Available P Research Articles

Long-term vegetable production significantly reduces the selenium adsorption in two typical plastic shed soils

Long-term vegetable production in plastic shed soil (PSS) and related soil management strategies stimulate the changes of soil properties and the mobilization of selenium (Se), causing risks to environmental soil quality and human health. Nevertheless, whether the greenhouse management (defined by the years of greenhouse vegetable production) and the greenhouse type have a synergistic effect on Se mobility in PSSs subjected to long-term vegetable production is still unclear. This study investigated the joint effects of greenhouse management and the properties of PSS on Se adsorption and desorption in soils collected from solar greenhouses (SG) and round arch plastic greenhouses (PG), which has been continuously cultivated respectively for 20 and 30 years in Tongshan County, Jiangsu Province, East China. Herein, we carried out a field survey coupled with batch experiments to investigate the adsorption and desorption behavior of Se in the SG and PG soils with different years of vegetable production. Results showed that greenhouse management had differentiated effects on soil properties and Se mobility in the two typical PSSs. Compared to the open field soils, long-term vegetable production generally increased soil nutrients (i.e., total P (TP), available P (AvP)), OM and Se desorption in the SG soil, while it significantly decreased Se adsorption in both typical PSSs. The soil pH had a downward trend with the increase of the years of vegetable production. The longer years of greenhouse vegetable production, the less Se adsorption capacity occurred in PSSs with annual decrease rates of 0.48 and 0.24 mg kg−1 yr−1 for the SG and PG soil, respectively, at 1.0 mg L−1 Se addition. Conversely, the ratio of Se desorption of the SG soils increased with longer vegetable production. The results of partial least squares regression (PLSR) explained the differences in Se adsorption and desorption between the SG and PG soil due to the changes in soil properties caused by the greenhouse management and greenhouse type. The fewer Se application is therefore recommended in the SG soils than in the PG soils after long-term greenhouse vegetable production.

Phosphorus Delivery Potential in Soil Amended with Rock Phosphate Enriched Composts of Variable Crop Residues under Wheat–Green Gram Cropping Sequence

ABSTRACT Understanding phosphorus (P) transformation in soil is necessary to develop sustainable P management practices. An experiment was carried out to evaluate the P fractions and P delivery potential in soil amended with rock phosphate (RP)-enriched composts under the wheat–green gram cropping sequence. The P mineralization study also revealed that the soil treated with RP-enriched composts showed a decline in available P during the initial stages of 30 days but improved significantly with the progress of time. Data emanated from the crop trials showed that significant buildup in available P (AP) was maintained under enriched compost-treated plot than unfertilized control in both the wheat and green gram crops. Total P (TP) increased by 37.4 and 48.9% under rice straw compost (RSC) and RSC+50% NPK-treated plots, respectively, over unfertilized control in wheat. However, the corresponding increases were 32.6 and 36.5% over control for green gram. After wheat, significant improvements in water-soluble P (WSP), microbial biomass P (MBP), and enzyme activities were found in plots receiving enriched composts. Based on information assessed from cluster analysis and principal component analysis, TP, WSP, citrate-soluble P, C/N ratio, and alkaline and acid phosphatase are considered their active role in compost maturity and quality, while TP, MBP, and AP are considered important parameters for P dynamics in soil. Enriched compost prepared using low-grade RP and crop residues could be an alternative and cost-effective option for mitigating the shortage of chemical fertilizers for crop production.

Long-term fertilization lowers the alkaline phosphatase activity by impacting the phoD-harboring bacterial community in rice-winter wheat rotation system

PhoD-harboring bacteria and the secreted alkaline phosphatases (ALP) are crucial in the regulation of soil phosphorus (P) cycling. However, the influential factors of these crucial indicators and their internal interactions remain controversial. Here, a long-term field experiment containing different fertilization regimes was conducted (chemical, organic, and no fertilizer applied). The results indicated that the richness and diversity of phoD-harboring bacterial community were significantly decreased after long-term fertilization. The applied fertilizer promoted the growth of competitive species, while phoD-harboring bacteria lost the advantage to outcompete other microorganisms after long-term fertilization. The decreased ALP activity was caused by the declined phoD gene abundance, which is attributed to the comprehensive effects of soil organic C (SOC), total nitrogen (TN), and various forms of P. The random forest models identified SOC, TN, and available P (AP) to be the dominant environmental factors in shaping the phoD-harboring bacterial community. In addition, some other forms of P such as organic P (Po), inorganic P (Pi) or total P (TP) also exerted significant effects. Different fertilization regimes changed the keystone genera that contributed significantly to soil ALP activities, while Pseudolabrys and Pseudomonas were predicted to be the most important genera regardless of different fertilization regimes. This study extends the understanding of the main process and mechanisms of P mobilization in response to different fertilization regimes.

