Galen Candace, Dawson Todd E, Stanton Maureen L
Division of Biological Sciences, University of Missouri, 65211, Columbia, MO, USA.
Section in Ecology and Systematics, Cornell University, Corson Hall, 14853-2701, Ithaca, NY, USA.
Oecologia. 1993 Aug;95(2):187-193. doi: 10.1007/BF00323489.
We investigated the role of photosynthesis by reproductive organs in meeting the carbon costs of sexual reproduction in the snow-buttercup, Ranunculus adoneus. The exposed green carpels of snow-buttercup flowers have 1-2 stomata each. Net carbon assimilation rates of flowers are negative during bud expansion, but rise to zero at maturity, and become positive during early fruit growth. Experimental removal of separate whorls of flower parts demonstrated that the showy, nectary-housing petals account for most of the respiration cost of flower presentation. Conversely, photosynthesis by female organs contributes to a flower's carbon balance. Dipteran pollinators of R. adoneus are most active in sunny mid-morning to mid-afternoon intervals. At this time of day, rates of carpel photosynthesis (A) meet respiratory costs of pollinator attraction in fully expanded flowers. Achenes remain photosynthetically active until dispersal, and positive net carbon assimilation rates characterize infructescences throughout fruit maturation. Photosynthetic rates of achenes are positively correlated with infructescence growth rates. We tested the causal basis of this relationship by experimentally shading developing infructescences. Mature achenes from shaded infructescences were 16-18% smaller than those from unshaded controls. Leaf photosynthetic rates did not differ between plants bearing shaded and unshaded seed heads. Since female reproductive organs are only 8% more costly in terms of caloric investment than male ones and contribute to their own carbon balance, it is plausible that the energy cost of male function equals or exceeds that of female function in this hermaphroditic species.
我们研究了生殖器官光合作用在满足雪叶毛茛（Ranunculus adoneus）有性生殖碳成本方面的作用。雪叶毛茛花朵外露的绿色心皮每个有1 - 2个气孔。花朵在花蕾膨大期间的净碳同化率为负，但在成熟时升至零，并在果实早期生长期间变为正。对花部各轮进行实验性去除表明，艳丽的、容纳蜜腺的花瓣占花朵展示呼吸成本的大部分。相反，雌性器官的光合作用有助于花朵的碳平衡。雪叶毛茛的双翅目传粉者在上午阳光充足到下午中段最为活跃。在一天中的这个时候，心皮光合作用速率（A）满足完全开放花朵吸引传粉者的呼吸成本。瘦果在散播前一直保持光合活性，并且在整个果实成熟过程中，果序的净碳同化率为正。瘦果的光合速率与果序生长速率呈正相关。我们通过对发育中的果序进行实验性遮光来测试这种关系的因果基础。来自遮光果序的成熟瘦果比未遮光对照的瘦果小16 - 18%。遮光和未遮光种子头的植株之间叶片光合速率没有差异。由于雌性生殖器官在热量投入方面仅比雄性生殖器官高8%，并且有助于自身的碳平衡，在这种雌雄同体物种中，雄性功能的能量成本等于或超过雌性功能是合理的。
