Abstract:

Reproductive allocation and sex allocation are central to plant life-history theory. Especially in recent years, more and more ecologists and evolutionists have focused on the sex allocation theory. Reproductive allocation discusses the trade-off between growth and reproduction, and sex allocation primarily studies the optimal allocation of resources to two sexes, which may explain the diversity of breeding systems in plants. To examine the adaptation of size-dependent resource allocation and discuss the effective factors on resource allocation, the variations of reproductive and sex allocation of five insect-pollinated hermaphrodite species in Ranunculaceae were studied in two populations, located separately at East Tibetan Alpine Meadow (3 500 m) and Sub-Alpine Meadow (2 900 m). Sampling positions were located in Maqu (101°53′ E, 35°58′ N) and Hezuo (102°53′ E, 34°55′ N) in Gansu Province, respectively. From June to September in 2001, we sampled stochastically by the different phenology of five species at floral stage including under- and above-ground parts. The samples collected were individually enclosed into sampling bottles and fixed in FAA (alcohol, formaldehyde, acetic acid, 8∶1∶1). The samples were heated to constant weight for 10 h at 65 ℃. Each individual was dissected into different parts, such as flowers (androecium, gynoecium and corolla etc.), roots, stems and leaves, then were weighed under the Sartorius Balances (10-4 g), and P/O (pollen/ovule ratios per flower) were counted in haemacytometer under the microscope. Individual size is represented by vegetative biomass. Reproductive allocation is the proportion of biomass of total flowers to vegetative biomass; sex allocation is the proportion of androecium biomass to biomass of total flowers. We used the power function Y=aXb to analyse relationships between individual size and reproductive components.Our results showed: 1) in all five species, the reproductive investment increases but the proportion of reproduction (reproductive allocation) decreases with increased individual size, which is consistent with the previous conclusions, indicating size-dependency of reproductive allocation at flowering. 2) there is significant negative size-dependent sex allocation in these species, in that the larger individual allocates more resources to female function (i.e. gynoecium). This means that plants can adjust the resource allocation between the two sexes by its status at flowering to gain higher fitness. However, the relationship between P/O (pollen/ovule ratio) and size is complicated and differs among species. 3) the trade-off between male and female allocation existed, and is influenced by environment. This result confirms the assumption of sex allocation theory