Land use modified impacts of global change factors on soil microbial structure and function: A global hierarchical meta-analysis.

Nitrogen cycling in terrestrial ecosystems is critical for biodiversity, vegetation productivity and biogeochemical cycling. However, little is known about the response of functional nitrogen cycle genes to global change factors in soils under different land uses. Here, we conducted a multiple hierarchical mixed effects meta-analyses of global change factors (GCFs) including warming (W+), mean altered precipitation (MAP+/-), elevated carbon dioxide concentrations (eCO2), and nitrogen addition (N+), using 2706 observations extracted from 200 peer-reviewed publications. The results showed that GCFs had significant and different effects on soil microbial communities under different types of land use. Under different land use types, such as Wetland, Tundra, Grassland, Forest, Desert and Agriculture, the richness and diversity of soil microbial communities will change accordingly due to differences in vegetation cover, soil management practices and environmental conditions. Notably, soil bacterial diversity is positively correlated with richness, but soil fungal diversity is negatively correlated with richness, when differences are driven by GCFs. For functional genes involved in nitrification, eCO2 in agricultural soils and the interaction of N+ with other GCFs in grassland soils stimulate an increase in the abundance of the AOA-amoA gene. In agricultural soil, MAP+ increases the abundance of nifH. W+ in agricultural soils and N+ in grassland soils decreased the abundance of nifH. The abundance of the genes nirS and nirK, involved in denitrification, was mainly negatively affected by W+ and positively affected by eCO2 in agricultural soil, but negatively affected by N+ in grassland soil. This meta-analysis was important for subsequent research related to global climate change. Considering data limitations, it is recommended to conduct multiple long-term integrated observational experiments to establish a scientific basis for addressing global changes in this context.

Organo-organic interactions dominantly drive soil organic carbon accrual.

Organo-mineral interactions have been regarded as the primary mechanism for the stabilization of soil organic carbon (SOC) over decadal to millennial timescales, and the capacity for soil carbon (C) storage has commonly been assessed based on soil mineralogical attributes, particularly mineral surface availability. However, it remains contentious whether soil C sequestration is exclusively governed by mineral vacancies, making it challenging to accurately predict SOC dynamics. Here, through a 400-day incubation experiment using 13 C-labeled organic materials in two contrasting soils (i.e., Mollisol and Ultisol), we show that despite the unsaturation of mineral surfaces in both soils, the newly incorporated C predominantly adheres to "dirty" mineral surfaces coated with native organic matter (OM), demonstrating the crucial role of organo-organic interactions in exogenous C sequestration. Such interactions lead to multilayered C accumulation that is not constrained by mineral vacancies, a process distinct from direct organo-mineral contacts. The coverage of native OM by new C, representing the degree of organo-organic interactions, is noticeably larger in Ultisol (~14.2%) than in Mollisol (~5.8%), amounting to the net retention of exogenous C in Ultisol by 0.2-1.3 g kg-1 and in Mollisol by 0.1-1.0 g kg-1 . Additionally, organo-organic interactions are primarily mediated by polysaccharide-rich microbial necromass. Further evidence indicates that iron oxides can selectively preserve polysaccharide compounds, thereby promoting the organo-organic interactions. Overall, our findings provide direct empirical evidence for an overlooked but critically important pathway of C accumulation, challenging the prevailing "C saturation" concept that emphasizes the overriding role of mineral vacancies. It is estimated that, through organo-organic interactions, global Mollisols and Ultisols might sequester ~0.1-1.0 and ~0.3-1.7 Pg C per year, respectively, corresponding to the neutralization of ca. 0.5%-3.0% of soil C emissions or 5%-30% of fossil fuel combustion globally.

Biobased, biodegradable and compostable plastics: chemical nature, biodegradation pathways and environmental strategy.

Increasing pollution of plastic waste is one of the major global environmental threats, deteriorating our land, water and air. The shift towards biobased, biodegradable and compostable plastics is considered a green alternative to petroleum-based plastic due to its renewable source or biodegradability. However, there is a misconception about biodegradable plastics and their degradability and behaviour after service life. Biobased, biodegradable and compostable plastics offer various benefits such as less carbon footprint, energy efficiency, independence and eco-safety. On the other hand, there are some disadvantages such as higher cost, limited recycling, misuse of terms and lack of legislation. Also, there is an urgent need for comparable international standard methods to define these materials as biodegradable material, or biocompostable material. There are some standards currently available, however, an in-depth detail and explanation of these standards is still missing. This review outlines the basic definition and chemical structure of biobased, biodegradable and compostable plastics; describes the degradation pathways of biodegradable and compostable plastics; and summarises current key applications of these materials together with possible future applications in different industries. Finally, strategies are developed for minimising the environmental impacts and the need for future research is proposed.

