Rhizobox Approach Research Articles

Pioneer and fibrous root seasonal dynamics of Vitis vinifera L. are affected by biochar application to a low fertility soil: A rhizobox approach

The present work analyzes the impact of biochar-induced modification of soil physico-chemical properties on intra-annual growth dynamics of pioneer and fibrous grapevine roots. A scanner inserted into a buried rhizobox with a transparent side facing the plant root system was used to acquire images of pioneer and fibrous roots of control and biochar-treated plants throughout the vegetative season. Images were analyzed with ImageJ software to measure root traits. Biochar treatment increased soil pH, nutrient concentration, and water content during the driest and warmest period, while bulk density was reduced. Analysis of both pioneer and fibrous root traits highlighted a single peak of growth during the vegetative season. Pioneer roots were thicker and grew faster than fibrous roots, which were longer and more numerous. Amelioration of physico-chemical properties of biochar-amended soil stimulated an earlier root lengthening, and a higher root number at the onset of the season, which resulted in a greater canopy development compared to control plants. Later, in summer, as a consequence of the higher water content of biochar-treated soil, plants modified their root architecture, lowering the number of fibrous roots probably because of the reduced need to exploit soil for water and nutrient uptake.

Diversity of NC10 bacteria associated with sediments of submerged Potamogeton crispus (Alismatales: Potmogetonaceae).

BackgroundThe nitrite-dependent anaerobic methane oxidation (N-DAMO) pathway, which plays an important role in carbon and nitrogen cycling in aquatic ecosystems, is mediated by “Candidatus Methylomirabilis oxyfera” (M. oxyfera) of the NC10 phylum. M. oxyfera-like bacteria are widespread in nature, however, the presence, spatial heterogeneity and genetic diversity of M. oxyfera in the rhizosphere of aquatic plants has not been widely reported.MethodIn order to simulate the rhizosphere microenvironment of submerged plants, Potamogeton crispus was cultivated using the rhizobox approach. Sediments from three compartments of the rhizobox: root (R), near-rhizosphere (including five sub-compartments of one mm width, N1–N5) and non-rhizosphere (>5 mm, Non), were sampled. The 16S rRNA gene library was used to investigate the diversity of M. oxyfera-like bacteria in these sediments.ResultsMethylomirabilis oxyfera-like bacteria were found in all three sections, with all 16S rRNA gene sequences belonging to 16 operational taxonomic units (OTUs). A maximum of six OTUs was found in the N1 sub-compartment of the near-rhizosphere compartment and a minimum of four in the root compartment (R) and N5 near-rhizosphere sub-compartment. Indices of bacterial community diversity (Shannon) and richness (Chao1) were 0.73–1.16 and 4–9, respectively. Phylogenetic analysis showed that OTU1-11 were classified into group b, while OTU12 was in a new cluster of NC10.DiscussionOur results confirmed the existence of M. oxyfera-like bacteria in the rhizosphere microenvironment of the submerged plant P. crispus. Group b of M. oxyfera-like bacteria was the dominant group in this study as opposed to previous findings that both group a and b coexist in most other environments. Our results indicate that understanding the ecophysiology of M. oxyfera-like bacteria group b may help to explain their existence in the rhizosphere sediment of aquatic plant.

Protease encoding microbial communities and protease activity of the rhizosphere and bulk soils of two maize lines with different N uptake efficiency

This study was carried out to understand the interplay of plant Nitrogen Utilizing Efficiency (NUE) with protease activity and microbial proteolytic community composition in the rhizosphere and bulk soils. Protease activity, diversity and abundance of protease genes (using DGGE and qPCR respectively of two key bacterial protease encoding genes: alkaline metallo-peptidase (apr) and neutral-metallopeptidases (npr)) were monitored in both rhizosphere and bulk soils from two maize in-bred lines L05 and T250 with higher and lower NUE respectively, using a rhizobox approach. Illumina sequencing was employed to assess the diversity of proteolytic communities encoding for the above-mentioned protease genes. Our results show higher enzyme activity, higher abundance and diversity of proteolytic genes in L05 maize rhizosphere, with higher NUE than in T250 maize rhizosphere.

