Cellular Cd^(2+)fluxes in roots confirm increased Cd availability to rice(Oryza sativa L.)induced by soil acidifications

Soil acidifications become one of the main causes restricting the sustainable development of agriculture and causing issues of agricultural product safety.In order to explore the effect of different acidification on soil cadmium(Cd)availability,soil pot culture and hydroponic(soil potting solution extraction)were applied,and non-invasive micro-test technique(NMT)was combined.Here three different soil acidification processes were simulated,including direct acidification by adding sulfuric acid(AP1),acid rain acidification(AP2)by adding artificial simulated acid rain and excessive fertilization acidification by adding(NH_(4))_(2)SO_(4)(AP3).The results showed that for direct acidification(AP1),DTPA-Cd concentration in field soils in Liaoning(S1)and Zhejiang(S2)increased by 0.167-0.217 mg/kg and 0.181-0.346 mg/kg,respectively,compared with control group.When soil pH decreased by 0.45 units in S1,the Cd content of rice stems,leaves and roots increased by 0.48 to 6.04 mg/kg and 2.58 to 12.84mg/kg,respectively,When the pH value of soil S1 and S2 decreased by 0.20 units,the average velocity of Cd^(2+)at 200μm increased by 10.03-33.11 pmol/cm~2/sec and 21.33-52.86pmol/cm^(2)/sec,respectively,and followed the order of AP3>AP2>AP1.In summary,different acidification measures would improve the effectiveness of Cd,under the same pH reduction condition,fertilization acidification increased Cd availability most significantly.

Salt stress-induced changes in soil metabolites promote cadmium transport into wheat tissues

Soil salinity is known to improve cadmium(Cd)mobility,especially in arid soils.However,the mechanisms involved in how salt stress-associated metabolic profiles participate in mediating Cd transport in the soil-plant system remain poorly understood.This study was designed to investigate the effects of salinity-induced changes in soil metabolites on Cd bioavailability.Sodium salts in different combinations according to molar ratio(NaCl:Na_(2)SO_(4)=1:1;NaCl:Na_(2)SO_(4):NaHCO_(3)=1:2:1;NaCl:Na_(2)SO_(4):NaHCO_(3):Na_(2)CO_(3)=1:9:9:1;NaCl:Na_(2)SO_(4):NaHCO_(3):Na_(2)CO_(3)=1:1:1:1)were applied to the Cd-contaminated soils,which increased soil Cd availability by 22.36%and the Cd content in wheat grains by 36.61%,compared to the control.Salt stress resulted in soil metabolic reprogramming,which might explain the decreased growth of wheat plants and increased Cd transport from the soil into wheat tissues.For example,down-regulation of starch and sucrose metabolism reduced the production of sugars,which adversely affected growth;up-regulation of fatty acid metabolism allowed wheat plants to maintain a normal intracellular environment under saline conditions;up-regulation of the tricarboxylic acid(TCA)cycle was triggered,causing an increase in organic acid synthesis and the accumulation of organic acids,which facilitated the migration of soil Cd into wheat tissues.In summary,salt stress can facilitate Cd transport into wheat tissues by the direct effect of salt-based ions and the combined effect of altered soil physicochemical properties and soil metabolic profiles in Cd-contaminated soils.

Effects of rape straw and red mud on extractability and bioavailability of cadmium in a calcareous soil

Screening of cost-effective soil amendments is important to develop ＂in situ＂ remediation techniques for cadmium （Cd） contaminated soils. In this study, different soil amendments, including red mud, a by-product of the alumina industry, and acid-treated, nano-treated by nanoparticle milling, nano and acid-treated red muds, zeolite, corn straw, and rape straw, were evaluated to immobilize Cd in two added levels （2 and 5 mg Cd·kg^-1 soil） in a calcareous soil by single and sequential extractions and by cucumber （Cucumis sativus L.） pot experiments. Results indicated that cruciferous rape straw significantly decreased the concentrations of water soluble, extractable Cd in soils, and Cd in cucumber plants, and it was more effective than gramineous corn straw. Also, red mud generally decreased the extractability and bioavailability of Cd added to calcareous soils more effectively than zeolite. Furthermore, the efficiency of red mud could be increased by the treatment of nano-particle milling due to the increase in specific surface area of red mud. It is potential to use rape straw and red mud as soil amendments to develop a cost-effective and efficient ＂in situ＂ rernediation technology for Cd mildly contaminated calcareous soils.