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Title: RADIATION USE EFFICIENCY AND LEAF CO2 EXCHANGE FOR DIVERSE C4 GRASSES

Author
item Kiniry, James
item Tischler, Charles
item VAN ESBROECK, G - NORTH CAROLINA STATE UNIV

Submitted to: Biomass and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Grass growth, in terms of dry material, can be described by leaf area growth, a function which describes how light is intercepted, and the efficiency of production of plant material per unit light intercepted. This last value is the radiation-use efficiency (RUE). The objective of this field study in Texas was to compare the RUE values and photosynthesis (CER) of four warm season grasses. Leaf area, dry mass, and CER were measured on several dates. Switchgrass had the greatest RUE whereas sideoats grama had the least. Big bluestem and eastern gamagrass values were intermediate. Differences among species for RUE were not consistent in CER measured on individual leaves. The CER values for sideoats grama were as great as those of switchgrass, whereas the RUE of sideoats grama was less than on-fourth as large. This discrepancy could not be accounted for by differences in partitioning to roots or by differences in production of soil carbon. When we stratified the leaf canopy of sideoats grama and switchgrass into 10 layers, and the CER of each was estimated, total canopy CER values were closely related to RUE values. Thus, total leaf area and canopy architecture appeared to be of greater importance to RUE than single leaf CER.

Technical Abstract: Grass biomass accumulation can be quantified by leaf area index (LAI) development, the Beer's Law light interception function, and radiation-use efficiency (RUE). The objective of this field study in Texas was to compare RUE values and leaf CO2 exchange rates (CER) of four C4 grasses. Biomass, LAI, and fraction of photosynthetically active radiation (PAR) intercepted were measured during three growing seasons. CER was measured on several dates. Switchgrass (Panicum virgatum L.) had the greatest RUE whereas sideoats grama [Bouteloua curtipendula (Michaux) Torrey] had the least. Big bluestem (Andropogon gerardii Vitman) and eastern gamagrass [Tripsacum dactyloides (L.) L.] values were intermediate. Differences among species for RUE were not consistent with CER differences. The CER values for sideoats grama were as great as those of switchgrass, whereas the RUE of sideoats grama was less than one-fourth as large. This discrepancy could not be accounted for by differences in partitioning to roots or by differences in production of soil carbon. The light extinction coefficients (k) of switchgrass were smaller than for sideoats grama, indicating that light was more effectively scattered over the leaf area of switchgrass. However, concurrent CER and incident PAR readings showed that the mean efficiency ratios of CER:PAR were not greater for switchgrass. When the leaf canopy of sideoats grama and switchgrass were each stratified into 10 layers, and the CER of each estimated, total canopy CER values were closely related to RUE values. Thus, total leaf area and canopy architecture appeared to be of greater importance to RUE than single leaf CER.