The co‐existence of multiple oak leaf flushes contributes to the large within‐tree variation in chemistry, insect attack and pathogen infection

Abstract

Summary Many plant species produce multiple leaf flushes during the growing season, which might have major consequences for within‐plant variation in chemistry and species interactions. Yet, we lack a theoretical or empirical framework for how differences among leaf flushes might shape variation in damage by insects and diseases. We assessed the impact of leaf flush identity on leaf chemistry, insect attack and pathogen infection on the pedunculate oak Quercus robur by sampling leaves from each leaf flush in 20 populations across seven European countries during an entire growing season. The first leaf flush had higher levels of primary compounds, and lower levels of secondary compounds, than the second flush, whereas plant chemistry was highly variable in the third flush. Insect attack decreased from the first to the third flush, whereas infection by oak powdery mildew was lowest on leaves from the first flush. The relationship between plant chemistry, insect attack and pathogen infection varied strongly among leaf flushes and seasons. Our findings demonstrate the importance of considering differences among leaf flushes for our understanding of within‐tree variation in chemistry, insect attack and disease levels, something particularly relevant given the expected increase in the number of leaf flushes with climate change.

Host-specific growth responses of Larix kaempferi and Quercus acutissima to Asian gypsy moth defoliation in central Korea

“…The rapid recovery in Q. acutissima may be the result of the same compensatory strategy against herbivory as seen in the above Quercus species. This is likely because Q. acutissima exhibits an indeterminate growth habit, with secondary leaf flushing occurring after defoliation 54 . Although L. kaempferi also has compensatory responses, such as increasing the rate of photosynthesis by the remaining leaves 55 , rapid growth recovery after defoliation was not observed in this study for this species.…”

Effects of experimental warming at the microhabitat scale on oak leaf traits and insect herbivory across a contrasting environmental gradient

“…Such lack of warming effects does not agree with results from other studies reporting increases in chemical defences with experimental warming in Q. rubra (Top et al 2017), Betula nana (Graglia et al 2001) and Populus tremuloides (Li et al 2021). Differences between studies in the timing of leaf collection could explain these differences in results, provided seasonal changes in plasticity responses to warming in phenolic compound concentrations (Hunter and Price 1992, Forkner and Hunter 2000) as well as changes in secondary chemistry with leaf ontogeny or between leaf flushes early versus later in the growing season which overrun warming effects (Matsuki et al 2004, van Asch and Visser 2007, Gaytán et al 2022).…”

Changes in the foliar fungal community between oak leaf flushes along a latitudinal gradient in Europe

“…infection (Gaytán et al, 2022;Marçais et al, 2009;Marçais & Desprez-Loustau, 2014), and this relationship between leaf flush and susceptibility might differ among plant species (Jain et al, 2019).…”

“…For example, in previous studies on oak trees, leaves from the second flush have been shown to be more susceptible to oak powdery mildew ( Erysiphe spp.) infection (Gaytán et al, 2022 ; Marçais et al, 2009 ; Marçais & Desprez‐Loustau, 2014 ), and this relationship between leaf flush and susceptibility might differ among plant species (Jain et al, 2019 ).…”