Quantifying the impacts of genetically engineered crops and deep soil C cycling on the sustainability of bioenergy crop production

Bioenergy can help mitigate climate change by providing a carbon-neutral fuel source. However, multiple challenges exist to achieving carbon neutrality including converting lignocellulosic materials to fuel and enhancing soil C sequestration during the growth of the feedstocks. To address these challenges, there have been recent efforts to genetically modify feedstocks to produce more energy dense oils that increase fuel conversion efficiency and to cultivate deep-rooted perennial feedstocks that can enhance soil C storage. However, the C consequences and efficacy of these solutions remain largely uncertain. To examine the C consequences of enhancing oil content of bioenergy feedstocks, I examined the impact of Sugarcane litter decomposition on soil carbon (C) formation and loss and determined if the genetic modifications to produce Oilcane alter these dynamics. To do this, I traced the fate of Sugarcane and Oilcane litter in protected and unprotected soil C pools. I found that both crops led to net soil C gains dominated by an accumulation of the litter as particulate organic carbon (POC) and that the genetic modifications to Oilcane did not substantially alter soil C dynamics. To investigate the efficacy of deep-rooted perennial feedstocks to build soil C, I linked depth gradients in root biomass with microbial activity and soil C stocks down to 1 meter to determine the predictors of soil C and soil C fractions with depth. I also performed a lab experiment where I examined differences between depths in the ability of simple C inputs to prime or build soil C. In the field, I excavated quantitative 1 m deep soil pits under 20-year-old Miscanthus plots and quantified, fine root biomass, total soil C, mineral-associated organic C (MAOC), particulate organic C (POC), microbial respiration, net nitrogen cycling, and enzyme activities. In the lab, I experimentally followed the fate of 13C labeled glucose into soil C fractions at each depth. I found that soil C and MAOC declined with depth and were best predicted by fine root biomass, representing inputs, microbial respiration, representing losses, and NAG activity, representing the recycling of microbial necromass. I also found that deep soils had a greater potential to minerally stabilize new simple C inputs than shallow soils due to the C inputs having a greater stabilizing than priming effect below 50cm. Collectively, my research shows that sustainable bioenergy solutions such as lipid enhanced Oilcane and growing deep-rooted perennial feedstocks may lead to enhanced soil C

Carbon and Beyond:The Biogeochemistry of Climate in a Rapidly Changing Amazon

The Amazon Basin is at the center of an intensifying discourse about deforestation, land-use, and global change. To date, climate research in the Basin has overwhelmingly focused on the cycling and storage of carbon (C) and its implications for global climate. Missing, however, is a more comprehensive consideration of other significant biophysical climate feedbacks [i.e., CH4, N2O, black carbon, biogenic volatile organic compounds (BVOCs), aerosols, evapotranspiration, and albedo] and their dynamic responses to both localized (fire, land-use change, infrastructure development, and storms) and global (warming, drying, and some related to El Niño or to warming in the tropical Atlantic) changes. Here, we synthesize the current understanding of (1) sources and fluxes of all major forcing agents, (2) the demonstrated or expected impact of global and local changes on each agent, and (3) the nature, extent, and drivers of anthropogenic change in the Basin. We highlight the large uncertainty in flux magnitude and responses, and their corresponding direct and indirect effects on the regional and global climate system. Despite uncertainty in their responses to change, we conclude that current warming from non-CO2 agents (especially CH4 and N2O) in the Amazon Basin largely offsets—and most likely exceeds—the climate service provided by atmospheric CO2 uptake. We also find that the majority of anthropogenic impacts act to increase the radiative forcing potential of the Basin. Given the large contribution of less-recognized agents (e.g., Amazonian trees alone emit ~3.5% of all global CH4), a continuing focus on a single metric (i.e., C uptake and storage) is incompatible with genuine efforts to understand and manage the biogeochemistry of climate in a rapidly changing Amazon Basin

Lipid‐enhanced Oilcane does not impact soil carbon dynamics compared with wild‐type Sugarcane

Abstract The carbon neutral potential of bioenergy relies in part on the ability of feedstocks to sequester carbon (C) in the soil. Sugarcane is one of the most widely used bioenergy crops, yet there remain unknowns about how it impacts soil C dynamics. In addition, Oilcane, a genetically modified version of Sugarcane has been produced to accumulate more energy‐dense oils and less soluble lignin, which enhances conversion efficiency but may also impact soil C cycling. Thus, our objectives were to examine the impact of Sugarcane litter decomposition on soil C formation and losses and determine if the genetic modifications to produce Oilcane alter these dynamics. To do this, we incubated bagasse (processed stem litter) and leaf litter from Sugarcane and Oilcane in microcosms with forest soil for 11 weeks. We used differences in natural abundance δ13C between C3 forest soil and C4 litter to trace the fate of the litter into respiratory losses as well as stable and unstable soil C pools. Our results show that genetic modifications to Oilcane did not substantially alter soil C dynamics. Sugarcane and Oilcane litter both led to net soil C gains dominated by an accumulation of the added litter as unstable, particulate organic C (POC). Oilcane litter led to small but significantly greater net soil C gains than Sugarcane litter due to greater POC formation, but the formation of stable, mineral associated organic matter (MAOC) did not differ between crop types. Sugarcane and Oilcane had opposing effects on tissue type where Sugarcane bagasse formed more MAOC, while Oilcane leaves preferentially remained as POC which may have important management implications. These results suggest that genetic modifications to Sugarcane will not significantly impact soil C dynamics; however, this may not be universal to other crops particularly if modifications lead to greater differences in litter chemistry

Low-Temperature UV Processing of Nanoporous SnO2 Layers for Dye-Sensitized Solar Cells

Connection of SnO2 particles by simple UV irradiation in air yielded cassiterite SnO2 porous films at low temperature. XPS, FTIR, and TGA-MS data revealed that the UV treatment has actually removed most of the organics present in the precursor SnO2 colloid and gave more hydroxylated materials than calcination at high temperature. As electrodes for dye-sensitized solar cells (DSCs), the N3-modified 1−5 μm thick SnO2 films showed excellent photovoltaic responses with overall power conversion efficiency reaching 2.27% under AM1.5G illumination (100 mW cm−2). These performances outperformed those of similar layers calcined at 450 °C mostly due to higher Voc and FF. These findings were rationalized in terms of slower recombination rates for the UV-processed films on the basis of dark current analysis, photovoltage decay, and electrical impedance spectroscopy studies