Nitrogen transformations in the rhizosphere of different tree types in a seasonally flooded soil

Plant roots strongly influence C and N availability in the rhizosphere via rhizodeposition and uptake of nutrients. An in situ rhizobox approach was used to compare rhizosphere effects of different tree species and clones on N cycling under seasonally flooded soil. We examined N mineralization and nitrification rates, inorganic N, and microbial biomass C (MBC) and N (MBN) in rhizosphere and bulk soils of three poplar clones, alder, and willow plantations in southeast China. Significant differences in soil pH, total N, soil organic C, MBC, MBN, and MBC/MBN were found between bulk and rhizosphere soils except alder. Compared to bulk soil, the net N mineralization and nitrification rates in rhizosphere soil across all tree species and clones increased by 124–228% and 108–216%, respectively. However, NO<sub>3</sub><sup>–</sup>-N was depleted in the rhizosphere soil mainly owing to the root uptake and rhizosphere microbial immobilization. The magnitude of rhizosphere effects on N transformations was considerably different among the tree species studied. Of the tested ones, alder had the greatest rhizosphere effect on N transformation, indicating different capacities of tree species to facilitate N turnover in the rhizosphere.

Seasonal and clonal variations of microbial biomass and processes in the rhizosphere of poplar plantations

Plant nutrient acquisition and dynamics are closely coupled with microbial activities and rhizosphere processes. This study was conducted using an in situ rhizobox approach and incubation experiments, with the primary goal to elucidate rhizosphere effects of different poplar clones at different sampling seasons on soil microbial processes and biomass content. Evaluations included pH, inorganic N (NO3−-N and NH4+-N), microbial biomass carbon (MBC) and nitrogen (MBN), enzyme activities related to N cycling, as well as net N mineralization and nitrification rates in rhizosphere soils of three poplar clones (Nanlin-895, NL-80351 and 75) at three periods of the year. The magnitude of rhizosphere effects varied with time and poplar genotypes. Significant variations in microbial biomass content and enzyme activities were observed among the tested three poplar clones; and microbial biomass content was positively correlated with soil NO3−-N concentration. The obtained results suggested that genotypes (clones or cultivars) had profound impacts on the rhizosphere microbial communities; and NO3−-N concentration rather than total inorganic N was the primary determinant of seasonal dynamics of microbial biomass and processes in the rhizosphere soils of poplar trees in a seasonally flooded soil.

Changes of microbial properties in (near-) rhizosphere soils after phytoextraction by Sedum alfredii H: A rhizobox approach with an artificial Cd-contaminated soil

The ultimate goal of soil remediation is to restore soil health. Soil microbial parameters are considered to be effective indicators of soil health. The aim of this study was to determine the effects of phytoextraction on microbial properties through the measurement of soil microbial biomass carbon, soil basal respiration and enzyme activities. For this purpose, a pre-stratified rhizobox experiment was conducted with the Cd hyperaccumulator Sedum alfredii H. for phytoextraction Cd from an artificial contaminated soil (15.81mgkg−1) under greenhouse conditions. The plant and soil samples were collected after growing the plant for three and six months with three replications. The results indicated that the ecotype of S. alfredii H. originating from an ancient silver mining site was a Cd-hyperaccumulator as it showed high tolerance to Cd stress, the shoot Cd concentration were as high as 922.6mgkg−1 and 581.9mgkg−1 at the two samplings, and it also showed high BF (58.4 and 36.8 after 3 and 6 months growth), and TF (5.8 and 5.1 after 3 and 6 months growth). The amounts of Cd accumulated in the shoots of S. alfredii reached to an average of 1206μgplant−1 after 6 months growth. Basal respiration, invertase and acid phosphatase activities of the rhizosphere soil separated by the shaking method were significantly higher (P<0.01) than that of the near-rhizosphere soil and the unplanted soil after 3 months growth, so were microbial biomass carbon, urease, invertase and acid phosphatase activities of the rhizosphere soil after 6 months growth. Acid phosphatase activity of the 0–2mm sub-layer rhizosphere soil collected by the pre-stratified method after 3 months growth was significantly higher (P<0.05) than that of other sub-layer rhizosphere soils and bulk soil, and so were microbial biomass carbon, basal respiration, urease, invertase and acid phosphatase activities of the 0–2mm sub-layer rhizosphere soil after 6 months growth. It was concluded that phytoextraction by S. alfredii could improve soil microbial properties, especially in rhizosphere, and this plant poses a great potential for the remediation of Cd contaminated soil.

