Reproductive efficiency and photosynthetic pathway in seed plants

We aimed at determining whether C-4 and CAM species had a higher reproductive efficiency than C-3 species because of their higher water- and nitrogen-use efficiency. The resource-limitation hypothesis was also examined in the context of photosynthetic pathway. Reproductive efficiency was evaluated by measuring fruit set (fruit/flower ratio), seed set (seed/ovule ratio), and relative fecundity (the proportion of well-developed seed formed per ovule per infrutescence), along with seed abortion, and flower, fruit and seed biomass were evaluated. Photosynthetic pathway was determined according to literature, taxonomy, leaf anatomy and carbon isotopic composition (delta C-13). Additionally, carbon and nitrogen content and nitrogen isotopic composition (delta N-15) were determined. Plant life form and breeding system were considered. The traits of delta C-13 and delta N-15 were found to be positively correlated to fruit set, seed set and relative fecundity. The C-4 species exhibited the highest values of fruit and seed set associated to the lowest biomass of flower, fruit, seed, and seed/fruit. The CAM species exhibited the highest values of flower and seed/fruit biomass and C-3 species had the highest values of fruit and seed biomass. Reproductive efficiency was negatively related to the cost of reproductive structures in C-3 species. The highest values of maximum relative fecundity were reached in CAM and C-4 species under contrasting costs of reproductive structures: high values of fruits and seeds biomass in CAM species and low values of fruit and seed biomass in C-4 species, suggesting that CAM species may reach high values of maximum fecundity irrespectively of fruit and seed cost. Patterns found in reproductive efficiency may be slightly modified according to life form and breeding system: fruit set was higher for annual than perennial herbs, which may be initially associated to the self-compatibility and autogamy of annual herbs. Fruit set increased from C-3 to CAM species for annual herbs and decreased from C-3 to CAM species for perennial herbs, indicating that C-4 and CAM photosynthetic pathways could be associated with the increment of reproductive efficiency in annual species. Besides the traditionally acknowledged relationship with resistance to stressful environments, reproductive strategies of C-4 and CAM plants could be also related to an increment in plant reproduction. (C) 2016 Elsevier GmbH. All rights reserved.