Study On The Masting Ecology Of The Dominant Species Of The Evergreen Broad-leaved Forest In Subtropical China

Masting is a common reproductive strategy regulating seedling regeneration of many perennial plant species,the feature of which the intermittent production of seeds.Plants benefit from masting by reduced seed predation and increased pollination efficiency owing to the effects of economics of scale.In the recent decades,plant masting is among the most popular topics in the field of ecology and plant science.The scientific questions related to masting,such as its patterns,formation mechanism and ecological consequences,have attracted widespread attention.Studies of plant masting help increase our understanding of plant evolution,animal-plant relationships,and reproduction strategies.Subtropical evergreen broad-leaved forest is a typical zonal vegetation in East Asia.It is widely distributed in the Yangtze River basin in China and provides extremely important ecosystem services.Using the dominant species of subtropical evergreen broad-leaved forests as model species,this study has conducted intensive investigations and discussions on plant masting,including its patterns,formation mechanisms and potential benefits and costs on plant seed-to-seedling transition.First,we obtained the annual fruiting data of 24 coexisting woody plants in the evergreen broad-leaved forests on Jinyun Mountain by field monitoring.We also compiled a database of annual fruiting data containing 277 woody plants worldwide from published literature.Basing on this data,we investigated the relationship between plant masting patterns and species phylogenetic relationships and foliar nutrient content.We found that:(1)Masting on woody plants was universal both at the community and global scale.However,there were interspecific differences in masting intensity,which were mainly related to plant functional traits,pollination modes,and dispersal modes;(2)There was a significant correlation between the species phylogenetic relationship and masting intensity,indicating that masting may be preserved during the evolution of plants;(3)There was a close relationship between plant foliar nutrient and masting intensity,species with lower foliar nutrient content and unbalanced N:P ratios had relative higher masting intensity.Second,we monitored the fruit production dynamics of three dominant tree species(i.e.,Castanopsis fargesii,Machilus nanmu and Symplocos lucida)of the evergreen broad-leaved forests on Jinyun Mountain for 6-8 years.Based on the data,we investigated the masting patterns at population and individual tree levels for the three tree species.We also investigated the potential effects of masting on seed mass using C.fargesii as a model species.We found that:(1)The three tree species all showed clear masting signs.However,the population-level masting intensity of C.fargesii was lower than that of the other two tree species.Also,the masting year of C.fargesii population was not synchronized with the other two tree species;(2)The reproductive ability of different individuals in the population was quite different,which was mainly influenced by tree sizes and the competition intensity of neighbors;(3)The stable annual large production of some individuals dominated the masting patterns of population;(4)There was a trade-off between seed production and seed mass of C.fargesii,and masting significantly reduced seed mass.Third,we quantitatively traced the seed fate and dispersal distance of 1,250 labeled C.fargesii seeds.Based on this data,we discussed the effects of changed competition intensity of rodents for seed resources caused by the masting on seed dispersal efficiency.We found that:(1)Changes in the competition intensity of rodents for seed resources caused by masting had significant impacts on seed dispersal.At the plot scale,masting weakened harvest rate,predation rate,dispersal rate and distance of seeds by rodents.At seed station scale,the existence of seed hot spots promoted the survival of seeds from neighboring seed stations but limited seed dispersal;(2)Rodents had different choices for seed mass at different dispersal stages.At the pre-dispersal stage,rodents tended to predate smaller seeds and dispersal larger seeds.At the post-dispersal stage,rodents tended to bury larger seeds and predate smaller seeds;(3)The dispersal distance of seeds by rodents was closely related to seed mass,larger seeds had farther dispersal distance.However,the relationship between seed mass and dispersal distance was affected by the competition intensity of rodents for seed resources.Finally,we investigated the effects of masting on seedling regeneration using C.fargesii as a model species.We conducted a continuous monitoring on the masting pattern and the seed-to-seedling transition of C.fargesii for 6 years.We evaluated the potential benefits and costs casing by masting at each stage during seed-to-seedling transition of C.fargesii and found that masting could not provide benefits at all stages of seed-to-seedling transition.On the contrary,it caused additional seed costs during the pre-dispersal stage,the seed germination stage,and the seedling establishment stage,thereby reducing the benefits of masting.The main effects of masting on C.fargesii seed-to-seedling transition were as follows(1)Masting resulted in a higher proportion of seeds escaping predation by at the pre-dispersal and dispersal stage and the recruitment of more newly germinated seedlings to support the predator satiation hypothesis;(2)Nevertheless,masting dramatically decreased seed germination rates due to its negative effects on seed mass.This resulted in the seed-to-seedling transition rate in mast years that was roughly half of that in non-mast years;(3)Masting negatively affected the spatial rearrangement of seeds resulting in a greater spatial aggregative distribution pattern of newly germinated seedlings;(4)The combined negative effects of smaller seeds and spatially aggregated seedlings reduced the fitness of the newly germinated seedlings.These results highlighted the importance of considering both positive and negative effects of masting across the entire seed-to-seedling transition phases.Inferences based on seed predation and recruitment of new seedlings alone would certainly lead to overly optimistic conclusions with regards to the benefits of masting.