Yield responses of invasive grasses to carbon doses Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/nv935562m

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  • The sagebrush steppe ecosystem of the northern Great Basin is severely degraded and continues to decline due in large part to the invasive, non-native annual grasses Bromus tectorum L. (cheatgrass) and Taeniatherum caput-medusae (L.) Nevski (medusahead). Restoration of invasive-dominated areas is difficult, but can be enhanced by adding a carbon source, which stimulates microbes to immobilize soil inorganic N and reduces yields of fast-growing ruderal plants. How much carbon is needed to induce this effect is uncertain, so our research objectives were to establish a response to increasing carbon doses and calculate the lowest dose where a significant response was observed for 1) biomass, density, and seed production of cheatgrass and medusahead; 2) soil microbial biomass C and N; and 3) inorganic soil N. In November 2005 we applied 12 carbon doses ranging from 0 to 2400 kg C/ha as sucrose to plots planted with cheatgrass and medusahead at two sites in the northern Great Basin. We measured aboveground plant biomass when plants matured in June and July 2006 and microbial biomass in November 2005, March 2006, and July 2006. Inorganic soil N was measured using mixed-bed resin capsules placed in situ for the duration of the study. For an increase in carbon dose of 100 kg C/ha, back-transformed mean medusahead biomass (g/m²) at one site decreased 6.8%. This was the only significant response to carbon doses for both target species across both sites. In addition to cheatgrass and medusahead, other ruderal plants established in our plots, and the biomass of this entire ruderal community decreased approximately 6% for an increase in carbon dose of 100 kg C/ha at both sites. Microbial biomass C increased 2-4 mg/kg for an increase in carbon of 100 kg C/ha at the two earliest sampling dates at both sites, while microbial biomass N increased at only one site at the earliest sampling date, and this increase was 0.3 mg/kg for an increase in carbon of 100 kg C/ha. Soil NO3₃⁻-N decreased at both sites with increasing carbon. For a significant reduction in ruderal biomass, we calculated lowest significant doses of 240-640 kg C/ha, but it remains to be determined if this reduction is sufficient to facilitate establishment of native perennials in northern Great Basin restoration projects.
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