Evaluating the convergence between eddy-covariance and biometric methods for assessing carbon budgets of forests

The eddy-covariance (EC) micro-meteorological technique and the ecology-based biometric methods (BM) are the primary methodologies to quantify CO2 exchange between terrestrial ecosystems and the atmosphere (net ecosystem production, NEP) and its two components, ecosystem respiration and gross primary production. Here we show that EC and BM provide different estimates of NEP, but comparable ecosystem respiration and gross primary production for forest ecosystems globally. Discrepancies between methods are not related to environmental or stand variables, but are consistently more pronounced for boreal forests where carbon fluxes are smaller. BM estimates are prone to underestimation of net primary production and overestimation of leaf respiration. EC biases are not apparent across sites, suggesting the effectiveness of standard post-processing procedures. Our results increase confidence in EC, show in which conditions EC and BM estimates can be integrated, and which methodological aspects can improve the convergence between EC and BM.


NEP
Reco GPP neces ancil no neces ancil no neces ancil no (a) production of volatile organic compounds, epiphytes and dissolved organic carbon Supplementary Table 8. Characteristics of the allometric relationships (AR) used to measure the standing biomass of above-(stem and branches) and belowground wood (coarse roots) and of the method used to measure leaf production (litter traps, LT, or AR) at the sites with biometric measurements of net primary production.    Table 10. Contribution of mycorrhiza production to total stand net primary production (NPP) from field-and culture studies. Data are reported for each site (for field studies), with mean ± s.e.m, minumum and maximum values, and number of replicates (for both field-and culture studies).

Supplementary Methods
We report here a summary of the methodological approach used at each site for the biometric determination of the production and respiratory components to estimate NEP, Reco and GPP.
Thus, the document provides site overviews about measurement techniques, protocols, measurement periods, replicates, data processing etc. However, note that this text does not necessary include all methodological information extracted from the literature for a given site Coarse roots: assumed 21% of aboveground wood respiration Leaves: NIGHTTIME: leaf dark respiration on cut branches with cuvette + IRGA (measurements during 2 months Jan-Feb 2007); replicates: n=30 trees, for each tree, one branch sunlit and one shaded. DAYTIME DATA: daytime respiration was assumed to be only 33% of the nighttime respiration to account for daytime photoinhibition of leaf dark respiration 5 Understory: not accounted Coarse woody debris: derived from data on amount of wood falling due to mortality multiplied by 76% (amount of dead wood respired away before entering the soil; this factor, 76%, is from another site) 5 Scaling Soil: TEMPORAL: averaged per month with no consideration of seasonality SPATIAL: basic calculation Stem: TEMPORAL: bimonthly averages with no consideration of seasonality (little seasonal variation in stem respiration was documented 5 SPATIAL: stem area (considering BRANCHES and that stem respiration constant with height). Relationship between woody NPP and woody respiration: the trees measured for woody respiration grew faster than the average trees in the plot. Therefore, when scaled to the plot level, respiratory fluxes were reduced by 11%. Leaves: TEMPORAL: The wet season respiration mean was applied to all months with >100 mm rain; for the dry season, measured dry season respiration was linearly scaled by the soil moisture saturation SPATIAL: LAI.

Changbai Mountains
Net primary production No data available meeting quality standard for our analysis

Metolius
Net primary production Stem and branches: allometry, 1996 30 Fine + coarse roots: derived from measurements of aboveground NPP and simulation of aboveground vs belowground NPP (average of 3-PG and PnNET-II 300 simulations) 31 Leaves: from specific leaf area (m2 leaf g-1 dry weight) and mean leaf area of newly expanded foliage, which was determined from a subsample of branches from at least 12 trees (in 1996) 30 Understory: NPP determination not mentioned

Tapajos km 67
Net primary production (from 5

and references therein)
Stem and branches: allometry Coarse roots: assumed some production-to-biomass ratio of aboveground wood and coarse root biomass being 21% of aboveground wood biomass Leaves: litter traps Fine roots: sequential coring (every two months for two years; 0-10 cm depth with correction for soil depth of 1. Fine roots: steady-state mass balance approach based on quantifying above-ground and below-ground litter input, assuming that heterotrophic respiration rates are equal to litter input rates, and allocating the remaining soil respiration to root respiration; at the clay sites, the mass balance approach provided root respiration consistent with trenching approach 5 . Soil -heterotrophic component: Rsoil -Rroot Stem: chambers + infrared gas analyzer (February, April, July, and October of 2004); replicates: 21 individual trees/large vines 108 Leaves: Leaf dark respiration rates assessed from light-response curves from 68 leaves from 26 individuals (with photosynthetic gas exchange system LI-6400, morning hours 08.00-13.00) 109