Allelopathy Among Prairie Grasses and its Possible Ecological Significance

The phytotoxic effect of four kinds of litter and three kindsof fresh material extracts of blue grama and western wheatgrasson seed germination of blue grama, western wheatgrass and buffalograss was tested. The four kinds of litter were collected fromthe Ecosystem Stress Area at the native shortgrass prairie site.These included litter from control, fertilized, irrigated, andfertilized plus irrigated plots. The three kinds of fresh materialswere harvested from blue grama and western wheatgrass growingunder growth chamber conditions at three distinct phenologicalstages. Results indicated that the fresh material extracts weremore phytotoxic than the litter extracts and among the formerthe fresh material harvested at the earlier phenological stagewas more phytotoxic than those collected at the advanced phenologicalstage. Chemical composition of litter and fresh material indicatedthat the fresh materials contained comparatively more phenolicsubstances than that of litter materials.     

Standing State and Cycling of Nitrogen in Soil-vegetation Components of Prairie Ecosystems

In the present paper, distribution of nitrogen in differentplant compartments and in the top 20 cm soil from three grasslandsites for a 3-year period at the time of peak standing crophas been studied. The sites represent short-grass, mixed-grass,and tall-grass prairies located, respectively, in Colorado,South Dakota, and Oklahoma. Partitioning, uptake, transfers,and release of nitrogen in the above-ground and below-groundcompartments were evaluated with respect to the abiotic factors.A positive linear relationship was found with the total nitrogencontent in shoots (g m^–2) and the annual precipitationas well as with the annual actual evapotranspiration. On theother hand, a negative linear relationship was found with thenitrogen per gram dry weight in shoots, and the annual precipitationand evapotranspiration. Inter-seasonal and inter-site variationsin the nitrogen content (g m^–2) in different plant compartmentsindicated significant differences. The short-grass and mixed-grassprairies indicated greater nitrogen content in the above-groundand below-ground plant tissues as compared to the tall-grassprairie. However the total nitrogen content in shoots from thetall-grass prairie was greater than that of short-grass or mixed-grassprairies which was mainly due to greater shoot biomass in thetall-grass prairie. The major portion of nitrogen (over 90 percent) in the system was retained in the soil while a fractionof nitrogen (4–8 per cent) resided in the biological material.The distribution of nitrogen in different plant compartments,the uptake, transfer, and release of nitrogen with respect toabiotic factors have been discussed in detail.     

The Influence of Stress Conditions on Chlorophyll Content of Two Range Grasses with Contrasting Photosynthetic Pathways

The influence of various treatments and temperature regimeson total chlorophylls and on the chlorophyll a:b ratio of westernwheatgrass and blue grama plants was investigated at differenttime intervals during the 120-day growth period. Western wheatgrass,a C₃ species, accumulated greater amounts of chlorophyll thandid blue grama plants, a C₄ species. Maximum concentrations(mg gd wt^–1) of chlorophylls in western wheatgrass andin blue grama were recorded at the lower (13/7°C) and higher(30/18°C) temperature regimes. Nitrogen fertilizer alonedecreased the chlorophyll content in both species. The chlorophylla:b ratio in blue grama ranged from an average of 2·00under irrigated plus fertilized conditions to 3·00 undercontrol and fertilized conditions. On the other hand, the chlorophylla:b ratio in western wheatgrass remained constant at 3·00throughout the growing season under various treatments and temperatureregimes.