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Crown carbon gain and elevated [CO 2 ] responses of understorey saplings with differing allometry and architecture
Author(s) -
E. Naumburg,
D. S. Ellsworth,
R. W. Pearcy
Publication year - 2001
Publication title -
functional ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.272
H-Index - 154
eISSN - 1365-2435
pISSN - 0269-8463
DOI - 10.1046/j.1365-2435.2001.00518.x
Subject(s) - crown (dentistry) , understory , biology , photosynthesis , biomass (ecology) , botany , allometry , specific leaf area , microsite , ecology , canopy , seedling , medicine , dentistry
1. Attempts at determining the physiological basis of species’ differences, such as the ability to grow in deep shade, have been of limited success. However, this basis is fundamental to predicting species’ responses to rising atmospheric CO 2 in the forest understorey. We linked a leaf photosynthesis and a tree architecture model to predict the effects of dynamic and steady state photosynthetic characteristics, crown architecture and elevated atmospheric CO 2 concentration ([CO 2 ]) on crown‐level carbon gain ( A crown ). Twenty‐four‐h A crown was modelled for shade‐tolerant Acer rubrum and shade‐intolerant Liriodendron tulipifera saplings growing for three years in a forest understorey under ambient and elevated [CO 2 ] in free‐air CO 2 enrichment. 2. Two factors best explained A crown in ambient [CO 2 ]: tree light environment and sapling allometry. Microsite light environment influenced carbon gain via daily photosynthetic photon flux (PFD), average diffuse PFD and sunfleck characteristics. Species differences in specific leaf area (SLA) and size‐related biomass allocation to leaves affected the effective leaf area and hence A crown . 3. At a common above‐ground biomass, small saplings (100 g above‐ground dry mass) of L. tulipifera had higher A crown than A. rubrum samples due to larger SLA and greater biomass allocation to leaves. Larger saplings of the two species had similar A crown due to greater carbon allocation to leaves with increasing plant size in A. rubrum vs L. tulipifera . For saplings > 800 g, A crown was greater in A. rubrum than in L. tulipifera . Enhancement of A crown by elevated [CO 2 ] on sunny days was similar for both species. 4. Overall, though the shade‐tolerant species had lower A crown than the shade‐intolerant species at a common small size, our results indicate that the relative performance of these species can reverse at larger sizes due to allocational differences. These results suggest that elevated [CO 2 ] may accelerate competition for light between A. rubrum and L. tulipifera as these species grow larger in the understorey.