Nutrient Turnover Research Articles

Linkages between soil nutrient turnover and above‐ground crop nutrient metabolism: The role of soil microbes

AbstractWith global agricultural practices increasingly focused on sustainability and efficiency, deciphering the complex relationship between soil nutrient turnover and crop nutrient uptake is critical for advancing crop productivity and environmental resilience. This study focuses on the nitrogen transformation process following dazomet soil fumigation and examines how soil microorganisms influence both soil nitrogen cycling and above‐ground crop nitrogen metabolism. Fumigation led to significant changes, with ammonium nitrogen increasing by 18.89%−94.82% and nitrate nitrogen decreasing by 30.20%−90.21% in tobacco roots, stems, and leaves. Fumigation also caused a notable shift in the soil microbial community, inhibiting ammonium‐oxidizing microorganisms while stimulating denitrifying microbes. These changes not only disrupted the nitrogen balance‐reducing soil nitrification by 72.91%−86.51% and increasing denitrification by 197%−324% but also had a cascading effect on above‐ground crop nitrogen metabolism. By altering the composition of microbial communities, the process directly influenced soil nutrient turnover, subsequently impacting nutrient availability and distribution in crop. The disruption in nitrogen balance further led to changes in the expression of key nitrogen metabolism enzymes and transporter genes. Specifically, genes related to nitrate and ammonium transporters, as well as amino acid and nitrogen metabolism enzymes, were upregulated. Structural equation modeling confirmed that the shifts in the microbial community were central to driving changes in both soil nutrient turnover and nitrogen distribution in the crop. These findings underscore the critical role of soil microbial communities as a link between soil nutrient cycling and above‐ground nutrient metabolism, highlighting their importance in regulating plant nutrient absorption and utilization. This suggests that optimizing microbial management strategies could lead to significant improvements in crop nutrient efficiency.

Differential mediation of biogeochemical processes through bioturbation by fiddler and sesarmid mangrove crabs.

Macrobenthic bioturbation is vital to facilitate nutrient turnover in estuarine ecosystems and drives spatial heterogeneity in the sediment matrix. In this study, we compared the sediment physico-chemical properties, microbial community structure and functional genes in vertically-stratified sediment samples from bioturbated (burrows of Parasesarma bidens and Tubuca arcuata) and non-bioturbated area in mangrove ecosystems (the Hanjiang River Estuary, Southern China). The result indicated that bioturbation by P. bidens and T. arcuata had significantly different effects on sediment properties, with the action of P. bidens enhancing nutrient accumulation while T. arcuata promoted N2O emission. Burrow microhabitats harbored distinctive microbial communities although the dominant phylum and genera shared considerable similarity with the control sediment surface with Woeseia dominating in vertical profiles across different habitats. Co-occurrence network analysis revealed that crab bioturbation promoted formation of less complex but more functionally-specialized microbial communities. Crab bioturbation enhanced nutrient metabolism and separated clusters in dendrogram demonstrated the species-specific effect between P. bidens and T. arcuata. Our work verified the significance of bioturbators in regulating biogeochemical processes and highlighted the species-specific bioturbation effect between two dominant mangrove crabs (P. bidens vs. T. arcuata).

Enhancement of alfalfa growth resistance by arbuscular mycorrhiza and earthworm in molybdenum-contaminated soils: From the perspective of soil nutrient turnover.

