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 0–20 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 (0–20 cm) was lower in poplar than in herbaceous buffers; the reverse was observed at greater depth. Highest coarse root biomass in the 40–60 cm depth range was observed in a poplar buffer, highlighting the deep rooted nature of poplars. On average, total soil C stocks (0–60 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 0–20 cm depth range (R2 = 0.79, p < 0.001), and in the whole soil profile (0–60 cm) (R2 = 0.65, p < 0.01), highlight the central role of fine root biomass in maintaining or increasing soil C stocks.
Highlights
Food security and global sustainability is threatened by the ongoing climate change, which may impact soil erosion processes, crop productivity and soil quality (Lal et al 2011)
Fine root biomass in surface soil (0–20 cm) tends to be lower in poplar buffers than in herbaceous buffers, while the reverse is observed at greater depth (Figure 2)
These relationships suggest that below 30 cm of depth (Figure 3), fine root biomass becomes greater in poplar buffers than in herbaceous buffers, while the reverse is observed above this depth
Summary
Food security and global sustainability is threatened by the ongoing climate change, which may impact soil erosion processes, crop productivity and soil quality (Lal et al 2011). Stump and large root biomass ranging from 12.3 to 29.6 t ha-1 and, small and fine root biomass ranging from 6.6 to 11 t ha-1 have been observed for different clones in a closely spaced 4 year-old plantation (10 000 stems ha-1) (Heilman et al 1994). In multispecies riparian buffer combining hybrid poplars and cool-season grass, a total root biomass of 14.3 t ha-1 was observed after 7 years (Tufekcioglu et al 2003). These studies suggest that poplar belowground biomass accumulation can be relatively high, but extremely variable, depending on the poplar system management and design, and depending on local ecological conditions. There is a need to assess belowground biomass in hybrid poplar riparian buffers across different sites in order to refine C stocks estimates in agroforestry systems
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