A Sampling Method for Measurement of Large Root Systems with Scanner‐Based Image Analysis

Abstract

Measurement of relatively small (<100 m total length, <6 g fresh wt.) root systems has been simplified by image analysis, but measuring larger root systems remains time‐consuming and inaccurate. Reliability of root estimation can be improved through identification of effective sampling methods. We devised a system for the collection of homogeneous root subsamples by air‐stirring in water. We optimized the subsampling technique and used a scanner‐based image analysis system to measure total root length, mean root diameter, and root surface area of three maize (Zea mays L.) genotypes with contrasting root morphologies: leafy reduced stature (LRS), leafy normal stature (LNS), and Pioneer 3905 (P3905), a commercial hybrid. Root length was determined for 957 subsamples. Confidence intervals were generated by software using the bootstrap resampling approach for optimizing sample size. Confidence intervals for mean estimates of each sample size were defined by ordering the evaluation function values from the smallest to the largest in a set of 5000 iterations. The lower and upper bounds of confidence intervals were also calculated using the standard procedure. This system allowed collection of homogeneous subsamples. Calculations showed that ∼10% of total root volume should be analyzed for estimation of the entire root system to be accurate within 10%. Although unreplicated, these data suggest that maize genotypes with the leafy trait have greater root lengths (1.75 km for LRS, 2.37 km for LNS, and 0.49 km for conventional commercial hybrid P3905) and a greater proportion of fine roots than the nonleafy type.

Sample size for measurement of root traits on common bean by image analysis

“…Thereby, scanning an entire root system of a single 45-day-old bean plant requires 4 hours and 53 minutes (±58 minutes), being a very laborious task that hampers its execution for a large number of plants. The amount of root placed on the sheet affects the accuracy of the estimates, since too many roots increase overlapping and crossing over (Costa et al, 2000), and depending on the size of sample, spreading roots can be very time-consuming (Richner et al, 2000). Bean root samples in the mounted sheets had mean dry mass of 60±11 mg and length of 7.4±1.1 m. Studying a digital line-intercept method, Farrell et al (1993) observed less variability on wheat (Triticum aestivum L.) root samples with total length varying from 2 to 4 m.…”

“…It must be noticed that a single plant was grown per pot, and each root sample corresponded indeed to one mounted acetate sheet. Studies with maize plants indicated that samples with 10% (Costa et al, 2000) or 20% (Rossiello et al, 1995) of total root volume produced satisfactory estimation of root length. The results of the present work indicate root samples of almost 15% of total root mass for estimating root traits of common bean.…”

“…The problem of large variation between replicate root samples is widely known, often requiring too many samples to obtain an accurate estimate of the mean . Computer electronic image analysis have made root examination faster and more accurate, and the desktop scanners available nowadays provide high quality optical resolution for recording root images, but root measurement is still time-consuming due to the great root length that can be found in a single plant (Costa et al, 2000;Richner et al, 2000).…”

“…For maize (Zea mays L.) plants, samples with 20% of total root volume produced satisfactory estimation of total root length by the photoelectric method (Rossiello et al, 1995), whereas 10% of total root volume can be sampled for estimation of the entire root system by image analysis with an accuracy within 10% (Costa et al, 2000). However, root morphology of dicotyledon plants is usually more complex than that of monocotyledons, many dicots possessing a taproot and basal roots from which lateral roots arise, and sometimes adventitious roots arising from nonroot tissues (O'Toole & Bland, 1987).…”

Effects of salt stress on eco-physiological characteristics in Robinia pseudoacacia based on salt-soil rhizosphere

“…Root morphology determines the ability of the plant to acquire soil resources (Costa et al, 2000;Shi et al, 2015). R. pseudoacacia seedlings decreased TRL and TRSA, which suggested that the ability of ion and water uptake decreased (Wang et al, 2006).…”