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Call number: LD2668 .T4 1961 P35

Typescript (photocopy). / Digitized by Kansas Correctional Industries

The analysis of the accumulating canopies of Dactvlis glornerata L., Festuca arundinacea Schreb., and Bromus inermis L. along with the regrowth potential under field conditions and under controlled environments (in light at three temperature regimes and in the dark at one temperature) for different stages of growth were studied. The analysis of the accumulating canopies showed that there was no difference among the grasses in CGR when averaging all weekly samplings. The non-structural carbohydrates in the stubble generally showed an inverse relation with the CGR. There were differences in total LAI among grasses when averaging the weekly cuts. The regrowth in the field after harvesting at different dates was found to be influenced by variation in temperature, LAI and soluble carbohydrates in the stubble, and change in the morphology of the accumulating canopies in late spring. The regrowths in 35/29 C, 26/21 C, and 18/31 C temperature were influenced by the LAI and carbohydrate content in the stubble, and by the change in the morphology of the grasses in late spring except in 35/29 C temperature regime the LAI in the stubble had only very little influence. The high temperature regime produced the least and the medium temperature regime the highest weight per tiller. The percent tiller regrowth was adversely affected by high temperature regime. In dark growth only a weak relationship existed between the soluble carbohydrates in the stubble and weight per tiller in regrowth. Better regrowth was observed when the accumulating canopies were cut prior to jointing than when cut later in all grasses. This suggests that utilizing forages prior to jointing will produce a good aftermath growth and persistence. The response of stubble LAI in cool environment to produce heavier tillers shows that frequent grazing can be made in early spring to obtain much needed forage in that period. This will keep the canopy short with high LAI in the stubble. The response in high temperature regime shows that stubble LAI had only little effect in producing heavier tillers in regrowth. Hence harvesting cool season forages at a time of low carbohydrate content, even with high LAI values in the stubble, is harmful to rapid regrowth when the temperature environments are high. / M.S.

Indiana University-Purdue University Indianapolis (IUPUI) / Carbon dioxide (CO2) level in the atmosphere has increased steadily since Pre-Industrial times. The need for a better understanding of the effects of elevated CO2 on plant physiology and growth is clear. Previous studies have focused on how plants are affected by either elevated CO2 or salinity, one of many environmental stresses for plants. However, little research has been focused on the interaction of these two factors. In my project, three common grass species were exposed to both elevated CO2 and salinity, so that the effects of either of these factors and the interaction of the two on these species could be examined. The CO2 levels were set to 400 µmol mol-1, close to the current concentration, or 760 µmol mol-1, projected to be reached by the end of this century. Salt solutions of 0, 25, 50, 75, and 100 mM NaCl with CaCl2 at lower rates (1% of each respective molarity for NaCl) were used to water the grasses, which are unlikely to experience prolonged exposure to salt conditions beyond this range in their natural habitats. The three common grass species studied in my experiment were Kentucky bluegrass (Poa pratensis L.) and red fescue (Festuca rubra L.), both C3 cool season grasses, as well as buffalo grass (Buchloe dactyloides (Nutt.) Engelm.), a C4 warm season grass. Each treatment had five replicates, bringing the total number of experimental pots to 150. Various growth parameters were monitored, and all data was statistically analyzed for statistical significance. My results showed that elevated CO2 had a stimulating effect on most growth parameters, particularly when plants were given more time to grow. In a 100-day growth experiment, CO2 affected the number and dry biomass of plants of all species, regardless of their C3 or C¬4 photosynthetic pathways. Salinity consistently inhibited germination and growth at all stages, from germination through plant emergences, numbers of established plants, and dry biomasses at harvest. Interactive effects of CO2 and salinity did occur, though often in seemingly specific instances rather than forming clear and consistent trends. My findings suggested that growth of common grasses would be enhanced by the rising level of CO2 in the atmosphere, but the effect would be modified by environmental stresses, such as salinity.