Effects Of Partial Substitution Of Chemical Fertilizer With Organic Manure Or Straw On Soil Phosphorus Speciation And Transformation In Greenhouse Vegetable Production

Excessive application of chemical fertilizers and organic manure is widespread in greenhouse vegetable production,leading to a wide range of serious problems such as excessive soil phosphorus（P）accumulation,microbial functional diversity reduction,and water environment contamination risk increase.It is of great significance to reduce the application of P and recommend P application scientifically in greenhouse vegetable production,which is conducive to the efficient use of nutrient resources and the maintenance of ecological environment security.The study was sampled in a long-term field experiment（which began in 2009）in a greenhouse vegetable production in Xiqing District,Tianjin municipality,China.Here,we combined Hedley P fractionation,liquid-state ³¹P nuclear magnetic resonance spectroscopy,X-ray absorption near-edge structure spectroscopy,microplate fluorometric assay,phospholipid fatty acid analysis,quantitative PCR,metagenomic sequencing and in-situ lysimeter in the field to investigate the effects of long-term organic substitution pattern on soil P speciation transformation characteristics,phosphatase activity,microbial community structure,P cycling functional genes,and P leaching in greenhouse vegetable production,and to analyze the interaction mechanism among fertilization pattern,soil microbial function,soil enzyme activity,and soil P speciation,which could provide the theoretical support for reducing P application and optimizing fertilization patterns in greenhouse vegetable production.The main findings are summarized as follows:1.The organic substitution pattern promoted soil P activation and increased vegetable yield.Compared with chemical fertilizer application alone,the organic substitution pattern increased the 10-year（2009-2019）total yields of celery and tomato by 6.9-13.8%and 8.6-18.1%,respectively.From the third to twentieth seasons of vegetables,the organic substitution pattern increased the vegetable yields,among which,a combination of 50%fertilizer nitrogen,25%organic manure nitrogen,and 25%straw nitrogen（2CN+2MSN treatment）was observed in the highest yield.The organic substitution pattern promoted the formation of Mg HPO₃ and Ca HPO₄（labile P）and reduced the accumulation of hydroxyapatite（stable P）in soil.The organic substitution pattern increased the contents of orthophosphate monoester and diester by 40.5-62.2%and 78.8-99.4%,respectively,increased the proportion of labile P and moderately labile P by 45.0-59.8%and 24.8-41.9%,respectively,and decreased the proportion of stable P by 11.1-13.5%.The organic manure substitution pattern and soil p H were the main factors affecting soil labile P,whereas straw substitution pattern and alkaline phosphatase activity were the main factors affecting soil moderately labile P.2.The organic substitution pattern promoted soil microbial growth and improved phosphatase activities.The organic substitution pattern increased total phospholipid fatty acid,fungal,bacterial,and actinomycetes contents by 74.5-134.2%,94.9-182.6%,67.6-124.1%,and 95.8-149%,respectively,and increased the activities of acid phosphomonoesterase,alkaline phosphomonoesterase,phosphodiesterase,and phytase by 153.9-318.0%,190.0-339.6%,124.7-193.4%,and 33.6-55.0%,respectively.The organic substitution pattern positively affected microbial biomass P（which increased by 46.0-115.7%）and then increased soil labile P contents.Soil C/P and arbuscular mycorrhizal fungi significantly and positively affected soil phosphatase activities.3.The organic substitution pattern enhanced the functional capacities involved in microbial inorganic P solubilization and organic P mineralization.The organic substitution pattern increased the functional genes relative abundance of inorganic P solubilization and organic P mineralization by 8.9-11.3%and 1.8-8.2%,respectively.Among them,the abundances of gcd,ppx,and pho D genes were increased by 8.7-123.8%,85.4-259.6%,and 82.0-165.7%,respectively.Alphaproteobacteria and Gammaproteobacteria containing gcd and pho D genes were important