Acid Phosphomonoesterase Activity Research Articles

Microbial Biomass and Rhizosphere Soil Properties in Response to Heavy Metal-Contaminated Flooding

Mining and metallurgy are the main sources of soil contamination with harmful metals, posing a significant threat to human health and ecosystems. River floodplains in the vicinity of metal mines or industrial plants are often subject to flooding with sediments containing heavy metals, which can be harmful to the soil ecosystem. This study aimed to investigate the microbial properties of the soil at a metal-contaminated site and to determine the significant relationships between the biological and chemical properties of the soil. The study site was located near the village of Gyöngyösoroszi, in the Mátra mountain region of Northwest Hungary. A phytoremediation experiment was conducted in a metal-polluted floodplain using willow and corn plantations. The soil basal respiration, substrate-induced respiration, soil microbial biomass carbon (MBC), acid phosphatase activities, and soil chemical properties were measured. The soil of the contaminated sites had significantly higher levels of As, Pb, Zn, Cu, Cd, and Ca, whereas the unpolluted sites had significantly higher levels of phosphorus and potassium. The substrate-induced respiration showed a positive correlation with MBC and negative correlations with the metabolic quotient (qCO2). The soil plasticity index and phosphorus showed a positive correlation with MBC, whereas salinity and the presence of Cd, Pb, Zn, As, and Cu showed a negative correlation. Acid phosphomonoesterase activity negatively correlated with the plant-available phosphorus content and MBC, but was positively correlated with the contents of toxic elements, including cadmium, lead, zinc, arsenic, and copper. This study found a significant correlation between the qCO2 and the toxic element content. This suggests that an enhanced metabolic quotient (qCO2), together with a decreased MBC/SOC ratio, could be used to indicate the harmful effect of soil contamination by heavy metals in floodplain soils.

No differences in phosphodiester-induced changes of phosphatase activities and bicarbonate-extractable inorganic phosphorus between long-term low and high phosphorus-fertilized soils

Soil organic phosphorus (P) mineralization is catalyzed by phosphatases synthesized by plants or microorganisms, particularly when organic P is present and inorganic P is limited. We investigated how P status affects the substrate induction response of phosphatase activities and changes in labile inorganic P (ΔNaHCO3-Pi) by adding phosphodiester to long-term low P and high P-fertilized soils. Phosphodiester addition significantly increased acid phosphomonoesterase activity and ΔNaHCO3-Pi, while exhibiting non-significant effect on phosphodiesterase activity. No significant differences were observed in phosphodiester-induced phosphatase activities and ΔNaHCO3-Pi between the low P and high P-fertilized soils. Our results indicate that phosphodiester may incentivize microbially mediated enzymatic P mineralization not necessarily for P but possibly for energy. This emphasizes the importance of phosphodiester in the development of microbial strategies for mobilizing soil P.

Soil enzyme activities in heavily manured and waterlogged soil cultivated with ryegrass (Lolium multiflorum)

Extended waterlogging (WL) conditions can alter soil enzyme activities and their role in maintaining healthy soils. We assessed the effects of soil moisture regimes (field capacity [FC] and WL) and phosphorus (P) rates (0, 15, 30, 45 kg available P ha–1) on ( i) soil enzymes and microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial biomass P (MBP); and ( ii) dissolved organic carbon (DOC) and total dissolved nitrogen (TDN). The treatments were tested in a 4-month greenhouse experiment using intact soil columns under annual ryegrass ( Lolium multiflorum). WL decreased the activity of β-glucosidase and acid phosphomonoesterase but increased N-acetyl-β-glucosaminidase in soils. These changes were associated with changes in MBC, DOC, MBN, and TDN, but not MBP. Anoxic conditions in WL soil promote the activity of anaerobes and contribute to the reduction of Fe oxyhydroxides and the release of DOC, TDN, and P in the soil solution. The activity of the extracellular enzymes decreased in WL with additions of slurry indicating adequate supply of C, N, and P. Our results also showed that both enzyme activities and microbial biomass were restricted in the upper soil layer with limited downward movement along the soil profile. We can conclude that since these enzymes control the hydrolysis of cellulose, phosphomonoester, and chitin, soil moisture influences the direction and magnitude of C, N, and P in manured and waterlogged soil cultivated with ryegrass.

