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Plants generally behave in different response mechanisms under stress. This study aims to reveal the effects of biochar on photosynthesis and antioxidant system of ryegrass and alfalfa at the early stage of salt-alkali stress. Four treatments were conducted in the pot experiment: saline-alkali stress treatment (C0, 150 mmol/L equal mol NaCl, Na2CO3, NaHCO3 mixed saline solution), saline-alkali stress +1% biochar (C1), saline-alkali stress +3% biochar (C2), saline-alkali stress +5% biochar (C3), and set blank control (CK) without additives. Conventional cultivation was also carried out before the experiment, and then a stress test was conducted 40 d later. The stress treatment lasted for a total of 14 d, where 100 mL mixed saline solution was added to C0, C1, C2, and C3 treatments at one time, and 100 mL deionized water was added to CK treatment. Subsequently, the response of ryegrass and alfalfa was determined on the 14th day of the experiment, including growth indices, photosynthetic characteristics, malondialdehyde content, and antioxidant enzyme activities under various levels of biochar addition. The results showed as follows: 1) 14 d salt-alkali treatment dominated the growth of ryegrass and alfalfa. Specifically, there was a significant decrease in biomass accumulation, net photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO2 concentration. But there was no significant effect on the chlorophyll content and root length. Furthermore, the content of malondialdehyde increased significantly, indicating the antioxidant system responded positively. Similarly, the activities of superoxide dismutase, peroxidase, and catalase increased to alleviate the saline-alkali stress on plants. 2) The addition of biochar effectively improved the stress resistance of perennial ryegrass and alfalfa, thereby inducing a positive response in the antioxidant system. As such, the salinity-alkalinity stress was effectively relieved, particularly from the osmotic stress. The malondialdehyde content decreased obviously, whereas the alfalfa superoxide dismutase increased significantly, indicating that the perennial ryegrass antioxidant system was given a priority with the decomposition of hydrogen peroxide enzyme. The biomass, plant height, and root length of ryegrass and alfalfa increased by 48.50%-82.34%, 31.19%--44.16%, and 17.15%-48.09%, respectively, under 3% biochar treatment, compared with that under the salt-alkali stress. Additionally, the stomatal conductance and transpiration rate increased by 118.69%-358.99%, and 98.66%-526.53%, and the chlorophyll content and net photosynthetic rate increased by 7.97% and 519.09%, respectively. 3) The antioxidant enzyme activities and malondialdehyde content of ryegrass and alfalfa remained stable or decreased with the increase of biochar amount under the short-term salt-alkali stress. A trend was also found that the promoting at a low supplemental level and inhibiting at a high supplemental level for the growth indexes and photosynthetic characteristics. Consequently, there was a significant effect of salinity-alkalinity stress on the growth of perennial ryegrass and alfalfa, where a positive response was found at the beginning of stress. Correspondingly, an optimal addition of biochar can be expected to improve the stress resistance of perennial ryegrass and alfalfa, while the positive reaction of the oxidation system can effectively relieve the short-term salinity-alkalinity stress. The best effect was also achieved in the 3% biochar application. The findings can provide a sound reference for the scientific application of biochar to promote crop growth and yield. [ABSTRACT FROM AUTHOR]

Greenhouse soil culture experiments were conducted to investigate the phytoextraction of uranium from topsoil by Lolium perenne L. The effects of addition of CaO2，Aspergillus niger fermentation broth and their combination on some of physiological characteristics of Lolium perenne L. and enhancement of uranium phytoextraction were investigated. The results showed that the separate application of high dosed A niger fermentation broth had a stimulative effect on Lolium perenne L. growth whereas the separate application of high dosed CaCb，the joint application of high dosed CaO2 and A niger fermentation broth both gave an inhibitive effect. Furthermore, all the treatments resulted in an increased accumulation of soluble protein in Lolium perenne L. leaves, among which the separate addition of 40 mL/kg fermentation broth generated the highest content， increasing by 511. 11 % compared to the control. The application of A niger fermentation alone led to the decreases in superoxide dismutase(SOD) activity and malondialdehyde(MDA) contents in Lolium perenne L. leaves, while the separate application of high dosed CaO2，joint application of high dosed Ca()2 and A niger fermentation broth both caused a reveres effect. Moreover, the uranium concentration in the soil solution and uranium phytoextraction raised in all the treatments, in which the combined application at 1 g/kg CaCb and 20 mL/kg fermentation broth showed the best effect ； uranium content in the ash of Lolium perenne L. above ground increased by 622, 80 %，and the total accumulation of uranium increased by 483. 65 % against the control. [ABSTRACT FROM AUTHOR]

