Allocation and dynamics of C and N within plant–soil system of ash and beech

Abstract

Forest management requires a profound understanding of how tree species affect C and N cycles in ecosystems. The large C and N stocks in forest soils complicate research on the effects of tree species on C and N pools. In-situ 13 C and 15 N labeling in undisturbed, natural forests enable not only tracing of C and N fluxes, but also reveal insight into the interactions at the plant-soilatmosphere interface. In-situ dual 13 C and 15 N pulse labeling of 20 beeches (Fagus sylvatica L.) and 20 ashes (Fraxinus excelsior L.) allowed tracing the fate of assimilated C and N in trees and soils in an unmanaged forest system in the Hainich National Park (Germany). Leaf, stem, root, and soil samples as well as microbial biomass were analyzed to quantify the allocation of 13 C and 15 N for 60 d after labeling and along spatial gradients in the soil with increasing distance from the stem. For trees of similar heights ( 4 m), beech (20%) assimilated twice as much as ash (9%) of the applied 13 CO 2 , but beech and ash incorporated similar 15 N amounts (45%) into leaves. The photosynthates were transported belowground through the phloem more rapidly in beech than in ash. Ash preferentially accumulated 15 N and 13 C in the roots. In contrast, beech released more of this initially assimilated 13 C (2.0% relative 13 C allocation) and 15 N (0.1% relative 15 N allocation) via rhizodeposition into the soil than ash (0.2% relative 13 C, 0.04% relative 15 N allocation), which was also subsequently recovered in microbial biomass. These results on C and N partitioning contribute to an improved understanding of the effects of European beech and ash on the C and N cycles in deciduous broad-leaved forest. Differences in C and N allocation patterns between ash and beech are one mechanism of niche differentiation in forests containing both species.

Agroforestry systems: Meta‐analysis of soil carbon stocks, sequestration processes, and future potentials

“…Mycorrhizal fungal hyphae are an important C pool in soil. Mycorrhizal fungi and fine roots transfer large proportions of primary production into soils, but the estimates vary substantially across studies (Janssens et al, ; Pausch & Kuzyakov, ; Sommer, Dippold, Flessa, & Kuzyakov, ). Additionally, the biological N fixation and nutrient mobilization from deep soils have increased soil fertility, prompting C sequestration (Araujo, Iwata, Jr, & Xavier, ; Balakrishna, Lakshmipathy, Bagyaraj, & Ashwin, ; Vallejo, Roldan, & Dick, ).…”

Can Carbon Fluxes Explain Differences in Soil Organic Carbon Storage under Aspen and Conifer Forest Overstories?

“…While reviews have suggested that, on average, half of soil respiration is autotrophic from recent photosynthate [77], the reported relative proportion of fixed C that is allocated belowground ranges from 10% to 90% [34]. Differences in C allocation between deciduous and evergreen trees, and trees with ectomycorrhizal (like most conifers) and arbuscular mycorrhizal (aspen have also arbuscular mycorrhizae) associations have been reported in literature [67,78,79]. Therefore, we hypothesize that the differences between SOC pools under aspen and conifer overstories are due to differences in belowground C allocation and microbial composition and activity in the rhizosphere.…”

Functional differences in the microbial processing of recent assimilates under two contrasting perennial bioenergy plantations

“…Previous isotopic tracer studies have shown a strong coupling between recently fixed plant photosynthates and belowground C allocation to roots, soil microbes and respiratory fluxes (Bahn et al, 2013;Barthel et al, 2014;Epron et al, 2011;Hogberg et al, 2008;Jin and Evans, 2010;Sommer et al, 2016;Street et al, 2013;Subke et al, 2012;Tavi et al, 2013;Weng et al, 2017). The fate of this C is ultimately controlled by the composition and activity of soil biota, however our understanding of the below ground C flux and its partitioning amongst roots, mycorrhizae and free living soil microbes is still limited (De Deyn et al, 2008;Stuart Chapin et al, 2009).…”