Phosphomonoesterase Activity Research Articles

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.

Short-term legacy effects of long-term nitrogen and water addition on soil chemical properties and micro-bial characteristics in a temperate grassland.

Nitrogen deposition and summer precipitation in eastern Inner Mongolia are predicted to increase in recent decades. However, such increases in nitrogen inputs and precipitation may not be continuous under the future new patterns of global change, with the direction and magnitude of which may change or weaken. The legacy effects of nitrogen and water addition after cessation on ecosystems are still unclear. Based on a 13-year nitrogen and water addition experiment in temperate grassland of northern China, we examined the short-term (2 years) legacy effects of historical nitrogen and water addition on soil physicochemical properties and microbial properties after the cessation of nitrogen and water addition in the 14th year. The results showed that the positive effects of historical nitrogen addition on most of soil nutrient variables diminished after two years of cessation, including ammonium nitrogen, nitrate nitrogen, dissolved organic carbon and nitrogen, and Olsen-P concentrations. In contrast, there were legacy effects on soil microbial characteristics. For example, the historical nitrogen input of 15 g N·m-2·a-1 reduced microbial biomass carbon, respiration, and alkaline phosphomonoesterase activity by 73.3%, 81.9%, and 70.3% respectively. It implied that microbial parameters restored slowly in comparison with soil nutrients, showing a hysteresis effect. Results of Pearson's correlation and redundancy analysis showed that the legacy effects of historical nitrogen addition on microbial parameters could be attributed to the negative effects of nitrogen addition on soil pH. Historical water addition showed significant legacy effects on soil pH, ammonium nitrogen, dissolved organic carbon and nitrogen, respiration, and soil enzyme activities, which significantly interacted with historical nitrogen addition. These results are of great significance to predict the changes in grassland ecosystem functions and services under the local environmental improvement conditions, and to reveal the restoration mechanism of degraded grassland.

Ecological restoration of tidal flat and its effects on soil characteristic and bacterial community

AbstractVegetation restoration is a vital ecological remediation technology for greening saline‐alkaline soils. However, little attention is paid to the seasonal changes of soil remediation under different vegetation coverage. This study investigated a recently restored coastal tidal flat located on the island of Zhoushan, by examining shifts in physicochemical properties, enzyme activities, and bacterial communities over 1 year. Soils under Suaeda australis (SUA), Phragmites australis (PHR), Tamarix chinensis (TAM), and two hybrid treatments (SUA+PHR and SUA+TAM) were collected seasonally. Results showed that the seasonal climate variations and vegetation types played important roles in soil physicochemical properties and soil enzyme activities during vegetation restoration. Vegetation could stimulate the activities of soil microbial enzymes, of which PHR‐covered soils exhibited higher catalase activities, higher alkaline phosphomonoesterase activities were observed in summer except for PHR. The combined communities had the highest urease activities in spring and summer, and the highest levels of polyphenol oxidase activity were found in summer or autumn. Furthermore, the bacterial alpha diversity revealed that SUA‐ and SUA+PHR‐covered soils were not markedly affected as the season progressed, whereas PHR and SUA+TAM were characterized by an increase–decrease trend, as well as TAM exhibited highest in autumn. Proteobacteria, Bacteroidetes, Acidobacteria, Actinobacteria, and Chloroflexi were the dominant phyla in each vegetation types. This study deepens our understanding of the effects of halophyte cultivation on coastal ecosystem phytoremediation.

Incorporating biotic phosphorus-acquisition strategies into soil phosphorus transformation under long-term salinization in a tidal wetland

Tidal wetland plants can maintain high primary productivity under salinization, even with low phosphorus (P) availability. However, little is known about how they adapt to salinization-induced ecosystem P limitation over time. We established mesocosms using tidal freshwater wetland soils and the salt-tolerant plant Cyperus malaccensis and subjected them to short-term (6 months) and long-term (3.5 years) salinization. Overall, short-term salinization did not change plant or microbial biomass nitrogen/P ratios, whereas long-term salinization increased both, indicating that short-term salinization did not alter ecosystem P limitation, but long-term salinization exacerbated it. Concurrently, short-term salinization reduced the moderately labile inorganic P (Pi) pool, whereas long-term salinization also reduced the hydrolyzable organic P (Po) and primary mineral P pools. During both short- and long-term salinization, moderately labile Pi mobilization exhibited a negative correlation with Fe sulfide concentration and a positive correlation with Fe(III) concentrations. These results suggested that both short- and long-term salinization obtained P through abiotic P-acquisition strategies. Mobilization of the primary mineral P pool and hydrolyzable Po pools was negatively linked to root arbuscular mycorrhizal fungi (AMF) biomass and soil alkaline phosphomonoesterase (ALP) activity, respectively. This indicated that long-term salinization acquired P via biotic P-acquisition strategies. Specifically, soil microorganisms increased fungi predominance and thereby increased ALP activity to convert hydrolyzable Po, while tidal wetland plants enhanced root AMF associations to release carboxylate to transform primary mineral P. Overall, our results highlight that abiotic P-acquisition strategies could offset the ecosystem P limitation during short-term salinization, whereas biotic P-acquisition strategies play a more important role in soil P transformation under long-term salinization. Through biotic P-acquisition, tidal wetland ecosystems can maintain high plant primary productivity through biotic P-acquisition even under P-limited conditions, exhibiting increased resilience to sea-level rise.

