Environmental Controls Over Net Exchanges of Carbon Dioxide From Contrasting Florida Ecosystems

Abstract

Net CO2 exchange estimated using eddy covariance and relaxed eddy accumulation indicated that evergreen pine upland and deciduous cypress wetland ecosystems in north‐central Florida had similar apparent light compensation points during the growing season (125 vs. 150 μmol PPFD·m−2·s−1), but that maximum rates at 1800 μmol PPFD·m−2·s−1 at the cypress ecosystem were only 59% of those at the pine ecosystem (8.9 vs. 15.2 μmol CO2·m−2·s−1). During both the summer and winter months at the pine ecosystem, net CO2 exchange in the daytime was a curvilinear function of PPFD, with no significant seasonal differences in slope or intercept. In contrast, net CO2 exchange at the cypress ecosystem was minimal during the daytime in the winter. Net CO2 exchange during the nighttime was an exponential function of air temperature at both sites, with Q10 values of 2.0 and 1.9 for the pine and cypress ecosystems, respectively. Lower nighttime fluxes of CO2 occurred at the cypress ecosystem across the entire temperature range. Both of these relatively sparse canopies stored CO2 during stable atmospheric conditions. Mean maximum net CO2 exchange during the daytime and mean nighttime net CO2 exchange for these ecosystems were highly contrasting, and together resulted in a relatively low rate of annual carbon accumulation in the wetland when compared to the aggrading pine ecosystem. However, values reported here are within the ranges of values for other boreal, temperate, and tropical forest ecosystems.

Hydrological and climatic responses of Pinus elliottii var. densa in mesic pine flatwoods Florida, USA

“…These conditions can facilitate stomatal closure and higher respiration [1,6], thus reducing growth. Vapor pressure deficit values of > 2 kPa have been shown to limit net CO 2 exchange in P. elliottii during the dry spring season [4], indicating stomatal closure effects on carbon assimilation under dry conditions. Interestingly, the dry hot spring is also the time when shoot and root elongation are occurring [17,18,22], putting further demands on carbohydrate supplies and thus potentially increasing the sensitivity of stem growth to any climate fluctuations during this time of year.…”

“…Interestingly, the dry hot spring is also the time when shoot and root elongation are occurring [17,18,22], putting further demands on carbohydrate supplies and thus potentially increasing the sensitivity of stem growth to any climate fluctuations during this time of year. In spite of the dry weather, total plant carbon gain is at its seasonal maximum during spring [4]; thus, any climate variation in potential evapotranspiration and precipitation could have a significant impact on the total carbon accumulated in any year. In our study, annual growth at two sites was highly correlated with spring P-PET, indicating the sensitivity of carbon gain to meteorological conditions during this time.…”

A Flexible Hybrid Model of Life Cycle Carbon Balance for Loblolly Pine (Pinus taeda L.) Management Systems

“…Stem residues were obtained by assuming a harvest efficiency of 88% of V [31][32][33][34]. It was assumed that C storage in soil was not affected by forest management in southern pines plantations [7,[35][36][37][38], therefore the model did not include changes in soil C. Carbon mass (MgC·ha −1 ) was calculated by using an average C content of 50% for loblolly pine and understory biomass components [6,39,40].…”

Modeling nighttime ecosystem respiration from measured CO2 concentration and air temperature profiles using inverse methods

“…Here, we compare these CSO E results to other proposed methods that attempt to constrain nighttime respiration. In particular, we used the so-called light response curve method [Lee et al, 1999], which is based on determining the intercept of the F t; h ð Þ and photosynthetically active photon flux density (PPFD) [Clark et al, 1999;Lai et al, 2002a;Law et al, 1999a]. The curve is expressed as:…”