Development and deployment of a field-portable soil O2 and CO2 gas analyzer and sampler.

Here we present novel method development and instruction in the construction and use of Field Portable Gas Analyzers study of belowground aerobic respiration dynamics of deep soil systems. Our Field-Portable Gas Analysis (FPGA) platform has been developed at the Calhoun Critical Zone Observatory (CCZO) for the measurement and monitoring of soil O2 and CO2 in a variety of ecosystems around the world. The FPGA platform presented here is cost-effective, lightweight, compact, and reliable for monitoring dynamic soil gasses in-situ in the field. The FPGA platform integrates off-the-shelf components for non-dispersive infrared (NDIR) CO2 measurement and electro-chemical O2 measurement via flow-through soil gas analyses. More than 2000 soil gas measurements have been made to date using these devices over 4 years of observations. Measurement accuracy of FPGAs is consistently high as validated via conventional bench-top gas chromatography. Further, time series representations of paired CO2 and O2 measurement under hardwood forests at the CCZO demonstrate the ability to observe and track seasonal and climatic patterns belowground with this FPGA platform. Lastly, the ability to analyze the apparent respiratory quotient, the ratio of apparent CO2 accumulation divided by apparent O2 consumption relative to the aboveground atmosphere, indicates a high degree of nuanced analyses are made possible with tools like FPGAs. In sum, the accuracy and reliability of the FPGA platform for soil gas monitoring allows for low-cost temporally extensive and spatially expansive field studies of deep soil respiration.

Natural gas pipeline leaks across Washington, DC.

Pipeline safety in the United States has increased in recent decades, but incidents involving natural gas pipelines still cause an average of 17 fatalities and $133 M in property damage annually. Natural gas leaks are also the largest anthropogenic source of the greenhouse gas methane (CH4) in the U.S. To reduce pipeline leakage and increase consumer safety, we deployed a Picarro G2301 Cavity Ring-Down Spectrometer in a car, mapping 5893 natural gas leaks (2.5 to 88.6 ppm CH4) across 1500 road miles of Washington, DC. The δ(13)C-isotopic signatures of the methane (-38.2‰ ± 3.9‰ s.d.) and ethane (-36.5 ± 1.1 s.d.) and the CH4:C2H6 ratios (25.5 ± 8.9 s.d.) closely matched the pipeline gas (-39.0‰ and -36.2‰ for methane and ethane; 19.0 for CH4/C2H6). Emissions from four street leaks ranged from 9200 to 38,200 L CH4 day(-1) each, comparable to natural gas used by 1.7 to 7.0 homes, respectively. At 19 tested locations, 12 potentially explosive (Grade 1) methane concentrations of 50,000 to 500,000 ppm were detected in manholes. Financial incentives and targeted programs among companies, public utility commissions, and scientists to reduce leaks and replace old cast-iron pipes will improve consumer safety and air quality, save money, and lower greenhouse gas emissions.

Re-assessment of plant carbon dynamics at the Duke free-air CO(2) enrichment site: interactions of atmospheric [CO(2)] with nitrogen and water availability over stand development.

*The potential for elevated [CO(2)]-induced changes to plant carbon (C) storage, through modifications in plant production and allocation of C among plant pools, is an important source of uncertainty when predicting future forest function. Utilizing 10 yr of data from the Duke free-air CO(2) enrichment site, we evaluated the dynamics and distribution of plant C. *Discrepancy between heights measured for this study and previously calculated heights required revision of earlier allometrically based biomass determinations, resulting in higher (up to 50%) estimates of standing biomass and net primary productivity than previous assessments. *Generally, elevated [CO(2)] caused sustained increases in plant biomass production and in standing C, but did not affect the partitioning of C among plant biomass pools. Spatial variation in net primary productivity and its [CO(2)]-induced enhancement was controlled primarily by N availability, with the difference between precipitation and potential evapotranspiration explaining most interannual variability. Consequently, [CO(2)]-induced net primary productivity enhancement ranged from 22 to 30% in different plots and years. *Through quantifying the effects of nutrient and water availability on the forest productivity response to elevated [CO(2)], we show that net primary productivity enhancement by elevated [CO(2)] is not uniform, but rather highly dependent on the availability of other growth resources.

