Abstract
Seed banks represent a reservoir of propagules important for understanding plant population dynamics. Seed viability in soil depends on soil abiotic conditions, seed species, and soil biota. Compared to the vast amount of data on plant growth effects, next to nothing is known about how arbuscular mycorrhizal fungi (AMF) could influence viability of seeds in the soil seed bank. To test whether AMF could influence seed bank viability, we conducted three two‐factorial experiments using seeds of three herbaceous plant species (Taraxacum officinale, Dactylis glomerata, and Centaurea nigra) under mesocosm (experiments 1 and 2) and field conditions (experiment 3) and modifying the factor AMF presence (yes and no). To allow only hyphae to grow in and to prevent root penetration, paired root exclusion compartments (RECs) were used in experiments 2 and 3, which were either rotated (interrupted mycelium connection) or kept static (allows mycorrhizal connection). After harvesting, seed viability, soil water content, soil phosphorus availability, soil pH, and hyphal length in RECs were measured. In experiment 1, we used inoculation or not with the AMF Rhizophagus irregularis to establish the mycorrhizal treatment levels. A significant negative effect of mycorrhizal hyphae on viability of seeds was observed in experiments 1 and 3, and a similar trend in experiment 2. All three experiments showed that water content, soil pH, and AMF extraradical hyphal lengths were increased in the presence of AMF, but available P was decreased significantly. Viability of seeds in the soil seed bank correlated negatively with water content, soil pH, and AMF extraradical hyphal lengths and positively with soil P availability. Our results suggest that AMF can have a negative impact on soil seed viability, which is in contrast to the often‐documented positive effects on plant growth. Such effects must now be included in our conceptual models of the AM symbiosis.
Highlights
Arbuscular mycorrhizal (AM) fungi are a key component of the soil ecosystem, especially in grasslands (Smith & Read, 2008)
Mycorrhizal plant growth responses range from positive to negative, suggesting that mycorrhizae operate along a mutualism–parasitism continuum, depending on the relative benefits and costs of the symbiosis (Johnson, Graham, & Smith, 1997; Johnson & Graham, 2013); such effects may differ for different plant life history stages (Varga, 2015)
We showed through our three complementary experiments, which employed different means of manipulating AM fungal abundance, and which were carried out in the field and in pots, that AM fungi had a clear and negative impact on soil seed viability for one of the three species of plants we examined
Summary
Arbuscular mycorrhizal (AM) fungi are a key component of the soil ecosystem, especially in grasslands (Smith & Read, 2008). They provide numerous services to plants, including enhanced nutrient uptake ( P), or increased plant resistance against pathogens and abiotic stressors (Smith & Read, 2008). Varga (2015) showed that AM fungi can negatively influence seed germination while still improving plant growth subsequently. Such early-stage effects are important in terms of understanding the net effects of the AM symbiosis on plants. There is a pressing need to know whether AM fungi can influence plant seeds and the soil seed bank
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