Response of Arabidopsis thaliana, seedlings to cadmium in relation to ammonium availability

Sorption and mobility of cadmium in soil impacted by irrigation waters

Soil contamination by Cd has drawn global attention, while how irrigation waters modulate Cd sorption and mobility in soil remains obscure. We address this by investigating how cropped sandy soil irrigated with different waters altered Cd sorption and mobility using a rhizobox experiment followed by a batch experiment. Maize were planted in the rhizoboxes and irrigated by reclaimed water (RW), livestock wastewater (LW) and deionized water (CK), respectively. The bulk soil sampled from each treatment after 60 days of growth was employed to measure the Cd sorption and mobility using the isothermal adsorption and desorption experiments. The results showed that, in a small rhizobox experiment, the adsorption rate of Cd by the bulk soil in the adsorption phase was much faster than the desorption rate in desorption phase. Irrigation with RW and LW both reduced the Cd adsorption capacity of soil, and the reducing degree brought by LW was more obvious. Cd desorption rate was very low but keep increasing in the desorption stage, and pre-RW irrigation had the potential to increase Cd desorption from soil. Although the results were obtained based on the bulk soil sampled from a rhizobox experiment, our study strongly suggests that the altered Cd adsorption and desorption behavior in the soil caused by the RW and LW irrigation may risk the farmland ecosystem and deserve more concern.

Nitrogen form regulates cadmium uptake and accumulation in Tanzania guinea grass used for phytoextraction

Plants benefit from the simultaneous uptake of nitrate (NO₃^-) and ammonium (NH₄⁺), which can influence the bioaccumulation of heavy metals. Nevertheless, there are no studies on the effect of nitrogen forms on grasses used for cadmium (Cd) phytoextraction. The objective was to evaluate the response of Panicum maximum cv. Tanzania to NO₃^-/NH₄⁺ ratios and Cd levels. A 3 × 3 factorial experiment was conducted under greenhouse conditions, in a randomized complete block design replicated three times, with three NO₃^-/NH₄⁺ ratios (100/0, 70/30 and 50/50) and three Cd levels (0.0, 0.5 and 1.0 mM). Although it increased plant total nitrogen concentration, Cd exposure reduced shoot and root growth. Moreover, it altered nitrogen metabolism and induced the accumulation of NO₃^- and NH₄⁺ mainly in shoots. The supply of 50/50 disturbed glutamine synthetase activity and changed root morphology under Cd toxicity. However, while the exclusive use of NO₃^- mitigated toxicity symptoms, by favoring Cd accumulation in roots and maintaining normal nitrogen metabolism, plants grown with 50/50 showed increased uptake, transport and accumulation of this metal. Thus, Cd uptake and accumulation are strongly related to the form of nitrogen available, and the supply of 50/50 increases the phytoextraction of this metal.

Partial replacement of nitrate by ammonium increases photosynthesis and reduces oxidative stress in tanzania guinea grass exposed to cadmium

In order to grow and effectively uptake and accumulate cadmium (Cd), plants used for phytoextraction have to cope with toxicity, which may be influenced by the supply of nitrate (NO₃^-) and ammonium (NH₄⁺). Thus, we evaluated the effect of these nitrogen forms on the photosynthetic and antioxidant enzyme activities of Panicum maximum cv. Tanzania (tanzania guinea grass) under Cd stress. Plants were grown in nutrient solution under greenhouse conditions and subjected to a 3 × 3 factorial experiment. They were supplied with three NO₃^-/NH₄⁺ ratios (100/0, 70/30 and 50/50) and exposed to three Cd rates (0.0, 0.5 and 1.0 mmol L^-1), being arranged in a randomized complete block design with three replications. Gas exchange parameters, oxidative stress indicators, proline concentration and antioxidant enzyme activities were studied. Exposure to Cd reduced photosynthesis by causing stomatal closure and impairing electron transport. However, the simultaneous supply of NO₃^- and NH₄⁺, particularly at a 50/50 ratio, restored gas exchange and improved the function of photosystem II, increasing the photosynthetic capacity of the grass. Plants grown with 50/50 showed reduced lipid peroxidation along with increased proline synthesis. Moreover, this NO₃^-/NH₄⁺ ratio increased the tolerance of tanzania guinea grass to Cd by inducing high superoxide dismutase and glutathione reductase activities in shoots and roots, respectively, maintaining cellular homeostasis and reducing oxidative stress. The negative effects of Cd on photosynthesis and on the balance between oxidants and antioxidants are attenuated by the partial replacement of NO₃^- by NH₄⁺ in the nutrient solution.