Reproduction alternation in trees: testing the resource depletion hypothesis using experimental fruit removal inQuercus ilex

Abstract

The key stones of resource budget models to explain mast seeding are that fruit production depletes tree stored resources, which become subsequently limiting to flower production the following year. These two hypotheses have, however, rarely been tested in forest trees. Using a fruit removal experiment, we tested whether preventing fruit development would increase nutrient and carbohydrates storage and modify allocation to reproduction and vegetative growth the following year. We removed all the fruits from nine adult Quercus ilex trees shortly after fruit set and compared, with nine control trees, the concentrations in nitrogen, phosphorus, zinc, potassium and starch in leaves, twigs and trunk before, during and after the development of female flowers and fruits. The following year, we measured the production of vegetative and reproductive organs as well as their location on the new spring shoots. Fruit removal prevented the depletion of nitrogen and zinc in leaves during fruit growth. It also modified the seasonal dynamics in zinc, potassium and starch in twigs, but had no effect on reserves stored in the trunk. Fruit removal increased the production of female flowers and leaves the following year, and decreased the production of male flowers. Our results show that resource depletion operates differently for male and female flowering, because the timing of organ formation and the positioning of flowers in shoot architecture differ between male and female flowers. Our results suggest that nitrogen and zinc availability constrain flower production in Q. ilex, but also that other regulatory pathways might be involved. They strongly encourage further experiments manipulating fruit development over multiple years to describe the causal relationships between variations in resource storage and/or uptake and male and female flower production in masting species.

Forecasting seed production in perennial plants: identifying challenges and charting a path forward

“…What determines masting and how predictable is it? Currently, we understand masting as a result of the interplay between weather and the internal resource dynamics of plants, and their combined impact on flower and seed development (Pearse et al, 2016;Pesendorfer et al, 2021;Bogdziewicz et al, 2020a;Roncé et al, 2023). Weather, as an external factor, has been demonstrated to impact various stages of the reproductive process, including flower initiation, pollination, and seed abortion (Kon & Noda, 2007;Koenig et al, 2015;Nussbaumer et al, 2020;Satake & Kelly, 2021).…”

Forecasting seed production in perennial plants: identifying challenges and charting a path forward

“…What determines masting and how predictable is it? Currently, we understand masting as a result of the interplay between weather and the internal resource dynamics of plants, and their combined impact on flower and seed development (Pearse et al ., 2016; Bogdziewicz et al ., 2020a; Pesendorfer et al ., 2021; Roncé et al ., 2023). Weather, as an external factor, has been demonstrated to impact various stages of the reproductive process, including flower initiation, pollination, and seed abortion (Kon & Noda, 2007; Koenig et al ., 2015; Nussbaumer et al ., 2020; Satake & Kelly, 2021).…”

Mast fruiting in a large tropical African legume tree provides evidence for the nutrient resource limitation hypothesis

“…So far, Han et al [38] and Han and Kabeya [39], have shown that nitrogen (N) storage and mobilization is important for triggering flowering in Fagus . Fernandez-Martinez et al [40] and Le Roncé et al [41] have indicated that phosphorus (P) and zinc (Zn), and N and Zn, respectively are likely involved in mast fruiting of temperate trees more widely. Carbon should not be laid aside completely as a co-resource though.…”

“…Han et al (2014) and Han and Kabeya (2017), for example, have shown that nitrogen (N) storage and mobilization is important for triggering flowering. Fernandez-Martinez et al (2017b) and Le Roncé et al (2023) have indicated that P and Zn, and N and Zn, respectively are likely involved in the mast fruiting of temperate forests. Carbon however should not be laid aside completely as a candidate resource as it usually operates in concert with N, phosphorus (P), potassium (K), and other elements, not just to build fruits and seeds but indirectly for growth and maintenance of other organs like roots for nutrient acquisition.…”