Plant cell wall degradation into fermentable sugars by cellulases is one of the greatest barriers to biofuel production. Expansin protein loosens the plant cell wall by opening up the complex of cellulose microfibrils and polysaccharide matrix components thereby increasing its accessibility to cellulases. We over-expressed cucumber expansin in maize kernels to produce enough protein to assess its potential to serve as an industrial enzyme for applications particularly in biomass conversion. We used the globulin-1 embryo-preferred promoter to express the cucumber expansin gene in maize seed. Expansin protein was targeted to one of three sub-cellular locations: the cell wall, the vacuole, or the endoplasmic reticulum (ER). To assess the level of expansin accumulation in seeds of transgenic kernels, a high throughput expansin assay was developed. The highest expressing plants were chosen and enriched crude expansin extract from those plants was tested for synergistic effects with cellulase on several lignocellulosic substrates. Activity of recombinant cucumber expansin from transgenic kernels was confirmed on these pretreated substrates. The best transgenic lines (ER-targeted) can now be used for breeding to increase expansin expression for use in the biomass conversion industry. Results of these experiments show the success of expansin over-expression and accumulation in transgenic maize seed without negative impact on growth and development and confirm its synergistic effect with cellulase on deconstruction of complex cell wall substrates.
Drainage systems are integral parts of agricultural landscapes and have the ability to intercept nutrient loading from runoff to surface water. This study investigated nutrient removal efficiency within replicated experimental agricultural drainage ditches during a simulated summer runoff event. Study objectives were to examine the influence of routine mowing of vegetated ditches on nutrient mitigation and to assess spatial transformation of nutrients along ditch length. Both mowed and unmowed ditch treatments decreased NO3 (-)-N by 79 % and 94 % and PO4 (3-) by 95 % and 98 %, respectively, with no significant difference in reduction capacities between the two treatments. This suggests occasional ditch mowing as a management practice would not undermine nutrient mitigation capacity of vegetated drainage ditches.
Core Ideas
Agricultural drainage ditches can be considered as carbon sinks.
Agricultural ditches can provide an optimum environment for carbon sequestration.
Soil topography influences spatial carbon storage within wetlands.
Soil bulk densities influence carbon storage in wetlands.
Agricultural ditches are capable of many ecological functions, including flood control and edge of field nutrient filtration. This study investigated the potential for carbon sequestration within mowed and unmowed experimental conventional and controlled (with weirs) agricultural drainage ditches. The study analyzed and compared spatial and temporal variation in soil organic carbon (OC) concentration (g C kg–1) and OC pool (kg C m–2) within a 3‐cm soil depth between treatments. Soil OC concentrations were quantified through combustion of organic matter (OM) at 400°C in a muffle furnace for 16 h using the loss on ignition (LOI) method. Soil bulk density was also determined for each ditch treatment. In both summer and winter, mean soil C concentration in ditches with weirs was similar to mean soil C concentration in ditches with no weirs (16.68 ± 0.49 vs. 16.47 ± 0.46 g C kg–1 in summer; 14.47 ± 0.75 vs. 16.27 ± 0.72 g C kg–1 in winter). Similar bulk densities (0.67 Mg m–3, on average) and OC contents in ditches furnished comparable C pools in ditches with weirs and no weirs respectively (28.08 ± 0.75 vs. 27.88 ± 0.68 kg C m–2 in summer; 26.44 ± 1.56 vs. 30.24 ± 1.40 g C kg–1 in winter). The studied drainage ditches can therefore be considered for their contributions to the C sink, given the high values of C pool observed in the ditch treatments. This suggests agricultural drainage ditches can offer a suitable environment for C sequestration.
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