While increases in atmospheric CO2 and temperature are becoming more clearly documented, interactive effects of these global change factors on plant nitrogen (N) availability and use is uncertain. Understanding these effects is important for determining future shifts in plant community structure and ecosystem function, as N-limitation is often a major constraint on ecosystem response to global change. Among the forms of N available to plants, relatively little is known about how global change is likely to impact sources of soil amino acids and uptake by plants. This study documents effects of elevated CO2 and warming on pools of amino acids present in soils in a semiarid mixed-grass prairie of North America and the potential for dominant native (Artemesia frigida and Bouteloua gracilis) and invasive (Linaria dalmatica) plants to acquire these dominant pools via growth chamber hydroponic culture experiments. Plant utilization of amino acids by dominant plant species was characterized by HPLC analysis and stable- and radio- isotope tracer methods.
Results/Conclusions
In contrast to patterns of soil amino acid pools observed in other ecosystem types, the dominant amino acids present in the mixed-grass prairie soil included alanine and phenylalanine rather than glycine. Although effects of warming on amino acid pools were inconclusive, elevated CO2 resulted in increased levels of these dominant amino acid pools. In a separate experiment, rapid uptake of alanine and phenylalanine from hydroponic solution was observed in A. frigida, B. gracilis and L. dalmatica in as early as 30 min after feeding. Isotopically labeled alanine added to hydroponic solution revealed species-specific allocation patterns in shoot tissue after 3 hrs. Our results suggest that shifts in organic nitrogen pools are likely to occur with climate warming and rising atmospheric [CO2] in the semiarid mixed-grass prairie. Further, several dominant and important plant taxa in this system have the capacity to take up amino acids from the rhizosphere. Flexibility and interspecific differences in the sources of N acquired by grassland plants, particularly the capacity to take up organic in addition to inorganic sources of N will have important ramifications for how grassland ecosystems respond to global change.
