Daytime Ecosystem Respiration Research Articles

Estimating daytime ecosystem respiration from eddy-flux data

To understand what governs the patterns of net ecosystem exchange of CO2, an understanding of factors influencing the component fluxes, ecosystem respiration and gross primary production is needed. In the present paper, we introduce an alternative method for estimating daytime ecosystem respiration based on whole ecosystem fluxes from a linear regression of photosynthetic photon flux density data vs. daytime net ecosystem exchange data at forest ecosystem level. This method is based on the principles of the Kok-method applied at leaf level for estimating daytime respiration. We demonstrate the method with field data and provide a discussion of the limitations of the method.

Altitudinal variation of ecosystem CO2 fluxes in an alpine grassland from 3600 to 4200 m

Recent studies have recognized the alpine grasslands on the Qinghai–Tibetan plateau as a significant sink for atmospheric CO2. The carbon-sink strength may differ among grassland ecosystems at various altitudes because of contrasting biotic and physical environments. This study aims (i) to clarify the altitudinal pattern of ecosystem CO2 fluxes, including gross primary production (GPP), daytime ecosystem respiration (Redaytime) and net ecosystem production (NEP), during the period with peak above-ground biomass; and (ii) to elucidate the effects of biotic and abiotic factors on the altitudinal variation of ecosystem CO2 fluxes. Ecosystem CO2 fluxes and abiotic and biotic environmental factors were measured in an alpine grassland at four altitudes from 3600 to 4200 m along a slope of the Qilian Mountains on the northwestern Qinghai–Tibetan Plateau during the growing season of 2007. We used a closed-chamber method combined with shade screens and an opaque cloth to measure several carbon fluxes, GPP, Redaytime and NEP, and factors, light-response curve for GPP and temperature sensitivity of Redaytime. Above- and below-ground biomasses and soil C and N contents at each measurement point were also measured. (i) Altitudinal pattern of ecosystem CO2 fluxes: The maximum net ecosystem CO2 flux (NEPmax), i.e. the potential ecosystem CO2 sink strength, was markedly different among the four altitudes. NEPmax was higher at the highest and lowest sites, approximately −7.4 ± 0.9 and −6.7 ± 0.6 μmol CO2 m−2 s−1 (mean ± standard error), respectively, but smaller at the intermediate altitude sites (3800 and 4000 m). The altitudinal pattern of maximum gross primary production was similar to that of NEPmax. The Redaytime, however, was significantly higher at the lowest altitude (3.4 ± 0.3 μmol CO2 m−2 s−1) than at the other three altitudes. (ii) Altitudinal variation of vegetation biomass: The above-ground biomass was higher at the highest altitude (154 ± 27 g DW m−2) than at the other altitudes, which we attribute mainly to the large biomass in cushion plants at the highest altitude. The small above-ground biomass at the lower altitudes was probably due to heavy grazing during the growing season. (iii) Features of ecosystem CO2 fluxes: Redaytime and GPP were positively correlated with above-ground biomass. The low ratio of Redaytime to GPP at either the measurement point or the site level suggests that CO2 uptake efficiency tends to be higher at higher altitudes, which indicates a high potential sink strength for atmospheric CO2 despite the low temperature at high altitudes. The results suggest that the effect of grazing intensity on ecosystem carbon dynamics, partly by decreasing vegetation biomass, should be clarified further.

Drought during canopy development has lasting effect on annual carbon balance in a deciduous temperate forest

* Climate change projections predict an intensifying hydrologic cycle and an increasing frequency of droughts, yet quantitative understanding of the effects on ecosystem carbon exchange remains limited. * Here, the effect of contrasting precipitation and soil moisture dynamics were evaluated on forest carbon exchange using 2 yr of eddy covariance and microclimate data from a 50-yr-old mixed oak woodland in northern Ohio, USA. * The stand accumulated 40% less carbon in a year with drought between bud-break and full leaf expansion (354 +/- 81 g C m(-2) yr(-1) in 2004 and 252 +/- 45 g C m(-2) yr(-1) in 2005). This was caused by greater suppression of gross ecosystem productivity (GEP; 16% = 200 g) than of ecosystem respiration (ER; 11% = 100 g) by drought. Suppressed GEP was traced to lower leaf area, lower apparent quantum yield and lower canopy conductance. The moisture sensitivity of ER may have been mediated by GEP. * The results highlight the vulnerability of the ecosystem to even a moderate drought, when it affects a critical aspect of development. Although the drought was preceded by rain, the storage capacity of the soil seemed limited to 1-2 wk, and therefore droughts longer than this are likely to impair productivity in the region.

Components of ecosystem respiration and an estimate of net primary productivity of an intermediate-aged Douglas-fir stand

