Microalgal biomass offers a promising biofertilizer option due to its nutrient-rich composition, adaptability, and environmental benefits. This study evaluated the potential of microalgal-based biofertilizers—microalgal Chlorella biomass, de-oiled microalgal biomass (DMB), and de-oiled and de-aqueous extract microalgal biomass (DAEMB)—in enhancing lettuce growth, soil nutrient dynamics, and microbial community composition. Lettuce seedlings were cultivated with these biofertilizers, and plant growth parameters, photosynthetic pigments, and nitrogen uptake were assessed. Soil incubation experiments further examined nutrient mineralization rates, while DNA sequencing analyzed shifts in rhizosphere microbial communities. Lettuce grown with these biofertilizers exhibited improved growth parameters compared to controls, with Chlorella biomass achieving a 31.89% increase in shoot length, 27.98% in root length, and a 47.33% increase in fresh weight. Chlorophyll a and total chlorophyll levels increased significantly in all treatments, with the highest concentrations observed in the Chlorella biomass treatment. Soil mineralization studies revealed that DMB and DAEMB provided a gradual nitrogen release, while Chlorella biomass exhibited a rapid nutrient supply. Microbial community analyses revealed shifts in bacterial and fungal diversity, with increased abundance of nitrogen-fixing and nutrient-cycling taxa. Notably, fungal diversity was enriched in biomass and DAEMB treatments, enhancing soil health and reducing pathogenic fungi. These findings highlight microalgal biofertilizers’ potential to enhance soil fertility, plant health, and sustainable resource use in agriculture.

In recent years, researchers have turned their attention to the co-cultivation of microalgae and plants as a means to enhance the growth of hydroponically cultivated plants while concurrently producing microalgal biomass. However, the techniques used require precise calibration based on plant growth responses and their interactions with the environment and cultivation conditions. This study initially focused on examining the impact of hydroponic nutrient concentrations on the growth of the microalga Chlorella sp. AARL G049. The findings revealed that hydroponic nutrient solutions with electrical conductivities (EC) of 450 µS/cm and 900 µS/cm elicited a positive response in microalgae growth, resulting in high-quality biomass characterized by an elevated lipid content and favorable properties for renewable biodiesel. The biomass also exhibited high levels of polyunsaturated fatty acids (PUFAs), indicating excellent nutritional indices. The microalgae culture and microalgae-free culture, along with inoculation-free lettuce (Lactuca sativa L. var. longifolia) and lettuce that was inoculated with plant growth actinobacteria, specifically the actinomycete Streptomyces thermocarboxydus S3, were subsequently integrated into a hydroponic deep-water culture system. The results indicated that several growth parameters of lettuce cultivated in treatments incorporating microalgae experienced a reduction of approximately 50% compared to treatments without microalgae, and lowering EC levels in the nutrient solution from 900 µS/cm to 450 µS/cm resulted in a similar approximately 50% reduction in lettuce growth. Nevertheless, the adverse impacts of microalgae and nutrient stress were alleviated through the inoculation with actinomycetes. Even though the co-cultivation system leads to reduced lettuce growth, the system enables the production of high-value microalgal biomass with exceptional biodiesel fuel properties, including superior oxidative stability (>13 h), a commendable cetane number (>62), and a high heating value (>40 MJ/kg). This biomass, with its potential as a renewable biodiesel feedstock, has the capacity to augment the overall profitability of the process. Hence, the co-cultivation of microalgae and actinomycete-inoculated lettuce appears to be a viable approach not only for hydroponic lettuce cultivation but also for the generation of microalgal biomass with potential applications in renewable energy.

The consumption of lettuce is associated with an increased risk of ingesting nitrate, a naturally occurring and potentially harmful compound that can have adverse effects on human health. Hydroponic cultivation systems serve as effective tools for regulating nutrient solutions and nitrogen availability, which are essential for controlling nitrate levels. However, the techniques for reducing nutrient levels need to be appropriately calibrated based on lettuce growth responses and their interactions with the environment and growing conditions. Previous studies have demonstrated that plant probiotic actinomycetes can alleviate nutritional stress in various crops. However, there is a noticeable gap in research concerning the effects of actinomycetes on hydroponically grown lettuce, particularly under nutrient-limiting conditions. This study aimed to evaluate the effectiveness of the actinomycete Streptomyces thermocarboxydus S3 in enhancing lettuce growth in a nutrient-restricted hydroponic system. The results indicated that the detrimental effects of nutrient stress on lettuce were mitigated by the inoculation of lettuce with S. thermocarboxydus S3. This mitigation was evident in various growth parameters, including leaf count, shoot length, and the fresh and dry weights of both shoots and roots. In the presence of nutritional stress, S. thermocarboxydus S3 likely mitigated the negative effects on lettuce by reducing hydrogen peroxide levels, presumably through the synthesis of H₂O₂-scavenging enzymes. Furthermore, S. thermocarboxydus S3 successfully survived and colonized lettuce roots. Therefore, the inoculation of lettuce with S. thermocarboxydus S3 offers significant advantages for promoting lettuce growth in nutrient-limited hydroponic systems.

