Cristian Daniel Torres

Testing individual inter-annual variations in flower production by means of retrospective analysis of meristem allocation in two tree species

High inter-annual variations in flower and seed production have been frequently reported for wind-pollinated tree species. Such variations have been generally studied from a population perspective. The present study focuses on the meristematic cost of flower production in main branches of Nothofagus obliqua and N. nervosa through a retrospective analysis of flower production over 4–5 consecutive years. In both species, the percentage of flowering nodes in one year varied between 0 and 55 %. In N. obliqua, total flower production was bimodally distributed: years of high and low production were more common than years of intermediate production. Bimodality was not significant either for total flower production in N. nervosa or for each flower type separately in both species. Flower production affected branching negatively, which meant a meristematic cost. Periodicity in flower production was uneven among co-specific trees; more than two consecutive years of high flower production were rare in all trees. Inter-annual variations in the production of staminate and pistillate flowers were synchronized. In N. nervosa, the production of pistillate flowers tended to be more variable among years than the production of staminate flowers. The applied technique helps in the assessment of individual variations of flower production and contributes to understanding factors promoting seed-production variations in tree species at population scale.

Morpho-physiological responses of Nothofagus obliqua to light intensity and water status, with focus on primary growth dynamics

Key messageIntra-individual variations of plant responses to environmental conditions are related to axis differentiation. Plastic responses include variations in primary growth, shoot allometry, leaves’ chlorophyll content and water use efficiency.AbstractPrimary growth affects plant plasticity by influencing the number, spatial arrangement and time of differentiation of the leaves. For Nothofagus obliqua, we evaluated if primary shoot growth dynamics determines short-term responses to environmental conditions, and intra-individual variations in such responses. Before bud-break, saplings were located in experimental conditions, combining two light treatments with two water supply treatments. For each individual, morphology, relative extension rate (RER), and relative leaf chlorophyll content (SPAD units) were registered for the annual shoot derived from the most distal bud of two axis categories: the main axis (trunk) and a main branch. For trunk shoots, we analysed the net photosynthetic rate at saturating photosynthetic photon flux density (Psat) of proximal and distal leaves. Shaded trees had higher RER, longer and more slender shoots, longer internodes, and higher leaf chlorophyll content than unshaded trees. The number of nodes was affected by water condition in trunk shoots, and by light condition in main branch shoots. Full sunlight stimulated the development of a branch following the length and growth direction of its parent shoot (relay branch). Shade would have promoted the development of neoformed leaves. Under shade and low water availability, water use efficiency was higher in distal than proximal leaves. Under high sunlight and water availability, leaves of relay branches presented slightly higher Psat with higher water loss than both proximal preformed leaves and distal leaves under the other tested conditions. This study highlights the need of assessing intra-individual variations in shoot acclimation in relation to axis differentiation.

Does water availability regulate biomass partitioning between trunk and branches

The extent to which a vertical trunk is differentiated from its branches is a key trait for the architecture of trees and may affect interspecific relationships. In this study, we analysed the effect of soil water availability on biomass partitioning for Nothofagus pumilio by means of a nursery experiment. Juvenile trees were subject to three irrigation conditions: no irrigation, intermediate irrigation and high irrigation. Irrigation conditions emulated the mean precipitation of the most representative environments inhabited by N. pumilio. Changes in soil water availability modified the biomass partitioning patterns of trees. In comparison to the other two conditions, high irrigation caused: (i) a higher ratio of biomass partitioning to stems than roots; (ii) more trunk growth in relation to its branches; and (iii) more photosynthetic organs relative to the aboveground biomass. Trunk size relative to that of its most recent branches was not increased by water availability. Water availability may play a significant role in the capacity of N. pumilio for space occupation due to the effects on axis differentiation.