Plant nitrogen acquisition and interactions under elevated carbon dioxide: impact of endophytes and mycorrhizae

Abstract

Both endophytic and mycorrhizal fungi interact with plants to form symbiosis in which the fungal partners rely on, and sometimes compete for, carbon (C) sources from their hosts. Changes in photosynthesis in host plants caused by atmospheric carbon dioxide (CO 2 ) enrichment may, therefore, influence those mutualistic interactions, potentially modifying plant nutrient acquisition and interactions with other coexisting plant species. However, few studies have so far examined the interactive controls of endophytes and mycorrhizae over plant responses to atmospheric CO 2 enrichment. Using Festuca arundinacea Schreb and Plantago lanceolata L. as model plants, we examined the effects of elevated CO 2 on mycorrhizae and endophyte (Neotyphodium coenophialum) and plant nitrogen (N) acquisition in two microcosm experiments, and determined whether and how mycorrhizae and endophytes mediate interactions between their host plant species. Endophyte-free and endophyte-infected F. arundinacea varieties, P. lanceolata L., and their combination with or without mycorrhizal inocula were grown under ambient (400 lmol mol À1 ) and elevated CO 2 (ambient 1 330 lmol mol À1 ). A 15 N isotope tracer was used to quantify the mycorrhiza-mediated plant acquisition of N from soil. Elevated CO 2 stimulated the growth of P. lanceolata greater than F. arundinacea, increasing the shoot biomass ratio of P. lanceolata to F. arundinacea in all the mixtures. Elevated CO 2 also increased mycorrhizal root colonization of P. lanceolata, but had no impact on that of F. arundinacea. Mycorrhizae increased the shoot biomass ratio of P. lanceolata to F. arundinacea under elevated CO 2 . In the absence of endophytes, both elevated CO 2 and mycorrhizae enhanced 15 N and total N uptake of P. lanceolata but had either no or even negative effects on N acquisition of F. arundinacea, altering N distribution between these two species in the mixture. The presence of endophytes in F. arundinacea, however, reduced the CO 2 effect on N acquisition in P. lanceolata, although it did not affect growth responses of their host plants to elevated CO 2 . These results suggest that mycorrhizal fungi and endophytes might interactively affect the responses of their host plants and their coexisting species to elevated CO 2 .

Arbuscular mycorrhiza improve growth, nitrogen uptake, and nitrogen use efficiency in wheat grown under elevated CO2

“…AM fungal colonization significantly improved N accumulation regardless CO 2 concentrations, and the greater 15 N recovery rate in the AM plants grown under elevated CO 2 further indicated the enhanced N uptake by those plants. Similar to these findings, enhanced N accumulation and uptake under elevated CO 2 concentration has been reported in AM plants of Trifolium repens (Gamper et al 2005), P. lanceolata (Chen et al 2007), Avena fatua (Cheng et al 2012), and in newly established grassland communities (Zavalloni et al 2012). The higher biomass and hence greater N demand of AM plants grown under CO 2 enrichment may partly explain the increased N accumulation.…”

“…However, the mechanisms underlying this phenomenon remain unknown. These and previous observations suggest that AM fungal mediated plant N uptake and partitioning is a complicated process and merits further investigations (Chen et al 2007;Cavagnaro et al 2011).…”

“…The higher biomass and hence greater N demand of AM plants grown under CO 2 enrichment may partly explain the increased N accumulation. However, a negative or no AM colonization effect on plant N uptake under elevated CO 2 has also been reported (Chen et al 2007). Furthermore, it was found that R. irregularis inoculation increased N partitioning into wheat roots.…”

“…Evidence indicates that AM fungi have a potential to improve plant N acquisition at elevated CO 2 (Gamper et al 2005;Cavagnaro et al 2007;Cheng et al 2012). Chen et al (2007) reported that AM fungal inoculation effects on plant N uptake at high CO 2 concentration were species-specific, with enhancing N acquisition in Plantago lanceolata L. but not in Festuca arundinacea Schreb. To date, however, the efficiency of the acquired N for C accumulation as well as its partitioning in different organs in wheat plants as influenced by AM fungal colonization under elevated CO 2 has not been investigated.…”

Positive association between mycorrhiza and foliar endophytes in Poa bonariensis, a native grass

“…Furthermore, Chen et al (2007) have suggested that endophytes may not affect mycorrhizal colonisation directly.…”