Root-system characteristics of plantation-grown Populus tomentosa adapted to seasonal fluctuation in the groundwater table

Abstract

Populus tomentosa developed a deep root system, wide-spreading and dense lateral roots, and structural roots exploring both deep and shallow soil resources to adapt to intense seasonal groundwater table fluctuation. To elucidate the root-system characteristics of P. tomentosa adapting to seasonal fluctuation in the groundwater table, coarse-root architecture and fine-root morphology were investigated in a P. tomentosa plantation under groundwater table fluctuation with an average annual amplitude of 363 cm. Three stands of different ages and planting densities were selected for root sampling, comprising 34 structural roots for assessment of root architecture, ten stumps for measurement of rooting depth and spread distance, and 2106 soil blocks (to 150 cm depth) for analysis of fine-root distribution. The average rooting depth of these stands was 200 cm (maximum root depth 270 cm), indicating that P. tomentosa can be phreatophytic. In 4- and 7-year-old stands, the average lateral root spread distances were 437 and 535 cm, respectively. About 23% of the root area density was distributed in the top-most 20 cm soil, which might help P. tomentosa to intercept rainwater efficiently and absorb shallow soil water resources when the uptake function of deep roots was inhibited by flooding. Some horizontal, inclined, and vertical structural roots were capable of exploring both deep and shallow soil layers. In conclusion, a deep root system, wide-spreading and dense lateral roots in shallow soil layers, and development of some structural roots exploring both deep and shallow soil resources may be the three coordinate rooting adaption strategies that permit P. tomentosa to thrive in sites subject to large fluctuation in the groundwater table.