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Nature farming is a farming system that entails cultivating crops without using chemical fertilizers and pesticides. The present study investigated the bacterial and fungal communities in the rhizosphere of soybean grown in conventional and nature farming soils using wild-type and non-nodulating mutant soybean. The effect of soil fumigant was also analyzed to reveal its perturbation of microbial communities and subsequent effects on the growth of soybean. Overall, the wild-type soybean exhibited a better growth index compared to mutant soybean and especially in nature farming. Nodulation and arbuscular mycorrhiza (AM) fungi colonization were higher in plants under nature farming than in conventionally managed soil; however, fumigation drastically affected these symbioses with greater impacts on plants in nature farming soil. The rhizosphere microbiome diversity in nature farming was higher than that in conventional farming for both cultivars. However, the diversity was significantly decreased after fumigation treatment with a greater impact on nature farming. Principal coordinate analysis revealed that nature farming and conventional farming soil harbored distinct microbial communities and that soil fumigation significantly altered the communities in nature farming soils but not in conventional farming soils. Intriguingly, some beneficial microbial taxa related to plant growth and health, including Rhizobium, Streptomyces, and Burkholderia, were found as distinct microbes in the nature farming soil but were selectively bleached by fumigant treatment. Network analysis revealed a highly complex microbial network with high taxa connectivity observed under nature farming soil than in conventional soil; however, fumigation strongly broke it. Overall, the results highlighted that nature farming embraced higher microbial diversity and the abundance of beneficial soil microbes with a complex and interconnected network structure, and also demonstrated the underlying resilience of the microbial community to environmental perturbations, which is critical under nature farming where chemical fertilizers and pesticides are not applied.

To understand the distribution of the cultivable fungal community in plant tissues from nature farming tomato plants, we sampled plants of seven different tomato cultivars and recovered 1742 fungal isolates from 1895 stem tissues sampled from three sites in Japan. Overall, the isolation frequency was low (3–13%) and the isolation and colonization frequencies did not vary significantly as a function of the cultivar. The fungi were divided into 29 unique operational taxonomic units (OTUs) with 97% ITS gene sequence identity, the majority of which belong to Ascomycota (99.3%). The dominant genera of cultivable endophytic fungi were Fusarium (45.1%), Alternaria (12.8%), Gibberella (12.0%), and Dipodascus (6.8%). The alpha diversity of the fungal endophytes varied among tomato cultivars. Ordination analysis performed to investigate patterns of endophyte community assemblages on the various cultivars revealed that host cultivars had a significant impact on the endophyte community assemblages in all the study sites. Some of the taxa Fusarium, Alternaria, and Penicillium were found on all cultivars, while few were uniquely present in different cultivars. The dominant taxa may be adapted to the particular microecological and physiological conditions present in tomato stems.

In the process of shale gas well drilling in the southern Sichuan Basin, China, lost circulation of high-density oil-based drilling fluid has become a main challenge. In this study, a novel oil-based crosslinking-curing lost circulation material (OBCC-LCM) system applicable for 100-150 °C shale formation was developed based on polyether, isocyanates and blocking agent. The performance of OBCC-LCM pills was comprehensively evaluated by testing fluidity, setting time, strength, elasticity and fracture sealing capacity. The OBCC-LCM pill setting time could be controlled in 70-120 min. The strength of the pill solid was 5.27-6.51 MPa after 360 min heating, and the volume almost restored to the original states after being compressed by 70%. The pill sealed fractures up to 5 mm wide under a differential pressure of 5.2-6.1 MPa, and a higher maximum fracture sealing capacity when being jointly used with bridging LCMs. The OBCC-LCM clearly demonstrated superior performance of good pumpability at room temperature, stability under high temperature, compatibility with oil-based drilling fluids, adaptability with various fracture widths and sustainability in induced fracture. It is suitable for curing loss of induced fracture in low permeability formation and loss of oil-based drilling fluid, especially for loss of oil-based drilling fluid in shale formations. [ABSTRACT FROM AUTHOR]

Nature farming is a farming system that entails cultivating crops without using chemical fertilizers and pesticides. The present study investigated the bacterial and fungal communities in the rhizosphere of soybean grown in conventional and nature farming soils using wild-type and non-nodulating mutant soybean. The effect of soil fumigant was also analyzed to reveal its perturbation of microbial communities and subsequent effects on the growth of soybean. Overall, the wild-type soybean exhibited a better growth index compared to mutant soybean and especially in nature farming. Nodulation and arbuscular mycorrhiza (AM) fungi colonization were higher in plants under nature farming than in conventionally managed soil; however, fumigation drastically affected these symbioses with greater impacts on plants in nature farming soil. The rhizosphere microbiome diversity in nature farming was higher than that in conventional farming for both cultivars. However, the diversity was significantly decreased after fumigation treatment with a greater impact on nature farming. Principal coordinate analysis revealed that nature farming and conventional farming soil harbored distinct microbial communities and that soil fumigation significantly altered the communities in nature farming soils but not in conventional farming soils. Intriguingly, some beneficial microbial taxa related to plant growth and health, including Rhizobium, Streptomyces, and Burkholderia, were found as distinct microbes in the nature farming soil but were selectively bleached by fumigant treatment. Network analysis revealed a highly complex microbial network with high taxa connectivity observed under nature farming soil than in conventional soil; however, fumigation strongly broke it. Overall, the results highlighted that nature farming embraced higher microbial diversity and the abundance of beneficial soil microbes with a complex and interconnected network structure, and also demonstrated the underlying resilience of the microbial community to environmental perturbations, which is critical under nature farming where chemical fertilizers and pesticides are not applied. [ABSTRACT FROM AUTHOR]

