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Your search keyword '"Hollinger D.Y."' showing total 2 results
Start Over Author "Hollinger D.Y." Topic biological sciences
2 results on '"Hollinger D.Y."'

1. Carbon dioxide exchange between an undisturbed old-growth temperate forest and the atmosphere

Author

Hollinger, D.Y., Kelliher, F.M., Byers, J.N., Hunt, J.E., McSeveny, T.M., and Weir, P.L.

Subjects
Atmospheric carbon dioxide -- Research, Old growth forests -- Research, Biological sciences, Environmental issues
Abstract

We used the eddy-correlation technique to investigate the exchange of CO2 between an undisturbed old-growth forest and the atmosphere at a remote Southern Hemisphere site on 15 d between 1989 and 1990. Our goal was to determine how environmental factors regulate ecosystem CO2 exchange, and to test whether present knowledge of leaf-level processes was sufficient to understand ecosystem-level exchange. On clear summer days the maximum rate of net ecosystem CO2 uptake exceeded 15 microns mol center dot m to the -2 center dot s to the -1, about an order of magnitude greater than the maximum values observed on sunny days in the winter. Mean nighttime respiration rates varied between approximately equal to -2 and -7 microns mol center dot m to the -2 center dot s to the -1. Nighttime CO2 efflux rate roughly doubled with a 10 degrees C increase in temperature. Daytime variation in net ecosystem CO2 exchange rate was primarily associated with changes in total photosynthetically active photon flux density (PPFD). Air temperature, saturation deficit, and the diffuse PPFD were of lesser, but still significant, influence. These results are in broad agreement with expectations based on the biochemistry of leaf gas exchange and penetration of radiation through a canopy. However, at night, the short-term exchange of CO2 between the forest and the atmosphere appeared to be regulated principally by atmospheric transport processes. There was a positive linear relationship between nocturnal CO2 exchange rate and downward sensible heat flux density. This new result has implications for the development of models for diurnal ecosystem CO2 exchange. The daytime light-use efficiency of the ecosystem (CO2 uptake/incident PPFD) was between 1.6 and 7.1 mmol/mol on clear days in the summer but decreased to 0.8 mmol/mol after frosts on clear winter days. Ecosystem CO2 uptake was enhanced by diffuse PPFD, a result of potentially global significance given recent increases in Northern Hemisphere haze.

Published
1994

2. Disentangling the role of photosynthesis and stomatal conductance on rising forest water-use efficiency

Author

Thomas Kolb, Jingfeng Xiao, Rosvel Bracho-Garrillo, Rossella Guerrieri, Kimberly A. Novick, Heidi Asbjornsen, Andrew D. Richardson, Benjamin D. Stocker, Mary E. Martin, Kenneth L. Clark, Katie A. Jennings, J. William Munger, Scott V. Ollinger, Soumaya Belmecheri, Sabina Dore, David Y. Hollinger, Guerrieri R., Belmecheri S., Ollinger S.V., Asbjornsen H., Jennings K., Xiao J., Stocker B.D., Martin M., Hollinger D.Y., Bracho-Garrillo R., Clark K., Dore S., Kolb T., William Munger J., Novick K., and Richardson A.D.

Subjects
0106 biological sciences, Water-use efficiency, Stomatal conductance, 010504 meteorology & atmospheric sciences, stable isotopes, AmeriFlux, Photosynthesis, Atmospheric sciences, 01 natural sciences, Basal area, chemistry.chemical_compound, water-use efficiency, CO2 fertilization, 0105 earth and related environmental sciences, Stable isotopes, Multidisciplinary, Moisture, Stable isotope ratio, Tree rings, Biological Sciences, 15. Life on land, Stable isotope, tree rings, chemistry, fertilization, 13. Climate action, Carbon dioxide, Environmental science, CO2, Tree ring, Temperate rainforest, Environmental Sciences, 010606 plant biology & botany
Abstract

Significance Forests remove about 30% of anthropogenic CO2 emissions through photosynthesis and return almost 40% of incident precipitation back to the atmosphere via transpiration. The trade-off between photosynthesis and transpiration through stomata, the water-use efficiency (WUE), is an important driver of plant evolution and ecosystem functioning, and has profound effects on climate. Using stable carbon and oxygen isotope ratios in tree rings, we found that WUE has increased by a magnitude consistent with estimates from atmospheric measurements and model predictions. Enhanced photosynthesis was widespread, while reductions in stomatal conductance were modest and restricted to moisture-limited forests. This result points to smaller reductions in transpiration in response to increasing atmospheric CO2, with important implications for forest–climate interactions, which remain to be explored., Multiple lines of evidence suggest that plant water-use efficiency (WUE)—the ratio of carbon assimilation to water loss—has increased in recent decades. Although rising atmospheric CO2 has been proposed as the principal cause, the underlying physiological mechanisms are still being debated, and implications for the global water cycle remain uncertain. Here, we addressed this gap using 30-y tree ring records of carbon and oxygen isotope measurements and basal area increment from 12 species in 8 North American mature temperate forests. Our goal was to separate the contributions of enhanced photosynthesis and reduced stomatal conductance to WUE trends and to assess consistency between multiple commonly used methods for estimating WUE. Our results show that tree ring-derived estimates of increases in WUE are consistent with estimates from atmospheric measurements and predictions based on an optimal balancing of carbon gains and water costs, but are lower than those based on ecosystem-scale flux observations. Although both physiological mechanisms contributed to rising WUE, enhanced photosynthesis was widespread, while reductions in stomatal conductance were modest and restricted to species that experienced moisture limitations. This finding challenges the hypothesis that rising WUE in forests is primarily the result of widespread, CO2-induced reductions in stomatal conductance.

Published
2021

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