Soil Alkaline Phosphatase Activity Research Articles

Cold-tolerant phosphate-solubilizing Pseudomonas strains promote wheat growth and yield by improving soil phosphorous (P) nutrition status.

It is well-known that phosphate-solubilizing bacteria (PSB) promote crop growth and yield. The information regarding characterization of PSB isolated from agroforestry systems and their impact on wheat crops under field conditions is rarely known. In the present study, we aim to develop psychrotroph-based P biofertilizers, and for that, four PSB strains (Pseudomonas sp. L3, Pseudomonas sp. P2, Streptomyces sp. T3, and Streptococcus sp. T4) previously isolated from three different agroforestry zones and already screened for wheat growth under pot trial conditions were evaluated on wheat crop under field conditions. Two field experiments were employed; set 1 includes PSB + recommended dose of fertilizers (RDF) and set 2 includes PSB - RDF. In both field experiments, the response of the PSB-treated wheat crop was significantly higher compared to the uninoculated control. In field set 1, an increase of 22% in grain yield (GY), 16% in biological yield (BY), and 10% in grain per spike (GPS) was observed in consortia (CNS, L3 + P2) treatment, followed by L3 and P2 treatments. Inoculation of PSB mitigates soil P deficiency as it positively influences soil alkaline phosphatase (AP) and soil acid phosphatase (AcP) activity which positively correlated with grain NPK %. The highest grain NPK % was reported in CNS-treated wheat with RDF (N-0.26%, P-0.18%, and K-1.66%) and without RDF (N-0.27, P-0.26, and K-1.46%), respectively. All parameters, including soil enzyme activities, plant agronomic data, and yield data were analyzed by principal component analysis (PCA), resulting in the selection of two PSB strains. The conditions for optimal P solubilization, in L3 (temperature-18.46, pH-5.2, and glucose concentration-0.8%) and P2 (temperature-17°C, pH-5.0, and glucose concentration-0.89%), were obtained through response surface methodology (RSM) modeling. The P solubilizing potential of selected strains at <20°C makes them a suitable candidate for the development of psychrotroph-based P biofertilizers. Low-temperature P solubilization of the PSB strains from agroforestry systems makes them potential biofertilizers for winter crops.

Enhancing Soil Health Through Microbial Inoculation and Changing Cultivation Methods in Rice-Wheat Cropping System

India’s rice-wheat cropping system (RWCS) is going through a paradigm shift to address resource degradation and sustainability issues. The increasing level of soil degradation has made soil biological health an important aspect of managing the problems of RWCS through understanding the role of microbes in enhancing soil health and by increasing the adoption of conservation agriculture-based practices. Our two-year study revealed that soil biological health, as measured by soil acetylene reductase activity (ARA), soil chlorophyll, microbial biomass carbon (MBC), soil dehydrogenase enzyme activity, and soil alkaline phosphatase activity (APA), was significantly impacted by the rice and wheat cultivation methods. The system of rice intensification (SRI) and zero tillage wheat (ZTW) system had significantly higher values for all the studied microbial parameters. The application of Anabaena-Pseudomonas biofilm formulation along with 75% recommended dose of nutrients (RDN) (90 kg N/ha and 19.35 kg phosphorus (P/ha) significantly improved all studied microbial parameters in both rice and wheat. The microbial properties such as dehydrogenase enzyme activity, alkaline phosphatase activity and microbial biomass carbon (MBC) had significantly higher values in treatment with RDN over 75% RDN indicating the role of optimal fertilization in soil biological health maintenance. A significant improvement in ARA and soil chlorophyll in inoculated treatment showed superior performance of inoculated microbes over inherent soil microbes in nitrogen fixation. The study of a combination of different rice and wheat cultivation methods and their influence in the long run on soil biological health in RWCS emphasizes the need for soil biological health maintenance considering its significant role in the system’s sustainability.

