Iron-biofortification is a sustainable food-based approach to combat iron deficiency by increasing iron content and bioavailability in agronomic crops. Siderophore producing microbes offer a sustainable and low-cost way to increase iron supply in crops. Also, certain substances released from organic amendments act as iron-chelators which increase the solubility as well as the availability of iron to plants. Present study investigated the role of siderophore-producing endophytic bacteria and biochar on iron-fortification of a novel crop quinoa in iron-limited saline conditions. The surface-disinfected seeds of quinoa were inoculated with Burkholderia phytofirmans PsJN (CFU = 10⁹) and sown in saline soil (EC 20 dS m⁻¹) amended with biochar (1% w/w). Results revealed that biochar and PsJN particularly when applied together significantly enhanced plant growth, grain yield, and grain nutrient contents of quinoa. Strikingly, iron concentration in quinoa grains was increased up to 71% by the combined application of biochar and PsJN. Moreover, plant physiological parameters were also improved significantly by the integrated application. However, enzymatic/non-enzymatic antioxidants activities were decreased by integrated treatment thus ameliorated salinity stress. Our study suggests that integrated application of siderophore-producing bacteria and biochar could be a promising, sustainable and cost-effective strategy which is easily integratable into the existing farming practices to achieve food fortification with micronutrients in developing countries.

Biochar is a potential material for making slow-releasing phosphorus (P) fertilizers for the sake of increasing soil P-use efficiency. The adsorption of phosphorus by pineapple leaf biochar (PB) prepared at different pyrolysis temperatures and its mechanism remain unclear. In order to study the effect of preparation temperature on the structural characteristics of biochar from pineapple leaves and the adsorption of phosphorus by biochar, pineapple leaves were used as raw materials to prepare biochar by restricting oxygen supply at 300 °C, 500 °C, and 700 °C. The structural characteristics and adsorption of phosphorus by pineapple leaf biochar at different temperatures (PB300, PB500, and PB700) were analyzed. The results showed the following: (1) The pore structure of biochar pyrolysis at 300 °C (PB300) did not significantly change, while the surface structure of biochar pyrolysis at 700 °C (PB700) significantly changed, the specific surface area (S_BET) increased by 26.91~37.10 times that observed in PB300 and PB500, and the pore wall became thinner. (2) The number of functional groups (C=O) in PB700 decreased, and the relative content of C-H/-CHO in PB500 and PB700 increased by 4.38 times that observed in PB300. (3) The adsorption of phosphorus by biochar was a multi-molecular layer chemisorption, accompanied by single-molecular-layer physical adsorption and intramolecular diffusion. For PB300, both the physical and chemical processes of the adsorption of PO₄³⁻ by biochar were weakened, and the chemical process was dominated by cationic (Ca²⁺, Mg²⁺, Fe³⁺, and Al³⁺) adsorption at 500 °C. For PB700, the physical adsorption dominated by pore size structure was the main process, and the physicochemical adsorption at 700 °C was significantly stronger than that observed at 300 °C and 500 °C. These results indicate that biochar prepared at 500 °C can save energy in the preparation process and has excellent physical and chemical structure, which can be used as the basic material for further modification and preparation of biochar phosphate fertilizer.