By leaching and weathering,the heavy metals in the copper mine tailings would release and pose potential danger to the environment.The key problem of ecological remediation for the copper mine tailings is substrate amendment.Through pot experiment and vegetated with Lolium perenne L.,the coal gangue sampled from a coal waste rock pile in Huainan coal field was added into the copper mine tailings and the behavior of heavy metals in the amended copper mine tailings were investiaged.Results indicated that the pH,organic matter and nutrient elements (total N,P and K) were markly improved by coal gangue application.Applying coal gangue could shift the Zn,Pb,Cd and Cu bound with exchangeable and carbonate fraction to those bound with Fe-Mn oxide,organic matter and residual fraction (except Pb and Cu associated with residual fraction in some treatments),and thus decreased DTPA-extractable Zn,Pb,Cd and Cu concentrations in copper mine tailings,resulting those metals decreased in the Lolium perenne L.as well.Generally,applying coal gangue reduced the bioavailability of heavy metals (Zn,Pb,Cd and Cu) in copper mine tailings-Lolium perenne L.system.However,the addition of coal gangue increased the Cr concentration in the amended tailings and increased the mobility of Cr,which also promoted the uptake of Cr by the Lolium perenne L..As a result,applying the coal gangue to the copper mine tailings immobilized the Zn,Pb,Cd and Cu in the tailings and brought in the Cr which could be effectively been absorbed in the Lolium perenne L..The coal gangue could be recognized as a potential waste-derived amendment for the ecological remediation of copper mine tailings. [ABSTRACT FROM AUTHOR]

The accumulation of heavy metals in crops is largely dependent on the availability of heavy metals in soils. Due to the differences of soil types and pollution characteristics, there is no widely recognized method for the determination of the bio-available heavy metals in soils such as Pb and Cd. In order to screen and establish suitable methods, the extractable abilities of five extractants (CaCl 2 , NH 4 OAc, HCl, EDTA, and DTPA) and Gradient Diffusion Film Technology (DGT) on four typical farmland soils with very different properties in Chongqing (acid purple soil, neutral purple soil, calcareous yellow soil and calcareous purple soil) were systematically compared. Simultaneously, pot experiments were carried out with Lolium perenne L. as an indicator plant to explore the relationship between the extractable soil Pb and Cd and their accumulation in plants. The feasibility of the tested methods were evaluated based on the extractability and co-relationships. The results showed that the extractability of the tested extractants for soil Pb and Cd varied a lot. HCl showed highest extractability on Pb in acid purple soil and calcareous yellow soil, while EDTA did the best in neutral purple soil and calcareous purple soil; HCl showed best extractability in all soils except calcareous purple soil, where EDTA was the best. Considering the correlation between the extraction amount and uptake by plant, all the extraction methods could be applied for the evaluation of the bioavailability of soils Pb and Cd except CaCl 2 for Pb due to its weak extractability for Pb for a specific soil type. For the comparison of heavy bioavailability in different soil types, EDTA-extractable Pb and DGT-extractable Cd were recommended due to their well co-relationships between extractable amount in soil and uptake by plant ( Lolium perenne L.) as indicated by the correlation coefficients of 0.941 and 0.919, respectively. HCl was relatively suitable as Cd extractant compared to others if DGT method could not be used.

Considering the serious pollution of heavy metal-chromium (Cr) in soil, there is an urgent need for effective selection of Cr-tolerant plant species. In order to gain fundamental insights into the tolerance and accumulation capabilities of Lolium perenne L. and Pharibitis purpurea (L.) Voigt under Cr stress, a pot experiment was conducted to investigate their growth, physiology and accumulation characteristics under Cr(Ⅲ) and Cr(Ⅵ) stress. The results showed the growth parameters could intuitively reflect the toxicity levels of Cr for plants. For instance, a low-level Cr(Ⅲ) (<250 mg·kg -1 ) in soil was good for plant growth as indicated by the significant elevation of plant height, root length and biomass in L. perenne ( P <0.05). However, Cr(Ⅵ) at all concentrations (≥25 mg·kg -1 ) in the soil inhibited the growth of both plant species, and the root length was particularly sensitive to the toxicity of Cr. The physiological parameters of plant represented both the toxicity of Cr and the tolerance of plants under Cr stress. A decrease of root activity and an increase of malonaldehyde content were observed under Cr stress, which indicated the physiological metabolism of plants was disturbed. In the presence of both Cr species, the proline content increased, which served as an indicator for both high Cr toxicity and increase of osmotic balance in plants. A rise in SOD and POD activity reflected the defense ability of plants against oxidative stress caused by Cr. In addition, the Cr-accumulation related parameters were the major standards for tolerant species selection. The Cr(Ⅵ) accumulation capacities of both plant species were greater than their Cr(Ⅲ) accumulation capacities. The maximum accumulation amounts of L. perenne and P. purpurea reached 957.4 mg·kg -1 and 743.3 mg·kg -1 in roots and 394.7 mg·kg -1 and 340.4 mg·kg -1 in shoots, respectively. In comparison with P. purpurea , L. perenne displayed a stronger Cr accumulation capacity in roots with a maximum bioaccumulation factor of 15.55. However, the transport ability of P. purpurea was superior to L. perenne . All of the parameters demonstrated that both L. perenne and P. purpurea could be used as alternative plants for phytoremediation of Cr-contaminated soil.