Progress 09/01/09 to 08/31/12
Outputs
OUTPUTS: Our research focused on the effects of earthworms on methane flux in temperate pastures and on the potential mechanisms involved. In November, 2009, we established 24 experimental plots each at Peckham Farm (PF), Kingston, and W. Alton Jones (WAJ), West Greenwich, both in southern Rhode Island. Three treatments (n=8) were implemented: (i) earthworms removed (D-), (ii) earthworms removed, counted and returned to the plot (D+), and (iii) undisturbed (U). Weekly methane flux measurements made from April to November, 2010. Soil moisture and temperature were continually recorded. Methane flux measurements were also made three times over a 24 hour period at each site to quantify diurnal patterns. We also designed and implemented a second experimental method that would determine an effect on methane flux by earthworms that did not disturb the soil. We determined methane flux in these supplemental plots at seven randomly selected locations in an area of the field adjacent to the manipulated plot experiment. Once gas sampling was completed, we sampled the soil under each chamber for pH, organic matter content, NH4 and NO3 concentrations, soil moisture, and soil temperature. Earthworms were counted, weighed and identified. We also examined the potential effects of earthworms on acetoclastic and hydrogenotrophic methanogenesis, and methane oxidation, using cast, burrow, and bulk soil from soils inoculated with anecic and epi-endogeic earthworms, the two most common earthworm ecological groups found at the research sites and a control soil. Soil from bulk, burrow or casts was transferred to microcosms with conditions manipulated to favor only one of the three processes - methane oxidation, hydrogenotrophic methanogenesis, or acetoclastic methanogenesis. Microcosms were periodically sampled for methane concentration in the headspace to determine process rates. PARTICIPANTS: Individuals: Jose Amador - Project Director Edward Avizinis - Master's Student janet Atoyan - Research Associate Andrew Giguere - Undergraduate Assistant Claire Staines - Undergraduate Assistant Training: 1 M.S. student 2 Undergraduate students TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Mean (s.d.) methane flux (ng CH4-C/m2/sec) in the undisturbed (U) treatment plots ranged from -97.9 to -20.1 at Peckham Farm (PF) & -42.1 to 1.7 at W. Alton Jones. CH4 flux in the earthworms removed (D-) treatment ranged from -95.4 to -13.7 at PF & -45.8 to -4.2 at WAJ. CH4 flux in the earthworms removed and returned (D+) treatment ranged from -73.4 to -14.4 at PF & -37.9 to -7.9 at WAJ. There were no overall significant differences in CH4 flux among treatments at PF. On 2 of 27 sampling dates, there was significantly higher CH4 consumption in D- than in D+ treatments. On 3 of 27 sampling dates the D- treatment had significantly lower CH4 consumption than the D+ treatment. By contrast, there was a significant overall difference in CH4 flux among treatments at WAJ, with no significant difference in earthworm population densities or biomass at the end of the experiment. Net CH4 consumption was significantly higher in D- than in D+ on 7 of 26 sampling dates. The results from WAJ support the hypothesis that plots with earthworms removed should have higher net CH4 consumption than plots with earthworms, whereas results from PF suggest no effect from earthworm removal on flux. Effects of earthworms on CH4 flux may be site-specific, contingent upon factors not quantified in this experiment. For the supplemental plots, mean (s.d.) CH4 flux (ng CH4-C/m2/sec) ranged from -79.8 to -17.3 at PF & -39.5 to -13.5 at WAJ. There was no relation between CH4 flux and earthworm population density or mass for either site. Using a backward-elimination stepwise multiple regression analysis we examined CH4 flux as a function of earthworm population parameters and soil properties. Results showed no relation between CH4 flux and any earthworm parameter for either site. Microcosm experiments yielded evidence for an effect of earthworms onCH4 dynamics. The anecic-cast treatment had a significantly lower CH4 oxidation rate than all other treatments in soil from both sites for 80% of the sampling events. All other treatments were similar to each other, with the exception of the epi-endogeic burrow soil at WAJ, which had a significantly higher methane oxidation rate than all other treatments at most sampling times. Anecic cast soil had significantly higher levels of NO3 and NH4 than all other treatments, suggesting an inhibitory effect on CH4 oxidation. There were no significant differences in rates of hydrogenotrophic methanogenesis among treatments at any time in soil from either site. There were no significant differences between rates of acetoclastic methanogenesis among treatments at any time in the PF soil. Acetoclastic methanogenesis rates ranged from 0 to 16.0 ug CH4-C/sec/g soil. There were significant differences in the rates of acetoclastic methanogenesis in WAJ soil.
