregory K.; Zhang, Xunzhong; Strickland, Michael S.; Chim, Bee K.; Diatta, Andre A. (2020-11)
    The illegal status of cannabis (Cannabis sativa L.) post-World War II resulted in a lack of research on agricultural practices. However, there is a resurgence of interest in cannabis due to diverse uses such as a rich source of cellulosic/woody fiber and construction uses, seed oil, bioenergy and pharmaceutical properties. The principle of an integrated plant nutrition system (IPNS) is to enable adaptation of plant nutrition and soil fertility management to local site characteristics, attempting to optimize use of inorganic, organic and biological resources. This project investigated the individual and combined use of inorganic, organic and biological fertilizer resources on cannabis before and after a period of moderate water stress. We evaluated the individual and combined effects of commercial synthetic fertilizer, humic acid (HA), manure tea and bioinoculant as inorganic, organic and biological resources, respectively on cannabis growth and physiological parameters. Our hypothesis was that the synergetic effects of HA + biofertilizers would improve cannabis growth. When compared to the control, the application of HA and biofertilizer alone, or in combination, increased plant height, chlorophyll content and photosynthetic efficiency by 55, 8 and 12%, respectively, after water stress. Cannabis biomass of treated plants was rarely different from the control. The combined application of HA + biofertilizer resulted in additive, but not synergistic, increases in measured parameter. Future research should focus on the effects of biostimulants on CBD/THC content due to the potential impact on the production of secondary metabolites in plants under stress.
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    Compositional differences in simulated root exudates elicit a limited functional and compositional response in soil microbial communities
    Strickland, Michael S.; McCulley, Rebecca L.; Nelson, Jim A.; Bradford, Mark A. (Frontiers, 2015-08-11)
    Inputs of low molecular weight carbon (LMW-C) to soil – primarily via root exudates– are expected to be a major driver of microbial activity and source of stable soil organic carbon. It is expected that variation in the type and composition of LMW-C entering soil will influence microbial community composition and function. If this is the case then short-term changes in LMW-C inputs may alter processes regulated by these communities. To determine if change in the composition of LMW-C inputs influences microbial community function and composition, we conducted a 90 day microcosm experiment whereby soils sourced from three different land covers (meadows, deciduous forests, and white pine stands) were amended, at low concentrations, with one of eight simulated root exudate treatments. Treatments included no addition of LMW-C, and the full factorial combination of glucose, glycine, and oxalic acid. After 90 days, we conducted a functional response assay and determined microbial composition via phospholipid fatty acid analysis. Whereas we noted a statistically significant effect of exudate treatments, this only accounted for ∼3% of the variation observed in function. In comparison, land cover and site explained ∼46 and ∼41% of the variation, respectively. This suggests that exudate composition has little influence on function compared to site/land cover specific factors. Supporting the finding that exudate effects were minor, we found that an absence of LMW-C elicited the greatest difference in function compared to those treatments receiving any LMW-C. Additionally, exudate treatments did not alter microbial community composition and observable differences were instead due to land cover. These results confirm the strong effects of land cover/site legacies on soil microbial communities. In contrast, short-term changes in exudate composition, at meaningful concentrations, may have little impact on microbial function and composition.
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    Herbivore species identity and composition affect soil enzymatic activity through altered plant composition in a coastal tallgrass prairie
    Prather, Chelse; Strickland, Michael S.; Laws, Angela; Branson, David (2017-09)
    Although single herbivore species are known to affect soil microbial communities, the effects of herbivore species identity and community composition on soil microbes and their functioning are unknown. We tested the effects of single orthopteran species and species combinations on soil enzymatic activity with an enclosure experiment in a coastal tallgrass prairie. Species effects on soil enzymatic activity were non-additive: one particular mixed feeding species (M. femurrubrum) resulted in 65% higher BG enzyme activity and 35% higher total hydrolytic enzyme activity, whereas certain combinations containing this species had little to no effects. These results suggest that critical species or combinations of species that strongly affect plant functional composition may also have strong effects on soil enzymatic functioning and nutrient limitation. (C) 2017 Elsevier Ltd. All rights reserved.
