Pedosphere最新文献

Soil ecosystem is experiencing stresses due to climate change, and soil inhabitants try to demonstrate their inherent resistance and resilience against those stresses. Application of nanomaterials as agricultural inputs could bring shifts in resistance and resilience patterns of soil microbes and associated enzymes, especially under short-term heat stress. With this background, the impacts of multi-walled carbon nanotube (MWCNT) on the resistance and resilience of soil biological indicators were evaluated. An incubation experiment was conducted with varied MWCNT concentrations (0, 50, 100, 250, and 500 mg kg^-1 soil) for 90 d after 24-h heat stress at 48 ± 2 °C to assess the impacts of MWCNT on soil enzyme activities and microbial populations vis-à-vis their resistance and resilience indices under short-term exposure to heat stress. Enzyme activities were reduced after exposure to heat stress. Resistance indices of enzyme activities were enhanced by MWCNT application on day 1 after heat stress, whereas there was no recovery of enzyme activities after 90-d incubation. Like soil enzyme activities, resistance index values of soil microbial populations followed the similar trend and were improved by MWCNT application. Multi-walled carbon nanotube has the potential to improve resistance indices of soil enzyme activities and microbial populations under heat stress, although they could not recover to their original state during periodical incubation after heat stress. This study helps to understand the relative changes of biological indicators under MWCNT and their ability to withstand heat stress.

Phosphorus (P) is an essential element for plant growth but is often limiting in ecosystems; therefore, improving the P fertilizer use efficiency is important. Biochar and arbuscular mycorrhizal fungi (AMF) may enhance P cycling in paddy soils that contain high content of total P but low content of available P (AP). In this study, the effects of biochar addition and Rhizophagus irregularis inoculation on the organic and inorganic P contents and phosphatase activities in paddy soils, rice seedling growth, and AMF colonization were investigated. Compared with no biochar addition, biochar addition enhanced the percentage of spore germination at day 7, hyphal length, most probable number, and mycorrhizal colonization rate of R. irregularis by 32%, 662%, 70%, and 28% on average, respectively. Biochar and R. irregularis altered soil P cycling and availability. Biochar and R. irregularis, either individually or in combination, increased soil AP content by 2%--48%. Rice seedlings treated with biochar and R. irregularis produced greater biomass, improved root morphology, and increased nutrient uptake compared with those of the control without biochar and R. irregularis. The results suggest that combined application of biochar and R. irregularis is beneficial to rice cultivation in paddy soils with high content of total P but low content of AP.

Mycorrhiza helper bacteria (MHB) can promote the formation and functioning of arbuscular mycorrhizal (AM) symbiosis, but their role and application potential in coping with soil-borne diseases are still unclear. A 14-week greenhouse pot experiment was conducted to obtain several actinomycete strains helping AM symbiosis in suppressing the Phytophthora blight of pepper (Capsicum annuum L.), using a soil inoculated with Phytophthora capsici after sterilization. Five Streptomyces strains, including S. pseudogriseolus, S. albogriseolus, S. griseoaurantiacus, S. tricolor, and S. tendae, as well as the AM fungus (Funneliformis caledonium) were tested. The Phytophthora blight severity reached 66% at full productive stage in the uninoculated control, and inoculation of F. caledonium, S. griseoaurantiacus, and S. tricolor alone significantly decreased (P < 0.05) it to 47%, 40%, and 35%, respectively. Compared to F. caledonium alone, additional inoculation of S. tricolor or S. tendae, which were isolated from the rhizosphere of a healthy individual in an infected field, significantly elevated (P < 0.05) root mycorrhizal colonization, root biomass, fruit yield, and total K acquisitions of pepper and further significantly decreased (P < 0.05) blight severity. According to the feature of enhancing disease-suppression by AM symbiosis, both S. tricolor and S. tendae were confirmed as MHB strains here. Specifically, S. tendae had a stronger performance in directly accelerating mycorrhization, while S. tricolor was also an antagonist to the pathogenic P. capsici. Furthermore, S. griseoaurantiacus with the independent disease-suppression function was not an MHB strain here. The redundancy analyses demonstrated that when AM fungus was present, root mycorrhizal colonization replaced soil pH becoming the main factor affecting pepper Phytophthora blight. Thus, S. tricolor and S. tendae seemed to have the value of preparation and application in the future to help AM symbiosis against pepper Phytophthora blight.

