RESULTS
There was a significant reduction on liana performance toward higher
latitudes (F (2,13) 2.37 p =0.015, fig. 1), reaching differences
up to 5 times on apical growth rate between liana species in the
northern and southern sites (Nahuelbuta 10.6
cm*month-1 v/s Aysén 2.1 cm*month-1,
Tukey HSD p= 0.017). At the same time, the loss of liana
performance was correlated with the increase in the percentage of loss
conductivity towards higher latitudes (Fig. 1) evidencing that cold
temperatures have negative effect over liana performance at higher
latitudes.
We observed marked differences in hydraulic traits strategies associated
to efficiency in water transport capacity along the latitudinal
gradient. The maximum specific hydraulic conductivity
(Ks_max) significantly differ between sites
(p =0.006), with a decreased 26.1 times in lianas species at the
northern site “Nahuelbuta” compared to the southern sites of the
gradient “Aysen” (Table 2, Tukey HSD p =0.001) and the middle
site “Puyehue” (Tukey HSD, p =0.027). Nahuelbuta lianas species
have a Ks_max of 28.7 Kg s-1m-1 MPa-1 while in Aysén they barely
reached 1.1 Kg s-1 m-1MPa-1 (Table 2). It must be added that the percentage
of loss conductivity (PLC) along the sites differ significantly
(p =0.01), increasing from 24.5% at the northern site to 37.5%
in the southern site (Table 2, Tukey HSD, Nahuelbuta differ from Puyehue
p=0.05 and Aysen p =0.04) intensified the loss of hydraulic
efficiency in liana species in the colder extreme of the gradient (Table
2), thus, the joint reduction in hydraulic transport capacity between
the liana species in Nahuelbuta and Aysén was 42 times.
We also detected differences in traits associated to hydraulic transport
safety. The lower water transport capacity of lianas at higher latitudes
was also correlated with the decrease in xylem vessel diameter, which
decreased 30% toward the southern site (Table 2). This also vessel
density differs between sites (p =0.04) increasing by 80%, and
wood density also differ between sites (p =0.04) and increase 19%
towards the south end of the gradient (Table 2). As mentioned before
water transport capacity is strongly modulated by freezing-thaw
embolism, which would have a strong impact on the relative growth rate.
Contrary to what we expected, root pressure did not increase with
latitude (Table 2, Tukey HSD only “Nahuelbuta” differ from “Puyehue”
p=0.02). Liana species in Puyehue showed the highest root pressure of
the gradient (32.7 kPa), followed by liana species in Aysén (13.7 kPa)
and Nahuelbuta (9.9 kPa). Based on this, lianas would be able to revert
embolism up to a maximum height of 1 meter on species in Nahuelbuta, 3.2
meter on species in Puyehue and 1.4 meter on species in Aysén, so root
pressure would have a significant effect only on the basal part of the
individual. However, we could have underestimated the root pressure for
the species in Aysén, since the measurements had to be repeated due to
manometers freezing on a couple of occasions.
We observed a decrease in the proportion of wide vessels toward the cold
extreme of the gradient (Fig. 2, exemplifying two species along the
latitudinal gradient). When considering that vessels with diameter
higher than 100 µm are responsible for most of Ks, we
estimated that 14.7% of the vessels are responsible for 69% of
theoretical hydraulic conductivity in Nahuelbuta. Meanwhile 7.6% of
vessels are responsible for 47% of theoretical hydraulic conductivity
in Puyehue. No species showed vessels with diameter higher to 100 µm in
Aysén, and all hydraulic conductivity was generated by narrow vessels.
The frequency distribution is significant different for diameter of
xylem vessel and relative contribution to total hydraulic conductivity,
as shown by the Kolmogorov-Smirnov test (Xylem vessel for the specieMitraria coccinea sp., in Nahuelbuta p =0.002, in Puyehuep =0.01, and Aysén p =0.001; Relative contribution to total
hydraulic conductivity for the specie Mitraria coccinea sp for
Nahuelbuta p =0.01, Puyehue p= 0.013, Aysén p =0.001;
Xylem vessel for the specie Hydrangea serratifolia sp in
Nahuelbuta p =0.003, Puyehue p =0.027, and Aysénp =0.001; Relative contribution to total hydraulic conductivity
for the specie Hydrangea serratifolia sp in Nahuelbutap =0.04, Puyehue p =0.022, and Aysén p =0.001. All
these results show that the relative contribution of large vessel
diameter to water transport was reduced along the latitudinal gradient,
evidencing a tradeoff between efficiency and vascular security in the
cold extreme.
The Principal Component Analysis based on all functional traits studied
shows that the first component explained 45.9% of the variation and the
second component explain 18.6% of the variation. This PCA analysis show
that high performance is related to high efficiency in water transport
(high specific hydraulic conductivity and wide vessels) (Fig.3). On the
other side, low performance was related to low efficiency in water
transport (high wood density, narrow vessels, and high percentage of
loss conductivity). This relationship between performance, efficiency or
safety in water transport is robust enough to functionally differentiate
liana communities between sites along the latitudinal gradient (Fig. 3).
The linear regression of the first and second component and the above
growth rate (AGR) for each site was significant in Nahuelbuta (Factor 1
R2= 0.71, p =0.017; Factor 2
R2=0.57 p =0.06; fig. 4), where traits that are
positively associated with growth rate were the maximum specific
hydraulic conductivity (Ks_max) and xylem vessel
diameter and density, on the contrary the percentage of loss
conductivity (PLC) and root pressure was negative related to growth
rate. In Puyehue data set, none of the components were significantly
related to above growth rate (AGR; Factor 1 R2= 0.007,
p=0.66; Factor 2 R2=0.039, p= 0.75, Factor 3
R2=0.14 , p=0.1; fig. 4). For Aysen, a low and nearly
significant linear regression (Factor 1 R2= 0.21,p = 0.06; Factor 2 R2= 0.34, p = 0.07;
fig. 4) was observed between the first and second component, the traits
that positively relate to growth rate was xylem vessel diameter, root
pressure and wood density, and negatively the percentage of loss
conductivity.