Canadian Forest Service Publications
Root production of hybrid poplars and nitrogen mineralization improve following mounding of boreal Podzols. 2013. Bilodeau-Gauthier, S.; Paré, D.; Messier, C.; Bélanger, N. Can. J. For. Res. 43:1092-1103.
Issued by: Laurentian Forestry Centre
Catalog ID: 35190
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Successful establishment of fast-growing trees could depend on early root development and the access to belowground resources. Boreal podzolic soils present a distinctive vertical zonation wherein nutrient availability and the presence of plant roots decline sharply with depth. Mechanical soil preparation that modifies the vertical arrangement of soil layers creates microsites with improved physical conditions but potentially lower nutrient availability. We compared the vertical distribution of proximal roots of young hybrid poplars in soil layers of mechanically prepared (by mounding) and unprepared microsites. We also evaluated the relationship between root distribution and the availability and mineralization of soil nitrogen. Hybrid poplar roots were less abundant in the surface organic layer of unprepared soils, whereas they proliferated in the buried organic layer of mounds. Total mineralized N was highest in the upper mineral layer of mounds, whereas it was similar between the buried organic layer of mounds and the unprepared organic layer. Altogether, mounding created conditions conducive to greater soil N mineralization and greater production and vertical distribution of proximal roots. This possibly provided access to a larger soil volume and greater soil nutrient pools, which may explain the success of mounding in terms of aboveground growth of hybrid poplars.
Plain Language Summary
The successful establishment of rapid growth tree plantations depends on several factors, including rapid root development and access to soil nutrients. Podzols, a type of boreal forest soil, are made up of several layers. Of course, the supply of nutrients and the presence of roots in these layers rapidly decrease as the depth from the soil surface increases.
The ground preparation work carried out prior to planting changes the vertical arrangement of soil layers and creates microsites offering better physical conditions. In this study, researchers compared the vertical distribution of the roots of young hybrid poplars in mechanically prepared soil (creation of mounds) and in unprepared soil. They also correlated the root distribution with the availability of soil nitrogen. They found that the roots were less abundant in unprepared soil. However, the roots proliferated in the organic layer and the upper mineral layer of the planting mounds. The creation of planting mounds also resulted in a greater availability of nitrogen in the mineral layer of the soil, but had no effect on the organic layer.
Access to a greater volume of soil and a bigger supply of nutrients could therefore explain the better plantation results observed when hybrid poplars are planted on sites with this type of ground preparation (mounds).