Limited thermal acclimation of photosynthesis in tropical montane tree species

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 °C in daytime ambient air temperature. Their physiological and growth performance was investigated at each site. The optimum temperature of net photosynthesis (ToptA) did not significantly increase in warm‐grown trees in either species. Similarly, the thermal optima (ToptV and ToptJ) and activation energies (EaV and EaJ) of maximum Rubisco carboxylation capacity (Vcmax) and maximum electron transport rate (Jmax) were largely unaffected by warming. However, Vcmax, Jmax and foliar dark respiration (Rd) at 25 °C 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 Jmax/Vcmax decreased with increasing leaf temperature for both species, but the ratio at 25 °C was constant across sites. Furthermore, in H. montana, stomatal conductance at 25 ºC 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, while 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.

Full text

Glob Change Biol. 2021;00:1–19.
|
1wileyonlinelibrary.com/journal/gcb
Received: 9 February 2021
|
Revised: 21 June 2021
|
Accepted: 28 June 2021
DOI : 10.1111/gcb .157 90
PRIMARY RESEARCH ARTICLE
Limited thermal acclimation of photosynthesis in tropical
montane tree species
Mirindi Eric Dusenge1,2,3,4 | Maria Wittemann1,4,5 | Myriam Mujawamariya1,5 |
Elisée B. Ntawuhiganayo5,6 | Etienne Zibera2 | Bonaventure Ntirugulirwa1,5,7 |
Danielle A. Way3, 8 ,9, 10 | Donat Nsabimana2 | Johan Uddling1,4 | Göran Wallin1
1Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden
2School of Forestry, Biodiversit y and Biological Sciences, College of Agriculture, Animal Sciences and Veterinary Medicine, University of Rwanda, Musanze,
Rwanda
3Department of Biology, The University of Western Ontario, London, ON, Canada
4Gothenburg Global Biodiversity Centre (GGBC), Universit y of Gothenburg, Gothenburg, Sweden
5Department of Biology, College of Science and Technology, University of Rwanda, Huye, Rwanda
6World Agroforestry (ICRAF), Huye, Rwanda
7Rwanda A griculture and Animal Resources Development Board, Kigali, Rwanda
8Division of Plant Sciences, Research School of Biology, The Australian National Universit y, Canberra, ACT, Australia
9Environmental and Climate Sciences Department, Brookhaven National Laborator y, Upton, NY, USA
10Nicholas School of the Environment, Duke University, Durham, NC , USA
This is an open access article under the terms of the Creat ive Commo ns Attri bution-NonCo mmercial License, which permits use, distribution and reproduction
in any medium, provided the original work is properly cited and is not used for commercial purposes.
© 2021 The Authors. Global Change Biology published by John Wiley & Sons Ltd.
Correspondence
Mirindi Eric Dusenge, Department of
Biology, The University of Western
Ontario, London, ON, N6A 5B7 Canada.
Email: mdusenge@uwo.ca
Göran Wallin, Department of Biological
and Environmental Sciences, University
of Gothenburg, P.O. Box 461, SE- 405 30
Gothenburg, Sweden.
Email: goran.wallin@bioenv.gu.se
Funding information
Svenska Forskningsrådet Formas,
Grant/Award Number: 2015- 1458;
Swedish research council, Grant/
Award Number: 2015- 03338; European
Union’s Horizon 2020, Grant/Award
Number: 844319; NSERC; Ontario Early
Researcher Award; Canada Foundation for
Innovation; Research School of Biology
at the Australian National University;
US Depar tment of Energy, Grant/Award
Number: DE- SC0012704; Swedish
strategic research area “Biodiversity and
Ecosystem services in a Changing Climate”
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 cli-
mates. 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 tempera-
ture. Their physiological and growth performance was investigated at each site. The
optimum temperature of net photosynthesis (ToptA) did not significantly increase in
warm- grown trees in either species. Similarly, the thermal optima (ToptV and ToptJ) and
activation energies (EaV and EaJ) of maximum Rubisco carboxylation capacity (Vcmax)
and maximum electron transport rate (Jmax) were largely unaffected by warming.
However, Vcmax, Jmax and foliar dark respiration (Rd) 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 Jmax/Vcmax decreased with in-
creasing 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

2
|
DU SENGE Et a l.
1 | INTRODUC TION
The temperature sensitivity of photosynthesis in tropical tree spe-
cies remains a significant uncertainty in predicting global forest pro-
ductivity and climate feedbacks in a warmer climate (Booth et al.,
2012; Mercado et al., 2018; Smith & Dukes, 2013). Global climate
models project a warming of 1– 1.5 and 4– 5℃ for the forested trop-
ical region during the present century under the best- and worst-
case climate change scenarios, respectively, compared to the period
1986– 2005 (IPCC, 2013). This degree of warming is small compared
to changes expected for higher latitudes, and which may thus lead
to the conclusion that tropical forests are at lower risk in future cli-
mates. However, tropical forests have experienced stable thermal
regimes both on short (e.g., seasonal) and geological timescales
(Trewin, 2014). It has therefore been hypothesized that these for-
ests have a narrow thermal niche with limited capacity to acclimate
(Janzen, 1967). It has also been shown that tropical plants are cur-
rently operating at temperatures that are close to their upper ther-
mal limits (Lloyd & Farquhar, 2008; Sentinella et al., 2020). Recent
findings show that both community- and ecosystem- scale photo-
synthetic thermal optima are close to the ambient air temperatures
currently experienced by tropical trees (Huang et al., 2019; Slot &
Winter, 2017a; Tan et al., 2017), suggesting that they will have to
thermally acclimate photosynthesis to avoid operating at supra-
optimal temperatures in future climates. However, few studies have
assessed the capacity of photosynthetic thermal acclimation in
tropical species (Booth et al., 2012; Mercado et al., 2018). Tropical
highland or montane tree species may be particularly sensitive to
warming, as recently seen in Andean studies along elevation gradi-
ents which show declines in the relative abundance of these species
within their historical habitat during recent decades (Duque et al.,
2015; Fadrique et al., 2018). This decline of highland species in their
native habitat is followed by the colonization of species initially from
lower and warmer elevation, in a process termed “thermophilization”
(Duque et al., 2015).
Thermal acclimation of net photosynthesis (An) typically results
in an upward shift in the thermal optimum (Topt A) of the instanta-
neous temperature response of An (Gunderson et al., 2009; Slot &
Winter, 2017b; Way, 2019; Way & Yamori, 2014; Yamori et al., 2014).
In most species, photosynthetic acclimation to warming results in an
increase of the ToptA by about 0.4 3– 0. 62℃ pe r 1℃ of war min g (Be rry
& Björkman, 1980; Kumarathunge et al., 2019; Way, 2019; Way &
Yamori, 2014). However, this estimate of the thermal sensitivity of
ToptA is heavily based on studies on temperate and boreal species
(Berry & Björkman, 1980; Kumarathunge et al., 2019; Sendall et al.,
2015; Way & Yamori, 2014). Of the relatively few studies on tropical
trees investigating responses of ToptA to elevated growth tempera-
tures, some report significant upward shifts in Topt A with warming
(Cunningham & Read, 2003; Kositsup et al., 2009; Read, 1990; Slot
& Winter, 2017b), while others do not (Carter et al., 2020; Crous
et al., 2018).
In temperate and boreal trees, adjustments in the shape of the
instantaneous temperature response of net photosynthesis and
its Topt A have been shown to be linked to changes in temperature
sensitivity of underlying process components such as thermal opti-
mum and activation energies of the maximum Rubisco carboxylation
capacity of Rubisco, Vcmax (ToptV and EaV), and the maximum elec-
tron transport rate, Jmax (ToptJ and EaJ), and the ratio of Jmax to Vcmax
(Jmax/Vcmax; Dusenge et al., 2020; Kumarathunge et al., 2019; Slot &
Winter, 2017b; Stefanski et al., 2019; Way, 2019; Yamaguchi et al.,
2016). So far in tropical tree species, shifts in ToptA with warming
were seen to coincide with decreases in the ratio of Jmax to Vcmax
(Kositsup et al., 2009; Slot & Winter, 2017b), probably reflecting
within- leaf resource allocation since photosynthesis is commonly
more carboxylation limited at higher temperatures (Smith & Keenan,
2020). The ToptV, ToptJ, EaV, EaJ and Jmax/Vcmax are also important pa-
rameters in dynamic global vegetation models when representing
net photosynthesis and its thermal acclimation (Kumarathunge et al.,
2019; Mercado et al., 2018). To date, only a very few studies have
investigated thermal acclimation of the temperature sensitivities
of Vcmax and Jmax in tropical trees (Crous et al., 2018; Fauset et al.,
2019; Kositsup et al., 2009; Smith & Dukes, 2017). However, none of
them was able to accurately determine ToptV and ToptJ. Clearly, more
studies that investigate the effect of warming on the temperature
sensitivities of Vcmax and Jmax and their relative importance to shifts
in ToptA are needed in tropical trees, and particularly in highland
species.
In addition to shifts in ToptA, acclimation of photosynthesis to
warming also affects the magnitude of photosynthetic rates. Shifts
in the magnitude of An at the new, warmer growth conditions are
warming. Total dry biomass increased with warming in H. montana but remained con-
stant 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 in-
creased in S. guineense. Overall, our findings show that in these two tropical montane
rainforest tree species, the capacity to acclimate the thermal optimum of photosyn-
thesis is limited while warming- induced reductions in respiration and photosynthetic
capacity rates are tightly coupled and linked to responses of leaf nitrogen.
KEY WORDS
Africa, biomass, climate change, leaf dark respiration, Vcmax and Jmax, warming

|
3
DUSENGE E t al.
largely driven by changes in the achieved rates of Vcmax, Jmax and
stomatal conductance (gs; Crous et al., 2018; Dusenge et al., 2020;
Scafaro et al., 2017; Way & Sage, 2008). Meta- analyses, dominated
by studies on boreal and temperate tree species, have showed that
Vcmax and Jmax rates measured at a common leaf temper ature of 25℃
(Vcmax25 and Jmax25) are largely unaltered by warming (Kattge et al.,
2009; Kumarathunge et al., 2019; Way & Oren, 2010). Across indi-
vidual studies, some did not find any effect of warming on either
Vcmax25 or Jmax25 (e.g., Bermudez et al., 2020; Carter et al., 2020;
Fauset et al., 2019; Lamba et al., 2018; Stefanski et al., 2019), while
others observed significant declines (e.g., Dusenge et al., 2015,
2020; Way & Sage, 2008), or increases (e.g., Crous et al., 2013) in
warm- grown plants. Therefore, there is no consistent acclimation
response of photosynthetic capacity to warming. The few data
available on tropical trees show that Vcmax25 and Jmax25 were not im-
pacted by warming (Scafaro et al., 2017; Crous et al., 2018; Fauset
et al., 2019; but see Kositsup et al., 2009).
Although gs decreases as a response to the short- term increases
in the vapor pressure deficit (VPD) that are typically associated with
increasing temperature (Grossiord et al., 2020; López et al., 2021;
Oren et al., 1999), gs may also acclimate to long- term warming. In
different tree species, gs increased (Marchin et al., 2016), decreased
(Dusenge et al., 2020; Fauset et al., 2019; Lamba et al., 2018) or re-
mained unchanged (Drake et al., 2015; Dusenge et al., 2020) with
growth at elevated temperatures. The few studies that explored the
warming effect on gs in tropical tree species showed that gs tends
to be reduced in warm- grown trees when measured at growth con-
ditions (Drake et al., 2015; Fauset et al., 2019). In tropical tree spe-
cies, gs often imposes strong limitations on An (Doughty & Goulden,
2008; Tan et al., 2017), and may thus partly underlie observed pro-
gressive reductions in tropical carbon sink strength and tree growth
during recent decades (Hubau et al., 2020; McDowell et al., 2018;
Sullivan et al., 2020). Thus, further studies on thermal adjustments
of both photosynthetic capacity and gs in tropical tree species grown
in field conditions are critically needed to improve our understand-
ing of how warming may affect net CO2 assimilation, tree growth
and plant- climate feedbacks of tropical forests in future climates
(Mercado et al., 2018).
Foliar respiration (Rd), which uses carbohydrates from photosyn-
thesis as substrate, supply energy for maintenance of leaf functions
and allocation of carbohydrates to other parts of the tree for growth
(O’Leary et al., 2019). It is thus a key determinant of forest growth
and carbon storage in future warmer climates. Although foliar res-
piration increases near exponentially with short- term increase in
temperature (Atkin & Tjoelker, 2003; O’Sullivan et al., 2013; Smith &
Dukes, 2017), it is commonly found that respiration acclimates and is
lower at a given temperature in warm- grown trees (e.g., Reich et al.,
2016; Slot & Kitajima, 2015; Zhu et al., 2020). This thermal acclima-
tion of respiration has also been observed in trees from the tropics
(Cheesman & Winter, 2013a, 2013b; Drake et al., 2015; Scafaro et al.,
2017; Slot et al., 2014; Slot & Winter, 2017b, 2018; Smith & Dukes,
2017). A recent study from the same elevation gradient experiment
used in this study (Rwanda- TREE), but with 16 montane tropical
tree species freely rooted in the soil, reported that thermal accli-
mation of leaf respiration at the warmer, lower- elevation sites led to
complete or even over- compensation of respiration (Mujawamariya
et al., 2020). Altogether, these findings suggest that foliar respiration
readily acclimates to warming, and may have little constraint on car-
bon availability for tropical tree growth in future climates.
The least- cost theory of photosynthesis posits that in any given
environment, An is optimized at the lowest cost, mainly associated
with nitrogen (N) and water uptake (Prentice et al., 2014; Smith
et al., 2019; Wright et al., 2003). Therefore, the biochemical de-
mand for (i.e., Rubisco carboxylation and associated N costs) and
supply of carbon (via stomatal conductance) are generally balanced
such that a given net CO2 assimilation rate is achieved at the lowest
water loss in any environment (Prentice et al., 2014). Furthermore,
based on optimality theory of photosynthetic capacity, Vcmax mea-
sured at a given common temperature should be lower in plants
grown in warmer growth conditions compared to their cool- grown
cou nter parts (Smith & Keenan, 2020; Wan g et al., 2020). This is be-
cause enzymatic reactions are faster at high temperatures; there-
fore, warm- grown plants can achieve optimal net CO2 assimilation
rates with a relatively lower photos ynthetic enzyme content (Smith
& Keenan, 2020; Yamori et al., 2014). Since both Rubisco carboxyl-
ation an d elec tro n trans port rates, an d the con ten t s of the en z ymes
that regulate each process (Rubisco and chlorophyll pigments) are
co- regulated (Lu et al., 2020; Maire et al., 2012; Wullschleger,
1993), then warm acclimated plants should consequently reduce
both Vcmax and Jmax. Since respiration is involved in providing en-
ergy for protein turn over, which is the largest factor that explains
variation in leaf Rd, then thermal acclimation of respiration should
closely follow that of photosynthetic capacity (Wang et al., 2020).
Therefore, with reduced metabolic leaf N content, then leaf res-
piration should also be suppressed in warm- grown plants (Wang
et al., 2020).
With the goal of improving our understanding of how tropical
trees respond to a warmer climate, we assessed the thermal ac-
climation capacity of net photosynthesis and its component pro-
cesses in two tropical montane tree species grown at three different
sites along an elevational gradient in the Rwanda- TREE (TRopical
Elevation Experiment) project. We further evaluated to what extent
these leaf physiological processes were linked to changes in leaf ni-
trogen status and tree growth responses at the different sites. Based
on previous research and proposed theories, the following four hy-
pothesized predictions were tested:
H1: The Topt of Anet, Vcmax and Jmax increases in a warmer climate,
but the acclimation is only partial (i.e., approximately 0.5℃ per 1℃
of warming).
H2: Based on both least- cost and photosynthetic optimality the-
ories, gs and photosynthetic capacity (i.e., Vcmax and Jmax) at a com-
mon temperature decrease with warming.
H3: Leaf Rd rates measured at a common leaf temperature shows
strong downward acclimation to warming.
H4: Thermal acclimation of photosynthetic capacity and leaf res-
piration are tightly correlated, and linked to leaf N.