Biopolymer as an additive for effective biochar-based rhizobial inoculant.

Biochar is an efficient and inexpensive carrier for bacteria that stimulate plant development and growth. In this study, different biopolymer additives (cellulose, xanthan gum, chitin and tryptone) were tested with different addition ratios (1:0.1, 1:0.5 and 1:1) on further enhancing biochar capacity for supporting the growth and activity of Bradyrhizobium japonicum (CB1809). We utilized pine wood biochar (PWBC) pyrolyzed at 400 °C as the base inoculum carrier. The shelf life and survival rate of CB1809 were counted using the colony-forming unit (CFU) method for up to 120 days. Peat served as a standard reference material against which all treatments were compared. Subsequent experiments evaluated the ability of carrier inoculants to promote Glycine max L. (soybean) plant growth and nodulation under different watering regimes, i.e., 55 % water holding capacity (WHC) (D0), 30 % WHC (D1) and, 15 % WHC (D2) using sandy loam soil. Results revealed that among different additives; xanthan gum with 1:0.5 to PWBC [PWBC-xanthan gum(1:0.5)] was observed as a superior formulation in supporting rhizobial shelf life and survival rate of CB1809. In pot experiments, plants with PWBC-xanthan gum(1:0.5) formulation showed significant increase in various physiological characteristics (nitrogenase activity, chlorophyll pigments, membrane stability index, and relative water content), root architecture (root surface area, root average diameter, root volume, root tips, root forks and root crossings), and plant growth attributes (shoot/root dry biomass, shoot/root length, and number of nodules). Additionally, a reduced enrichment of isotopic signatures (δ13C, δ15N) was observed in plants treated with PWBC-xanthan gum(1:0.5), less enrichment of δ15N indicates an inverse link to nodulation and nitrogenase activity, while lower δ13C values indicates effective water use efficiency by plants during drought stress. These results suggest that biopolymers supplementation of the PWBC is useful in promoting shelf life or survival rate of CB1809.

The role of edaphic variables and management practices in regulating soil microbial resilience to drought - A meta-analysis.

Environmental disturbances such as drought can impact soil health and the resistance (ability to withstand environmental stress) and resilience (ability to recover functional and structural integrity after stress) of soil microbial functional activities. A paucity of information exists on the impact of drought on soil microbiome and how soil biological systems respond to and demonstrate resilience to drought stress. To address this, we conducted a systematic review and meta-analysis (using only laboratory studies) to assess the response of soil microbial biomass and respiration to drought stress across agriculture, forest, and grassland ecosystems. The meta-analysis revealed an overall negative response of microbial biomass in resistance (-31.6 %) and resilience (-0.3 %) to drought, suggesting a decrease in soil microbial biomass content. Soil microbial respiration also showed a negative response in resistance to drought stress indicating a decrease in soil microbial respiration in agriculture (-17.5 %), forest (-64.0 %), and grassland (-65.5 %) ecosystems. However, it showed a positive response in resilience to drought, suggesting an effective recovery in microbial respiration post-drought. Soil organic carbon (SOC), clay content, and pH were the main regulating factors of the responses of soil microbial biomass and respiration to drought. In agriculture ecosystem, soil pH was primarily correlated with soil microbial respiration resistance and resilience to drought, potentially influenced by frequent land preparation and fertilizer applications, while in forest ecosystem SOC, clay content, and pH significantly impacted microbial biomass and respiration resistance and resilience. In grassland ecosystem, SOC was strongly associated with biomass resilience to drought. The impact of drought stress on soil microbiome showed different patterns in natural and agriculture ecosystems, and the magnitude of microbial functional responses regulated by soil intrinsic properties. This study highlighted the importance of understanding the role of soil properties in shaping microbial responses to drought stress for better ecosystem management.

The origin of suspended particulate matter in the Great Barrier Reef.

