Tradeoffs among root functional traits for phosphorus acquisition in 13 soybean genotypes contrasting in mycorrhizal colonization.

BACKGROUND AND AIMS: Plants have adapted to acquire phosphorus (P) primarily through advantageous root morphologies, responsive physiological pathways and associations with mycorrhizal fungi. Yet, to date, little information exists on how variation in arbuscular mycorrhizal (AM) colonization is coordinated with root morphological and physiological traits to enhance P acquisition. METHODS: Thirteen root functional traits associated with P acquisition were characterized at full bloom stage in pot cultures under low soil P availability conditions for 13 soybean genotypes contrasting in AM colonization. KEY RESULTS: Significant variation in root functional traits was observed in response to low P stress among the 13 tested soybean genotypes contrasting in AM colonization. Genotypes with low AM colonization exhibited greater root proliferation but with less advantageous root physiological characteristics for P acquisition. In contrast, genotypes with high AM colonization exhibited less root growth but higher phosphatase activities and carboxylate content in the rhizosheath. Root dry weights, and contents of carbon and P were positively correlated with root morphological traits of different root orders and whole root systems, and were negatively correlated with AM colonization of fine roots and whole root systems, as well as rhizosheath phosphatase activities and carboxylate contents. These results taken in combination with a significant positive correlation between plant P content and root morphological traits indicate that root morphological traits play a primary role in soybean P acquisition. CONCLUSIONS: The results suggest that efficient P acquisition involves tradeoffs among carbon allocation to root proliferation, mycorrhizal symbiosis or P-mobilizing exudation. Complementarity and complexity in the selection of P acquisition strategies was notable among soybean genotypes contrasting in AM colonization, which is closely related to plant C budgeting.

Arbuscular mycorrhizal fungi-induced mitigation of heavy metal phytotoxicity in metal contaminated soils: A critical review.

The heavy metal pollution is a worldwide problem and has received a serious concern for the ecosystem and human health. In the last decade, remediation of the agricultural polluted soil has attracted great attention. Phytoremediation is one of the technologies that effectively alleviate heavy metal toxicity, however, this technique is limited to many factors contributing to low plant growth rate and nature of metal toxicities. Arbuscular mycorrhizal fungi (AMF) assisted alleviation of heavy metal phytotoxicity is a cost-effective and environment-friendly strategy. AMF have a symbiotic relationship with the host plant. The bidirectional exchange of resources is a hallmark and also a functional necessity in mycorrhizal symbiosis. During the last few years, a significant progress in both physiological and molecular mechanisms regarding roles of AMF in the alleviation of heavy metals (HMs) toxicities in plants, acquisition of nutrients, and improving plant performance under toxic conditions of HMs has been well studied. This review summarized the current knowledge regarding AMF assisted remediation of heavy metals and some of the strategies used by mycorrhizal fungi to cope with stressful environments. Moreover, this review provides the information of both molecular and physiological responses of mycorrhizal plants as well as AMF to heavy metal stress which could be helpful for exploring new insight into the mechanisms of HMs remediation by utilizing AMF.

Boron supply alleviates cadmium toxicity in rice (Oryza sativa L.) by enhancing cadmium adsorption on cell wall and triggering antioxidant defense system in roots.

Cadmium (Cd) pollution is a key concern globally that affects plant growth and productivity. Boron (B) is a micronutrient that helps in the formation of the primary cell wall (CW) and alleviates negative effects of toxic elements on plant growth. Nonetheless, knowledge about how B can reduce Cd toxicity in rice seedlings is not enough, particularly regarding CW-Cd adsorption. Therefore, the current experiment investigated the alleviative role of B on Cd toxicity in rice seedling. The experiment was carried out with 0 µM and 30 µM H3BO3 under 50 µM Cd toxicity in hydroponics. The results showed that Cd exposure alone inhibited plant growth parameters and caused lipid peroxidation. Moreover, Cd toxicity led to obvious visible toxicity symptoms on the leaves. However, increasing the availability of B alleviated Cd toxicity by reducing Cd concentration in plant tissues and improving antioxidative system. Moreover, cell wall pectin and hemicellulose adsorbed a significant amount of Cd. Fourier-Transform Infrared spectroscopy (FTIR) spectra exhibited that cell wall functional groups were increased by B application. Scanning electron microscopy (SEM) equipped with energy-dispersive X-ray (EDX) microanalysis confirmed the higher Cd binding onto CW. The findings of this investigation showed that B could mitigate Cd stress by decreasing Cd uptake and encouraging Cd adsorption on CW, and activation of the protective mechanisms. The present results might help to increase rice productivity on Cd polluted soils.