Plant, microbial and ecosystem carbon use efficiencies interact to stabilize microbial growth as a fraction of gross primary production

Abstract

The carbon use efficiency of plants (CUE ) and microorganisms (CUE ) determines rates of biomass turnover and soil carbon sequestration. We evaluated the hypothesis that CUE and CUE counterbalance at a large scale, stabilizing microbial growth (μ) as a fraction of gross primary production (GPP). Collating data from published studies, we correlated annual CUE , estimated from satellite imagery, with locally determined soil CUE for 100 globally distributed sites. Ecosystem CUE , the ratio of net ecosystem production (NEP) to GPP, was estimated for each site using published models. At the ecosystem scale, CUE and CUE were inversely related. At the global scale, the apparent temperature sensitivity of CUE with respect to mean annual temperature (MAT) was similar for organic and mineral soils (0.029°C ). CUE and CUE were inversely related to MAT, with apparent sensitivities of -0.009 and -0.032°C , respectively. These trends constrain the ratio μ : GPP (= (CUE × CUE )/(1 - CUE )) with respect to MAT by counterbalancing the apparent temperature sensitivities of the component processes. At the ecosystem scale, the counterbalance is effected by modulating soil organic matter stocks. The results suggest that a μ : GPP value of c. 0.13 is a homeostatic steady state for ecosystem carbon fluxes at a large scale.

Global pattern and controls of soil microbial metabolic quotient

“…There was also consistency in the relative importance of environmental factors controlling MMQ and CUE between this study and Sinsabaugh et al. (). Biological factors, followed by edaphic factors and meteorological factors, were the dominant controls for both MMQ and CUE as shown by SEM.…”

“…Our mean MMQ was similar to the microbial respiratory carbon turnover calculated from qCO 2 and CUE using an independent data set (Sinsabaugh et al. ). Theoretically, higher CUE means more carbon is assimilated into microbial biomass, and less carbon enters microbial biomass respire as BR, corresponding to a lower MMQ; lower CUE indicates less carbon is assimilated into microbial biomass and higher MMQ.…”

“…Thus, a negative correlation between MMQ and carbon use efficiency is expected, which has been verified in Sinsabaugh et al. (). Sinsabaugh et al.…”

“…Sinsabaugh et al. () estimated a global mean biomass turnover time of 67 ± 22 d based on a mean microbial CUE of 0.25–0.30. This estimate is consistent with the global average for MMQ_Soil (1.8 μmol C·h −1 ·mmol MBC −1 ) and MMQ_Ref (1.5 μmol C·h −1 ·mmol MBC −1 ), which correspond to a respiration based MBC turnover times of 23 and 28 d, respectively, assuming that MMQ = (μ/ B )/(CUE/(1 − CUE).…”

Plant economic strategies of grassland species control soil carbon dynamics through rhizodeposition

“…Furthermore, we found that the microbial metabolic quotient (qCO 2 ) was positively related to both R H ‐SOC new and RPE (Figure c). This suggests that an enhanced rhizodeposition by acquisitive species increase microbial allocation of energy to mineralization activities relative to growth (Shahzad et al, ), potentially in relation with a reduction in N availability by enhanced root N uptake, a lower carbon use efficiency and a faster turnover of microbial biomass (Chen et al, ; Sinsabaugh, Moorhead, Xu, & Litvak, ). This variation in microbial activity could also potentially be linked to the selection of rhizosphere microbiomes with contrasting SOC mineralization abilities by plant species with different economic strategies (Pascault et al, ; Schimel & Schaeffer, ).…”