4
|
DU SENGE Et a l.
2 | MATERIALS AND METHODS
2.1 | Experimental sites
This study was conducted within the Rwanda- TREE project
(www.rwand atree.com) established at three different experi-
mental plantation sites along an elevation gradient in Rwanda,
central Africa, set up to represent a possible climate change
scenario. The sites were high- elevation Sigira (2400 m a.s.l.,
S2°30′54″; E29°23′44″; hereafter denoted “HE”), mid- elevation
Rubona (1600 m a.s.l., S2°28′30″; E29°46′49″; hereafter denoted
“ME”) and low- elevation Ibanda- Makera (1300 m a.s.l., S2°6′31″;
E30°51′16″E; hereafter denoted “LE”). Identical multi- species
plantations, each composed of 1800 trees representing 20 na-
tive species, were established in January 2018 at the sites. HE
is considered as the control site as most species used in this ex-
periment naturally grow in the neighbouring montane rainforest,
named Ny un gwe National Park. Fur ther details of the expe riment
can be found in Mujawamariya et al. (2020). In this study, we re-
port findings from a parallel study using the same sites and plant
material as in the main experiment, but in which eight species
were grown in 11- litre pots using the soil from the Sigira site at
all three sites, to eliminate soil as a possible confounding fac-
tor. The soil of the main plot, from where the soil to the pots
were taken, was classified as an Ultisol with clay texture with pH
(KCl) = 3.3 ± 0.13 (mean ± SD); bulk density = 0.99 ± 0.13 g cm−3;
Organic C = 3.8 ± 0.6%; NH 4+ an d NO3− = 39 ± 11 g m−3 and avail-
able p = 18 ± 4 g m−3.
2.2 | Environmental data
During the 1- year growing period (1st Februar y 2018 to 31st
January 2019) for the trees used in this study, weather parameters
were recorded every 30 min at all sites. The HE site had an annual
mean average air temperature of 15.1℃ while both the ME and
LE sites were about 5℃ warmer (20.0 and 20.4℃, respectively)
compared to the HE site. However, the diurnal temperature varia-
tion differs between ME and LE, with the latter site having warmer
days and cooler nights. The mean daytime (~12 h) air temperatures
were 17, 22.4 and 23.8℃ and mean monthly maximum air tem-
peratures were 23.8, 28.6 and 31.4℃ for HE, ME and LE, respec-
tively. Nighttime is coolest at HE (13.2℃), but between the two
lower- elevation sites, the LE site (16.6℃) is 0.9℃ cooler than the
ME site (17.5℃). The mean air temperature of the coldest and the
warmest month differed depending on site between 1.8 and 2.1℃
on diurnal basis and 2.7 and 3.0℃ on daytime basis. The daytime
(16.2, 21.9 and 23.6℃, for HE, ME, and LE, respectively) and night-
time (13.2, 17.6, 17.7℃, for HE, ME, and LE, respectively) tem-
peratures during the 4- month period (1st February to 25th May)
preceding and during the gas exchange measurements campaign
did not differ very much from the corresponding temperatures for
the 1- year growing period (provided above). The mean daytime air
temperatures were 16.2, 21.9 and 23.6℃, while the nighttime air
temperatures were 13.2, 17.6, 17.7℃, for HE, ME and LE, respec-
tively. However, the mean monthly maximum air temperatures for
the 4- month period were relatively cooler compared to the 1- year
period temperatures at each site. The mean monthly maximum air
temperatures for the 4- month period were 21.5, 27 and 29.6℃ for
HE, ME and LE, respectively.
The relative distribution of precipitation over the year is simi-
lar across all three sites where the highest rainfall period is March–
May followed by the major dry period in June– August. However, the
sites differ in total annual precipitation. From February to January
2018/19, HE, ME and LE received 2100, 1576 and 1046 mm in total
precipitation, respectively. Throughout the experiment, the daytime
vapor pressure deficit (VPD, kPa) increased from HE site to the two
lower- elevation sites, with a mean value of 0.88, 1.31, 1.39 kPa for
HE, ME and LE, respectively, representing on average a 49%– 58%
higher daytime air VPD in warmer, lower- elevation sites compared
to the cool, high- elevation site. Due to high cloud cover at the HE
site, the mean daytime photosynthetic photon flux density (PPFD)
is lower (660 µmol m−2 s
−1) compared to the lower- elevation sites
which received on average 807 and 760 µmol m−2 s
−1 ME and LE,
respectively, during 2018.
2.3 | Plant material
The two species used in this study, early- successional Harungana
montana (Spirlet) and late- successional Syzygium guineense (Wild.)
DC, were grown from seeds collected in Nyungwe National Park
and propagated in a nursery established at the ME site. Both species
are abundant tree species in Nyungwe (Nyirambangutse et al., 2017;
Ziegler et al., 2020). After seedlings had established roots (with a
height of 43.4 ± 1.4 and 48.8 ± 1.6 cm, mean ± SE, for S. guineense
and H. montana, respectively), they were transferred to 11- liter pots,
and eight pots of each species were randomly assigned to each of
the three experimental sites in mid- January 2018. At the time of
plantation, the total dry mass of the S. guineense and H. montana
seedlings were 7.2 ± 2.7 and 8.0 ± 1.9 g, respectively, based on ini-
tial harvests of eight seedlings per species, randomly selected from
the same populations as the potted seedlings. Seedlings were then
grown at the sites for 1 year until harvest in January 2019. The pots
were buried in the ground to avoid unnatural diurnal soil tempera-
ture variation. Seedlings were fertilized during nursery cultivation
but not afterwards. However, no major nutrient or pot limitations
during the experiment were likely indicated by the continued growth
until the end of the study (Figure S1). Throughout the study, seed-
lings were watered to maintain a moist growth medium throughout
the experiment. Since the three sites differ in total annual precipi-
tation, watering was also done a bit differently across sites. At the
high- elevation site (HE), which receives the highest total annual pre-
cipitation (see details above), the watering was done twice a week,
while at both the intermediate (ME) and lowest (LE), which receive
relatively lower total precipitation, the watering was done every day.

|
5
DUSENGE E t al.
On each watering day, each plant was given 2 L of water in the early
evening.
2.4 | Gas exchange measurements
Leaf gas exchange measurements were conducted between 23rd April
2018 and 25th May 2018, 3– 4 months after placing pots at the ex-
perimental sites, using two portable photosynthesis systems (Li- Cor
6400 XT, Li- Cor Inc.). On both instruments, the 6400- 88 expanded
temperature control kit was installed on IRGA sensor head to expand
the temperature control. One healthy (i.e., green without visible dam-
age from herbivores) leaf from each of four to six seedlings of each
species at each site were measured. These leaves were developed
under the new growth conditions at each site. Light- saturated net CO2
assimilation rates (An) were measured at varying intercellular CO2 con-
centrations (Ci), producing A- Ci curves. These A- Ci curves were meas-
ured at a PPFD (photosynthetic photon flux density) of 1800 µmol
photons m−2 s−1, air flow rate of 400 µmol s−1 and at five leaf tempera-
tures (19, 25, 30, 35 and 40℃). The target relative humidity in the leaf
cuvette was between 60% and 70%. However, at 35 and 40℃, this
target could not be achieved (varying between 35% and 50%) despite
the addition of approximately 10 ml of water in the soda lime column.
Therefore, the VPD in the leaf cuvette increased with the measuring
leaf temperature (Figure S2). Only the leaf temperature in the cuvette
was controlled; therefore, the rest of the plant was exposed to am-
bient temperature in the field. After the target leaf temperature was
reached, the leaf was given 10– 15 min to acclimate before starting an
A- Ci. The A- Ci curve was started once gas exchange was stable at a
reference CO2 concentration of 40 0 µmol mol−1; CO2 concentrations
were then changed sequentially to 250, 125, 50, 400, 600, 800, 1200,
1600 and 2000 and 400 µmol mol−1. Due to the difficulty of reaching
35 and 40℃ on cooler days, particularly in HE, and also of maintaining
a reasonable minimum gs (considered to be 0.025 mol H2O m−2 s−1 in
this study, also see Vårhammar et al., 2015) at these leaf temperatures,
there were fewer replicates with reliable Vcmax and Jmax data (two to
four instead of five) at 35 and 40℃.
During A- Ci curve measurements, a neighboring leaf, right next
to the one being measured, was covered by aluminum foil for at least
30 min to be measured for dark- adapted respiration (Rd). At the end
of the A- Ci curves, the light source in the leaf cuvette was turned
off, the reference CO2 concentration was set to 400 µmol mol−1,
and the air flow rate was decreased to 250 µmol s−1 before clamping
on to the neighbouring leaf without exposing it to daylight. After
reaching stability, three dark respiration points with a 10- s interval
were taken at a leaf temperature of 25℃. These three points were
averaged to get one value of Rd for each measured leaf. These three
Rd measurements for each leaf did not differ by more than 0.1 μmol
m−2 s−1 in any leaf. Empty chamber measurements (i.e., with no leaf
in the LI- 6400 XT leaf cuvette) were also collected at the end of
each A- Ci curve (i.e., empt y A- Ci cur ve) and leaf respiration measure-
ments. These measurements were used to correct for any instru-
ment noise prior to data analyses.
2.5 | Parameterization of photosynthesis models
The C3 photosynthesis model developed by Farquhar et al. (1980)
was used to estimate Vcmax and Jmax from the A- Ci curves, using
the “fitacis” function and the “bilinear” fitting method from the
“plantecophys” R package (Duursma, 2015) in R version 3.6.3 (R
Core Team, 2020). We maintained the default temperature de-
pendencies of the CO2 compensation point in the absence of mi-
tochondrial respiration (Γ*) and the Michaelis– Menten constants
for CO2 and O2 (Kc and Ko) from Bernacchi et al. (2001). Apparent
values of Vcmax and Jmax, parameterized based on intercellular CO2
concentrations (Ci), are reported. Values of Jmax are reported only
when the Jmax- limited photosynthesis (Aj) part of the A- Ci cur ve
had at least two data points, or from one single data point if Ci
>1000 μmol m−2 s
−1 and/or Aj was at least 10% lower than the
Vcmax- limited photosynthesis (Ac) predicted at the Ci value of that
point. Based on these criteria, we could not parameterize Jmax for
14 out of 146 total fitted A- Ci curves. The triose phosphate use
(TPU) was also fitted, but An was not visibly TPU- limited in any of
the A- Ci curves.
The first An data point at a reference CO
2 concentration of
400 µmol mol−1 was retrieved from each A- Ci curve measurement,
and the temperature response of An was fitted using a nonlinear
quadratic function (Battaglia et al., 1996):
where An (T) is the An (µmol m−2 s−1) at a given air temperature T (°C)
and Aopt is the An at the optimum temperature (Topt).
To estimate to what extent stomatal conductance and light res-
piration (Rday) may have influenced the shifts in Topt, we re- calculated
net photosynthesis (A287) and gross photosynthesis (i.e., including
Rday; Ag287) at a common Ci of 287 µmol mol−1 (i.e., with Ci/Ca ratio
of 0.7 considering an ambient atmospheric CO2 concentration of
410 ppm) using parameterized Vcmax, Jmax and Rday (only for A287) in
the following equations:
where O is the intercellular concentrations of O2, Kc and Ko are the
Michaelis– Menten coefficients of Rubisco activity for CO2 and O2, re-
spectively, and Γ* is the CO2 compensation point in the absence of
mitochondrial respiration. Values at 25℃ and temperature sensitivities
of Γ*, Kc and Ko were taken from Bernacchi et al. (20 01). To account for
differences in air pressure from different sites (caused by differences
in altitude), Ci and O concentrations were converted in unit pascal.
A287 and Ag287 were considered as the minimum of Ac and Aj.
Using Equation (1), ToptA287 and ToptA g287 were estimated.
(1)
An
(T)=A
opt
−b
(
T−T
opt)2,
(2)
A
c=
Vcmax

Ci−Γ
∗

Ci+Kc

1+O
KO
−Rday
,
(3)
Aj=Jmax
4×

Ci−Γ
∗

C
i
+2Γ∗

−Rday
.

