Inoculations with arbuscular mycorrhizal fungi increase vegetable yields and decrease phoxim concentrations in carrot and green onion and their soils

Abstract

Background: As one of the most widely used organophosphate insecticides in vegetable production, phoxim (C(12)H(15)N(2)O(3)PS) is often found as residues in crops and soils and thus poses a potential threat to public health and environment. Arbuscular mycorrhizal (AM) fungi may make a contribution to the decrease of organophosphate residues in crops and/or the degradation in soils, but such effects remain unknown.

Methodology/principal findings: A greenhouse pot experiment studied the influence of AM fungi and phoxim application on the growth of carrot and green onion, and phoxim concentrations in the two vegetables and their soil media. Treatments included three AM fungal inoculations with Glomus intraradices BEG 141, G. mosseae BEG 167, and a nonmycorrhizal control, and four phoxim application rates (0, 200, 400, 800 mg l(-1), while 400 mg l(-1) rate is the recommended dose in the vegetable production system). Carrot and green onion were grown in a greenhouse for 130 d and 150 d. Phoxim solution (100 ml) was poured into each pot around the roots 14d before plant harvest. Results showed that mycorrhizal colonization was higher than 70%, and phoxim application inhibited AM colonization on carrot but not on green onion. Compared with the nonmycorrhizal controls, both shoot and root fresh weights of these two vegetables were significantly increased by AM inoculations irrespective of phoxim application rates. Phoxim concentrations in shoots, roots and soils were increased with the increase of phoxim application rate, but significantly decreased by the AM inoculations. Soil phosphatase activity was enhanced by both AM inocula, but not affected by phoxim application rate. In general, G. intraradices BEG 141 had more pronounced effects than G. mosseae BEG 167 on the increase of fresh weight production in both carrot and green onion, and the decrease of phoxim concentrations in plants and soils.

Conclusions/significance: Our results indicate a promising potential of AM fungi for enhancing vegetable production and reducing organophosphorus pesticide residues in plant tissues and their growth media, as well as for the phytoremediation of organophosphorus pesticide-contaminated soils.

Figure 1. Root mycorrhizal colonization (%) (means ± SE, n = 3) of carrot and green onion.

BEG 141 and BEG 167: G. intraradices BEG 141 and G. mosseae BEG 167, respectively.

Figure 2. Shoot (above X-axis) and root (below X-axis) fresh weights (means ± SE, n = 3) of carrot (A) and green onion (B).

Control, BEG 141 and BEG 167: non-AM-inoculation control, G. intraradices BEG 141 and G. mosseae BEG 167, respectively.

Figure 3. Shoot (above X-axis) and root (below X-axis) phoxim concentrations (means ± SE, n = 3) of carrot (A) and green onion (B).

Control, BEG 141 and BEG 167: non-AM-inoculation control, G. intraradices BEG 141 and G. mosseae BEG 167, respectively.

Figure 4. Soil phoxim concentrations (A) and phosphatase activity (B) (means ± SE, n = 3) after carrot and green onion harvest.

Control, BEG 141 and BEG 167: non-AM-inoculation, G. intraradices BEG 141 and G. mosseae BEG 167, respectively.