Natural degradation process of Salix psammophila sand barriers regulates desert soil microbial biomass C:N:P stoichiometry and homeostasis

The Salix psammophila sand barrier is widely used to control wind-sand disasters in desert areas. Importantly, the means through which the natural degradation of the sand-buried section of these sand barriers contributes to the community-level microbial elemental homeostasis of desert soils remains elusive. In this study, we conducted long-term field in situ sampling experiments over a nine-year period in a typical study area in the desert region of northwest China. Chloroform fumigation and high-throughput sequencing were used to determine soil microbial biomass and the diversity of fungi and bacteria. Combined with sand barrier decay characteristics, soil physicochemical factors, and extracellular enzyme activities, we explored the dynamic balance of soil microbial element ratios and key driving factors. The results show that natural degradation of S. psammophila sand barriers increased microbial biomass C and N contents in desert soil, with seven years being the most important turning point. The consistent increase in the soil microbial C:N:P stoichiometry ratios was primarily directly caused by an increase in the mass loss and changes in the fungal diversity. Microbial C:N and N:P ratios were well limited over time, suggesting homeostatic regulation of microorganisms, but the C:P ratio was not homogenized at the community level. The higher microbial C:P and N:P ratios indicated that microorganisms were limited by P after five years of sand barrier degradation. This was primarily related to a decrease in the soil alkaline phosphatase activity. However, microorganisms mitigated P limitation by altering the fungal community structure. These results constitute new evidence in our understanding of the relationships between S. psammophila sand barriers and soil element stoichiometry and the subsequent effects on microorganisms and community-level elemental homeostasis. This work advances the current understanding of artificial interventions in ecological restoration and desertification control.

Grazing promotes soil phosphorus cycling by enhancing soil microbial functional genes for phosphorus transformation in plant rhizosphere in a semi-arid natural grassland

Soil microorganisms play a key role in soil P transformation and cycling in grassland ecosystems, while the microbial mechanisms of animal grazing mediating soil P processes are not fully understood. We conducted a grazing experiment in a typical steppe grassland in Inner Mongolia, to explore the responses of microbial communities in rhizosphere and bulk soils to grazing intensity for understanding the mechanisms of grazing affecting P cycling. We determined soil physico-chemical properties and alkaline phosphatase activities, and measured soil microbial diversity and the relative abundance of microbial P-transformation genes by metagenomics in the rhizosphere and bulk soils of a Stipa grandis dominated grassland under three grazing intensities (no-, moderate, and heavy grazing). We found that (i) grazing significantly increased soil available P concentration and soil alkaline phosphatase activity; (ii) grazing increased the abundance of bacterial, but not fungal communities, and the enhanced abundance of rhizosphere bacteria promotes the P-cycling potential; (iii) grazing increased the relative abundance of the genes responsible for microbial P-uptake and transport, and inorganic P solubilization and organic P mineralization in rhizosphere soil, but not in bulk soil; (iv) grazing reduced the node degree of the network of the genes involved in P-transformation, but it increased the node degree of the genes encoding alkaline phosphatase and the C–P lyase multi-enzyme complex in the rhizosphere soil. The grazing-induced changes in the abundance of microbial functional genes are beneficial to P-solubilization and mineralization. Our results indicate a divergent effect of grazing on soil microbial communities and their functional genes involved P-transformation in rhizosphere and bulk soils, and represent an important progress towards the understanding of the mechanisms of microbial regulation of P cycling in grassland ecosystems.

Changes in soil properties and the phoD-harboring bacteria of the alfalfa field in response to phosphite treatment.

- Phosphite and phosphate increase the total phosphorus and available phosphorus.- The pH was the dominant factor influencing the phoD-harboring bacterial community under phosphite fertilizer.- The response of soil properties and phoD-harboring bacterial community to phosphate and phosphite fertilizers differed in the alfalfa field.

