Resource manipulation reveals flexible allocation rules to growth and reproduction in a Mediterranean evergreen oak

Aims In plants,resource allocation to growth and reproduction may depart from trade-off expectations if(i)investment in growth and reproduction relies on different resource pools,(ii)allocation to reproduction is dependent upon reaching some growth threshold or(iii)reproduction is developmentally linked to growth,both functions relying on the same resource pool.We examined the effects of enhanced resource level on patterns of resource allocation to growth and reproduction in holm oak(Quercus ilex sbsp.ballota),a Mediterranean evergreen tree.Methods In the experimental year(2003),we manipulated the amount of soil nutrients in autumn(to increase nutrient uptake during shoot elongation in the following spring)and soil water in summer(to increase water uptake during acorn growth).Indicators of growth and male and female reproduction were estimated in the preexperimental(2002),experimental(2003)and post-experimental(2004)years.Important Findings Fertilized trees produced significantly longer shoots,but the number of female flowers per shoot was not affected by treatments.The production of male catkins was also enhanced by fertilization.Irrigation did not affect the production of female flowers or abortion rates.Growth and female reproduction showed no consistent relationship in untreated trees,but resource addition elicited a growth-female reproduction trade-off in the experimental year.The sign of this significant relationship changed in the post-experimental year,indicating the existence of lagged effects of resource manipulation on acorn production.Overall,patterns of allocation to growth and reproduction varied as a function of sex,resource availability and year,a result consistent with extreme allocational plasticity in holm oak.

comIntraspecific variation in heritable secondary metabolites and defensive strategies in a relict tree

Aims Key herbivory interaction traits such as plant defensive compounds may differ among populations of a single species due to the spatial variation in herbivore feeding guilds and the strength of the interac-tion.Moreover,the genealogy of population lineages could represent an additional source of variation interacting with the predominant eco-clinal trends.We tested for the existence of genetically based intraspecific variation in chemical defence profiles across the range of the relict tree Prunus lusitanica L.Additionally,we investigated geographical variation in defence inducibility and tested for the exist-ence of a trade-off between qualitative and quantitative defences.Methods We conducted a greenhouse experiment where 210 plants were grown under a common environment,comprising 10 different pop-ulations throughout the distribution range of the species and span-ning three separate regions:iberia,Morocco and Macaronesia.To test for the inducibility of defences,we artificially defoliated plants.Three treatments were established within each population:undam-aged,defoliated and sampled after 2 h,and defoliated and sampled after 72 h.The concentration of cyanogenic glycosides(prunasin)and phenolics was determined in leaf samples for all treatments.Important findings Basal levels of cyanogenics and phenolics significantly differed among populations and regions across the range of P.lusitanica,with this variation having a heritable basis.Cyanogenics(pruna-sin)were significantly higher in ancient Macaronesian populations,while phenolic concentrations were larger in iberia.The higher cyanogenic levels found in Macaronesia could be a consequence of the known stronger herbivory pressure in the islands than in iberia or the likely longer coevolutionary history with herbivores in this region.These findings indicate that the geographical variation of key ecological traits such plant chemical defences can be imprinted by phylogeographical signals,particularly in relict species.Regarding defence inducibility,prunasin increased after simulated herbivory whereas phenolics mostly decreased after defoliation.Variation in defence inducibility across populations and regions was evident,although no consistent patterns related to the variation in herbivore feeding guilds were observed,particularly among regions with and without ungulate browsing pressure.Finally,a trade-off among induced levels of qualitative(prunasin)and quantitative(phenolics)defences was detected in one of the defoliated treatments,likely as a result of a stronger resource limitation in damaged plants.