Land reclamation increased organic P fractions and phosphatase activities, and strengthened the co-occurrence networks of phoD community in calcareous soils

Organic phosphorus (Po) is an important constituent of P pool. Soil phoD community is primarily involved Po transformation. However, influences of agriculturally-driven land-use change on different Po fractions, phosphatase activities and phoD community are largely unknown. Here, an investigation was carried out containing three treatments: vegetable field (VF), cropland (CF) and uncultivated land (UL). Various Po fractions were measured by Hedley’s sequential extraction and 31P-NMR methods. The activities of alkaline phosphomonoesterase (ALP), acid phosphomonoesterase (ACP), phosphodiesterase activity (PD) and phytase were assayed; the abundance, and diversity of phoD community and its co-occurrence networks were analyzed. Compared with the UL treatment, soil total organic P (total-Po) in the VF and CF treatments significantly increased by 75.9% and 53.0%, respectively, mainly attributed to the increases in NaHCO3-Po, NaOH-Po and C.HCl-Po. 31P-NMR spectra showed that, when land was reclaimed from uncultivated land into agriculture fields (i.e., VF and CF), myo-inositol hexaphosphate (myo-IHP), α-glycerophosphate (α-glyc) and β-glycerophosphate (β-glyc) were increased by 9.5, 3.9 and 2.0 times, respectively. The activities of ACP, ALP and PD in the VF and CF treatments were higher than in the UL treatment. The α-diversity of phoD community was also significantly increased by land reclamation. Moreover, the linkage between soil Po and Po-cycling-related biological parameters (ACP, ALP and PD and phoD community) was more pronounced by NaHCO3-Po and NaOH-Po than the Po fractions measured by 31P-NMR method. Topological parameters (edges, node degree, and betweenness centrality) of phoD community’s network in the VF and CF networks were higher than in the UL network, implying that land reclamation favored to construct a more cooperative network of phoD community. Collectively, our findings demonstrated that when uncultivated land was converted to cropland, soil Po was notably increased, and phoD community’s co-occurrence network was also strengthened. The outcomes of this study emphasize that when land was reclaimed from nature (uncultivated land) into agriculture fields, the fertilization strategy of organic combined with chemical fertilizers application was beneficial for improving P fertility and assembling organic P-cycling related community.

Phosphate-Solubilizing Bacteria with Low-Solubility Fertilizer Improve Soil P Availability and Yield of Kikuyu Grass.

Inoculation with phosphate-solubilizing bacteria (PSB) and the application of phosphorus (P) sources can improve soil P availability, enhancing the sustainability and efficiency of agricultural systems. The implementation of this technology in perennial grasses, such as Kikuyu grass, for cattle feed in soils with high P retention, such as Andisols, has been little explored. The objective of this study was to evaluate the productive response of Kikuyu grass and soil P dynamics to BSF inoculation with different P sources. The experiment was conducted on a Kikuyu pasture, which was evaluated for 18 months (September 2020 to March 2022). Three P fertilizers with different solubility levels were applied: diammonium phosphate (DAP) (high-solubility), rock phosphate (RP), and compost (OM) (low-solubility). Moreover, the inoculation of a PSB consortium (Azospirillum brasilense D7, Rhizobium leguminosarum T88 and Herbaspirillum sp. AP21) was tested. Inoculation with PSB and fertilization with rock phosphate (RP) increased soil labile P and acid phosphomonoesterase activity. Increased grass yield and quality were related with higher soil inorganic P (Pi) availability. This study validated, under field conditions, the benefits of PSB inoculation for soil P availability and Kikuyu grass productivity.

Distribution Characteristics and Influencing Factors of Soil Biological Indicators in Typical Farmland Soils

Soil biodiversity drives soil-based ecosystem services and is an important indicator of soil health. To understand the responses of important soil biological indicators to different farmland use contexts, 72 fields in three agricultural regions of China were used as research objects. The distribution characteristics and the factors influencing six indicators (carbon and nitrogen contents of soil microbial biomass (MBC, MBN, respectively), soil respiration (SR), soil catalase activity (CAT), soil acid phosphomonoesterase activity (APA), and soil earthworms) were investigated using field monitoring and indoor analysis. The MBC, SR, CAT, and APA indicators showed significant differences among the regions (p < 0.05). Correlation and redundancy analyses indicated that the important factors affecting MBC, MBN, and soil respiration were cation exchange capacity, total N, organic matter, hydrolytic N, and soil bulk density, whereas the important factors affecting APA and earthworms were total phosphorus, available phosphorus, and available potassium. None of these factors had a significant effect on CAT. Climatic conditions, soil types, and farmland practices all have complex impacts on soil biodiversity. The results showed that attention should be paid to improving the physical conditions of the soil and to increasing soil fertility levels when establishing sustainable farm management patterns.

