Publications (51) View all
-
Article: Soil [N] modulates soil C cycling in CO2-fumigated tree stands: a meta-analysis.
[show abstract] [hide abstract]
ABSTRACT: Under elevated atmospheric CO(2) concentrations, soil carbon (C) inputs are typically enhanced, suggesting larger soil C sequestration potential. However, soil C losses also increase and progressive nitrogen (N) limitation to plant growth may reduce the CO(2) effect on soil C inputs with time. We compiled a data set from 131 manipulation experiments, and used meta-analysis to test the hypotheses that: (1) elevated atmospheric CO(2) stimulates soil C inputs more than C losses, resulting in increasing soil C stocks; and (2) that these responses are modulated by N. Our results confirm that elevated CO(2) induces a C allocation shift towards below-ground biomass compartments. However, the increased soil C inputs were offset by increased heterotrophic respiration (Rh), such that soil C content was not affected by elevated CO(2). Soil N concentration strongly interacted with CO(2) fumigation: the effect of elevated CO(2) on fine root biomass and -production and on microbial activity increased with increasing soil N concentration, while the effect on soil C content decreased with increasing soil N concentration. These results suggest that both plant growth and microbial activity responses to elevated CO(2) are modulated by N availability, and that it is essential to account for soil N concentration in C cycling analyses.Plant Cell and Environment 12/2010; 33(12):2001-11. · 5.22 Impact Factor -
Chapter: Issues in Modelling Plant Ecosystem Responses to Elevated CO2: Interactions with Soil Nitrogen
11/2007: pages 165 - 186; , ISBN: 9780470988695 -
Article: Interactive effects of atmospheric carbon dioxide and leaf nitrogen concentration on canopy light use efficiency: a modeling analysis.
[show abstract] [hide abstract]
ABSTRACT: Potential increases in plant productivity in response to increasing atmospheric CO(2) concentration are likely to be constrained by nutrient limitations. However, the interactive effects of nitrogen nutrition and CO(2) concentration on growth are difficult to define because both factors affect several aspects of growth, including photosynthesis, respiration, and leaf area. By expressing growth as a product of light intercepted and light use efficiency (epsilon), it is possible to decouple the effects of nutrient availability and CO(2) concentration on photosynthetic rates from their effects on other aspects of plant growth. I used measured responses of leaf photosynthesis to leaf nitrogen (N) content and CO(2) concentration to parameterize a model of canopy radiation absorption and photosynthesis, and then used the model to estimate the response of epsilon to elevated CO(2) concentration for Pinus radiata D. Don, Nothofagus fusca (Hook. f.) Ørst. and Eucalyptus grandis W. Hill ex Maiden. Down-regulation of photosynthesis at elevated CO(2) was represented as a reduction in either leaf N content or leaf Rubisco activity. The response of epsilon to elevated CO(2), which differed among the three species, was analyzed in terms of the underlying relationships between leaf photosynthesis and leaf N content. The response was independent of leaf N content when photosynthesis was down-regulated to the same extent at low and high leaf N content. Interactive effects of N availability and CO(2) on growth are thus likely to be the result of either differences in down-regulation of photosynthesis at low and high N availability or interactive effects of CO(2) and N availability on other aspects of plant growth.Tree Physiology 02/1996; 16(1_2):201-209. · 2.88 Impact Factor -
Article: Carbon budget of Pinus sylvestris saplings after four years of exposure to elevated atmospheric carbon dioxide concentration.
[show abstract] [hide abstract]
ABSTRACT: To study the responses of Scots pine (Pinus sylvestris L.), a commercially important tree species in Europe, to future increases in atmospheric CO2 concentration ([CO2]), we grew saplings for 4 years in the ground in open-top chambers in ambient or ambient + 400 micromol mol(-1) CO2, without supplemental addition of nutrients and water. Carbon (C) budgets were developed for trees in both CO2 treatments based on productivity and biomass data obtained from destructive harvests at the end of the third and fourth years of treatment, and simulations of annual gross photosynthesis (P(tot)) and maintenance respiration by the model MAESTRA. Simulated P(tot) was enhanced by elevated [CO2], despite significant down-regulation of photosynthetic capacity. The subsequent increase in C uptake was allocated primarily to tissues with limited longevity (needles and fine roots), which explains why the measured annual increment in woody biomass did not differ between CO2 treatments. Thus, our results suggest that accelerated stem growth only occurs in the first 2 years in the presence of elevated [CO2] and that forest rotations will not be shortened significantly in response to increasing [CO2]. In elevated [CO2], a higher proportion of available C was allocated below ground, resulting in altered biomass distribution patterns. In trees of equal size, measured ratios of fine root/needle biomass and belowground/aboveground biomass were almost twice as large in the elevated [CO2] treatment. Although there are uncertainties in scaling from saplings to mature canopies, the data indicate that, in nutrient-limited Scots pine forests, elevated [CO2] is unlikely to accelerate tree growth significantly, but is likely to increase C inputs to soil.Tree Physiology 04/2005; 25(3):325-37. · 2.88 Impact Factor -
Article: Physiological basis of the light use efficiency model.
[show abstract] [hide abstract]
ABSTRACT: The observation that, for unstressed plants, light use efficiency of a plant canopy, defined as the ratio of net primary productivity (NPP) to absorbed photosynthetically active radiation (APAR), is approximately constant with respect to changes in APAR, implies that NPP can be modeled using a linear relationship with APAR. However, such a linear relationship is counter-intuitive because the relationship between leaf photosynthesis and absorbed light is strongly nonlinear. Three arguments have been advanced to explain the observed linear relationship between NPP and APAR. In this paper, a detailed, physiologically based model of canopy radiation absorption and photosynthesis (MAESTRO) was used to analyze these arguments. The first argument is that the canopy is structured so that radiation is distributed throughout the canopy such that most leaves are exposed to non-saturating quantum flux density, resulting in a linear response of canopy photosynthesis to APAR. Simulations of MAESTRO indicated that this explanation is inadequate, because daily values of canopy photosynthetic light use efficiency calculated with MAESTRO were highly variable regardless of canopy structure. The second argument is that variability in light use efficiency decreases with increasing time scale. The simulations showed that this is true to some extent, although simulated annual canopy photosynthetic light use efficiency still varies across sites with different LAI or light climate. The third argument is that changes in canopy nitrogen content act both to maximize net canopy photosynthesis and to keep light use efficiency constant. This argument could not be tested with the model, but the failure of the first two explanations suggests that this third explanation deserves closer attention.Tree Physiology 04/1998; 18(3):167-176. · 2.88 Impact Factor