Molybdenum (Mo) acts as a crucial nutrient for plant development, yet excessive soil exposure can cause detrimental effects. Molybdenosis symptoms remain subtle in many plants, largely due to the safeguarding functions of soil organisms, the fundamental biological mechanisms lack clarity. In this study, we explored the potential mechanisms for amending Mo-exposed soils with soil microbe-arbuscular mycorrhizal fungi (AMF) and soil fauna, specifically earthworms, to enhance model plant-alfalfa growth resistance through soil nutrient turnover perspectives. Our findings illustrated that excessive Mo exposure disrupted soil nutrient turnover, manifesting as exacerbated microbial C and N metabolic limitations. Consequently, this interference intensified nutrient competition between alfalfa and soil microbes, thereby impeding alfalfa nutrient uptake and growth resistance. The synergistic application of AMF and earthworms alleviated microbial C (8.55% ∼ 28.23%) and N (11.14% ∼ 37.55%) metabolic limitations by modulating soil enzyme activities, particularly P-acquiring enzyme. This co-approach facilitated enhanced C and N accumulation in alfalfa, thus improving its growth resistance (24.15% ∼ 123.74%) under Mo exposure. Furthermore, in contrast to singular treatments, the combination of AMF and earthworms bolstered mutual Mo tolerance, amplifying biological benefits for alfalfa growth. Earthworms promoted AMF colonization and the secretion of glomalin-related soil proteins (GRSP), while AMF alleviated Mo accumulation and oxidative stress in earthworms. Additionally, the AMF-induced regulation of gut metabolism reduced earthworm mortality and minimized weight loss. Our study underscores the necessity of maintaining soil biodiversity when utilizing Mo fertilizers to mitigate the potential risks of Mo over-exposure affecting soil nutrient turnover and plant growth.

When plastisphere and drilosphere meet: Earthworms facilitate microbiome and nutrient turnover to accelerate biodegradation of agricultural plastic films

When plastisphere and drilosphere meet: Earthworms facilitate microbiome and nutrient turnover to accelerate biodegradation of agricultural plastic films

Bio-irrigation Promotes Reactive Phosphorus Recycling in an Oxidized Sedimentary Environment

Bio-irrigation by burrowing macrofauna regulates benthic functioning via direct and indirect effects on sediment properties, microbial activities, oxygen dynamics, and organic matter and nutrient turnover. The effects of macrofauna bio-irrigation on benthic nitrogen cycling have been thoroughly investigated, whereas those on phosphorus (P) are comparatively understudied. This is surprising as such effects contribute to sediment oxidation and have a large potential to regulate P mobility and increase P retention. Dissolved oxygen (O2) and inorganic phosphorus (DIP) fluxes, pore water chemistry (DIPpw, Fe[II]pw, Mn[II]pw, pHpw, and oxidation–reduction potential (ORPpw)), and solid-phase Fe(III) pools were measured in reconstructed sediments without or with surface (the amphipod Corophium volutator) and deep (the polychaete Alitta succinea) burrowing macrofauna. Sediments and burrowing macrofauna were collected from the Goro Lagoon (Po River Delta, Italy) in April 2022. Measurements were carried out after a 2-week preincubation to allow sediment conditioning by bioturbators (e.g., burrow construction, bio-irrigation, burrow wall oxidation, steady chemical gradients within sediments and between pore and bottom waters). ORPpw analysis suggested that bio-irrigated sediments were less reduced, and Fe solid-phase analysis suggested a tendency towards an increase in the Fe(III) pool in deep bio-irrigated sediments. Both bioturbators stimulated O2 fluxes and DIP recycling (by a factor of ~ 2), and halved DIPpw, Fe(II)pw, and Mn(II)pw concentrations. The amphipod contributed to DIP fluxes via direct excretion, whereas polychaete excretion was negligible. Polychaetes contributed to DIP fluxes by ventilation of deep burrows within DIP-rich pore water. Bio-irrigation by both burrowers simultaneously promoted higher DIP recycling and sediment oxidation, ensuring the mobilization of a limiting nutrient and preventing the accumulation of reduced chemical species in the surface sediment.

