Multi-factor correlation analysis of the effect of root-promoting practices on tobacco rhizosphere microecology in growth stages.

Some agronomic practices not only promote the development of crop roots and increase overall plant performance but also affect colonisation by rhizosphere microorganisms. However, the composition and temporal dynamics of the tobacco rhizosphere microbiota under different root-promoting practices are poorly understood. Here, we characterised the tobacco rhizosphere microbiota at the knee-high, vigorous growing, and maturity stages under the application of potassium fulvic acid (PFA), γ-Polyglutamic acid (PGA), soymilk root irrigation (SRI), and conventional fertilization (CK) and its correlation with root characteristics and soil nutrients. The results showed that three root-promoting practices notably improved the dry and fresh root weights. Total nitrogen and phosphorus, available phosphorus and potassium, and organic matter contents in the rhizosphere markedly increased at the vigorous growing stage. The rhizosphere microbiota was changed through root-promoting practices. However, with tobacco growth, the change of rhizosphere microbiota showed a pattern of slow first and then fast and the microbiota of different treatments gradually approached. SRI reduced plant-pathogenic fungi but increased chemoheterotrophic and phototrophic bacteria, and arbuscular mycorrhizal fungi. PFA and PGA markedly increased arbuscular mycorrhizal and ectomycorrhizal fungi at the knee-high stage, which benefitted tobacco nutrient absorption. The correlation between rhizosphere microorganisms and environmental factors varied at different growth stages. Notably, the rhizosphere microbiota was more sensitive to environmental factors at the vigorous growing stage, and the interactions were more complex than in other stages. Furthermore, a variance partitioning analysis showed that the influence of root-soil interaction on the rhizosphere microbiota increased with tobacco growth. Overall, all three root-promoting practices could improve root characteristics, rhizosphere nutrient, and rhizosphere microbiota to varying degrees and increase the tobacco biomass, among which PGA had the most obvious effect and most suitable for tobacco cultivation. Our findings revealed the role of root-promoting practices in shaping the rhizosphere microbiota during plant growth and elucidated the assembly patterns and environmental drivers of crop rhizosphere microbiota driven by the application of root-promoting practices in agricultural production.

[Effect of Organic Material Amendments on Soil Respiration in Tobacco Fields of Central Henan].

A field experiment was conducted to study the effects of different organic material amendments on soil respiration in a flue-cured tobacco field. Five treatments were set up:no fertilizer (NF), chemical fertilizer (NPK), chemical fertilizer+ryegrass (NPKG), chemical fertilizer+wheat straw (NPKS), and chemical fertilizer+tobacco straw biochar (NPKB). The results showed that:① Compared with that under NPK, NPKG and NPKS decreased the temperature sensitivity (Q10) of total soil respiration and heterotrophic respiration, whereas NPKB increased the Q10 of heterotrophic respiration. The two-factor fitting model of soil respiration and soil hydrothermal factors accounted for 50%-80% of the variation in soil respiration. ② The addition of organic materials significantly increased the content of soil soluble organic carbon (DOC) and root dry matter. Soil heterotrophic respiration(Rh) was significantly positively correlated with DOC content, and soil autotrophic respiration(Ra) was significantly parabolically correlated with root biomass, with an R2 of 0.327-0.634. ③ Soil respiration increased first and then decreased during the tobacco growth period. Compared with that under the NF treatment, the NPK treatment significantly promoted soil respiration and its components. Compared with those of the NPK treatment, Rsrates were significantly increased by 20.08%, 10.32%, and 9.88% under the NPKG, NPKS, and NPKB treatments, respectively; Rh rate increased by 24.21%, 16.51%, and 11.68% respectively, and Ra rate was increased by 15.12% in the NPKG treatment. In summary, straw returning and biochar addition significantly increased Rh by increasing soil DOC, thereby promoting Rs. Incorporation of ryegrass not only increased the Rh but also increased Ra by promoting the growth and development of roots and therefore the Rs.

Effect of biochar on the accumulation and distribution of cadmium in tobacco (Yunyan 87) at different developmental stages.

Cadmium (Cd) easily accumulates in tobacco, which endangers public health through Cd exposure from smoking. However, its uptake, translocation, and distribution in tobacco plants during plant development or its response to biochar application are poorly understood. A pot experiment was conducted with tobacco (Yunyan 87) grown in soil severely contaminated with Cd (30 mg kg-1) amended with 0, 1, and 2% (w/w) tobacco stem-derived biochar (BC). The absorption and accumulation of Cd in all parts of the tobacco plants were most active from the rosette stage to the fast growing stage, during which approximately 90% of the Cd deposited in the tobacco leaves occurred, especially in the lower leaves. The Cd concentrations in most plant parts without added biochar decreased significantly by 52.61-78.30% due to the rapid increase in biomass (dilution effect), although the Cd concentration in the lower leaves increased by 48.89% (P < 0.05). However, with the slowdown of the growth rate of tobacco at the maturity stage, the proportion of Cd accumulation in roots and stems without biochar addition increased by 29.01%, resulting in an increased Cd concentration in roots and stems by 63.29-86.80% (P < 0.05). In the different growth stages, the application of biochar reduced the contents of DTPA-extractable and exchangeable Cd in the soil by 5.11-35.14% and 9.20-54.05%, respectively, thus reducing the absorption, accumulation and concentration of Cd in all parts of the tobacco plant. In addition, the inhibitive effect of biochar on the Cd concentration in the leaves was weak at the rosette stage (22.17-53.72%) compared with the other stages (46.14-78.88%), and the degree of inhibition of biochar on the Cd concentration in the middle leaves (37.94-59.24%) was lower than that in the upper and lower leaves (49.04-73.54%) at all developmental stages. However, the long-term remediation effect of biochar on soil Cd contamination needs to be further verified, and the combination of biochar and other technologies should receive additional attention.

