Inoculating microbial inoculants to speed up the decomposition of returning straw is currently a hot topic. Meanwhile, the soil moisture content (SMC) could change the diversity, abundance, and metabolism of the soil microbial community structure, which affects the straw degradation rate under the straw returning condition. In this research, rumen microorganisms with strong decomposing abilities in natural systems were used as inoculants to promote straw decomposing and returning to the field. The effects of the SMC on straw decomposition under rumen fluid (RF)-induced returning were investigated. Experiments were conducted for 30 days with typical paddy soil in the south of China under conditions of 30%, 70%, and 100% SMC. With an increase in the SMC within a certain range (30~100%), the decomposition rate of straw showed a trend of first rising and then falling. Treatments of 70% SMC with RF addition generally achieved the maximum rate of straw degradation. The peak value was 49.96%, which was 2.67-fold higher than the treatments of 30% SMC with RF addition (18.74%) and 24.1% higher than those of the control with 70% SMC (40.3%) (p < 0.05). Moreover, a straw structural analysis proved that at 70% SMC, microorganisms from RF favored the destruction of functional groups on the straw surface and the degradation of cellulose. Meanwhile, it was shown that RF could promote the decay of straw, leading to increments in enzyme activities and soil nutrients. The higher the soil moisture content, the higher the key soil enzyme activities. This indicates that the diversity and abundance of cellulose-degrading bacteria and fungi in soil microorganisms and rumen microorganisms were changed with different soil moisture contents. The experimental findings suggest an innovative way to further utilize rumen microorganisms.

Pomelo peel (PP) is a kind of solid waste that is produced in the processing industry of honey pomelo. This study deeply explored the feasibility of recycling PP in the form of hydrochar (HC) by microwave-assisted hydrothermal carbonization (HTC) technology. Under the non-catalytic reaction conditions, the yield of hydrochar initially increased with the rise of reaction temperature (150–210 °C) until it remained relatively stable after 210 °C. Under the CaO-catalytical reaction condition, the yield of hydrochar did not change much at first (150–190 °C) but decreased significantly when the reaction temperature exceeded 190 °C. After the microwave-assisted HTC treatment, the PP-derived HC presented higher aromaticity, carbonization degree, porosity, and caloric value. Compared with raw PP, the nutrients in HC were more stable (conducive to being used as slow-release fertilizer). The application of CaO increased the pH value of HC and effectively promoted the accumulation of phosphorus in HC. The HC produced at 210 °C without any catalyst possessing a high devolatilization ability. Additionally, the HC obtained at 190 °C with CaO as the catalyst presented a high combustion property. In general, PP-derived HC showed great application potential in the field of soil remediation/improvement and solid fuels. This preliminary study would undoubtedly provide some important fundamental understanding of the microwave-assisted HTC of PP.

Soil microorganisms are well known to play a crucial role in carbon and nutrient cycling within terrestrial ecosystems. Numerous research efforts have demonstrated that nitrogen deposition can change forest soil microbial diversity and community composition; however, it is still unclear how nitrogen deposition will affect the soil microbial diversity and community composition in subtropical forests under the background of increasing drought. Consequently, over a period of 2.5 years, we carried out an experiment using two N addition regimes and three soil water treatment levels to reveal the effects of nitrogen, drought, and the influence of their interaction on the diversity and community composition of soil microorganisms. Overall, we found that both N addition and drought decreased the bacterial Shannon and Simpson indices yet had no significant effect on fungal diversity. In the well-watered treatments, nitrogen addition did not significantly reduce bacterial diversity, while in the moderate drought and severe drought treatments, N addition significantly decreased bacterial diversity, reducing the Shannon and Simpson indices by 27.05% and 0.13%, respectively, in the severe drought treatment. Drought significantly altered the community composition of bacteria regardless of N addition. N addition significantly changed the community composition of bacteria under moderate drought treatments, while both N addition and drought had less significant effects on the fungal community composition. The soil water content, fine root biomass, and soil pH were significantly correlated with bacterial community composition, which explained 53.3%, 11.1%, and 8.7% of the changes in soil bacterial community composition, respectively. These results suggest that drought may intensify the inhibitory effect of nitrogen on bacterial diversity and change the magnitude and direction of the impact of nitrogen on the composition of the bacterial community.

A novel multifunctional isoamylase, MIsA from Myxococcus sp. strain V11, was expressed in Escherichia coli BL21(DE3). Sequence alignment revealed that MIsA is a typical isoamylase that belongs to glycoside hydrolase family 13 (GH 13). MIsA can hydrolyze the α-1,6-branches of amylopectin and pullulan, as well as the α-1,4-glucosidic bond in amylose. Additionally, MIsA demonstrates 4-α-D-glucan transferase activity, enabling the transfer of α-1,4-glucan oligosaccharides between molecules, particularly with linear maltooligosaccharides. The K_m, K_cat, and V_max values of the MIsA for amylopectin were 1.22 mM, 40.42 µmol·min^–1·mg^–1, and 4046.31 mM·min^–1. The yields of amylopectin and amylose hydrolyzed into oligosaccharides were 10.16% and 11.70%, respectively. The hydrolysis efficiencies were 55%, 35%, and 30% for amylopectin, soluble starch, and amylose, respectively. In the composite enzyme hydrolysis of amylose, the yield of maltotetraose increased by 1.81-fold and 2.73-fold compared with that of MIsA and MTHase (MCK8499120) alone, respectively.

Straw returning has been evidenced to be an effective strategy for straw utilization. Nevertheless, numerous adverse effects on straw direct returning have been widely reported. It is safer to fully degrade the straw and then return it to the soil. This strategy has been shown to significantly improve soil nutrients. However, the effect on rice growth is unclear. In this study, a pot experiment was conducted by using different types of mushroom residues with chemical fertilizer for field return, compared to the conventional method of applying chemical fertilizer alone, and straw return with or without fertilizer. It was found that the return of mushroom residues to the field could increases the soil organic matter content by 16.9–23.5%, the alkaline nitrogen by 39.1–47.4%, and the available potassium by 6.8–10.8%. Furthermore, mushroom residues were found to reduce the population of fungi and bacteria in the soil to a certain extent and increase the number of actinomycetes. Moreover, it was determined that mushroom residues elevated the nutrient content in plants, accelerated the tillering rate, and increased the number of tillers. This ultimately led to an increase in rice yield components, such as thousand-grain weight and the effective number of spikes. Mushroom residues can mimic the benefits of straw return while minimizing potential harm to rice yields. This study provides an effective strategy for the resource utilization of straw.

With the increasing shortage of fossil energy and various environmental problems caused by the burning of fossil energy, clean and recyclable new energy has received more and more attention. Lignocellulosic biomass can generate clean energy such as methane and hydrogen through anaerobic digestion. However, the structure of lignocellulose is complex, and its hydrolysis process becomes the rate-limiting step in the anaerobic digestion process. The development of more efficient agricultural waste pretreatment technology is still the most effective way to improve the hydrolysis efficiency and energy conversion efficiency of anaerobic fermentation. The researchers used various pretreatment methods to improve the anaerobic digestion of lignocellulose. This paper introduces the latest research progress in the field of agricultural waste fermentation and its pretreatment. Because of its high oxygen–carbon ratio, lignocellulosic is generally a much poorer energy carrier than fossil fuels, therefore the development of anaerobic digestion applications is particularly important. Summing up previous reports, biological pretreatment using bacteria and enzymatic pretreatment has better performances and to be the least expensive of lignocellulosic transformation and application in the biogas production process.