Seasonal changes in the viability and abundance of bacterial cells in the snowpack ecosystem of a High Arctic ice cap

ABSTRACT Microbes play an essential role in nutrient turnover within Arctic environments, and their contribution to biogeochemical cycles can depend on several factors, including but not limited to cell viability. In this study, we employed the SYBR-PI dual cell stain to epifluorescence microscopy to enumerate proportions of potentially viable and non-viable bacterial cell populations within a melting snowpack on an ice cap, Foxfonna in Svalbard. Non-viable cells dominated on Foxfonna (2.5 ± 0.36 × 107 cells m−2) during the June to early July period, when biological production was usually at its peak. Furthermore, non-viable cells also dominated the total cell abundance within superimposed ice (223 ± 242 cells mL−1) and glacial ice (695 ± 717 cells mL−1) beneath the snow. We propose that the rapid, early loss of cell viability was caused by a number of abiotic and biotic factors. Hence, necromass (dead cell residue) contributed to the export of organic matter to downstream ecosystems.

Bilberry Expansion in the Changing Subalpine Belt.

Bilberry (Vaccinium myrtillus L.) expansion in subalpine and alpine ecosystems is increasing due to climate change and reduced land management. This review examines bilberry traits, environmental responses, and ecosystem impacts. As a stress-tolerant chamaephyte, bilberry thrives in acidic, nutrient-poor soils across various habitats. It propagates effectively through rhizomes and demonstrates a phalanx growth form. Bilberry's growth and distribution are influenced by elevation, soil structure, pH, water availability, and nitrogen content. Mycorrhizal associations play a crucial role in nutrient uptake. The species modifies the microclimate, facilitates litter accumulation, and influences soil microbial communities, affecting nutrient turnover and biodiversity. Bilberry shows moderate tolerance to herbivory and frost, with the ability to recover through rapid emergence of new ramets. However, severe or repeated disturbances can significantly impact its abundance and reproductive success. Climate warming and atmospheric nitrogen deposition have accelerated bilberry growth in treeline ecotones. The management of bilberry expansion requires a nuanced approach, considering its resilience, historical land-use changes, and environmental factors. The goal should be to limit, not eliminate, bilberry, as it is a natural part of subalpine communities. Long-term comparative monitoring and experimental manipulation are necessary for effective management strategies.

Interactions between Sugarcane Leaf Return and Fertilizer Reduction in Soil Bacterial Network in Southern China Red Soil.

Microbes may play an important role in the sugarcane leaf degradation and nutrient conversion process. Soil bacterial communities are more or less involved in material transformation and nutrient turnover. In order to make better use of the vast sugarcane leaf straw resources and reduce the overuse of chemical fertilizers in the subtropical red soil region of Guangxi, a pot experiment, with three sugarcane leaf return (SLR) amounts [full SLR (FS), 120 g/pot; half SLR (HS), 60 g/pot; and no SLR (NS)] and three fertilizer reduction (FR) levels [full fertilizer (FF), 4.50 g N/pot, 3.00 g P2O5/pot, and 4.50 g K2O/pot; half fertilizer (HF), 2.25 g N/pot, 1.50 g P2O5/pot, and 2.25 g K2O/pot; and no fertilizer (NF)], was conducted to assess the interactions of different SLR amounts and chemical FR levels in the soil bacterial network and the relationship between the soil properties and bacterial network by using Illumina Miseq high-throughput sequencing technology. According to the results of the soil bacterial community compositions and diversity, the soil bacterial network was changed during maize growth. SLR exerted a stronger effect on soil bacterial function than FR. Returning the sugarcane leaf to the field increased the diversity of the soil bacteria network. The bacterial communities were consistently dominated by Acidobacteria, Actinobacteria, and Bacteroidetes across all treatments, among which Actinobacteria was the most abundant bacteria type by almost 50% at the phylum level. The analysis results of the experimental factor on maize growth showed that the effect of SLR was lower than that of FR; however, this was opposite in the soil bacterial community structure and diversity. The soil bacterial network was significantly correlated with the soil total K, available N and organic matter contents, and EC. The soil bacteria community showed different responses to SLR and FR, and the FF in combination with FS partly increased the complexity of the soil bacteria network, which can further benefit crop production and soil health in the red soil region.