6
|
DU SENGE Et a l.
The temperature responses of Vcmax and Jmax were fitted using
the following peaked Arrhenius function from (Medlyn et al., 2002):
where kopt is the process rate (i.e., Vcmax or Jmax; µmol m−2 s−1) at the
optimum temperature, Topt is exp resse d in degree s Kelvin (ToptV or ToptJ;
°K), Hd (kJ mol−1) is the deactivation energy term that describes the
decline in enzyme activity at supra- optimal temperature, Ea (kJ mol−1)
is the activation energy term that describes the initial exponential in-
crease in enzyme activity with increasing temperature, R is the uni-
versal gas constant (8.314 J mol−1 K
−1) and Tk is a given temperature
in degrees Kelvin. The value of Hd was fixed at 200 kJ mol−1 to avoid
over- parameterization (Dreyer et al., 2001; Medlyn et al., 2002).
To calculate the magnitude of the shifts of ToptA, ToptV and ToptJ in
response to increased growth temperatures, these parameters were
regressed against daytime growth temperature for the 4- month pe-
riod preceding and during gas exchange measurements campaign.
2.6 | Leaf structural and chemical analyses and
plant biomass
After gas exchange measurements, measured leaves were collected
and discs of known area were taken using a puncher and dried at
70℃ until they reache d a const ant weight. The leaf dr y mass per unit
leaf area (LMA) was subsequently determined. The dry discs were
ground to a fine powder which was analyzed for leaf N content using
an elemental gas analyzer (EA 1108; Fison Instruments).
After 1 year, all eight trees per species and site combination
were harvested and separated into roots, stem and leaf components.
Roots were separated from soil by washing them with clean water,
and a sieve was used to retain all the fine roots after washing. All
harvested components were dried at 70℃ to a constant weight and
thereafter weighed separately to determine dry mass for each com-
ponent and individual tree.
2.7 | Statistical analyses
Since for many of the individual leaves it was difficult to parameterize
Equation (1) and in a few cases Equation (4), we fit these two equa-
tions on data pooled across each species and site combination. Then,
to test whether the fitted parameters from these two equations
significantly differed among sites, we used the Welch's t test (see
details of the equations for the test in the supplementary material)
by making three separate tests with each test comparing two sites
(Table 1). To reduce the type I error among these multiple pairwise
comparisons, two sites were judged to differ at a p- value threshold
of 0.01 (i.e., if p < 0.01). Other measured tr aits for each species were
analyzed by a one- way ANOVA with site as the main factor and a
significant difference was assessed at a p- value threshold of 0.05
(p < 0.05; Table 2). When a significant site main ef fect was detected,
we used post- hoc Tukey's significance tests to evaluate differences
among sites using emmeans (Lenth, 2021) and multcomp (Hothorn
et al., 2008) R packages. To test whether increasing growth tem-
peratures affected the temperature response of Vcmax , Jmax, gs and
An for each species, we used a one- way repeated- measures ANOVA
(Table 3) using a mixed- effects analysis approach with lme function
from the nlme R package (Pinheiro et al., 2019) and with method set
to the maximum likelihood (ML; Field et al., 2012). In this analysis,
the leaf temperature and site were the main effects and each indi-
vidual tree (across different leaf temperatures) as a random factor.
All the data in figures and tables are reported as means ± SE. All
analyses were performed in R version 3.6.3 (R Core Team, 2020).
3 | RESULTS
3.1 | Leaf nitrogen and morphological traits
In H. montana, leaf nitrogen content on an area basis (leaf Na) was
significantly lower (37%) in seedlings grown at both the ME and LE
sites compared to their counterpart s grown at the HE site (2.3 g m−2 ;
Tables 2 and 4). In S. guineense, leaf Na was significantly different
across sites, where leaf Na was 4% and 21% lowe r at LE and ME sites,
respectively, compared to seedlings grown at HE (2.3 g m−2; Tables
2 and 4). Site differences for leaf Nm were similar to those for Na in
both species since leaf mass per unit leaf area (LMA) was constant
across sites in both species (Tables 2 and 4).
3.2 | Warming effect on temperature sensitivity
parameters of underlying biochemical processes of
net photosynthesis
The shape of the temperature response curve of neither the maxi-
mum carboxylation rates of Rubisco (Vcmax) nor the maximum elec-
tron transport rates (Jmax) was significantly altered by rising growth
temperature in either species (Figure 1; Table 3). In H. montana,
the thermal optimum of Vcmax (ToptV) was not significantly differ-
ent in seedlings across the three sites, despite being 1.8 ± 1.8 ˚C
and 3.6 ± 1.8℃ higher in seedlings at LE and ME sites, respectively,
than in seedlings grown at the coolest, HE site (Tables 1 and 4). In
S. guineense, ToptV was also not significantly different in seedlings
across the three sites, although ToptV was on average 2.3 ± 1.8℃
higher in seedlings grown at LE site compared to seedlings grown at
both ME and HE sites (Tables 1 and 4). These small and statistically
non- significant shifts in ToptV at lowe r com pare d to the high est el eva -
tion sites represent a 0.35 and 0.22℃ rise in ToptV per 1℃ increase in
daytime mean growth temperature for H. montana and S. guineense,
respectively (Figure S3). Unlike S. guineense in which the thermal
optimum of Jmax (ToptJ) was similar across the three sites, in H. mon-
tana, TOptJ signi fic antl y dif fere d among si tes, being unex pect edly 4℃
(4)
f
Tk=kopt
Hdexp Ea
(
Tk−Topt
)
TkRTopt 
Hd−Ea

1−exp

Hd(Tk−Topt)
T
k
RT
opt ,

|
7
DUSENGE E t al.
lower at LE compared to ME, while the Topt J of the HE was inte rme di-
ate and not significantly different from the other two sites (Tables 1
and 4). The shift in ToptJ in H. montana was 0.16℃ per 1℃ of warm-
ing, averaged for ME and LE (Figure S1). The activation energy of
Vcmax (EaV ) and Jmax (EaJ) did not significantly differ in seedlings of
either species across the three sites (Tables 1 and 4). Although mean
values EaV showed a progressive decline towards lower- elevation
and warmer sites, this change was not significant as there was large
variation in the values for this parameter (Tables 1 and 4). For both
species, the ratio of Jmax to Vcmax decreased with increasing leaf
TAB LE 1 Statistical outputs of the Welch t test on the temperature sensitivity parameters of net photosynthesis and photosynthetic
capacity
Harungana montana Syzygium guineense
ToptA
ToptA287 ToptA 287
HE ME LE HE ME LE
df T- value df T- value df T- value df T- value df T- value df T- value
HE 71.45 51.6
ME 80.03 80.2
LE 80.2 80.07
ToptAg287 ToptA g287
df T- value df T- value df T- value df T- value df T- value df T- value
HE 71.35 6 1
ME 80.1 80.3
LE 80.6 50.8
Harungana montana Syzygium guineense
ToptA
HE ME LE HE ME LE
df T- value df T- value df T- value df T- value df T- value df T- value
HE 71.1 60.6 70.1 70.4
ME 80.4 80.3
VcmaxOpt
HE 84.6 76.9 82.9 74.1
ME 82.2 60.4
JmaxOpt
HE 7 5 6 6.4 81.6 72.4
ME 70.9 70.4
ToptV
HE 72.1 71.1 70.05 81.5
ME 80.9 71.3
EaV
HE 90.6 80.8 80.3 51.4
ME 80.2 50.8
ToptJ
HE 81.5 7 1 7 1.6 40.07
ME 82.8 50.5
EaJ
HE 7.6 0.4 80.05 80.009 51.3
ME 80.4 51.5
Note: Bold numbers represent p- value less than 0.01 (p < 0.01). HE, High elevation; ME, Intermediate elevation; LE, Low elevation; df, degrees of
freedom; maximum carboxylation rates of Rubisco at the thermal optimum (VcmaxOpt, µm ol m−2 s−1); maximum electron transport rate at the thermal
optimum (JmaxOpt, µmol m−2 s−1); thermal optimum of Vcmax (ToptV, ℃); thermal optimum of Jmax (ToptJ, ℃); activation energy of Vcmax (Eav); activation
energy of Jmax (EaJ); thermal optimum of net CO2 assimilation (ToptA, ℃); thermal optimum of net CO2 assimilation at a common intercellular CO2
concentration (Ci) of 287 µmol mol−1 (ToptA 287, ℃); thermal optimum of gross CO2 assimilation at a common Ci of 287 µmol mol−1 (ToptAg2 87, ℃).

8
|
DU SENGE Et a l.
temperature, although the slopes differed among sites in both spe-
cies. In H. montana, Jmax/Vcmax decreased more strongly at LE and HE
compared to ME, while in S. guineense Jmax/Vcmax decreased more
strongly at HE compared to other two sites (Figure 1e,f).
3.3 | Warming effects on rate of net
photosynthesis and its thermal optimum
The responses of net photosynthesis (An) to short- term leaf tem-
perature variation exhibited different site differences between the
two species (Figure 2a,b; Table 3). At each site and species, An was
relatively constant between 18 and 30℃ and declined above this
temperature range. However, in H. montana, An was substantially
higher between 18 and 30˚C at HE compared to ME and LE sites
(both of which had similar An rates in this leaf temperature range),
but dropped drastic ally at leaf temperatures above 30℃ to net CO2
assimilation rates comparable to the other two sites (Figure 2a;
Table 3). In contrast, in S. guineense, An rates decreased at leaf
temperatures above 30℃, but An rates were similar among sites
throughout the entire measuring temperature range (Figure 2b;
Table 3). Decreases in An above 30℃ in both species were largely
driven by stomatal closure (Figure 2c,d) associated with high VPD
in the leaf chamber at these high leaf temperatures (Figure 2c,d;
Figures S2 and S4). Furthermore, the thermal optimum of An did
not significantly shift in response to warmer growth conditions
at lower- elevation sites in either species (Tables 1 and 4). In H.
montana, the non- significant shifts in the thermal optimum of An
(ToptA) were 3.2 and 1.9℃ higher in seedlings grown at ME and LE
sites, respectively, compared to those grown at cool, HE site. In S.
guineense, the corresponding shifts were only 0.4 and 1.4℃ (Tables
1 and 4). These small shifts in ToptA represent on aver age a chan ge of
0.34 and 0.16℃ per 1℃ of warming for H. montana and S. guineense,
respectively (Figure S3).
Since the shift in ToptA with a rise in growth temperature is also
affected by the simu ltane ous adj ustme nts in stomatal condu ctance
and leaf respiration (in addition to biochemical components), we
explored further to what extent these two processes may have im-
pacted the shifts in ToptA. The thermal optimum estimated from An
at a common intercellular CO2 concentration (Ci) of 287 (ToptA287)
was not significantly different from the corresponding ToptA value
within each site in either species (Tables 1 and 4), suggesting that
stomatal conductance did not control the thermal optimum of An
across different sites. This was due to a similar response of gs to
increasing leaf- to- air vapour pressure deficit inside the leaf cham-
ber (VPDL) as measurement temperature rises across all sites and
in either species (Figure 2a,b; Figures S2 and S4; Table 3). Similarly,
the thermal optimum of gross photosynthesis at a common Ci of
TAB LE 2 Summary report of ANOVA showing F- values and p- values for effect of site on chemical, morphological, photosynthetic
capacity and plant biomass in Harungana montana and Syzygium guineense
Harungana montana Syzygium guineense
Variable dfSite dfRes F- value p- value dfSite dfRes F- value p- value
Nm221 40.1 <0.0001 217 60.011
Na221 27. 3 <0.00 01 217 5.8 0.012
LMA 221 1.6 0.2 217 0.4 0.7
Vcmax25 214 30.7 <0.0001 212 4.5 0.034
Jmax25 213 36.7 <0.0001 212 4.5 0.035
Jmax25/Vcmax25 213 0.4 0.7 212 0.2 0.8
gs25 214 0.5 0.6 212 4.1 0.043
An25 214 8.3 0.0042 212 0.4 0.7
Rd25 213 30.2 <0.0001 212 11.9 0.0014
Total biomass 214 11.6 0.0011 212 1.5 0.3
Root biomass ratio 214 0.5 0.6 212 9.4 0.0036
Stem biomass ratio 214 0.7 0.5 212 3.2 0.076
Leaf biomass ratio 214 1.7 0.2 212 2.8 0.099
Total leaf biomass 221 6.3 0.0073 216 0.13 0.9
Total stem biomass 221 10.2 0.0 008 216 1.9 0.2
Total roots biomass 221 11.9 0.0004 216 4.3 0.031
Note: Bold numbers represent p- value less than 0.05 (p < 0.05). Total leaf nitrogen expressed on area (Na, g m−2) and dry mass (Nm, g g−1) basis; leaf
mass per unit area (LMA, g m−2 ); maximum carboxylation rates of Rubisco (Vcmax25, µmol m−2 s−1) and maximum electron transport rate (Jmax 25, µmol
m−2 s−1) measured at 25℃; the ratio of Jm ax25 to Vcmax25 (Jmax25/Vcmax25); stomatal conductance (gs25, mol H2O m−2 s−1 ), net CO2 assimilation rate (An25,
μmol m−2 s−1) and foliar dark respiration rate (Rd25, μmol m−2 s−1) measured at 25℃; total biomass (g); fractions of total biomass allocated to roots
(Root biomass ratio), stem (Stem biomass ratio), leaves (Leaf biomass ratio), total leaf biomass (g), total stem biomass (g) and total roots biomass (g); df:
degrees of freedom.