Mix‐cropping of rice and water mimosa (Neptunia oleracea Lour.) increases rice photosynthetic efficiency, yield, grain quality and soil available nutrients

Cereal cultivation with legumes plays an important role in improving biodiversity and productivity. However, there are limited references concerning rice/legume mix-cropping in paddy fields. An aquatic leguminous plant, water mimosa (Neptunia oleracea Lour.), was introduced and a related field experiment of two seasons (early and late seasons in 2019) was carried out to explore the effects of rice/water mimosa mix-cropping on rice growth, yield, grain quality and soil nutrients in the present study. Three treatments - rice monocropping, rice/water mimosa intercropping and mix-cropping - were employed in this study. Results showed that rice grew better with greater height, tiller number, chlorophyll content, actual photosynthetic efficiency [Y(II)], maximum photochemical efficiency (Fv /Fm ) and photochemical quenching coefficient (qP) in the intercropping and mix-cropping treatments. In addition, the intercropping and mix-cropping treatments increased nutrient uptake of nitrogen (N) by11.89-24.42%, phosphorous (P) by 17.75-36.61% and potassium (K) by 19.22-47.44%, and rice yield by 19.9% and 21.8%. Conversely, the non-photochemical quenching coefficient (NPQ), chalkiness degree and chalky rate of rice were lower in the intercropping and mix-cropping treatments relative to those in the monocropping treatments. Notably, soil alkali-hydrolysable N (AN), available P (AP) and K (AK) contents were the highest in the mix-cropping treatments among the three cropping systems. We suggest that rice/water mimosa mix-cropping is an environmentally friendly agroecological system with a higher output and can be extended for green rice production and largely applied in the paddy field. © 2021 Society of Chemical Industry.

Enhanced Lead (Pb) immobilization in red soil by phosphate solubilizing fungi associated with tricalcium phosphate influencing microbial community composition and Pb translocation in Lactuca sativa L.

Phosphate (P) minerals and phosphate solubilizing fungi (PSF) play essential roles in lead (Pb) immobilization, but their roles in driving Pb bioavailability and ecological risks in red soil remains poorly understood. In this study, the inoculation of P. oxalicum and TCP successfully enhanced available P (AP) and urease concentrations in artificially Pb contaminated red soil. Combined P. oxalicum and TCP inoculation significantly reduced Pb bioavailability, bioaccessibility, leachability and mobility by increasing soil AP concentration and forming stable Pb-P compounds during the 21-day experiment. Soil AP and Pb bioavailability play an important role in shifting soil microbial communities induced by co-occurrence of P. oxalicum and TCP. Combined P. oxalicum and TCP could notably promote the relative abundances of predominant soil genus to enhance microbial resistance to soil Pb. Likewise, coexistence of P. oxalicum and TCP showed the highest biomass and better branch root development of Pb-stressed in lettuces (Lactuca sativa L.) in pot experiment, and significantly reduced up to 88.1% of Pb translocation from soil to root over control. The reductions of Pb translocation and accumulation in root in P. oxalicum + TCP treatment could enhance the oxidase activities and alleviate the oxidative damages of H2O2 and O2.- in shoot tissues. Our study provided strong evidence to use PSF associated with P materials for the stable and eco-friendly soil Pb remediation.

Organic material with balanced C‐nutrient stoichiometry and P addition could improve soil P availability with low C cost

