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We examined plant community responses to interactions between arbuscular mycorrhizal (AM) fungi and availability of atmospheric CO2 and soil N. Communities of 14 plant species were grown in mesocosms containing living or killed AM fungal inoculum, ambient or elevated atmospheric CO2 and low or enriched soil N. After one growing season, significantly different plant communities existed in the different treatments. Plant species richness was lowest in +N mesocosms and highest in +AM + CO2 mesocosms. At ambient CO2, AM fungi reduced richness but at elevated CO2 they increased it. This was caused by changes in mortality rates of several C3 forbs and may suggest that CO2 enrichment ameliorates the carbon cost of some...
In order to better elucidate fixed-C partitioning, nutrient acquisition and water relations of prairie grasses under elevated [CO2], we grew the C4 grass Bouteloua gracilis (H.B.K.) lag ex Steud. from seed in soil-packed, column-lysimeters in two growth chambers maintained at current ambient [CO2] (350 ?L L?1) and twice enriched [CO2] (700 ?L L?1). Once established, plants were deficit irrigated; growth chamber conditions were maintained at day/night temperatures of 25/16�C, relative humidities of 35%/90% and a 14-hour photoperiod to simulate summer conditions on the shortgrass steppe in eastern Colorado. After 11 weeks of growth, plants grown under CO2 enrichment had produced 35% and 65% greater total and root...
Ecosystem water-use efficiency (EWUE) is an indicator of carbon-water interactions and is defined as the ratio of carbon assimilation (GPP) to evapotranspiration (ET). Previous research suggests an increasing long-term trend in annual EWUE over many regions, and is largely attributed to the physiological effects of rising CO2. The seasonal trends in EWUE, however, have not yet been analyzed. In this study, we investigate seasonal EWUE trends and responses to various drivers during 1982-2008. The seasonal cycle for two variants of EWUE, water-use efficiency (WUE, GPP/ET) and transpiration-based WUE (WUEt, the ratio of GPP and transpiration), is analyzed from 0.5° gridded fields from four process-based models and...
Plants of four Great Basin grass species were grown from seed in two greenhouses at low (340 ? l l-1) and high (680 ? l l-1) CO2 concentration. In all four species, high CO2 promoted mean increases in the number of basal stems, leaf area, specific leaf weight and above-ground dry weight. High CO2 resulted in an increase in CO2 assimilation in two C3 grasses but not in a C4 grass, while all three species showed decreases in stomatal conductance. Mean increases of 60% in aboveground dry weight and 80% in water-use-efficiency are consistent with previously reported high CO2 effects on grasses. No consistent differential effects of high CO2 were observed when comparing annual vs perennial species. Global CO2 enrichment...
Ecosystem water-use efficiency (EWUE) is an indicator of carbon-water interactions and is defined as the ratio of carbon assimilation (GPP) to evapotranspiration (ET). Previous research suggests an increasing long-term trend in annual EWUE over many regions, and is largely attributed to the physiological effects of rising CO2. The seasonal trends in EWUE, however, have not yet been analyzed. In this study, we investigate seasonal EWUE trends and responses to various drivers during 1982-2008. The seasonal cycle for two variants of EWUE, water-use efficiency (WUE, GPP/ET) and transpiration-based WUE (WUEt, the ratio of GPP and transpiration), is analyzed from 0.5° gridded fields from four process-based models and...