|
9
DUSENGE E t al.
287 ppm (ToptAg287 ) did not significantly differ from ToptA at ei-
ther site and in any of the species (Tables 1 and 4). However,
ToptAg287 seemed lower than ToptA at the LE site for either species
(Tables 1 and 4), implying that day respiration may have played
a role in photosynthetic thermal acclimation in seedlings at the
warmest site to some extent.
TAB LE 3 Summary report of the repeated- measures ANOVA for the temperature response curves of Harungana montana and Syzygium
guineense, showing F- values and p- values for effects of leaf temperature (Tleaf ), site and their interaction
dfnum dfden
Harungana montana
dfnum dfden
Syzygium guineense
F- value p- value F- value p- value
VcmaxRel Tleaf 159 54.8 <0.0001 149 15.2 0.0003
Site 214 0.1 0.9 212 0.01 0.98
Tleaf:Site 259 0.7 0.5 249 0.4 0.65
JmaxRel Tleaf 149 0.06 0.8 146 0.2 0.2
Site 213 0.1 0.8 212 0.4 0.8
Tleaf:Site 249 2.0 0.1 246 0.9 0.5
Jmax/Vcmax Tleaf 149 256 <0.0001 146 299 <0.0001
Site 213 0.097 0.9 212 0.9 0.4
Tleaf:Site 249 5.2 0.0083 246 8.8 0.0006
gsTleaf 159 115 <0.0001 150 140 <0.0001
Site 214 0.7 0.5 212 6.5 0.012
Tleaf:Site 259 1.6 0.2 250 0.08 0.9
AnTleaf 159 189 <0.0001 150 155 <0.0001
Site 214 5.7 0.015 212 0.14 0.9
Tleaf:Site 259 9.5 0.0003 250 0.3 0.8
Note: Bold numbers represent p- value less than 0.05 (p < 0.05). Traits analyzed were as follows: relative maximum carboxylation rate of Rubisco
(VcmaxRel); maximum electron transport rate (JmaxRel); stomatal conductance (gs, mol H2O m−2 s−1); net CO2 assimilation rate (An, μmol m−2 s−1); df:
degrees of freedom.
TAB LE 4 Chemical, morphological, and photosynthetic traits measured in Harungana montana and Syzygium guineense seedlings grown at
the three sites
Harungana montana Syzygium guineense
HE ME LE HE ME LE
Nm23.8 ± 1.2a13 .9 ± 0.1b13 .5 ± 0.4b20.7 ± 1a15.7 ± 1.2b20.0 ± 1ab
Na2.3 ± 0.1 a1.5 ± 0.1b1.4 ± 0.1b2.4 ± 0.1a1 .9 ± 0.1b2.3 ± 0.1ab
LMA 96.9 ± 3.1a108.2 ± 7.2a106. 2 ± 2.4a1 17. 7 ± 3.1a11 9.3 ± 4.9a114. 2 ± 3.3a
VcmaxOpt 89.4 ± 4.4a62.4 ± 3.8ab 51. 4 ± 3.3b78.5 ± 3.9a60.9 ± 4.7b59 ± 2.7b
JmaxOpt 152. 4 ± 9.4a95.5 ± 6.4b84.3 ± 5b123.1 ± 8.5a103.4 ± 8.8ab 98.8 ± 5.4b
ToptV 32.8 ± 0.9a36.4 ± 1.4a34.6 ± 1.3a32.9 ± 1.09a32.8 ± 1.5a35.2 ± 1.08a
EaV 76.9 ± 21.7a60.8 ± 18.6a54.8 ± 16.8a78.7 ± 24a66.0 ± 27.5a41 .8 ± 9.8a
ToptJ 30.8 ± 1.2ab 33.3 ± 1.1a29. 3 ± 0.9b27. 5 ± 0.9a2 9.9 ± 1.2a2 7. 8 ± 4a
EaJ 25.0 ± 10.9a32.9 ± 13.7a25.9 ± 12.3a39.5 ± 24. 3a3 9.8 ± 21.8a5.7 ± 8.8a
ToptA 20.8 ± 1.6a24. 0 ± 2.3a22.7 ± 2 .9a21.3 ± 1.9a21.7 ± 2.8a22.7 ± 2.8a
ToptA287 23.7 ± 1.0 4a24.1 ± 2.4a22.2 ± 3.4a24.7 ± 0.8a22 .7 ± 2.9a22.4 ± 3.3a
ToptAg287 23.7 ± 1.2a23.8 ± 2 .9a20. 2 ± 3.5a23.7 ± 0.9a23.1 ± 2.6a14 .6 ± 9.2a
Note: Letters after each value represent group comparisons across the three sites (HE, High elevation; ME, intermediate elevation; LE, low elevation)
generated from a Tukey post- hoc test (p < 0.05). Total leaf nitrogen expressed on area (Na, g m−2) and dry mass (Nm, mg g−1) basis; leaf mass per unit
area (LMA , g m−2); maximum carbox ylation rates of Rubisco at the thermal optimum (VcmaxOpt, µmol m−2 s−1); maximum electron transport rate at
the thermal optimum (Jmax Opt, µmol m−2 s−1 ); thermal optimum of Vcmax (ToptV, ℃); thermal optimum of Jmax (ToptJ, ℃); activation energy of Vcmax (Eav);
activation energy of Jmax (EaJ); thermal optimum of net CO2 assimilation (ToptA, ℃); thermal optimum of net CO2 assimilation at a common intercellular
CO2 concentration (Ci) of 287 µmol mol−1 (ToptA287, ℃); thermal optimum of gross CO2 assimilation at a common Ci of 287 µmol mol−1 (ToptA g287, ℃).
Means ± SE, n = 4– 8.

10
|
DU SENGE Et a l.
3.4 | Warming effect on stomatal conductance
Stomatal conductance decreased with increasing leaf temperature
and was not significantly different among the three sites across
the measuring temperature range of 18– 40℃ in either species
(Figure 2c,d; Table 3). However, when assessed at a standard leaf
temperature of 25℃ (gs25), gs25 in S. guineense was 25% and 50%
higher in seedlings at ME and LE sites, respectively, compared to
those at HE site (Figure 3b; Table 2). In H. montana, gs25 was not sig-
nificantly different between sites (Figure 3a; Table 2).
3.5 | Warming effect on photosynthetic
capacity rates
Photosynthetic capacity at a common leaf temperature of 25℃ (i.e.,
Vcmax25 and Jmax25) was significantly affected by increased growth tem-
perature in both species (Figure 4a– d). In H. montana, Vcmax25 decreased
by 45% and 48% in see dling s grown at th e ME an d LE site s, res pecti vel y,
compared to those grown at the HE site (Figure 4a; Table 2). Similarly,
Jmax25 was 49% lower in seedlings grown at both ME and LE sites than
those grown at HE site (Figure 4c; Table 2). In S. guineense, Vcmax25 and
Jmax25 were also reduced, but to a lesser extent compared to H. mon-
tana, decreasing by 20%– 25% at both ME and LE sites compared to HE
site (Figure 4b,d; Table 2). For both species, the ratio of Jmax25 to Vcmax25
(Jmax25/Vcmax25) was constant across all three sites (Figure 4e,f; Table 2).
The photosynthetic capacity at the thermal optimum was also
generally reduced by warming in both species. In H. montana, Vcmax
at the thermal optimum (VcmaxOpt) was 30% and 43% lower in seed-
lings grown at the ME and LE sites, respectively, compared to seed-
lings grown at the HE site (Tables 1 and 4). The corresponding values
for Jmax at the thermal optimum (JmaxOpt) were 37% and 45% (Tables
1 and 4). In S. guineense, the VcmaxOpt also significantly decreased by
22% and 25% in seedlings grown at ME and LE sites, respectively,
compared to seedlings grown at HE (Tables 1 and 4). However, the
JmaxOpt was not significantly different between sites (Tables 1 and 4).
3.6 | Warming effect on leaf dark respiration
Leaf dark respiration at a common leaf temperature of 25℃ (Rd25) ac-
climated to warming in both species (Figure 5; Table 2). In H. montana,
Rd25 was 37% and 53 % lower in se e d lings gr own at the ME and LE sites,
respectively, compared to seedlings grown at the HE site (Figure 5a;
Table 2). In S. guineense, Rd25 was on average 32% lower at both lower-
elevation sites compared to HE site (Figure 5b; Table 2). When data
were pooled across sites within each species, Rd25 was positively re-
lated to Vcmax25 and Jmax25 (Figure 6; Table S1), suggesting a coordi-
nated thermal acclimation between respiration and photosynthesis.
3.7 | Warming effect on plant
biomass and allocation
Plant biomass was differently affected by increased growth tem-
perature in the two species. In H. montana, the dry biomass was
112% and 184% higher in seedlings grown at the ME and LE sites,
respectively, compared to seedlings grown at the HE site (Figure 7a;
Table 2). Moreover, the dry biomass of leaves, stem and roots in-
creased by the same order of magnitude at warmer sites (Figure S5;
Table 2). However, the proportion of biomass allocated to roots (31%),
FIGURE 1 Temperature responses of photosynthetic capacity
in Harungana montana (a, c, e) and Syzygium guineense (b, d, f) grown
at different sites in Rwanda- TREE. (a, b) Relativized maximum
carboxylation rate of Rubisco (VcmaxRel), (c, d) maximum electron
transport rate (JmaxRel) and (e, f) the ratio of Jmax to Vcmax (Jmax/Vcmax).
Symbol colors represent different sites (high- elevation Sigira,
HE = white circle; intermediate- elevation Rubona, ME = grey circle;
low- elevation Makera, LE = black circle). Solid blue line (a– d) is the
overall regression line fitted with Equation (4) when sites do not differ.
Black lines (e, f) represent simple linear regressions fitted for different
sites (HE = solid line; ME = long- dashed; LE = dotted). Means ± SE.
n = 4– 6. In (c), the few leaves measured at 35℃ had unreliable
Jmax fits in two cases, thus no data point is shown. In each site and
species, each Vcmax and Jmax was relativized by the maximum mean
value across leaf temperatures. Maximum values (in μmol m−2 s−1)
for H. montana: Vcmax (HE = 87.05, ME = 63.43, LE = 54.07), Jmax
(HE = 152.55, ME = 94.19, LE = 86.02), and for S. guineense: Vcmax
(HE = 76.88, ME = 61.20, LE = 60.7), Jmax (HE = 127.1, ME = 101. 8,
LE = 101.83)

|
11
DUSENGE E t al.
stem (20%) and leaves (49%) did not differ significantly across sites
(Figure 7c,e,g). By contrast, total biomass in S. guineense was similar
across all three sites (Figure 7b; Table 2), but the allocation to roots
increased at warmer sites (Figure 7d) while allocation to leaves and
stem did not significantly differ between sites (Figure 7f,h; Figure S5).
4 | DISCUSSION
In this study, we report findings from the first comprehensive field
study investigating the instantaneous temperature responses of
photosynthesis and how they acclimate to long- term warming in
tropical tree species. Trees of two montane species with contrasting
successional strategies were grown in the field in 11- liter pots with
similar soil, along an elevation gradient in the Rwanda- TREE project.
Surprisingly, the optimal temperature of Vcmax, Jmax and An did not
significantly increase with warming in any species. However, both
photosynthetic capacity (Vcmax and Jmax) and leaf respiration (Rd) sig-
nificantly decreased in a coordinated manner at warmer sites. Plant
biomass was strongly increased by warming in H. montana seedlings
while it was constant across sites in S. guineense.
4.1 | Effect of growth temperature on
photosynthetic temperature sensitivity parameters
Surprisingly, despite a 7.4℃ increase in growth temperature (con-
sidering the 4- month period preceding and during the gas exchange
FIGURE 2 Gas exchange responses
to temperature in Harungana montana (a,
c) and Syzygium guineense (b, d) grown at
different sites in Rwanda- TREE. (a, b) Net
CO2 assimilation rate (An, μmol m−2 s−1 );
(c, d) stomatal conductance (gs, mol H2O
m−2 s−1). Symbol colors represent different
sites (high- elevation Sigira, HE = white
circle; intermediate- elevation Rubona,
ME = grey circle; low- elevation Makera,
LE = black circle). Solid blue line (b, c)
is the overall regression line fitted with
Equation (4) when sites do not differ.
Black lines (a, d) are linear regressions
fitted for different sites (HE = solid line;
ME = long- dashed; LE = dotted). (a, b) are
fitted with Equation (1) and (c, d) with a
quadratic function. Means ± SE. n = 4– 6
FIGURE 3 Stomatal conductance
(gs25, mol H2O m−2 s−1) measured at 25℃
in Harungana montana (a) and Syzygium
guineense (b) grown at different sites
in Rwanda- TREE. Colors represent
different sites (high- elevation Sigira,
HE = white; intermediate- elevation
Rubona, ME = grey; low- elevation
Makera, LE = black). Different letters on
bars represent differences across the
three sites (Tukey post- hoc test, p < 0.05).
Means ± SE. n = 4– 6

