Understanding the mechanisms that maintain the coexistence of plant species is critical to addressing the global biodiversity crisis. Increasing attention has been paid to interactions between plants and soil microbes (plant-soil feedback, PSF), which can not only promote plant coexistence by increasing stabilizing effects but also hinder it by generating competitive fitness differences. However, the predictive power of the PSF has been questioned in recent studies because estimates of microbially mediated coexistence have correlated poorly with the outcomes of plant interactions observed in the field. This discrepancy may be due to the approaches typically used in PSF research, such as measuring PSF effects on a single vital rate or using soil conditioned for a short time period and without considering abiotic contexts. Here, I examined the effects of soil inoculum with different training histories and training environments (with and without added nutrients) on germination, seedling survival, and biomass of four grassland species. I then examined whether predictions of microbially mediated coexistence of four species pairs were sensitive to the vital rate identity, conditioning history, and soil training environment. I found that conspecific inoculum trained for longer had increasingly positive and negative effects on germination and biomass, respectively, although the effects of inoculum history varied across species and training environments. Estimates of microbially mediated outcomes were directly related to the vital rate used: when based on biomass and seedling survival, all four pairs were predicted to coexist, but only two pairs could do so when based on germination due to much reduced or even negative stabilization. Although coexistence predictions were not significantly related to conditioning history (including the effects of both variable conditioning durations and combinations of conditioning species) or nutrient treatments, both factors had a significant effect on stabilization. These results suggest that predictions of microbially mediated coexistence may be biased when based on a single vital rate, such as plant growth. To obtain more realistic and accurate outcome estimates, PSF effects should be integrated across different life stages, considering the temporal and abiotic contexts of these effects specific to a focal study system.

• Keywords
• fitness differences, plant coexistence, plant–soil feedback, soil microbes, soil nutrients, stabilization, temperate grassland, temporal context,
• MeSH
• Biomass MeSH
• Germination MeSH
• Grassland MeSH
• Soil * chemistry   MeSH
• Soil Microbiology * MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Soil * MeSH

The aim of this study was to compare plant-soil interactions in the native range of two congeneric European species differing in their invasive success in the world: a globally invasive Cirsium vulgare and non-invasive C. oleraceum. We assessed changes in soil nutrients and soil biota following soil conditioning by each species and compared performance of plants grown in self-conditioned and unconditioned soil, from which all, some or no biota was excluded. The invasive species depleted more nutrients than the non-invasive species and coped better with altered nutrient levels. The invasive species had higher seedling establishment which benefited from the presence of unconditioned biota transferred by soil filtrate. Biomass of both species increased in soil with self-conditioned soil filtrate and decreased in soil with self-conditioned whole-soil inoculum compared to unconditioned filtrate and inoculum. However, the increase was smaller and the decrease greater for the invasive species. The invasive species allocated less biomass to roots when associated with harmful biota, reducing negative effects of the biota on its performance. The results show that in the native range the invasive species is more limited by self-conditioned pathogens and benefits more from unconditioned mutualists and thus may benefit more from loss of effectively specialized soil biota in a secondary range. Our study highlights the utility of detailed plant-soil feedback research in species native range for understanding factors regulating species performance in their native range and pinpointing the types of biota involved in their regulation.

• Keywords
• Arbuscular mycorrhizal fungi (AMF), Enemy release hypothesis, Mycorrhizal inoculation potential (MIP), Phospholipid/neutral fatty acid analysis (PLFA/NLFA), Plant invasiveness, Structural equation modelling,
• MeSH
• Plant Roots MeSH
• Mycorrhizae * physiology   MeSH
• Soil MeSH
• Soil Microbiology MeSH
• Plants MeSH
• Introduced Species MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Soil MeSH