Linking Biomass Productivity to Genotype-Specific Nutrient Cycling Strategies in Mature Hybrid Poplars Planted Along an Environmental Gradient

Abstract

This study used three hybrid poplar (Populus × spp.) clones (13 years old) with different parentages planted in three abandoned farmland sites along a regional gradient of elevation and soil fertility in southern Québec (Canada). We evaluated the effects of plantation site and clone on nutrient concentrations in green foliage and leaf litter, on leaf litter mass remaining, on soil properties and on biomass yield. Green foliage and leaf litter nutrient concentrations, and litter decomposition, are under strong genetic and environmental control in hybrid poplars. Clone-specific correlation patterns between green foliage and leaf litter nutrient concentrations were observed, as well as between soil nutrient availability and foliage or leaf litter nutrient concentrations. Despite the wide variations in soil nutrient availability and elevation between sites, only the clone effect was significant on biomass yield. An increase in N and P resorption proficiency with declining soil NO 3 and P availability, observed in all clones, could explain stable yields of each clone across sites. The most productive clones (DN × M-915508 and M × B-915311) were more proficient at resorbing N, P and K, while the least productive clone (D × N-131) had the highest N, P and K concentrations in green foliage and in litter. The ability of clone M × B-915311 to maintain high litter Ca and Mg concentrations on sites with soil characterised by lower pH, lower base saturation and lower nutrient availability (NO 3 , P, Ca and Mg) may also be linked to its high and stable productivity. Differences in litter quality between clones did not yield significant differences in soil properties or in litter mass remaining after 2 years. However, short-term decay trajectories varied between clones. As litter mass remaining was strongly correlated to elevation, the plantation site significantly affected leaf litter mass remaining, which ranged from 4.5 to 35.5% between sites after 2 years.

Planting Density and Site Effects on Stem Dimensions, Stand Productivity, Biomass Partitioning, Carbon Stocks and Soil Nutrient Supply in Hybrid Poplar Plantations

“…Clone DN×M-915508 is also known to have a relatively high productivity across a wide range of environmental conditions, even on sites presenting nutrient limitations [7]. This generalist genotype was found to be highly proficient at resorbing growth limiting nutrients (N and P) from senesced leaves, especially when site fertility declined [54]. Such a nutrient cycling strategy may allow clone DN×M-915508 to cumulate aboveground biomass at similar rate in both narrower and wider spacings, despite that the supply of growth limiting nutrients (N and P) in soil tends to decline with increasingly narrow spacing on the more fertile sites (Brompton and Mégantic) (Figure 4a,b).…”

Allometric Equations for Estimating Compartment Biomass and Stem Volume in Mature Hybrid Poplars: General or Site-Specific?

“…This widely used clone has shown good productivity across a wide range of environmental conditions [45][46][47][48][49]. Each plantation had six different planting densities (plots): (1) In each plot, a total of 20 trees was initially planted and plots were separated by two buffer rows.…”

Abiotic and biotic factors controlling fine root biomass, carbon and nutrients in closed-canopy hybrid poplar stands on post-agricultural land

“…balsamifera ——Leaf litter N concentration0.681.230.830.04<0.0001Leaf litter P concentration0.0380.1310.0860.006<0.0001Leaf litter K concentration0.341.060.320.08<0.0001Leaf litter Ca concentration2.222.493.660.06<0.0001Leaf litter mass remaining after 1 yr (% of initial mass)49.635.133.83.90.02Aboveground biomass of sampled trees (kg/tree)169.197.9154.18.20.0001Aboveground woody biomass yield (t/ha/yr)7.584.588.140.570.002Mean values of soil nutrient supply rates (across three sampling periods) were used in the ANOVA. Leaf litter nutrient concentration and woody biomass yield data were collected in the same experimental design the year preceding fine root sampling (after 13 growing seasons), while leaf litter mass remaining data were collected during the year of fine root sampling (14 th growing season) 49 .…”

“…In addition, there are large variations in foliage and leaf litter chemistry between hybrid poplar genotypes from different parentages. Often, genotypes related to the Aigeiros section have higher nutrient concentrations in foliar tissues (green or senescent), than genotypes related to the balsam poplar ( Tacamahaca ) section 49,54,55 . However, such a trend was not observed for fine root nutrient concentrations 26 .…”

“…The following hypotheses were tested: (1) an inverse relationship should be observed between soil fertility and live fine root biomass; (2) a compensatory response in fine root biomass should be observed for genotype DN × M, which produces low quality and slow decaying leaf litter 49 ; (3) live fine root biomass should be higher in the spring, while dead fine root biomass should be higher in the fall; (4) the higher foliage and leaf litter nutrient concentrations of genotype D × N 49 , should be reflected in fine roots; and (5) nutrient concentrations in fine roots should be positively related to nutrient supply in the soil, and to nutrient concentrations in leaves (green foliage and leaf litter).…”