12
|
DU SENGE Et a l.
FIGURE 4 Photosynthetic capacity in
Harungana montana (a, c, e) and Syzygium
guineense (b, d, f) grown at different
sites in Rwanda- TREE. (a, b) Maximum
carboxylation rate of Rubisco (Vcmax25,
μmol m−2 s−1), (c, d) maximum electron
transport rate (Jmax25, μmol m−2 s−1) and (e,
f) ratio of Jmax25 to Vcmax25 (Jmax25/Vcmax25)
at measured at 25℃. Colors represent
different sites (high- elevation Sigira,
HE = white; intermediate- elevation
Rubona, ME = grey; low- elevation
Makera, LE = black). Different letters on
bars represent differences across the
three sites (Tukey post- hoc test, p < 0.05).
Means ± SE. n = 4– 6
FIGURE 5 Leaf dark respiration
measured at 25℃ (Rd25, μmol m−2 s−1 )
in Harungana montana (a) and Syzygium
guineense (b) grown at different sites
in Rwanda- TREE. Colors represent
different sites (high- elevation Sigira,
HE = white; intermediate- elevation
Rubona, ME = grey; low- elevation
Makera, LE = black). Different letters on
bars represent differences across the
three sites (Tukey post- hoc test, p < 0.05).
Means ± SE. n = 4– 6

|
13
DUSENGE E t al.
measurements campaign), ToptA did not significantly increase in
either species in our study (Table 1), suggesting a limited capacity
of photosynthesis to acclimate to warmer growth temperatures in
these tropical montane rainforests tree species. The statistically
non- significant shifts in ToptA were on average 0.34– 0.16℃ per 1℃
for H. montana and S. guineense, respectively (Figure S3). This range
was comparable to the non- significant shifts in thermal optimum of
Vcmax (ToptV; 0.22 and 0.35℃ per 1℃ of warming for S. guineense and
H. montana, respectively), indicating that possible shifts in ToptA are
controlled biochemically by thermal acclimation of Rubisco carboxy-
lation. The shift in ToptA in this study is lower than the value previ-
ously observed in a tropical lowland study (0.47℃ per 1℃; Slot &
Winter, 2017b), and in global meta- analyses dominated by temper-
ate and boreal tree species (0.43– 0.62℃; Kumarathunge et al., 2019;
Yamori et al., 2014). Therefore, based on our data, we conclude that
thermal acclimation of ToptA is either lacking or weaker than in most
previous studies, which mostly included temperate and boreal tree
species. Our first hypothesis of partial Topt acclimation is therefore
neither completely supported nor rejected. Although it is possible
that the temperature sensitivity of net photosynthesis across sites
may have been potentially affected by differences in leaf N, there is
currently little support for this effect (Tarvainen et al., 2017).
4.2 | Effect of growth temperature on stomatal
conductance
In our study, gs at a given leaf temperature increased with warm-
ing, particularly in the leaf temperature range between 25 and
35℃, but this increase was significant in S. guineense only (Figures 2
and 3). In the short term, gs typically decreases with the increasing
VPD accompanying an increase in temperature (Figures S2 and S4;
Grossiord et al., 2020; López et al., 2021; Oren et al., 1999). The de-
crease acts to prevent water loss in high- VPD air, but simultaneously
restricts the CO2 supply for photosynthesis (Farquhar & Sharkey,
1982). At our experimental sites, the two warmer, lower- elevation
sites had on average 49– 58% higher daytime air VPD compared
to the cool, high- elevation site. However, trees growing in a warm
climate with high VPD may acclimate their water uptake, trans-
port system and stomatal regulation to increase their gs at a given
VPD (Marchin et al., 2016). This happened in our study, at least for
S. guineense, which increased both gs and allocation of biomass to
roots in seedlings grown at lower elevations with relatively warmer
and drier conditions (Figures 3b and 7d). This response contrasts the
least- cost theory (Prentice et al., 2014) and our second hypothesis.
Clearly, additional studies that explore long- term responses of gs to
high temperature and VPD are needed (Grossiord et al., 2020; López
et al., 2021; Marchin et al., 2016; Oren et al., 1999). Such knowledge
is critical since the response of gs to global change factors has been
identified as an important factor that will dictate climate change re-
sponses of terrestrial productivity, hydrology and energy balance
(Cernusak et al., 2019; Grossiord et al., 2020), particularly for tropi-
cal forests (Doughty & Goulden, 2008; McDowell et al., 2018; Tan
et al., 2017).
4.3 | Effect of growth temperature on
photosynthetic capacity
In both species, photosynthetic capacity measured at a common leaf
temperature of 25℃ (i.e., Vcmax25 and Jmax 25) decreased substantially
at increased growth temperature (Figure 4). The decrease in photo-
synthetic capacity was largely driven by reduced leaf N with warm-
ing (also previously observed in Crous et al., 2018; Dusenge et al.,
2020; Scafaro et al., 2017; Way & Sage, 2008), but the effect re-
mained also after normalization for differences in leaf N (Figure S6;
Table S2). These results suggest that the decreased photosynthetic
capacity at warmer sites was caused by both decline in total leaf N
FIGURE 6 Relationship between foliar respiration and photosynthetic capacity. Foliar dark respiration rate (Rd25, μmol m−2 s−1), maximum
carboxylation rates of Rubisco (Vcmax25, μmol m−2 s−1), maximum electron transport rates (Jmax25, μmol m−2 s−1) measured at 25℃. Lines
represent simple linear regressions for different species (Harungana montana = dashed; circle; Syzygium guineense = solid, triangle). Colors
represent different sites (high- elevation Sigira, HE = white; intermediate- elevation Rubona, ME = grey; low- elevation Makera, LE = black).
Data points represent measured seedlings for each of the two species. Adjusted R2 is 0.58 for both (a) and (b)

14
|
DU SENGE Et a l.
and a lower relative allocation of leaf N into photosynthetic com-
pounds. These findings are consistent with our second hypothesis
and in line with least- cost optimality theory predicting that photo-
synthetic capacity and leaf nutrient demand should be reduced with
warming (Fürstenau Togashi et al., 2018; Smith & Keenan, 2020;
Wang et al., 2020). With higher enzymatic efficiency at increased
temperature, plants should decrease leaf nutrient concentrations
and allocate more nutrients to new leaves and other plants organs
(e.g., roots) for maximized overall growth in a warmer environment
(Wang et al., 2020).
Based on the optimality theory predictions (Wang et al., 2020),
thermal acclimation of Vcmax25 should lead to a 14% and 28% re-
duction at the ME and LE, respectively, compared to HE site
(Mujawamariya et al., 2020). These values are in good agreement
with observations for S. guineense, where Vcmax25 was decreased by
23% at both lower- elevation sites. However, in H. montana, Vcmax25
decreased by 45% and 48% at the ME and LE, respectively. These
large reductions in H. montana may partly reflect some pot limita-
tion, with this species showing strongly increased growth at the two
warmer sites, in contrast to S. guineense (Figure 7). Although being
in the direction predicted by optimality theory, our findings contrast
to previous studies on tropical species which did not find any signif-
icant effect of warming on basal rates of photosynthetic capacity
(Carter et al., 2020; Crous et al., 2018; Scafaro et al., 2017).
We did not see any reduction of the Jmax25/Vcmax25 ratio with
warming (Figure 4), which is otherwise commonly reported in several
individual studies and meta- analyses (e.g., Bermudez et al., 2020;
Dusenge et al., 2015, 2020; Kattge et al., 2009; Kumarathunge et al.,
2019; Stefanski et al., 2019). However, similar to our findings, there
was also no warming- induced decrease in Jmax/Vcmax ratio in other
previous studies with tropical trees (Crous et al., 2018; Scafaro
et al., 2017). Decreases in Jmax/Vcmax may occur as a mechanism that
offset increasing carboxylation limitation of photosynthesis under
warm conditions as gs declines and photorespiration increases. In
our study, the constant Jmax/Vcmax may be explained by increased
CO2 supply via observed warming- induced increase in stomat al con-
ductance at 25℃ (observed in both species but significant only in
S. guineense; Figure 5a,b). This may have stimulated carboxylation
with no further need to alter resource allocation between the two
biochemical processes. Our results therefore indicate that whether
decreased or maintained Jmax25/Vcmax25 is optimal in warmer condi-
tions depends on the response of gs and its influence on Ci.
4.4 | Thermal acclimation of foliar dark respiration
In our study, Rd25 was lower in warm- grown seedlings compared to
cool- grown counterparts in both species, consistent with our third
hypothesis (Figure 5). These results are also consistent with those
from several previous studies on tropical trees (Slot & Kitajima,
2015; Slot et al., 2014; Slot & Winter, 2018; Smith & Dukes, 2017;
Zhu et al., 2020). Thermal acclimation of leaf Rd25 was stronger in H.
montana than in S. guineense. This sp eci es di fferen ce in ther mal accli-
mation of Rd may be linked to the stronger warming- induced decline
in both leaf N (as also seen in Crous et al., 2017; Dusenge et al., 2020)
and photosynthetic capacity in H. montana compared to S. guineense
(Table 2; Figure 4a– d). Strong thermal acclimation of Rd was also ob-
served in a companion study from the same experimental sites but
with an extended number of species (16 early- and late- successional
species) freely rooted in the soil (Mujawamariya et al., 2020).
Values of Rd25 were positively related to both Vcmax25 and Jmax 25
(Figure 6), suggesting that thermal acclimation of Rd was coordi-
nated with thermal acclimation of photosynthetic capacity, con-
sistent with our fourth hypothesis. These findings agree with the
optimality theory of photosynthetic capacity recently proposed by
Wang et al. (2020), which demonstrated that thermal acclimation of
FIGURE 7 Total plant biomass and allocation in Harungana
montana (a, c, e, g) and Syzygium guineense (b, d, f, h). (a, b) Total
seedling biomass; (c, d) the proportion of total plant biomass
allocated to roots (Root mass ratio), (e, f) stems (Stem mass ratio)
and (g, h) leaves (Leaf mass ratio). Colors represent different sites
(high- elevation Sigira, HE = white; intermediate- elevation Rubona,
ME = grey; low- elevation Makera, LE = black). Different letters on
bars represent differences across the three sites (Tukey post- hoc
test, p < 0.05). Means ± SE. n = 4– 6

