Effect of tree mixtures and water availability on belowground complementarity of fine roots of birch and pine planted on sandy podzol

Abstract

Aims We investigated whether tree species growing in mixtures and under different water supply would segregate their fine roots vertically, produce more fine roots overall, or only in specific soil layers. Methods We examined the biomass, morphology, and distribution of fine roots down to 90 cm (forest floor, 0-5, 5-15, 15-30, 30-60, 60-90 cm) in pure and mixed stands of 10-year-old birch and pine trees, planted on a sandy podzol with discontinuous hardpan and seasonal high water table, following a randomized block design with four blocks receiving irrigation and four blocks left unirrigated during summer. Results Our results did not show any vertical root segregation between birch and pine in mixed plots. None of the species overyielded belowground throughout, but pine developed more roots in the top soil layer under irrigation. Both species had shallower fine root distributions in wet conditions, especially birch that was more plastic than pine in response to irrigation. Conclusions Both species followed similar ecological strategies, occupying and competing for the same layers of the soil profile, under both control and irrigated conditions. However, the greater allocation of pine roots at the top soil horizons under irrigated conditions suggests locally favourable niches can lead to depthspecific asymmetric competition. This sheds new light on vertical niche partitioning of young tree mixtures under varying environmental conditions.

Effects of mixing tree species and water availability on soil organic carbon stocks are depth dependent in a temperate podzol

“…However, we found limited evidence of greater root biomass in mixed plots (Table 1). Instead, our data suggest that asymmetric competition (i.e., niche partitioning) along the soil profile may have resulted in greater organic matter inputs through rhizodeposition and root turnover at intermediate soil horizons (Altinalmazis-Kondylis et al, 2020;Jacob, Hertel, & Leuschner, 2014). Greater C inputs may in turn increase microbial activity and C storage due to the incorporation of microbially-derived compounds in the organic matter (Cotrufo, Wallenstein, Boot, Denef, & Paul, 2013;Lange et al, 2015), mainly in the upper part of the soil profile (Balesdent et al, 2018).…”

“…Given that oak trees were relatively small at the time of measurement, we developed a specific equation to estimate aboveground oak biomass using total height (Porté et al, 2009). The fine roots (<2 mm in diameter) were sorted for each soil layer, cleaned in water, dried and weighed to estimate fine root biomass (Altinalmazis-Kondylis et al, 2020). Litter mass loss was assessed over 1 year using litterbags (10 Â 18 cm 2 nylon mesh with a diameter of 48 μm) filled with 9 g of leaf litter (Fanin, Hättenschwiler, Schimann, & Fromin, 2015).…”

Tree species identity drives nutrient use efficiency in young mixed‐species plantations, at both high and low water availability

“…However, ion‐exchange methods can underestimate soil nutrient availability if nutrients released by forest floor decomposition are rapidly taken up by fine roots. While the resins were placed at 8 cm depth, fine root density in temperate forests have been found to be high in the forest floor organic layer and first 5–10 cm of mineral soil (Altinalmazis‐Kondylis et al, 2020).…”

Species- and Age-Specific Growth Reactions to Extreme Droughts of the Keystone Tree Species across Forest-Steppe and Sub-Taiga Habitats of South Siberia

“…Indeed, Zhang et al [85] noted a deep root system in larch, while pine receives water from the upper soil horizons [86,87]. Silver birch on poor stony soils also forms a shallow root system [88,89], but has a more pronounced plasticity of root architecture compared to pine [90,91]. Thus, the gradient of the degree of transpiration and growth maintenance during drought (pine-birch-larch in ascending order) corresponds to the ability of trees to use water from deep soil horizons.…”