Metagenomic insights into the effects of organic and inorganic agricultural managements on soil phosphorus cycling

Microbes play important roles in regulating soil phosphorus (P) cycling in agroecosystems. However, little is known about how P-cycling microbes respond to organic and inorganic agricultural managements in terms of their functional and phylogenetic traits. Here, metagenomics was used to determine effects of P-cycling functional genes and taxa on soil P availability in a forage (Broussonetia papyrifera) monoculture ecosystem under organic (inoculating arbuscular mycohrrizal fungi (AMF) and intercropping legume (Medicago sativa)) and inorganic (adding chemical nitrogen (N) and P fertilizers) managements. The results showed that soil available P (AP) in plots with both legume and AMF addition was increased by 54.3 % compared with the control and was1.6–2.4 times higher than in plots with N or P fertilization. The abundance of ppa involved in inorganic-P solubilization was significantly increased after adding both legume and AMF compared with P-addition treatment. Soil alkaline phosphatase activity increased with P fertilizer addition and was positively correlated with soil AP. The abundances of phoA and phnI involved in organic-P mineralization were significantly higher under P fertilization treatment than under N fertilization treatment. Soil total N and AP were the key drivers on interactions among P-transportation genes, organic-P mineralization genes and taxa related to P-transportation. Overall, organic agricultural management increases soil P availability by increasing the potential of inorganic-P solubilization, while inorganic agricultural management regulates P availability via altering the potential of organic-P mineralization. These findings could provide a better understanding of the mechanisms that drive soil P availability under organic and inorganic agricultural managements.

Impact of In-situ Paddy Straw Burning on Soil Enzyme Activity, Soil Microbial Population and Green House Gas Emissions in Sandy Loam Soil

The rice - maize cropping system is one of the predominant cropping systems in Telangana state, which also produces large quantities of residues, whose disposal is a major problem. A large quantity of paddy straw is burnt on the farm to clear the field for succeeding crop. On the farm, a significant amount of paddy straw is burned to prepare the land for a subsequent crop. Burning crop residue damages the air and results in the loss of a significant amount of biomass plant nutrients and the entire amount of carbon. The purpose of the study was to investigate the impact of paddy straw burning on soil biological properties (enzyme activities, microbial population) and to know the amount of green house gas (GHG) emissions released due to burning of residue, under two tillage systems viz., no tillage and conventional tillage. Results indicated that there was a significant decrease in soil microbial population, dehydrogenase activity (41.52% in NT and 40.07% in CT), acid and alkaline phosphatase activity and urease activity in soil due to residue burning. It also indicated that there was a rise in CO2, CH4 and N2O emissions 48 hours after residue burning. It can be concluded that crop residue burning leads to decrease in the enzyme activities and soil microbial population. It also leads to rise in green house gas emissions. The impact of rice straw burning on different microbial genera has to be further studied by researchers.

Long-term high-P fertilizer input shifts soil P cycle genes and microorganism communities in dryland wheat production systems

Phosphorus (P) fertilizer input influences crop yield, soil P cycling, and phosphate-solubilizing microorganism (PSM) communities, which play a key role in obtaining soil available phosphorus. However, the responses of soil P cycle genes and PSM communities to long-term high-P fertilizer application are less known in the Chinese Loess Plateau. In this study, metagenomics was used to explore the shifts in the abundance and compositions of soil P cycle genes and PSM communities at a long-term (14 years) trial site with four P fertilization rates. Long-term high-P (200 kg P2O5 ha−1 year−1) inputs resulted in a decrease in the abundance of the P-starvation response genes (phoR and phoP), the high-affinity phosphate-specific transporter (pst), the inorganic P-solubilization, and organic P-mineralization genes (gcd, pqq, and phoD). Long-term P inputs increased the abundance of phosphate-solubilizing bacteria but decreased the abundance of phosphate-solubilizing fungi and weakened the relationship of relevant key soil P genes. Soil total P, inorganic P, available P (AP), dissolved organic C contents, and alkaline phosphatase (ALP) activity were significantly related to soil P cycle genes and PSM community structure. In conclusion, the changes in soil P cycle genes and microbial P solubilization capacity under long-term P input conditions were mainly regulated by soil AP content and ALP activity, while long-term high-P inputs increased soil mineral P immobilization by altering the expression of soil P cycle genes and the PSM functional profiles. These consequences provide a new view for the study of soil P cycles in agricultural ecosystems with P inputs.

