Green Needlegrass and Blue Grama in Controlled Environments

Green needlegrass [St@ viridula Trin. ] and blue grama [Boutelouu gracilis (H.B.K.) Lag. ] possess the Ca and Cd photosynthetic pathways, respectively. Objectives of this study were to compare growth analysis traits of green needlegrass and blue grama and to determine the effects of 2 temperature regimes on seedling growth characteristics of both species. Seedlings of 2 accessions each of green needlegrass and blue grama were grown in growth chambers under 200 C day-150 C night (20-15’ C) and 25” C day-200 C night (25-200 C) temperature regimes (with a 15hr photoperiod). Beginning 2 weeks after planting, seedlings were harvested twice a week for 3 weeks. Growth analysis traits were calculated with data obtained from each harvest using exponential regression equations. Net assimilation rates of blue grama were higher than those of green needlegrass at both temperatures. Seedling growth of blue grama was more rapid at 25-20” than at 20-15’ C, while seedling growth of green needlegrass did not differ between temperatures. Blue grama seedlings exhibited higher relative growth rates than green needlegrass seedlings at 25-200 C but not at 20-15’ C. Green needlegrass accessions differed for relative growth rates at 2520” C, which indicated the possibility of selecting for rapid seedling growth. Authors arc former graduate research assistant, Department of Range Science. Colorado State University, Fort Collins; now assistant professor, College of Agriculture. Texas A&l University, Kingsville. Texas 78363; plant physiologis! , USDA-ARS. Crop Research Laboratory, Fort Collins (deceased): and assoaate professor. Department of Range Science. Colorado State University. Fort Collins 80523. Research was supported in part by the U.S. Department of Energy under Contract No. DE-AS02-76EV04018. Manuscript accepted October 29. 1984. Seedling Growth Amount of leaf area present and net assimilation rate (NAR) govern the rate of seedling growth. Growth analysis provides a means of determining the relative importance of leaf area and net assimilation rate in seedling growth rates (Patterson et al. 1978). Potter and Jones (1977) found plant growth to be more closely correlated with leaf area partitioning coefficient (LAP) than with NAR. LAP indicates that extent of partitioning of daily assimilation into new leaf area. Relative leaf area expansion rate (K.) is the product of NAR and LAP. Various investigators have reported high correlations between relative leaf area expansion rates and growth (Potter and Jones 1977, Patterson et al. 1978, Townsend and Wilson 1981). Green needlegrass (Stipa viridulu Trin.) possesses the Cs photosynthetic pathway (Wailer and Lewis 1979). Blue grama [Boufelouagrucilis (H.B.K.) Lag. ], a common associate of green needlegrass throughout much of its range, possesses the Cd pathway. Growth rates of blue grama and green needlegrass would be expected to differ because of the physiological dissimilarities between the 2 species. Objectives of this study were to use growth analysis traits to (I) explain differences in seedling growth rates between blue grama and green needlegrass and (2) determine the influence of temperature on seedling growth of each species. Growth analysis can be used in screening plant materials for traits that enhance seedling vigor (Townsend and Wilson 1978,198l). A third objective of the study was to determine the influence of accession on seedling growth of each species. 410 JOURNAL OF RANGE MANAGEMENT 38(5), September 1985 Materials and Methods Seeds of Lodorm and accession SD-93 green needlegrass were obtained from the USDA Soil Conservation Service Plant Materials Center at Bismarck, N. Dak. Lodorm is a variety of green needlegrass with reduced seed dormancy (Larson and Carter 1970). Blue grama accessions were PM-K-1482 and PM-K-1483. Accession PM-K-1482 is a synthetic blend of 6 blue grama accessions that originated in Nebraska and northern Kansas. Accession PM-K-1483 is a synthetic blend of 12 blue grama accessions from southern Kansas and northwestern Texas. Table 1. Definitions and units of measurement of traits wed to describe seedling growth of 2 accessions each of green needlegrass and blue grenu. Trait Definition2 Units Net assimilation rate (NAR)J Leaf area partitioning coefficient (LAP)’ Seeds were planted in plastic pots (15 cm diameter by 15 cm deep) filled with autoclaved sandy loam soil. Thirty seeds were placed in each pot and covered with 2 mm of soil. Soil in each pot was watered to approximately field capacity. Seeds were then covered with a 2cm layer of dry soil. Relative leaf area expansion rate (K.) Relative growth rate (K,) The experiment was conducted in 2 sequential phases: (1) a 14day emergence and initial seedling growth phase and (2) a 2 Iday temperature treatment phase. In the first phase pots were placed in a growth chamber at a 20-15°C temperature regime with a 1%hr photoperiod. Photosynthetic photon flux density (PPFD) was 400 PE Mm2 s-l. Pots were subirrigated to retain the dry surface layer of soil. Soil below the dry layer was maintained at about field capacity. Relative rate of shoot development (KS) dW/dt