Measurements
Five plants were randomly selected from each treatment. To scan root traits of every plants, the roots were severed from the shoot at the root collar and then were gently washed with running tap water over a sieve with a mesh size of 0.2 mm. Each root sample was scanned in water with a flatbed scanner (Epson Perfection V700 Photo, Seiko Epson Corporation, Nagano, Japan). Subsequently, the images were analyzed using the software winRHIZO (Regent Instruments Canada Inc., Quebec, QC, Canada). Root traits analyzed were total root length (calculated using a one pixel thinned image and multiplying the number of pixels by pixel size), root surface area (calculated by determining the root diameter and length), root volume (calculated using the root surface area and length), an root tips (Wang and Zhang 2009). After scanning, root samples were oven-dried at 65°C to constant weights and weighed to determine root dry biomass. Root tissue density (RTD) was determined by the ratio of root dry biomass to root volume. Specific root length (SRL) was estimated by the ratio of total root length to root dry biomass.