Plastic mulching significantly improves soil enzyme and microbial activities without mitigating gaseous N emissions in winter wheat-summer maize rotations

Plastic mulching is an important agricultural practice to increase crop yield by increasing soil temperature and moisture. Plastic mulching can also affect soil greenhouse gas emissions [e.g., N 2 O emissions and NH 3 volatilization] and soil characteristics such as soil enzyme and microbial activities, but the simultaneous effects of plastic mulching on these parameters and the potential links between them are rarely evaluated. Here, we conducted a field study to investigate the concurrent responses of N 2 O emissions, NH 3 volatilization, soil enzyme and microbial activities, soil dissolved organic C (DOC) and N (DON), and crop yield to plastic mulching (mulching) and no mulching (ambient) under consecutive winter wheat–summer maize rotation cycles in China’s Loess Plateau. The mulching treatment significantly increased soil water-filled pore spaces (WFPS) and soil temperature during growing cycle 1 (2018–2019 winter wheat and 2019 summer maize) and cycle 2 (2019–2020 winter wheat and 2020 summer maize). Averaged across both growing cycles, the mulching treatment significantly increased winter wheat yield by 31.8 %, summer maize yield by 36.4 %, soil NO 3 – -N content by 18.2 %, NH 4 + -N content by 27.4 %, cumulative N 2 O emissions by 34.0 % and NH 3 volatilization by 50.6 %, relative to the ambient treatment. Moreover, the mulching treatment significantly enhanced soil alkaline phosphatase, invertase, catalase, and urease activities and soil microbial biomass C and N contents in the 0–10 cm soil layer across both growing cycles. This study revealed a tradeoff, with plastic mulching significantly improving crop yields and soil enzyme and microbial activities but not mitigating N 2 O emissions or NH 3 volatilization. Our results highlight that simultaneously documenting gaseous N emissions and changes in soil properties under plastic mulching can advance the understanding of sustainable agriculture in semi-arid areas. • Soil water-filled pore spaces and soil temperatures differed highly in plastic mulching and no mulching. • Plastic mulching had higher grain yield and soil mineral N content than no mulching. • Plastic mulching significantly improved soil enzyme and microbial activities. • Plastic mulching increased NH 3 volatilization and N 2 O emissions.

The Effect and Influence Mechanism of Soil Salinity on Phosphorus Availability in Coastal Salt-Affected Soils

Soil salinization is a problem that arouses the world’s attention. Soil salinity is an important limitation for agriculture production in coastal area. Phosphorus is a very important nutrient element in the process of plant growth, and its effectiveness affects plant growth to a great extent. In this study, soil available phosphorus and its component in Hedley phosphorus classification were found to be affected by soil salinity in coastal areas of Jiangsu Province. Several key environmental factors changed under the saline environment of the coastal areas, such as soil salinity, soil pH, and soil alkaline phosphatase activity. These environmental factors were significantly correlated with soil available phosphorus. Results showed that there were significant correlations between soil salinity and other environmental factors, and soil salinity and alkaline phosphatase activity were the main influencing factors of soil available phosphorus in this study. Significant positive correlation was found between alkaline phosphatase activity and soil salt content, and soil salinity was considered as the most important impact factor for soil available phosphorus as it affected the surrounding environment, and the soil alkaline phosphatase could be considered as the direct influencing factor for soil available phosphorus. Analysis between the soil alkaline phosphatase activity and phosphorus component showed that soil alkaline phosphatase activity could increase the proportion of active inorganic phosphorus and medium active inorganic phosphorus in soil phosphorus pool, which explained the effect of soil alkaline phosphatase activity on soil available phosphorus.

