Yes, you read the title correct. A recent study in 2016 by Mahmood Maighal and his team showed that arbuscular mycorrhizal fungi (AMF) can negatively affect seed bank viability. Now don’t get too carried away here-the positive effects of AMF outweigh the negative ecological interactions. Though, to gain a comprehensive understanding of these forest floor inhabitants, we must consider all interactions, both positive and negative.
In this modern, human influenced world, seed banks are increasingly important to maintain forest health. These propagules allow plant populations to bounce back after natural and human disturbances. Up until recently, seed viability was thought to be largely influenced by abiotic factors like soil water content and pH. As it turns out, these factors are easily manipulated by AMF. Nobody before these scientists had made this connection.
Using the seeds of three grassland herbaceous plants (Taraxacum officinale, Dactylis glomerata, and Centaurea nigra) three experiments were used to test how the seeds responded to conditions with and without mycorrhizae. The first two experiments used more controlled mesocosm conditions while the third was applied to field conditions. By housing the seeds in root exclusion compartments (RECs) they were able to see how the seeds responded to the presence or absence of AMF. 30-μm-nylon mesh ensured that only hyphae penetrate the RECs in the mycorrhizal treated seeds.
Soil factors influenced by AMF. Maighal et al. 2016.
Two of the plant species used in this experiment did not have a significantly different seed viability with the AMF treatment. On the contrary, Centaurea nigra seed viability did however significantly decease with AMF treatments. Besides seed viability, soil pH, water content, and available phosphorus were analyzed at the end of each experiment. Across the board, available phosphorus decreased, while both soil water and pH increased with AMF treatments. These alterations in the soil environment are the main culprit in the reduction of Centaurea nigra seed viability.
Viability of seeds significantly reduced in Centaurea nigra. Maighal et al. 2016.
This study highlights that AMF can have a negative impact on some ecological characteristics. Although only one species had a reduced seed viability with the addition of an AMF treatment, and these reductions were only minor, these data are irrefutable. Mycorrhizae quite clearly change the soil environment to enhance nutrient and water sequestering. These changes enhance the delivery of nutrients to their plant partner without recognizing seeds as potential future hosts. Interestingly, all three species used were in fact mycorrhizal plant species that pair with AMF, so you would think their mutualist wouldn’t negatively impact their fitness. Again, in nature, symbiotic relationships do occur, but species focus on their own fitness more so than the fitness of potential symbionts.
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