Microbial activity and habitat heterogeneity in surface soil in a high-mountain grassland landscape (Central Apennines, Italy)

A spatially intensive sampling of surface soil layers (81 stratified-randomized sampling points across a 14 km2 study area) was performed in a high-mountain grassland landscape (Central Apennines, Italy) in July 2017, in order to describe the heterogeneity of microbial habitats and measure their microbial enzymatic activity. Three different microbial habitat types were identified via Hierarchical Cluster Analysis on the basis of 14 (measured or remote-sensed) environmental variables (including chemical and physical soil properties, topographic and geomorphological features and vegetation cover): (i) sub-acidic, at high elevation, with high vegetation cover (of mostly acidophytic/mesophytic species) and high silt content, and the lowest clay content; (ii) sub-acidic, at low elevation, with a high vegetation cover and a very low stone cover, with the highest sand and the lowest silt content, and the highest available phosphorus; (iii) very shallow soil, mainly stone-covered, at high elevation, with the highest pH values, on steep slopes, with the highest content of organic matter and the highest water holding capacity. The third habitat showed the highest enzymatic activity (b-glucosidase, β-cellobiohydrolase and leucine-arylamidase) involved in C and N cycling, while the more acidic and deeper soils, typical of sinkhole or slope areas, favoured the acid phosphomonoesterase activity involved in P cycle thanks to the establishment of the rhizospheric activity of the herbaceous plant species. Moreover, we analysed the relative importance of environmental variables on the total enzyme activities via Boosted Regression Trees (BRT): the results highlighted - for the first time as far as we know - the importance of topographic factors such as slope inclination in predicting the microbial functional capacity in a mountain grassland ecosystem. We conclude that the different enzymatic activity patterns found in the three habitats suggest diverse microbial functions with respect to nutrient cycling, within a small landscape and a relatively homogeneous land-cover.

Differences in available phosphorus in temperate and subtropical forest soils

Soil P availability is influenced by the acid phosphomonoesterase (ACP) activity, microbial biomass P (MBP), pH, and other soil properties. To date, there is no clear understanding about how the enzyme catalytic efficiency (Vmax/Km) and the abundance of the phoC and phoD genes that encode ACP and alkaline phosphomonoesterase (ALP) influence the available P contents at different depths in temperate and subtropical forest soils. We investigated how the soil enzyme kinetic parameters, phoC and phoD gene abundance, pH, total P contents, and other soil properties influenced the P availability in soils from a temperate forest (ChangBai Mountain) and a subtropical forest (QianYanZhou Plantation). The results showed that the DNA contents and the ACP and ALP activities were positively correlated with the available P contents in the temperate forest soil. The phoC and phoD gene abundance and the ALP activity were positively correlated with the available P contents in the subtropical forest soil. The ACP-Vmax/Km and DNA contents were positively correlated with the available P contents in topsoil (0–10 cm). The total P contents, pH, MBP, and ACP-Vmax/Km in subsoil (10–30 cm) were positively correlated with the available P contents. A structural equation model showed that DNA content had the greatest effect on the soil available P in temperate forest soil, and phoC and phoD gene abundance had the greatest effect on the soil available P in subtropical forest soil. The mechanism of H+ dissolution affected the P availability through low pH in the topsoil and weathering in the subsoil. Overall, these findings provided an improved understanding about how the catalytic efficiencies of ACP and ALP and the phoC and phoD gene abundance, influenced the P availability in temperate and subtropical forest soils at different depths. We also gained insights into how the P availability was affected by H+ dissolution and the parent material in topsoil and subsoil, respectively.