Biodegradation of poly-3-hydroxybutyrate after soil inoculation with microbial consortium: Soil microbiome and plant responses to the changed environment

Biodegradable plastics play a vital role in addressing global plastics disposal challenges. Poly-3-hydroxybutyrate (P3HB) is a biodegradable bacterial intracellular storage polymer with substantial usage potential in agriculture. Poly-3-hydroxybutyrate and its degradation products are non-toxic; however, previous studies suggest that P3HB biodegradation negatively affects plant growth because the microorganisms compete with plants for nutrients. One possible solution to this issue could be inoculating soil with a consortium of plant growth-promoting and N-fixing microorganisms. To test this hypothesis, we conducted a pot experiment using lettuce (Lactuca sativa L. var. capitata L.) grown in soil amended with two doses (1 % and 5 % w/w) of P3HB and microbial inoculant (MI). We tested five experimental variations: P3HB 1 %, P3HB 1 % + MI, P3HB 5 %, P3HB 5 % + MI, and MI, to assess the impact of added microorganisms on plant growth and P3HB biodegradation. The efficient P3HB degradation, which was directly dependent on the amount of bioplastics added, was coupled with the preferential utilization of P3HB as a carbon (C) source. Due to the increased demand for nutrients in P3HB-amended soil by microbial degraders, respiration and enzyme activities were enhanced. This indicated an increased mineralisation of C as well as nitrogen (N), sulphur (S), and phosphorus (P). Microbial inoculation introduced specific bacterial taxa that further improved degradation efficiency and nutrient turnover (N, S, and P) in P3HB-amended soil. Notably, soil acidification related to P3HB was not the primary factor affecting plant growth inhibition. However, despite plant growth-promoting rhizobacteria and N2-fixing microorganisms originating from MI, plant biomass yield remained limited, suggesting that these microorganisms were not entirely successful in mitigating the growth inhibition caused by P3HB.

Organic fertilizer substitution benefits microbial richness and wheat yield under warming

Climate warming poses a serious threat to soil biodiversity and crop yield. Application of organic fertilizer has been extensively practiced to improve soil health and crop productivity. However, information is limited about the effects of organic fertilizer on microbial communities and diversity (richness) under warming. Thus, to investigate the interactive effects of temperature (ambient temperature and warming) and fertilizer (chemical fertilizer and partial substitution of chemical fertilizer with organic fertilizer) on microbial properties and wheat yield, a two-factorial pot experiment was conducted using soils with high and low fertility The results showed that warming and organic fertilizer had minor effects on bacterial Shannon and Simpson indexes. Due to concomitant reductions in soil moisture, warming decreased the average Chao index by 5.4 % and Ace index by 3.8 % for soils with high and low fertility (P < 0.05). High-throughput sequence presented that dominated genus was Bacillus with spore-forming ability. Under warming and drying conditions, microbes with adaptive traits (spore-forming ability) would outcompete the other microbes, and decrease microbial Chao and Ace index (richness). However, organic fertilizer counteracted the adverse effects of warming on microbial richness attributed to positive interaction between temperature and fertilizer on soil nutrients and organic carbon. The strong relationships between bacterial richness and wheat yield, as well as soil nutrients, highlighted the importance of soil biodiversity in improving soil nutrients and crop productivity. Partial substitution of chemical fertilizer with organic fertilizer significantly increased wheat yield by 27.1 % and 14.9 % under ambient temperature and by 28.0 % and 19.6 % under warming for soils with high and low fertility, respectively. Overall, this study provided the possibility to increase bacterial richness related to nutrient turnover and crop production by organic fertilizer application with reduced chemical fertilizer, especially under climate warming.