Long-term excessive application of nitrogen fertilizer induces secondary salinization of soil, which results in inhibiting plant growth. In addition, soil moisture deficiency also affects plant growth. To investigate the effects of excessive nitrogen fertilizer and soil moisture deficiency on the antioxidant enzyme system, plant water relations analyzed through pressure-volume (P-V) curve, and photosynthetic light response parameters in tomato (Solanum lycopersicum L. Myoko) seedlings, an indoor experiment of about 50 d was conducted using two irrigation water amounts based on field capacity (soil moisture deficiency: 50%-80%; adequate water: 70%-80%), two nitrogen fertilizer rates (moderate nitrogen; excessive nitrogen fertilizer: 0.585 g/pot) and two types of irrigation water (tap water and microbial diluent). The results showed that excessive nitrogen fertilizer (N) and soil moisture deficiency (W) reduced the biomass of tomato seedlings. In comparison to CK (combination of adequate water and tap water quality), microbial dilution (EM) increased plant biomass by 5.2%. Also, the nitrogen application increased chlorophyll relative contents (SPAD). The maximum net photosynthetic rate (Pc) decreased with nitrogen application and increased with EM application and irrigation amount. Excessive nitrogen application increased the plant nitrate reductase activity (NR). The plant NR in the N treatment showed a 13.0% increase compared to CK, and the plant NR in the treatment of nitrogen application with water deficiency (WN) increased 34.0% compared to water deficiency (W). After applying excessive nitrogen, N, EM-N, WN, EM-WN respectively increased the plant nitrate reductase activity by 13.0%, 22.9%, 34.0%, and 28.6%, compared with the corresponding treatment with moderate nitrogen (i.e., CK, EM, W and EM-W). In addition, the activities of antioxidant enzymes [superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT)] in four treatments of nitrogen application (N, EM-N, WN, EM-WN) also increased significantly. Both soil moisture and nitrogen fertilizer significantly affect the parameters of osmotic adjustment, which is manifested in the reduction of osmotic potential (pFT), and the increase in the osmotic concentration (Cosm) and concentration difference (Cosm). But the decrease in the relative water content of apoplast (ap) indicated that water deficiency and excessive nitrogen reduced the water absorption and water retention capacity of tomatoes to a certain extent. In conclusion, excessive nitrogen application and soil moisture deficiency inhibit plant growth significantly in this experiment. Meanwhile, microbial dilution can alleviate excessive nitrogen fertilizer and water stress to some extent, but the effect was not significant. [ABSTRACT FROM AUTHOR]

Concerns about the soil salinity caused by excessive fertilization have prompted scientists to clarify the detailed mechanisms and find techniques to alleviate the damage caused by this kind of soil salinity. Aims of this study were to elucidate the effect of soil salinity caused by nitrate fertilization and the differences in salinity effect between nitrate salts and NaCl salt with analyses at various levels of crop physiology and molecular biology. A microbial inoculation was also tried to verify whether it could alleviate the salinity-induced loss and damages. In three experiments (Exp I, II and III), nitrate salts (NS) of Ca(NO3)2 and KNO3 were applied to potted tomato plants to simulate the soil salinity caused by fertilization and a microbial inoculant (MI) was applied. Photosynthesis was measured using Li-6400. Osmotic adjustment was analyzed using the mathematically modeled pressure-volume curve; O2 - concentration and activity of SOD and nitrate reductase were measured. Expression of nitrate reductase gene and the stress-responsive gene DREB2 was analyzed using the real-time PCR method. In Exp I and II, where the applied NS amount was moderate, NS application at low concentration induced increases in O2 - and MDA concentrations and plants acclimated to the soil salinity as the treatment prolonged for weeks. The acclimation was contributed by osmotic adjustment, activation of SOD and re-compartmentation of cell water between symplasm and apoplasm. These adjustments might be ultimately attributed to up-regulation of stress-responsive genes such as DREB2 as well as the nitrate reductase (NR) gene. However, in Exp III, applications of NaCl and NS at high concentration could not show positive effects as NS did. Application of MI synergistically increased the xerophytophysiological regulation caused by NS and alleviated the salinity damage in addition to its own positive effects on the tomato plants. Different from NaCl, nitrate salts at low application rate increased the total biomass and fruit yield of tomato and induced up-regulation expression of stress-responsive genes and the consequent active osmotic adjustment. However, nitrate application at high level negatively affected tomato plants irrespective of the gene up-regulations. Application of MI alleviated the salinity damage and synergistically increased the xerophytophysiological regulation caused by the soil salinity in addition to its positive effects on the tomato crop but the detailed mechanisms needed to be clarified in future further studies. [ABSTRACT FROM AUTHOR]