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    An integrated plant nutrition system (IPNS) for corn in the Mid-Atlantic USA
    Da Cunha Leme Filho, Jose Franco; Thomason, Wade E.; Evanylo, Gregory K.; Zhang, Xunzhong; Strickland, Michael S.; Chim, Bee K.; Diatta, Andre A. (2021-03-16)
    Current trends in agriculture have moved toward more sustainable cultivation systems with higher efficiency of input use. A variety of materials, derived from different resources, can serve as a crop nutrient sources. An Integrated Plant Nutrition System (IPNS) uses the combined and harmonious use of inorganic, organic and biological nutrient resources to maximize efficiency of inputs. We evaluated the effects of commercial nitrogen (N) fertilizer, humic acid compounds (HA), compost/manure teas and bioinoculants as inorganic, organic and biological resources, respectively and their synergy over three years on corn (Zea mays L.) in the Mid-Atlantic USA. The individual and combined application of HA and biofertilizer following the IPNS influenced corn height and leaf greenness to varying degrees, most likely due to biostimulant effects. In 2017, corn height, NDVI, greenness and vigor responded positively to biostimulant application to varying magnitudes and growth stages, however grain yield and nutrient content were not affected. In combined studies from 2018 and 2019 corn height was not impacted by biostimulant application but NDVI, photosynthetic efficiency, greenness and vigor were increased at different doses and corn growth stages. The combined use of HA + biofertilizer (Microlife Humic + Microgeo) was the only treatment leading to increased grain yield. This study demonstrates that the individual and combined application of HA and biofertilizer can influence corn growth and vigor at various points during the growing season. However, the current study cannot conclusively confirm that the integrated use of HA and biofertilizers (IPNS) is a better practice than the application of each compound individually.
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    Metagenomic Analysis of Antibiotic Resistance Genes in Dairy Cow Feces following Therapeutic Administration of Third Generation Cephalosporin
    Chambers, Lindsey R.; Yang, Ying; Littier, Heather; Ray, Partha P.; Zhang, Tong; Pruden, Amy; Strickland, Michael S.; Knowlton, Katharine F. (PLOS, 2015-08-10)
    Although dairy manure is widely applied to land, it is relatively understudied compared to other livestock as a potential source of antibiotic resistance genes (ARGs) to the environment and ultimately to human pathogens. Ceftiofur, the most widely used antibiotic used in U.S. dairy cows, is a 3rd generation cephalosporin, a critically important class of antibiotics to human health. The objective of this study was to evaluate the effect of typical ceftiofur antibiotic treatment on the prevalence of ARGs in the fecal microbiome of dairy cows using a metagenomics approach. β-lactam ARGs were found to be elevated in feces from Holstein cows administered ceftiofur (n = 3) relative to control cows (n = 3). However, total numbers of ARGs across all classes were not measurably affected by ceftiofur treatment, likely because of dominance of unaffected tetracycline ARGs in the metagenomics libraries. Functional analysis via MG-RAST further revealed that ceftiofur treatment resulted in increases in gene sequences associated with “phages, prophages, transposable elements, and plasmids”, suggesting that this treatment also enriched the ability to horizontally transfer ARGs. Additional functional shifts were noted with ceftiofur treatment (e.g., increase in genes associated with stress, chemotaxis, and resistance to toxic compounds; decrease in genes associated with metabolism of aromatic compounds and cell division and cell cycle), along with measureable taxonomic shifts (increase in Bacterioidia and decrease in Actinobacteria). This study demonstrates that ceftiofur has a broad, measureable and immediate effect on the cow fecal metagenome. Given the importance of 3rd generation cephalospirins to human medicine, their continued use in dairy cattle should be carefully considered and waste treatment strategies to slow ARG dissemination from dairy cattle manure should be explored.
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    Microbes as Engines of Ecosystem Function: When Does Community Structure Enhance Predictions of Ecosystem Processes?