AbstractBackgroundCarbon (C) addition to promote phosphorus (P) turnover by microbes is recommended to increase soil P availability. The C‐nutrient stoichiometry of organic materials (OM) are the primary factors in controlling soil P availability and C storage.MethodsA pot experiment was carried out to investigate the effects of different organic matter (OM) with equal carbon input [soybean dregs (SD), chicken manure (CM), and vermicompost (VC), 1000 mg C kg–1 soil] under three P levels (0, 10, and 20 mg P per kg dry soil) on soil P availability, C content, and plant growth in high P fixing soils.ResultsPlant biomass and shoot P content were significantly increased in P and OM addition treatment. Application of OM or P alone had no effect on soil available P (AP) but increased the microbial P (MBP). Compared with P addition alone, soil potential AP pool (the sum of soil AP and MBP content) was increased by 89%–200% in both OM and P addition soil. Soil potential AP pool and dissolved organic carbon (DOC) in VC treatment were significantly increased compared with those in CM and SD treatments. On day 60, compared with VC treatment, SD and VC treatments significantly increased alkaline phosphatase (ALP) but decreased soil organic carbon (SOC) content, in which ALP was negatively correlated with SOC and net C balance.ConclusionA small amount of P and vermicompost addition, which had a balanced carbon‐nutrient stoichiometric ratio, was an effective measurement in improving soil AP pool and C content in P‐fixing soil.

Imbalanced nitrogen–phosphorus input alters soil organic carbon storage and mineralisation in a salt marsh

A large imbalance in soil nitrogen (N) and phosphorus (P) inputs induced by anthropogenic activities is anticipated to profoundly influence soil carbon (C) budgets in salt marshes. In this study, we hypothesized that imbalances in the nitrogen–phosphorus (N–P) input would result in the nonlinear response of soil organic carbon (SOC) content, fractions and mineralization to the N–P input ratio. We applied three N–P input ratios (low (5:1), medium (15:1), high (45:1)) in a salt marsh of the Yellow River Delta (YRD) for four years (in which N added increased from 8.67 to 26.01 g N m−2 y−1 and P added decreased from 1.73 to 0.58 g P m−2 y−1) and quantified their impacts on SOC fractions and SOC mineralisation. The control treatment did not receive fertilization. The results showed that the N and P input led to overall increases in the availability of soil nutrients (i.e., inorganic N (IN) and available P (AP)), stimulation of plant biomass and changes of microbial community structure (i.e., γ- and δ-Proteobacteria and Acidobacteria). N and P input increased soil dissolved organic carbon (DOC) and decreased aromatic DOC components through improving N availability and stimulating plant growth. Notably, though, there may be a threshold N–P input ratio between 15:1 and 45:1 that, once crossed, triggers the loss of SOC. Appropriate increase in N availability induced by low and medium N-P input ratios would stimulate the SOC mineralization. However, excessive N-P input ratio would reduce SOC mineralization. Path analysis indicated that N–P input ratios dominantly regulate SOC mineralisation by changing soil DOC and microbial biomass (MBC)contents and microbial community structure. Thus, we speculate that the continuous increase in N input causes a growing N–P imbalance that reduces SOC stocks, despite a reduction in SOC mineralisation.

High throughput sequencing-based analysis of the soil bacterial community structure and functions of Tamarix shrubs in the lower reaches of the Tarim River.

Tamarix is a dominant species in the Tarim River Basin, the longest inland river in China. Tamarix plays an important role in the ecological restoration of this region. In this study, to investigate the soil bacterial community diversity in Tamarix shrubs, we collected soil samples from the inside and edge of the canopy and the edge of nebkhas and non-nebkhas Tamarix shrubs located near the Yingsu section in the lower reaches of Tarim River. High throughput sequencing technology was employed to discern the composition and function of soil bacterial communities in nebkhas and non-nebkhas Tamarix shrubs. Besides, the physicochemical properties of soil and the spatial distribution characteristics of soil bacteria and their correlation were analyzed. The outcomes of this analysis demonstrated that different parts of Tamarix shrubs had significantly different effects on soil pH, total K (TK), available K (AK), ammonium N (NH4+), and available P (AP) values (P < 0.05), but not on soil moisture (SWC), total salt (TDS), electrical conductivity (EC), organic matter (OM), total N (TN), total P (TP), and nitrate N (NO3−) values. The soil bacterial communities identified in Tamarix shrubs were categorized into two kingdoms, 71 phyla, 161 classes, 345 orders, 473 families, and 702 genera. Halobacterota, unidentified bacteria, and Proteobacteria were found to be dominant phyla. The correlation between the soil physicochemical factors and soil bacterial community was analyzed, and as per the outcomes OM, AK, AP, EC, and NH4+ were found to primarily affect the structure of the soil bacterial community. SWC, TK and pH were positively correlated with each other, but negatively correlated with other soil factors. At the phyla level, a significantly positive correlation was observed between the Halobacterota and AP, OM as well as Bacteroidota and AK (P < 0.01), but a significantly negative correlation was observed between the Chloroflexi and AK, EC (P < 0.01). The PICRUSt software was employed to predict the functional genes. A total of 6,195 KEGG ortholog genes were obtained. The function of soil bacteria was annotated, and six metabolic pathways in level 1, 41 metabolic pathways in level 2, and 307 metabolic pathways in level 3 were enriched, among which the functional gene related to metabolism, genetic information processing, and environmental information processing was found to have the dominant advantage. The results showed that the nebkhas and canopy of Tamarix shrubs had a certain enrichment effect on soil nutrients content, and bacterial abundance and significant effects on the structure and function of the soil bacterial community.

