Functional traits
We measured 22 functional traits, 19 continuous traits and three
categorical traits (Table 2 ). Functional traits were measured
in three healthy reproductive individuals per species. For functional
traits associated to leaves we measured three mature leaves exposed to
full light, using the standard protocols from the handbook for easy
measurement of plant functional traits worldwide (Cornelissen et
al. , 2003). Plant height (m) was measured in the field as the distance
from the ground to the top of the main photosynthetic tissues. Leaf area
was measured with a flatbed scanner (Hewlett Packard G3010). All weight
measurements to estimate specific leaf area (SLA: total leaf area/leaf
dry mass mm2 mg-1), leaf dry matter
content (LDMC): leaf dry mass/leaf fresh mass mg g-1),
and seed mass (mg) were obtained using a 0.01 mg precision balance
(Sartorius MSE 125p). Leaf dry mass was obtained after drying samples in
the oven (Lab-line Imperial V convection oven n) at 70˚C for 72 h). Leaf
toughness (Fp N mm-1) was assessed
with a punch test using a modified Pesola (Schindellegi Switzerland;
(Kitajima and Poorter, 2010)). Leaf thickness (mm) was measured using a
0-25 mm external micrometer (Redline mechanics). For traits related to
nutrient acquisition and nutritional status, leaf nitrogen concentration
(LNC, mg g-1), leaf carbon concentration (LCC, mg
g-1) and leaf phosphorus concentration (LPC, mg
g-1), we measured one leaf per individual. The first
two were determined by an elemental analyzer and the last one by
colorimetric analysis in the Soil and Water laboratory at the
Universidad Nacional de Colombia, Bogota.
We also classified species qualitative traits of pubescence, spinescence
and dispersal syndrome. Pubescence is a very important characteristic
for plants in this ecosystem because it regulates leaf temperature,
increases reflectance and may act as first line of defense against
herbivores (Hanley et al. , 2007; Seelmann et al. , 2007;
Wang et al. , 2015) and may facilitate fog capture and slow
release of water, a key trait in the functionality of the paramo as a
water reservoir. We defined three categories for this trait: a
non-pubescent leaf for glabrous foliar laminas, a high pubescent leaf if
it had > 30% of the lamina covered with trichomes, and low
pubescent leaf when < 30% of the lamina was covered with
trichomes. For spinescence, we defined two categories: with and without
spines. Data on the dispersal syndrome for each species was obtained
from the literature or from personal observations following
Pérez-Harguindeguy et al. , 2013, including anemochory (wind
dispersal), endozoochory (internal animal transport), exozoochory
(external animal transport), hydrochory (dispersal by water) and
barochory (dispersion by gravity).
We measured the following traits related to leaf gas exchange and water
balance using an open infrared gas exchange analyzer Li-Cor 6400XT
(Li-Cor, Lincoln Nebraska): light-saturated photosynthetic rate (µmol
CO2 m-2 s-1), leaf
transpiration rate (mol H2O m-2s-1), the ratio between intercellular
CO2/ambient CO2, and water use
efficiency (how much water is lost for each CO2assimilated). These values were obtained on sunny mornings during the
wet season, between 10:00 and 12:00 hours, setting the light intensity
to 1800 µmol photons m-2 s-1, the
CO2 concentration to 400µmol mol-1 and
the relative humidity to 60%.
To evaluate the drought tolerance of the species we measured the leaf
water potentials at pre-dawn and midday during the end of the dry
season. Those values were measured following standard protocols, using a
pressure chamber (PMS, Corvallis Oregon). The pre-dawn water potential,
when transpiration is at its minimum, provides an indication of the
water potential of the soil. Midday water potential is affected by any
cuticular and stomatal transpiration and therefore broadly captures the
integrated effects of plant traits and the environment on the minimum
water potential a plant reaches in natural conditions (Bhaskar and
Ackerly, 2006), a value known to be correlated to turgor loss point and
other drought tolerance traits (Bartlett et al. , 2016).
Additionally, we measured the cuticular conductance
(g min) by registering the change in mass of
hydrated leaves as they dried in the laboratory bench for 6-8 hours and
measuring the slope after the stomata had closed, following the protocol
described in Scoffoni et al. , 2018. Ambient temperature and
relative humidity were measured simultaneously and fluctuated minimally
during the measurements. Weight measurements were taken using a 0.01 mg
precision balance (Sartorius MSE 125p). Leaf area at the beginning and
at the end of the process was measured with a flatbed scanner (Hewlett
Packard G3010).
Each set of traits were always measured during the same week (i.e. one
week the height of all plants, one week the leaf area, etc.) or maximum
in two weeks for variables that are more time consuming to get, to
reduce the variation due to environmental seasonal changes on the
traits. Most traits were collected during the rainy season, but on sunny
clear days, except for those traits that inform us about species
tolerance to drought that were taken at the end of the dry season. Seed
mass data was taken whenever the species were reproducing. A detailed
list of all measured traits and their probable role is listed inTable 2 .