How does long-term complete submergence influence sex ratio and resource allocation of a dioecious shrub, Salix variegata Franch.?

Abstract

The dioecious Salicaceae species are regarded as suitable plant species for artificial restoration of riparian vegetation which is largely destroyed by human activities. However, the research examining how their sex ratio and resource allocation will change under long-term complete submergence is scarce. We studied sex ratio, mortality, resource allocation and flowering phenology of both males and females of the shrub Salix variegata Franch. after 30 days, 60 days and 120 days of simulated complete submergence. The increasing mortality revealed that the change of sex ratio was observed primarily because more females died under the complete submergence. The total biomass and vegetative biomass of the females decreased faster than that of the males. The males significantly decreased their number of catkins and reproductive allocations of resources. The females, however, did not change significantly, suggesting that the males were more flexible in adjusting their resource allocation in reproduction under complete submergence. The above/below ground biomass of the males and females decreased significantly with increasing duration of complete submergence, indicating that S. variegata reserve more resources to root under complete submergence. The flowering phenology of the males and females were both disturbed. The initiation date of flowering was more delayed, and the flowering duration was shortened more for the males than the females. The overlap of flowering phenology of the males and females, however, was at least 75%, even after 120 days of complete submergence. The results indicated that males have stronger complete submergence resistance abilities because they could more flexibly adjust their resource allocation strategy compared to the females. Based on those findings, we suggest that male S. variegata should be planted in riparian zones subject to flooding for longer than 2 months to establish a stable population.