The increasing demand for agricultural land is driving deforestation, which contributes to rising greenhouse gas emissions—a primary driver of climate change. Agroforestry systems present a valuable alternative approach for mitigating these emissions. This study investigates the influence of various agroforestry systems on key parameters for assessing soil carbon dynamics, including soil carbon stock, microbial biomass carbon (MBC), and microbial respiration (MR) in northern Thailand. The study compared different agroforestry systems, such as coffee monoculture (CA), coffee intercropped with forest trees (CF), coffee intercropped with persimmon trees (CP), and natural forest (NF), as reference areas. Soil samples were collected from three depths (0–20, 20–40, and 40–60 cm) across three seasons (rainy, cold, and summer). Results showed that soil carbon from land use changes from NF to coffee agroforestry systems led to a 12.10% increase in CF and an 11.89% decrease in CP. The CA system showed a non-significant 9.06% decrease compared to the natural forest. MBC levels were higher in the agroforestry coffee areas (CF and CP), comparable to those in NF. However, CA exhibited significantly lower MBC (p < 0.05) compared to other treatments. While MBC and MR showed a positive correlation, higher MBC did not necessarily indicate increased microbial activity or significant dissolved organic carbon (DOC) accumulation. Environmental factors, particularly seasonal variations, significantly influenced the results across all three investigations. This study demonstrates that both agroforestry coffee systems (CF and CP) more effectively mitigate deforestation impacts and enhance soil fertility compared to coffee monoculture. For carbon stock enhancement specifically, CF emerged as the optimal choice.

Background: Tomato, a fruit with a high vitamin content, is popular for consumption and economically important in Thailand. However, in the past year, the extensive usage of chemicals has significantly decreased tomato yields. Plant Growth-Promoting Rhizobacteria (PGPR) is an alternative that can help improve tomato production system growth and yield quality while using fewer chemicals. The present study aimed to determine whether endophytic actinomycetes promote growth and fruit quality of tomato (Solanum lycopersicum). Methods: The experiment was conducted in a net-houses at the Center for Agricultural Resource System Research, Faculty of Agriculture, Chiang Mai University, Chiang Mai province, Thailand. The randomized completely block design (RCBD) was carried out for four treatments with three replications, which was control, inoculation with TGsR-03-04, TGsL-02-05 and TGsR-03-04 with TGsL-02-05 in tomato plant. Isolated Actinomycetes spp. of each treatment was then inoculated into the root zone of tomato seedlings and analyzed by Scanning Electron Microscopy (SEM). The height of tomato plants was measured at 14, 28, 56, and 112 days after transplanting. Final yield and yield quality of tomato was assessed at the maturity phase. Results: The SEM result illustrated that the roots of tomato seedlings from all treatments were colonized by endophytic actinomycetes species. This contributed to a significant increase in plant height at 14 days after transplanting (DAT), as found in the TGsR-03-04 treatment (19.40 cm) compared to the control. Besides, all inoculated treatments enhanced tomato yield and yield quality. The highest weight per fruit (47.38 g), fruit length (52.37 mm), vitamin C content (23.30 mg 100 g⁻¹), and lycopene content (145.92 µg g⁻¹) were obtained by inoculation with TGsR-03-04. Moreover, the highest yield (1.47 kg plant⁻¹) was obtained by inoculation with TGsL-02-05. There was no statistically significant difference in the number of fruits per plant, fruit width, brix, and antioxidant activity when various inoculations of endophytic actinomycetes were applied. Therefore, the use of endophytic actinomycetes in tomato cultivation may be an alternative to increase tomato yield and yield quality.

Modern agriculture requires alternatives to counteract the price volatility and environmental impacts of synthetic fertilizers. Mealworm frass (MF) is being explored as a novel biofertilizer in sustainable agriculture. However, the in-depth characterization of its biofertilization potential is lacking. Similarly, the mechanistic role of its associated microbiota towards improving early plant growth response is unexplored. These are the gaps the current study addresses. Initially, the particle size and nutrient distribution of the MF were characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS). Subsequently, microbial isolation and molecular identification characterized the MF-associated microbiome. Isolates were thereafter screened via various plant growth promotion (PGP) assays. Nutrient mineralization rates were calculated through soil incubation experiments. MF and chicken manure (CM) were incorporated into the soil at 1% (w/w) using a Completely Randomized Design (CRD) with three replications. Additionally, the effects of the MF on Chinese kale (CK) growth and yield were evaluated under greenhouse conditions using a Randomized Complete Block Design (RCBD). The results showed that MF had uniform nutrient distribution: high organic matter content (63.38%), the presence of essential nutrients (5.09% N, 1.71% P, and 2.82% K), and a low C:N ratio (6.69). Furthermore, the characterized MF microbiota comprised plant growth-promoting genera such as Streptomyces , Microbacterium , Brucella , Staphylococcus , and Rothia , which fix nitrogen, solubilize K & P, and produce IAA. Moreover, nutrients were released rapidly for plant uptake (7-day nitrogen mineralization rate = 93.75 mg kg ⁻¹ day ⁻¹ ). The CK growth trials showed that MF + 50% chemical fertilizer (CF) yielded the highest fresh weight (141.73 g plant ⁻¹ ) and crop quality (vitamin C: 227.97 mg plant ⁻¹ ; antioxidant activity: 238.10 µmol TE g ⁻¹ ). Usually, MF alone and MF + 50% CF outperformed CF and CM alone, respectively, in improving various plant growth responses, nutrient uptake, antioxidant activity, and vitamin C content ( p < 0.05). Taken together, our findings mechanistically portray MF (aided by PGP microbiota) as a biofertilizer for both organic and integrated farming systems. Further scale-up studies are recommended to fully justify the use of MF biofertilizer as a substitute for CF towards circular economy and agricultural sustainability principles. Graphical abstract