[Effects of Chemical Fertilizer Reduction Substitute with Organic Fertilizer on Soil Functional Microbes and Lemon Yield and Quality].

To clarify the effects of non-rhizosphere/rhizosphere soil functional microbes (nitrifiers, denitrifiers, and phosphorus-solubilizing microorganisms) on lemon yield and quality, the lemon fruit and non-rhizosphere/rhizosphere soil were selected as subjects. To explore the correlation between non-rhizosphere/rhizosphere soil functional microbes and lemon yield and quality under a chemical fertilizer reduction substitute with organic fertilizer, traditional fruit quality determination and multiple molecular techniques were used. The results showed that:① 30% chemical fertilizer reduction substitute with organic fertilizer increased the nitrification intensity and phosphatase activity but effectively controlled the denitrifying enzyme activity. ② The chemical fertilizer reduction substitute with organic fertilizer significantly decreased the abundances of nitrifiers and nirS/nirK-harboring denitrifiers and significantly increased the abundances of nosZ-harboring denitrifier and phoD-harboring microorganisms. However, the diversities of functional microbial community structure did not have clear regularity under chemical fertilizer reduction substitute with organic fertilizer. ③ Compared with that under the application of chemical fertilizer and organic fertilizer alone, lemon yield and quality were the highest under the 30% reduction of chemical fertilizer substitute with organic fertilizer. ④ Nitrogen and its related microbes significantly affected lemon yield through internal and external quality. Phosphorus and its related microbes affected lemon yield mainly through internal quality. In addition, the influence factors of non-rhizosphere soil and rhizosphere soil on lemon intrinsic quality were obviously different. Altogether, these results showed that the 30% reduction of chemical fertilizer substitute with organic fertilizer significantly affected soil nitrogen and phosphorus functional microorganisms and further improved lemon yield and quality.

[Effect of Combined Application of Biochar with Chemical Fertilizer and Organic Fertilizer on Soil Phosphatase Activity and Microbial Community].

To study changes in phosphatase activity, we examined the diversity of phoC and phoD gene microbial communities in the rhizosphere and non-rhizosphere soil of plants under the treatment of chemical fertilizer and organic fertilizer combined with biochar. These results can provide a certain theoretical guidance for the conversion of insoluble phosphorus in the soil phosphorus pool to the inorganic phosphate ion that can be absorbed by plant roots and also provide a certain experimental basis for the improvement of the availability of phosphorus in the soil and the agricultural utilization of biochar. In this study, corn stalks and rice husk stalks were used as test materials, and the pot experimental method was adopted using the following treatments:set control (CK), traditional fertilization (F), chemical fertilizer+20 t·hm-2 rice husk biochar (FP), chemical fertilizer+10 t·hm-2rice husk biochar+10 t·hm-2 corn biochar (FPM), organic fertilizer+20 t·hm-2 rice husk biochar (PP), and fresh organic fertilizer+20 t·hm-2 rice husk biochar (NPP). We determined the rhizosphere and non-rhizosphere soil acid phosphatase (ACP) activity and alkaline phosphatase (ALP) activity and used T-RFLP technology to analyze the diversity of phoC and phoD genes in order to clarify the impact of biochar on the micro-ecosystem formed by the plants, soil, and microorganisms. The results showed that:① the ALP and ACP activities of each treatment in the non-rhizosphere soil were lower than that of CK. In the rhizosphere soil, the ALP activity was significantly increased after the combined application of chemical fertilizer and organic fertilizer with biochar, and the ACP activity in the rhizosphere soil was higher than that in the non-rhizosphere soil. ② The combined application of biochar with chemical fertilizers and organic fertilizers significantly increased the diversity of phoC and phoD genes communities in rhizosphere and non-rhizosphere soils (P<0.05); the diversity and richness of microbial communities in rhizosphere soil were higher than that in non-rhizosphere soils. ③ ACP activity was negatively correlated with phoC gene microbial community, and most ALP activity was positively correlated with phoD microbial community.

[Responses of Soil PhoC and PhoD Gene Microbial Communities to the Combined Application of Biochar with Chemical Fertilizers and Organic Fertilizers].

