Abstract
In tropical mountains, trees are the dominant life form from sea level to above 4,000-m altitude under highly variable thermal conditions (range of mean annual temperatures: <8 to >28°C). How light-saturated net photosynthesis of tropical trees adapts to variation in temperature, atmospheric CO2 concentration, and further environmental factors, that change along elevation gradients, is not precisely known. With gas exchange measurements in mature trees, we determined light-saturated net photosynthesis at ambient temperature (T) and [CO2] (A sat) of 40 tree species from 21 families in tropical mountain forests at 1000-, 2000-, and 3000-m elevation in southern Ecuador. We tested the hypothesis that stand-level averages of A sat and leaf dark respiration (R D) per leaf area remain constant with elevation. Stand-level means of A sat were 8.8, 11.3, and 7.2 μmol CO2 m−2 s−1; those of R D 0.8, 0.6, and 0.7 μmol CO2 m−2 s−1 at 1000-, 2000-, and 3000-m elevation, respectively, with no significant altitudinal trend. We obtained coefficients of among-species variation in A sat and R D of 20–53% (n = 10–16 tree species per stand). Examining our data in the context of a pan-tropical A sat data base for mature tropical trees (c. 170 species from 18 sites at variable elevation) revealed that area-based A sat decreases in tropical mountains by, on average, 1.3 μmol CO2 m−2 s−1 per km altitude increase (or by 0.2 μmol CO2 m−2 s−1 per K temperature decrease). The A sat decrease occurred despite an increase in leaf mass per area with altitude. Local geological and soil fertility conditions and related foliar N and P concentrations considerably influenced the altitudinal A sat patterns. We conclude that elevation is an important influencing factor of the photosynthetic activity of tropical trees. Lowered A sat together with a reduced stand leaf area decrease canopy C gain with elevation in tropical mountains.
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Claims 8
Claim · model-written summary
Stand mean light-saturated photosynthesis was 8.8, 11.3 and 7.2 μmol CO2 m−2 s−1 at 1000, 2000 and 3000 m, without a significant altitudinal trend.
Verbatim
e0“Stand-level means of A sat were 8.8, 11.3, and 7.2 μmol CO2 m−2 s−1; those of R D 0.8, 0.6, and 0.7 μmol CO2 m−2 s−1 at 1000-, 2000-, and 3000-m elevation, respectively, with no significant altitudinal trend”
t0“Tropical Trees”
Claim · model-written summary
Stand mean leaf dark respiration was 0.8, 0.6 and 0.7 μmol CO2 m−2 s−1 across the three elevations, with no significant trend.
Verbatim
e0“those of R D 0.8, 0.6, and 0.7 μmol CO2 m−2 s−1 at 1000-, 2000-, and 3000-m elevation, respectively, with no significant altitudinal trend”
t0“Tropical Trees”
Claim · model-written summary
Among-species variation in photosynthesis and respiration was 20–53%.
Verbatim
e0“coefficients of among-species variation in A sat and R D of 20–53%”
t0“Tropical Trees”
Claim · model-written summary
Pantropical area-based photosynthesis decreased by 1.3 μmol CO2 m−2 s−1 per km altitude increase.
Verbatim
e0“area-based A sat decreases in tropical mountains by, on average, 1.3 μmol CO2 m−2 s−1 per km altitude increase”
t0“tropical trees”
Claim · model-written summary
Pantropical area-based photosynthesis decreased by 0.2 μmol CO2 m−2 s−1 per K temperature decrease.
Verbatim
e0“or by 0.2 μmol CO2 m−2 s−1 per K temperature decrease”
e1“area-based A sat decreases in tropical mountains”
t0“tropical trees”
Claim · model-written summary
Leaf mass per area increased with altitude.
Verbatim
e0“an increase in leaf mass per area with altitude”
t0“tropical trees”
Claim · model-written summary
Geological and soil fertility conditions and foliar N and P influenced altitude patterns in photosynthesis.
- Taxon
- tropical treest0
- Compound
- foliar N and Pe0
- Outcome
- altitudinal A sat patternse0
- Setting
- Local geological and soil fertility conditionse0
Not reportedDirection
Verbatim
e0“Local geological and soil fertility conditions and related foliar N and P concentrations considerably influenced the altitudinal A sat patterns”
t0“tropical trees”
Claim · model-written summary
Reduced photosynthesis and stand leaf area decreased canopy carbon gain with elevation.
Verbatim
e0“Lowered A sat together with a reduced stand leaf area decrease canopy C gain with elevation in tropical mountains”
t0“tropical trees”