River run-off has long been regarded as the largest source of organic-rich suspended particulate matter (SPM) in the Great Barrier Reef (GBR), contributing to high turbidity, pollutant exposure and increasing vulnerability of coral reef to climate change. However, the terrestrial versus marine origin of the SPM in the GBR is uncertain. Here we provide multiple lines of evidence (13C NMR, isotopic and genetic fingerprints) to unravel that a considerable proportion of the terrestrially-derived SPM is degraded in the riverine and estuarine mixing zones before it is transported further offshore. The fingerprints of SPM in the marine environment were completely different from those of terrestrial origin but more consistent with that formed by marine phytoplankton. This result indicates that the SPM in the GBR may not have terrestrial origin but produced locally in the marine environment, which has significant implications on developing better-targeted management practices for improving water quality in the GBR.

Detecting microplastics in organic-rich materials and their potential risks to earthworms in agroecosystems.

Microplastics (MPs) are a major emerging contaminant in agroecosystems, due to their significant resistance to degradation in terrestrial environments. Although previous investigations have reported the harmful effects of MPs contamination on soil biological properties, still little is known about the characteristics and fate of MPs in biosolid-amended soils and their risks to soil biota, particularly earthworms. We determined microplastics' concentration, size distribution, and chemical composition in 3 sewage sludge biosolids and 6 biosolid-amended agricultural soils. In addition, we assessed the potential short-term risks of MPs to earthworms' (Amynthas Gracilis and Eisenia Fetida) survival rate and fitness in an environmentally relevant exposure study (28 days). Biosolid-amended soils (1000-3100 MPs kg-1 dry mass) showed ≈30 times lower MPs content than investigated biosolids (55400-73800 MPs kg-1 dry mass), with microplastic fragment to fibre ratios between 0.2 and 0.6 and 0.3-0.4 in soils and biosolids, respectively. Total MPs dry mass was also ≈19 times lower in assessed soils (12-26 mg kg-1) than biosolids (328-440 mg kg-1). On average 77% and 80% of plastic fragments had a lower dimension than 500 µm, while 50% and 67% of plastic fibres had a length of less than 1000 µm in soil and biosolid samples, respectively. Polyethylene (23.6%) was the major source of microplastic contamination in biosolid-amended soils, while polyethylene terephthalate (41.6%) showed the highest concentration in biosolid samples. Spiked polyethylene MPs did not show any significant effect on earthworms' survival rate (93-99%). However, biosolid application significantly (P < 0.05) decreased survival rate of Eisenia Fetida (81%) but showed no significant effect on Amynthas Gracilis (93%). Biosolid amendment significantly (P < 0.05) decreased earthworms' growth rate, with higher impact on Eisenia Fetida than Amynthas Gracilis, while there were no significant differences between control and microplastic spiked treatments. The overall decrease in MPs concentration of earthworm casts, compared with initial MPs concentrations in soil, indicated that the investigated species did not bioaccumulate MPs during the exposure experiment.

Biochar surface properties and chemical composition determine the rhizobial survival rate.

Biochar may be potentially used as a rhizobial carrier due to its specific chemical compositions and surface properties, but the relationship between these properties and rhizobial survival rate is largely unknown. Here, we analysed the physicochemical characteristics and carrier potential of six types of biochars made from various feedstocks at 600 °C using slow pyrolysis method, and results were compared with conventional carrier material peat. Liquid suspension of Bradyrhziobium japonicum CB1809 was used to inoculate all the carrier materials. Shelf life and survival rate was determined via colony forming unit (CFU) method for up to 90 days under two storage temperature conditions (28 °C and 38 °C). The determined physicochemical characteristics of biochars were categorized into major elements, trace elements, relative ratios, surface morphology, functional groups, and key basic properties; and their interaction to shelf life was analysed using hypothesis-oriented structure equation modelling (path analysis). Results revealed that different types of biochars had different capacity to impact on shelf life due to their different physicochemical properties. Among all biochars pine wood BC was the most suitable carrier with the highest counts of 10.11 Log 10 CFU g-1 and 9.76 Log 10 CFU g-1 at the end of 90 days at 28 °C and 38 °C storage, respectively. Path analysis revealed that rhizobial shelf life was largely explained by total carbon (TC), manganese (Mn), specific surface area (SSA), pore size, CO (ketonic carbon), and O-CO (carboxyl carbon) functional groups, and all these indicators exhibited positive direct impact on shelf life. Pinewood BC showed the highest values of Mn, SSA, pore size and functional groups (CO and O-CO), contributing to its highest rhizobial shelf life and survival rate among other biochars and peat tested.