Introduction: Tropical regions are characterized by high temperatures and abundant rainfall, which facilitate rapid carbon mineralization. However, research on soil organic carbon conversion efficiency (Esoc) in these areas is currently constrained by a lack of robust data support.Methods: This study used nylon - bags with typical tropical organic materials (pineapple leaf (PAL), banana stems (BAS), coconut husk (CCH), and organic fertilizer (OF)) to explore how mixing straw with latosol impacts soil organic carbon conversion efficiency (Esoc) and products, and to understand the relationships among Esoc, material composition (glycolipid, hemicellulose, cellulose, lignin), and enzyme activity.Results: CCH had the highest Esoc, from 37.79% to 96.87%, followed by OF with 26.71%–63.12%. The Esoc of PAL and BAS was 34.57% and 25.32% at 90 days, and 7.59% and 2.55% at 1080 days. The main factor that determines the difference in carbon conversion efficiency is the composition of organic materials. Compared with CK treatment, the soil organic carbon for PAL and BAS at 90_days was mainly O–alkyl–C, anomertic–C, and N–alkyl/methoxyl–C, with an unstable structure. The decomposition products of CCH mainly consisted of anomertic–C, aromatic–C, O–alkyl–C, carbonyl–C, and N–alkyl/methoxyl–C. The increased organic carbon in OF - mixed soil was mainly N–alkyl/methoxyl–C and anomertic–C. In the short-term (90 days), PAL, BAS, and OF increased the quantity and diversity of soil microorganisms, as well as the activities of xylosidase and cellobiohydrolase. CCH mainly enhanced soil phenol oxidase activity and maintained microbial biomass stabilityin the long-term (1080 days).Discussion: This study revealed the changes of microbial diversity and enzyme activity under different organic materials. The promotion effects of PAL and BAS on microbial biomass, diversity and enzyme activity in the short term and the maintenance effects of CCH on the stability of microbial biomass in the later period were investigated, which provided a new basis for further exploring the function and mechanism of microorganisms in soil ecosystems.

Background: Returning pineapple leaves (PAL), banana stems (BAS), coconut husks (CCH), and organic fertilizer (OF) to the field is an important method for soil improvement. However, the effects of these materials on the soil remain unclear. Methods: This study employed a nylon-bag experiment filled with the above-mentioned materials to investigate the impacts on soil physicochemical properties and microbial community structure. Results: The short term acidification caused by PAL was due to the significant increase in isobutyric, isovaleric, and hexanoic acids. PAL and BAS promoted the formation of >0.25 mm aggregates in the short term (90 days). C and N were most abundant in 2 mm soil aggregates. The dominant biomarkers in the soil treated with PAL were Koribacteraceae, Chrysozymaceae, Trimorphomycetaceae, and Tremellales. The main biomarkers of soil treated with BAS were Caulobacteraceae, Aspergillaceae, Onygenales, and Ceratostomataceae. The dominant biomakers in the soil treated with CCH and OF were richer than those in soil treated with PAL and BAS. Conclusions: The long term return effects of CCH and OF are better than those of PAL and BAS.

Introduction: Previous studies indicate that the combined supply of both nitrate nitrogen (NO₃⁻) and ammonium nitrogen (NH₄⁺) is more beneficial for pineapple growth than the exclusive supply of either NO₃⁻ or NH₄⁺ alone. However, the optimal ratio of NO₃⁻:NH₄⁺ that maximizes pineapple growth remains to be fully elucidated, which limits the optimization of nitrogen fertilizer management in pineapple cultivation. Methods: Uniform plantlets of Ananas comosus L. cv. Comte de Paris were subjected to hydroponic experiments with five NO₃⁻:NH₄⁺ ratios (0:100, 30:70, 50:50, 70:30, and 100:0) and a fixed total nitrogen concentration of 4 mM. The shoot and root growth characteristics, as well as carbon (C) and nitrogen (N) accumulation traits of pineapple plants, were systematically investigated. Additionally, the NO₃⁻ and NH₄⁺ uptake rates of roots were determined. Results: Compared with other treatments, the NO₃⁻:NH₄⁺ ratio of 70:30 significantly increased total root length and surface area, and exhibited the highest NO₃⁻ uptake rate. With increasing nitrate proportions in the nitrogen supply, plant N uptake and the contents of chlorophyll a (Chl a) and chlorophyll b (Chl b) were significantly increased. Specifically, relative to the sole NH₄⁺ treatment (0:100), the 70:30 ratio treatment increased leaf area by 61.10%, leaf dry matter content by 24.40%, plant N accumulation by 19.49%, and plant C accumulation by 21.62%. Enhanced N uptake and photosynthetic pigment synthesis facilitated leaf area expansion, thereby promoting overall plant growth. Discussion: These results indicate that a NO₃⁻:NH₄⁺ ratio of 70:30 is optimal for pineapple growth, as it effectively enhances both root and shoot development and improves C and N accumulation. This finding provides valuable insights for optimizing nitrogen fertilizer management strategies, which is crucial for promoting pineapple productivity in practical cultivation.