Plant and Soil最新文献

Aim

Compaction of slope soils can substantially hinder root penetration of grass cover, which may be alleviated through the colonisation of arbuscular mycorrhizal (AM) fungi and aggregate stabilisation. We investigated aggregate stabilisation and breakdown mechanisms in compacted dense mycorrhizal soils.

Methods

A pot-culture experiment with seven treatments (five replicates per treatment) was implemented. In a local decomposed granitic soil, we inoculated two grass species (Chrysopogon ziaanioides and Cynodon dactylon) with AM fungi. We used loose soil to grow C. dactylon to compare it with compacted dense soil, as well as pots without a plant and/or fungal inoculation for comparison. After 20 weeks of cultivation, we measured root and AM fungal characteristics, soil organic matter and aggregate properties by dry sieving, wet sieving and Le Bissonnais methods.

Results

Compaction led to the formation of macro-aggregates (> 0.25 mm) but had a negative influence on the aggregate stability. The fungal inoculation increased polysaccharide production and aggregate stability in the compacted soil vegetated with C. dactylon. The inoculated C. ziaanioides showed a similar level of aggregate stability as the inoculated C. dactylon, but the uninoculated group demonstrated higher aggregate stability compared with the inoculated group owing to root decomposition. The aggregate stability against various breakdown mechanisms was related to the established aggregate hierarchy and qualitative organic matter inputs.

Conclusion

Soil organic matter supplied by grass species together with the mediation of AM fungal hyphae played a crucial role in the systemic enhancement of aggregate stability in the compacted soil.

Background and aims

Nitrogen (N) deposition usually has adverse effects on various ecosystems. Farmland intercropping is a well-known planting model and agroecosystem with multiple benefits. However, research on N deposition in farmland, especially for intercropping systems remains limited.

Methods

Field experiments were conducted in three seasons to examine the effects of rice monocropping and rice-water mimosa (Neptunia oleracea Lour.) intercropping systems on rice growth and soil properties under N deposition. The simulated N deposition rate was set at two levels, which included low N (LN) deposition at a rate of 40 kg·ha⁻¹·yr⁻¹ N and high N (HN) deposition at a rate of 120 kg·ha⁻¹·yr⁻¹ N, which were applied in addition to 180 kg·ha⁻¹·yr⁻¹ N fertilization during the overall growth period of rice.

Results

With increasing N deposition, rice plant height, average root diameter and water mimosa yield, above-ground dry weight decreased in the monocropping treatment. Meanwhile, water mimosa yield, above-ground dry weight, and all of the indices of root morphology in 2022 early season decreased with the increasing N deposition in the rice-water mimosa intercropping system. Contents of soil total manganese (Mn), total zinc (Zn), total calcium (Ca), and cellobiosidase activity also declined with increasing N deposition. However, the land equivalent ratio (LER) of the intercropping system was greater than 1 even under N deposition. In addition, compared with monocropping, intercropping increased dry weight of stem and leaves, average root diameter of rice, contents of soil total nitrogen, total phosphorous, total Mn, total Zn, total Ca and the activity of acid phosphatase, and also enhanced soil microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP), gram-positive bacteria, gram-negative bacteria, fungi, bacteria, methane-oxidizing bacteria contents and fungi/bacteria ratio.

Conclusion

The experiment results suggest that N deposition caused negative impacts on rice farming system. However, rice and water mimosa intercropping systems can reduce the negative effects of N deposition (especially LN) on rice and soil. The findings demonstrate that this intercropping system is advantageous under N deposition (especially LN) than rice monocropping.

Background and aims

Salinity causes significant environmental stress that restricts plant growth and development, and arbuscular mycorrhizal fungi (AMF) can use different mechanisms to protect plants against salt stress. The aim of this study was to explore the local and systemic effects of AMF in alfalfa plants under uniform and non-uniform salinity and the abilities of the AMF that underlie these effects.

Methods

Alfalfa (Medicago sativa L.) plants were subjected to uniform (200/200 mM NaCl) and non-uniform (0/200 mM NaCl) salt stress using a split-root system, with one or both root compartments inoculated or not inoculated with the AMF Rhizophagus irregularis.

Results

We observed that the inoculation with AMF ameliorated the negative effects of salt stress by enhancing the dry weight, plant growth rate, photosynthesis, and the activities of antioxidant enzymes, including catalase, peroxidase, and superoxide dismutase. These effects contributed to maintaining an ionic and nutritive balance and resulted in lower levels of lipid peroxidation and contents of H₂O₂ under both uniform and non-uniform salinity treatments, particularly when the whole root system was inoculated with AMF. Under non-uniform salinity, when the high-saline root side was inoculated with AMF, the oxidative defense was restricted to that compartment, and the AMF played a key role in alleviating the damage caused by salt stress. Conversely, when AMF was inoculated on the non-saline root side, both root compartments exhibited systemic oxidative defense mechanisms, which highlighted the significance of functional equilibrium within the root system at enhancing salt tolerance.

