Differences in clonal growth between female and male plants of Rhus typhina Linn. and their diurnal changes in photosynthesis and chlorophyll fluorescence
火炬树雌雄母株克隆生长差异及其光合荧光日变化

Because resources are limited, plants must allocate resources between growth and reproduction to maximize lifetime fitness. The clonal reproduction pattern of male plants may be different from that of females: the female plants may have to allocate resources to both seed production and clonal reproduction, while the male plants may have to allocate resources only to clonal growth. The Staghorn sumac (Rhus typhina Linn.) is an exotic tree species in China; it is dioecious and grows clonally. We hypothesized (1) that the clonal growth of male plants of R. typhina is greater than that of the female plants and (2) that this ecological difference can be explained by male plants either allocating a high proportion of photosynthetic products to clonal growth or males having a higher net photosynthetic rate. Finally, we hypothesized that (3) female and male plants of R. typhina may differ in the number of the clonal ramets, their photosynthetic physiological parameters, and their fluorescence parameters. In order to explore whether male and female plants of R. typhina had different colonization abilities and to analyze their diurnal changes in photosynthesis and chlorophyll fluorescence, we measured growth indicators and used a CIRAS-2 portable photosynthesis system and a FMS-2 PAM-2100 Chlorophyll Fluorometer. Growth indicators, chlorophyll content, and diurnal changes in photosynthetic parameters of both female and male plants growing in a sample plot were compared and analyzed. Based on the above, we can reveal the resources utilization efficiency of male and female plants of R. typhina and the buffering abilities to strong light between the male and female plants of R. typhina at noon.The results showed that: 1) Male plants were superior to females in clonal growth as indicated by ramet size and ramet number, and they produced clonal ramets one year earlier than females. 2) Males used light energy, water, and CO2 more efficiently than females, and their net photosynthetic rate (Pn) was higher. This observation explains why male plants of R. typhina were better able to use resources than females.3) Under natural conditions, the potential efficiency of primary conversion of light energy of PS II (Fv/Fm) for the male plants decreased smoothly and the non-photochemical quenching coefficient (qN) increased slowly in measuring period. However, the minimum value of the Fv/Fm for the female plant occurred at 11:00, and the peak value of qN occurred at the same time. Therefore, although the male plant did not show obvious light photoinhibition, but female did. Based on the diurnal changes of the nonphotochemical quench (qN) under high light intensity, female plants were better able to dissipate heat than male plants. Our results demonstrated that the light utilization efficiency, water use efficiency, carbon utilization efficiency, and net photosynthetic rate of male plants of R. typhina were all higher than those of female plants. Thus, male plants are able