Livestock grazing-exclusion under global warming scenario decreases phosphorus mineralization by changing soil food web structure in a Tibetan alpine meadow

The exclusion of grazing has been used extensively in alpine meadows on the Tibetan Plateau. Studies, however, have shown reported recent trends of decreasing concentrations of soil nutrients because of grazing exclusion and climate change. The effects of excluding grazing on the soil biogeochemical process of phosphorus cycling in alpine meadows are unclear, especially under climatic warming. We conducted a 5-year grazing-exclusion and warming-manipulation experiment to examine the effects of excluding grazing on fractions of soil phosphorus, microbial and nematode communities and enzymatic activities in treatments of low grazing intensity, grazing exclusion, and combined grazing exclusion and warming. Our results indicated that excluding grazing significantly decreased bacterivore and omnivore-predator densities, phoD gene abundance and alkaline phosphomonoesterase activity (in the 0–5 cm layer by −34, −41, −38 and −42 %) at altitudes of 3850 m, 4000 m, 4150 m and 4250 m, respectively. Structural equation modeling indicated that bacterivores positively affected phoD gene abundance, alkaline phosphomonoesterase activity and inorganic‑phosphorus fractions. Combined grazing exclusion and warming significantly decreased bacterivore and omnivore-predator densities but significantly increased fungivore density (in the 0–5 cm layer by 238, 172, 119 and 65 %) at altitudes of 3850, 4000, 4150 and 4250 m, respectively. Structural equation modeling also indicated that the combined grazing-exclusion and warming treatment increased the soil fungi and fungivores, but the higher abundances of fungi and fungivores did not significantly affect acid phosphomonoesterase activity or inorganic‑phosphorus fractions. Alternatively, the combined grazing-exclusion and warming treatment significantly increased the concentrations of amorphous and free aluminum, which were positively correlated with the maximum adsorption of phosphorus. The combined grazing-exclusion and warming treatment thus significantly decreased the availability of resin phosphorus (−63, −51, −81 and −67 %) in the 0–5 cm layer at altitudes of 3850, 4000, 4150 and 4250 m, respectively. Our results suggested that light grazing (0.5 yak ha−1 year−1) could increase phosphorus mineralization and the activity of soil enzymes in alpine meadows under global warming. An adequate load of livestock pressure at each altitude can be an effective management technique, mainly under warming, to maintain an adequate, sustainable and equilibrated phosphorus cycle in the plant-soil system.

Alteration of the organic wheat rhizobiome and enzyme activities by reduced tillage and diversified crop rotation

The acreage of organic agriculture continues to grow world-wide. Growing organic crops relies on soil tillage for weed control, and organic soil inputs for nutrient supply, because chemical inputs are not permitted. Organic inputs build soil organic C, a key determinant of soil quality, but tillage-induced C losses through erosion and decomposition reduce soil organic C. Crop rotations also supply nutrients and break pest cycles. In 2014 (normal rainfall) and 2015 (below-normal rainfall), we investigated whether reduced tillage (low tillage vs high tillage), and diversification of a 2-year forage pea green manure (GM)-wheat rotation to a 4-year rotation (simplified rotation vs diversified rotation) altered the soil microbiome and enzyme activities in the rhizosphere of organic wheat in a trial that had been established in 2010. Planctomycetes and Gemmatimonadetes were more abundant under high tillage than low tillage in both rotations. The Shannon index of α-diversity was greater in the diversified rotation than the simplified rotation under high tillage. Microbial biomass C (MBC) was greater in the diversified rotation than the simplified rotation in 2014. The relative abundances of Gemmatimonadetes, Proteobacteria and Tharmarchaeota were greater in the diversified rotation than the simplified rotation under high tillage. Low tillage increased the activity of acid phosphomonoesterase (P cycling), and in 2014, the activity of this enzyme was greater in the diversified rotation than the simplified rotation. The growing season precipitation shaped the soil microbiome (α- and β-diversity) the most: the drier-than-normal 2015 had less microbial biomass C (MBC), Actinobacteria, Bacteroidetes, Proteobacteria and enzyme activities than the normal 2014, but vice-versa for α-diversity, AD3, Armatimonadetes and Chloroflexi. Therefore, although the growing season affected these soil microbial properties more than tillage or crop rotation, both low tillage and crop diversification altered the soil microbial community composition and increased the soil P cycling potential

Crawfish shell- and Chinese banyan branch-derived biochars reduced phytoavailability of As and Pb and altered community composition of bacteria in a contaminated arable soil