Effects of Organic Fertilizer Combined with Chemical Fertilizer on Nutrients, Enzyme Activities, and Rice Yield in Reclaimed Soil

ABSTRACT A field experiment was conducted to explore the effects of combined application of organic and chemical fertilizers (organic-chemical fertilizers) on reclaimed soil fertility and rice yield. The experiment involved five treatments: no nitrogen (N) fertilizer (CK1), 100% chemical fertilizer N (CK2), 40% chicken manure N + 60% chemical fertilizer N (T1), 40% vermicompost N + 60% chemical fertilizer N (T2), 40% rapeseed meal fertilizer N + 60% chemical fertilizer N (T3). Organic-chemical fertilizers maintained or increased rice yield. Rice yields of T2 and T3 increased by 6.7% and 8.9%, respectively, as compared with CK2. T1 showed similar value of rice yield with CK2. Organic-chemical fertilizers application increased contents of soil organic C (SOC), total N (TN), alkali-hydrolyzable N (AN), NH4 +-N, NO3 –N, available phosphorus (AP), available potassium (AK) as well as CEC by 10.5%~15.9%, 8.9%~39.3%, 16.9%~74.5%, 38.1%~77.2%, 18.3%~136.5%, 27.7%~75.0%, 16.1%~24.7% and 7.2 ~ 26.0%. T3 had highest soil TN, AN, NH4 +-N, NO3 –N, CEC as well as T2 showed the highest contents of soil AP and AK. Organic-chemical fertilizers application increased soil sucrase (S-SC), urease (S-UE) and catalase (S-CAT) activities. The highest soil S-SC activity was detected in T3, and the highest soil S-UE and soil alkaline phosphatase (S-AKP) activities were observed in T2. Rice yield was positively related to SOC, TN, AN, NH4 +-N, NO3 –N, AP and AK as well as S-SC, S-UE and S-AKP activities. In conclusion, 40% organic N + 60% chemical N application could improve soil fertility and rice yield in reclaimed soils, with rapeseed meal fertilizer the most effective organic N source, followed by vermicompost and chicken manure.

Changes in soil phosphorus fractions associated with altered vegetation and edaphic conditions across a chronosequence of revegetated dunes in a desert area

Revegetation through the establishment of woody vegetation on bare active dunes is an effective approach to restore degraded dune systems. Revegetation can affect soil inorganic and organic phosphorus (Pi and Po) cycling and storage by modifying biotic and abiotic conditions (vegetation characteristics and soil properties, respectively). However, how shrub revegetation and revegetation age affect soil P fractions and how biotic and abiotic factors interact to mediate revegetation effects on P fractions are poorly understood. To address these questions, we conducted a field survey in an artificially established chronosequence of revegetated dunes in a desert area of China, with five differently aged revegetated sites (19, 32, 46, 55, and 63 years) and an adjacent non-revegetated control site. We investigated changes in soil Pi and Po fractions of decreasing lability (labile P: resin Pi and NaHCO3-extractable Pi/Po; moderately labile P: NaOH-extractable Pi/Po; recalcitrant P: HCl-extractable Pi/Po and residual P) and vegetation and edaphic properties as predictors. Boosted regression trees analysis was used to evaluate the contributions of individual predictors to variability in P fractions, and structural equation modeling was used to determine the interactive effects of multiple predictors. Concentrations of soil P fractions were 65–114% greater in revegetated sites compared with the non-revegetated control, but the magnitude of this effect varied with revegetation age. Furthermore, soil total P and its fraction concentrations increased with revegetation age, but the accumulation rates of total P and most P fractions were greatest during the first 19 years after revegetation. Revegetation-induced soil total and available P increases were caused by multiple factors, including enhanced P inputs from dust deposition and plants due to increased vegetation cover and surface litter and root biomass, and enhanced Po and Pi mobilization due to increased soil alkaline phosphatase activity and decreased soil pH. Edaphic properties exerted greater controls over the spatiotemporal dynamics of soil P than vegetation changes, but the key influential factors differed among P fractions. We conclude that revegetation significantly increased the labile, moderately labile, and non-labile P pools and that the effects of revegetation were fraction- and time-dependent, with important implications for managing soil P cycling in revegetated desert ecosystems.