predictors of soil Olsen-P.Soil p H had significant negative effects on the functional genes of inorganic P solubilization and organic P mineralization.Soil C/P and N/P significantly positively affected the functional genes of inorganic P solubilization and organic P mineralization capacities.The gcd,ppx,and pho D genes were positively correlated with Olsen-P and labile P contents in soil.4.The organic substitution pattern improved the stability of soil aggregates and increased the contents of labile P within>2 mm and 2～0.25 mm macroaggregate.The organic substitution pattern increased the mean weight diameter（MWD）and geometric mean diameter（GMD）by 17.1-39.4%and32.4-77.3%,respectively.MWD and GMD were positively correlated with labile P and moderately labile P contents in soil.The organic substitution pattern increased the contents of resin-P,Na HCO₃-P（labile P）,and Na OH-P（moderately labile P）within>2 mm and 2～0.25 mm macroaggregate by 17.5-36.9%,13.6-47.4%,and 15.5-40.9%,respectively,whereas decreased the contents of dil.HCl-P（stable P）within different size aggregates by 12.6%on average.Compared with other size aggregates,0.25～0.053 mm microaggregate was observed in the higher labile P and moderately labile P contents,and>2 mm macroaggregate was observed in the higher moderately labile P contents.5.The organic substitution pattern improved the activities of the extracellular enzyme within different sizes aggregates,and increased the relative abundance of P-solubilizing bacteria within the<0.053 mm silt and clay fraction.The organic substitution pattern increased the activities ofβ-glucosidase（βG）,β-Cellobiohydrolase（CBH）,andβ-1,4-N-acetylglucosaminidase（NAG）within different size aggregates by 28.5%,141.2%,and 110.5%on average,respectively,and increased the activity of phosphatase（PHOS）within>2 mm and 2～0.25 mm macroaggregate by 89.1%and 51.4%on average,respectively.The 0.25～0.053 mm microaggregates were observed in higher activities ofβG,CBH,NAG,and PHOS than other size aggregates.Soil microbial growth was limited by nitrogen.The organic substitution pattern alleviated the microbial nitrogen restriction by increasing the ratio of carbon harvesting enzyme to nitrogen harvesting enzyme within>2 mm and 2～0.25 mm macroaggregate.The<0.053 mm silt and clay fraction was observed in a higher relative abundance of P-solubilizing bacteria.The straw substitution pattern increased the relative abundance of P-solubilizing bacteria within different size aggregates,and increased the relative abundance of P-solubilizing fungi within 0.25～0.053 mm microaggregates and<0.053 mm silt and clay fraction.6.The organic substitution pattern promoted moderately labile P formation and reduced soil P leaching loss.The organic substitution pattern increased the 10-year（2009-2019）total yields of celery and tomato by 6.9-13.8%and 8.6-18.1%,respectively.From the third to twentieth seasons of vegetables,the organic substitution pattern increased the vegetable yields,among which,a combination of 50%fertilizer nitrogen,25%organic manure nitrogen,and 25%straw nitrogen（2CN+2MSN treatment）was observed in the highest yield.The organic substitution pattern increased labile P contents in the 0～40 cm soil layers by 13.7-54.2%and the main forms were Mg HPO₄ and Ca HPO₄（the proportion were 6.9-10.1%and 9.4-24.8%,respectively）.There were significant positive correlations between vegetable yield with labile P and moderately labile P contents in the 0～40 cm soil layers.The straw substitution pattern reduced labile P contents in the 60～100 cm soil layers by 7.8-16.1%and increased moderately labile P contents in the 0～80 cm soil layers by 6.1-33.3%.The organic substitution pattern significantly reduced the leaching volume,total P,and particulate P leaching amounts by 11.7-27.8%,21.3-48.8%,and45.0-66.4%,respectively.Combined 50%chemical fertilizer nitrogen,25%organic manure nitrogen,and 25%straw nitrogen（2CN+2MSN treatment）was a more effective fertilization pattern for developing sustainable P management practices in greenhouse vegetable production by comprehensively considering the vegetable yields,soil P transformation,P cycling microorganisms functional characteristics,and P leaching losses.