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Trade‐offs in low‐light CO 2 exchange: a component of variation in shade tolerance among cold temperate tree seedlings
Author(s) -
Walters M. B.,
Reich P. B.
Publication year - 2000
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.1365-2435.2000.00415.x
Subject(s) - biology , photosynthesis , shade tolerance , botany , specific leaf area , saccharum , respiration , temperate forest , respiration rate , horticulture , temperate climate , canopy
1. Does enhanced whole‐plant CO 2 exchange in moderately low to high light occur at the cost of greater CO 2 loss rates at very‐low light levels? We examined this question for first‐year seedlings of intolerant Populus tremuloides and Betula papyrifera , intermediate Betula alleghaniensis , and tolerant Ostrya virginiana and Acer saccharum grown in moderately low (7·3% of open‐sky) and low (2·8%) light. We predicted that, compared with shade‐tolerant species, intolerant species would have characteristics leading to greater whole‐plant CO 2 exchange rates in moderately low to high light levels, and to higher CO 2 loss rates at very‐low light levels. 2. Compared with shade‐tolerant A. saccharum , less‐tolerant species grown in both light treatments had greater mass‐based photosynthetic rates, leaf, stem and root respiration rates, leaf mass:plant mass ratios and leaf area:leaf mass ratios, and similar whole‐plant light compensation points and leaf‐based quantum yields. 3. Whole‐plant CO 2 exchange responses to light (0·3–600 µmol quanta m −2 s −1 ) indicated that intolerant species had more positive CO 2 exchange rates at all but very‐low light (< 15 µmol quanta m −2 s −1 ). In contrast, although tolerant A. saccharum had a net CO 2 exchange disadvantage at light > 15 µmol quanta m −2 s −1 , its lower respiration resulted in lower CO 2 losses than other species at light < 15 µmol quanta m −2 s −1 . 4. Growth scaled closely with whole‐plant CO 2 exchange characteristics and especially with integrated whole‐plant photosynthesis (i.e. leaf mass ratio × in situ leaf photosynthesis). In contrast, growth scaled poorly with leaf‐level quantum yield, light compensation point, and light‐saturated photosynthetic rate. 5. Collectively these patterns indicated that: (a) no species was able to both minimize CO 2 loss at very‐low light (i.e. < 15 µmol quanta m −2 s −1 ) and maximize CO 2 gain at higher light (i.e. > 15 µmol quanta m −2 s −1 ), because whole‐plant respiration rates were positively associated with whole‐plant photosynthesis at higher light; (b) shade‐intolerant species possess traits that maximize whole‐plant CO 2 exchange (and thus growth) in moderately low to high light levels, but these traits may lead to long‐term growth and survival disadvantages in very‐low light (< 2·8%) owing, in part, to high respiration. In contrast, shade‐tolerant species may minimize CO 2 losses in very‐low light at the expense of maximizing CO 2 gain potential at higher light levels, but to the possible benefit of long‐term survival in low light.