Modern agricultural practices have posed a detrimental impact on the environment due to their intensive use to meet the food demands of an ever-increasing population. In this context, microalgal bioinoculants, specifically cyanobacteria and green microalgae, have emerged as sustainable options for agricultural practices to improve soil organic carbon, nutrient availability, microbial quality, and plant productivity. An overview of current and future perspectives on the use of microalgal bioinoculants in agriculture practices is presented in this review, along with a discussion of their interactions with soil biotic and abiotic factors that affect soil fertility, plant health, and crop productivity. The benefits of microalgal bioinoculants include releasing agronomically important metabolites (exopolymers and phytohormones) as well as solubilizing soil nutrients. Furthermore, they function as biocontrol agents against soil-borne pathogens and facilitate the establishment of rhizosphere communities of agricultural importance. So far, very few studies have explored the basic mechanisms by which microalgal bioinoculants interact with soil biotic and abiotic factors. In recent years, advanced molecular techniques have contributed to a better understanding of these interactions.

More than 80% of plants form mutualistic symbiotic relationships with arbuscular mycorrhizal fungi (AMF), and the application of fertilizers, such as nitrogen (N) and phosphorus (P) fertilizers, is a common agricultural management practice to improve crop yield and quality. However, the potential effects of long-term N and P fertilization on the AMF community in the rainfed agricultural system of the Loess Plateau of China are still not well understood. In this study, a long-term field experiment was conducted based on orthogonal design, with three N levels (0, 90, and 180 kg ha⁻¹ year⁻¹) and three P levels (0, 90, and 180 kg ha⁻¹ year⁻¹) for wheat fertilization. Changes in AMF community and correlations between AMF community composition, soil environmental factors, and wheat yield component traits were analyzed using traditional biochemical methods and high-throughput sequencing technology. The results showed that long-term N and P addition had a significant effect on the AMF community structure and composition. Nitrogen application alone significantly reduced the richness and diversity of AMF community, whereas the combined application of N and P significantly increased the richness and diversity of AMF community. The AMF community was driven mainly by soil available P, total P, and pH. There was a significant positive correlation between Glomus abundance and wheat yield and a significant negative correlation between Paraglomus abundance and wheat yield. Long-term N and P addition directly increased crop yield and affected yield indirectly by influencing soil chemical properties and the AMF community. Combined application of N and P both at 90 kg ha⁻¹ year⁻¹ could improve the ecological and physiological functions of the AMF community and benefit the sustainable development of rainfed agriculture.

Nitrogen (N) is one of the most limited nutrients of terrestrial ecosystems, whose losses are prevented in tightly coupled cycles in finely tuned systems. Global change-induced N enrichment through atmospheric deposition and application of vast amounts of fertilizer are now challenging the terrestrial N cycle. Arbuscular mycorrhizal fungi (AMF) are known drivers of plant-soil nutrient fluxes, but a comprehensive assessment of AMF involvement in N cycling under global change is still lacking. Here, we simulated N enrichment by fertilization (low/high) in experimental grassland microcosms under greenhouse conditions in the presence or absence of AMF and continuously monitored different N pathways over nine months. We found that high N enrichment by fertilization decreased the relative abundance of legumes and the plant species dominating the plant community changed from grasses to forbs in the presence of AMF, based on aboveground biomass. The presence of AMF always maintained plant N:phosphorus (P) ratios between 14 and 16, no matter how the soil N availability changed. Shifts in plant N:P ratios due to the increased plant N and P uptake might thus be a primary pathway of AMF altering plant community composition. Furthermore, we constructed a comprehensive picture of AMF's role in N cycling, highlighting that AMF reduced N losses primarily by mitigating N leaching, while N₂O emissions played a marginal role. Arbuscular mycorrhizal fungi reduced N₂O emissions directly through the promotion of N₂O-consuming denitrifiers. The underlying mechanism for reducing N leaching is mainly the AMF-mediated improved nutrient uptake and AMF-associated microbial immobilization. Our results indicate that synergies between AMF and other soil microorganisms cannot be ignored in N cycling and that the integral role of AMF in N cycling terrestrial ecosystems can buffer the upcoming global changes.