Publications
- Avizinis, E.J., and J.A. Amador. 2012. Response of nitrous oxide flux to addition of anecic earthworms to an agricultural field. ISRN Soil Science (pending)
- Avizinis, E.J. 2012. The Indirect Effect of Earthworms on Methane Flux in Two Temperate Pasture Soils. M.S. Thesis, University of Rhode Island, Kingston, RI. 78 pages.
- Avizinis, E., A. Giguere, C. Staines, and J. A. Amador. 2011. Earthworm community composition in two managed pasture sites in southern Rhode Island. Abstracts of the Northeast Natural History Conference, Albany, NY.
- Avizinis, E. and J. A. Amador. 2010. Effect of earthworms on methane flux in temperate pastures. Abstracts of the ASA-CSA-SSSA International Annual Meetings, Long Beach, CA.
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Progress 09/01/10 to 08/31/11
Outputs
OUTPUTS: To gain a mechanistic understanding of the role of earthworms in CH4 flux dynamics in the field, we measured their effects on CH4 production (acetoclastic & hydrogenotrophic methanogenesis) and methane oxidation processes in microcosm experiments. To obtain soil appropriate for these measurements, we inoculated mesocosms containing soil from each of our two field sites with anecic earthworms, epi-endogeic earthworms, or no earthworms (control). After 90 d we removed samples of cast, burrow, and bulk soil (anecics), burrow and bulk soil (epi-endogeics) and bulk soil (control) and measured process rates. CH4 oxidation rate peaked at 62 h for Peckham Farm (PF) and 64 h for W. Alton Jones (WAJ) for all treatments. Peak rates (ug CH4-C/sec/g) ranged from 4.1 to 9.5 at PF and from 4.6 to 9.4 at WAJ. Anecic-cast soil had a significantly lower oxidation rate than all other treatments at both sites on 80% of the sampling events. All other treatments were similar to each other, with the exception of the epi-endogeic burrow soil which, at WAJ, had a significantly higher methane oxidation rate than all other treatments at all sampling times. NO3 and NH4 levels at the end of the experiment were similar for all treatments for soil from both sites, with the exception of the anecic casts, which had significantly higher levels of NO3 and NH4. Rates of hydrogenotrophic methanogenesis were highest at 68 h for PF soil and 71 h for WAJ. Maximum methanogenesis rates (ug C-CH4/g/sec) ranged from 0.64 to 2.35 (PF) and 0.63 to 3.14 (WAJ). There were no significant differences in rates of hydrogenotrophic methanogenesis among treatments at any time in the PF or WAJ soil, except at 71 h, when the epi-endogeic bulk soil had significantly higher rates than the epi-endogeic burrow soil, the anecic burrow soil, and the anecic cast soil. In the PF soil, NO3 (ug NO3-N/g) in anecic casts was 2,111 and 5,141 in WAJ, significantly higher than for all other treatments. Extractable NH4 (ug NH4-N/g) in the anecic cast soil were 35.0 in PF soil and 299 in WAJ soil, significantly higher than for all other treatments. Rates of acetoclastic methanogenesis in PF soil ranged from 0 to 16.0 ug CH4-C/sec/g, with no clear temporal trend in the rate of acetoclastic methanogenesis. There were no significant differences in rate of methanogenesis among treatments in PF soil on any sampling time. By contrast, there were significant differences in the rates of acetoclastic methanogenesis in WAJ soil at 115 h and 144 h. At 115 h, the epi-endogeic burrow treatment had significantly higher rates than the control, the epi-endogeic bulk treatment, the anecic burrow treatment, and the anecic cast treatment. At 144 h, the epi-endogeic burrow treatment had significantly higher rates of methanogenesis than the control, the epi-endogeic bulk treatment, and the anecic burrow treatment. No NO3 was detected in any treatment for either site. NH4 levels (ug NH4-N/g) in anecic casts were 188 in PF soil and 62 in WAJ soil, and were significantly higher for than all other treatments. PARTICIPANTS: Jose A. Amador, Principal Investigator Janet Atoyan, Research Associate Edward Avizinis, Graduate Student Andrew Giguere, Undergraduate Student TARGET AUDIENCES: Target audiences include other scientists and graduate and undergraduate students. Our efforts have been directed at (i) informing other scientists of the results of our work through presenting our work at the annual meeting of the Soil Science Society of America,(ii) including the results our our research in three courses taught by the PI: Introduction to Soil Science (100) students, Soil Microbiology (15 students) and Microbial Ecology of Soils and Sediments (7 students), and (iii) providing training opportunities for undergraduate (1 student) and graduate (1 student) students through active participation in the design and execution of the experiments and analysis and interpretation of the results. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Our results provide some insight into the mechanisms behind the differences observed previously in field experiments. On multiple days at both sites there was a significant effect of earthworms in the field, with a lower methane methane consumption (more negative flux). Measurement of methane oxidation rates in microcosms showed that anecic-cast treatments had significantly lower methane oxidation rates than all other treatments. Higher earthworm population densities, specifically anecic earthworms, would presumably have more earthworm casts, which may translate into lower methane oxidation rates and less methane consumption in soil. Anecic cast soil also had the highest levels of extractable NO3 and NH4, suggesting an inhibitory effect of elevated inorganic N on methane oxidation. Our results may also explain differences in CH4 flux between sites. Field flux data suggest that the presence of earthworms had a more consistent effect on CH4 flux at WAJ, resulting in less net CH4 consumption. Measurements of potential rates of acetoclastic methanogenesis showed that WAJ soil had higher rates of methanogenesis in the epi-endogeic burrow, anecic bulk, and anecic cast treatments, suggesting that earthworms may support an augmented response to anaerobic conditions through effects on acetoclastic methanogenesis.