|
15
DUSENGE E t al.
Rd follow closely that of Vcmax to maintain optimal photosynthesis
with efficient use of resources in a given environment. This ther-
mal acclimation in leaf respiration can, in turn, be achieved via sev-
eral biochemical processes including reductions in Cytochrome C
Oxidase (COX) content, a key central respiratory protein (Rashid
et al., 2019), decreases in mitochondrial density (Armstrong et al.,
2006) or changes in some intermediates of glycolysis and tricarbox-
ylic acid cycle (Rashid et al., 2020). The strong correlation between
thermal acclimation of leaf respiration and photosynthesis likely re-
flects both the dependence of respiration on substrate from pho-
tosynthesis (Dusenge et al., 2019; Mujawamariya et al., 2020) and
the reduced energy required to maintain less, but more efficient leaf
proteins (particularly Rubisco) in warm- grown plants (Wang et al.,
2020).
4.5 | Effect of growth temperature on tree
growth and biomass allocation
Growth and allocation of dry biomass to different plant organs
(roots, stem and leaves) responded differently to warming between
the two species (Figure 7). In H. montana (early- successional and
fast- growing species), the total dry biomass significantly increased
at the warmer sites, while in S. guineense (late- successi onal an d slow-
growing species), it remained constant across all sites. With respect
to tree biomass components, for H. montana, dry biomass of leaf,
stem and roots also increased at warmers sites, but with no changes
in biomass allocation. In contrast, for S. guineense, only the dry bio-
mass of roots increased at warmers sites, while the dry biomass of
both leaves and stems was largely constant across all sites (Figure
S5). Contrasts in tree growth responses to warming between the
two species may be linked to differences in their responses of both
leaf physiology and leaf production.
In H. montana, increases in leaf biomass with warming may
have been the main driver of higher total biomass at warmer sites,
despite concomitant declines in net photosynthesis. Net CO2 as-
similation decreased by 31%– 34% in both lower sites compared to
the high- elevation site (Figure S7). The Rd25 decreased even more
strongly by 37 and 53% at the mid and low elevation, respectively
(Figure 5). Again, assuming a Q10 value of 2.3, this Rd downregula-
tion resulted in constant and lower Rd at average nighttime growth
temperatures at ME and LE sites, respectively; that is, complete
or over- compensatory thermal acclimation. Increased growth at
warmer sites in H. montana may, therefore, be attributed to two
linked processes. First, a greatly increased leaf biomass (Figure S5)
and likely also increased total canopy leaf N (Figure S8) in a warmer
climate may have resulted in increased canopy carbon fixation in
spite of lower leaf level rate s. Se cond, if a sim ilarl y str ong dow nreg-
ulation of respiration was present in plant parts other than upper-
canopy leaves, the strong downregulation in respiration at the
warmest site (i.e., lower rates at ambient night temperature) may
have contributed to increased carbon availability for tree growth
with warming.
By contrast, S. guineense maintained similar net CO2 assimilation
rates across the three sites (Figure S7). In addition, leaf respiration at
25℃ decreased by 32% at the two lower- elevation sites. Assuming a
Q10 value of respir ation of 2.3 (Atkin & Tjoelker, 2003; Sl ot & Winter,
2017b; Weerasinghe et al., 2014), this implies approximately homeo-
stasis in Rd at mean nighttime growth temperatures (Mujawamariya
et al., 2020). Therefore, S. guineense may have maintained relatively
similar An and Rd rates across all three sites, and when combined
with similar sites leaf biomass, it largely resulted in constant growth
across all sites.
Overall, our findings indicate that montane fast- growing and
early- successional species (pioneer) will respond more positively
to warming compared to slow- growing and late- successional coun-
terparts (climax). H. montana (a shade intolerant, early- successional
and a fast- growing species) is common in secondary forests that are
formed either naturally after creation of canopy gaps within an old
forest (e.g., landslides, tree falls) or after human disturbances (e.g.,
forest fires, mining). The environmental conditions within these gaps
are characterized by higher light and temperature variability com-
pared to understory environments (Lebrija- Trejos et al., 2011), where
species such as S. guineense (shade- tolerant, late- successional and
slow- growing species) commonly regenerate (Nyirambangutse et al.,
2017). Growth in H. montana may, therefore, be more responsive
to increased temperature when grown at warmer, lower- elevation
sites, where radiation is also higher due to lower cloud cover
(Gliniars et al., 2013; Mujawamariya et al., 2020). In addition, physi-
ological plasticit y in early- successional species in response to warm-
ing, which has been indicated in some studies (Slot & Winter, 2017b,
2018), may also be an important factor. In our study, this physiolog-
ical plasticity was observed in leaf respiration (Figure 5). In contrast,
late- successional S. guineense may be less stimulated by increased
growth temperatures. Our findings are in line with results from some
previous controlled experimental studies, but with tropical lowland
species, which showed that early- successional species tend to re-
spond more positively to warming compared to late- successional
specie s (Cheesman & Winter, 2013a , 2013b). However, a rece nt con-
trolled experimental study on tropical lowland tree species did not
find any effects of warming across nine early- and late- successional
species (Slot & Winter, 2018). More experimental tropical studies,
especially in field settings and with a larger species representation
from each functional group, are still needed to draw a firm conclu-
sion to whether early- and fast- growing versus late- successional and
slow- growing species respond differently to warming.
5 | CONCLUSIONS
Our study demonstrates that photosynthetic thermal acclimation is
limited in tropical montane tree species. In both species, the thermal
optima of net photosynthesis and underlying biochemical processes
(Vcmax and Jmax) did not significantly shift in response to higher growth
temperature. However, photosynthetic capacity and leaf dark res-
piration synchronously acclimated by decreasing with increasing

16
|
DU SENGE Et a l.
growth temperatures. Growth was stimulated by warming in the
montane early- successional and fast- growing species but not in the
late- successional and slow- growing species correlating with species
differences in total leaf biomass. Our findings suggest that dynamic
global vegetation models (DGVMs) should not generalize the partial
thermal acclimation of the optimum of net photosynthesis derived
from meta- analyses dominated by temperate and boreal species for
tropical montane rainforest tree species. Moreover, DGVMs should
also consider the tight coordination in thermal acclimation of leaf
respiration and photosynthetic capacity when predicting feedback
between terrestrial vegetation and climate.
ACKNOWLEDGEMENTS
This study was funded by the Swedish Research Council for
Environment, Agricultural Sciences and Spatial Planning (Formas;
grant 2015- 1458) and the Swedish research council (VR; grant 2015-
03338). MED was also funded by the European Union’s Horizon 2020
research and innovation programme under the Marie Sklodowska-
Curie grant agreement No 844319. DAW acknowledges funding
from the NSERC Discovery program, an Ontario Early Researcher
Award, the Canada Foundation for Innovation, and the Research
School of Biology at the Australian National University. DAW was
also supported in part by the US Department of Energy contract
number DE- SC0012704 to Brookhaven National Laboratory. JU
and GW were also supported by the Swedish strategic research
area “Biodiversity and Ecosystem services in a Changing Climate”
(BECC; http://www.becc.lu.se/). We are also grateful to the Rwanda
Agriculture and Animal Resources Development Board for provid-
ing the sites for the Rwanda- TREE experiment (https://www.rwand
atree.com).
DATA AVAIL AB I LI T Y STATE MEN T
The data that support the findings of this study are available from
the corresponding author upon reasonable request.
ORCID
Mirindi Eric Dusenge https://orcid.org/0000-0003-4218-0911
Danielle A. Way https://orcid.org/0000-0003-4801-5319
Johan Uddling https://orcid.org/0000-0003-4893-1915
Göran Wallin https://orcid.org/0000-0002-5359-1102
REFERENCES
Armstrong, A. F., Logan, D. C., & Atkin, O. K. (20 06). On the developmen-
tal dependence of leaf respiration: Responses to short- and long-
term changes in growth temperature. American Journal of Botany,
93, 1633– 1639. https://doi.org/10.3732/ajb.93.11.1633
Atkin, O. K., & Tjoelker, M. G. (2003). Thermal acclimation and the
dynamic response of plant respiration to temperature. Tre nds
in Plant Science, 8, 343– 351. https://doi.org/10.1016/S1360
- 1 3 8 5 ( 0 3 ) 0 0 1 3 6 - 5
Battaglia, M., Beadle, C., & Loughhead, S. (1996). Photosynthetic tem-
perature responses of Eucalyptus globulus and Eucalyptus nitens. Tree
Physiolog y, 16, 81– 89. https://doi.org/10.1093/treep hys/16.1- 2.81
Bermudez, R., Stefanski, A., Montgomery, R. A., & Reich, P. B. (2020).
Short and long- term responses of photosynthetic capacity to
temperature in four boreal tree species in a free- air warming and
rainfall manipulation experiment. Tree Physiology, 41, 89– 102.
https://doi.org/10.1093/treep hys/tpaa115
Bernacchi, C. J., Singsaas, E. L., Pimentel, C., Portis, A. R. Jr, & Long, S.
P. (2001). Improved temperature response functions for models of
Rubisco- limited photosynthesis. Plant, Cell & Environment, 24, 253–
259. https://doi.org/10.1111/j.1365- 3040.2001.00668.x
Berry, J., & Björkman, O. (1980). Photosynthetic response and adaptation
to temperature in higher plants. Annual Review of Plant Physiology, 31,
491– 543. https://doi.org/10.1146/annur ev.pp.31.060180.002423
Booth, B. B. B., Jones, C. D., Collins, M., Totterdell, I. J., Cox, P. M., Sitch,
S., Huntingford, C., Betts, R. A., Harris, G. R., & Lloyd, J. (2012).
High sensitivity of future global warming to land carbon cycle pro-
cesses. Environmental Research Letters, 7, 024002. ht tps://doi.org/1
0.1088/1748- 9326/7/2/0240 02
Carter, K. R., Wood, T. E., Reed, S. C., Schwartz, E. C., Reinsel, M. B.,
Yang, X., & Cavaleri, M. A. (2020). Photosynthetic and respiratory
acclimation of understory shrubs in response to in situ experimen-
tal warming of a wet tropical forest. Frontier s in Forests and Global
Change, 3. https://doi.org/10.3389/ffgc.2020.576320
Cernusak, L. A., Goldsmith, G. R., Arend, M., & Siegwolf, R. T. W. (2019).
Effect of vapor pressure deficit on gas exchange in wild- type and
abscisic acid- insensitive plants. Plant Physiology, 181, 1573– 1586.
https://doi.org/10.1104/pp.19.00436
Cheesman, A. W., & Winter, K. (2013a). Growth response and acclima-
tion of CO2 exchange characteristics to elevated temperatures in
tropical tree seedlings. Journal of Experimental Botany, 64, 3817–
3828. https://doi.org/10.1093/jxb/ert211
Cheesman, A. W., & Winter, K. (2013b). Elevated night- time tempera-
tures increase growth in seedlings of two tropical pioneer tree
species. New Phytologist, 197, 1185– 1192. https://doi.org/10 .1111/
nph.12098
Crous, K. Y., Drake, J. E., Aspinwall, M. J., Sharwood, R. E., Tjoelker, M. G.,
& Ghannoum, O. (2018). Photosynthetic capacity and leaf nitrogen
decline along a controlled climate gradient in provenances of two
widely distributed Eucalyptus species. Global Change Biology, 24,
4626– 46 44. ht tp s://doi.o rg /10.1111/gcb.14330
Crous, K. Y., Quentin, A. G., Lin, Y.- S., Medlyn, B. E., Williams, D. G.,
Barton, C. V. M., & Ellsworth, D. S. (2013). Photosynthesis of tem-
perate Eucalyptus globulus trees outside their native range has
limited adjustment to elevated CO2 and climate warming. Global
Change Biology, 19, 3790– 38 07. https://doi.org/10.1111/gcb.12314
Crous, K. Y., Wallin, G., Atkin, O. K., Uddling, J., & Af Ekenstam, A.
(2017). Acclimation of light and dark respiration to experimental
and seasonal warming are mediated by changes in leaf nitrogen
in Eucalyptus globulus. Tree Physiology, 37, 1069– 1083. https://doi.
org/10.1093/treep hys/tpx052
Cunningham, S. C., & Read, J. (2003). Do temperate rainforest trees
have a greater ability to acclimate to changing temperatures than
tropical rainforest trees? New Phytologist, 157, 55– 64. https://doi.
org/10.1046/j.1469- 8137.2003.00652.x
Doughty, C. E., & Goulden, M. L. (2008). Are tropical forests near a
high temperature threshold? Journal of Geophysical Research, 113,
G00B07. https://doi.org/10.1029/2007J G000632
Drake, J. E., Aspinwall, M. J., Pfautsch, S., Rymer, P. D., Reich, P. B.,
Smith, R. A., Crous, K. Y., Tissue, D. T., Ghannoum, O., & Tjoelker,
M. G. (2015). The capacity to cope with climate warming declines
from temperate to tropical latitudes in two widely distributed
Eucalyptus species. Global Change Biology, 21, 459– 472. https://doi.
org /10.1111/gcb.12729
Dreyer, E., Le Roux, X., Montpied, P., Daudet, F. A., & Masson, F. (2001).
Temperature response of leaf photosynthetic capacity in seedlings
from seven temperate tree species. Tree Physiology, 21, 223– 232.
https://doi.org/10.1093/treep hys/21.4.223
Duque, A., Stevenson, P. R., & Feeley, K. J. (2015). Thermophilization
of adult and juvenile tree communities in the northern tropical