Humic Acid Modified by Being Incorporated Into Phosphate Fertilizer Increases Its Potency in Stimulating Maize Growth and Nutrient Absorption.

Humic acid-enhanced phosphate fertilizer (HAP) is widely applied in Chinese agriculture due to its high efficiency. Although the structural composition and physicochemical properties of humic acid (HA) are significantly altered during HAP production, a clear understanding of the mechanisms underlying the biological effects of HA extracted from HAP fertilizer (PHA) on plant growth is still lacking. In the current study, we extracted PHA from HAP and assessed its effects on the dry biomass, phosphorus (P) and nitrogen (N) uptake, and P absorption rate of maize seedlings when supplied at different concentrations (2.5, 5, 10, and 25 mg C L-1) in the hydroponic culture. The root vigor, root plasma membrane H+-ATPase activity, and root nitrate reductase activity were also determined as the representative indicators of the root capacity for nutrient absorption, and used to clarify the mechanism by which PHA affects the maize growth and nutrient absorption. The results showed that the dry biomass, phosphorus uptake, nitrogen uptake, and average phosphorus absorption rates were significantly higher by 14.7-27.9%, 9.6-35.1%, 17.9-22.4%, and 22.1-31.0%, respectively, in plants treated with 2.5-5 mg C L-1 PHA compared to untreated controls. Application of 10-25 mg C L-1 raw HA resulted in similar stimulatory effects on plant growth and nutrient absorption. However, higher levels of PHA (10-25 mg C L-1) negatively impacted these indicators of plant growth. Furthermore, low PHA or high raw HA concentrations similarly improved root vigor and root plasma membrane H+-ATPase and nitrate reductase (NR) activities. These results indicate that lower concentrations of PHA can stimulate maize seedling growth and nutrient absorption to an extent that is comparable to the effect of higher concentrations of raw HA. Thus, the proportion of HA incorporated into HAP could be lower than the theoretical amount estimated through assays evaluating the biological effects of raw HA.

Long-Term Exposure to Phenanthrene Induced Gene Expressions and Enzyme Activities of Cyprinus carpio below the Safe Concentration.

Phenanthrene (PHE) is a typical compound biomagnified in the food chain which endangers human health and generally accumulates from marine life. It has been listed as one of the 16 priority PAHs evaluated in toxicology. In order to evaluate the changes of CYP1A GST mRNA expression and EROD GST enzyme activity in carp exposed to lower than safe concentrations of PHE. Long-term exposure of carp to PHE at lower than safe concentrations for up to 25 days. The mRNA expression level and cytochrome P450 (CYP1A/EROD (7-Ethoxylesorufin O-deethylase)) and glutathione S-transferase (GST) activity were measured in carp liver and brain tissue. The results showed that PHE stress induced low-concentration induction and high-concentration inhibition of CYP1A expression and EROD enzyme activity in the liver and brain of carp. In both two organs, GST enzyme activity was also induced. However, the expression of GST mRNA was first induced and then inhibited, after the 15th day. These results indicate that long-term exposure to PHE at lower than safe concentrations still poses a potential threat to carp's oxidase system and gene expression.

Rare earth elements (REE) for the removal and recovery of phosphorus: A review.

There is little doubt that 'rock phosphate' reserves are decreasing, with phosphorus (P) peak to be reached in the coming decades. Hence, removal and recovery of phosphorus (P) from alternative nutrient-rich waste streams is critical and of great importance owing to its essential role in agricultural productivity. Adsorption technique is efficient, cost-effective, and sustainable for P recovery from waste streams which otherwise can cause eutrophication in receiving waters. As selective P sorption using rare earth elements (REE) are gaining considerable attention, this review extensively focuses on P recovery by utilising a range of REE-incorporated adsorbents. The review briefly provides existing knowledge of P in various waste streams, and examines the chemistry and behaviour of REE in soil and water in detail. The impact of interfering ions on P removal using REE, adsorbent regeneration for reuse, and life cycle assessment of REE are further explored. While it is clear that REE-sorbents have excellent potential to recover P from wastewaters and to be used as fertilisers, there are gaps to be addressed. Future studies should target recovery and reuse of REE as P fertilisers using real wastewaters. More field trials of synthesized REE-sorbents are highly recommended before practical application.