Continuous half-hourly chamber-measured belowground ( R s) and eddy covariance (EC)-measured total ecosystem ( R e) respiration in a 56-year-old Pacific west coast Douglas-fir stand from 2003 to 2005 were analyzed to study their seasonal and interannual variability. Seasonal variation in both R s and R e was better predicted by soil temperature at the 5 cm depth than at any other depth and air temperature. R e was more responsive than R s to changes in temperature and soil water content. While nighttime ( R sn) and daytime ( R sd) soil respiration showed no difference in their response to soil temperature, daytime ecosystem respiration ( R ed) was less responsive than its nighttime counterpart ( R en) to changes in soil temperature. Half-hourly R ed was almost always smaller than R en possibly due to photoinhibition while daily total R ed was higher than daily total R en during summer and spring months but smaller in winter and autumn months with the latter due to fewer daylight hours. A distinct seasonal pattern in the R s to R e ratio was observed. The 3-year mean seasonal R s/ R e was at its minimum of 0.52 in spring followed by 0.63 in summer, 0.81 in autumn and a maximum of 0.86 in winter. Both daily total and half-hourly R sd/ R ed were larger than R sn/ R en. It appears that the different responses of R s and R e to environmental variables arise as a result of seasonal variations in photosynthesis, mobilization and use of stored carbohydrates, and differences in the phenology of aboveground and belowground plant tissues. On an annual basis, R s accounted for 62% of R e with the latter accounting for 86% of the carbon (C) assimilated in annual photosynthesis or gross primary productivity (GPP), leaving the net C sequestration efficiency (1 − R e/GPP) at 14%. In the relatively dry year of 2003, both R s and R e as well as GPP were the lowest but with the highest net ecosystem productivity (NEP) of the 3 years. The relatively wetter growing season soil moisture regime in 2005 resulted in the highest R e and GPP. Partitioning of R s into its autotrophic and heterotrophic components indicated that 54% of GPP was respired back to the atmosphere as autotrophic respiration and an additional 32% was lost in the decomposition of litterfall and soil organic matter. The mean annual estimate of net primary productivity (NPP) at 843 g C m −2 accounted for 47% of the mean annual GPP of 1815 g C m −2.

Partitioning European grassland net ecosystem CO 2 exchange into gross primary productivity and ecosystem respiration using light response function analysis

Tower CO 2 flux measurements from 20 European grasslands in the EUROGRASSFLUX data set covering a wide range of environmental and management conditions were analyzed with respect to their ecophysiological characteristics and CO 2 exchange (gross primary production, P g, and ecosystem respiration, R e) using light-response function analysis. Photosynthetically active radiation ( Q) and top-soil temperature ( T s) were identified as key factors controlling CO 2 exchange between grasslands and the atmosphere at the 30-min scale. A nonrectangular hyperbolic light-response model P( Q) and modified nonrectangular hyperbolic light–temperature-response model P( Q, T s) proved to be flexible tools for modeling CO 2 exchange in the light. At night, it was not possible to establish robust instantaneous relationships between CO 2 evolution rate r n and environmental drivers, though under certain conditions, a significant relationship r n = r 0 e k T T s was found using observation windows 7–14 days wide. Principal light-response parameters—apparent quantum yield, saturated gross photosynthesis, daytime ecosystem respiration, and gross ecological light-use efficiency, ɛ = P g/ Q, display patterns of seasonal dynamics which can be formalized and used for modeling. Maximums of these parameters were found in intensively managed grasslands of Atlantic climate. Extensively used semi-natural grasslands of southern and central Europe have much lower production, respiration, and light-use efficiency, while temperate and mountain grasslands of central Europe ranged between these two extremes. Parameters from light–temperature-response analysis of tower data are in agreement with values obtained using closed chambers and free-air CO 2 enrichment. Correlations between light-response and productivity parameters provides the possibility to use the easier to measure parameters to estimate the parameters that are more difficult to measure. Gross primary production ( P g) of European grasslands ranges from 1700 g CO 2 m −2 year −1 in dry semi-natural pastures to 6900 g CO 2 m −2 year −1 in intensively managed Atlantic grasslands. Ecosystem respiration ( R e) is in the range 1800 < R e < 6000 g CO 2 m −2 year −1. Annual net ecosystem CO 2 exchange (NEE) varies from significant net uptake (>2400 g CO 2 m −2 year −1) to significant release (<−600 g CO 2 m −2 year −1), though in 15 out of 19 cases grasslands performed as net CO 2 sinks. The carbon source was associated with organic rich soils, grazing, and heat stress. Comparison of P g, R e, and NEE for tower sites with the same characteristics from previously published papers obtained with other methods did not reveal significant discrepancies. Preliminary results indicate relationships of grassland P g and R e to macroclimatic factors (precipitation and temperature), but these relationships cannot be reduced to simple monofactorial models.

Estimation of daytime ecosystem respiration to determine gross primary production of a mountain meadow

Gross primary production ( F GPP) may be calculated from net ecosystem CO 2 exchange ( F NEE), measured, for example, by means of the eddy covariance method, provided an estimate of daytime ecosystem respiration is available. The latter is now often estimated by extrapolating functional relationships between nighttime F NEE, when F GPP is zero, and temperature to daytime conditions. The present paper deals with one problem associated with this approach, namely the reduction of leaf respiration in light relative to darkness, which causes an overestimation of daytime ecosystem respiration, and hence F GPP. The overestimation of F GPP is quantified for a mountain meadow in the Austrian Alps using a coupled model of the reduction of leaf dark respiration as a function of light intensity and within-canopy radiative transfer. For the two study years analysed in the present paper, model simulations suggest a reduction of F GPP by 11–13% and 13–17%, for a low and a high estimate of the maximum leaf-level reduction of dark respiration, respectively. This reduction is shown to be most sensitive to the ratio between F GPP and total ecosystem respiration, as well as to the ratio between leaf and total ecosystem respiration. The largest factors of uncertainty in this modelling approach are the cause for and the actual level of the reduction of leaf dark respiration in light. The significance of the present findings for estimating F GPP of other sites is discussed.