Nutrient acquisition in mycorrhizal lettuce plants under different phosphorus and nitrogen concentration

This study aimed to determine the combined effects of N (1, 5 or 9 mM) and P (0.1 or 0.5 mM) fertilization on mycorrhizal and non-mycorrhizal lettuces. Plant growth, macro and micronutrient assimilation, and specific absorption rate (SAR) were measured. Arbuscular mycorrhizal (AM) colonization and extraradical mycelium development were also examined. The high availability of N and P in the soil reduced the content of macro and micronutrients in AM plants. At the lowest P application (0.1 mM), the AM colonization increased nutrient acquisition at all N levels tested. However, the highest application of N and P to the soil reduced the uptake of N, P, K, Mn and Zn in AM compared to non-AM lettuce plants. These fertilizer levels were also inhibitory to AM-intra and extraradical colonization. In contrast to non-AM plants, AM colonization increased SAR values at the lowest N and P levels for nearly all the nutrients, and decreased the amount of nutrients absorbed per unit of root mass at the highest N and P levels applied. Results demonstrated some negative effects of high N and P application in soil on the acquisition of N, P, K, Fe, Mn and Zn for mycorrhizal plants. (C) 2003 Elsevier Ireland Ltd. All rights reserved.