The structure and chemical composition of cell walls play a vital role in the bioconversion and utilization of plants. In the present study, the cell wall structure and chemical composition of pith and rind from sunflower stalks were compared and correlated to their nanofibrillation efficiency with ultrasonic treatment. Mild chemical pretreatment using 1% or 4% NaOH without any bleaching process were applied prior to ultrasonication nanofibrillation. Significant structural and chemical differences were demonstrated between the pith and rind, with the former exhibiting a much lower lignin and hemicellulose contents, higher pectin, much looser cell structure and higher cell wall porosity than the latter. Alkaline treatment alone was sufficient to eliminate most of the hemicellulose and pectin from stalk pith, whereas only partial removal of hemicellulose and lignin was achieved for the woody rind part. After 30 min of ultrasonic treatment, the stalk pith exhibited fully defibrillated fibrils with a continuous and entangled micro/nanofibrillated network, whereas numerous micron-sized fiber and fragments remained for the rind. The results indicated that stalk pith is less recalcitrant and easier to be fibrillated with ultrasonication than rind, which must be correlated to their distinct differences in both structure and chemical composition.

The utilization of biogas slurry is critical for the sustainable development of animal husbandry. Biomass carbon adsorption is a feasible method for the recycling of nutrients from biogas slurry. However, research on the co-adsorption of ammonia nitrogen and phosphate is scarce. Herein, soybean straw was utilized as the raw material to prepare Ca²⁺-modified biochar (CaSSB), which was investigated for its ammonia nitrogen and phosphate adsorption mechanisms. Compared with natural biochar (SSB), CaSSB possesses a high H/C ratio, larger surface area, high porosity and various functional groups. Ca²⁺-modified soybean straw biochar exhibited excellent adsorption performance for NH₄⁺–N (103.18 mg/g) and PO₄³⁻−P (9.75 mg/g) at pH = 6, using an adsorbent dosage of 2 g/L. The experimental adsorption data of ammonia nitrogen by CaSSB corresponded to pseudo-second-order kinetics and the Langmuir isotherm model, suggesting that the adsorption process was homogeneous and that electrostatic attraction might be the primary adsorption mechanism. Meanwhile, the adsorption of phosphate conformed to pseudo-second-order kinetics and the Langmuir–Freundlich model, whose mechanism might be attributed to ligand exchange and chemical precipitation. These results reveal the potential of CaSSBs as a cost-effective, efficient adsorbent for the recovery of ammonium and phosphate from biogas slurry.

Soil acidification reduces the abundance and activity of beneficial microorganisms, impairs tea plant growth, and ultimately leads to a decline in tea quality. Maintaining healthy soil is critical for sustainable tea agriculture. However, the interactive effect of biochar and nitrogen fertilizer on the microbial community structure and function in acidic tea plantation soils remains unclear. This study was designed to explore whether the co-application of biochar and fertilizer could enhance soil properties and maintain microbial health in tea plantations. Three treatments were set up through a controlled pot experiment: no fertilizer or biochar application (B₀N₀), fertilizer without biochar (B₀N₁), and biochar with fertilizer (B₁N₁). High-throughput sequencing technology was used to investigate the characteristics of soil microbial communities in tea plantations. Biochar amendment increased soil pH by 0.8 units, organic matter and total nitrogen by 13.5% and 21.4%, and reduced NH₄⁺-N and NO₃⁻-N leaching by 10.8% and 12.9%, respectively. It also modulated microbial community structure, enhanced the abundance of nitrogen-cycling genes (e.g., narB, nirK, nosZ), and influenced nitrogen availability through adsorption. Nitrate was identified as the main factor shaping microbial communities under fertilization. These results highlight the potential of biochar as a sustainable amendment to improve soil health and nitrogen retention in tea cultivation systems. Further field studies are warranted to validate its efficacy in enhancing tea productivity and reducing environmental nitrogen losses under real-world conditions.

Raw lignocellulosic biomass offers a low-input route for nutrient capture, yet its internal tissue heterogeneity is rarely considered when adsorption behavior is interpreted. Here, Giant Juncao (Pennisetum giganteum; also reported as Cenchrus fungigraminus) straw was separated into rind and pith to determine how native tissue architecture and cell-wall chemistry relate to ammonium (NH₄⁺) and phosphate adsorption. The pith occupied 72.33% of stem volume but only 26.85% of dry mass and had a much lower basic density than the rind (0.072 vs. 0.570 g·cm⁻³). It also showed a larger N₂-accessible specific surface area (2.67 vs. 1.13 m²·g⁻¹), greater pore volume (0.006 vs. 0.001 cm³·g⁻¹), higher pectin content (20.58 vs. 14.81 mg·g⁻¹), and lower cellulose crystallinity (48.28% vs. 57.30%). These contrasts were accompanied by tissue-dependent NH₄⁺ uptake: the rind and pith adsorbed 4.19 ± 1.02 and 10.36 ± 1.54 mg·g⁻¹, respectively, whereas whole straw reached 13.80 ± 0.23 mg·g⁻¹ under the same comparison conditions. Phosphate uptake was less tissue-sensitive (19.57–22.40 mg·g⁻¹). More than 90% of the 24 h uptake was reached within 60 min. Nonlinear least-squares fitting, evaluated by multiple criteria (R², SSE, RMSE, χ², or AIC), identified the pseudo-second-order kinetic model and the Langmuir–Freundlich isotherm as the best empirical descriptions of the measured data. Spectroscopic changes were consistent with participation of oxygen-containing cell-wall groups in nutrient retention, but did not uniquely resolve molecular binding pathways. The results show that tissue-scale architecture and heterogeneous lignocellulosic chemistry jointly shape nutrient uptake in minimally processed Giant Juncao and support further evaluation of the unseparated feedstock in real wastewater and nutrient-reuse scenarios.