Salinity decreases dissolved organic carbon in the rhizosphere and increases trace element phyto‐accumulation

Abstract

Soil degradation processes, such as organic matter (OM) depletion, accompanied by metal contamination and salinization are becoming a serious threat to crop production and human food security. A glasshouse study was conducted to assess a factorial combination of salinity (0, 20, 40 and 60 mm NaCl) and cadmium (Cd) (0.3, 2.5 and 5.4 mg Cd kg−1) in organic soil (>90% OM) and their influence on dissolved organic carbon (DOC) in the rhizosphere and phyto‐accumulation in radish (Raphanus sativus L. var. sativus). A 34‐day exposure to increasing NaCl salinity significantly decreased DOC concentration in the radish rhizosphere solution and increased trace element (copper, Cu; zinc, Zn; and Cd) concentrations in the rhizosphere as well as in leaf/fruit tissues of radish. Soil contamination by Cd progressively raised concentrations in soil solution, but markedly reduced total concentration of Cu and Zn in the rhizosphere and leaves of radish. The NICA‐Donnan chemical speciation/distribution modelling confirmed the predominance of dissolved organic reactive surfaces (from fulvic acid for example) in Cu and Cd chemisorption/complexation processes over the whole range of applied NaCl and Cd treatments. In contrast, Zn speciation was dominated by an organically‐complexed pool at low salinity (0–20 mm NaCl), and free Zn2+ was the most important species at increased salinity (≥40 mm NaCl). In conclusion, because of the diminished pool of DOC under excessive salinity, the biogeochemistry of Cu, Zn and Cd in the rhizosphere can be affected in a way that would enhance solubility and phyto‐accumulation of these trace metals in food crops.

Using Humus on Golf Course Fairways to Alleviate Soil Salinity Problems

“…Salinity not only accelerates the decrease of soil OM but also increases the accumulation of harmful trace elements in plants (Ondrasek et al, 2012), inhibits the microbial activity in soils (Setia et al, 2014), and delays the decomposition of soil organic residues (Peinemann et al, 2005). Soil properties deteriorate as OM diminishes (Wong et al, 2010) because soil OM is important for nutrient recycling, cation exchange capacity, water holding, and structure stability.…”

Neighbour effects of purslane (Portulaca oleracea L.) on Cd bioaccumulation by soybean in saline soil

“…The enhancement of Cd uptake by co-planted soybean in contaminated soils under saline condition might be attributed to the increase of the labile Cd concentration pool (Phytoenrichment) in the shared rhizosphere ( Figure 3) and reduction of Cd uptake by co-occurred purslane (Figure 4). Ondrasek et al (2012) reported that salinity, induced by NaCl, increased Cd solubility in the rhizosphere, as a consequence of dissolved organic carbon (DOC) diminution. They mentioned that salinity-induced DOC reduction might decrease Cd-DOC complexation, and consequently increase the uptake of free Cd ion (Cd 2+ ) by plant.…”

Soil Interfaces in a Changing World

“…The role of organic matter in the control of metal ions was investigated by Ondrasek et al (2012) in a study of the effect of salinity on dissolved organic matter (DOM) in the rhizosphere of radish and consequently on solubility and phyto‐accumulation of Cu, zinc and cadmium. The depletion of DOM with excessive salinity favoured desorption of these potentially hazardous trace metals from the soil organic colloids, thus enhancing their solubility/mobility and therefore possible accumulation in food crops.…”