    Graham, Emily B.; Knelman, Joseph E.; Schindlbacher, Andreas; Siciliano, Steven; Breulmann, Marc; Yannarell, Anthony; Bemans, J. M.; Abell, Guy; Philippot, Laurent; Prosser, James; Foulquier, Arnaud; Yuste, Jorge C.; Glanville, Helen C.; Jones, Davey L.; Angel, Foey; Salminen, Janne; Newton, Ryan J.; Buergmann, Helmut; Ingram, Lachlan J.; Hamer, Ute; Siljanen, Henri M. P.; Peltoniemi, Krista; Potthast, Karin; Baneras, Lluis; Hartmann, Martin; Banerjee, Samiran; Yu, Ri-Qing; Nogaro, Geraldine; Richter, Andreas; Koranda, Marianne; Castle, Sarah C.; Goberna, Marta; Song, Bongkeun; Chatterjee, Amitava; Nunes, Olga C.; Lopes, Ana R.; Cao, Yiping; Kaisermann, Aurore; Hallin, Sara; Strickland, Michael S.; Garcia-Pausas, Jordi; Barba, Josep; Kang, Hojeong; Isobe, Kazuo; Papaspyrou, Sokratis; Pastorelli, Roberta; Lagomarsino, Alessandra; Lindstrom, Eva S.; Basiliko, Nathan; Nemergut, Diana R. (Frontiers, 2016-02-24)
    Microorganisms are vital in mediating the earth's biogeochemical cycles; yet, despite our rapidly increasing ability to explore complex environmental microbial communities, the relationship between microbial community structure and ecosystem processes remains poorly understood. Here, we address a fundamental and unanswered question in microbial ecology: 'When do we need to understand microbial community structure to accurately predict function?' We present a statistical analysis investigating the value of environmental data and microbial community structure independently and in combination for explaining rates of carbon and nitrogen cycling processes within 82 global datasets. Environmental variables were the strongest predictors of process rates but left 44% of variation unexplained on average, suggesting the potential for microbial data to increase model accuracy. Although only 29% of our datasets were significantly improved by adding information on microbial community structure, we observed improvement in models of processes mediated by narrow phylogenetic guilds via functional gene data, and conversely, improvement in models of facultative microbial processes via community diversity metrics. Our results also suggest that microbial diversity can strengthen predictions of respiration rates beyond microbial biomass parameters, as 53% of models were improved by incorporating both sets of predictors compared to 35% by microbial biomass alone. Our analysis represents the first comprehensive analysis of research examining links between microbial community structure and ecosystem function. Taken together, our results indicate that a greater understanding of microbial communities informed by ecological principles may enhance our ability to predict ecosystem process rates relative to assessments based on environmental variables and microbial physiology.
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    Quantifying short-term responsiveness and consistency of soil health parameters in row crop systems. Part 1: Developing a multivariate approach
    Gyawali, Ayush Joshi; Strickland, Michael S.; Thomason, Wade E.; Reiter, Mark S.; Stewart, Ryan D. (Elsevier, 2022-05-01)
    Quantifying soil health requires measuring different physical, chemical and biological soil properties, yet limits in time and resources often restrict the number of parameters that can be analyzed. The main objective of this research was to identify soil health parameters that showed measurable and consistent responses to reduced tillage and cover cropping over a short (2-year) study period. In September 2015, four treatments – reduced tillage with cover crops, reduced tillage without cover crops, conventional tillage with cover crops and conventional tillage without cover crops – were installed in five sites across Virginia. Sites were managed for corn or tobacco production. Soils were analyzed for 32 properties associated with soil health, and cash crop yields were also measured in September 2016 and September 2017. A multivariate approach was used to detect treatment differences and determine parameters driving those differences. We then developed two new indices to quantify the responsiveness and consistency of soil health parameters. The results showed that surface soil layers had more parameters with significant differences between treatments than subsurface layers. Tillage effects were observed within 0.5 years, which may be due to the lack of tillage history in 4 of the 5 sites. Cover crop effects appeared after 1.5 years, indicating that this practice can also induce changes in soil properties over relatively short periods. Soil aggregate stability, potassium, calcium, magnesium, boron and cash crop yield were the most responsive parameters to reduced tillage and cover crop practices, while aggregate stability also showed high consistency. These findings suggest that aggregate stability effectively indicated short-term changes in soil health within row cropping systems of Virginia.
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    Response of soil microbial community composition and function to a bottomland forest restoration intensity gradient
    Strickland, Michael S.; Callaham, Mac A., Jr.; Gardiner, Emile S.; Stanturf, John A.; Leff, Jonathan W.; Fierer, Noah; Bradford, Mark A. (2017-10)
    Terrestrial ecosystems are globally under threat of loss or degradation. To compensate for the impacts incurred by loss and/or degradation, efforts to restore ecosystems are being undertaken. These efforts often focus on restoring the aboveground plant community with the expectation that the belowground microbial community will follow suit. This 'Field of Dreams' expectation - if you build it, they will come - makes untested assumptions about how microbial communities and their functions will respond to aboveground-focused restoration. To determine if restoration of aboveground plant communities equates to restoration of belowground microbial communities, we assessed the effects of four forest restoration treatments - varying in intensity from unmanaged to interplanting tree species - on microbial (i.e. prokaryotic and fungal) community composition and function (i.e. catabolic profiles and extracellular enzyme activities). Additionally, effects of the restoration treatments were compared to both degraded (i.e. active arable cultivation) and target endpoint communities (i.e. remnant bottomland forest) to determine the trajectory of intensifying aboveground restoration efforts on microbial communities. Approximately 16 years after the initiation of the restoration treatments, prokaryotic and fungal community composition, and microbial function in the four restoration treatments were intermediate to the endpoint communities. Surprisingly, intensification of aboveground restoration efforts led to few differences among the four restoration treatments and increasing intensification did not consistently lead to microbial communities with greater similarity in composition and function to the target remnant forest communities. Together these results suggest that belowground microbial community composition and function will respond little to, or will lag markedly behind, intensifying aboveground restoration efforts. Reliance on a Field of Dreams' approach, even if you build it better, may still lead to belowground microbial communities that remain uncoupled from aboveground communities. Importantly, our findings suggest that restoring aboveground vegetation may not lead to the intended restoration of belowground microbial communities and the ecosystem processes they mediate.
