Root biomass and soil carbon distribution in hybrid poplar riparian buffers, herbaceous riparian buffers and natural riparian woodlots on farmland
Fortier, J.;B. Truax;D. Gagnon;F. Lambert. 2013.
Abstract
The objectives of this study were to compare coarse root (diameter > 2 mm) and fine root (diameter < 2 mm)
biomass, as well as distribution of soil carbon stocks in 3 types of riparian land uses across 4 sites located in
farmland of southern Québec, Canada: (1) hybrid poplar buffers (9th growing season); (2) herbaceous buffers; (3)
natural woodlots (varying in tree species and age). For all land uses most of the root biomass was within the
0%u201320 cm depth range. Total coarse root biomass, to a 60 cm depth, ranged from 8.8-73.7 t/ha in woodlots, 0.6-
1.3 t/ha in herbaceous buffers, and 9.2-27.3 t/ha in poplars. Total fine root biomass ranged from 2.68-8.64 t/ha in
woodlots, 2.60-3.29 t/ha in herbaceous buffers, and 1.86-2.62 t/ha in poplars. Total root biomass was similar or
higher in poplar buffers compared to a 27 year-old grey birch forest. This indicates that poplar buffers accelerated
riparian soil colonisation by roots compared to natural secondary succession. Generally, fine root biomass in the
surface soil (0%u201320 cm) was lower in poplar than in herbaceous buffers; the reverse was observed at greater depth.
Highest coarse root biomass in the 40%u201360 cm depth range was observed in a poplar buffer, highlighting the deep
rooted nature of poplars. On average, total soil C stocks (0%u201360 cm) were greater in woodlots than in riparian buffers.
On most sites, soil C stocks tended to be lower in poplar buffers compared to adjacent herbaceous buffers,
especially in surface soil, probably because of lower fine root biomass in poplar buffers. Across all sites and land
uses, highest soil C stocks at the different soil depths were found in the soil layers of woodlots that also had the
greatest fine root biomass. Strong positive linear relationships between fine root biomass and soil C stocks in the
0%u201320 cm depth range (R2 = 0.79, p < 0.001), and in the whole soil profile (0%u201360 cm) (R2 = 0.65, p < 0.01), highlight the
central role of fine root biomass in maintaining or increasing soil C stocks.
Key Words
Agroforestry; Afforestation; Agriculture; Land use; Coarse roots; Fine roots; Vertical distribution
