133
5.5.2 Variation Among Populations in Common Garden Trials
Annual growth synchronization with climate usually reflects a compromise between
tolerance to cold and optimization of growth. In trees of temperate climates, the
initiation and cessation of primary growth determine the duration of the stem elongation period and indicate the transition between resistant and frost-vulnerable
stages. Therefore, the synchronization is critical for both optimal biomass production and fitness. Because of its wide latitudinal range, N. pumilio is expected to
show deep phenological differences among populations.
Torres et al. (2017) carried out a population variation study concerning the bud
burst process, including the entire latitudinal range of the species. They installed a
high-density provenance trial in Trevelin Forest Station of INTA (43° 7′ 17″S, 71°
33′ 41″W, 390 m asl) representing 12 Argentine populations (4 blocks, 24 seedlings
per block, N = 1152). Budburst phenology was registered in all seedlings every
3 days during 3 months at the beginning of their second growing season, according
to five phenophases as described in Chap. 3 for Nothofagus alpina. The population
factor had a significant effect on the day of the year to reach phenophase 3 (completely open buds) and explained 21% of the total variance. However, a geographically defined pattern was not found.
Similarly, Mondino (2014) studied the effect of the main environmental gradients on the phenology of the growth process. First, he installed a greenhouse provenance trial in Trevelin Forest Station with 27 potted seedlings (in a three-block
design) from each of 11 Argentine populations from the Province of Chubut, representing a two degrees’ latitudinal range and a 600 mm precipitation range. At the
beginning of the second growing season, the height of each seedling was measured
every 10 days in order to build individual growth curves fitting a Boltzmann sigmoidal model by regression. Growth initiation (t 10 : time to reach 10% of the season
growth) and cessation (t 90 : time to reach 90% of the season growth) were estimated
in days since the first changes in the budburst phenology (bud swelling). Interaction
between latitude and precipitation factors, as well as significance of the precipitation level, was not detected. On the other hand, the latitude factor was significant for
t 90 and for the duration of the growing season (Dur = t 90 – t 10 ) (northern populations
ceased growing later and presented a longer growing period).
In a new study, Mondino et al. (2019) collected seeds from six populations from
three altitudinal levels (200 m of difference between each other) in two sites of similar latitude and precipitation regime and installed a greenhouse provenance trial
similar to the previous one. Again, the height of each seedling was measured every
10 days during the second growing season, and individual growth curves were
regressed. The average final height of the entire trial was 29.2 cm. Interaction
between altitude and site and differences between sites were not significant for any
of the traits considered. On the contrary, significant differences among altitudinal
levels were shown for several variables (t 10 and Dur among them), and in all of
them, the significance was due to the difference between the highest-level plants
and the other two undifferentiated. Thus, in both sites, seedlings from the uppermost
5 Nothofagus pumilio and N. antarctica: The Most Widely Distributed…
5.5.2 Variation Among Populations in Common Garden Trials
Annual growth synchronization with climate usually reflects a compromise between
tolerance to cold and optimization of growth. In trees of temperate climates, the
initiation and cessation of primary growth determine the duration of the stem elongation period and indicate the transition between resistant and frost-vulnerable
stages. Therefore, the synchronization is critical for both optimal biomass production and fitness. Because of its wide latitudinal range, N. pumilio is expected to
show deep phenological differences among populations.
Torres et al. (2017) carried out a population variation study concerning the bud
burst process, including the entire latitudinal range of the species. They installed a
high-density provenance trial in Trevelin Forest Station of INTA (43° 7′ 17″S, 71°
33′ 41″W, 390 m asl) representing 12 Argentine populations (4 blocks, 24 seedlings
per block, N = 1152). Budburst phenology was registered in all seedlings every
3 days during 3 months at the beginning of their second growing season, according
to five phenophases as described in Chap. 3 for Nothofagus alpina. The population
factor had a significant effect on the day of the year to reach phenophase 3 (completely open buds) and explained 21% of the total variance. However, a geographically defined pattern was not found.
Similarly, Mondino (2014) studied the effect of the main environmental gradients on the phenology of the growth process. First, he installed a greenhouse provenance trial in Trevelin Forest Station with 27 potted seedlings (in a three-block
design) from each of 11 Argentine populations from the Province of Chubut, representing a two degrees’ latitudinal range and a 600 mm precipitation range. At the
beginning of the second growing season, the height of each seedling was measured
every 10 days in order to build individual growth curves fitting a Boltzmann sigmoidal model by regression. Growth initiation (t 10 : time to reach 10% of the season
growth) and cessation (t 90 : time to reach 90% of the season growth) were estimated
in days since the first changes in the budburst phenology (bud swelling). Interaction
between latitude and precipitation factors, as well as significance of the precipitation level, was not detected. On the other hand, the latitude factor was significant for
t 90 and for the duration of the growing season (Dur = t 90 – t 10 ) (northern populations
ceased growing later and presented a longer growing period).
In a new study, Mondino et al. (2019) collected seeds from six populations from
three altitudinal levels (200 m of difference between each other) in two sites of similar latitude and precipitation regime and installed a greenhouse provenance trial
similar to the previous one. Again, the height of each seedling was measured every
10 days during the second growing season, and individual growth curves were
regressed. The average final height of the entire trial was 29.2 cm. Interaction
between altitude and site and differences between sites were not significant for any
of the traits considered. On the contrary, significant differences among altitudinal
levels were shown for several variables (t 10 and Dur among them), and in all of
them, the significance was due to the difference between the highest-level plants
and the other two undifferentiated. Thus, in both sites, seedlings from the uppermost
5 Nothofagus pumilio and N. antarctica: The Most Widely Distributed…