Quantification of belowground plant response via rhizotron root image analysis is difficult and time-consuming, yet a plant's root response is of great interest to many researchers. Here, we present an automated, time efficient method for examining digital rhizotron images. A total of 285 digital images (218 mm by 300 mm) were collected using a flatbed scanner from 16 rhizotron boxes from an experiment designed to evaluate the root response of Dalmatian toadflax, Linaria dalmatica (L.) Miller to herbivory by the Dalmatian toadflax stem mining weevil, Mecinus janthinus Germar, a widely used biological control agent. Images were quantified for root length and area using two methods: manually digitizing images using Root Measurement System (RMS) software, and semi-automated analysis using Feature Analyst^TM, an extension for a geographic information system. Feature Analyst length and area values were highly positively correlated with RMS area values, but were not correlated with RMS length measurements. The semi-automated Feature Analyst approach required one-eighth of the time required to analyze images using the manual RMS method. Feature Analyst for digital image analysis warrants more investigation, but appears to be a promising method for quantifying belowground plant characteristics.

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To investigate the environmental regulation of root function, xylem sap was annually collected from Populus nigra and the proteins in the sap were analyzed. A 25 kDa xylem sap protein (XSP25) was found to be most abundant in the xylem sap in winter and mass spectrometry analyses showed its high similarity to abscisic acid (ABA)-inducible basic secretory protein reported in tobacco BY-2 cells. By utilizing the information of whole genome sequence of Populus, PmXSP25 was cloned from Populus maximowiczii, naturally growing poplar in Japan. The expression of PmXSP25 was abundant in root at December and February and strongly enhanced by ABA application to the autumn root. We suggest that dormancy- inducing short day length and low temperature promote the synthesis of XSP25 in root, possibly via ABA, as an adaptation to the winter environment.

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Deciduous trees show annual periodicity in shoot growth and development, but such periodicity is not well investigated in roots. To clarify the seasonal fluctuation in root functions, xylem sap from Populus nigra branches was analyzed for 2 years. Various xylem sap components including calcium, potassium, glucose, and proteins showed seasonal fluctuations with peaks from winter to spring. Abscisic acid (ABA) was the most abundant hormone in the xylem sap throughout all seasons and showed two peaks from late autumn to spring. We hypothesize that low temperature in winter promotes metal loading into the xylem sap and the synthesis of proteins and sugars in roots as an adaptation to the winter environment and to prepare for spring bud burst.

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In the study, the influence of stand density on quantitative and morphological parameters of fine roots with the diameter less than 2 mm was analysed. The results confirmed the differences of the fine root distributions and the total fine root mass between stands with different density. The Norway spruce stand with lower stem density has a lower overall fine root mass but, at the same time, a higher fine root mass regarding the single tree. In the litter (Ol, Of-horizons), the fine roots are present only in the plot with higher density. The cumulative proportion of fine root biomass in the layer 0-10 cm reaches 67% in the plot with lower density and 78% in the plot with higher density. In the lower density plot, a lower proportion of fine roots in the diameter class under 0.25 mm was found in all analysed parameters. Specific root length, root surface area and root tissue density reflect the different diameter structure of fine roots in the surveyed plots. We suppose the stand density significantly affects the fine root system, especially by the change of moisture regime in the litter and in the upper parts of the A-horizon. Despite the high fine root dynamics of single trees, the Norway spruce stand with the lower stem density is not able to effectively utilize the entire soil space.

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Because windbreaks are planted for sustainable agriculture but may lower crop yields near them due to competition, suitable competition mitigation methods must be applied at the windbreak-crop interface to increase crop yields. Effective underground competition management requires information on important root variables such as preferential root growth direction and root length density (RLD, root length per unit volume of soil). This study examined root isotropy (i.e., uniformity in all directions) in windbreak- grown cadaghi (Corymbia torelliana) trees in south Florida and developed an empirical relationship between RLD and number of roots (N) per unit of surface of soil exiting the trench face. Numbers of roots exiting the frontal face parallel to the windbreak (N_X), vertical face perpendicular to the frontal face (N_Y), and basal horizontal face (N_Z) of 10 x 10 x 10 cm soil cubes were counted. Cadaghi roots were anisotropic and had horizontal growth preference. Average root numbers were ranked N_X>N_Y>N_Z. Both N_X and the average root number exiting X, Y and Z faces of the soil cube (N_AVG) were significant variables for estimating RLD. The coefficients of N_X and N_AVG were 1.1 and 3.1. These results should be helpful to manage underground competition effectively at the windbreak-crop interface to improve crop yields.