Effects of long-term straw returning on distribution of aggregates and nitrogen, phosphorus, and potassium in paddy

In order to understand the composition and stability of soil aggregate in paddy filed, as well as the changes of soil aggregate-associated nitrogen (N), phosphorus (P) and potassium (K) after straw addition combined with chemical fertilization, soil samples were collected from a 34-year positioning experiment with three treatments, including no chemical fertilizer (CK), chemical fertilizer only (NPK), and straw addition plus chemical fertilizer (NPKS). The composition of water-stable aggregates at the soil layers of 0-20 cm and 20-40 cm were analyzed with the wet sieving method, as well as the distribution characteristics, contribution rate and activation rate of soil aggregate-associated N, P, and K. Results showed that the fractions of >2 mm and 0.25-1 mm aggregates dominated the soil water-stable aggregates in paddy field, while the contribution of <0.053 mm aggregates was lowest. Compared with CK, NPKS treatment increased the contents of >2 mm and 1-2 mm aggregates at the layers of 0-20 and 20-40 cm, and reduced the contents of 0.053-0.25 mm and <0.053 mm. Similar result in NPK treatment was observed at the layer of 0-20 cm. Compared with tat under the NPK treatment, mean weight diameter (MWD) and geometric mean diameter (GMD) increased by 3.9%-15.5% and 6.3%-41.7% in NPKS treatment, respectively. However, the unstable aggregate index (ELT) reduced by 5.7%-28.7% in the NPKS treatment. NPKS significantly increased the contents of total N (TN), available P (AP), and available K (AK) in soil aggregates, especially in the >0.25 mm aggregates. There were no significant diffe-rences about alkali-hydrolysable N (AN) and total K (TK) between NPK and NPKS treatments. The nutrient contribution of soil aggregates in paddy field was affected by aggregate composition. NPKS significantly increased the contribution of AN, AP, and AK within >1 mm aggregates. In all, straw addition combined with chemical fertilizer could increase the stability of soil aggregates at the layers of 0-20 cm and 20-40 cm, and increase the contents of soil aggregate-associated N, P and K, especially for the >1 mm aggregates. Our results provided insights into ensuring soil quality and sustainable development of resources in paddy field by adjusting the ratio of soil C to N.

Silicon Application Modulates the Growth, Rhizosphere Soil Characteristics, and Bacterial Community Structure in Sugarcane

Silicon (Si) deficiency, caused by acidic soil and rainy climate, is a major constraint for sugarcane production in southern China. Si application generally improves sugarcane growth; however, there are few studies on the relationships between enhanced plant growth, changes in rhizosphere soil, and bacterial communities. A field experiment was conducted to measure sugarcane agronomic traits, plant nutrient contents, rhizosphere soil enzyme activities and chemical properties, and the rhizosphere bacterial community diversity and structure of three predominant sugarcane varieties under two Si treatments, i.e., 0 and 200 kg of silicon dioxide (SiO2) ha−1 regarded as Si0 and Si200, respectively. Results showed that Si application substantially improved the sugarcane stalk fresh weight and Si, phosphorus (P), and potassium (K) contents comparing to Si0, and had an obvious impact on rhizosphere soil pH, available Si (ASi), available P (AP), available K (AK), total phosphorus (TP), and the activity of acid phosphatase. Furthermore, the relative abundances of Proteobacteria showed a remarkable increase in Si200, which may be the dominant group in sugarcane growth under Si application. Interestingly, the AP was noticed as a major factor that caused bacterial community structure differences between the two Si treatments according to canonical correspondence analysis (CCA). In addition, the association network analysis indicated that Si application enriched the rhizosphere bacterial network, which could be beneficial to sugarcane growth. Overall, appropriate Si application, i.e., 200 kg SiO2 ha−1 promoted sugarcane growth, changed rhizosphere soil enzyme activities and chemical properties, and bacterial community structures.