Resource stoichiometry, vegetation type and enzymatic activity control wetlands soil organic carbon in the Herbert River catchment, North-east Queensland.

Wetlands are highly productive ecosystem with great potential to store carbon (C) and retain nitrogen (N) and phosphorus (P) in their soil. Changes in vegetation type and land use can affect organic matter inputs and soil properties. This work aimed to examine how these changes affected elemental stoichiometry and C-, N-, and P- associated enzyme activities and wetland soil organic C stock. We quantified organic C concentrations, and stoichiometric ratios of C, N, and P in total and microbial biomass pools, along with the activities and ratios of C-, N-, and P-associated enzymes for soils of natural coastal wetlands with different vegetation types, namely Melaleuca wetland (Melaleuca spp), mangrove forests (Bruguiera spp), and saline marsh (Eleocharis spp). We also compared these natural wetlands to an adjacent sugarcane plantation to understand the effects of vegetation types. Hypothesis-oriented path analysis was used to explore links between these variables and soil organic C stocks. Tidal forested soils (0-30 cm) had the highest organic C, N, and P contents and potential activities of C-, N-, P- acquiring enzymes, compared with other vegetation types. Mangroves soils had the highest total soil C:N and microbial biomass C:P ratios. Microbial biomass C:P ratios were significantly and positively related to total C:P, while microbial biomass N:P ratios were positively associated with total soil C:P and N:P ratios. Path analysis suggested that soil organic C stock was largely explained by total C:P ratio, microbial biomass N:P ratios, total P content, and the ratio of C- and P-associated enzymes. Different types of wetlands have different soil properties and enzymatic activities, implying their different capacity to store and process C and N. The resource quality and stoichiometry direct influence the organic C stock.

Latitudinal patterns of terrestrial phosphorus limitation over the globe.

Phosphorus limitation on terrestrial plant growth is being incorporated into Earth system models. The global pattern of terrestrial phosphorus limitation, however, remains unstudied. Here, we examined the global-scale latitudinal pattern of terrestrial phosphorus limitation by analysing a total of 1068 observations of aboveground plant production response to phosphorus additions at 351 forest, grassland or tundra sites that are distributed globally. The observed phosphorus-addition effect varied greatly (either positive or negative), depending significantly upon fertilisation regime and production measure, but did not change significantly with latitude. In contrast, phosphorus-addition effect standardised by fertilisation regime and production measure was consistently positive and decreased significantly with latitude. Latitudinal gradient in the standardised phosphorus-addition effect was explained by several mechanisms involving substrate age, climate, vegetation type, edaphic properties and biochemical machinery. This study suggests that latitudinal pattern of terrestrial phosphorus limitation is jointly shaped by macro-scale driving forces and the fundamental structure of life.

Persistence of atrazine and trifluralin in a clay loam soil undergoing different temperature and moisture conditions.

Dissipation kinetics of atrazine and trifluralin in a clay loam soil was investigated in a laboratory incubation experiment under different temperature and moisture conditions. The soil was spiked with diluted atrazine and trifluralin concentrations at 4.50 and 4.25 mg/kg soil, respectively, the moisture content adjusted to 40, 70, and 100% of field capacity (FC) and then incubated in three climatic chambers at 10, 20, and 30 °C. For each of the herbicides, soil samples were collected at 0, 7, 21, 42, 70, and 105 days and analysed by Gas Chromatography-Electron Capture Detector (GC-ECD). A stochastic gamma model was used to model the dissipation of herbicides from the clay loam soil by incorporating environmental factors as covariates to determine half-life and days to complete dissipation. Results showed that temperature played a greater role on atrazine persistence than soil moisture; while the interaction effect of temperature and moisture was significant on the persistence of trifluralin over time. Atrazine dissipated more rapidly at 30 °C compared to 10 and 20 °C, with a half-life of 7.50 days and 326.23 days to reach complete dissipation. Rapid loss of trifluralin was observed at 70% moisture content when incubated at 30 °C, with a half-life of 5.80 days and 182.01 days to complete dissipation. It was observed that the half-life of both herbicides tended to double with every 10 °C decreases of temperature over the range tested. The model indicated that both atrazine and trifluralin have the potential to persist in clay loam soil for several years at temperature ≤20 °C; which could potentially affect following crops in rotation.

Soil organic matter formation is controlled by the chemistry and bioavailability of organic carbon inputs across different land uses.

