The rate of carbon turnover in soil is a balance between the input of carbon by plants through their roots and associated fungi and the loss of carbon due to plant and microbial respiration, oxidation and leaching. Soil carbon dynamics are notoriously difficult to measure, and being able to separate total soil respiration into its autotrophic and heterotrophic components would help understanding of carbon cycling processes. Where autotrophic respiration originates from roots and their associated mycorrhizal fungi, using newly fixed carbon, and heterotrophic respiration originates from the breakdown of older soil organic matter. By calculating the δ¹³C signature of respired CO₂ (the ratio of the abundances of C isotopes ¹²C and ¹³C) it is possible to determine whether it is of heterotrophic or autotrophic origin. In this study a 6 chamber, constant CO₂ concentration measuring apparatus was developed to determine both the rate of CO₂ efflux and to collect undisturbed CO₂ samples for isotope analysis. This apparatus was tested using live soil samples with different δ¹³C values (-22 ‰ to -27 ‰) and respiration rates (2 – 8 µmol m⁻² s⁻¹) obtained from various locations in New Zealand. Testing involved taking samples using the respiration apparatus, then incubating the same samples in a bag, and then comparing the two. There was no difference between the results from the soil respiration apparatus and the bags (R²=0.96, p=0.0002). Twelve microcosms including soil and grass were extracted from a newly converted dairy farm and placed into in growth cabinets. Diurnal courses of partitioned soil respiration were made over 24 hours with constant soil temperature to eliminate temperatures effect on soil respiration. Half were then covered with 90% shade cloth for 12 days to test if a reduction in light (and therefore newly fixed carbon) would have any effect on soil respiration. There was a significant reduction in soil respiration, yet no detectable change in the δ¹³C of soil respired CO₂ under heavily shaded treatment. There was however there was a shift towards heterotrophic dominated respiration. This shows that while L. perenne is resilient to surrounding conditions it is susceptible to change if exposed to different conditions for prolonged periods of time. The use of this new technique in the field will allow improved understanding of factors effecting soil C efflux.

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Conversion of native forests to turfgrass-dominated residential landscapes under a wide range of management practices results in dramatic changes to vegetation and soils, which may affect soil carbon storage. To better understand the effects of landscape conversion and management on soil carbon, we conducted a study on residential properties in the Valley and Ridge physiographic province of southwest Virginia to compare soil carbon storage and dynamics between turfgrass landscapes and the surrounding mixed oak forests from which they were developed. Sixty-four residential properties ranging from 5 to 52 years since site development were investigated. Soil samples were collected from lawns and adjacent forest stands to a depth of 30 cm and analyzed for carbon and nitrogen content. Additional measurements taken were soil bulk density, temperature, moisture, and total soil CO₂ efflux rate. Homeowners participating in the study completed a survey on their lawn management practices so that the effects of specific practices (e.g. fertilization) and intensity levels on carbon dynamics could be analyzed. Also included in the survey were 11 questions regarding the homeowners' commitment to the environment. Homeowners were assigned an environmental commitment score based on their responses which was compared with lawn management practices in order to identify any connection between environmental attitude and lawn management practices. Total soil carbon content to 30 cm depth of lawn (6.5 kg C/m²) and forest (7.1 kg C/m²) marginally differed (P=0.08); however, lawn soil contained significantly greater C than forest soil at the 20-30 cm depth (0.010 vs. 0.007 g C/cm³, P=.0137). There was a weak negative relationship between carbon in the lawn and time since development at the 20-30 cm depth (P=0.08), but no significant relationship between time and C content at shallower depths. We found a positive relationship between time since development and percent C of lawn at the 0-5 cm depth (P=0.04), whereas there was a negative relationship with percent C and time at the 20-30 cm depth (P=0.03). Based on the homeowner survey, we found a positive correlation between lawn fertilization frequency and both lawn nitrogen content (P=.07) and lawn carbon content (P=.0005) in the top 0-5 cm of soil. Nitrogen content was greater in lawn than forest soil at the 0-5 cm depth (0.0025 vs. 0.0018 g/cm³³, P<.0001) and the 5-10 cm depth (0.0013 vs. 0.0009 g/cm³, P <.0001). There was a positive relationship (P=0.059) between overall environmental commitment score and level of management intensity. Higher environmental commitment (EC) score corresponded with a higher level of management intensity (fertilizer and pesticide use). Our results indicate that converting unmanaged Appalachian hardwood forest into managed, turf-grass dominated residential homesites results in similar soil organic concentration and depth distribution as the previous forest within a short period of time following development. Although total soil carbon does not differ between lawn and forest, lawn may develop greater density at 20-30cm depth over time. Fertilization enhances carbon and nitrogen content in the upper 0-5cm in lawns. Homeowners who feel that they are more strongly committed to the environment are more likely to apply higher levels of fertilizer to their lawn. / Master of Science