Studies On The Reproductive Ecology Of Broussonetia Papyrifera

Recently,life history theory in plant has been one of the hot spots in ecology. Trade-off theory is the most basic hypothesis of the life history evolutionary theory. Nowadays the studies on trade-offs of plant is mostly focusing on herbs,however,the trade-offs of woody plant were unclear,especially dioecious ones.This study plots were located in Laoban mountain(N 102°51′～103°12′,E 29°40′～30°14′),Ya'an,Sichuan, China.Broussonetia Papyrifera,a dioecious plant,were selected as study material, Quadrates with a contiguous grid were carried out to study the spatial distribution pattern of Broussonetia Papyrifera,and biomass were used as the currency,the trade-offs of the Broussonetia Papyrifera on the module and plant level were discussed,and try to get reasonable explanations.Field investigation and data analysis were done in the past one year.The results were as follows:1.The spatial distribution patterns were clumpy in plot 1 and plot 2,but random distribution in plot 3.The aggregation intensity als0 changed with block sizes.The max intensity and max intensity block sizes were different.The spatial distribution patterns of sapling and mature tree were clumpy in plot 1 and plot 2,and medium tree was clumpy biased(except plot 3).Generally,the medium tree had higher clump than sapling and mature tree.And the trend of aggregation intensity from sapling to mature tree increased firstly and then declined.The population of Broussonetia Papyrifera was in a stable stage.2.The spatial distribution patterns of male and female population were clumpy in plot 1 and plot 2,but random distribution in plot 3.And the juvenile population of all plots was clumpy.Aggregation intensity of different sex population was in an order:plot 2＞plot 1＞plot 3 for the male,plot 1＞plot 3＞plot 2 for the female,and plot 1＞plot 2＞plot 3 for the juvenile.3.Males invest more biomass in reproductive structures than females,but females invest more vegetative structures than males during flowering.There was a positive correlation between the biomass of male inflorescence and vegetative structures.And there was no trade-off between vegetative and reproductive during flowering.The number and size had certain trade-off,but no significant difference(Male:r=0.687,P=-0.068;Female: r=0.259,P=-0.209).4.We failed to detect any significant trade-off,and there was even a weak positive relationship between fruit production and relative growth in females(r=0.3694,P=0.03). There was a fruit size-number trade-off,but no significant difference(r=0.256,P=-0.204), and a significant negative relation was present between mean weight per fruit and seed number,indicating a trade-off(r=-0.651,P＜0.01).5.The annual growth of DBH was greater in males than females,but no significance (F=7.805,P=0.858).The distance of female to the nearest female and female to the nearest male(F=1.336,P=0.034) were more distant than male to male(F=15.335,P＜0.01), and marked significantly.Males have more biomass than females in flowering,however, when fruit production was taken into account,females showed a higher overall reproductive investment.There was a trade-off between males and females on its reproductive function.6.The indexes of the soil in each plots had no significant difference,and the biomass distribution of fruiting and flowering among each plot also had no significant difference, and the mean seed sizes and number among each plot had significant difference.The environment had little influence on trade-off between growth and reproduction,and had certain influence on seed size and number in this study.7.Mean seed size was normally distributed,with a 1.34 times range in magnitude. There was little variation coefficient between intra and inter-individuals(2.54%,5.04%), and mean seed size might hide part variation among intra-individual,the variation of seed size was based on intra-fruits or inter-population.8.There was a reproductive structure size-number trade-off in Broussonetia Papyrifera, and the reproductive investment of males and females were different in flowering and fruiting.The trade-offs in different growth stages were not detected in this study.