Response of Siratro to Vesicular‐Arbuscular Mycorrhizal Fungi: II. Efficacy of Selected Vesicular‐Arbuscular Fungi at Different Phosphorus Levels

Abstract

The effect of two selected species of vesicular-arbuscular mycorrhizal (VAM) fungi, Glomus etunicatum and Glomus intraradices, on the growth of Macroptilium atropurpureum Urb. cv. Siratro in nonpasteurized soil with applied P levels of 2.5, 10, 20, and 40 mg kg−1 was studied under greenhouse conditions. At 2.5 mg kg−1 of applied P, there was no difference in the shoot dry and root fresh weights between inoculated and control plants. At all but 2.5 mg kg−1 of applied P, plants inoculated with either G. etunicatum or G. intraradices had higher shoot dry and root fresh weights than the control. The increase of shoot dry weight was greater for plants inoculated with G. etunicatum than for G. intraradices. Plants inoculated with G. etunicatum in pasteurized soil had significantly greater total P and N than control plants at low and intermediate levels of applied P, but not at the highest level. Overall, inoculated plants had significantly greater plant P concentration than control plants. For both fungi, increasing P above 2.5 mg kg−1 increased the percentage and total root length colonized by VAM fungi. There was a significant correlation between shoot dry weight and mycorrhizal root colonization of Siratro, expressed as either percentage or total root length colonized, for all inoculated treatments. We conclude that inoculation with effective VAM fungal species can significantly increase the growth of Siratro over a practical range of P in soils that have an ineffective indigenous population of VAM fungi under amended soil conditions.