DEVELOPMENT OF WATER SOFTENING METHOD BY USING NATURAL ADSORBENT: TEMPLE WASTE

Nowadays, Heavy metals are the prime concern due to their adverse effects on the environment and human beings. It is discharged from various industries such as mining, metal finishing, electroplating, glass, textiles, ceramics, and storage batteries. Copper is the metal used in many electronic devices and involved in other production processes. On the other hand, the amount of floral waste generated from temples and festivals/celebrations are increasing day by day, its impact on the solid waste management process is huge and it creates a fouling smell when it is disposed of improperly. Therefore, the present aim of the project is to utilize the waste flowers for the development of Biochar where it is used in the removal of heavy metal i.e., copper from synthetic wastewater. The other advantage of floral Biochar is the increase in soil organic matter (SOM) which can influence the soil microclimate, microbial community structure, biomass turnover, and mineralization of nutrients. The preparation, physicochemical properties, and adsorption mechanisms of floral waste Biochar in removing copper metal from synthetic wastewater have been discussed in this study. Key Words: optics, photonics, light, lasers, templates, journals

Earthworms enhance the performance of organic amendments in improving rice growth and nutrition in poor ferralsols

In the Highlands of Madagascar, providing organic amendments (OAs) is the main farmer fertilization practice in upland rainfed agrosystems dominated by nutrient-depleted Ferralsols. Therefore, enhancing the performance of OAs on plant functions is particularly important for improving both plant productivity and agrosystem sustainability. Earthworms are well-known ecosystem engineers involved in the decomposition of organic matter and play a critical role in nutrient turnover. Inoculating earthworms could be a promising approach to improve the fertilizer performance of OAs. However, there is limited knowledge regarding the interaction between earthworms and OAs of varying biochemical qualities on plant growth and nutrition. In this microcosm experiment, we assessed the effect of different types of OAs (i.e., unamended control, conventional farmyard manure, kraal manure, improved farmyard manure, compost, vermicompost, urban waste, taroka, poultry droppings, pig manure) and earthworm inoculation (with and without earthworms) on the growth and nutrition of rice. The endogeic species Pontoscolex corethrurus (Rhinodrilidae) was used in the experiment. After eight weeks of growth, the poultry droppings had the best fertilizer performance, followed by improved farmyard manure and pig manure in treatments without earthworms. The main driver of fertilizer performance appeared to be the quality of OAs. However, other mechanisms, such as an increase in soil pH, may also play a significant role. The inoculation of earthworms significantly enhanced the fertilizer performance of OAs but the magnitude of this enhancement depends on the OAs. Overall, OAs with low fertilizer performance showed a more pronounced response to earthworms. Additionally, earthworms improved the performance of high-quality OAs likely by enhancing the availability of P and Mg. Our findings emphasize the synergistic effects of earthworms and OAs of various qualities on plant growth and nutrition, offering valuable insights for improving fertilization practices in nutrient-poor Ferralsols of Madagascar.

Disinfectant-induced ammonia oxidation disruption in microbial N-cycling process in aquatic ecosystem after the COVID-19 outbreak

Anthropogenic activities significantly impact the elemental cycles in aquatic ecosystems, with the N-cycling playing a critical role in potential nutrient turnover and substance cycling. We hypothesized that measures to prevent COVID-19 transmission profoundly altered the nitrogen cycle in riverine ecosystems. To investigate this, we re-analyzed metagenomic data and identified 60 N-cycling genes and 21 host metagenomes from four urban reaches (one upstream city, Wuhan, and two downstream cities) along the Yangtze River. Our analyses revealed a marked decrease in the abundance of bacterial ammonia monooxygenase genes, as well as in the host, ammonia-oxidizing autotrophic Nitrosomonas, followed by a substantial recovery post-pandemic. We posited that discharge of sodium hypochlorite (NaOCl) disinfectant may be a primary factor in the reduction of N-cycling process. To test this hypothesis, we exposed pure cultures of Nitrosomonas europaea to NaOCl to explore the microbial stress response. Results indicated that NaOCl exposure rapidly compromised the cell structure and inhibited ammonia oxidation of N. europaea, likely due to oxidative stress damage and reduced expression of nitrogen metabolism-related ammonia monooxygenase. Using the functional tagging technique, we determined that NaOCl directly destroyed the ammonia monooxygenase protein and DNA structure. This study highlights the negative impacts of chlorine disinfectants on the function of aquatic ecosystems and elucidates potential mechanisms of action.