Soil organic matter (SOM) formation involves microbial transformation of plant materials of various quality with physico-chemical stabilisation via soil aggregation. Land use and vegetation type can affect the litter chemistry and bioavailability of organic carbon (OC), and consequently influence the processing and stabilisation of OC into SOM. We used 13C nuclear magnetic resonance (13C NMR) and hot-water extraction to assess the changes in chemical composition and labile OC fractions during the transformation processes from leaf to litter to SOM depending on land use and vegetation type. The hot-water-extractable OC (HWEOC) decreased from leaf (43-65 g kg-1) to litter (19-23 g kg-1) to SOM (8-16 g kg-1) similar in four land use types: grassland, sugarcane, forest and banana. These trends demonstrated the uniform converging pathways of OC transformation and increasing stability by SOM formation. The preferential decomposition and decrease of labile OC fractions (∑% di-O-alkyl, O-alkyl and methoxyl) from leaf (54-69%) to SOM (41-43%) confirmed the increasing stability of the remaining compounds. Despite differences in the biochemical composition of the leaf tissues among the vegetation types, the proportions of labile OC fractions in SOM were similar across land uses. The OC content of soil was higher in forest (7.9%) and grassland (5.2%) compared to sugarcane (2.3%) and banana (3.0%). Consequently, the HWEOC per unit of soil weight was higher in forest and grassland (2.0 and 1.2 g kg-1 soil, respectively) compared to sugarcane and banana (0.3 and 0.4 g kg soil-1, respectively). The availability of labile SOM is dependent on the quantity of SOM not the chemical composition of SOM. In conclusion, labile OC fractions in SOM, as identified by 13C NMR, were similar across land use regardless of vegetation type and consequently, SOM formation leads to convergence of chemical composition despite diversity of OC sources.

Tracing the sources of sediment and associated particulate nitrogen from different land uses in the Johnstone River catchment, Wet Tropics, north-eastern Australia.

While the ecosystem of the Great Barrier Reef (GBR), north-eastern Australia, is being threatened by the elevated levels of sediments and nutrients discharged from adjacent coastal river systems, the source of these detrimental pollutants are not well understood. Here we used a combined isotopic (δ13C, δ15N) and geochemical (Zn, Pt and S) signatures and stable isotope analysis in R (SIAR) mixing model to estimate the contribution of different land uses to the sediment and associated particulate nitrogen delivered to the Johnstone River. Results showed that rainforest was the largest contributor of suspended and bed sediments in the river estuary (both 33.1%), followed by banana (26.7%, 20.4%), sugarcane (21.5%, 21.4%) and grazing (18.7%, 25.1%). However, bananas and sugarcane land uses had the highest contribution to sediments delivered to the coast per unit of area. This will help land managers to prioritise on-ground activities to improve water quality in the GBR lagoon.

Global meta-analysis shows pervasive phosphorus limitation of aboveground plant production in natural terrestrial ecosystems.

Phosphorus (P) limitation of aboveground plant production is usually assumed to occur in tropical regions but rarely elsewhere. Here we report that such P limitation is more widespread and much stronger than previously estimated. In our global meta-analysis, almost half (46.2%) of 652 P-addition field experiments reveal a significant P limitation on aboveground plant production. Globally, P additions increase aboveground plant production by 34.9% in natural terrestrial ecosystems, which is 7.0-15.9% higher than previously suggested. In croplands, by contrast, P additions increase aboveground plant production by only 13.9%, probably because of historical fertilizations. The magnitude of P limitation also differs among climate zones and regions, and is driven by climate, ecosystem properties, and fertilization regimes. In addition to confirming that P limitation is widespread in tropical regions, our study demonstrates that P limitation often occurs in other regions. This suggests that previous studies have underestimated the importance of altered P supply on aboveground plant production in natural terrestrial ecosystems.

Aggregational differentiation of ureolytic microbes in an Ultisol under long-term organic and chemical fertilizations.

