The utilization of Chlorella for the dual goals of biofuel production and wastewater nutrient removal is highly attractive. Moreover, this technology combined with flue gas (rich in CO2) cleaning is considered to be an effective way of improving biofuel production. However, the sterilization of wastewater is an energy-consuming step. This study aimed to comprehensively evaluate a cost-effective method of culturing Chlorella pyrenoidosa in unsterilized piggery wastewater for biofuel production by sparging air or simulated flue gas, including algal biomass production, lipid production, nutrient removal rate and the mutual effects between algae and other microbes. The average biomass productivity of C. pyrenoidosa reached 0.11 g L−1 day−1/0.15 g L−1 day−1 and the average lipid productivity reached 19.3 mg L−1 day−1/30.0 mg L−1 day−1 when sparging air or simulated flue gas, respectively. This method achieved fairish nutrient removal efficiency with respect to chemical oxygen demand (43.9%/55.1% when sparging air and simulated flue gas, respectively), ammonia (98.7%/100% when sparging air and simulated flue gas, respectively), total nitrogen (38.6%/51.9% when sparging air or simulated flue gas, respectively) and total phosphorus (42.8%/60.5% when sparging air or simulated flue gas, respectively). Culturing C. pyrenoidosa strongly influenced the microbial community in piggery wastewater. In particular, culturing C. pyrenoidosa enriched the abundance of the obligate parasite Vampirovibrionales, which can result in the death of Chlorella. The study provided a comprehensive evaluation of culturing C. pyrenoidosa in unsterilized piggery wastewater for biofuel production. The results indicated that this cost-effective method is feasible but has considerable room for improving. More importantly, this study elucidated the mutual effects between algae and other microbes. In particular, a detrimental effect of the obligate parasite Vampirovibrionales on algal biomass and lipid production was found.

The long-term excessive use of chemical fertilizers may result in soil degradation, but manure and straw application is considered to be an effective approach for alleviating this problem. The aim of this study is to examine the long-term impacts of different fertilization patterns on soil quality variables in a wheat–sweet potato rotation system. Four treatments were conducted in a field trial for a duration of twelve years, including (1) no fertilizer (control, CK); (2) application of mineral fertilizers (NPK) alone; (3) NPK with crop straw return (NPKs); (4) combined use of NPK and farmyard manure (NPKm). Thirteen physical, chemical, and biological soil parameters were measured. The results showed that the NPKm and NPKs significantly improved the proportion of macroaggregates (>0.25 mm) by 24.7% and 21.9% compared to the NPK alone, respectively. The proportion of microaggregates (0.053–0.25 mm) under the NPKm was 47.4% significantly higher than the NPKs. Additionally, the NPKm resulted in a 22.2% and 19.6% increase in the SOC content than the NPK and NPKs, respectively. In terms of soil-available K, the NPKs resulted in levels that were 42.1% and 49.6% higher than the NPKm and NPK alone, respectively. Long-term fertilization significantly decreased soil pH by 0.95–1.85 units compared to the control, whereas manure application could alleviate soil acidification, as shown when the pH increased by 10.6–18.7%. The NPKm and NPKs resulted in significantly increased soil pHs by 10.6% and 18.7% compared to the NPK alone, respectively. In addition, the NPKm and NPKs increased N-acetyl-β-D-glucosaminidase activity by 52.6% and 60.3% compared to the NPK alone. Determined by the minimum data set method, the NPKm treatment exhibited the highest soil quality index, followed by the NPKs and NPK. Our findings suggested that the combined use of chemical fertilizers with organic amendments proved beneficial for enhancing soil quality.

Rooted single leaves of sweet potato (Ipomoea batatas L.) produce and translocate photosynthates, thus representing an ideal model for characterising the source–sink relationships and responses to various environments. A hydroponics culture study was conducted with rooted single leaves of sweet potato to determine intraspecific variation in growth, biomass partitioning, and associated physiological changes in response to variable potassium (K) supply among genotypes Ji22 (low K-use efficiency), Nan88 (high K-uptake efficiency) and Xu28 (high K-use efficiency). Potassium deficiency suppressed biomass accumulation in blades, petioles and roots in all three genotypes. Root length of diameters <0.25 mm and 0.25–0.5 mm was significantly less for K-deficient than K-sufficient roots of all genotypes, but the difference was proportionally greater in the K-inefficient genotype Ji22 than the other two genotypes. Potassium deficiency also severely inhibited net photosynthesis of blades in Nan88 and Ji22, as well reducing photosynthate translocation, increasing starch, hexose and sucrose concentrations, and decreasing K concentration in blades. The genotypes varied in photosynthesis-related responses to the K deficiency. Xu28 had greater blade K concentration and net photosynthesis as well as stable maximum quantum yield of photosystem II (FV/FM, with FV = FM – F0) under K deficiency, possibly because of a better source–sink balance and more efficient translocation of photosynthates to roots and K to blade compared with genotypes Ji22 and Nan88. Impaired phloem loading during K deficiency was associated with a decline in photosynthetic rate and decreased carbohydrate supply from blades, resulting in restricted root growth.

Although conservation tillage (CT), polyacrylamide (PAM), and biochar (BC) are each known to enhance soil organic carbon (SOC), their combined short-term effects on SOC sequestration and fertilizer-nitrogen (N) recovery remain unclear. A ¹⁵N-tracing study involving two tillage regimes (rotary tillage (RT) and CT) and four amendments (no amendment (CK), PAM, BC, and PAM + BC (PMC)) was conducted across two seasons from a wheat–maize rotation in an infertile soil. Compared with RT, the crop-recovered fertilizer-N under CT was significantly increased by 15.2%. Relative to CK, the SOC stock, non-labile SOC (NLOC) stock, and total fertilizer-N recovery were increased by 15.9–28.7%, 19.5–48.5%, and 10.10–57.37 kg N ha⁻¹, respectively, in BC amendment under both RT and CT. Soil aggregate stability was significantly improved in PAM amendment, particularly under CT and in the maize season, thereby reducing SOC lability. The structural equation model indicated that the short-term promotion of fertilizer-N recovery was driven by the increase in total SOC and NLOC. The adoption of PMC under CT exhibited the lowest SOC lability and the highest total fertilizer-N recovery at the end of the trial. These findings demonstrated the short-term effectiveness of integrating CT, PAM, and BC to enhance fertilizer-N recovery by promoting crop N utilization and increasing the quantity and quality of SOC.