Arbuscular mycorrhizal fungi-15-Fold enlargement of the soil volume of cotton roots for phosphorus uptake in intensive planting conditions

To find the hyphal growth of cotton plants and its response to phosphorus (P) application under field conditions, a rhizobox method was used in a field experiment with different P fertilizer levels to collect the soil samples at different distances from the cotton root surface, and measured hyphal density, pH value and soil available P content distribution. We found that the hyphal growth range of cotton can extend to 30 mm from the root surface (under zero P addition), meaning that the cotton root increased its P absorption range by 15-fold under the hyphal growth. Within this range, the hyphal density was controlled by soil P content change. On the one hand, the hyphal extent decreased gradually away from the cotton roots with the increase of the soil available P content. On the other hand, a negative correlation was observed between the hyphal density and the soil available P content in different soil locations of distance away from the cotton root surface. We conclude that under a certain soil available P, the promotion or inhibition for hyphal growth was driven by soil available P change.