Resource Reallocation Patterns In Sagittaria Trifolia Following Differential Pollination Within Inflorescences

Due to limited overall resource during plants' reproduction,tradeoffs are often observed between different physiological functions and organs,in order to improve the fitness of individuals in a particular environment.Although resource allocation to reproduction through time and space have long attracted ecologists and yielded many ecological principles,resource reallocation,the possibility of resource movement among flowers during fruit production,has been rarely examined and largely taken for granted.The present study was aimed to empirically explore resource redistribution patterns among flowers within inflorescences in response to differential pollination intensity.Using a common herb Sagittaria trifolia,we conducted an experiment to examine resource redistribution patterns among flowers within inflorescences following supplemental pollination for single,partial,or all the flowers in simple and complex inflorescences.Our study differs from previous studies in that all flowers and fruits within inflorescence were maintained with no artificial thinning.The fruit set,seed production,average seed weight and germination rate between flowers of different manipulations or different treatment levels were compared within each inflorescence type,in order to reveal the possibility of resource reallocation and the limiting factors for reproduction on a fine scale.At simple inflorescence level,compared with controlled pollination,Sagittaria trifolia with flower-level supplemental pollination(YJH)had a significantly higher fruit-set.There seemed no obvious difference on seed number and average seed weight between supplemental-and controlled-pollinated flowers.Sagittaria trifolia inflorescences with supplemental pollination(YJX)and controlled pollination did not differ in fruit-set,seed number,and average seed weight.In the YJH treatment,flowers with supplemental pollination had a significantly higher fruit-set than other controlled flowers of the same individual.However,for any given flower in the YJX treatment,its fruiting probability was not as high as that for YJH,both of which were equally supplemental-pollinated.For controlled flowers,there was no difference in fruit-set between internal(YJHX)and external controls(XZX).There was no difference in germination rate between YJH and YJHX.In complex inflorescences,for all three variables investigated,there were significant differences between main and lateral branches.Flowers on the main branch had higher fruiting probability,more and heavier seeds than lateral ones.However,for fruits on lateral branches,there was no significant difference between supplemental-and controlled-pollinated flowers with regard to fruit-set,seed number and average seed weight.The same pattern held for comparisons on main branches as well.The germination rate did not vary between main and lateral branches in complex inflorescences with control pollination.Taken together,the results pointed out that resource reallocation took place in simple inflorescence in response to differential pollination.The elevated reproduction in flower-level supplemental pollination was a result of simultaneous addition of pollen and resource through redistribution among flowers.Moreover,our results showed that a flowering branch should be an operational IPU during reproduction in this species.Given the complexity in flowering structure and phenology of flowering plants,more studies are needed to understand the patterns and mechanisms of intra-inflorescence resource allocation.