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Title: Plant nitrogen acquisition and interactions under elevated CO2- impact of endophytes and mycorrhizae

item CHEN, XIN
item TU, CONG
item Burkey, Kent

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2006
Publication Date: 5/1/2007
Citation: Chen, X., Tu, C., Burton, M., Watson, D., Burkey, K.O., Hu, S. 2007. Plant nitrogen acquisition and interactions under elevated CO2- impact of endophytes and mycorrhizae. Global Change Biology. 13:1238-1249.

Interpretive Summary: Rising atmospheric carbon dioxide has the potential to impact ecosystems by altering competition between plant species. In this study, competition between a grass (endophyte-free fescue) and a forb (plantago) was assessed in controlled environments under ambient and elevated carbon dioxide. While plant biomass increased for both species under elevated carbon dioxide, the relative increase was much greater for plantago than for fescue when the two species were grown in competitive mixtures. The greater performance of plantago relative to fescue was associated with colonization of plantago roots by mycorrhizal fungi leading to increased nitrogen up take from the soil. The results suggest that elevated carbon dioxide predicted under future climate scenarios will stimulate beneficial fungi and associated nutrient acquisition leading to enhanced competitive ability of plants that form symbiotic associations with these microorganisms.

Technical Abstract: Atmospheric CO2 enrichment generally stimulates plant photosynthetic activity and enhances C allocation for plant symbionts such as mycorrhizae. This in turn may modify plant species interactions through differentially impacting plant nutrient acquisition. However, direct evidence illustrating this scenario is still limited. We examined how elevated CO2 affects plant growth and whether mycorrhizae mediate interactions between a non-mycorrhizal plant, endophyte-free Festuca arundinacea Schreb. and a highly mycorrhizal forb, Plantago lanceolata L. in a microcosm experiment. Festuca arundinacea Schreb, Plantago lanceolata L., and their combination with or without mycorrhizal inoculation were grown at ambient (400 'mol mol-1) and elevated CO2 (ambient + 330 'mol mol-1) levels. The 15N isotope tracer was introduced to quantify the mycorrhizally mediated N acquisition of plants. Elevated CO2 stimulated the growth of P. lanceolata more significantly than F. arundinacea, increasing the shoot biomass ratio of P. lanceolata to F. arundinacea in the mixture. It also increased mycorrhizal colonization of P. lanceolata roots, but did not show any effects on F. arundinacea. Mycorrhizae increased the shoot biomass ratio of P. lanceolata to F. arundinacea under both CO2 concentrations with a more profound impact found under the elevated than ambient CO2 level. Elevated CO2 and mycorrhizae enhanced 15N and total N uptake of P. lanceolata in both monoculture and mixture but had either no or even negative effects on N acquisition of F. arundinacea, altering N distribution between these two species in the mixture. These results suggest that CO2-stimulation of mycorrhizae and their nutrient acquisition may enhance the competitive ability of mycorrhizal species over fescue plants under future CO2 scenarios.