Abstract
Soil acidity is a major constraint on plant productivity. Arbuscular mycorrhizal (AM) fungi support plant colonization in acidic soil, but soil acidity also constrains fungal growth and diversity. Fungi in extreme environments generally evolve towards specialists, suggesting that AM fungi in acidic soil are acidic-soil specialists. In our previous surveys, however, some AM fungi detected in strongly acidic soils could also be detected in a soil with moderate pH, which raised a hypothesis that the fungi in acidic soils are pH generalists. To test the hypothesis, we conducted a pH-manipulation experiment and also analyzed AM fungal distribution along a pH gradient in the field using a synthesized dataset of the previous and recent surveys. Rhizosphere soils of the generalist plant Miscanthus sinensis were collected both from a neutral soil and an acidic soil, and M. sinensis seedlings were grown at three different pH. For the analysis of field communities, rhizosphere soils of M. sinensis were collected from six field sites across Japan, which covered a soil pH range of 3.0–7.4, and subjected to soil trap culture. AM fungal community compositions were determined based on LSU rDNA sequences. In the pH-manipulation experiment the acidification of medium had a significant impact on the compositions of the community from the neutral soil, but the neutralization of the medium had no effect on those of the community from the acidic soil. Furthermore, the communities in lower -pH soils were subsets of (nested in) those in higher-pH soils. In the field communities a significant nestedness pattern was observed along the pH gradient. These observations suggest that the fungi in strongly acidic soils are pH generalists that occur not only in acidic soil but also in wide ranges of soil pH. Nestedness in AM fungal community along pH gradients may have important implications for plant community resilience and early primary succession after disturbance in acidic soils.
Highlights
Soil acidity, represented by high-concentrations of proton, aluminum, and manganese in the soil solution, is a strong constraint on diversity of soil bacteria [1,2] and fungi [3,4], fungi seem to be less sensitive to pH than bacteria [5]
Clone libraries were raised from each amplicon, and about 1000, 500, 400, and 800 Arbuscular mycorrhizal (AM) fungal sequences were obtained in the pH-manipulation experiment, An et al [23], Kawahara and Ezawa [24], and the recent surveys, respectively (2700 sequences in total)
Ten phylotypes that are likely to belong to Glomeraceae, but could not be assigned to the known genera were named as unassigned Glomeraceae (UnG1–10), while four phylotypes that were likely to belong to Glomeromycota but could not be assigned to any of the families were named as uncultured Glomeromycota (Unc1–4)
Summary
Soil acidity, represented by high-concentrations of proton, aluminum, and manganese in the soil solution, is a strong constraint on diversity of soil bacteria [1,2] and fungi [3,4], fungi seem to be less sensitive to pH than bacteria [5]. Arbuscular mycorrhizal (AM) fungi are the obligate biotrophs that associate with most land plants, deliver phosphorus (P) to the host plant [9], and play a significant role in the establishment of early-successional species in acidic soil [10,11]. AM fungal diversity decreases with increasing soil acidity [3], which is due to the variability of acid-tolerance among species/isolates of the fungi [12,13,14,15]. Information about AM fungal species that inhabit acidic soils, is quite limited [19,20,21], and further, distribution of the species along pH gradients (i.e. from acidic to neutral pH) remains unexplored
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