Conclusion

The findings indicate that AMF ameliorates the effects of salt stress through distinct antioxidant defenses and ion regulatory mechanisms under non-uniform salinity. Phosphorus uptake and ion regulation were more effective in the AMF-inoculated root side under both the uniform and non-uniform salinity conditions.

Background & aims

Mycorrhizal fungi are well known to enhance nutrient acquisition through hyphal foraging beyond the root depletion zone. However, plant species vary widely in the degree to which they rely on mycorrhizal fungi for nutrient acquisition. Species which rely more on mycorrhizal colonization are expected to perform poorly in soils with lower density/availability of mycorrhizal partners. Mycorrhizal fungal density/availability is expected to be influenced by the mycorrhizal guild of dominant plant neighbors. However, little is known how the local density/availability of mycorrhizal partners may affect fungal colonization, root morphological traits and plant growth.

Methods

We inoculated seedlings of ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) tree species with soils from ECM-dominated forests or AM-dominated open fields. We evaluated seedling mycorrhizal colonization, root morphology and growth in response to these inocula.

Results

Both AM species (Acer rubrum L. and Ulmus americana L.) had higher AM colonization rates when inoculated with AM-dominated open field soils. However, only Acer grew better and invested less in autonomous root-based foraging, when inoculated with AM-dominated soils. Responses of ECM species to soil inocula were more nuanced. Both species remained unresponsive to inoculation treatment. Populus tremuloides Michx. ECM colonization was higher when inoculated with ECM-dominated soils, while neither root morphology nor mycorrhizal colonization responded to inoculum origin for Quercus rubra L.

Conclusion

Our results show that local variation in mycorrhizal fungal abundance does not necessarily lead to an integrated adjustment of autonomous foraging traits. In addition, we found that the variation in root colonization degree of seedlings from different species was not always accompanied with an increase of seedling performance.

Background and aims

Crop wild relatives, exposed to strong natural selection, exhibit effective tolerance traits against stresses. While an aggressive root proliferation phenotype has long been considered advantageous for a range of stresses, it appears to be counterproductive under drought due to its high metabolic cost. Recently, a parsimonious root phenotype, metabolically more efficient, has been suggested to be better adapted to semiarid environments, although it is not clear that this phenotype is a trait exhibited by crop wild relatives.

Methods

Firstly, we analysed the root phenotype and carbon metabolism in four Medicago crop wild relatives adapted to a semiarid environment and compared them with the cultivated M. truncatula Jemalong (A17). Secondly, we exposed the cultivated (probably the least adapted genotype to aridity) and the wild (the most common one in arid zones) M. truncatula genotypes to water deficit. The carbon metabolism response in different parts of their roots was analysed.

Results

A reduced carbon investment per unit of root length was a common trait in the four wild genotypes, indicative of an evolution towards a parsimonious root phenotype. During the water deficit experiment, the wild M. truncatula showed higher tolerance to drought, along with a superior ability of its taproot to partition sucrose and enhanced capacity of its fibrous roots to maintain sugar homeostasis.

Conclusion

A parsimonious root phenotype and the spatial specialization of root carbon metabolism represent two important drought tolerance traits. This work provides relevant findings to understand the response of Medicago species roots to water deficit.

Background and Aims

This review explores how soil texture and nutrient availability influence root exudate composition and their effects on rhizosphere microbial dynamics and disease suppression, ultimately affecting plant health and resilience.

Results

The findings reveal that clay soil has a dense structure and limited aeration. As a stress response, clay soil restricts root growth, prompts plants to release more exudates to enhance nutrient uptake and attracts beneficial microbes. In contrast, sandy soil, due to its loose texture, is easier for roots to penetrate, often resulting in less exudation. Nutrient availability plays a pivotal role in shaping exudate profiles, such as coumarins and organic acids, which recruit beneficial microbes like Pseudomonas and Trichoderma harzianum, aiding in nutrient acquisition and disease suppression. The interaction between soil texture and nutrient levels creates a dynamic environment that shapes microbial community structure and promotes disease suppression.

Conclusion

This review highlights the current understanding of how variations in soil texture and nutrient levels impact root exudates and microbial communities in the rhizosphere. It also identifies key gaps, particularly the need for long-term field studies to explore these interactions under diverse environmental conditions. These insights are critical for developing targeted rhizosphere management strategies, paving the way for more resilient and productive agricultural systems.

Background and aim

Nutrient availability plays a crucial role in both litter decomposition and decomposer communities. However, the specific effects of Epichloë endophytes on soil decomposer communities during the decomposition of their host litter under fertilized conditions are still unclear.

Methods

In this study, qPCR combined with Illumina sequencing was conducted to reveal the responses of functional gene communities involved in organic P recycling (phoD), nitrification (AOA/AOB-amoA), and denitrification (nirS/nirK) to Epichloë gansuensis-mediated decomposition of Achnatherum inebrians litter under different P addition treatments. Meanwhile, soil physicochemical properties and enzyme activities were measured.

