Doctor of Philosophy / Department of Agronomy / Clenton E. Owensby / Most rangelands are harvested at some point during the year and removal of plant leaf area and biomass alters a host of ecosystem processes including gas exchange. An experiment was conducted in 2005 and 2006 to study the effects of
clipping tallgrass prairie at different dates on water vapor and CO2 fluxes. A portable,
non-steady-state chamber was designed to measure CO2 and water vapor fluxes from
small plots in less than 40 s. A combination of sunlit and shaded readings allowed
measurements of net carbon exchange (NCE) and ecosystem respiration (RE); by summing NCE and RE, gross canopy photosynthesis (GCP) was calculated. Throughout the two-year study, the chamber had a minimal effect on microclimate, i.e.,
average chamber temperature increased 2.9° C, while chamber pressure increased
only 0.3 Pa during measurements, and photosynthetically active radiation attenuation was 10%. The immediate effect of all clipping treatments was a loss of leaf area that led to reductions in GCP, NCE, and RE and in most cases decreased water vapor flux. Further patterns of carbon flux were governed by the amount of water stress during
canopy development, while water vapor flux rates varied with water availability.
Canopies that developed during periods of low water stress quickly increased carbon
flux rates following precipitation after a mid-season drought. However, flux rates of
canopies, which developed during the mid-season drought, responded considerably
slower to subsequent water availability. A separate experiment was conducted from
June-October of 2006 to estimate GCP, leaf area index (LAI), and total aboveground
biomass with a hyperspectral radiometer. Indices such as the Normalized Difference
Vegetation Index and the Simple Ratio were used to estimate LAI and biomass had
poor correlations with measured values. However, GCP was significantly correlated to
all six indices derived in this study. While GCP measured from June-October was
significantly correlated with all indices, removal of the senesced canopy scans recorded
during October greatly increased the relationship.
| Identifer | oai:union.ndltd.org:KSU/oai:krex.k-state.edu:2097/342 |
| Date | January 1900 |
| Creators | Murphy, John Thomas |
| Publisher | Kansas State University |
| Source Sets | K-State Research Exchange |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
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