WORK CARRIED OUT
H1. We set up experiments on potted young trees in favourable environmental conditions and monitored mature trees in fertile sites. We investigated experiments for (i) trees subjected to high fertilization (2-4 species, 3-4 years; Belgium, Spain and Norway) and (ii) trees subjected to high fertilization and favourable temperature (2 species, 2 years; Belgium). We monitored mature trees on fertile sites in Belgium, Spain, Norway and Sweden (4 species, 15 sites, up to 7 years). The relationship between leaf senescence and tree growth was determined by measuring autumn leaf chlorophyll and/or coloration and stem xylogenesis. For a limited number of experiments (2 years, Belgium; 1 year, Spain and Norway) branch- and root xylogenesis, as well as fine root elongation, were also measured.
H2. We set up experiments on potted young trees in unfavourable environmental conditions and monitored mature trees in infertile sites. We investigated experiments of (i) trees subjected to low fertilization (2-4 species, 3-4 years; Belgium, Spain and Norway) and (ii) trees subjected to drought and low fertilization (2 species, 2 years; Belgium). We monitored mature trees on infertile sites in Belgium (3 species, 2 sites, 7 years). The impact of photoperiod on leaf senescence was studied by measuring leaf chlorophyll and/or coloration and comparing across years. An additional experiment was performed (WP1; 2 species, 2 years; Belgium) where the impact of photoperiod on leaf senescence was directly tested by subjecting trees in growing chambers to modified seasonal photoperiod.
H3. We compared results of young and mature trees from the experiments / monitoring performed to test H1 and H2.
H4. We compared the results of the four species studied in the experiments and forest monitoring performed to test H1 and H2 in Belgium, Spain and Norway.
H5. The testing of this hypothesis become unnecessary as the expectations were not met. Additional research was performed to test for alternative hypotheses e.g. the control of budburst timing on senescence timing.
RESULTS
A total of 15 international peer-reviewed articles have been produced, and six additional papers are in preparation. The following key tools were developed: (i) multiple databases of leaf senescence for experimental young trees and mature forest trees, (ii) a new methodology to determine tree growth cessation in autumn based on X-ray CT, (iii) a new European database of autumn tree growth (xylogenesis), and (iv) new modelling frameworks to estimate the timing of leaf senescence and stem growth cessation in deciduous trees in autumn.
The results have been presented in 11 international conferences / events. At least 9 (video)interviews of LEAF-FALL PI and team members on the topic of the project have appeared on the national media of four countries (Belgium, Spain, Switzerland, The Netherlands) (e.g. universiteitvanvlaanderen.be/college/how-do-leaves-know-when-to-fall).
