Resource manipulation through experimental defoliation has legacy effects on allocation to reproductive and vegetative organs inQuercus ilex

Abstract

Background and Aims In plants, high costs of reproduction during some years can induce trade-offs in resource allocation with other functions such as growth, survival and resistance against herbivores or extreme abiotic conditions, but also with subsequent reproduction. Such trade-offs might also occur following resource shortage at particular moments of the reproductive cycle. Because plants are modular organisms, resource allocation strategies to reproduction can also vary among hierarchical levels. Using a defoliation experiment, our aim was to test how allocation to reproduction was impacted by resource limitation. Methods We applied three levels of defoliation (control, moderate and intense) to branches of eight Quercus ilex trees shortly after fruit initiation and measured the effects of resource limitation induced by leaf removal on fruit development (survival, growth, and germination potential), and on the production of vegetative and reproductive organs the year following defoliation. Key Results We found that defoliation had little impact on fruit development. Fruit survival was not affected by the intense defoliation treatment, but reduced by moderate defoliation, and this result could not be explained by an upregulation of photosynthesis. Mature fruit mass was not affected by defoliation, nor was seed germination success. However, in the following spring, defoliated branches produced less shoots and compensated leaf loss by overproducing leaves at the expense of flowers. Therefore, resource shortage decreased resource allocation to reproduction the following season but did not affect sex ratio. Conclusions Our results support the idea of a regulation of resource allocation to reproduction beyond the shoot scale. Defoliation had larger legacy effects than immediate effects.

Drought acclimation of Quercus ilex leaves improves tolerance to moderate drought but not resistance to severe water stress

“…From a gas‐exchange perspective, these responses to rainfall exclusion allow the maintenance of a positive leaf carbon balance for longer periods and the maximisation of the water use efficiency (Holloway‐Phillips & Brodribb, 2011; Limousin et al, 2013). Perhaps more importantly in the evergreen Q. ilex , drought acclimation may also maintain the turgor necessary for growth during longer periods of time (Lempereur et al, 2015), and the source of photo‐assimilates necessary to the initiation of future organs in buds and the accumulation of reserves in seeds, two processes that occur during the water‐limited summer (Bykova et al, 2018; Le Roncé et al, 2020). Such an increased tolerance to moderate drought seems however to be a risky behaviour in case of severe drought as it does not increase the leaf resistance to severe water stress.…”

Climate warming causes mast seeding to break down by reducing sensitivity to weather cues

“…For example, seasonal deviations from mean weather values trigger changes in flowering hormone synthesis responsible for flower bud formation and explain interannual variation in masting grasses (Kelly et al, 2013; Turnbull et al, 2012). This process is likely to interact further with plant resource state such that depleted resource pools after bumper crops limit flower production in subsequent years (Crone et al, 2009; Le Roncé et al, 2020; Monks et al, 2016). Once flowers are initiated, pollen limitation can enforce synchrony and interannual variation in seed production though pollen coupling, another endogenous process in which pollination success increases with flower density (Kelly et al, 2001; Satake & Iwasa, 2000).…”

PhenoCaB: a new phenological model based on carbon balance in boreal conifers

“…At low levels of defoliation, the number of buds is not influenced, as compensation can be observed with the formation of epicormic buds (Piene, 1989). As defoliation severity increases, there are fewer buds, influencing carbon allocation and thus phenology at growth resumption (Fournier et al ., 2020; Le Roncé et al ., 2020). All the above‐mentioned data inputs and their units are listed in Table S2.…”

“…In the boreal shrub Vaccinium angustifolium , fewer leaf buds were related to earlier budbreak, whereas fewer flowers per bud correlated with earlier flowering (Fournier et al ., 2020), showing how carbon partitioning among growth units can have direct effects on phenology. In this context, natural defoliation has a legacy effect that induces changes in bud and shoot–leaf allometry (Le Roncé et al ., 2020). Defoliation in Pinus sylvestris causes a reduced number of needle pairs in buds (Millard et al ., 2001) and fewer buds to set in autumn (Rook, 1985).…”

“…Defoliation in Pinus sylvestris causes a reduced number of needle pairs in buds (Millard et al ., 2001) and fewer buds to set in autumn (Rook, 1985). In Quercus ilex , fewer shoots form the year following defoliation; however, a higher number of leaves are produced, indicating a more significant carbon allocation to vegetative growth (Le Roncé et al ., 2020). Therefore, defoliation can be used to test how carbon allocation to primary growth units (buds) affects phenology through mechanistic modelling of the plant carbon balance.…”