Soil C, N and P bioavailability and cycling following amendment with shrub willow chips

Potato ( Solanum tuberosum L.) crops are often cultivated in coarse-textured soils with low soil organic matter and high nitrate leaching risk. Incorporating shrub willow chips into soil could enhance soil properties, while temporally immobilizing N and thus reducing N leaching. We performed a laboratory incubation study and a field experiment to evaluate the effects of shrub willow chips applied at increasing rates in the fall after the potato harvest on C, N and P cycling, soil pH and moisture, and on barley ( Hordeum vulgare L.) yield in the following year. In comparison with the control, willow chip incorporation at the rates of 40 and 60 Mg ha−1 increased total C content, but it did not affect the activity of C cycling enzymes. Willow chip addition at these rates also induced nitrate immobilization and reduced barley grain yield and total N uptake, but increased the activity of N cycling enzymes (β-1,4- N-acetylglucosaminidase and leucine aminopeptidase). Mehlich-3 extractable P content and phosphomonoesterase activity were not affected by willow chip addition. Our results suggest that shrub willow chips increased total organic C and immobilized N following their incorporation and can thus mitigate nitrate leaching after the potato harvest. The N immobilization was short lived and was not observed over second winter. We recommend to seed a forage legume in the spring following shrub willow chip incorporation. Willow chip incorporation is an effective means of increasing soil organic carbon.

Long-term implementation of a silvopastoral system enhances soil P availability and bacterial diversity

A silvopastoral system (SPS) is defined as a type of agroforestry system wherein grasses combine with legumes, shrubs, and trees for animal nutrition. Its use, as an alternative to grasslands, represents a promising strategy to increase livestock industry sustainability. In this work, we explored the long-term impact of the implementation of a SPS on soil P nutrition, soil phosphomonoesterase activity, and microbial diversity. For this, we harnessed a 9-year-old SPS consisting of a tree (Alnus acuminata), two shrubs (Sambucus nigra and Sambucus peruviana), and a grass (Cenchrus clandestinrr44us), as well as a nearby pasture consisting solely of the C. clandestinus grass, which we used for comparison. We collected samples during the rainy and dry seasons. The implementation of the SPS enhanced the availability of labile soil P, compared to the nearby pasture; this increase concomitantly occurred with a decrease of moderately-labile P. We also noted that labile Pi and Po significantly correlated with alkaline phosphomonoesterase activity, suggesting a potential role of this soil enzymatic activity on P availability within the SPS. There was an increase of diversity and a shift in the bacterial community in the SPS compared to the pasture. Within the SPS, the tree and shrub strips had the largest influence on soil P availability and phosphomonesterase activity. Altogether, this study documents the benefits of the implementation of a SPS on soil P availability and bacterial diversity.

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

Phosphomonoesterases Activity in Phosphorus-fertilized and Mycorrhizae-inoculated Cassava’s Rhizosphere in Two Savanna Agro–ecologies of Nigeria

Rhizosphere is a bio–influenced zone of soil where the interaction of microorganism and plant roots occurred tailored by the activity of soil enzymes. The activity of the enzymes depends largely on the physical and chemical characteristics of the soil environment. Experiment was carried out to examine the activity of phosphomonoesterases in the rhizosphere of cassava planted in two sites (Samaru and Minjibir) located in savanna ecologies of Nigeria. Soils from rhizosphere of the cassava were sampled from each treatment in an experiment involving split plot design. The treatments included 3 main plots (phosphorus rates at 0, 17.5 and 35 kg P2O5 ha–1) and 3 sub–plots (mycorrhizal inoculants: Glomygel and Mycodrip; and a Control). The Result of the analysis indicated higher activities of the phosphomonoesterases (acid and alkaline phosphatases) in Samaru site than Minjibir. The former recorded higher acid and alkaline phosphates activities over the latter with a magnitude of 96.84% and 43.65% respectively. This is attributed to the variability in the soil characteristics between the two sites. The main effect of P fertilizer indicated that 0 kg P2O5 ha–1 recorded a significantly (p<0.05) higher phosphomonoesterases activity than application of 17.5 and 35 kg P2O5 ha–1. Inoculation with mycorrhizae also increased the activities of the phosphomonoesterases in both sites which indicate increase mycorrhizal colonization as a result of inoculation. It is concluded therefore, that the activity of phosphomonoesterases in the rhizosphere can be affected by fertilization as well as enhanced by inoculation with the influence of soil characteristics.

