Despite its fundamental role for carbon (C) and nutrient cycling, rhizodeposition remains ‘the hidden half of the hidden half’: it is highly dynamic and rhizodeposits are rapidly incorporated into ...microorganisms, soil organic matter, and decomposed to CO2. Therefore, rhizodeposition is rarely quantified and remains the most uncertain part of the soil C cycle and of C fluxes in terrestrial ecosystems. This review synthesizes and generalizes the literature on C inputs by rhizodeposition under crops and grasslands (281 data sets). The allocation dynamics of assimilated C (after 13C‐CO2 or 14C‐CO2 labeling of plants) were quantified within shoots, shoot respiration, roots, net rhizodeposition (i.e., C remaining in soil for longer periods), root‐derived CO2, and microorganisms. Partitioning of C pools and fluxes were used to extrapolate belowground C inputs via rhizodeposition to ecosystem level. Allocation from shoots to roots reaches a maximum within the first day after C assimilation. Annual crops retained more C (45% of assimilated 13C or 14C) in shoots than grasses (34%), mainly perennials, and allocated 1.5 times less C belowground. For crops, belowground C allocation was maximal during the first 1–2 months of growth and decreased very fast thereafter. For grasses, it peaked after 2–4 months and remained very high within the second year causing much longer allocation periods. Despite higher belowground C allocation by grasses (33%) than crops (21%), its distribution between various belowground pools remains very similar. Hence, the total C allocated belowground depends on the plant species, but its further fate is species independent. This review demonstrates that C partitioning can be used in various approaches, e.g., root sampling, CO2 flux measurements, to assess rhizodeposits’ pools and fluxes at pot, plot, field and ecosystem scale and so, to close the most uncertain gap of the terrestrial C cycle.
Despite its fundamental role for carbon (C) and nutrient cycling, rhizodeposition remains “the hidden half of the hidden half”: it is highly dynamic and rhizodeposits are rapidly incorporated into microorganisms, soil organic matter, and decomposed to CO2. Therefore, rhizodeposition is rarely quantified and remains the most uncertain part of C fluxes in terrestrial ecosystems. This review synthesizes and generalizes the literature on C inputs by rhizodeposition under crops and grasslands.
The burgeoning global market for soil microbial inoculants for use in agriculture is being driven by pressure to increase sustainable crop production by managing pests and diseases without ...environmental impacts. Microbial inoculants, based predominantly on bacteria and fungi, are applied to soil as alternatives to conventional inorganic fertilizers (biofertilizers) or to carry out specific functions including biocontrol of pests and diseases (biopesticides), or for bioremediation and enhancement of soil characteristics. While some soil inoculants such as rhizobia have a long and successful history of use, others have performed inconsistently in the field and failed to live up to their promise suggested by laboratory testing. A more precise understanding of the ecology and modes of action of inoculant strains is key to optimizing their efficacy and guiding their targeted use to situations where they address key limitations to crop production. This will require greater collaboration between science disciplines, including microbiology, plant and soil science, molecular biology and agronomy. Inoculants must be produced and formulated to ensure their effective establishment in the soil and practicality of implementation alongside existing cropping practices. New approaches to strain selection and construction of beneficial microbial consortia should lead to more efficacious inoculant products. Extensive and rigorous field evaluation of inoculants under a range of soil and environmental conditions has rarely been undertaken and is urgently needed to validate emerging inoculant products and underpin successful implementation by growers, especially in a market that is largely unregulated at present.
Bacterial wilt caused by
Ralstonia solanacearum
, is one of the serious soil-borne diseases in flue-cured tobacco production areas in China. However, it was found that the occurrence of bacterial ...wilt not only varied with different cultivars but also varied with various sites even under the condition of planting the same variety. It suggests that the occurrence of bacterial wilt could be controlled by regulating soil microorganism and the growth environment. Therefore, the relationship between microorganism’s diversity in the rhizosphere and actual incidences were evaluated on the number of symptomatic plants and the functional diversity of soil microorganisms in field trials on two sites. The results showed that the incidence of bacterial wilt in the same cultivar was varied between the two experimental sites. However, the same trend was found in the number of rhizospheric microbes among the three varieties except for fungi. Also, a good relationship was found between the number of pathogens, microbial functional diversity in the rhizosphere, and actual incidences. The utilization intensity of carbohydrates, amino acids, carboxylic acids, polymers, amines, and carbon utilization of rhizospheric soil microbial community was negatively related with the occurrence of bacterial wilt while it was on the opposite for the utilization intensity of phenolic acids. The results revealed that the mechanism for resistance in flue-cured tobacco was directly associated with the number of pathogenic microorganisms in rhizosphere and the diversity of rhizospheric microbes. By improving the diversity of rhizospheric microbes, the incidence of tobacco bacterial wilt disease can be reduced.
Background and Aims
Soil microorganisms play a crucial role in promoting growth and development, nutrient absorption, and disease resistance in poplar plantations. Long-term planting decays soil ...nutrient contents and changes the microfloral structure, and pathogenic microorganisms accumulate. It is of great significance to clarify the distribution and synergistic relationships between beneficial and pathogenic microorganisms in plantation soil for solving the long-term planting obstacles of poplar plantation.
Methods
High-throughput sequencing, culture, pure bacterial identification, functional verification, and bioinformatics methods were used to explore the population and functional characteristics of the soil microorganisms in the perennial poplar forest, identify the main pathogenic and beneficial microorganisms in the soil, and investigate the synergistic relationships among the microorganisms in the system.
Results
An evaluation of soil from a perennial poplar plantation revealed the presence of many beneficial microbes, such as
Bacillus, Sphingomonas
,
Variovorax
, and
Streptomyces
, as well as pathogenic microorganisms, including
Fusarium
and
Alternaria
. Most of these microorganisms were enriched in the rhizosphere soil. The study found that phosphorus was the driving factor affecting soil microorganisms, with available phosphorus (K = 0.189) and pH value (K = 0.113) significantly affecting fungal phylogeny. Bacterial community assembly processes were deterministic (βNTI < − 2), while those of fungi were stochastic (− 1 > βNTI > − 2). The microbial network in the rhizosphere was more stable than that in the bulk soil. This study expands our knowledge of the functional microbial germplasm resources of forest plantations and provides a theoretical basis for soil remediation in perennial poplar plantations.
Summary
Fine roots, and their functional traits, influence associated rhizosphere microorganisms via root exudation and root litter quality. However, little information is known about their ...relationship with rhizosphere microbial taxa and functional guilds.
We investigated the relationships of 11 fine root traits of 20 sub‐arctic tundra meadow plant species and soil microbial community composition, using phospholipid fatty acids (PLFAs) and high‐throughput sequencing. We primarily focused on the root economics spectrum, as it provides a useful framework to examine plant strategies by integrating the co‐ordination of belowground root traits along a resource acquisition–conservation trade‐off axis.
We found that the chemical axis of the fine root economics spectrum was positively related to fungal to bacterial ratios, but negatively to Gram‐positive to Gram‐negative bacterial ratios. However, this spectrum was unrelated to the relative abundance of functional guilds of soil fungi. Nevertheless, the relative abundance of arbuscular mycorrhizal fungi was positively correlated to root carbon content, but negatively to the numbers of root forks per root length.
Our results suggest that the fine root economics spectrum is important for predicting broader groups of soil microorganisms (i.e. fungi and bacteria), while individual root traits may be more important for predicting soil microbial taxa and functional guilds.
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