|
17
DUSENGE E t al.
Andes. Proceedings of the National Academy of Sciences of the United
States of America, 11 2, 10744– 10749. https://doi.org/10.1073/
pnas.15065 70112
Dusenge, M. E., Duarte, A. G., & Way, D. A. (2019). Plant carbo n metabo-
lism and climate change: Elevated CO2 and temperature impacts on
photosynthesis, photorespiration and respiration. New Phytologist,
221, 32– 49. https://doi.or g/10.1111/nph .15283
Dusenge, M. E., Madhavji, S., & Way, D. A . (2020). Contrasting acclima-
tion resp onses to eleva ted CO2 and wa rmi ng be t we en an evergreen
and a deciduous boreal conifer. Global Change Biology, 26, 3639–
3657. https://doi.org/10.1111/gcb.15 084
Dusenge, M. E., Wallin, G., Gårdesten, J., Niyonzima, F., Adolfsson, L.,
Nsabimana, D., & Uddling, J. (2015). Photosynthetic capacity of
tropical montane tree species in relation to leaf nutrients, suc-
cessional strategy and growth temperature. Oecologia, 17 7, 1183–
1 1 9 4 . h t t p s : / / d o i . o r g / 1 0 . 1 0 0 7 / s 0 0 4 4 2 - 0 1 5 - 3 2 6 0 - 3
Duursma, R. A . (2015). Plantecophys— An R package for analysing and
modelling leaf gas exchange data. PLoS ONE , 10 , e014 334 6. http s://
doi.org/10.1371/journ al.pone.0143346
Fadrique, B., Báez, S., Duque, Á., Malizia, A., Blundo, C., Carilla, J., Osinaga-
Acosta, O., Malizia, L., Silman, M., Farfán- Ríos, W., Malhi, Y., Young,
K. R., Cuesta, C. F., Homeier, J., Peralvo, M., Pinto, E., Jadan, O.,
Aguirre, N., Aguirre, Z., & Feeley, K. J. (2018). Widespread but het-
erogeneous responses of Andean forests to climate change. Nature,
564, 2 0 7 – 2 1 2 . h t t p s : / / d o i . o r g / 1 0 . 1 0 3 8 / s 4 1 5 8 6 - 0 1 8 - 0 7 1 5 - 9
Farquhar, G. D., & Sharkey, T. D. (1982). Stomatal conductance and pho-
tosynthesis. Annual Review of Plant Physiology, 33, 317– 345. https://
doi.org/10.1146/annur ev.pp.33.060182.001533
Farquhar, G. D., von Caemmerer, S., & Berry, J. A. (1980). A biochemical
model of photosynthetic CO2 assimilation in leaves of C3 species.
Planta, 149, 78– 90. https://doi.org/10.1007/BF003 86231
Fauset, S., Oliveira, L., Buckeridge, M. S., Foyer, C. H., Galbraith, D.,
Tiwari, R., & Gloor, M. (2019). Contrasting responses of stomatal
conductance and photosynthetic capacity to warming and elevated
CO2 in the tropical tree species Alchornea glandulosa under heat-
wave conditions. Environmental and Experimental Botany, 158, 28–
39. https://doi.org/10.1016/j.envex pbot.2018.10.030
Field, A., Miles, J., & Field, Z. (2012). Discovering statistics using R. Sage
Publishing.
Fürstenau Togashi, H., Prentice, I. C., Atkin, O. K., Macfarlane, C., Prober,
S. M., Bloomfield, K. J., & Evans, B. J. (2018). Thermal acclimation
of leaf photosynthetic traits in an evergreen woodland, consistent
with the coordination hypothesis. Biogeosciences, 15, 3461– 3474.
h t t p s : / / d o i . o r g / 1 0 . 5 1 9 4 / b g - 1 5 - 3 4 6 1 - 2 0 1 8
Gliniars, R., Becker, G. S., Braun, D., & Dalitz, H. (2013). Monthly stem
increment in relation to climatic variables during 7 years in an East
African rainforest. Tre es , 27, 1129– 1138. ht tps://doi.org /10.1007/
s 0 0 4 6 8 - 0 1 3 - 0 8 6 3 - 3
Grossiord, C., Buckley, T. N., Cernusak, L. A., Novick, K. A., Poulter, B.,
Siegwolf, R. T. W., Sperry, J. S., & McDowell, N. G. (2020). Plant
responses to rising vapor pressure deficit. New Phytologist, 226,
1550– 1566. ht tps://doi.or g/10.1111/nph .16485
Gunderson, C. A., O’Hara, K. H., Campion, C. M., Walker, A. V., &
Edwards, N. T. (2009). Thermal plasticity of photosynthe-
sis: The role of acclimation in forest responses to a warm-
ing climate. Global Change Biology, 16 , 2272– 2286. https://doi.
org/10.1111/j.1365- 2486.2009.02090.x
Hothorn, T., Bretz, F., & Westfall, P. (2008). Simultaneous inference in
general parametric models. Biometrical Journal, 50(3), 346– 363.
https://doi.org/10.1002/bimj.20081 0425
Huang, M., Piao, S., Ciais, P., Peñuelas, J., Wang, X., Keenan, T. F., Peng,
S., Berry, J. A., Wang, K., Mao, J., Alkama, R., Cescatti, A., Cuntz,
M., De Deurwaerder, H., Gao, M., He, Y., Liu, Y., Luo, Y., Myneni, R.
B., … Janssens, I. A. (2019). Air temperature optima of vegetation
productivity across global biomes. Nature Ecology & Evolution, 3,
7 7 2 – 7 7 9 . h t t p s : / / d o i . o r g / 1 0 . 1 0 3 8 / s 4 1 5 5 9 - 0 1 9 - 0 8 3 8 - x
Hubau, W., Lewis, S. L., Phillips, O. L., Affum- Baffoe, K., Beeckman,
H., Cuní- Sanchez, A., Daniels, A. K., Ewango, C. E. N., Fauset, S.,
Mukinzi, J. M., Sheil, D., Sonké, B., Sullivan, M. J. P., Sunderland, T.
C. H., Taedoumg, H., Thomas, S. C., White, L. J. T., Abernethy, K. A.,
Adu- Bredu, S., … Zemagho, L. (2020). Asynchronous carbon sink
saturation in African and Amazonian tropical forests. Nature, 579,
8 0 – 8 7 . h t t p s : / / d o i . o r g / 1 0 . 1 0 3 8 / s 4 1 5 8 6 - 0 2 0 - 2 0 3 5 - 0
IPCC. (2013). Climate change 2013: The physical science basis. In T. F.
Stocker, D. Qin, G.- K. Plattner, M. Tignor, S. K. Allen, J. Boschung,
A. Nauels, Y. Xia, V. Bex, & P. M. Midgley (Eds.), Contribution of
working group I to the fifth asse ssment report of the Intergovern mental
Panel on Climate Change. Cambridge University Press, 1535 pp.
Janzen, D. H. (1967). Why mountain passes are higher in the trop-
ics. The American Naturalis t, 101(9 19), 23 3– 2 49. ht tps ://doi.
org/10.1086/2824 87
Kattge, J., Knorr, W., Raddatz, T., & Wirth, C. (20 09). Quantifying photo-
synthetic capacity and its relationship to leaf nitrogen content for
global- scale terrestrial biosphere models. Global Change Biology, 15,
976– 991. https://doi.org/10.1111/j.1365- 2486.2008 .01744.x
Kositsup, B., Montpied, P., Kasemsap, P., Thaler, P., Améglio, T., & Dreyer,
E. (2009). Photosynthetic capacity and temperature responses of
photosynthesis of rubber trees (Hevea brasiliensis Müll. Arg.) ac-
climate to changes in ambient temperatures. Tree s, 23, 357– 365.
h t t p s : / / d o i . o r g / 1 0 . 1 0 0 7 / s 0 0 4 6 8 - 0 0 8 - 0 2 8 4 - x
Kumarathunge, D. P., Medlyn, B. E., Drake, J. E., Tjoelker, M. G.,
Aspinwall, M. J., Battaglia, M., Cano, F. J., Carter, K. R., Cavaleri,
M. A., Cernusak, L. A., Chambers, J. Q., Crous, K. Y., De Kauwe, M.
G., Dillaway, D. N., Dreyer, E., Ellsworth, D. S., Ghannoum, O., Han,
Q., Hikosaka, K., … Way, D. A . (2019). Acclimation and adaptation
components of the temperature dependence of plant photosynthe-
sis at the global scale. New Phytologist, 222, 768– 784. https://doi.
org /10.1111/np h.15668
Lamba, S., Hall, M., Räntfors, M., Chaudhary, N., Linder, S., Way, D. A.,
Uddling, J., & Wallin, G. (2018). Physiological acclimation damp-
ens initial effects of elevated temperature and atmospheric CO2
concentration in mature boreal Norway spruce. Plant, Cell &
Environment, 41, 30 0– 313 . https://doi.org/10.1111/pce.13079
Lebrija- Trejos, E., Pérez- García, E. A., Meave, J. A., Poorter, L., & Bongers,
F. (2011). Environmental changes during secondary succession in a
tropical dry forest in Mexico. Journal of Tropical Ecology, 27, 477–
489. https://doi.org/10.1017/S0266 46741 1000253
Lenth, R. V. (2021). emmeans: Estimated marginal means, aka least-
squares means. R package version 1.6.0. https://CRAN.R- proje
ct.org/packa ge=emmeans
Lloyd, J., & Farquhar, G. D. (20 08). Effects of rising temperatures and
[CO2] on the physiology of tropical forest trees. Philosophical
Transactions of the Royal Society of London. Series B, Biological
Sciences, 363, 1811– 1817. https://doi.org/10.1098/rstb.2007.0032
Lópe z, J., Way, D. A., & Sadok, W. (2021). Sys te mic ef fec ts of risin g atmo-
spheric vapor pressure deficit on plant physiology and productiv-
ity. Global Change Biology, 27, 1704– 1720. https://doi.org/10.1111/
gcb.15548
Lu, X., Ju, W., Li, J., Croft, H., Chen, J. M., Luo, Y., Yu, H., & Hu, H. (2020).
Maximum carboxylation rate estimation with chlorophyll content
as a prox y of rubisco content. Journal of Geophysical Research:
Biogeosciences, 125. https://doi.org/10.1029/2020J G005748
Maire, V., Martre, P., Kattge, J., Gastal, F., Esser, G., Fontaine, S., &
Soussana, J.- F. (2012). The coordination of leaf photosynthesis
links C and N fluxes in C3 plant species. PLoS ONE, 7. ht tp s://doi.
org/10.1371/journ al.pone.0038345
Marchin, R. M., Broadhead, A . A., Bostic, L. E., Dunn, R. R ., & Hoffmann,
W. A. (2016). Stomatal acclimation to vapour pressure deficit dou-
bles transpiration of small tree seedlings with warming. Plant, Cell
& Environment, 39, 2221– 2234. ht tps://doi.org /10.1111/pce.12790
McDowell, N., Allen, C. D., Anderson- Teixeira, K., Brando, P., Brienen, R.,
Chambers, J., Christoffersen, B., Davies, S., Doughty, C., Duque, A.,

