My question concerns fruiting of trees in general. However, I live in a tropical country (Philippines) where mango trees are ubiquitous, so I'll use it in stating my question.
The question is about >>seasonal<< trees — trees that produce flowers and fruit in season, i.e., they produce flowers and fruits at specific months of the year and never in the other months.
The main question is:
What is/are the environmental stimulus(es) which trigger the flowering of seasonal trees.
During summers here, one can't help but notice the fruiting of mango trees everywhere. On closer observation, the process really starts late in the year when the trees start producing flowers. It takes a few months for the fruits to develop, grow, and ripen. The fruits are ready for picking during the second quarter of the following year.
Has anybody figured out for certain the environmental stimuli that trigger the production of flowers in seasonal trees?
I have several guesses:
(1) The annual fluctuation in daily average temperatures; if this is the case, then the trees' biochemical makeup must have an amazing sensitivity to temperature as stimulus because annual variations in daily average temperature here does not exceed about 10°C (20°F). (2) The annual fluctuations of the level of the water table under the ground. During the months (november or december) when the flowers start to appear in mango trees, the rainy season is nearing its end, so the water table must be near highest during these months. But this is complicated by the el niño / la niña cycles, which alter the length of the rainy season and the amount of precipitation received by the ground, which must have an effect on the height of the water tables. Nevertheless, the flowering and fruiting seasons seem to have no noticeable change: they still occur at the same months of the year! (3) The annual variations in the solar irradiation received by the trees. If this is the case, then, like in guess # 1, then the trees' biochemical makeup must have an amazing sensitivity to irradiation as stimulus because the annual variation in the solar irradiation is only about 25% (at 14°N latitude, with the earth's tilt at 23.5°).
At any rate, I would also like to get a glimpse of the biochemical cascades involved, the hormones, signalling pathways, proteins, etc.