Ureolytic microorganisms play a crucial role in soil nitrogen transformation. Soil aggregates and associated microbes are reported to modify the impact of agricultural management on soil nutrient cycling. However, the responses of ureolytic microbial communities in various soil aggregates to long-term fertilization regimes are still unclear in acid soils. In this study, we characterized the ureolytic microflora as well as urease activity in three soil aggregate fractions (2-0.25, 0.25-0.053, <0.053 mm) from an Ultisol with 26-year fertilization experiment. The results showed that long-term chemical fertilization (NPK) significantly decreased the abundance, richness and activity of ureolytic microbial community across soil aggregates (P < .05) due to strong soil acidification. While manure application (M and MNPK) could mitigate these negative impacts and markedly (P < .05) improved the abundance, α-diversity and activity of soil ureolytic microflora. Long-term fertilization regimes also drove the differentiation of ureolytic microbial compositions in soil aggregates (Adonis, F = 17.4, P = .001, R2 = 33.6%), and manure application appeared to be the most important driver. This variation partly contributed to the aberrance of soil urease activity (structure equation model, path coefficient: 0.45, P = .008). No significant differences were found for ureolytic microbial community among soil aggregates, which was in accordance with the distribution patterns of soil nutrients, indicating the dominant role of resources availability in determining ureolytic microbiota in micro-environment. The ureolytic microbial community among different soil aggregates responded uniformly to long-term fertilizations. Our study revealed that manure application was a sustainable fertilization regime to alleviate the loss of soil ureolytic microbial diversity and activity in acid soils.

Long-term nutrient inputs shift soil microbial functional profiles of phosphorus cycling in diverse agroecosystems.

Microorganisms play an important role in soil phosphorus (P) cycling and regulation of P availability in agroecosystems. However, the responses of the functional and ecological traits of P-transformation microorganisms to long-term nutrient inputs are largely unknown. This study used metagenomics to investigate changes in the relative abundance of microbial P-transformation genes at four long-term experimental sites that received various inputs of N and P nutrients (up to 39 years). Long-term P input increased microbial P immobilization by decreasing the relative abundance of the P-starvation response gene (phoR) and increasing that of the low-affinity inorganic phosphate transporter gene (pit). This contrasts with previous findings that low-P conditions facilitate P immobilization in culturable microorganisms in short-term studies. In comparison, long-term nitrogen (N) input significantly decreased soil pH, and consequently decreased the relative abundances of total microbial P-solubilizing genes and the abundances of Actinobacteria, Gammaproteobacteria, and Alphaproteobacteria containing genes coding for alkaline phosphatase, and weakened the connection of relevant key genes. This challenges the concept that microbial P-solubilization capacity is mainly regulated by N:P stoichiometry. It is concluded that long-term N inputs decreased microbial P-solubilizing and mineralizing capacity while P inputs favored microbial immobilization via altering the microbial functional profiles, providing a novel insight into the regulation of P cycling in sustainable agroecosystems from a microbial perspective.

Stoichiometric control on riparian wetland carbon and nutrient dynamics under different land uses.

Riparian wetland provides important ecosystem function, such as water filtration and nutrient retention. When land use change in upland from native forest to sugarcane cultivation have important impacts on carbon (C) and nutrient availability in downstream wetland systems. Here, we examined concentrations and stoichiometry of C and nutrients in total, labile, biomass pools in upland soil, riparian wetland and sediment along two distinct transects (sugarcane versus forest). Sugarcane cultivation significantly reduced total C, nitrogen (N), labile C and N in riparian soils by 69%, 62%, 33% and 45%, respectively, but significantly increased NO3--N and δ15N by 99% and 56% in riparian areas. The presence of native forest resulted in significantly higher NH4+-N concentrations in downstream wetlands. Concentrations of microbial biomass C and N were generally lower, but the abundance of genes associated with nitrifiers (ammonia oxidizing bacteria and archaea) was higher in the sugarcane transect than in the forest transect. These significantly differences between two transects could be attributed to different organic inputs and biogeochemical processes associated with the different vegetation types and management practices in the upland systems. Difference in δ13C signature from the two transects further confirmed the significant influence of vegetation type on downstream wetlands. Sugarcane cultivation led to a consistent stoichiometric shift in both resource and microbial biomass towards lower C:P and N:P ratios across upland soils, wetlands and sediment, compared with the forest transect. The average total and microbial biomass C:N:P ratios in soil under sugarcane were 136:9:1 and 180:33:1, respectively. The average total and microbial biomass C:N:P ratios in soil under forest were 410:22:1 and 594:76:1, respectively. It is concluded that since microbial demand of C and nutrients is driven by the stoichiometry of the biomass, which is regulated by the resource stoichiometry, a change of resource induced by upland land use change leads to a shift in the stoichiometry of microbial biomass C, N and P.