Understanding variations in soil properties and microbial communities in bamboo plantation soils along a chromium pollution gradient

With high biomass productivity and resistance to heavy metals (HM) stress, bamboo has strong potential for HM phytoremediation. However, few studies have been conducted under field conditions to explore changes in soil physicochemical and microbial properties of bamboo forests with HM-contaminated soils. This study established bamboo (Phyllostachys praecox) plantations in five Cr-contaminated sites with different pollution levels (low, L; low-moderate, LM; moderate, M; moderate-high, MH; and high, H). We determined soil chemical properties, total and available Cr content, as well as bacterial and fungal community structures from 0 to 20 cm depth along the pollution gradient, and evaluated their interactions. The results revealed a corresponding decrease in soil pH, alkali-hydrolysable N (AN), along with urease and sucrase activities, as Cr pollution increased. In contrast, total organic carbon (TOC) increased with increasing Cr pollution. Soil available P (AP) and acid phosphatase activity did not differ significantly. Different pollution level resulted in distinct bacterial and fungal communities, with Proteobacteria, Acidobacteria, Actinobacteria, Ascomycota, and Basidiomycota being the dominant phyla across the five bamboo soils. Both total Cr (TCr) and HCl-extractable Cr (ACr) negatively correlated with alpha indices (Chao1 and Shannon) for bacteria but not for fungi, indicating that the latter is more resistant to Cr pollution. Decrease in soil pH and increase in TCr and ACr from L to H were closely related to the shift of bacterial and fungal communities. These changes reduced soil N and C cycles. Our findings suggest that improving soil acidic conditions and N availability enhances carbon and nitrogen cycles via altering soil microbial structure and activities. This, in turn, can increase phytoremediation efficiency in the bamboo ecosystem.

Significant soil degradation is associated with intensive vegetable cropping in a subtropical area: a case study in southwestern China

Abstract. Within the context of sustainable development, soil degradation driven by land use change is considered a serious global problem, but the conversion from growing cereals to vegetables is a change that has received limited attention, especially in subtropical regions. Here, we studied the effects of the conversion from paddy rice to an oilseed rape rotation to vegetable production in southwestern China on soil organic carbon (SOC), total nitrogen (TN), the C/N ratio, pH, phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) based on face-to-face farmer surveys and soil analysis. In the vegetable cropping system, fertilizer application often exceeds the crop demand or levels recommended by the local extension service several times over. Thus, the crop use efficiency of N, P, K, Ca, and Mg was only 26 %, 8 %, 56 %, 23 %, and 28 %, respectively. In the vegetable cropping system studied, SOC, C stock, TN, and N stock were decreased significantly due to low organic inputs from crop residues and high tillage frequency. Furthermore, the soil C/N ratio decreased slightly; available P (AP) in the topsoil increased by 1.92 mg kg−1 for every 100 kg ha−1 of P surplus, and the critical levels of AP and CaCl2-soluble P in P leaching were 104 and 0.80 mg P kg−1. Besides, compared to the current paddy–rape rotation system, a clear trend of soil acidification was observed in the vegetable fields. However, increasing the contents of soil Ca and Mg significantly alleviated topsoil acidification, with the effect increasing over time. Given our findings, the potential benefits of conservation agricultural practices, integrated soil–crop system management strategies, and agricultural technology services for recovering the degraded soil and improving the vegetable productivity are discussed here.

One-Year Monitoring of Daily Earthworm Cast Production: Surface Cast Contribution to Soil Fertility in a Subtropical Forest