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Flooding reduces soil oxygen necessary for root growth. In some mesophytes low levels of oxygen are mitigated by the formation of aerenchyma or expansion of intercellular spaces. But root immersion in water may have effects on roots in addition to reducing oxygen levels. At temperatures >15°C Pisum sativum primary roots develop cavities in the centers of their vascular cylinders in response to saturated or flooded conditions. In the present study we compared the response of flooded pea roots to their response to hypoxia without flooding by using an innovative system that allows separation of the gas environment of a root system from that of its shoot system. Seedlings were flooded after 4 d growth and compared to seedlings in unflooded medium and to seedlings in the gas-manipulation experiment. At 25°C in slightly moist vermiculite, roots 4 d after planting were exposed to a gas mixture with 10.5% oxygen and shoots to 20.5% oxygen and compared to normoxic controls. Oxygen levels in all containers were monitored, root growth was measured, and frequency and size of vascular cavities were determined for all treatments. Under flooding and low-oxygen gas, root growth was suppressed and vascular cavity frequency was strongly enhanced compared to controls. Significant differences in root growth responses were not seen between these differing hypoxic conditions, but low-oxygen gas caused larger cavities than flooding, which suggests flooding with water may have subtle effects different than simple hypoxia.

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Macrophytes play a significant role in the functioning of hydroecosystems. Their activities include changes at the physiological and anatomical levels toward the action of various pollutants. This study was intended to reveal some features in aerenchyma formation in roots of Typha angustifolia exposed to various concentrations of nitrate nitrogen and salicylic acid. It was found that the resistance of T. angustifolia to nitrate nitrogen is mediated by redistribution of aerenchyma formation in the root system. The action of salicylic acids results in decreasing influence of nitrate nitrogen in two types of adventitious roots. Features of aerenchyma formation in the soilborne roots and aquatic ones were different.

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The editorial office of Plant Root notes the following correction on behalf of the author. The second author in one of the cited papers was incorrect in the original article. [Page 11, left column, “O′Toole and Cruz 1983”; Page 16, right column, “O′Toole JC, Cruz RT 1983”]

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Arabidopsis root growth kinetics were investigated with high temporal and spatial resolution in combination with detailed statistical analysis to resolve presence of diurnal modulation of root tip displacement. In particular, high resolution video imaging was used to monitor root-tip displacement of Arabidopsis thaliana seedlings over several days. Root growth kinetics were sampled and statistically analyzed in two different photoperiods: long day LD (16 h-8 h) and equal LD (12 h-12 h) light. Diurnal root elongation kinetics exhibited five highly reproducible phases, one of these being a maximum of root growth rate displayed 1-2 h after the light on phase. Then, during the later part of the light period, root growth rate decreased. Several hours before darkening root elongation rates started to increase, with a profound decrease immediately after darkness. Subsequent to this dark-induced reduction in root growth rate the remaining part of the night was characterized by increasing growth activity. Together, tip elongation, in Arabidopsis roots is modulated by strong diurnal rhythms that are maintained in both photoperiods used and also in continuous illumination.

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For the promotion of environment-friendly agriculture, use of organic fertilizers and green materials is increasingly attempted in rice farming. Although effects of organic fertilizers on soil bacteria in the rhizosphere can differ from those in non-rhizosphere soil, microbiological studies that specifically address the rice rhizosphere still limited. This study was undertaken to investigate the impact of organic fertilizers on soil bacteria communities through comparison of rhizosphere soils and bulk soils. Effects of soil types and seasonal change were also analyzed. Rice plants (Oryza sativa L. cv. Nipponbare) were cultivated in a lowland paddy field of Andosol soil. Applications of compost and rice bran in combination with chemical fertilizer were compared with control soil (chemical fertilizer only). Soil 16S rDNA extracted from rhizosphere soil collected using ultrasonic treatment of rice roots and from bulk soils were analyzed using PCR-denaturing gradient gel electrophoresis (DGGE). Principal component analysis based on PCR-DGGE profiles revealed clear differences in the community structures of soil bacteria between rhizosphere and bulk soils. Furthermore, rhizosphere bacterial community structures of compost and rice bran treatments were plainly different from that of control, and changed with the seasons. The organic fertilizers showed pronounced effects on bacterial communities until mid-summer, but small effects in autumn. Results of this study suggest that the rhizosphere microorganisms in paddy fields can be modified through organic fertilizer management. Moreover, effects of organic fertilizer application, soil type, and phenology on soil bacteria appear depending on interaction with the rice rhizosphere effects in paddy fields.

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