Dataset Information

Effects of field-grown transgenic switchgrass carbon inputs on soil organic carbon cycling.

ABSTRACT: Genetic engineering has been used to decrease the lignin content and to change the lignin composition of switchgrass (Panicum virgatum L.) to decrease cell wall recalcitrance to enable more efficient cellulosic biofuel production. Previous greenhouse and field studies showed that downregulation of the gene encoding switchgrass caffeic acid O-methyltransferase (COMT) and overexpression of the switchgrass PvMYB4 (MYB4) gene effectively improved ethanol yield. To understand potential environmental impacts of cultivating these transgenic bioenergy crops in the field, we quantified the effects of field cultivation of transgenic switchgrass on soil organic carbon (SOC) dynamics. Total and active SOC as well as soil respiration were measured in soils grown with two COMT-downregulated transgenic lines (COMT2 and COMT3), three MYB4-overexpressed transgenic lines (L1, L6, and L8), and their corresponding non-transgenic controls. No differences in total SOC, dissolved organic carbon (DOC), and permanganate oxidizable carbon (POXC) were detected between transgenic and non-transgenic treatments for both COMT (10.4-11.1 g kg-1 for SOC, 60.0-64.8 mg kg-1 for DOC, and 299-384 mg kg-1 for POXC) and MYB4 lines (6.89-8.21 g kg-1 for SOC, 56.0-61.1 mg kg-1 for DOC, and 177-199 mg kg-1 for POXC). Soil CO2-carbon (CO2-C) production from the COMT2 transgenic line was not significantly different from its non-transgenic control. In contrast, the COMT3 transgenic line had greater soil CO2-C production than its non-transgenic control (210 vs. 165 µg g-1) after 72 days of laboratory incubation. Combining the improvement in ethanol yield and biomass production reported in previous studies with negligible change in SOC and soil respiration, COMT2 could be a better biofuel feedstock than COMT3 for environmental conservation and cost-effective biofuel production. On the other hand, MYB4 transgenic line L8 produced more biomass and total ethanol per hectare while it released more CO2-C than the control (253 vs. 207 µg g-1). Long-term in situ monitoring of transgenic switchgrass systems using a suite of soil and environmental variables is needed to determine the sustainability of growing genetically modified bioenergy crops.

SUBMITTER: Xu S

PROVIDER: S-EPMC6800523 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Effects of field-grown transgenic switchgrass carbon inputs on soil organic carbon cycling.

Xu Sutie S Ottinger Sarah L SL Schaeffer Sean M SM DeBruyn Jennifer M JM Stewart C Neal CN Mazarei Mitra M Jagadamma Sindhu S

PeerJ 20191016

Genetic engineering has been used to decrease the lignin content and to change the lignin composition of switchgrass (Panicum virgatum L.) to decrease cell wall recalcitrance to enable more efficient cellulosic biofuel production. Previous greenhouse and field studies showed that downregulation of the gene encoding switchgrass caffeic acid O-methyltransferase (COMT) and overexpression of the switchgrass PvMYB4 (MYB4) gene effectively improved ethanol yield. To understand pot ...[more]

PMID: 31637134

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Project description:Background:Genetic engineering has been effective in altering cell walls for biofuel production in the bioenergy crop, switchgrass (Panicum virgatum). However, regulatory issues arising from gene flow may prevent commercialization of engineered switchgrass in the eastern United States where the species is native. Depending on its expression level, microRNA156 (miR156) can reduce, delay, or eliminate flowering, which may serve to decrease transgene flow. In this unique field study of transgenic switchgrass that was permitted to flower, two low (T14 and T35) and two medium (T27 and T37) miR156-overexpressing 'Alamo' lines with the transgene under the control of the constitutive maize (Zea mays) ubiquitin 1 promoter, along with nontransgenic control plants, were grown in eastern Tennessee over two seasons. Results:miR156 expression was positively associated with decreased and delayed flowering in switchgrass. Line T27 did not flower during the 2-year study. Line T37 did flower, but not all plants produced panicles. Flowering was delayed in T37, resulting in 70.6% fewer flowers than controls during the second field year with commensurate decreased seed yield: 1205 seeds per plant vs. 18,539 produced by each control. These results are notable given that line T37 produced equivalent vegetative aboveground biomass to the controls. miR156 transcript abundance of field-grown plants was congruent with greenhouse results. The five miR156 SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) target genes had suppressed expression in one or more of the transgenic lines. Line T27, which had the highest miR156 overexpression, showed significant downregulation for all five SPL genes. On the contrary, line T35 had the lowest miR156 overexpression and had no significant change in any of the five SPL genes. Conclusions:Because of the research field's geographical features, this study was the first instance of any genetically engineered trait in switchgrass, in which experimental plants were allowed to flower in the field in the eastern U.S.; USDA-APHIS-BRS regulators allowed open flowering. We found that medium overexpression of miR156, e.g., line T37, resulted in delayed and reduced flowering accompanied by high biomass production. We propose that induced miR156 expression could be further developed as a transgenic switchgrass bioconfinement tool to enable eventual commercialization.

Project description:Gravel and sand mulching is an indigenous technology that has been used for increasing soil temperature and improving crop yield and water use efficiency for at least 300 years in northwestern China. However, long-term application of inorganic fertilizer with gravel and sand mulch could decrease the soil organic carbon content, and how to improve soil fertility under gravel and sand mulching remains largely unknown. Thus, we evaluated the effects of the application of inorganic (chemical) and organic (manure) fertilizers on the distribution of soil aggregates and their associated organic carbon in a field mulched with gravel and sand. A 5-year (2014-2018) field experiment was conducted in the arid region of northwestern China. Total organic carbon (TOC), permanganate oxidizable carbon (POC), TOC reserves in soil aggregates with different particle sizes, and watermelon (Citrullus lanatus) productivity in gravel-mulched fields were analysed for the following six fertilization modes: no N fertilizer input as a control (CK), N fertilizer without organic fertilizer (CF), and organic fertilizer replacing 25%, 50%, 75%, and 100% of mineral nitrogen (recorded as OF-25%, OF-50%, OF-75% and OF-100%, respectively). The results showed that, higher manure to nitrogen fertilizer ratios were positively correlated with the percentage of soil macroaggregates (> 0.25 mm), mean weight diameter (MWD), TOC and POC concentrations, and their ratios in different particle sizes. Compared with CF, the treatments with 50% to 100% organic fertilizer significantly increased TOC storage (5.91-7.84%) in the soil profile (0-20 cm). Moreover, the CF treatment did not increase SOC concentrations or TOC storage, compared with CK. The fruit yield (2014-2018) of watermelon significantly increased by an average of 31.38% to 45.70% in the treatments with 50% to 100% organic fertilizer, respectively, compared with CF. Our results suggest that the partial replacement of chemical fertilizer with organic manure (OF-50%, OF-75% and OF-100%) could increase the proportion of macroaggregates, POC and TOC concentrations, and TOC stock in aggregates with different particle size and improve the yield of watermelon in the gravel fields of arid northwestern China mulched with gravel and sand.

Dataset Information

Effects of field-grown transgenic switchgrass carbon inputs on soil organic carbon cycling.

Publications

Effects of field-grown transgenic switchgrass carbon inputs on soil organic carbon cycling.

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