The process of earthworm casting plays an important role in soil fertility. The contributions of earthworm casts to soil nutrients dynamics cannot be fully understood unless the temporal changes in earthworm cast production and the related nutrient resource pools are explored in the field. Here, we recorded the daily surface cast production of earthworms and monthly change patterns of carbon (C), nitrogen (N) and phosphorous (P) in casts in a subtropical plantation for one year and compared the nutrient concentrations and microbial community traits (structure and bacterial activity) in casts with those in bulk soils. Our objectives were to characterize the temporal patterns of earthworm cast production and the C and nutrients in casts and to assess the potential contribution of earthworm casts to soil fertility. The results showed that the annual surface cast production at the study site was 8.3 tons ha−1; monthly cast production was &gt;80 g m−2 during April to November and &lt;30 g m−2 during December to March. The annual outputs of total organic C (TOC), total N (TN) and total P (TP) in surface casts were 68.10, 4.84 and 0.38 g m−2, respectively; the annual outputs of available P (AP), NH4+-N and NO3−-N were 22.4, 147.0 and 61.3 mg m−2, respectively. The concentrations of TOC and TN in casts were higher during warm months, but NH4+-N was higher during cold months, while both the concentrations of TP and AP in casts were constant throughout the year. The nutrient concentrations were 1.6–4.3-fold greater, and the microbial biomass C and N contents were 7–8-fold greater in earthworm casts than those in bulk soils. However, the bacterial stress index (BSI) was significantly greater in casts than in the bulk soil, which implies that bacteria in casts were under stress. Accordingly, the ratio of fungal to bacterial biomass (F/B) was significantly higher in casts than in the bulk soil. Earthworm casting activity can process forest soil into a “new soil”, which forms large amounts of earthworm-induced hotspots of soil fertility. These resource pools in casts, with monthly fluctuated C and N and constant P, could be more readily accessed by fungi rather than bacteria. Earthworm casting activity potentially changes both the nutrients available and the interactions of plants and rhizosphere microbiota.

Differentiating bacterial community responses to long-term phosphorus fertilization in wheat bulk and rhizosphere soils on the Loess Plateau

Mineral phosphorus (P) fertilizers are frequently applied to fields to support high crop yields, but long-term P input changes soil chemical and biological fertility. In the present study, based on a long-term P experiment (with three P levels (0 (P0), 50 (P50), and 100 (P100) kg P2O5 ha−1 yr−1)), we evaluated the effects of P input on the bacterial community in wheat bulk (BS) and rhizosphere (RS) soils. Compared to the control (P0), the P50 and P100 treatments significantly (P < 0.05) increased soil available P (AP) in the BS and RS, but they did not affect the numbers of observed species or diversity, and these indices were significantly lower in the RS than in the BS. Additionally, P fertilization changed the bacterial community compositions in both RS and BS, with minor changes in the RS but major changes in the BS; the bacterial community in the RS was different from that in the BS, with weaker network complexity but closer relationships among the bacterial taxa. An average of 2.95% of all the analyzed genes were involved in P metabolism, with a higher abundance in RS than in BS samples; however, no differences among the three treatments were observed in the BS or RS samples. In conclusion, long-term P fertilization had little impact on bacterial community diversity but changed the community compositions in wheat BS and RS; the changes in the bacterial community and functional profiles in the rhizosphere soil were mainly mediated by roots, which could help supply more available P to the plants.

Combined organic amendments and mineral fertilizer application increase rice yield by improving soil structure, P availability and root growth in saline-alkaline soil

In saline-alkaline soil, soil structural stability and phosphorus (P) availability are the limiting factors for crop yield. Organic amendments are proved to play a key role in soil quality, P availability and plant growth. A field experiment was carried out with different organic amendments level in the Yellow River Delta, five treatments were designed: (i) Control (no fertilization), (ii) NK (255 kg N ha−1 year−1 and 229 kg K ha−1 year−1), (iii) NPK (128 kg P2O5 ha−1 year−1 plus NK), (iv) NPKC1 (450 kg C ha−1 year−1 plus NPK) and (v) NPKC2 (900 kg C ha−1 year−1 plus NPK). The main results showed that: compared with NPK treatment, the mean weight diameter (MWD) of soil aggregates was increased by 33.8 % and 47.1 % in NPKC1 and NPKC2 treatments, respectively. And the percentage of water-stable aggregate (WSA) was also improved by 30.5 % and 40.16 % in NPKC1 and NPKC2 treatments, respectively. This was due to the increase of soil exchangeable Ca, soil organic carbon (SOC) and particulate organic carbon (POC) content, and the decrease in soil bulk density and exchangeable Na content, as well. Meanwhile, soil available P (AP), total P (TP), dicalcium P (Ca2-P) and octacalcium P (Ca8-P) contents were significantly increased with organic amendments addition. Based on the increase of soil structural stability and P availability, especially the accumulation of inorganic P (Pi) in soil macro-aggregates, root surface area and plant P use efficiency (PUE) were improved, which resulted in the grain yield increased by 12.2 % and 16.6 % in NPKC1 and NPKC2 treatments, respectively. Consequently, combined organic amendments and mineral fertilizer application were better in improving the soil structural stability, P availability and plant growth in saline-alkaline area.