Tree species composition influences enzyme activities and microbial biomass in the rhizosphere: a rhizobox approach.

Monoculture causes nutrient losses and leads to declines in soil fertility and biomass production over successive cultivation. The rhizosphere, a zone of usually high microbial activities and clearly distinct from bulk soil, is defined as the volume of soil around living roots and influenced by root activities. Here we investigated enzyme activities and microbial biomass in the rhizosphere under different tree compositions. Six treatments with poplar, willow, and alder mono- or mixed seedlings were grown in rhizoboxes. Enzyme activities associated with nitrogen cycling and microbial biomass were measured in all rhizosphere and bulk soils. Both enzyme activities and microbial biomass in the rhizosphere differed significantly tree compositions. Microbial biomass contents were more sensitive to the changes of the rhizosphere environment than enzyme activities. Tree species coexistence did not consistently increase tested enzyme activities and microbial biomass, but varied depending on the complementarities of species traits. In general, impacts of tree species and coexistence were more pronounced on microbial composition than total biomass, evidenced by differences in microbial biomass C/N ratios stratified across the rhizosphere soils. Compared to poplar clone monoculture, other tree species addition obviously increased rhizosphere urease activity, but greatly reduced rhizosphere L-asparaginase activity. Poplar growth was enhanced only when coexisted with alder. Our results suggested that a highly productive or keystone plant species in a community had greater influence over soil functions than the contribution of diversity.

Variation in rhizosphere soil microbial index of tree species on seasonal flooding land: An in situ rhizobox approach

Microbial activity of the tree rhizosphere provides important information relating to the selection of tree species for afforestation of the degraded land. This study was conducted using an in situ rhizobox approach, with the aims of establishing a viable technique for sampling desired rhizosphere soil and assessing the feasibility of rhizosphere soil microbial index (RSMI) as an indicator to screen tree species for the seasonal flood land of Yantse River, China. The characteristics examined include soil pH, soil organic carbon (SOC), soil total nitrogen (TN), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial quotients, enzyme activities (urease, proteinase, asparaginase and catalase) and relative growth rate of tree species, while the RSMI was calculated by principal component analysis. The results indicated that microbial properties of rhizosphere soil were significantly affected by trees species planted under seasonal flooding lands. Microbial biomass and its activity in the rhizosphere have a great ecological significance, and MBC, pH, MBN/TN, MBC/MBN and MBC/SOC could be most important properties for appraising rhizosphere soil quality. The RSMIs calculated by integrating microbial properties were different from various sampling positions of rhizosphere soil, and a significant difference in RSMI was observed among the five tree species for all sampling positions. The in situ rhizobox approach taken in this study can be used as an available method for sampling rhizosphere soil, and sampling the soil at 0–4mm distance from the root mats as rhizosphere soil is reliable. Results from this study suggested that tree species having an RSMI>0.5 would be used for afforestation at the seasonal flooding lands of Yangtse River.

