This paper studies the influence of four modifiers (organic-inorganic composite modifiers, inorganic polymer compound modifiers, polyacrylate compound modifiers, organic polymer compound modifiers) on soil pH, cation exchange capacity (CEC), Cd concentration and their distribution and migration in the soil profile under high Cd concentration (40 mg/kg) during continuous remediation tub experiment. The results showed that: (1) Four modifiers significantly increased the pH and CEC in each soil layer, and inorganic polymer compound modifiers providing the best results in the 0 �20 cm soil layer. (2) There is an extremely significant negative correlation between the carbonate-bound Cd and exchangeable Cd, with considerable effect in the 0 �20 cm and 20 �40 cm soil layers. The inorganic polymer compound modifiers had the best effect on the soil exchangeable Cd. (3) Both pH and CEC in all soil layers were negatively correlated with exchangeable Cd and positively correlated with other forms. (4) Fourier transform infrared spectrometry (FTIR) analysis showed that the modifiers immobilize soil Cd mainly through chemical precipitation, complexation and adsorption so as to reduce the bioavailability of Cd. Thus, we concluded that four modifiers are suitable for Cd mediation/Cd stabilization purposes.
Soil salinization and alkalization can cause great losses to agricultural production in arid regions. Cotton, a common crop in arid and semi-arid regions in China, often encounters saline stress and alkaline stress. In this study, NaCl (8 g·kg−1), Na2CO3 (8 g·kg−1), and a compound material (an organic polymer compound material) were mixed with field soil before cotton sowing, and the ion content, photosynthetic characteristics, and metabolite levels of the new cotton leaves were analyzed at the flowering and boll-forming stage, aiming to clarify the photosynthetic and metabolic mechanisms by which compound material regulates cotton’s tolerance to saline stress and alkaline stress. The results showed that the application of the compound material led to an increase in the K+/Na+ ratio, stomatal conductance (Gs), efficiency of PSII photochemistry (ψPSⅡ), potential activity (Fv/Fo), and chlorophyll content (Chla and Chlb), as well as the abundances of D-xylonic acid and DL-phenylalanine in the NaCl treatments. Additionally, there were increases in the K+ content, K+/Na+ ratio, Chla/b ratio, net photosynthetic rate (Pn), transpiration rate (Tr), ψPSⅡ, and D-saccharic acid abundance in the Na2CO3 treatments. A correlation analysis and a metabolic pathway analysis revealed that the compound material mainly regulated the photosynthetic characteristics of and the ion balance in the new leaves through regulating the abundance of key metabolites when the cotton was under NaCl stress or Na2CO3 stress. Furthermore, the positive impact of the compound material on the cotton’s NaCl stress tolerance was stronger than that on the cotton’s Na2CO3 stress tolerance.
Abstract. Soil salinity mediates microorganisms and soil process, like soil organic carbon (SOC) cycling. Yet, how soil salinity affects SOC mineralization via shaping bacterial communities diversity and composition remains elusive. Therefore, soils were sampled along a salt gradient (salinity at 0.25 %, 0.58 %, 0.75 %, 1.00 % and 2.64 %) and incubated for 90 days to investigate i) SOC mineralization (i.e. soil priming effects induced by cottonseed meal, as substrate) and ii) responsible bacteria community, by using high throughput sequencing and natural abundance 13C isotopes (to partition cottonseed meal derived CO2 and soil derived CO2. We observed negative priming effect during first 28 days of incubation but turned to positive priming effect after day 56. Negative priming at the early stage might be due to the preferential utilization of cottonseed meal. The followed positive priming decreased with the increase of salinity, which might be caused by the decreased alpha diversity of microbial community in soil with high salinity. Specifically, soil pH and EC along salinity gradient were the dominant variables modulating the structure of microbial community and consequently SOC priming (estimated by distance-based multivariate analysis and path analysis). By adopting O2PLS, priming effects were linked with specific microbial taxa, e.g., Proteobacteria (Luteimonas, Hoeflea and Stenotrophomonas) were the core microbial genus that attributed to the substrate induced priming effects. Here, we highlight that the increase of salinity reduced the diversity of microbial community and shifted dominant microorganisms that determined SOC priming effects, which provides a theoretical basis for understanding of SOC dynamics and microbial drivers under salinity gradient.
Oilseed rape not only has the function of improve saline and alkaline soils, but also alleviate the local feed shortage. However, medium- and high-degree soil salinization and alkalinization always inhibit the growth of oilseed rape. Studies have shown that compound material can improve the tolerance to saline and alkaline stress of crops, but the difference in the regulation mechanism of compound material on oilseed rape in saline and alkaline soils is not clear. This study explored the difference through determining the leaf ion contents, physiological indexes, transcriptomics, and metabolomics of oilseed rape in salinized soil (NaCl 8 g kg-1) and alkalinized soil (Na2CO3 8 g kg-1) at full flowering stage, respectively after the application of compound material. The results showed that in salinized and alkalinized soil, the compound material upregulated the genes related to the regulation of potassium ion transport, and changed the amino acid metabolic pathway, which reduced the contents of Na+, malondialdehyde (MDA), and relative conductivity (REC) in leaves, and increased the contents of K+ and Mg2+ and the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). However, there were differences in the regulation mechanism of compound material in salinized and alkalinized soil. In salinized soil, the compound material improved the tolerance of oilseed rape to saline stress by upregulating transcription factors mannose-1-phosphate guanylyltransferase (GPMM) and Glutamine--fructose-6-phosphate transaminase (GFPT) and downregulating phosphomannomutase (PMM) to change nucleotide metabolism pathway and lipid metabolism pathway. In alkalized soil, the compound material improved the tolerance of oilseed rape to alkaline stress by upregulating transcription factors Phenylalanine ammonia lyase (PAL) to change the biosynthesis pathway of other secondary metabolites. Therefore, the compound material can improve the tolerance of oilseed rape to saline and alkaline stress by regulating the genetic adaptability and apparent plasticity, but the mechanisms were different. This study provides a practical method for the ecological environment restoration and the development of animal husbandry.
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