It is not just a ‘trade‐off’: indications for sink‐ and source‐limitation to vegetative and regenerative growth in an old‐growth beech forest

Abstract

Summary Controls on tree growth are key issues in plant physiology. The hypothesis of our study was that the interannual variability of wood and fruit production are primarily controlled directly by weather conditions (sink limitation), while carbon assimilation (source limitation) plays a secondary role. We analyzed the interannual variability of weather conditions, gross primary productivity (GPP) and net primary productivity (NPP) of wood and fruits of an old‐growth, unmanaged Fagus sylvatica forest over 14 yr, including six mast years. In a multiple linear regression model, c. 71% of the annual variation in wood‐NPP could be explained by mean air temperature in May, precipitation from April to May (positive influence) and fruit‐NPP (negative influence). GPP of June to July solely explained c. 42% of the variation in wood‐NPP. Fruit‐NPP was positively related to summer precipitation 2 yr before (R2 = 0.85), and negatively to precipitation in May (R2 = 0.83) in the fruit years. GPP had no influence on fruit‐NPP. Our results suggest a complex system of sink and source limitations to tree growth driven by weather conditions and going beyond a simple carbon‐mediated ‘trade‐off’ between regenerative and vegetative growth.

Continent-wide tree fecundity driven by indirect climate effects

“…Continent-wide impacts of climate change are being governed by the indirect effects that come through the condition of individuals. Global change science has steadily improved understanding of direct responses, including photosynthetic rates, water use, and demography 25 , 55 , 56 and the abundances of species 40 . Lagging behind is the understanding of interactions and indirect effects 18 ; individual responses to climate do not predict responses of canopies 57 , just as species responses do not predict outcomes of competition 40 .…”

Holm oak fecundity does not acclimate to a drier world

“…This result is consistent with previous studies showing that the carbon used for fruit development is provided mainly by recent uptake of photo‐assimilates (Hoch et al ., 2013; Ichie et al ., 2013; Han et al ., 2016), and it suggests that Q. ilex acorn production might be limited by the availability of carbon resources. Other studies conducted in temperate forest ecosystems on Q. petraea or F. sylvatica have, however, failed to observe such a relationship between GPP and seed production (Delpierre et al ., 2016; Mund et al ., 2020). In the Mediterranean context of our study, where the ecosystem carbon uptake is driven by water availability in summer (Rambal et al ., 2014), GPP and acorn production are both largely influenced by water stress.…”

Temporal variability in tree responses to elevated atmospheric CO2

“…Carbon costs associated to reproductive processes, especially in fruiting trees, can also result in a seasonal increase in C sink demand, which largely varies throughout plant ontogeny (e.g. Fujii & Kennedy, 1985;Mund et al, 2020;Ribeiro, Machado, Habermann, Santos, & Oliveira, 2012;Tixier et al, 2020). As a result, the intensity of the eCO 2 -induced A n stimulation in Jatropha curcas (Kumar, Chaitanya, Ghatty, & Reddy, 2014) and Coffea arabica (Rakocevic et al, 2020) increased during flowering and fruit ripening.…”