Partial Substitution of Mycorrhizal Fungi for Phosphorus Fertilization in the Greenhouse Culture of Citrus

Abstract

The interaction between P fertilization of citrus and the mycorrhizal fungus Glomus fasciculatus was examined in a greenhouse study. A low fertility loamy sand (4.6 ppm P) was provided with all necessary soil nutrients except P. This soil received superphosphate [Ca(H2PO4)2 · H2O] at rates of 0, 6, 28, 56, 278, and 556 ppm of P. Seven replicate mycorrhizal and nonmycorrhizal Brazilian sour orange and Troyer citrange seedlings were grown at each P fertility level. After 5 months, mycorrhizal sour orange which received 0 fertilizer P were similar in size to non‐mycorrhizal sour orange which were fertilized with 278 ppm P. Mycorrhizal citrange which received 0 fertilizer P were similar in size to nonmycorrhizal citrange which were fertilized with 56 ppm P. Dry weights of mycorrhizal sour orange seedlings were significantly greater than nonmycorrhizal sour orange seedlings when fertilized with 0, 6, 28, and 56 ppm P (947, 1089, 347, and 253% greater, respectively). Dry weights of mycorrhizal citrange seedlings were significantly greater than nonmycorrhizal citrange seedlings only when fertilized with 0 and 6 ppm P (746 and 300% greater, respectively). The %P in leaves of both citrus cultivars was enhanced by the mycorrhizal association at all P fertility levels. Variation in absorption of K, Mg, and Na by the citrus cultivars appeared to be primarily influenced by P concentrations of the seedlings. Variation in absorption of Zn, Cu, and Mn appeared to be influenced by both P concentrations of the seedlings and the presence of the mycorrhizal fungus. The number of G. fasciculatus spores/cm3 of soil which were associated with inoculated plants decreased with increasing P fertility levels. With mycorrhizal sour orange, numbers of spores decreased from 10.1 spores/cm3 soil at 56 ppm P soil to 0 spores/cm3 soil with plants at 556 ppm P. With mycorrhizal citrange, numbers of spores decreased from 5.7 spores/cm3 soil at 28 ppm P to 0 spores/cm3 soil at 56 ppm P. No correlation was found between soil P or % P in leaves, roots or stems of seedlings and the elimination of spore production.

II. Responses to rock phosphates

“…Increasing levels of soluble P fertiliser generally depress mycorrhizal infection levels in plant roots (Baylis 1967;Mosse 1973;Menge et al 1978), butthe experimental results discussed in this paper confirm earlier reports that mycorrhizal infection levels are usually unaffected by high levels of rock phosphate (Daft & Nicholson 1966;Powell 1977;Powell & Daniel 1978a) even when this fertiliser is effectively stimulating plant growth.…”

“…Growth responses to mycorrhizal inoculation should be compared with the growth responses possible from using phosphorus fertiliser alone (Abbott & Robson 19n;Hall 1978;Menge et al 1978). Powel1 (1980) showed that white clover in pot experiments responded to mycorrhizal inoculation in two highly P-retentive soils at superphosphate rates up to 1770 kg.ha -(.…”

Distribution of Arbuscular Mycorrhizal Fungi in Upland Field Soil of Japan: 2. Spore Density of Arbuscular Mycorrhizal Fungi and Infection Ratio in Soybean and Maize Fields

“…These findings indicate that an increase in the available soil phosphorus due to the application of phosphorus fertilizers lowers the density of AM fungi spores in the soil. There have been many reports that the more phosphorus fertilizer applied, the lower the spore density (Menge et al, 1978;Isobe et al, 1993;Kahiluoto et al, 2001). In other words, to increase the density of AM fungi spores in soil, it is important to avoid excessive application of phosphorus fertilizers.…”

Root Exudation in Relation to Supply of Phosphorus and Its Possible Relevance to Mycorrhizal Formation

“…In addition, it is now clear that phosphorus is also important in the control of VA mycorrhizal infection of root systems (Mosse, 1972(Mosse, , 1973Sanders, 1975;Menge et al, 1977). However, the mechanism of phosphorus control of mycorrhizal symbiosis needs to be determined.…”