Globally, soil contamination with arsenic (As) and lead (Pb) has become a severe environmental issue. Herein, a pot experiment was conducted using pak choi (Brassica chinensis L.) to investigate the effects of biochars derived from crawfish (Procambarus clarkia) shells (CSB) and Chinese banyan (Ficus microcarpa) branches (CBB) on the phytoavailability of As and Pb, and bacterial community composition in soils. Our results showed that the application of CSB and CBB decreased the concentrations of DTPA-extractable Pb in soils ranging from 26.8 % to 28.8 %, whereas CSB increased the concentration of NH4H2PO4-extractable As in soils, compared to the control. Application of both biochars reduced the uptake of As and Pb in the edible part of pak choi. In addition, application of CBB significantly (P < 0.05) increased the activities of α-glucosidase, β-glucosidase, cellobiohydrolase, and acid phosphomonoesterase by 55.0 %, 54.4 %, 195.1 %, and 76.7 %, respectively, compared to the control. High-throughput sequencing analysis revealed that the predominant bacteria at the phyla level in both biochar-treated soils were Firmicutes, Proteobacteria, and Actinobacteriota. Redundancy and correlation analyses showed that the changes in bacterial community composition could be related to soil organic carbon content, As availability, and nutrient availability in soils. Overall, the Chinese banyan branch biochar was more suitable than the crawfish shell biochar as a potential amendment for the remediation of soils co-contaminated with As and Pb.

Contrasting distribution of enzyme activities in the rhizosphere of European beech and Norway spruce.

Recent policies and silvicultural management call for forest regeneration that involve the selection of tree species able to cope with low soil nutrient availability in forest ecosystems. Understanding the impact of different tree species on the rhizosphere processes (e.g., enzyme activities) involved in nutrient mobilisation is critical in selecting suitable species to adapt forests to environmental change. Here, we visualised and investigated the rhizosphere distribution of enzyme activities (cellobiohydrolase, leucine-aminopeptidase, and acid phosphomonoesterase) using zymography. We related the distribution of enzyme activities to the seedling root morphological traits of European beech (Fagus sylvatica) and Norway spruce (Picea abies), the two most cultivated temperate tree species that employ contrasting strategies in soil nutrient acquisition. We found that spruce showed a higher morphological heterogeneity along the roots than beech, resulting in a more robust relationship between rhizoplane-associated enzyme activities and the longitudinal distance from the root apex. The rhizoplane enzyme activities decreased in spruce and increased in beech with the distance from the root apex over a power-law equation. Spruce revealed broader rhizosphere extents of all three enzymes, but only acid phosphomonoesterase activity was higher compared with beech. This latter result was determined by a larger root system found in beech compared with spruce that enhanced cellobiohydrolase and leucine-aminopeptidase activities. The root hair zone and hair lengths were significant variables determining the distribution of enzyme activities in the rhizosphere. Our findings indicate that spruce has a more substantial influence on rhizosphere enzyme production and diffusion than beech, enabling spruce to better mobilise nutrients from organic sources in heterogeneous forest soils.

Synergistic enhancement of the phytostabilization of a semiarid mine tailing by a combination of organic amendment and native microorganisms (Funneliformis mosseae and Bacillus cereus)

The goal of this work was to evaluate the effects of fermented sugar beet residue and inoculation with a native arbuscular mycorrhizal (AM) fungus, Funneliformis mosseae (Nicol. and Gerd.) Gerd. and Trappe, or a native bacterium, Bacillus cereus Frankland & Frankland, alone or in combination, on the establishment of Lygeum spartum L. seedlings grown in a mine tailing under semiarid conditions. We conducted a field study to analyse root and shoot dry biomass, shoot nutrient contents, mycorrhization, plant nitrate reductase (NR) and acid phosphomonoesterase activities, soil enzyme activities and aggregate stability. Ten months after field transplanting, it was found that the three experimental factors had interacted synergistically with regard to shoot and root biomass, with increases of about 410% and 370%, respectively relative to plants in the untreated soil. The treatment combining all three factors increased the root content of all heavy metals, and the levels of nitrogen (N), phosphorus, potassium and NR activity in shoot tissues, whereas it decreased root acid phosphomonoesterase activity. Soil dehydrogenase, protease and β-glucosidase activities, total N content and aggregate stability were increased by the combined treatment. In conclusion, the combination of the organic amendment, the native AM fungus and the native bacterium can be regarded as a suitable tool for phytostabilization with L. spartum due to its ability to enhance the tolerance of plants to heavy metals, improve the plant nutritional status and increase the soil microbial function related to the C cycling.