Optimizing the synthetic nitrogen rate to balance residual nitrate and crop yield in a leguminous green-manured wheat cropping system.

Nitrate that originates from agriculture is linked to a series of deleterious environmental consequences that are closely related to human health. Therefore, it is vital to design cropping systems that can produce acceptable crop yields while minimizing the impact of surplus soil nitrate. To develop quantitative estimations, data from 2008 to 2016 were evaluated using multiple regression models. A split-plot field experiment was conducted, with the main treatments of growing Huai bean, soybean and mung bean in summer as leguminous green manure (LGM) while fallow as the control. Four synthetic N rates (0, 108, 135 and 162kgha-1) were applied as sub-treatments at wheat seeding. The N accumulation for LGMs ranged from 61 to 90kgha-1, and that of Huai bean was 46% higher than the average value of soybean and mung bean (P<0.05). The threshold of total N for wheat to produce the highest yields was 141kgha-1. For the LGM treatments, residual nitrate accumulated below the root-zone soil was not significantly increased even when their total N inputs were higher than that of fallow with 162kgha-1 of synthetic N. The estimated nitrate-holding capacity of the root-zone soil for the LGM treatments ranged from 104 to 117kgha-1, and the corresponding synthetic N limits were 97-130kgha-1. Considering the target of producing high wheat yields while keeping the residual nitrate in the root-zone soil, the optimal synthetic N rates for LGM treatments were 52-80kgha-1. In conclusion, growing LGMs can maintain high crop yield and mitigate the environmental impact of residual nitrate by substantially replacing the synthetic N to avoid nitrate leaching to deeper soils.

Coupling life-cycle assessment and the RothC model to estimate the carbon footprint of green manure-based wheat production in China.

Reducing the carbon footprint (CF) of crop production is an efficient way to mitigate climate change. Growing legume green manure (LGM) instead of summer fallow may achieve this goal by lowering synthetic nitrogen (N) fertilizer needs and replenishing the depleted soil carbon (C) pool. The Rothamsted Carbon (RothC) model was incorporated into the Life-Cycle Assessment (LCA) to evaluate the present and projected CFs of green manure-based wheat production systems in dryland agriculture on the Loess Plateau of China. The field study included four main treatments (Huai bean, soybean and mung bean grown as green manure in summer and fallow as control) and four synthetic N rates (0, 108, 135 and 162kgNha-1) applied at wheat sowing. Soybean as LGM increased averaged wheat yield over 4 synthetic N rates by 8% compared with fallow (P<0.05), and synthetic N requirement was reduced by 33% without compromising the wheat yield for all the main treatments. Although LGM treatments had higher greenhouse gas (GHG) emissions from agricultural inputs, the greater amount of C inputs elevated the corresponding SOC stocks (SOCS) by 14-24% after 8years, thus significantly reducing the CF by 25-51% compared with fallow. The modelled SOCS equilibrium indicates that the CF for cropping systems with LGM will be 53-62% lower than fallow and 23-37% lower compared with their current level. In conclusion, introducing legume green manure instead of summer fallow is a highly efficient measure for persistent CF reduction, and coupling the RothC model and LCA is an alternative method to predict the long-term impact of different cropping systems on GHG emissions.

Soil Water Balance and Water Use Efficiency of Dryland Wheat in Different Precipitation Years in Response to Green Manure Approach.

Winter wheat (Triticum aestivum L.) monoculture is conventionally cultivated followed by two to three months of summer fallow in the Loess Plateau. To develop a sustainable cropping system, we conducted a six-year field experiment to investigate the effect of leguminous green manure (LGM) instead of bare fallow on the yield and water use efficiency (WUE) of winter wheat and the soil water balance (SWB) in different precipitation years in a semi-arid region of northwest China. Results confirmed that planting LGM crop consumes soil water in the fallow season can bring varied effects to the subsequent wheat. The effect is positive or neutral when the annual precipitation is adequate, so that there is no significant reduction in the soil water supplied to wheat. If this is not the case, the effect is negative. On average, the LGM crop increased wheat yield and WUE by 13% and 28%, respectively, and had considerable potential for maintaining the SWB (0-200 cm) compared with fallow management. In conclusion, cultivation of the LGM crop is a better option than fallow to improve the productivity and WUE of the next crop and maintain the soil water balance in the normal and wet years in the Loess Plateau.

Gadolinium promoted proliferation in mouse embryo fibroblast NIH3T3 cells through Rac and PI3K/Akt signaling pathways.

Nephrogenic systemic fibrosis (NSF) is a fibrosing disorder disease developed in patients with underlying renal insufficiency following exposure to gadolinium-based contrast agents (GBCAs). Previous studies have demonstrated that GdCl3 can promote NIH3T3 fibroblast cell proliferation, which provide a new clue to the role of GBCAs in the development of NSF. In the present study, we further clarify the molecular mechanism of Gd-promoted proliferation. The results showed that intervention with the Rac inhibitor NSC23766 abrogated Gd-promoted proliferation. The levels of active Rac1 significantly increased in Gd-treated cells detected by pull-down assays. In addition, the phosphorylation of Akt was significantly elevated in the treatment group, which was blocked by NSC23766. NSC23766 also reduced the migration of NIH3T3 cells enhanced by Gd. Moreover, the F-actin cytoskeleton was strengthened and the mitotic cell numbers was significantly increased after exposure to Gd. These results suggest that Rac and PI3K/Akt signaling pathways, as well as integrin-mediated signal pathway may play important roles in Gd-induced cell proliferation. In addition, under serum-free condition, Gd could decrease ROS accumulation and increase NIH3T3 cell survival.