Bacteriological Assessment of Lake Water samples in Raipur, Chhattisgarh: A Comprehensive Analysis of Water Samples

Abstract: The assessment of water quality is crucial, relying on both physico-chemical and microbiological standards. A comprehensive understanding of these parameters is essential to guide quality maintenance. Bacterial activity plays a pivotal role in decomposition, significantly influencing nutrient turnover and contributing to the biogeochemical cycle's foundation. Microbial diversity and dominance are integral to the biogeochemical cycle. However, bacterial and viral diseases transmitted through water, such as cholera, typhoid, and hepatitis, pose significant health risks during monsoon and summer seasons. Different regions adhere to various standards for water and potable water. Lakes play a vital role in determining groundwater quality, the primary source of potable water for rural populations, often consumed with minimal treatment. The quality of lake water is a matter of concern for public health, particularly due to the presence of indicator bacteria such as fecal coliforms, fecal streptococci, fecal staphylococci, and Enterobacteriaceae. In this study, lake water samples were meticulously analyzed for various bacterial loads, including total coliforms, fecal coliforms, E. coli, Staphylococcus, and Streptococcus. These bacterial indicators not only serve as determinants of water quality but also raise serious concerns about the health of humans and animals relying on these water bodies. In summary, this research delves into the microbiological aspects of water quality in lakes, emphasizing the significance of bacterial indicators and their potential impact on public health. The findings contribute valuable insights for developing strategies to safeguard water quality and mitigate health risks associated with waterborne diseases.

Environmental drivers of increased ecosystem respiration in a warming tundra.

Arctic and alpine tundra ecosystems are large reservoirs of organic carbon1,2. Climate warming may stimulate ecosystem respiration and release carbon into the atmosphere3,4. The magnitude and persistency of this stimulation and the environmental mechanisms that drive its variation remain uncertain5-7. This hampers the accuracy of global land carbon-climate feedback projections7,8. Here we synthesize 136 datasets from 56 open-top chamber in situ warming experiments located at 28 arctic and alpine tundra sites which have been running for less than 1 year up to 25 years. We show that a mean rise of 1.4 °C [confidence interval (CI) 0.9-2.0 °C] in air and 0.4 °C [CI 0.2-0.7 °C] in soil temperature results in an increase in growing season ecosystem respiration by 30% [CI 22-38%] (n = 136). Our findings indicate that the stimulation of ecosystem respiration was due to increases in both plant-related and microbial respiration (n = 9) and continued for at least 25 years (n = 136). The magnitude of the warming effects on respiration was driven by variation in warming-induced changes in local soil conditions, that is, changes in total nitrogen concentration and pH and by context-dependent spatial variation in these conditions, in particular total nitrogen concentration and the carbon:nitrogen ratio. Tundra sites with stronger nitrogen limitations and sites in which warming had stimulated plant and microbial nutrient turnover seemed particularly sensitive in their respiration response to warming. The results highlight the importance of local soil conditions and warming-induced changes therein for future climatic impacts on respiration.

