Fig. 2. Responses of plants to nZnOin a 20-day exposure. (a) Number of the first-, and the second-order lateral roots (EC50, 1st- order=237 mg/L, EC50, 2nd-order=210mg/L); (b) stemlength
(EC50=305mg/L); (c) average surface area per leaf (EC50=420mg/L); (d) volumeof nutrient solution uptake (EC50=127mg/L). Arrows (↓) indicate the value of EC50. Asterisks indicate
the degree of significant difference from the control (⁎⁎: p b 0.01 and ⁎⁎⁎: p b 0.001).