Effect of different levels and sizes of walnut seed residues on phosphorus availability and alkaline phosphatase activity in calcareous soil

A laboratory experiment has been carried out in the College of Science-University of Salahaddin to study the effect of different levels (0,5,10 and 15%) and sizes(250 and 1000µm) of walnut seeds residues and (160mg.kg-1) phosphorus fertilization on the concentration of phosphorus availability and alkaline phosphatase activity in calcareous soil during 15 and 30 days period of incubation, the experimental design in factorial complet randomize design (C.R.D) with three replications. The results indicated that the application of different levels of walnut seed residues decreases the concentration of phosphorus availability and alkaline phosphatase activity, however the results revealed that combination between levels and sizes of sieved walnut seed residues and phosphorus fertilizer significantly (p≤0.05) affected the alkaline phosphatase activity and the concentration of available phosphorus, the highest values (29.633 µgPNPg-1.hr-1and 6.442mg.kg-1) have been recorded in treatments combination received 1000µm, 15% walnut seed residues and phosphorus fertilizer, respectively.

Application of humic acid compound fertilizer for increasing sweet potato yield and improving the soil fertility

Combined application of humic acid (HA) and multi-nutrient fertilizer improve nutrient utilization and increase crop yield. To give insight about the application of HA compound fertilizer in sweet potato production, a field experiment was conducted the effect of humic acid-nitrogen, phosphorus, and potassium compound fertilizer (HA-NPK) on soil nutrient contents, soil enzyme activity, soil microorganism community structure and yield of sweet potato. Results showed that compared to nitrogen, phosphorus, and potassium compound fertilizer (NPK) treatment, the activated humic acid- nitrogen, phosphorus, and potassium compound fertilizer (HA-NPK1) and non-activated humic acid- nitrogen, phosphorus, and potassium compound fertilizer (HA-NPK2) treatment significantly increased the plant biomass and storage root yield. Increase in yield from application of HA-NPK1 was significantly larger than those from HA-NPK2. The HA-NPK1 treatment greatly increased the content of readily available phosphorus, potassium and soil organic matter, enhanced the enzyme activity of soil urease, invertase, alkaline phosphatase and catalase. The numbers of soil bacteria, fungi and actinomycetes in the HA-NPK1 treatment were significantly higher than the NPK treatment. In conclusion, the application of the activated HA-NPK in sweet potato production could be used effectively to increase soil quality, facilitate the growth of sweet potato and increase its yield under similar conditions to this work.

Application of cotton straw biochar and compound Bacillus biofertilizer decrease the bioavailability of soil cd through impacting soil bacteria

BackgroundCd seriously threatens soil environment, remedying Cd in farmland and clearing the response of soil environment to modifiers in Cd-contaminated soils is necessary. In this study, the effects of cotton straw biochar and compound Bacillus biofertilizer used as modifiers on the biochemical properties, enzyme activity, and microbial diversity in Cd-contaminated soils (1, 2, and 4 mg·kg−1) were investigated.ResultsThe results showed that both cotton straw biochar and compound Bacillus biofertilizer could improve the soil chemical characteristics, including the increase of soil C/N ratio, electrical conductance (EC) and pH, and the most important decrease of soil available Cd content by 60.24% and 74.34%, respectively (P < 0.05). On the other hand, adding cotton straw biochar and compound Bacillus biofertilizer in Cd stressed soil also improved soil biological characteristics. Among them, cotton straw biochar mainly through increasing soil alkaline phosphatase activity and improve bacteria abundance, compound Bacillus biofertilizer by increasing soil invertase, alkaline phosphatase, catalase, and urease activity increased bacterial community diversity. On the whole, the decrease of soil available Cd was mainly caused by the increase of soil pH, C/N, urease and alkaline phosphatase activities, and the relative abundance of Acidobacteria and Proteobacteria.ConclusionsIn summary, the applications of cotton straw biochar and compound Bacillus biofertilizer could decrease soil available Cd concentration, increase soil bacterial community diversity and functions metabolism, and reduce the damage of Cd stress, compared with cotton straw biochar, compound Bacillus biofertilizer was more effective in immobilizing Cd and improving soil environmental quality.

