Silicon and arbuscular mycorrhizal species complement in improving soil characteristics, sulfur metabolism and antioxidant defense responses in arsenic stressed Cajanus cajan (L.) Millsp

Abstract

ABSTRACT Arsenic (As) is a major soil contaminant that restricts plant growth and metabolism. Silicon-Si and arbuscular mycorrhizae-AM have the potential to impart As stress tolerance. The study assessed relative and cumulative effects of Si and mycorrhizal species; Claroideoglomus etunicatum-M1 and Rhizoglomus intraradices-M2 in alleviating AsV and AsIII toxicities in pigeonpea [Cajanus cajan (L.) Millsp.]. Arsenic reduced mycorrhizal symbiosis, nutrient availability and plant biomass by inducing oxidative stress. Si and AM inoculations decreased metalloid uptake and reactive species generation, with higher benefits under M2, followed by Si, then M1. Higher efficiency of M2 corresponded to its colonization ability and glomalin production as well as its capability of enhancing nutrient uptake by modulating soil enzymes (alkaline phosphate-ALP and arylsulfatase-aryl-S) activities. In addition, S metabolism and antioxidant system got up-regulated, leading to increased synthesis of thiol compounds and antioxidants in the order M2>Si>M1. Accumulated thiols further reduced As translocation by chelating and immobilizing metalloid in plant roots. Moreover, significantly higher As tolerance could be recorded when plants were supplemented with a combination of +Si+M2, indicating functional complementarity between the two amendments. The study, thus, demonstrated introduction of Si and AM in the rhizosphere as a promising strategy for inducing As tolerance to pigeonpea.