Distribution Characteristics of phoD-Harbouring Bacterial Community Structure and Its Roles in Phosphorus Transformation in Steppe Soils in Northern China

The phoD-harbouring bacterial community is responsible for much of the hydrolysis of organic phosphorus (Po) in soils and is therefore significant for the improvement of soil phosphorus (P) availability. However, the distribution of phoD-harbouring bacterial community structure and how it regulates the soil P fractions in steppe soils remain largely unknown. It is necessary to assess these relationships to maintain sustainable development on the steppe. We sampled soils from three steppe types across Inner Mongolia, China. Illumina high-throughput sequencing was used to quantify the bacterial phoD gene. The dominant phoD-harbouring genera were Amycolatopsis (5–11%), Bacillus (6–13%), Bradyrhizobium (3–8%) and Pseudomonas (3–5%) across all steppe soils. The relative abundances of phoD-harbouring Amycolatopsis and Bacillus increased significantly as available P (AP) decreased, while the relative abundances of Bradyrhizobium, Pseudomonas and Methylobacterium were significantly positively correlated with AP content. Redundancy analysis showed that the soil stoichiometric ratio of carbon (C), nitrogen (N) and P had a strong effect on the phoD-harbouring bacterial community structure. Correlation analyses further indicated that only phoD-harbouring Dietzia and Sphingomonas had a significant correlation with alkaline phosphatase activity and that they increased P availability by mineralizing Po. phoD-harbouring Frankia and Methylobacterium were positively correlated with labile-Po and negatively correlated with non-labile inorganic P. Moreover, phoD-harbouring Bacillus and Bradyrhizobium promoted the conversion of the non-labile Po pool into the labile Po pool, which can be attributed to microbial immobilization. Not all bacteria carrying the phoD gene promote soil P availability through mineralization or are induced not only in a P-repressible manner. Members of the phoD-harbouring bacterial community employ flexible P use strategies and can be strongly activated by their nutrient preferences and environmental conditions.

Different traits from the paddy soil and upland soil regulate bacterial community and molecular composition under long-term fertilization regimes

Fertilization-induced changes in soil properties from the paddy soil and upland soil may directly regulate bacterial community composition, which usually coincide with shifts in molecular composition of soil organic carbon (SOC) in the upland soil. However, systematical comparisons lack on how regulators vary with cropping systems under the same weather conditions and soil parent materials. Here, we simultaneously investigated the changes of soil physicochemical parameters and shifts in the bacterial community and SOC molecular composition in two adjacent rice and maize fields that have received five fertilization regimes for more than 30 years. The separation of the bacterial community composition among the treatments from the paddy soil was mainly determined by soil nitrate-N, and that from the upland soil was mainly determined by soil available P (AP) and pH. The SOC molecular composition from the paddy soil was separated by the treatments with N application or not, with those treatments with N application being enriched with CCH3 and aromatic CC, and those without N application being enriched with aromatic CH. These changed C functional groups showed close association with amorphous Fe2O3. For the upland soil, the SOC molecular composition was separated by the treatments with P application or not, with those treatments with P application being enriched with OCH, and those without P application being enriched with CH/CH2. These changed C functional groups had close association with AP and total P. Our results indicated inconsistent separation patterns and regulators of the bacterial community and SOC molecular composition among the treatments of the paddy soil and upland soil, and suggested that the relatively dominant role of the fertilization-induced changes in soil properties or other soil microbes that controlled the SOC molecular composition over the bacteria measured in the present study.