Soil microorganisms have an important influence on the transformation of soil nutrients. As functional genes encoding phosphatase, phoC and phoD provide effective means for detecting the types, abundance, and community structure of microorganisms in the environment, and studying the changes in the diversity of phoC and phoD gene microbial communities in the rhizosphere and non-rhizosphere soil of the plant rhizosphere and non-rhizosphere soil under the treatment of chemical fertilizer and organic fertilizer combined with biochar can provide a scientific basis for the agricultural utilization of biochar. In this study, corn stalks and rice husk stalks were used as test materials, and the pot experiment method was used to set the following treatments:control (CK), traditional fertilization (F), chemical fertilizer+20 t·hm-2 rice husk biochar (FP), chemical fertilizer+10 t·hm-2 rice husk biochar+10 t·hm-2 corn biochar (FPM), organic fertilizer+20 t·hm-2 rice husk biochar (PP), and fresh organic fertilizer+20 t·hm-2 rice husk biochar (NPP). The community structure of phoC and phoD genes in rhizosphere and non-rhizosphere soil was analyzed by using T-RFLP and fluorescence quantitative PCR technology to clarify the response characteristics of phoC and phoD genes to the addition of biochar. The results showed that:① In rhizosphere soil and non-rhizosphere soil, the phoD gene community structure was more complicated than that of phoC, and the number of end restriction fragments of the phoC gene increased after chemical fertilizer and organic fertilizer were combined with biochar. ② The combined application of biochar with chemical fertilizer and organic fertilizer reduced the copy number of the phoC gene in non-rhizosphere soil compared with that in the CK. Compared with that in the CK, the copy number in the FP, FPM, PP, and NPP treatments decreased by 9.18%, 11.46%, 10.97%, and 13.76%, respectively. Organic fertilizer combined with biochar increased the copy number of the phoD gene in rhizosphere soil by 2.48% and 5.16% in the PP and NPP treatments, respectively, compared with that in the CK. ③ Total phosphorus in the soil was the main factor affecting the phoC gene microbial community structure in non-rhizosphere soil (P<0.01), whereas the phoC gene microbial community structure in rhizosphere soil was regulated by a variety of environmental factors. pH was the most critical factor affecting the phoD gene copy number, and the copy number of phoD gene was significantly correlated with soil nitrate nitrogen and pH. The combined application of biochar with chemical fertilizers and organic fertilizers can promote the growth and reproduction of microorganisms that function in soil phosphorus conversion, which is of great significance for improving the utilization of phosphorus fertilizers.

[Effect of Optimized Fertilization and Biochar Application on Phosphorus Loss in Purple Soil Sloping Farmland].

Phosphorus is an essential nutrient for crop growth, but the input of excess phosphorus is a significant cause of eutrophication. This study explored the relationship between fertilization methods and phosphorus loss in actual production, providing a theoretical basis for scientific fertilization and rational reduction of fertilizer application. In the experiment, a wild-type OD flow plot was used to monitor the occurrence of multiple rainfall runoff and sediment yield in purple soil sloping farmland in 2017-2018. Four different schemes of non-fertilizer treatment, conventional fertilization treatment, optimized fertilization treatment, and reduced fertilization combined with biochar were studied. The effects of soil flow, surface runoff, and sediment phosphorus loss on purple soil sloping farmland were analyzed. The results showed that:①The total yield of each treatment was optimized (20737.23 L) > conventional (18513.17 L) > CK (18134.58 L) > biochar (13594.85 L), and the total sediment yield of each treatment was CK (1998 kg·hm-2) > biochar (1884 kg·hm-2) > optimized (1681 kg·hm-2) > conventional (910 kg·hm-2). The middle stream of soil is the main type of runoff in the rainy season, accounting for 60.14%-87.34% of the total output flow. The total amount of sediment produced by each treatment was not significantly different from that of the conventional treatment (P>0.05). ②The flux of total phosphorus loss in each treatment was characterized by sediment > surface runoff > soil middle flow. Phosphorus lost through the middle stream of soil is the least, accounting for only 2.63%-12.91% of the flux of total phosphorus loss, while the flux of sediment loss of phosphorus can reach 63.74%-78.74%, and thus is the main output route of soil phosphorus loss. ③The application of biochar can effectively reduce the abortion flow in the soil of purple soil sloping land, and the loss flux of orthophosphate in the middle stream, which are 49.94% and 56.45% lower than the conventional treatment, respectively. However, the interception effect on surface runoff is not good, and there is no significant influence on the flux loss of particulate phosphorus. At the same time, the flux of total phosphorus in surface runoff and sediment is significantly increased by 73.28% and 123.53%, respectively, compared with conventional treatment (P<0.05). Therefore, to control the loss of phosphorus in purple soil sloping farmland in southwest China, we should focus on reducing the occurrence of soil sediment loss. Bio-carbon should be further optimized in the practical application of agricultural production with the phosphorus fertilizer input ratio.