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.

Close relationship between the gene abundance and activity of soil extracellular enzyme: Evidence from a vegetation restoration chronosequence

Extracellular enzymes (EEs) play vital roles in the transformations of soil organic matter, yet the regulators of EE activity remain unclear. Inducible EE production predicts that EE activity is determined by microbial nutrient status. Alternatively, EE production can be constitutive (continuous and baseline-level expression of EE gene regardless of the nutrient status), and in this case EE gene abundance potentially affects EE activity. Here, we examined whether EE gene abundance was a key regulator of EE activity along a vegetation restoration chronosequence. For the four hydrolytic EEs related to microbial acquisition of carbon, nitrogen and phosphorus, their gene abundance ratios (obtained from metagenomic sequencing) were positively related to corresponding activity ratios (R2 = 0.43–0.94). These relationships were maintained in the structural equation modeling when the effects of microbial nutrient status and soil property were considered. The gene-enzyme link was further confirmed by the positive relationship between the absolute abundance of phoD gene (obtained from qPCR analysis) and the alkaline phosphomonoesterase activity. Overall, our results suggest that constitutive EE production may contribute significantly to soil EE activity. The direct gene-enzyme link highlights the development of gene-informed Earth system models to better predict the soil carbon dynamics under global change.

Alteration of the soil microbiome and enzyme activities by forage-applied manure from cattle fed the methane inhibitor 3-nitrooxypropanol supplement

The microbial fermentation of plant feed by ruminants produces enteric methane (CH4), a potent greenhouse gas. Supplementing ruminant diets with an experimental methane inhibitor, 3-nitrooxypropanol (3-NOP), has been shown to decrease enteric CH4 production, but the effect of manure from these cattle on the soil microbiome has not been studied. In 2017 and 2018, we examined the effects of stockpiled manure and composted manure from cattle fed 3-NOP supplement alone or in combination with monensin (an ionophore) on soil permanganate-oxidizable C, microbial biomass C (MBC), the composition and diversity of prokaryotic and fungal communities, and the activities of β-glucosidase (C cycling), N-acetyl-β-glucosaminidase (C and N cycling), acid and alkaline phosphomonoesterases (P cycling), and arylsuphatase (S cycling) in a forage cropping system. Stockpiled or composted manure from cattle fed 3-NOP increased MBC in 2017, fungal α-diversity in 2018 and the relative abundance of Actinobacteriota, but it decreased the relative abundances of Acidobacteriota and Basidiomycota, relative to stockpiled or composted manure from cattle that were not fed 3-NOP. In 2017, relative to the conventional stockpiled manure, 3-NOP in stockpiled manure increased the activities of N-acetyl-β-glucosaminidase and acid phosphomonoesterase, but these effects were not observed for composted manure. Monensin, when used in combination with 3-NOP, did not affect any of the soil parameters measured in this study. The core microbiome found in 90 % of the soil samples included the bacterial and fungal genera Vicinamibacteraceae and Solicoccozyma, respectively. Therefore, 3-NOP manure or compost altered the composition of the soil microbiome, and the 3-NOP in stockpiled manure increased the potential activities of enzymes involved in C-and-N and P cycling in the first year of the study, and fungal α-diversity in the second year, but no negative or persistent effects of 3-NOP on enzyme activities were observed.

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.

Effects of long-term phosphorus addition on soil ratios of phosphomonoesterase to phosphodiesterase in three tropical forests

AbstractSoil microorganisms in tropical forests can adapt to phosphorus (P)-poor conditions by changing the activity ratios of different types of phosphatases. We tested whether microorganisms in P-poor tropical forest soils increased the phosphomonoesterase (PME) to phosphodiesterase (PDE) activity ratio, because a one-step enzymatic reaction of monoester P degradation might be more adaptive for microbial P acquisition than a two-step reaction of diester P degradation. A continuous 10-year P addition experiment was performed in three tropical forests. The activities of PME and PDE, and their ratio in soil, were determined under the hypothesis that the P-fertilized plots where P shortage is relieved would have lower PME:PDE ratios than the unfertilized controls. We demonstrated that long-term P addition in tropical forest soil did not alter the PME:PDE ratio in primary and secondary forests, whereas P fertilization elevated the PME:PDE ratio in planted forest. These results were in contrast to previous results. The long-term, large-scale P fertilization in our study may have reduced litter- and/or throughfall-derived PDE, which negated the lowered PME:PDE ratio via exogenous P inputs.

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.