Distribution Characteristics of Soil Phosphorus Forms and Phosphatase Activity at Different Altitudes in the Soil of Water-Level-Fluctuation Zone in Pengxi River, Three Gorges Reservoir

Phosphatases play important roles in converting organic phosphorus into inorganic phosphorus in soil. However, studies from this perspective on the water-level-fluctuation zone (WLFZ) of the Three Gorges Reservoir are limited. In this study, phosphatase activity and the forms of phosphorus were analyzed. Soil samples were collected in the river basin of the Penxi River in the WLFZ during a drying period. The correlation between phosphatase activity and phosphorus forms and the impacts of phosphatase activity on the phosphorus forms were analyzed. The results showed that the contents of H2O-Pi, NaHCO3-Pi, and NaOH-Pi in the soils of the WLFZ were higher than those in the soils by the river. In addition, a higher altitude resulted in higher contents of bio-enzymatically hydrolysable phosphorus and NaOH-Po. Furthermore, redundancy analysis (RDA) showed that the contents of organic matter and amorphous Fe and Mn were the main factors affecting soil organic phosphorus forms. The average activities of acid phosphomonoesterase (ACP), alkaline phosphomonoesterase (ALP), phosphodiesterase (PDE) (all in p-NP), and phytase (PAE) (in P) in the soils of the WLFZ were 1.40, 2.60, 0.44, and 11.43 μmol·(g·h)-1, respectively. Moreover, the activities of different phosphatases increased with altitude. Soil plant biomass and microbial biomass were important reasons for the difference in spatial distribution of phosphatase activity in the soil of the WLFZ. Phosphatase activities were significantly positively correlated with the contents of organic phosphorus forms but negatively correlated with the content of bioavailable phosphorus. A higher soil phosphatase activity and a lower content of bioavailable phosphorus were usually detected in soil samples taken at a higher altitude. In the early stage of flooding, phosphatase converted organic phosphorus into inorganic phosphorus at a relatively high rate, and the risk of phosphorus release to the overlying water body was also high. This study contributed to a comprehensive understanding of the geochemical cycle of soil phosphorus in the soil of the WLFZ.

Multi-year and multi-site effects of recurrent glyphosate applications on the wheat rhizosphere microbiome

Glyphosate (N-(phosphonomethyl)glycine) is broad-spectrum herbicide that is extensively used worldwide, but its effects on the soil microbiome are inconsistent. To provide a sound scientific basis for herbicide re-review and registration decisions, we conducted a four-year (2013–2016) study in which we consecutively applied glyphosate to a wheat (Triticum aestivum L.)–field pea (Pisum sativum L.)–canola (Brassica napus L.)–wheat crop rotation at five sites in the Canadian prairies. The glyphosate rates were 0, 1, 2, 4 and 8 kg ae ha−1, applied pre-seeding and post-harvest every year. The wheat rhizosphere was sampled in the final year of the study and analysed for microbial biomass C (MBC), the composition and diversity of the microbiome, and activities of β-glucosidase, N-acetyl-β-glucosiminidase, acid phosphomonoesterase and arylsulphatase. Glyphosate did not affect MBC, the composition and diversity of prokaryotes and fungi, and the activities of three of the four enzymes measured in the wheat rhizosphere. The one effect of glyphosate was a wave-like response of N-acetyl-β-glucosaminidase activity with increasing application rates. The experimental sites had much greater effects, driven by soil pH and organic C, on the soil microbiome composition and enzyme activities than glyphosate. Soil pH was positively correlated with the relative abundance of Acidobacteriota but negatively correlated with that of Actinobacteriota and Basidiomycota. Soil organic C was positively correlated with the relative abundances of Proteobacteriota and Verrucomicrobiota, but negatively correlated with the relative abundance of Crenachaeota. The activity of acid phosphomonoesterase declined with increasing relative abundance of Acidobacteriota, but increased with that of Actinobacteriota and Basidiomycota. The activity of N-acetyl-β-glucosaminidase also increased with increasing relative abundance of Actinobacteriota but decreased with that of Mortierellomycota. β-glucosidase activity also decreased with increasing relative abundance of Mortierellomycota. The core fungal species observed in at least 90% of the samples were Humicola nigrescens, Gibberella tricincta and Giberella fujikuroi. Therefore, this multi-site study on the Canadian prairies revealed no significant effects of 4-year applications of glyphosate applied at different rates on most soil microbial properties despite differences in the properties among sites. However, it is important to keep evaluating glyphosate effects on the soil microbiome and its functioning because it is the most widely used herbicide worldwide.