Microplastic pollution is a global and ubiquitous environmental problem in the oceans as well as in the terrestrial environment. We examined the fate of microplastic polystyrene (MPS) beads in experimental soil in the presence and absence of symbiotic arbuscular mycorrhizal fungi (AMF) and simulated acid rain (SAR) to determine whether the combinations of these three factors altered the growth of white clover Trifolium repens. We found that MPS, SAR, or AMF added singly to soil did not alter T. repens growth or yields. In contrast, MPS and AMF together significantly reduced shoot biomass, while SAR and MPS together significantly reduced soil available phosphorus independent of AMF presence. Microplastic polystyrene, AMF, and SAR together significantly reduced soil NO₃^--N. Arbuscular mycorrhizal fungi added singly also enriched the beneficial soil bacteria (genus Solirubrobacter), while MPS combined with AMF significantly enriched the potential plant pathogenic fungus Spiromastix. Arbuscular mycorrhizal fungi inoculation with MPS increased the abundance of soil hydrocarbon degraders independent of the presence of SAR. In addition, the abundance of soil nitrate reducers was increased by MPS, especially in the presence of AMF and SAR. Moreover, SAR alone increased the abundance of soil pathogens within the fungal community including antibiotic producers. These findings indicate that the coexistence of MPS, SAR, and AMF may exacerbate the adverse effects of MPS on soil and plant health.

Straw return is a sustainable soil fertility-building practice, which can affect soil microbial communities. However, how straw return affects arbuscular mycorrhizal fungi (AMF) is not well explored. Here, we studied the impacts of different straw management treatments over eight years on the structure and functioning of AMF communities in a rice-wheat rotation system. The straw management treatments included no tillage with no straw (NTNS), rotary tillage straw return (RTSR), and ditch-buried straw return (DBSR). The community structure of AMF was characterized using high-throughput sequencing, and the mycorrhizal functioning was quantified using an in situ mycorrhizal-suppression treatment. Different straw management treatments formed unique AMF community structure, which was closely related to changes in soil total organic carbon, available phosphorus, total nitrogen, ammonium, and nitrate. When compared with NTNS, RTSR significantly increased Shannon diversity in 0--10 cm soil layer, while DBSR increased it in 10--20 cm soil layer; DBSR significantly increased hyphal length density in the whole ploughing layer (0--20 cm), but RTSR only increased it in the subsurface soil layer (10--20 cm). The mycorrhizal responses of shoot biomass and nutrient (N and P) uptake were positive under both straw return treatments (RTSR and DBSR), but negative under NTNS. The community composition of AMF was significantly correlated to hyphal length density, and the latter was further a positive predictor for the mycorrhizal responses of plant growth and nutrient uptake. These findings suggest that straw return can affect AMF community structure and functioning, and farmers should manage mycorrhizas to strengthen their beneficial effects on crop production.

Cadmium (Cd) contamination in soil poses a huge threat to plants even at low concentrations; Broussonetia papyrifera has great potential in remediation of soil heavy metal contamination. However, whether exogenous indole-3-acetic acid (IAA) application and arbuscular mycorrhizal fungi (AMF) have synergistic effects on Cd tolerance of B. papyrifera remains unclear. To investigate the effects of AMF inoculation and IAA application on the tolerance of B. papyrifera to Cd stress, two experiments were conducted: the first to investigate the effect of AMF (Rhizophagus irregularis) inoculation on the tolerance of B. papyrifera to Cd stress and the second to investigate the combined effects of AMF inoculation and IAA application on the tolerance of B. papyrifera to Cd stress. Parameters including endogenous hormone concentration, antioxidant defense response, malondialdehyde (MDA) content, and gene expression related to antioxidant enzyme system and hormone were measured. The results indicated that AMF alleviated Cd toxicity of B. papyrifera by reducing MDA content and improving antioxidant enzyme activities and Cd absorption capacity. Furthermore, the combination of AMF inoculation and IAA application had a synergetic effect on the tolerance of B. papyrifera to Cd stress through upregulating BpAUX1 and BpAUX2, which might contribute to root growth and root xylem synthesis, and by upregulating BpSOD2 and BpPOD34 to enhance the antioxidant enzyme system. This work provides a new insight into the application of IAA in the remediation of soil Cd pollution by mycorrhizal plants.