Heterogeneous soil conditions influence fungal alkaline phosphatase activity in roots of Lotus corniculatus

- First study of intraradical fungal alkaline phosphatase activity in the field.
- Fungal alkaline phosphatase activity in roots is influenced by soil heterogeneity.
- Consistently higher fungal alkaline phosphatase activity in clay-silt fragments.
- Fungal alkaline phosphatase activity increases with soil depth in sandy soil.
- Higher root density can cause decreases of fungal alkaline phosphatase activity.

Extremes in soil water, temperature, pH and inorganic nutrient availability can highly influence mycorrhizal formation and nutrient acquisition. However, the influence of soil heterogeneity and seasonal soil changes on fungal alkaline phosphatase (ALP) activity in mycorrhizal roots is unknown. Whether the activity of intraradical fungal ALP is influenced by soil texture heterogeneity, soil depth, nutrient concentrations and root density during the growing season were addressed in this research. The root system of Lotus corniculatus grown on a reclamation site was analyzed for intraradical mycorrhizal ALP activity in 0-10, 10-20 and 20-30 cm depth increments of sandy soil and in clay-silt fragments (mostly localized in 10-20 cm) from May to September. Root length density and water soluble nutrient contents in sandy soil and clay-silt fragments were determined for each sample. Soil water content and soil temperature data of a nearby site were used for climate conditions on sampling dates. Fungal ALP activity in roots growing in clay-silt fragments was higher than in those growing in sandy soil, independent of sampling date. Fungal ALP activity in sandy soil increased with soil depth which is related to decreasing root densities and lower nutrient concentrations. However, nutrient dense clay-silt fragments significantly positively influenced local mycorrhizal ALP activity in L. corniculatus roots, suggesting that the ability of mycorrhizae to selectively take up phosphorus and other nutrients from those nutrient hot spots is enhanced and could play a significant role in successful establishment of pioneer plant species on infertile reclamation sites.