Untargeted metabolomics to study changes in soil microbial community in response to tillage practices

Soil microbes are the main drivers of nutrient turnover in agro-ecosystems. The series of biochemical processes involved by these microorganisms are inseparable from the regulation of metabolites in the root-zone soils. Therefore, understanding the evolution of microbial communities driven by root-zone soil metabolites will help optimize agricultural management practices. Based on a field experiment, we explore the changes in soil properties, microbes, and metabolites under three tillage practices such as no-tillage with straw mulching (NTS), rotary tillage, and plough tillage with straw returning (RTS and PTS) based on untargeted metabolomics. We found that NTS helped to enhance nutrient contents and enzyme activities in the 0–20 cm soil layer. Specifically, compared with RTS and PTS, NTS increased grain yield by 6.4 % and 8.5 %, and SOC by 13.3 % and 5.7 %, respectively, but decreased pH by 2.8 % and 1.1 %. In addition, compared with NTS, RTS and PTS decreased the fungal richness by 16.5 % and 8.1 %, and decreased the fungal shannon index by 16.4 % and 9.2 %. However, tillage practices did not result in substantial differences in the alpha diversity of bacterial community. Both bacterial and fungal community composition were substantially affected by tillage practices and they were both significantly correlated with soil metabolites. In the symbiotic networks, NTS significantly increased the abundance of microorganisms with high connectivity, while RTS significantly increased the concentration of metabolites with high connectivity. Amino acids, as the main drivers, were significantly and positively associated with bacterial and fungal community composition, mainly enriched in the metabolic pathways of D − glutamine and D − glutamate metabolism and arginine and proline metabolism, and correlated with soil properties negatively and carbohydrates positively, directly or indirectly affecting soil microbial community composition. Our findings would provide new insight into metabolomics for the in-depth understanding of the metabolic mechanism for soil microbial community changes in dryland wheat fields under different tillage practices.

Global contribution of invertebrates to forest litter decomposition.

Forest litter decomposition is an essential component of global carbon and nutrient turnover. Invertebrates play important roles in litter decomposition, but the regional pattern of their effects is poorly understood. We examined 476 case studies across 93 sites and performed a meta-analysis to estimate regional effects of invertebrates on forest litter decomposition. We then assessed how invertebrate diversity, climate and soil pH drive regional variations in invertebrate-mediated decomposition. We found that (1) invertebrate contributions to litter decomposition are 1.4 times higher in tropical and subtropical forests than in forests elsewhere, with an overall contribution of 31% to global forest litter decomposition; and (2) termite diversity, together with warm, humid and acidic environments in the tropics and subtropics are positively associated with forest litter decomposition by invertebrates. Our results demonstrate the significant difference in invertebrate effects on mediating forest litter decomposition among regions. We demonstrate, also, the significance of termites in driving litter mass loss in the tropics and subtropics. These results are particularly pertinent in the tropics and subtropics where climate change and human disturbance threaten invertebrate biodiversity and the ecosystem services it provides.

Earthworm communities and their relation to above‐ground organic residues and water infiltration in perennial cup plant (Silphium perfoliatum) and annual silage maize (Zea mays) energy plants

AbstractPerennial energy cropping systems are hailed as a sustainable way of mitigating and potentially adapting to climate change. As a result of the absence of tillage, soils cropped with perennials like cup plant (Silphium perfoliatum) promote abundant and functionally diverse earthworm communities. Hence, ecosystem service provision because of earthworm activity and functional redundancy, for example, litter decomposition, water infiltration and nutrient turnover, is considerably enhanced in perennial cropping systems. We studied the abundance and functional role of earthworms in non‐tilled perennial systems and reduced‐tilled annual systems to assess their relationship with the respective above‐ground organic residues and their implications for the soil water dynamic. We sampled earthworms and simultaneously measured the saturated infiltration rate for two consecutive years in cup plant and maize (Zea mays) fields. Furthermore, we sampled above‐ground litter each trimester in both systems and analysed the total C and N content and CN ratios. Our field investigations revealed significantly higher earthworm abundance, species diversity and richness in cup plant systems likely because of the absence of tillage and the formation of a litter layer. High abundances of juveniles in both maize and cup plant systems pointed to harsh habitat conditions likely because of temperature variations, waterlogging and bulk density. The respective field litter was of minor importance as a food source in both systems because of poor quality, but may positively affect the soil water balance in cup plant systems. Earthworm populations in maize may have been supported by organic fertilizer while earthworm populations in cup plants may have additionally benefitted from the extensive root network and a higher on‐site plant diversity. Reduced tillage regimes in maize systems may have enhanced saturated infiltration rates. A direct link between earthworms and infiltration was not validated, but may not be excluded in the future, as earthworm populations may develop slowly because of adverse habitat conditions. Our results show that perennials support abundant and diverse earthworm populations and indicate the importance of functional redundancy and the diversity of food sources. The combination of both earthworm abundance and perennial cropping systems is capable of increasing on‐site ecosystem stability and supporting adaptation to climate change by increasing functional redundancy and, ultimately, providing ecosystem services. The noticeable occurrence of the latter, however, may be delayed because of the slow establishment of earthworm communities and delayed build‐up of ecosystems stability. Hence, a transitional phase is inevitable to reap the benefits of perennial energy cropping systems and must be accounted for.

