Demographic response to transplantation explained by traits
Six species decreased, and five species increased in cover in the warmer
sites compared to the origin. Five decreased in frequency but increased
or showed no change in cover (Table S1, Figures S8-S9). Of the full
trait space, the first four axes explained 63% of the variation (21%,
15%, 15% and 12%). The first axis separated species based on their
water use efficiency measured with the gas-analyser
(WUEinst, WUEint, E). The second axis
separated species with high values of δ13C and
δ18O enrichment (i.e. “conservative” water use
strategy) and large size (width, leaf area) from small species with
“prolific” water use strategy. The third axis separated species which
increased their WUEinst after transplanting (high
WUEinst.PI), had a high sensitivity of respiration to
temperature (high Q10) and low leaf nitrogen content
from species with opposite traits. The fourth axis separated species
with prostate growth form (high CSI), high stomatal conductance, high
nighttime transpiration and low temperature optima for photosynthesis
from tall, erect and deep-rooted species with opposite physiological
traits (Figure S10).
A species’ position on the second trait axis correlated with its
demographic response to increasing temperature both when measured as
cover (χ2(1) = 5.69, p = 0.017, Figure S11a) and
frequency (χ2(1) = 14.5, p < 0.001;
interaction axis2 × temperature, Figure 1a, Tables S4-S5). Small species
in terms of width and leaf area with high life-time stomatal conductance
(low δ18O) and low water use efficiency (low
δ13C; “prolific” water use strategy) declined in
cover and frequency at the warmer relative to cooler sites.
Additionally, a species’ position on the first PCA axis correlated with
its frequency change: species with high WUEinst and
WUEint and low E reduced in frequency more than species
with opposite traits at all sites (χ2(1) = 5.55, p =
0.019; Figure S11b). A species’ position on the two other trait axes did
not correlate with their demographic response to warming (Table S5). The
best LMMs derived from model selection (including initial cover or
frequency, temperature and its interactions with traits, and species
identity) explained 59% of the variation in cover and 69% in
frequency, of which species identity explained 25% and 12%, and traits
explained 10% and 12% (Table S3).
At the community-level, turfs transplanted to lower elevations were more
likely to contain larger species (height and width; (F(1,48) = 4.88, p =
0.03; F(1,48) = 15.08, p < 0.001) with a conservative water
use strategy (high δ13C and δ18O;
F(1,48) = 68.57, p < 0.001; F(1,48) = 4.54, p = 0.04; Figure
3, Figure S12bc and Table S6).
Several traits (WUEins, gsnight,
Enight, δ18O, δ13C)
showed plasticity, and the direction of the change differed between
species (Figures S4-S7, S13). Notably, photosynthesis and respiration
were on average similar when measured at +0°C and +3°C (i.e. there was
no clear evidence of acclimation, Figure S4a,f). None of the plasticity
indices nor the parameters describing species’ ability to rapidly adjust
to temperature (Topt, Ω, Q10) were
important predictors of the demographic changes. Even though
transplantation to lower elevations favored species with conservative
water use, it resulted in higher life-time stomatal conductance and
lower water use efficiency (low δ18O enrichment and
δ13C) within species (Figures S5-S6).