The relevance of seed size in modulating leaf physiology and early plant performance in two tree species

Abstract

The size of seeds and the microsite of seed dispersal may affect the early establishment of seedlings through different physiological processes. Here, we examined the effects of seed size and light availability on seedling growth and survival, and whether such effects were mediated by water use efficiency. Acorns of Quercus petraea and the more drought-tolerant Quercus pyrenaica were sowed within and around a tree canopy gap in a subMediterranean forest stand. We monitored seedling emergence and measured predawn leaf water potential (^Ppd), leaf nitrogen per unit area (N a ), leaf mass per area, leaf carbon isotope composition (5 C) and plant growth at the end of the first summer. Survival was measured on the next year. Path analysis revealed a consistent pattern in both species of higher <5 13 C as W pd decreased and higher <5 13 C as seedlings emerged later in the season, indicating an increase in 13 C as the growing season is shorter and drier. There was a direct positive effect of seed size on S C in Q. petraea that was absent in Q. pyrenaica. Leaf 5 C had no effect on growth but the probability of surviving until the second year was higher for those seedlings of Q. pyrenaica that had lower <5 13 C on the first year. In conclusion, leaf <5 13 C is affected by seed size, seedling emergence time and the availability of light and water, however, leaf <5 13 C is irrelevant for first year growth, which is directly dependent on the amount of seed reserves.

Increased root investment can explain the higher survival of seedlings of ‘mesic’ Quercus suber than ‘xeric’ Quercus ilex in sandy soils during a summer drought

“…Numerous studies have reported that bigger acorns lead to increased seedling growth, which can improve seedling performance by providing the resources to grow deep and extensive root systems, giving access to water from deep within the soil profile (Stock et al 1990, Triphati and Khan 1990, Osunkoja et al 1994, Gómez 2004, Ramírez-Valiente et al 2009Rodríguez-Calcerrada et al 2011). In fact, strong associations have been reported between acorn mass and survival in Q. ilex and Q. suber (Gómez 2004, Ramírez-Valiente et al 2009.…”

“…These studies suggest that root investment might be critical in allowing both Q. ilex and Q. suber to cope with water stress during prolonged droughts. In addition, seed mass is also considered a key trait determining the successful recruitment of seedlings, particularly in dry environments (Leishman and Westoby 1994, Seiwa 2000, Baraloto et al 2005, Rodríguez-Calcerrada et al 2011. The importance of seed mass lies in the influence that it exerts on traits such as above-and belowground growth during seedling establishment under both competitive and resourcelimiting conditions (Moles and Westoby 2004).…”

“…Rodríguez et al 2011). Evolutionary trade-offs between drought tolerance and avoidance The fact that Q. suber, which is usually found in more mesic areas than Q. ilex, survived better under dry conditions opens a debate on whether rainfall and the severity and length of the dry season are the main selective forces shaping the distribution ranges of Q. ilex and Q. suber.…”

Different light acclimation strategies of two coexisting tree species seedlings in a temperate secondary forest along five natural light levels

“…Q. mongolica, the light demanding tree species, was characterized by particularly large seeds, which provided abundant energy reserves for initial seedling survival under light-shortage conditions (Geritz et al, 1999). The large acorns lead to taller seedlings with high carbohydrate reserves and nutrients, which facilitates seedling survival and growth under resource-limitation conditions (Ramírez-Valiente et al, 2009;Hallett et al, 2011;Rodríguez-Calcerrada et al, 2011).…”

An Analysis of the Distribution of Seed Size: A Case Study of the Gymnosperms

“…Seed size is a central trait of plant ecology and evolution (Moles et al, 2005a;2005b), conditioning the probability of seed abundance and dispersal (Guo et al, 2000), predation, germination (Pearson et al, 2002), and seedling survival, even within a single species (Obeso et al, 2011). Additionally, evidence of early plant performance can be found by examining the distribution of seed size (Rodríguez-Calcerrada et al, 2011).…”