C distribution and utilization in blue grama as affected by temperature, water potential and defoliation regimes.

Water stress and temperature effects on growth, translocation and reallocation of C assimilated by blue grama (Bouteloua gracilis (H.B.K.) Lag. ex Steud.) were studied for sods extracted from shortgrass prairie. The sods were kept at either 24°/16° or 34°/16°C (day/nigh) temperatures and were labeled at two phenological stages. Three soil water potential (Ψ ) regimes of approximately 0 to -1, 0 to -15, and 0 to -30 bars were maintained by wetting and drying cycles. Reproductive plants retained more C in aboveground organs, used more assimilated C for respiration, and allocated a higher proportion of photosynthate to the labile fraction than did plants labeled at a vegetative stage. Low temperature and a Ψ of 0 to -30 bars resulted in greater C translocation to belowground organs, but a larger proportion of the C went into structural components. Sods stressed to-30 bars and maintained at higher temperatures had higher respiration losses of C. No significant differences in allocation and respiration uses of C were found among sods grown at field capacity and at 0 to-15 bars Ψ .During regrowth of clipped sods, more than 60% of the labile C in belowground organs was respired within four weeks. Higher respiration losses of labile C were found in severely water stressed sods that regrew under the higher temperature regime. Use of labile C for regrowth of new foliage was greatest for sods kept under conditions of high temperatures and optimum to moderate Ψ . Height growth and biomass increas of new foliage were significantly less for sods stresses to -30 bars. No significant differences in reallocation or respiration losses of C, growth, and biomass increases were observed for sods maintained at field capacity and 0 to -15 bars. These results suggested that physiological processes in blue grama were affected and could not recover fully when plants were subjected to severe water stress. However, upon relief of stress, those sods maintained at a moderate soil water stress level to 0 to -15 bars were capable of rapid recovery. Significance of these findings is discussed in the context of evolutionary success of blue grama in a semi-arid environment.