The importance of rare versus abundant phoD-harboring subcommunities in driving soil alkaline phosphatase activity and available P content in Chinese steppe ecosystems

The alkaline phosphatase-harboring community (the phoD community hereafter) plays an important role in organic P mineralization. Here, we comparatively studied the biogeographical patterns of abundant and rare phoD subcommunities and their roles in mediating soil phosphatase (ALP) activity and available P content in three representative steppe regions in China, namely the Inner Mongolian Plateau, the Loess Plateau, and the Qinghai-Tibetan Plateau. The results indicated that soil ALP activity, available P content, soil and microbial biomass C:P, N:P ratios varied significantly among steppe regions. Significant differences in diversity, metabolic energy and assembly processes were observed between abundant and rare phoD subcommunities. First, richness of the rare taxa was significantly higher than that of the abundant subcommunities. Second, testing of metabolic theory of ecology showed that rare subcommunities had a higher metabolic activation energy than the abundant taxa. Thirdly, deterministic other than stochastic processes dominated in the community assembly of both subcommunities. Soil pH was the key environmental determinant in community assembly processes for both subcommunities. The relationships among P-cycling parameters and between these parameters and phoD diversity were scale-dependent. The phylogenetic beta diversity of the rare phoD taxa had higher correlations with P-cycling parameters than that with the abundant taxa. More rare than abundant genera were significantly correlated with P limitation and ALP activity at different spatial scales. The rare Frankia was the key genus detecting P limitation, producing ALP and enhancing soil available P in Qinghai-Tibet.

Biochemical phosphorus transformations in a calcareous soil as affected by earthworm, cow manure and its biochar additions

Application of raw or char material may modify the influence of earthworm activity on soil phosphorus (P) transformation. The purpose of this study was to investigate the effect of cow manure or cow manure biochar addition and its interaction with earthworm on organic (Po) and inorganic (Pi) P fractions, alkaline phosphatase activity and P-solubilizing bacteria (PSB) in a calcareous soil of semi-arid region. For this purpose, the soil was amended with cow manure and its biochar in 4 levels (0, 1, 2 and 5%) in the absence and presence of earthworm (Eisenia fetida). The treatments were then incubated for 90 days. The monitoring of earthworms was also carried out after 30 and 90 days incubation. The results showed an increase in weight of earthworms in control and cow manure amended soils at both incubation times. However, application of cow manure biochar resulted in mortality and an initial weight loss of earthworms (36–85%) at 30 days incubation. This negative effect decreased over time, so that the earthworms recovered in 1% biochar amended soil. Amendment additions increased proportion of NaHCO3-Pi and NaOH-Pi but decreased proportion of HCl-Pi, residual-P, NaOH-Po and HCl-Po, making P more available in soil. The impact of cow manure biochar on the NaHCO3-Pi and NaOH-Pi fractions was stronger than that of cow manure. Earthworm decreased the proportion of Pi fractions but increased the proportion of Po fractions, indicating a transformation of P from Pi to Po forms. Alkaline phosphatase activity and PSB number were also increased as affected by earthworm and amendment (especially cow manure) additions. No significant interaction between earthworm and amendment additions was observed (p < 0.05), indicating that the influence of earthworm on P transformations was not dependent on amendment additions. Overall, we concluded that biochar can be useful for the amendment of semi-arid calcareous soil in terms of P availability, but the negative response of earthworms to biochar and its effect on other soil processes should be taken into consideration.