Long-term cover crops improved soil phosphorus availability in a rain-fed apple orchard

The objective of this present study was to understand the distribution patterns of various forms of soil phosphorus (P) and the biotic and abiotic factors affecting the soil P fractions under long-term cover crops. Here, we investigated the characteristics of soil P forms, community structure of P-solubilizing bacteria (using 16S rRNA) and the related enzyme activity under clean tillage (CT), 14 years of white clover (WC, Trifolium repens L.) and orchard grass (OG, Dactylis glomerata L.) cover crops in a rain-fed apple orchard on the Weibei Loess Plateau, China. Relative to CT treatment, long-term cover crops enhanced the bioavailability of soil P by increasing the contents of total phosphorus (TP), microbial phosphorus (MBP), organic phosphorus (Po) and certain forms of inorganic phosphorus (e.g. Al-P, Ca2-P, Ca8-P and Fe-P) in the surface soil, in addition, WC treatment also increase the available P (AP) contents in the topsoil. A redundant analysis (RDA) showed that soil organic matter (SOM), NH4+-N and pH were the key environmental factors affecting the morphological changes of soil P. In addition, the effects of long-term cover crops on soil P forms were mainly concentrated in the topsoil, and the WC treatment had a greater impact on soil P composition than the OG treatment. Interestingly, long-term cover crops effectively increased the abundances of P-solubilizing bacteria, such as Streptomyces, Sphingomonas, Nocardioides and Haliangium, and enhanced the alkaline phosphatase (ALP) activity. Overall, long-term cover crops were an effective strategy to activate soil P as they improve the soil environment.

Biogeochemical stoichiometry of soil and plant functional groups along a primary successional gradient following glacial retreat on the eastern Tibetan plateau

Di-nitrogen (N2)-fixing plants are crucial for vegetation development following glacial retreat; however, there is currently limited understanding of how the shifting of N2-fixing and non N2-fixing plant groups may influence the stoichiometric composition of the developing plant community and associated soils. Carbon (C), nitrogen (N), and phosphorus (P) concentrations and elementary stoichiometry were investigated in soil and the N2-fixing and non-N2-fixing plant communities across a 127-yr glacial primary succession chronosequence on the eastern slope of the Qinghai-Tibetan Plateau. Soil organic C (SOC), total N (TN), and available P (AP) gradually increased along succession, but total P (TP) was greatest at the 37-yr site, resulting in an increasing trend of soil N:P and a decreasing trend of N:AP ratios along the chronosequence. N2-fixing species had higher foliar N and P concentrations than non-N2-fixing species and exhibited a higher leaf N:P ratios in early stages (37 yr and younger) of the succession. Elementary concentration and C, N, P stoichiometry in plant leaves were strongly associated with both N2-fixing and non-N2 fixing plant biomasses, while those in soils were related only with the biomass of non-N2 fixing species. The community-weighted leaf N:P ratios increased from 14.0 at 7-yr to 19.9 at 59-yr and then decreased to 12.9 at 127-yr after glacial retreat, suggests the ecosystem as a whole is not N- or P-limited at the beginning of primary succession, but may become P-limited at the middle stages and then shift towards N limitation at the late successional stages. The results confirm that both N2-fixing and non-N2-fixing species can overcome N limitation in the early primary succession and highlights the different roles of pioneer N2-fixing and non-N2-fixing species in mediating vegetation and soil C, N and P stoichiometry with primary succession following glacial retreat.

Vegetation Degradation of Guanshan Grassland Suppresses the Microbial Biomass and Activity of Soil

Changes in vegetation influence the function of grassland ecosystems. A degradation of the vegetation type has been found from high to low altitudes in Guanshan grassland in the order of forest grassland (FG) &lt; shrub grassland (SG) &lt; herb grassland (HG). However, there is poor information regarding the effect of vegetation degradation on soil microbes in Guanshan grassland. Therefore, our study evaluated the impact of vegetation degradation on the microbial parameters of soil, as well as the mechanisms responsible for these variations. Soils were sampled from 0 to 30 cm under the FG, SG, and HG in Guanshan grassland for determining the microbial biomass, enzymatic activities, basal respiration (BR), and metabolic quotient (qCO2) in April and July 2017. The results showed that vegetation types are important factors that obviously influence the above-mentioned soil microbial properties. The FG and SG had significantly higher soil microbial biomass, enzymatic activities, and BR than those of the HG, but markedly lower qCO2 (p &lt; 0.05). Soil pH, available nitrogen (AN), organic carbon (SOC), total phosphorus (TP), available P (AP), and total N (TN) were key factors in the decline in the soil microbial biomass and microbial activities of the degraded vegetation. Moreover, slope aspects also affected the soil microbial properties, with the east slope having higher soil microbial biomass, enzymatic activities, and BR and lower qCO2 than the west slope. Conclusively, vegetation degradation has led to a decline in the soil microbial biomass and microbial activities, indicating the degradation of the Guanshan grassland ecosystem.