18
|
DU SENGE Et a l.
Espirito- Santo, F., Fisher, R., Fontes, C. G., Galbraith, D., Goodsman,
D., Grossiord, C., Hartmann, H., Holm, J., Johnson, D. J., … Xu, X.
(2018). Drivers and mechanisms of tree mor tality in moist tropical
forests. New Phytologist, 219, 851– 869. ht tps://doi.or g/10.1111/
nph.15027
Medlyn, B. E., Dreyer, E., Ellsworth, D., Forstreuter, M., Harley, P. C.,
Kirschbaum, M. U. F., Le Roux, X., Montpied, P., Strassemeyer, J.,
Walc roft, A., Wang , K., & Lo ust au, D. (20 02). Tem perat ure resp ons e
of parameters of a biochemically based model of photosynthesis. II.
A review of experimental data. Plant, Cell & Environment, 25, 1167–
1179. https://doi.org/10.1046/j.1365- 3040.2002.00891.x
Mercado, L. M., Medlyn, B. E., Huntingford, C., Oliver, R. J., Clark, D. B.,
Sitch, S., Zelazowski, P., Kattge, J., Harper, A. B., & Cox, P. M. (2018).
Large sensitivity in land carbon storage due to geographical and
temporal variation in the thermal response of photosynthetic ca-
pacity. New Phytologist, 218, 1462– 1477. https://doi.org/10.1111/
nph.15100
Mujawamariya, M., Wittemann, M., Manishimwe, A., Ntirugulirwa, B.,
Zibera, E., Nsabimana, D., Wallin, G., Uddling, J., & Dusenge, M.
E. (2020). Complete or over- compensatory thermal acclimation of
leaf dark respiration in African tropical trees. New Phytologist, 229,
254 8– 2561. ht tps://doi.org /10.1111/nph.17038
Nyirambangutse, B., Zibera, E., Uwizeye, F. K., Nsabimana, D., Bizuru,
E., Pleijel, H., Uddling, J., & Wallin, G. (2017). Carbon stocks and
dynamics at different successional stages in an Afromontane tropi-
cal forest. Biogeosciences, 14, 1285– 1303. https://doi.org/10.5194/
b g - 1 4 - 1 2 8 5 - 2 0 1 7
O’Lear y, B. M., Asao, S., Millar, A. H., & Atkin, O. K. (2019). Core princi-
ples which explain variation in respiration across biological scales.
New Phytologist, 222, 670– 686. htt ps://doi.org/10.1111/nph.15576
O’Sullivan, O. S., Weerasinghe, K. W. L. K., Evans, J. R., Egerton, J. J. G.,
Tjoelker, M. G., & Atkin, O. K. (2013). High- resolution temperature
responses of leaf respirat ion in snow gum (Eucalyptus pauciflora) re-
veal high- temperature limits to respiratory function. Plant, Cell &
Environment, 36, 1268– 1284. https://doi.org/10.1111/pce.12057
Oren, R., Sperry, J. S., Katul, G. G., Pataki, D. E., Ewers, B. E., Phillips,
N., & Schäfer, K. V. R. (1999). Survey and synthesis of intra- and
interspecific variation in stomatal sensitivity to vapour pressure
deficit. Plant, Cell & Environment, 22, 1515– 1526. https://doi.
org/10.1046/j.1365- 3040.1999.00513.x
Pinheiro, J., Bates, D., DebRoy, S., Sarkar, D., & R Core Team. (2019). nlme:
Linear and nonlinear. https://CRAN.R- proje ct.org/packa ge=nlme
Prentice, I. C., Dong, N., Gleason, S. M., Maire, V., & Wright, I. J. (2014).
Balancing the costs of carbon gain and water transport: Testing a
new theoretical framework for plant functional ecology. Ecology
Letter s, 17, 82– 91. https://doi.org/10.1111/ele.12211
R Core Team. (2020). R: A language an d environment for statistical comput-
ing. R Foundation for Statistical Computing. https://www.R- proje
ct.org/
Rashid, F. A. A., Crisp, P. A., Zhang, Y., Berkowitz, O., Pogson, B. J., Day,
D. A., Masle, J., Dewar, R. C., Whelan, J., Atkin, O. K., & Scafaro,
A. P. (2019). Molecular and physiological responses during thermal
acclimation of leaf photosynthesis and respiration in rice. Plant, Cel l
& Environment, 43, 594– 610. https://doi.or g/10.1111/pce.13706
Rashid, F. A. A., Scafaro, A. P., Asao, S., Fenske, R., Dewar, R. C., Masle,
J., Taylor, N. L., & Atkin, O. K. (2020). Diel and temperature driven
variation of leaf dark respiration rates and metabolite levels in rice.
New Phytologist, 228, 56– 69. htt ps://doi.org/10.1111/n ph.16661
Read, J. (1990). Some effects of acclimation temperature on net pho-
tosynthesis in some tropical and extra- tropical Australasian
Nothofagus species. The Journal of Ecolog y, 78, 100. https://doi.
org /10.2307/2261039
Reich, P. B., Sendall, K. M., Stefanski, A., Wei, X., Rich, R. L., &
Montgomery, R. A. (2016). Boreal and temperate trees show strong
acclimation of respiration to warming. Nature, 531, 633– 636.
https://doi.org/10.1038/natur e17142
Scafaro, A. P., Xiang, S., Long, B. M., Bahar, N. H. A., Weerasinghe, L. K.,
Creek, D., Evans, J. R., Reich, P. B., & Atkin, O. K. (2017). Strong
thermal acclimation of photosynthesis in tropical and temperate
wet- forest tree species: The importance of altered Rubisco content.
Global Change Biology, 23, 278 3– 280 0. https://doi.org/10.1111/
gcb.13566
Sendall, K. M., Reich, P. B., Zhao, C., Jihua, H., Wei, X., Stefanski, A., Rice,
K., Rich, R. L., & Montgomery, R. A . (2015). Acclimation of photo-
synthetic temperature optima of temperate and boreal tree species
in response to experimental forest warming. Global Change Biology,
21, 1342– 1357. https://doi.org/10.1111/gcb.12781
Sentinella, A. T., Warton, D. I., Sherwin, W. B., Offord, C. A., & Moles, A.
T. (2020). Tropical plants do not have narrower temperature toler-
ances, but are more at risk from warming because they are close to
their upper thermal limits. Global Ecolog y and Biogeography, 29(8),
1387– 1398. ht tps://doi.org/10.1111/geb.13117
Slot, M., & Kitajima, K. (2015). General patterns of acclimation of leaf
respiration to elevated temperatures across biomes and plant
types. Oecologia, 17 7, 885– 900. https://doi.org/10.1007/s0044
2 - 0 1 4 - 3 1 5 9 - 4
Slot, M., Rey- Sánchez, C., Gerber, S., Lichstein, J. W., Winter, K., &
Kitajima, K. (2014). Thermal acclimation of leaf respiration of trop-
ical trees and lianas: Response to experimental canopy warming,
and consequences for tropical forest carbon balance. Global Change
Biology, 20, 2915– 2926. https://doi.org/10.1111/gcb.12563
Slot, M., & Winter, K. (2017a). In situ temperature response of photosyn-
thesis of 42 tree and liana species in the canopy of two Panamanian
lowland tropical forests with contrasting rainfall regimes. New
Phytologist, 214, 1103– 1117. https://doi.org/10.1111/nph.144 69
Slot, M., & Winter, K. (2017b). Photosynthetic acclimation to warming
in tropical forest tree seedlings. Journal of Experimental Botany, 68,
2275– 2284. https://doi.org/10.1093/jxb/erx071
Slot, M., & Winter, K. (2018). High tolerance of tropical sapling growth
and gas exchange to moderate warming. Functional Ecology, 32,
599– 611. https://doi.org/10.1111/1365- 2435.13001
Smith, N. G., & Dukes, J. S. (2013). Plant respiration and photosyn-
thesis in global- scale models: Incorporating acclimation to tem-
perature and CO2. Global Change Biology, 19, 45– 63. https://doi.
org /10.1111/j.1365- 2486. 2012. 02797.x
Smith, N. G., & Dukes, J. S. (2017). Short- term acclimation to warmer
temperatures accelerates leaf carbon exchange processes across
plant types. Global Change Biology, 23, 4840– 4853. https://doi.
org /10.1111/gcb.13735
Smith, N. G., & Keenan, T. F. (2020). Mechanisms underlying leaf pho-
tosynthetic acclimation to warming and elevated CO2 as inferred
from least- cost optimality theory. Global Change Biology, 26, 5202–
5216. https://doi.org/10.1111/gcb.15212
Smith, N. G., Keenan, T. F., Colin Prentice, I., Wang, H., Wright, I. J.,
Niinemets, Ü., Crous, K. Y., Domingues, T. F., Guerrieri, R., Yoko
Ishida, F., Kattge, J., Kruger, E. L., Maire, V., Rogers, A., Serbin, S.
P., Tarvainen, L., Togashi, H. F., Townsend, P. A., Wang, M., … Zhou,
S.- X. (2019). Global photosynthetic capacity is optimized to the en-
vironment. Ecology Letters, 22, 506– 517. https://doi.org/10.1111/
ele.13210
Stefanski, A., Bermudez, R., Sendall, K. M., Montgomery, R. A., & Reich,
P. B. (2019). Surprising lack of sensitivity of biochemical limitation
of photosynthesis of nine tree species to open- air experimental
warming and reduced rainfall in a southern boreal forest. Global
Change Biology, 26, 746– 759. https://doi.org/10.1111/gcb.14805
Sullivan, M. J. P., Lewis, S. L., Affum- Baffoe, K., Castilho, C., Costa,
F., Sanchez, A. C., Ewango, C. E. N., Hubau, W., Marimon, B.,
Monteagudo- Mendoza, A ., Qie, L., Sonké, B., Martinez, R. V.,
Baker, T. R., Brienen, R. J. W., Feldpausch, T. R., Galbraith, D., Gloor,
M., Malhi, Y., … Phillips, O. L. (2020). Long- term thermal sensitiv-
ity of Earth’s tropical forests. Science, 368, 869– 874. https://doi.
org/10.1126/scien ce.aaw7578

|
19
DUSENGE E t al.
Tan, Z.- H., Zeng, J., Zhang, Y.- J., Slot, M., Gamo, M., Hirano, T., Kosugi, Y.,
da Rocha, H. R., Saleska, S. R., Goulden, M. L., Wofsy, S. C., Miller,
S. D., Manzi, A. O., Nobre, A. D., de Camargo, P. B., & Restrepo-
Coupe, N. (2017). Optimum air temperature for tropical forest
photosynthesis: Mechanisms involved and implications for climate
warming. Environmental Research Letters, 12, 054022. https://doi.
org /10.1088/1748- 9326/aa6f 97
Tarvainen, L., Lutz, M., Räntfors, M., Näsholm, T., & Wallin, G. (2017).
Temperature responses of photosynthetic capacity parameters
were not affected by foliar nitrogen content in mature Pinus sylves-
tris. Physiologia Plantarum, 162, 370 – 378. https://doi.org/10.1111/
ppl.12605
Trewin, B. (2014). The climates of the tropics, and how they are changing.
State of the Tropics 2014 Report, 39– 57.
Vårhammar, A., Wallin, G., McLean, C. M., Dusenge, M. E., Medlyn, B. E.,
Hasper, T. B., Nsabimana, D., & Uddling, J. (2015). Photosynthetic
temperature responses of tree species in Rwanda: Evidence of pro-
nounced negative effects of high temperature in montane rainfor-
est climax species. New Phytologist, 206, 1000– 1012. https://doi.
org /10.1111/np h.13291
Wang, H., Atkin, O. K., Keenan, T. F., Smith, N. G., Wright, I. J., Bloomfield,
K. J., Kattge, J., Reich, P. B., & Prentice, I. C . (2020). Acclimation of
leaf respiration consistent with optimal photosynthetic capacity.
Global Change Biology, 26, 2573– 2583. https://doi.org/10 .1111/
gcb.1498 0
Way, D. A. (2019). Just the right temperature. Nature Ecolog y & Evolution,
3, 7 1 8 – 7 1 9 . h t t p s : / /d o i . o r g / 1 0 . 1 0 3 8 / s 4 1 5 5 9 - 0 1 9 - 0 8 7 7 - 3
Way, D. A., & Oren, R. (2010). Differential responses to changes in growth
temperature between trees from different functional groups and
biomes: A review and synthesis of data. Tree Physiology, 30, 669–
688. https://doi.org/10.1093/treep hys/tpq015
Way, D. A., & Sage, R. F. (2008). Elevated growth temperatures re-
duce the carbon gain of black spruce [Picea mariana (Mill.) B.S.P.].
Global Change Biology, 14 , 624– 636. https://doi.org/10.1111/
j.1365- 2486.2007.01513.x
Way, D. A., & Yamori, W. (2014). Thermal acclimation of photosynthe-
sis: On the importance of adjusting our definitions and accounting
for thermal acclimation of respiration. Photosynthesis Research, 119,
8 9 – 1 0 0 . h t t p s : / / d o i . o r g / 1 0 . 1 0 0 7 / s 1 1 1 2 0 - 0 1 3 - 9 8 7 3 - 7
Weerasinghe, L. K., Creek, D., Crous, K. Y., Xiang, S., Liddell, M. J.,
Turnbull, M. H., & Atkin, O. K. (2014). Canopy position affects the
relationships between leaf respiration and associated traits in a
tropical rainforest in Far North Queensland. Tree Physiology, 34,
564– 584. https://doi.org/10.1093/treep hys/tpu016
Wright, I. J., Reich, P. B., & Westoby, M. (2003). Least- cost input mixtures
of water and nitrogen for photosynthesis. The American Naturalist,
161, 98– 111. https://doi.org/10.1086/344920
Wullschleger, S. D. (1993). biochemical limitations to carbon assimilation
in C3 plants— A retrospective analysis of the A/C i curves from 109
species. Journal of Experimental Botany, 44, 907– 920. https://doi.
org/10.1093/jxb/44.5.907
Yamaguchi, D. P., Nakaji, T., Hiura, T., & Hikosaka, K. (2016). Effects of
seasonal change and experimental warming on the temperature
dependence of photosynthesis in the canopy leaves of Quercus ser-
rata. Tree Physiology, 36, 1283– 1295. https://doi.org/10.1093/treep
hys/tpw021
Yamori, W., Hikosaka, K., & Way, D. A. (2014). Temperature response of
photos ynthe si s in C3, C4, and CAM plants: Temperature acclimation
and temperature adaptation. Photosynthesis Research, 119, 101– 117.
h t t p s : / / d o i . o r g / 1 0 . 1 0 0 7 / s 1 1 1 2 0 - 0 1 3 - 9 8 7 4 - 6
Zhu, L., Bloomfield, K. J., Asao, S., Tjoelker, M. G., Egerton, J. J. G., Hayes,
L., Weerasinghe, L. K., Creek, D., Griffin, K. L., Hurry, V., Liddell, M.,
Meir, P., Turnbull, M. H., & Atkin, O. K. (2020). Acclimation of leaf
respiration temperature responses across thermally contrasting
biomes. New Phytologist, 229, 1312– 1325. https://doi .org/10.1111/
nph.16929
Ziegler, C., Dusenge, M. E., Nyirambangutse, B., Zibera, E., Wallin, G.,
& Uddling, J. (2020). Contrasting dependencies of photosynthetic
capacity on leaf nitrogen in early- and late- successional tropical
montane tree species. Frontiers in Plant Science, 11. htt p s://d oi.
org/10.3389/fpls.2020.500479
SUPPORTING INFORMATION
Additional supporting information may be found online in the
Supporting Information section.
How to cite this article: Dusenge, M. E., Wittemann, M.,
Mujawamariya, M., Ntawuhiganayo, E. B., Zibera, E.,
Ntirugulirwa, B., Way, D. A., Nsabimana, D., Uddling, J., &
Wallin, G. (2021). Limited thermal acclimation of
photosynthesis in tropical montane tree species. Global
Change Biology, 00, 1– 19. https://doi.org/10.1111/gcb.15790