Pinus pinaster seedlings and their fungal symbionts show high plasticity in phosphorus acquisition in acidic soils

Abstract

Young seedlings of maritime pine (Pinus pinaster Soland in Aït.) were grown in rhizoboxes using intact spodosol soil samples from the southwest of France, in Landes of Gascogne, presenting a large variation of phosphorus (P) availability. Soils were collected from a 93-year-old unfertilized stand and a 13-year-old P. pinaster stand with regular annual fertilization of either only P or P and nitrogen (N). After 6 months of culture in controlled conditions, different morphotypes of ectomycorrhiza (ECM) were used for the measurements of acid phosphatase activity and molecular identification of fungal species using amplification of the ITS region. Total biomass, N and P contents were measured in roots and shoots of plants. Bicarbonate- and NaOH-available inorganic P (Pi), organic P (Po) and ergosterol concentrations were measured in bulk and rhizosphere soil. The results showed that bulk soil from the 93-year-old forest stand presented the highest Po levels, but relatively higher bicarbonate-extractable Pi levels compared to 13-year-old unfertilized stand. Fertilizers significantly increased the concentrations of inorganic P fractions in bulk soil. Ergosterol contents in rhizosphere soil were increased by fertilizer application. The dominant fungal species was Rhizopogon luteolus forming 66.6% of analysed ECM tips. Acid phosphatase activity was highly variable and varied inversely with bicarbonate-extractable Pi levels in the rhizosphere soil. Total P or total N in plants was linearly correlated with total plant biomass, but the slope was steep only between total P and biomass in fertilized soil samples. In spite of high phosphatase activity in ECM tips, P availability remained a limiting nutrient in soil samples from unfertilized stands. Nevertheless young P. pinaster seedlings showed a high plasticity for biomass production at low P availability in soils.

Diversity in phosphorus mobilisation and uptake in ectomycorrhizal fungi

“…Higher values of surface-bound ACP have also been measured in ectomycorrhizal roots (see, e.g. Ali et al 2009; van Aarle and Plassard 2010) and hyphae (van Aarle and Plassard 2010) belonging to ectomycorrhizal plants grown in soil with a low level of available P, confirming the results obtained in vitro. In contrast, it seems that the presence of organic P did not activate the production of ACP in ECM fungi as no differences in enzyme production were found after growth on inorganic and organic P sources (Antibus et al 1992;Nygren and Rosling 2009).…”

Differential effects of soil chemistry on the foliar resorption of nitrogen and phosphorus across altitudinal gradients

“…Utilizing stable P forms requires energy associated with the release of organic acids or phosphatases for solubilizing recalcitrant inorganic or organic P forms (Cairney, ). Ali, Louche, Legname, Duchemin, and Plassard () observed that P uptake by mycorrhizal fungi is not sufficient to fulfil the P requirement of the host when P inorg‐avail levels are too low. Our results suggest that P resorption represents a cost‐effective strategy to cope with P deficiency when the P inorg‐avail content in the soil is low.…”

The Effect of Re-Planting Trees on Soil Microbial Communities in a Wildfire-Induced Subalpine Grassland

“…Xylanase is produced and released mostly by fungi in the forest environment [46]. Ali et al [47] showed that in coniferous tree species such as Pinus taeda L., ectomycorrhizal fungi produce extracellular phosphatase to improve phosphorus uptake. In our study, the mature forest soil had higher fungal biomass than other soils and provided more xylanase and phosphatase (Table 3).…”