Improving models of fine root carbon stocks and fluxes in European forests

Abstract

Fine roots and above‐ground litterfall play a pivotal role in carbon dynamics in forests. Nonetheless, direct estimation of stocks of fine roots remains methodologically challenging. Models are thus widely used to estimate these stocks and help elucidate drivers of fine root growth and turnover, at a range of scales. We updated a database of fine root biomass, necromass and production derived from 454 plots across European forests. We then compared fine root biomass and production to estimates obtained from 19 different models. Typical input variables used for the models included climate, net primary production, foliage and above‐ground biomass, leaf area index (LAI), latitude and/or land cover type. We tested whether performance could be improved by fitting new multiple regression models, and explored effects of species composition and sampling method on estimated fine root biomass. Average fine root biomass was 332 g/m2, and necromass 379 g/m2, for European forests where the average fine root production was 250 g m−2 year−1. Carbon fraction in fine roots averaged 48.4%, and was 1.5% greater in broadleaved species than conifers. Available models were poor predictors of fine root biomass and production. The best performing models assumed proportionality between above‐ and below‐ground compartments, and used remotely sensed LAI or foliage biomass as key inputs. Model performance was improved by use of multiple regressions, which revealed consistently greater biomass and production in stands dominated by broadleaved species as well as in mixed stands even after accounting for climatic differences. Synthesis. We assessed the potential of existing models to estimate fine root biomass and production in European forests. We show that recalibration reduces by about 40% errors in estimates currently produced by the best available models, and increases three‐fold explained variation. Our results underline the quantitative significance of fine roots (live and dead) to the global carbon cycle.

Carbon contents and fine root production in tropical silvopastoral systems

“…The average carbon content (39.4%) of fine root biomass in our study was lower compared to 48.4% in forest fine roots reported by Neumann et al (2020). The C percentage in fine roots was also lower than the woody tree and grass biomass (Table 3).…”

“…Regionally, there are more studies regarding fine root dynamics on temperate and boreal ecosystems than in tropical ecosystems (Cai et al, 2019; Feng, Wang, Zhu, Fu, & Chen, 2018; Finér, Ohashi, Noguchi, & Hirano, 2011; Lehtonen et al, 2016). The relationship between FRP and SOC storage vary between land use types and ecological conditions (Chen, Hobbie, Reich, Yang, & Robinson, 2019; Finér, Zverev, Palviainen, Romanis, & Kozlov, 2019; Neumann, Godbold, Hirano, & Finér, 2020). Due to the large extensions of land surface currently under pastures with the potential to reconvert as silvopastures, understanding fine root dynamics on C inputs in different tropical SPS help farmers and decision‐makers in finding ecologically sound strategies to increase environmental services (Adewopo et al, 2014; Hertel, Harteveld, & Leuschner, 2009; Shi et al, 2018; Sollenberger, Kohmann, Dubeux, & Silveira, 2019).…”

Evaluating an exponential respiration model to alternative models for soil respiration components in a Canadian wildfire chronosequence (FireResp, v1.0)

“…These modeling approaches could examine the effects of gross primary productivity on soil respiration components (Zhuang et al, 2002;Pumpanen et al, 2003;Vargas et al, 2010;Pumpanen et al, 2015;Phillips et al, 2017). For sites that cannot be instrumented continuously (such as the ones studied here), this model data integration could be supported with periodic surveys of aboveground biomass and other remote sensing data (Neumann et al, 2020).…”

“…For the field samples an estimate of root carbon C R was assumed to be proportional to total tree biomass collected at each plot (Härkönen et al, 2011;Neumann et al, 2020). A summary of all input variables is reported in Table 1.…”

Diurnal and seasonal variations on soil CO2 fluxes in tropical silvopastoral systems

“…Furthermore, such differences are related to higher OM and silt contents in the L + P system compared with the L + C (Table 1). The silty texture of the soil in L + P system could have facilitated a greater capacity for water infiltration and fine root activity during this period (Munroe & Isaac, 2014; Villanueva‐López et al ., 2016a, 2016b), which increase root respiration and consequently, increase soil CO 2 fluxes (Liu et al ., 2002; Joffre et al ., 2003; Neumann et al ., 2020). Some studies (Munroe e Isaac, 2014; Mattsson et al ., 2015; Montejo‐Martínez, 2020) showed that the roots are more easily distributed in deeper soil layers during the rainy season as a result of the growth of thicker tree roots.…”