[Effects of Different Forest Vegetation Types on Soil Nitrogen-Related Microbial Communities and Functions in Jinyun Mountain].

To clarify the response of a nitrogen-related microbial community and function to different vegetation types in subtropical forest, soil samples were collected for analysis from the topsoil of five vegetation types in the Jinyun Mountain National Nature Reserve, i.e., coniferous forest, broadleaf forest, mixed broadleaf-coniferous forest, P. pubescen forest, and grassland. To analyze the microbial abundance, community, and function discrepancy between different vegetation soils, multiple molecular techniques, such as terminal restriction fragment length polymorphism (T-RFLP) and quantitative polymerase chain reaction (qPCR) analysis, and nitrogen-related microbial enzyme activity procedures were used. The results showed:① The denitrifying enzyme activity was much higher than nitrifying potential in Jinyun Mountain National Nature Reserve, and the two enzyme activities were much lower in coniferous forest soil than in the other vegetation soils (P<0.05). In addition, dissolved organic carbon, soil water content, and total nitrogen were the key environmental factors controlling enzyme activity. ② The qPCR data showed that the abundance of nitrogen-related microbes was highest in P. pubescen forest, whereas it was lowest in coniferous forest. The abundances of the three nitrogen-related microbes were all significantly correlated with dissolved organic carbon, total nitrogen, available nitrogen, total potassium, and available potassium (P<0.01). ③ Based on T-RFLP data, the α-diversity of nitrogen-related microbes was highest in broadleaf forest, whereas it was lowest in P. pubescen forest. Principal co-ordinates analysis (PCoA) showed that the community structure of ammonia-oxidizing archaea responded significantly to different vegetations, and the community structure of nitrogen-related microbes showed the most difference in coniferous forest. In addition, distance-based redundancy analysis (db-RDA) showed that the community structure of nitrogen-related microbes was mainly shaped by dissolved organic carbon (P<0.001), available nitrogen (P<0.002), and soil water content (P<0.001). ④ Soil-denitrifying enzyme activity was mainly affected by the abundance of nirS-denitrifiers, ammonia-oxidizing archaea, and the community structure of nitrogen-related microbes, whereas nitrifying potential was only controlled by the abundance of ammonia-oxidizing archaea. Above all, subtropical forest vegetation significantly affects the abundance and community structure of soil nitrogen-related microbes, thereby changing their function of controlling the soil nitrogen cycle. This study can provide basic data for the coupling mechanism between soil microbes and N2O release in subtropical forests in China.

[Content of Soil Phytolith-Occluded Organic Carbon in Different Land Use Patterns at Jinyun Mountain].

Phytolith-occluded organic carbon (PhytOC) is a form of long-term storage of soil organic carbon, which is of great significance for soil carbon sequestration. Taking six land use patterns in southwest China as the research object, including coniferous and broad-leaved mixed forest, bamboo forest, orchard, dry land, paddy field, and grassland, we compare the distribution of the PhytOC content under the different land use patterns in different depth sections of 0-20, 20-40, 40-60, and 60-100 cm. In addition, we estimate the storage of phytOC and analyze the carbon sequestration characteristics of the terrestrial ecosystems. According to the results, the soil organic carbon and phytolith mean content in the bamboo forest were the highest in the soil profile, at 16.75 g·kg-1 and 59.66 g·kg-1, respectively. In all soil layers, the phytolith content of the bamboo forest soil was significantly higher than that in other land use patterns (P<0.05). The average content of soil phytOC in the six land use patterns ranged from 0.55 to 1.96 g·kg-1, and the phytOC content of each layer of bamboo forest was higher than that in other land uses. The total carbon storage of phytOC in the bamboo forest soil, at 23.45 t·hm-2, was significantly higher than that of other soil use methods (P<0.05). Statistical analysis showed that soil silicon had a significant positive correlation with the soil phytolith and the soil phytOC (P<0.01). The soil phytolith and phytolith carbon content in different land use patterns generally showed a decrease with an increase in soil depth, and a certain surface enrichment phenomenon was noted.