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Biogeochemistry
Vol. 122 (1), 2015, Pages: 47-59

A larger investment into exudation by competitive versus conservative plants is connected to more coupled plant–microbe N cycling

Eva Kaštovská, Keith Edwards, Tomáš Picek, Hana Šantrucková

Department of Ecosystem Biology, Faculty of Science, University of South Bohemia, Branišovská 31, 370 05, České Budějovice, Czech Republic.

Abstract

Plant–microbe interactions actively control nitrogen (N) cycling in the ecosystem. We hypothesize that the investment into exudation and the coupling of plant–microbe N cycling will be larger in competitive plants compared to the more conservative species. Root exudation of competitive (Glyceria maxima) and conservative (Carex acuta) plants was estimated by 13C-CO2 labeling. Seasonal changes in plant, microbial, and soil soluble N pools as well as potential net microbial N transformations were determined to interconnect the C and N cycling within grassland ecosystems dominated by these species. We showed that competitive Glyceria, as compared to conservative Carex, appears to affect soil N cycling through a more direct temporal and spatial influence on soil microbes due to a larger investment into root exudation. This makes the system highly dynamic, with faster soil N cycling and pronounced seasonal N redistribution between plants and microbes. The conservative Carex, irrespective of its larger root system, invested less C to exudation. In this case, the plant–microbe relationships appear to be less-coupled in time and space with the plant N supply likely relying mainly on the relatively slow microbial mineralization of organic matter than on rhizosphere priming effect. We showed that differences in soil N cycling associated with competitive versus conservative plants are closely connected with their different investments into root exudation, which govern the coupling of plant–microbe interactions in time and space.

Keywords: Plant growth strategy, Exudation, Grassland, Labile N, Microbial biomass, The plant–microbe interaction.


 
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