Quantification and uncertainty of root growth stimulation by elevated CO₂in mature temperate deciduous forest

Abstract

Increasing CO2 levels are a major global challenge, and the extent to which increasing anthropogenic CO2 emissions can be mitigated by natural carbon sinks remains poorly understood. The uptake of elevated CO2 (eCO2) by the terrestrial biosphere, and subsequent sequestration as biomass in ecosystems, may act as a negative feedback in the carbon budget, but remains hard to quantify in natural ecosystems. Here, we combine large-scale field observations of fine root stocks and flows, derived from belowground imaging and soil cores, with image analysis, stochastic modelling, and statistical inference, to elucidate belowground root dynamics in a mature temperate deciduous forest under free-air CO2 enrichment to 150ppm above ambient levels. Using over 67k frames of belowground observation, we observe that eCO2 leads to relatively faster root production (a peak volume fold change of 4.52 ± 0.44 eCO2 versus 2.58 ± 0.21 control). We identify an increase in existing root elongation relative to root mass decay as the likely causal mechanism for this acceleration. Direct physical analysis of biomass and width measurements from 552 root systems recovered from soil cores support this picture, with lengths and widths of fine roots significantly increasing under eCO2 . We use dynamic measurements to estimate fine root contributions to net primary productivity, finding an increase under eCO2, with an estimated mean annual 204 ± 93 g dw m-2 yr-1 eCO2 versus 140 ± 60 g dw m-2 yr-1 control. We also quantify and discuss the uncertainties in such productivity measurements. This multi-faceted approach thus sheds quantitative light on the challenging characterisation of the eCO2 response of root biomass in mature temperate forests.

Mass concentration measurements of autumn bioaerosol using low-cost sensors in a mature temperate woodland free-air carbon dioxide enrichment (FACE) experiment: investigating the role of meteorology and carbon dioxide levels

“…Although the literature states a small number of cases of where individual fungal species do respond directly to eCO 2 , it is likely that the main effects would be secondary, for example, competition between autotrophs and heterotrophs for nutrients or an increase in leaf litter production resulting in an increase the population of decomposer fungi. There is evidence for increased autotrophic productivity under eCO 2 at the BIFoR FACE site in the form of increased leaf-scale photosynthesis (Gardner et al, 2020) and fine-root production (Ziegler et al, 2021). Whether this increased autotrophic productivity primes or competes with fungal activity requires further work.…”

Mass concentrations of autumn bioaerosol in a mature temperate woodland Free Air Carbon Dioxide Enrichment (FACE) experiment: investigating the role of meteorology and carbon dioxide levels

“…Although the literature states a small number of cases of where individual fungal species do respond directly to eCO2, it is likely that the main effects would be secondary, for example, competition between autotrophs and heterotrophs for nutrients, or an increase in leaf litter production resulting in an increase the population of decomposer fungi. There is evidence for increased autotrophic productivity under eCO2 at BIFoR FACE in the form of increased leaf-scale photosynthesis (Gardner et al, 2020) and fine root production (Ziegler et al, 2021). Whether this increased autotrophic productivity primes, or competes with, fungal activity requires further work.…”

Reply on CC2

“…Although the literature states a small number of cases of where individual fungal species do respond directly to eCO2, it is likely that the main effects would be secondary, for example, competition between autotrophs and heterotrophs for nutrients, or an increase in leaf litter production resulting in an increase the population of decomposer fungi. There is evidence for increased autotrophic productivity under eCO2 at BIFoR FACE in the form of increased leaf-scale photosynthesis (Gardner et al, 2020) and fine root production (Ziegler et al, 2021). Whether this increased autotrophic productivity primes, or competes with, fungal activity Another possible reason for not picking up an eCO2 response in fungal bioaerosols in the full dataset is that the maximum diameter of the particles that can be detected by the OPCs is 10 µm, which does exclude several fungal species, including those known to be present in the BIFoR forest during the experimental duration.…”