The effects of plant size and light availability on male and female reproductive success and functional gender in a hermaphrodite tree species,Magnolia stellata

Abstract

Plant size and light availability may affect male and (or) female reproductive success and their relative contribution (functional gender). To test this hypothesis, we identified parents of 184 seedlings in a local population within a metapopulation of a hermaphroditic, insect-pollinated tree species, Magnolia stellata (Siebold & Zucc.) Maxim., using 14 nuclear and 3 chloroplast microsatellite markers. Parent pairs of all the seedlings were determined, and both seed and pollen parents could be distinguished for 49.5% of the seedlings. We also measured the parents’ plant size (diameter at breast height of the thickest ramet within each genet; DBHt) and the relative photosynthetic photon flux density (rPPFD) they received. The proportion of seedlings that originated from selfing was 20.7%. The number of seedlings parental trees produced as seed parents (S) was positively affected by DBHtand rPPFD. DBHt(but not rPPFD) also positively affected the number of seedlings sired as pollen parents (P). The femaleness of the parental trees (S/(S + P)) was positively affected by DBHt, probably because DBHthad a stronger effect on the trees’ reproductive success as seed parents than on their success as pollen parents. These results suggest that plant size affects not only reproductive success (male and female), but also functional gender.