Increased belowground biomass and soil CO2 fluxes after a decade of carbon dioxide enrichment in a warm-temperate forest.

Atmospheric CO2 concentrations have risen 40% since the start of the industrial revolution. Beginning in 1996, the Duke Free-Air CO2 Enrichment experiment has exposed plots in a loblolly pine forest to an additional 200 microL/L CO2 compared to trees growing in ambient CO2. This paper presents new belowground data and a synthesis of results through 2008, including root biomass and nutrient concentrations, soil respiration rates, soil pore-space CO2 concentrations, and soil-solution chemistry to 2 m depth. On average in elevated CO2, fine-root biomass in the top 15 cm of soil increased by 24%, or 59 g/m2 (26 g/m2 C). Coarse-root biomass sampled in 2008 was twice as great in elevated CO2 and suggests a storage of approximately 20 g C x m(-2) x yr(-1). Root C and N concentrations were unchanged, suggesting greater belowground plant demand for N in high CO2. Soil respiration was significantly higher by 23% on average as assessed by instantaneous infrared gas analysis and 24-h integrated estimates. N fertilization decreased soil respiration and fine-root biomass by approximately 10-20% in both ambient and elevated CO2. In recent years, increases in root biomass and soil respiration grew stronger, averaging approximately 30% at high CO2. Peak changes for root biomass, soil respiration, and other variables typically occurred in midsummer and diminished in winter. Soil CO2 concentrations between 15 and 100 cm depths increased 36-60% in elevated CO2. Differences from 30 cm depth and below were still increasing after 10 years' exposure to elevated CO2, with soil CO2 concentrations >10000 microL/L higher at 70- and 100-cm depths, potentially influencing soil acidity and rates of weathering. Soil solution Ca2+ and total base cation concentrations were 140% and 176% greater, respectively, in elevated CO2 at 200 cm depth. Similar increases were observed for soil-solution conductivity and alkalinity at 200 cm in elevated CO2. Overall, the effect of elevated CO2 belowground shows no sign of diminishing after more than a decade of CO2 enrichment.

Coupling diurnal cytosolic Ca2+ oscillations to the CAS-IP3 pathway in Arabidopsis.

Various signaling pathways rely on changes in cytosolic calcium ion concentration ([Ca2+]i). In plants, resting [Ca2+]i oscillates diurnally. We show that in Arabidopsis thaliana, [Ca2+]i oscillations are synchronized to extracellular Ca2+ concentration ([Ca2+]o) oscillations largely through the Ca2+-sensing receptor CAS. CAS regulates concentrations of inositol 1,4,5-trisphosphate (IP3), which in turn directs release of Ca2+ from internal stores. The oscillating amplitudes of [Ca2+]o and [Ca2+]i are controlled by soil Ca2+ concentrations and transpiration rates. The phase and period of oscillations are likely determined by stomatal conductance. Thus, the internal concentration of Ca2+ in plant cells is constantly being actively revised.

Trading water for carbon with biological carbon sequestration.

Carbon sequestration strategies highlight tree plantations without considering their full environmental consequences. We combined field research, synthesis of more than 600 observations, and climate and economic modeling to document substantial losses in stream flow, and increased soil salinization and acidification, with afforestation. Plantations decreased stream flow by 227 millimeters per year globally (52%), with 13% of streams drying completely for at least 1 year. Regional modeling of U.S. plantation scenarios suggests that climate feedbacks are unlikely to offset such water losses and could exacerbate them. Plantations can help control groundwater recharge and upwelling but reduce stream flow and salinize and acidify some soils.

Nitric oxide represses the Arabidopsis floral transition.

The correct timing of flowering is essential for plants to maximize reproductive success and is controlled by environmental and endogenous signals. We report that nitric oxide (NO) repressed the floral transition in Arabidopsis thaliana. Plants treated with NO, as well as a mutant overproducing NO (nox1), flowered late, whereas a mutant producing less NO (nos1) flowered early. NO suppressed CONSTANS and GIGANTEA gene expression and enhanced FLOWERING LOCUS C expression, which indicated that NO regulates the photoperiod and autonomous pathways. Because NO is induced by environmental stimuli and constitutively produced, it may integrate both external and internal cues into the floral decision.