Phosphorus acquisition strategies of arbuscular mycorrhizal and ectomycorrhizal trees in subtropical plantations

AbstractTrees form symbioses with different fungi to exploit soil nutrients, such as phosphorus (P). There is no precise information about the exact strategies by which arbuscular mycorrhizae (AM) and ectomycorrhizae (EM) species facilitate P acquisition and thereby regulate soil P availability in the P‐limited subtropical forests. We investigated the plant traits and rhizosphere soil properties related to the P acquisition strategies of seven AM and seven EM tree species in a subtropical plantation in China. The available P content, which was related to acid phosphomonoesterase activity, was higher in the rhizosphere soils of the AM trees than in those of the EM trees. The higher P content in the absorptive fine roots indicated that the AM trees absorbed more P from the soil than the EM trees. The leaf P adsorption efficiency indicated that AM trees resorbed more aboveground P than EM trees. Results from structural equation modelling demonstrated that AM trees were dominated by bacteria, which contributed to the low pH, while EM trees were dominated by ectomycorrhizal and saprophytic fungi that secreted acid phosphomonoesterase to mine P in the rhizosphere soil. The AM trees had higher mycorrhizal colonisation rates than the EM trees, while the EM trees had higher specific root lengths than the AM trees, which suggests that the AM trees tended to depend on mycorrhizae, while EM trees tended to depend on roots, to scavenge P from soil. Our findings suggest that, to influence the P availability and alleviate P deficiencies, the AM trees resorbed more P aboveground and mined and scavenged more P belowground than the EM trees.Highlights P availability was higher in the rhizospheres of AM trees than EM trees. AM trees resorbed more aboveground P than EM trees. AM trees mined soil P mainly by decreasing pH, whereas EM trees by secreting ACP. AM trees depended more on mycorrhizae, whereas EM trees on roots, scavenging soil P.

Soil Enzyme Activity Behavior after Urea Nitrogen Application.

Understanding how fertilizer application (particularly N, the most used chemical fertilizer worldwide) interacts with soil microbes is important for the development of best management practices that target improved microbial activity to enhance sustainable food production. This study was conducted to determine whether urea N rate and time of application to maize (Zea mays) influenced soil enzyme activity. Enzyme activity was determined by monitoring fluorescein diacetate (FDA) hydrolysis, ß-glucosidase, acid-phosphomonoesterase, and arylsulfatase activities. Experiments were conducted from 2014 through 2016 to compare single (fall or spring applications) and split applications of N at varying N rates under irrigation (Becker) and rainfed conditions (Lamberton and Waseca) in MN, USA. Nitrogen rates varied by location and were based on University of Minnesota guidelines. Soil samples were collected seven times each season. Nitrogen application split into two applications increased FDA activity by 10% compared with fall and spring applied N at Waseca. Fall or spring N application decreased arylsulfatase activity by 19% at Becker and by between 13% and 16% at Lamberton. ß-Glucosidase and acid-phosphomonoesterase activities were unaffected by N application. Sampling time and year had the greatest impact on enzyme activity, but the results varied by location. A negative linear relationship occurred between FDA and ß-glucosidase activity at all three sites. In summary, urea N application had small effects on enzyme activity at the sites studied, suggesting that some form of organic N could be more important than the ammonium provided by urea.

Identification and Classification of the Dissolved Substances from Sludge Biochar and Their Effects on the Activity of Acid Phosphomonoesterase

Soil extra-cellular enzymes are the main driving force for microbial and biochemical processes, which makes them sensitive indicators for soil health and quality. Returning large amounts of sludge or its biochar to farmland may introduce exogenous substances into soil and have a significant impact on soil enzymatic activity. This study aimed to evaluate the effects of substances dissolved from sludge biomass and its biochar added at different amounts and produced at various temperatures (200 °C, 300 °C, and 450 °C) on the activity of acid phosphomonoesterase. Results showed that the activity of acid phosphomonoesterase was significantly inhibited by these dissolved substances from biochar pyrolyzed at different temperatures, especially at high concentrations of 50 mgC L−1 and upon the exposure to DBC200. The conformation of acid phosphomonoesterase became loose and flexible after exposure to dissolved organic matter (DOM) extracted from biochar in terms of reduced α-Helix contents and increased β-Turn contents as deduced from circular dichroism spectra. According to the results of multiple linear regression, it can be concluded that the increased contents of arsenic as well as protein-like components within dissolved substances may be responsible for the inhibited enzymatic activities and the altered enzymatic conformation. Our findings provide evidence that the pyrolysis of sludge at a higher temperature would be helpful to reduce its negative impacts on the soil ecosystem.