Publications
- Avizinis, E., A. Giguere, C. Staines, and J. A. Amador. 2011. Earthworm community composition in two managed pasture sites in southern Rhode Island. Abstracts of the Northeast Natural History Conference, Albany, NY.
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Progress 09/01/09 to 08/31/10
Outputs
OUTPUTS: To examine the relationship between earthworms and methane flux in temperate pastures we established twenty-four experimental plots in November of 2009 at university-managed pastures in Kingston and West Greenwich, both in southern Rhode Island. Three different treatments (n=8) were implemented: (i) earthworms removed (D-), (ii) earthworms removed, counted and returned to plots (D+), and (iii) undisturbed (UN). We also determined earthworm population density and community composition at the end of the experiment. In addition to the established plots, we sampled from additional plots once per week alternating at each site, by inserting seven closed chamber gas containers into the soil at seven randomly selected locations from a predetermined area of the field adjacent to the area of the established experimental plot. To test the hypothesis that earthworms decrease net soil methane consumption in the established plots, we examined differences in methane flux between treatments using two-way repeated measures ANOVA with one factor being time and the second factor being treatment(UN, D+, and D-). Overall, there were no significant differences between treatments (P=0.4716) at the Kingston site. However, there were significant differences between treatments on particular dates. By contrast, we determined that there was an overall significant difference between treatments (P=0.0312) at the West Greenwich site. Furthermore, the difference was in support of our hypothesis. The results show that plots with earthworms (D+) had significantly less net methane consumption than plots without earthworms (D-) (P=0.0100). We also found that there is no significant difference between D+ and UN treatments (P=0.3123), suggesting that the disturbance of digging and hand sorting had no effect on methane flux. For the alternate plot flux comparisons, we used multiple linear regression stepwise with backward elimination (a=0.05 to eliminate) to test methane flux as the dependent variable against the independent variables - time, earthworm count and mass, ecological group, number of adult earthworms, number of juvenile earthworms, nitrate, ammonium, soil moisture and temperature, and pH - to determine the relationship between these variables and methane flux. In Kingston we determined that the only significant factors related to methane flux were ammonium (P=0.002), soil moisture (p<0.001), temperature (P=<0.001), and date of sample (P=0.010). There was no significant relation found for earthworm count (P=0.188), earthworm mass (p=0.068), nor any of the ecological groups. At West Greenwich we determined that the only significant factor related to methane flux was soil moisture (P=0.029). There was no significant relation found for earthworm count (p=0.542), earthworm mass (P=0.987), nor any of the ecological groups. At West Greenwich we determined that the only significant factor related to methane flux was soil moisture (P=0.029). There was no significant relation found for earthworm count (p=0.542), earthworm mass (P=0.987), nor any of the ecological groups. PARTICIPANTS: Jose A. Amador, Principal Investigator Janet Atoyan, Research Associate Edward Avizinis, Graduate Student Andrew Giguere, Undergraduate Student Claire Staines, Undergraduate student TARGET AUDIENCES: Target audiences include other scientists and graduate and undergraduate students. Our efforts have been directed at (i) informing other scientists of the results of our work through presenting our work at the annual meeting of the Soil Science Society of America,(ii) including the results our our research in two courses taught by the PI: Introduction to Soil Science (100 students) and Soil Microbiology (15 students), and (iii) providing training opportunities for undergraduate (2 students) and graduate (1 student) students through active participation in the design and execution of the experiments and analysis and interpretation of the results. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Our results do not support our hypothesis that earthworms will decrease net methane consumption in soil. We will continue to explore differences among sites and experimental designs to elucidate the extent to which earthworms may play a role in controlling the flux of methane from pasture soils.
Publications
- Avizinis, E., A. Giguere, and J. A. Amador. 2010. Effect of Earthworms On Methane Flux In Temperate Pastures. Abstracts of the 2010 Soil Science Society of America International Meeting, Long Beach, CA.
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