Abstract
Abstract The temperature sensitivity of physiological processes and growth of tropical trees remains a key uncertainty in predicting how tropical forests will adjust to future climates. In particular, our knowledge regarding warming responses of photosynthesis, and its underlying biochemical mechanisms, is very limited. We grew seedlings of two tropical montane rainforest tree species, the early‐successional species Harungana montana and the late‐successional species Syzygium guineense , at three different sites along an elevation gradient, differing by 6.8℃ in daytime ambient air temperature. Their physiological and growth performance was investigated at each site. The optimum temperature of net photosynthesis ( T optA ) did not significantly increase in warm‐grown trees in either species. Similarly, the thermal optima ( T optV and T optJ ) and activation energies ( E aV and E aJ ) of maximum Rubisco carboxylation capacity ( V cmax ) and maximum electron transport rate ( J max ) were largely unaffected by warming. However, V cmax , J max and foliar dark respiration ( R d ) at 25℃ were significantly reduced by warming in both species, and this decline was partly associated with concomitant reduction in total leaf nitrogen content. The ratio of J max / V cmax decreased with increasing leaf temperature for both species, but the ratio at 25℃ was constant across sites. Furthermore, in H . montana , stomatal conductance at 25℃ remained constant across the different temperature treatments, while in S . guineense it increased with warming. Total dry biomass increased with warming in H . montana but remained constant in S . guineense . The biomass allocated to roots, stem and leaves was not affected by warming in H . montana , whereas the biomass allocated to roots significantly increased in S . guineense . Overall, our findings show that in these two tropical montane rainforest tree species, the capacity to acclimate the thermal optimum of photosynthesis is limited while warming‐induced reductions in respiration and photosynthetic capacity rates are tightly coupled and linked to responses of leaf nitrogen.
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Claims 14
Claim · model-written summary
Photosynthetic optimum did not significantly increase in warm-grown Harungana.
- Taxon
- Harungana montanae1
- Treatment
- warm‐growne0
- Outcome
- optimum temperature of net photosynthesise0
- Direction
- did not significantly increasee0
Not reportedComparator
Verbatim
e0“The optimum temperature of net photosynthesis ( T optA ) did not significantly increase in warm‐grown trees in either species”
e1“the early‐successional species Harungana montana and the late‐successional species Syzygium guineense”
Claim · model-written summary
Photosynthetic optimum did not significantly increase in warm-grown Syzygium.
- Taxon
- Syzygium guineense
Syzygium guineensee1 - Treatment
- warm‐growne0
- Outcome
- optimum temperature of net photosynthesise0
- Direction
- did not significantly increasee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The optimum temperature of net photosynthesis ( T optA ) did not significantly increase in warm‐grown trees in either species”
e1“the early‐successional species Harungana montana and the late‐successional species Syzygium guineense”
Claim · model-written summary
Warming left thermal optima and activation energies of photosynthetic capacities largely unaffected.
- Taxon
- tropical montane tree speciest0
- Treatment
- warminge0
- Outcome
- thermal optima ( T optV and T optJ ) and activation energies ( E aV and E aJ )e0
- Direction
- largely unaffectede0
Not reportedComparator
Verbatim
e0“the thermal optima ( T optV and T optJ ) and activation energies ( E aV and E aJ ) of maximum Rubisco carboxylation capacity ( V cmax ) and maximum electron transport rate ( J max ) were largely unaffected by warming”
t0“tropical montane tree species”
Claim · model-written summary
Warming reduced Vcmax and Jmax in both species.
- Taxon
- tropical montane tree speciest0
- Treatment
- warminge0
- Outcome
- V cmax , J maxe0
- Direction
- reducede0
- Setting
- 25℃e0
Not reportedComparator
Verbatim
e0“V cmax , J max and foliar dark respiration ( R d ) at 25℃ were significantly reduced by warming in both species”
t0“tropical montane tree species”
Claim · model-written summary
Warming reduced foliar dark respiration in both species.
- Taxon
- tropical montane tree speciest0
- Treatment
- warminge0
- Outcome
- foliar dark respiration ( R d )e0
- Direction
- reducede0
- Qualifier
- 25℃e0
Not reportedComparator
Verbatim
e0“V cmax , J max and foliar dark respiration ( R d ) at 25℃ were significantly reduced by warming in both species”
t0“tropical montane tree species”
Claim · model-written summary
Declines in photosynthetic capacity and respiration were partly associated with lower leaf nitrogen.
- Taxon
- tropical montane tree speciest0
- Organ / stage
- leafe0
- Outcome
- this declinee0
- Qualifier
- reduction in total leaf nitrogen contente0
Not reportedDirection
Verbatim
e0“this decline was partly associated with concomitant reduction in total leaf nitrogen content”
t0“tropical montane tree species”
Claim · model-written summary
Jmax/Vcmax ratio decreased as leaf temperature increased in both species.
Verbatim
e0“The ratio of J max / V cmax decreased with increasing leaf temperature for both species”
t0“tropical montane tree species”
Claim · model-written summary
Jmax/Vcmax at 25℃ was constant across sites.
Verbatim
e0“the ratio at 25℃ was constant across sites”
t0“tropical montane tree species”
Claim · model-written summary
Harungana stomatal conductance stayed constant across temperature treatments.
- Taxon
- H . montanae0
- Treatment
- different temperature treatmentse0
- Outcome
- stomatal conductancee0
- Direction
- remained constante0
- Qualifier
- 25℃e0
Not reportedComparator
Verbatim
e0“in H . montana , stomatal conductance at 25℃ remained constant across the different temperature treatments”
Claim · model-written summary
Syzygium stomatal conductance increased with warming.
- Taxon
- S . guineenseSyzygium guineensee0
- Treatment
- warminge0
- Outcome
- stomatal conductancee0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“stomatal conductance at 25℃ remained constant across the different temperature treatments, while in S . guineense it increased with warming”
Claim · model-written summary
Harungana dry biomass increased with warming.
Not reportedComparator
Verbatim
e0“Total dry biomass increased with warming in H . montana”
Claim · model-written summary
Syzygium dry biomass remained constant with warming.
- Taxon
- S . guineenseSyzygium guineensee0
- Treatment
- warminge0
- Outcome
- Total dry biomasse0
- Direction
- remained constante0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Total dry biomass increased with warming in H . montana but remained constant in S . guineense”
Claim · model-written summary
Harungana root, stem and leaf biomass allocation was unaffected by warming.
- Taxon
- H . montanae0
- Treatment
- warminge0
- Outcome
- biomass allocated to roots, stem and leavese0
- Direction
- not affectede0
Not reportedComparator
Verbatim
e0“The biomass allocated to roots, stem and leaves was not affected by warming in H . montana”
Claim · model-written summary
Syzygium root biomass allocation increased with warming.
- Taxon
- S . guineenseSyzygium guineensee0
- Outcome
- biomass allocated to rootse0
- Direction
- increasede0
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the biomass allocated to roots significantly increased in S . guineense”