Mutualistic interaction between arbuscular mycorrhiza fungi and soybean roots enhances drought resistant through regulating glucose exudation and rhizosphere expansion

Glucose is one of the low molecular weight components of root exudates to mediate the cross-talk between plants and microbes, but less is known about their contribution to drought resistance of plants and root-associated microbiome. To fill this knowledge gap, we optimized the visualization of glucose exudation and coupled it with another in situ tool – soil zymography ‒ as well as destructive analysis of enzyme kinetics (β-glucosidase; acid phosphomonoesterase) and microbial biomass. This helped identify how microbial functionality ‒ affected by drought and P limitation ‒ will show more resistance in the hotspots of soybean rhizosphere (grown in the rhizoboxes for 10 weeks) associated with arbuscular mycorrhizal fungi (AMF) symbiosis than those without AMF. Drought reduced glucose exudation, mainly allocated to root tips, and narrowed the rhizosphere enzymatic hotspot by three times. However, AMF inoculation enhanced glucose exudation compared to non-mycorrhizal plants and enlarged enzymatic hotspot area by 53% under drought condition. Despite the 50% reduction in β-glucosidase and acid phosphomonoesterase activities owing to water deficit, AMF symbiont triggered up to 36% enzyme activities in correlation with the non-mycorrhizal ones. Therefore, the drought resistance of these two enzymes was enhanced by up to 63% in mycorrhizal plants. The biomass of microbial phosphorus increased by 45% under drought AMF-conditioned plants. We conclude that the cooperation between soybean and AMF induced the formation of favorable microsites around the root, specifically in overlapping localities between rhizosphere and mycorrhizosphere, characterized by enhanced glucose release, increasing rhizosphere expansion, high enzyme activities and shortened substrate turnover time. This, in turn, contributed to the stronger resistance of microbial functions (e.g., enzyme expression) to drought stress in the rhizosphere hotspots. Thus, in response to AMF inoculation and consequent high glucose availability, rhizosphere microorganisms increased P mining rate in those hotspots remaining active despite water scarcity.

Flooding and straw returning regulates the partitioning of soil phosphorus fractions and phoD-harboring bacterial community in paddy soils.

Flooding and straw returning are effective agricultural practices in promoting phosphorus (P) availability in paddy soils. However, little is known about the effects of these practices and their interaction on the soil P pools and functional microbes responsible for soil P mobilization. Our 4-year paddy field experiment aimed to analyze the responses of soil P fractions and phoD-harboring bacterial communities in a double-rice cropping system to intermittent flooding (IF) and continuous flooding (CF), in plots with (+ S) and without (-S) straw return. Compared to IF, CF significantly increased soil citrate-P and marginally decreased the HCl-P fractions, suggesting that the stable inorganic P pools are transferred to labile inorganic P at lower redox potentials. Compared to the -S treatments, + S treatments significantly increased the labile organic fractions (enzyme-P). Correspondingly, a decreased soil total organic P concentration was observed in + S treatment. Additionally, + S treatment significantly increased the activity of acid phosphomonoesterase and alkaline phosphomonoesterase and the abundance of phoD-harboring bacteria. These results indicated that straw promoted organic P minimization to release orthophosphate. The diversity of the phoD-harboring bacteria and complexity of the co-occurrence network decreased under the CF + S treatment; however, all keystone species of the phoD-harboring bacteria were retained in this oxygen-deficient environment. This study highlights that irrigation regimes mediate the processes of inorganic P mobilization, while straw returns regulate the processes of organic P mineralization. Additionally, flooding could be a more effective agricultural practice than straw returning to promote soil P availability in paddy soils. KEY POINTS: •Soil P pools and phoD-harboring bacteria communities were assessed. •Straw return mainly affects the mineralization of organic P. •Continuous flooding mainly affects the mobilization of inorganic P.