Arbuscular mycorrhizal fungal communities associated with two dominant species differ in their responses to long‐term nitrogen addition in temperate grasslands

Abstract

Arbuscular mycorrhizal (AM) fungi are important components of grassland ecosystems and are sensitive to enhanced atmospheric nitrogen (N) deposition. Enhanced N deposition has been widely reported to reduce species richness and alter species composition across different types of grasslands world‐wide. Despite extensive studies on effects of N deposition on AM fungal communities of grasslands, few studies have specifically focused on effects of N deposition on AM fungi associated with dominant species in grasslands. We investigated long‐term (12‐year) effects of N addition (80 kg ha−1 year−1) on AM fungal community richness in roots and rhizosphere biomass of two dominant plant species (forb Artemisia frigida and grass Stipa krylovii) in temperate steppes of northern China. We found that AM fungi associated with the two dominant plant species differed in their responses to N addition. Nitrogen addition led to a significant reduction in AM fungal richness colonized in roots, and biomass in the rhizosphere of A. frigida, while N addition had little impacts on AM fungi colonized in roots and rhizosphere of S. krylovii. Nitrogen addition significantly reduced AM fungal colonization in roots and AM fungal spore density in the rhizosphere soils of A. frigida. In contrast, N addition had no effect on AM fungal colonization in roots and spore density in the rhizosphere of S. krylovii. Nitrogen addition markedly suppressed photosynthetic rates in A. frigida due to excessive foliar accumulation of manganese. The N‐induced reduction in photosynthetic rates reduced allocation of C into roots in A. frigida, leading to a lower root/shoot ratio, and suppression of AM fungal community associated with A. frigida. The inhibition of AM fungi would render A. frigida less competitive in terms of acquisition of mineral nutrients in soils, thus contributing to its loss in the steppe community under conditions of elevated N deposition. These findings provide a mechanistic explanation for N‐evoked differential responses of AM fungal communities associated with A. frigida and S. krylovii by linking soil properties and host plants to AM fungal communities. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13081/suppinfo is available for this article.

Global negative effects of nutrient enrichment on arbuscular mycorrhizal fungi, plant diversity and ecosystem multifunctionality

“…Limitation of C supply to the AMF may intensify the competition among species (Johnson et al ., 2015). This, in turn, may lead to a loss of some fungal species and promote the dominance of certain AMF species (Johnson, 1993; Dumbrell et al ., 2010; Johnson, 2010; Johnson et al ., 2015; Zheng et al ., 2018). Second, nutrient addition affects mycorrhizal–plant trading partnerships, which are based upon the exchange of host plant C for phosphorus (P) and nitrogen (N) (Johnson, 2010).…”

Nitrogen‐induced acidification, not N‐nutrient, dominates suppressive N effects on arbuscular mycorrhizal fungi

“…Results from field studies have, however, been much more variable. Although combination of high N and P often suppresses AMF, positive (Krashevska, Sandmann, Maraun, & Scheu, 2014; Treseder & Allen, 2002), negative (Jiang et al., 2018; Johnson, Wilson, Wilson, Miller, & Bowker, 2015; Treseder & Allen, 2002) and neutral (Camenzind et al., 2014; Zheng et al., 2018) effects of N or P inputs have been documented in different studies. Indeed, positive, negative and neutral N effects on AMF were observed in five different (mesic to semi‐arid) grasslands in a same study (Egerton‐Warburton, Johnson, & Allen, 2007; Johnson, Rowland, Corkidi, Egerton‐Warburton, & Allen, 2003).…”

“…AMF responses to nutrient additions have been understood in the context of the cost–benefit of host plants as plant C allocation to AMF is likely dictated by the Law of Minimum (Johnson et al., 2015). Consequently, availability of soil N relative to P, or the N:P stoichiometry for host plant, has been identified as the important determinant for AMF responses to nutrient inputs (Johnson, 2010; Johnson et al., 2015; Zheng et al., 2018). A couple of predictions can thus be derived: N addition to a P‐limiting soil would increase AMF, but to a P‐rich soil would decrease AMF.…”

Carbon for nutrient exchange between arbuscular mycorrhizal fungi and wheat varies according to cultivar and changes in atmospheric carbon dioxide concentration

“…Taking consideration of AMF in widescale agricultural management decisions requires changes in current practice, although it has been argued that sufficient data corroborating the nutritional benefit of AMF in agricultural crops to warrant these shifts are currently lacking (Rillig et al, ; Ryan & Graham, ). A prevailing assertion is that cereals are generally negatively or neutrally affected by AMF colonization (Rillig et al, ; Smith & Smith, ); the fungi are assumed to offer little nutritional benefit to plants selectively bred for fine and dense root architecture optimized for nutrient‐acquisition efficiency, especially under high‐nutrient environments (Smith & Smith, ; Wen et al, ; Zheng et al, ). Despite two meta‐analyses suggesting an overall benefit of AMF to crop nutrient uptake and grain yield (Lekberg & Koide, ; Zhang, Lehmann, Zheng, You, & Rillig, ), a sceptical view remains in the literature with regard to the utility of AMF in modern and future agriculture (e.g.…”