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    The Role of Volatile Organic Compounds on Soil Microbial Communities and Ecosystem Processes
    McBride, Steven Glynn II (Virginia Tech, 2020-04-17)
    Soil microorganisms are primarily limited by carbon (C) availability. The majority of C entering belowground food webs comes directly from local flora. Plant derived labile C compounds affect microbial community structure and function, which in turn drive ecosystem function. Research has focused on dissolved organic C (DOC) from litter leachates and root exudates. These compounds are often readily assimilable by soil microorganisms and are precursors for stable soil organic matter formation. Due to diffusion limitation DOC rarely travels far beyond its origin, meaning most soil microorganisms are unable to access these compounds unless they are located near the C source. However, recent studies have illuminated the importance of volatile organic compounds (VOCs) in soil ecosystems. VOCs are produced in abundance and, as vapors, they are able to travel through soil more rapidly than DOC. This dissertation aims to investigate the importance of VOCs commonly produced during the decomposition of leaf litter. We used three separate microcosm experiments to answer the following questions. 1) How do abundant VOCs affect microbial activity in soil? 2) How do VOCs affect nitrogen (N) transformations and the microbes associated with N transformations? 3) How do VOCs affect microbial community composition? 4) Are VOCs from decomposing litter incorporated into soil C pools? In chapter 2, we show that methanol and acetone – common litter derived VOCs – increase microbial activity and labile soil C, while also decreasing available nitrate, and ammonia oxidizing archaea. Interestingly, this decrease in nitrifiers did not affect nitrification rate after VOC addition was ceased. In chapter 3, we demonstrate that soil microbial taxa respond differently to DOC and VOCs at different soil moisture levels. Specifically, DOC primarily affected taxa abundance in wetter soils, while the insoluble VOC α-pinene had the largest impact at lower moisture levels, and methanol affected abundance at all moisture levels. Finally, in chapter 4, we demonstrate that VOCs from decomposing leaf litter altered soil bacterial and fungal communities, and VOC derived C entered all measured soil organic matter pools without direct contact between decomposing litters and the soil. This work demonstrates the importance of VOCs on soil microbial communities and ecosystem function. The VOC induced increase in microbial activity, and the effects of VOCs at low moisture levels suggest that VOCs may function in the bulk soil in a manner similar to DOC in rhizosphere soil. Additionally, the incorporation of VOC-C into soil organic matter pools identifies a hitherto unrecognized mechanism for soil organic matter formation.
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    What We Talk about When We Talk about Soil Health
    Stewart, Ryan D.; Jian, Jinshi; Gyawali, Ayush Joshi; Thomason, Wade E.; Badgley, Brian D.; Reiter, Mark S.; Strickland, Michael S. (American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, 2018-11-01)
    Despite a nationwide emphasis on improving soil health in the United States, current measurement protocols have little consistency. To survey assessment practices, we conducted a meta-analysis of cover crop (n = 86) and no-tillage (n = 106) studies and compiled reported indicators, cropping systems, and soil sampling protocols from each. We then analyzed which indicators significantly responded to cover crop usage after 1 yr and 2 to 3 yr. Our results showed that out of 42 indicators, only 8 were reported in >20% of studies. Thirteen indicators showed >10% relative response after 1 to 3 yr; the remainder lacked either sufficient observations or consistent results. Looking forward, we propose that emphasis should be placed on (i) pursuing dynamic indicators (e.g., aggregate stability), (ii) standardizing sampling protocols, and (iii) developing a common framework for information sharing. These efforts will generate new insight into soil health across systems, ultimately ensuring that soil health science is useful to producers and regulators.