Tree species diversity increases fine root productivity through increased soil volume filling

Abstract

Summary 1.Although fine roots (< 2 mm in diameter) account for a major share of the production of terrestrial ecosystems, diversity effects on fine root productivity and their mechanisms remain unclear. 2. We hypothesized that: (i) fine root productivity increases with tree species diversity, (ii) higher fine root productivity is a result of greater soil volume filling due to species-specific patterns of root placement and proliferation, and (iii) differences in fine root productivity and soil volume filling associated with tree species diversity are more pronounced in summer when plants are physiologically active and demand for water and nutrients is at its greatest. 3. We investigated the effects of tree species diversity on fine root productivity and soil volume filling of boreal forest stands that have grown naturally for 85 years on similar sites. 4. Annual fine root production was 19-83% higher in evenly mixed-than single-species-dominated stands, and increased with tree species evenness, but not tree species richness. Fine root biomass was higher in evenly mixed-than single-species-dominated stands in summer months, but not in spring or fall. Higher fine root productivity in evenly mixed-than single-species-dominated stands was realized by filling more soil volume horizontally and vertically in the forest floor in the mixtures of deep-and shallow-rooted species vs. the deeper mineral soil in the mixtures of deeprooted species. 5. Synthesis. Our results provide some of the first direct evidence for below-ground species complementarity in heterogeneous natural forests, by demonstrating that tree species evenness increases fine root productivity by filling/exploiting the soil environment more completely in space and time, driven by differences in the inherent rooting traits of the component species and variations of root growth within species.

Forest Carbon Sequestration: The Impact of Forest Management

“…Carbon content per unit of biomass may also vary, depending on whether stands are mixed or monospecific. Additionally, belowground biomass is difficult to estimate and often excluded from estimates, and niche complementarity between species can also occur belowground (Brassard et al, 2013). These issues underscore the need for more research focusing on carbon storage in mixed-species forests, in order to determine whether they fix more CO 2 than monospecific forests.…”

Soil labile organic carbon and carbon-cycle enzyme activities under different thinning intensities in Chinese fir plantations

“…However, the SOC concentrations were lower in the control than in the thinned sites in the autumn. Thinning may have allowed for the establishment of shrubs and graminoids with higher decomposition rates than the conifers in the summer (Table 1, S1), which allowed the thinned sites to compensate for the reduced total carbon inputs through an increased proportion of more rapidly decomposable leaf litter and root litter during the autumn (Chen and Shrestha, 2012;Brassard et al, 2013). The SOC differed significantly only over the four sampling dates in the upper soil, and the warmer months (July and October) had higher SOC values than January and April.…”

Drivers of nitrogen leaching from organic layers in Central European beech forests

“…Decreased N release during decomposition seems unlikely because several studies on the relationship between plant diversity and organic matter turnover reported no or a positive e ect of plant diversity on N release (e.g., Blair et al 1990;Wardle et al 1997;Fornara et al 2009;Rosenkranz et al 2012). Lower dissolved N uxes in more diverse forests could instead have resulted from increased N demand of the vegetation as related to the greater productivity of more diverse forests (Morin et al 2011;Paquette and Messier 2011;Brassard et al 2013). However, forest biomass consists largely of trees which had an opposing effect in our study (Fig.…”

“…Spatial niche complementarity would most likely be related to rooting traits. In boreal forests, neroot productivity increased with tree species evenness by more horizontal and vertical space lling in the organic layer in mixtures of deep-rooting and shallowrooting species (Brassard et al 2013). Additional functional niche partitioning would be related to the preference and ability of various plant species and their mycorrhizal associations to use di erent N forms.…”

“…While this implies a relationship with functional diversity, no study yet tested the in uence of plant diversity in the canopy and the understory on N uxes in organic layers. This is surprising given the positive relationship of plant diversity to N use e ciency in grasslands (Tilman et al 1996;Kahmen et al 2006) and to primary productivity and canopy N uptake in forests (Morin et al 2011;Brassard et al 2013;Schwarz et al 2014). …”