Results

Both E. gansuensis infection and P addition exerted limited effect on the abundance and diversity of phoD-harboring microbial community. In the E. gansuensis-free (E−) samples, 60 mM P addition significantly increased the gene copies of AOA-amoA and significantly decreased those of AOB-amoA. Additionally, P addition decreased the richness and diversity of the nirK-harboring community in the E− samples, while E. gansuensis appeared to alleviate this response. P addition decreased the relative abundance of nirS-harboring Acidovorax and Azospirillum, while increasing the nirK-harboring Rhodopseudomonas and Bosea. Mantel’s test showed that E. gansuensis infection decreased the correlation between nitrifier communities and soil properties. Furthermore, nirS- and nirK-harboring communities showed a similar correlation pattern with soil properties in both E+ and E− soil samples.

Conclusions

This study demonstrates the important roles of E. gansuensis on nitrifier and denitrifier communities during its host grass decomposition under different P nutrient conditions, facilitating our comprehensive understanding of the ecological significance of Epichloë endophytes.

Aims

Plant health is closely associated with the rhizosphere microbial community. Predatory protists can regulate the rhizosphere microbes and thereby affect plant health. However, there is limited research on how the exogenous addition of predatory protists influences plant rhizosphere microbiome across plant growth.

Methods

Here, we isolated a predatory protist species, named Naegleria sp. QL92, from healthy tomato rhizosphere soil, which can effectively suppress bacterial wilt. We investigated the impact of predatory protist addition on the rhizosphere bacterial community across tomato growth stages in pots.

Results

We found that the predatory protist of Naegleria significantly altered the community structure and composition of the rhizosphere bacteria during the seedling, flowering and fruiting stages of tomato growth. Moreover, the relative abundances of bacterial phylum of Proteobacteria, Gemmatimonadetes, and Nitrospirae as well as majority bacterial genera, especially Pseudomonas were increased during the seedling stage after Naegleria addition. Naegleria inoculation reduced the density of the Ralstonia solanacearum pathogen, which was negatively correlated with Pseudomonas relative abundance. The addition of Naegleria also increased the connections within rhizosphere bacterial communities, resulting in a complex microbial network.

Conclusions

Overall, our study highlighted the application of predatory protists as puppet masters of rhizosphere bacterial communities with enriching plant beneficial microbes, which offer new venues to manage rhizosphere microbial communities to support healthy plant growth in sustainable agriculture.

Aims

Plant diversity loss is increasingly recognized to affect ecological functions such as primary productivity and nutrient cycling, yet how the diversity of organic materials derived from plant litter influences soil microbial processes is largely unclear.

Methods

A laboratory microcosm experiment was conducted to explore the effects of litter species diversity on soil enzyme activity and microbial community in a Mongolian pine (Pinus sylvestris var. mongolica) plantation of Northeast China in 2018. Leaf litter of Mongolian pine was decomposed with the senesced aboveground materials of three dominant understory species in all possible combinations.

Results

The decomposition of mixed-species litter showed more cases of antagonistic effects on the activities of soil acid phosphomonoesterase, N-acetyl-β-D-glucosaminidase and β-glucosidase and the amount of fungal PLFAs, and synergistic effects on soil cellulase activity, the ratio of Gram-positive to Gram-negative bacteria, and the amount of actinomycetes PLFAs. Litter species composition had significant non-additive influence on soil enzyme activities and microbial community composition. According to the results of constrained redundancy analyses, litter chemical composition was significantly correlated with soil enzyme activities and microbial community composition, while the chemical diversity and stoichiometric dissimilarity had no significant effects on soil enzyme activity.

Conclusions

Our results indicate that the non-additive decomposition effects of mixed-species litter on soil enzyme activities and microbial community composition depended primarily on litter species composition, which is partly explained by litter chemical composition rather than litter chemical diversity and stoichiometric dissimilarity. Our findings highlight the intricate legacy effects of species loss on soil microbial processes.

Background and aims

Intercropping is an effective practice for increasing crop diversity and achieving sustainable agricultural development, especially in areas with limited agricultural land. Although the nitrogen turnover and trade-off responses of plant–soil systems to intercropping have been extensively studied, quantitative information on the association between P and crop productivity is lacking. Therefore, in this study, we aimed to elucidate the effects of intercropping on plant P concentration, uptake, and use efficiency and soil P availability.

Methods

We conducted a quantitative meta-analysis using a database containing 453 comparisons from 56 peer-reviewed studies.

Results

Intercropping significantly increased the soil available P concentration and phosphatase activity by 14.68% and 11.74%, respectively, compared with monocropping. However, the effects of intercropping on other P characteristics and grain yield were not significant. Among the evaluated influencing factors, crop type (cereal or legume) had the greatest effect on soil P availability, followed by soil pH and P fertilizer input. Regression analysis revealed that plant P concentration and uptake were significantly and linearly correlated with soil available P concentration and phosphatase activity. Notably, in maize–legume intercropping systems, maize exhibited increased P concentration and uptake and increased grain yield, whereas legumes exhibited constrained growth.

Conclusion

Overall, we determined that intercropping improves soil P availability, depending on the ecological environment, nutrient management, and intercropping system. This study serves as a valuable reference for effective P fertilizer input in cereal–legume intercropping systems under different management practices.