Soil phosphorus transformation and plant uptake driven by phosphate-solubilizing microorganisms.

Phosphorus (P) is an important nutrient for plants, and a lack of available P greatly limits plant growth and development. Phosphate-solubilizing microorganisms (PSMs) significantly enhance the ability of plants to absorb and utilize P, which is important for improving plant nutrient turnover and yield. This article summarizes and analyzes how PSMs promote the absorption and utilization of P nutrients by plants from four perspectives: the types and functions of PSMs, phosphate-solubilizing mechanisms, main functional genes, and the impact of complex inoculation of PSMs on plant P acquisition. This article reviews the physiological and molecular mechanisms of phosphorus solubilization and growth promotion by PSMs, with a focus on analyzing the impact of PSMs on soil microbial communities and its interaction with root exudates. In order to better understand the ability of PSMs and their role in soil P transformation and to provide prospects for research on PSMs promoting plant P absorption. PSMs mainly activate insoluble P through the secretion of organic acids, phosphatase production, and mycorrhizal symbiosis, mycorrhizal symbiosis indirectly activates P via carbon exchange. PSMs can secrete organic acids and produce phosphatase, which plays a crucial role in soil P cycling, and related genes are involved in regulating the P-solubilization ability. This article reviews the mechanisms by which microorganisms promote plant uptake of soil P, which is of great significance for a deeper understanding of PSM-mediated soil P cycling, plant P uptake and utilization, and for improving the efficiency of P utilization in agriculture.

Drought shifts soil nematode trophic groups and mediates the heterotrophic respiration

Abstract As the most diverse metazoan taxa, soil nematodes serve a diversity of functions in soil food webs and thus can regulate microbial community composition and affect organic matter decomposition and nutrient turnover rates. Because nematodes depend on water films to access food resources, drought can negatively affect nematode–microbial food webs, yet the impacts of drought on nematode diversity and abundance and how these changes may influence food web members and their functions are hardly explored. Here, we coupled research along a drought gradient in arid and semiarid grasslands with a detailed intact plant–soil microcosm experiment to explore the patterns and mechanisms of how drought impacts nematode abundance and carbon footprint, microbial phospholipid fatty acid (PLFA) and heterotrophic soil respiration. Overall, in the field and the microcosm experiments, we found that nematode abundance, carbon footprint and diversity, microbial PLFA and heterotrophic respiration were reduced under drier conditions. In addition, drought altered nematode and microbial community composition, through reducing the nematode channel ratio and increasing the relative fungivorous nematode abundance and the fungal to bacterial ratio. The soil decomposition channel shifted from a bacterial to a fungal pathway in response to drought, indicating decelerated heterotrophic respiration under drought. These results highlight the important contribution of soil nematodes and their associated microbial food web to soil carbon cycling. Our findings underscore the need to incorporate key soil fauna into terrestrial ecosystem model evaluation.