Localisation of nitrate in the rhizosphere of biochar-amended soils

A wheat seedling rhizobox approach was used to differentiate between the rhizosphere and non-rhizosphere (bulk) soil amended with low and high rates of biochar (20 and 60 t ha −1 vs. control). Nitrate (NO 3 −) was added as the main nitrogen (N) source because emerging biochar research points to reduced NO 3 − loss through leaching and gaseous loss as nitrous oxide. The rhizosphere under the different treatments were distinct ( P = 0.021), with greater soil-NO 3 − and biochar-NO 3 − contents in the high biochar treatment. Biochar addition increased wheat root length ratio ( P = 0.053) and lowered root N uptake ( P = 0.017), yet plant biomass and N content were similar between treatments. The results indicate localisation of NO 3 − within the rhizosphere of biochar-amended soils which has implications for NO 3 − loss and improved nitrogen use efficiency.

Root allocation in metal-rich patch by Thlaspi caerulescens from normal and metalliferous soil—new insights into the rhizobox approach

We compared root responses to spatial heterogeneity of Zn and Ni in Thlaspi caerulescens J. and C. Presl from normal (NM plants) and metalliferous soil (M plants). We investigated whether the strong metal accumulation capacity of NM plants (compared to M plants) was related to a greater capacity of roots to grow towards metal-enriched soil compartments. Two similar experiments were conducted in summer (slow growth) and spring (high growth), respectively. Our study is the first to show that NM plants of T. caerulescens have the ability to allocate more roots in the Zn-enriched compartment of soil. However, the positive response to Zn by roots of NM plants does not explain their higher Zn accumulation capacity as M plants express a similar level of root allocation in Zn-enriched compartment of soil. In M plants, root response to the Zn-rich compartment appears to be more susceptible to variations in growth conditions. Preferential root allocation in Ni-enriched compartment was consistently found in M plants only, suggesting that Ni supply is critical in their native metalliferous soil. Our study also illustrates bias in the interpretation of root allocation studies using two dimensional boxes, as interferences between root response to metal and root chirality have been highlighted.

Nutrient distribution across wheat rhizosphere with oxamide and ammonium sulfate as N source

Analysis of the behavior of slow releasing nitrogen fertilizers in the rhizosphere soil of agricultural crops is essential for their effective use. This work presents a comparative study of the effects of oxamide and ammonium sulfate as different N sources on the relative mobility of some nutritionally important anions and cations and their relevance to plant growth, root development, and pH distribution pattern in the rhizosphere of wheat (Triticum aestivum cv. Nourin No. 61). Experiment was conducted on a Japanese upland alluvial soil through a rhizobox approach. In the central compartment (CC) of the oxamide and ammonium sulfate treated rhizoboxes, four uncontaminated and homogeneous wheat seedlings germinated on a sterile petridish were grown for nearly two months. During the growing period plant height was recorded weekly. After the growing period, rhizoboxes were dismantled for soil sampling and photography of roots. Soil samples from each compartment of the two rhizoboxes were used for the analysis of CI-, N03 -, SO4 2-, Ca2+, Mg2+, K+, NH4 +-N, N03 --N and measurement of pH. Compared with ammonium sulfate, the distribution of anions and cations from the distant compartments to the central ones over a distance of 3–5 mm along with a better plant growth, high rooting density, and high pH confirmed that oxamide was an efficient nitrogen fertilizer.

Ionization in the upper atmosphere of the earth

This study was carried out to understand the interplay of plant Nitrogen Utilizing Efficiency (NUE) with protease activity and microbial proteolytic community composition in the rhizosphere and bulk soils. Protease activity, diversity and abundance of protease genes (using DGGE and qPCR respectively of two key bacterial protease encoding genes: alkaline metallo-peptidase (apr) and neutral-metallopeptidases (npr)) were monitored in both rhizosphere and bulk soils from two maize in-bred lines L05 and T250 with higher and lower NUE respectively, using a rhizobox approach. Illumina sequencing was employed to assess the diversity of proteolytic communities encoding for the above-mentioned protease genes. Our results show higher enzyme activity, higher abundance and diversity of proteolytic genes in L05 maize rhizosphere, with higher NUE than in T250 maize rhizosphere.