Simulated root exudates stimulate the abundance of Saccharimonadales to improve the alkaline phosphatase activity in maize rhizosphere

Plants promote the mineralization of soil organic phosphorus by secreting phosphatase into the rhizosphere, in addition they promote the growth of bacteria which also release phosphatase to the rhizosphere. Sugars are the main component of root exudates and a key driver of soil microbial activity. In this study, we added different concentrations of a range of sugars found in root exudates to the soil during maize growth to investigate whether sugars could stimulate alkaline phosphatase activity. Sugars increased alkaline phosphatase activity in soil, while different sugars increased this activity to different extents. Small concentration of sugars did not stimulate alkaline phosphatase activity in the rhizosphere, change the bacterial community structure or select phosphatase producing species such as Saccharimonadales. However, alkaline phosphatase activity was enhanced by larger concentration of added sugars, which increased indigenous soil Saccharimonadales abundance. Notwithstanding this, Saccharimonadales were rare in the microbial taxa at the order level and their relative abundance was only 2.1%–4.9% at different sugar concentration levels. Our results suggest that addition of sugars selected for indigenous soil Saccharimonadales, enhancing alkaline phosphatase activity in the rhizosphere. These rare microbial taxa may be a key species in soil phosphorus cycling.

Effects of Alkali-Activated Algae Biochar on Soil Improvement after Phosphorus Absorption: Efficiency and Mechanism

Biochar is often used for the removal of phosphorus in wastewater. However, the improper treatment of adsorbed biochar might cause secondary pollution. In order to promote the recycling and harmless utilization of biochar with adsorbed phosphorus, a new modified biochar (ABC) was prepared from cyanobacteria in this study. The maximum adsorption capacity of ABC calculated from the Langmuir isotherm model was 38.17 mg·g−1. ABC was used to absorb phosphorus in wastewater, whose product (ABC/P) was used for soil improvement and soybean cultivation. The results showed that adding the proper amount of ABC/P could significantly increase the pH of the soil (from 6.52 ± 0.04 to 7.49 ± 0.08), organic matter content (from 34.02 ± 0.41 to 47.05 ± 0.14 g·kg−1), cation exchange capacity (from 3.01 ± 0.18 to 3.76 ± 0.07 cmol·kg−1), water-holding capacity (from 28.78 ± 0.34 to 35.03 ± 0.31%), effective phosphorus content, and total phosphorus content. Meanwhile, the soil alkaline phosphatase activity was improved. The plant height, root length, and fresh quality were promoted by planting soybeans in ABC/P-improved soil and were better than those of the control group. Therefore, ABC/P, as a new type of phosphorus fertilizer, has the potential for soil amendment for legume crops.

Effects of mixed irrigation using brackish water with different salinities and reclaimed water on a soil-crop system

AbstractTo explore the effects of mixed irrigation on soil and crops, a pot experiment was conducted in two salinity levels of brackish water, four levels of mixed brackish-reclaimed water and freshwater irrigation as the control. The soil Na-Cl to Ca-SO4 contents changed, and activities of soil alkaline phosphatase and polyphenol oxidase changed, exhibiting a ‘V’-shaped curve with increasing the proportion of reclaimed water in the mixture. At the same brackish-reclaimed water level, there were no significant differences in alkaline phosphatase and polyphenol oxidase activities except for soil alkaline phosphatase activity decreasing significantly with the increase in salinity under brackish water irrigation. Mixed irrigation obviously improved superoxide dismutase activity but no significant influences on aboveground dry weight, underground biomass or crop physiological indexes (chlorophyll, soluble protein, malondialdehyde, peroxidase, catalase). Based on the integrated biological response index version 2 (IBRv2), the deviation of reclaimed water irrigation was the smallest, followed by 1:1 and 1:2 (3, 5 g/L brackish water salinities, respectively), with IBRv2 values of 7.94, 12.55 and 16.04. Therefore, considering the soil-crop characteristics, limited daily water amount and inadequate pipeline facilities for reclaimed water, the brackish-reclaimed water ratio should be 1:1 and 1:2 at 3, 5 g/L of brackish water, respectively.