According to cost-benefit theory, a tradeoff between maximum performance (e.g., speed) and endurance is found in athletes and some animals. Similarly, a tradeoff between leaf photosynthetic capacity (performance) and its maintenance in adverse seasonal conditions (endurance) would be expected based on cost-benefit theory.
Dr. ZHANG Yongjiang of Xishuangbanna Tropical Botanical Garden (XTBG) and his collaborators tested a novel hypothesis for a tradeoff between photosynthetic capacity and its maintenance into unfavorable conditions. Cycads tend to have long leaf lifespans and a diversity of leaf morphology, structure, and photosynthetic capacity, and thus represent an ideal system for testing this leaf design hypothesis.
They compiled a dataset for seasonal dynamics in light saturated photosynthetic CO2 assimilation for evergreen seed plants including angiosperms and conifers from published studies of temperate sites around the world. They conducted a common garden experiment to minimize the influence of diverse growing conditions with 29 cycad species in two gardens with a pronounced cool season and substantial chilling temperatures: Xishuangbanna Tropical Botanical Garden (XTBG) and Fairylake Botanical Garden (FBG), Southern China.
They found strong support for the hypothesized tradeoff between maximum photosynthetic rate in the favorable season and the ability to maintain photosynthesis seasonally in both the analysis of published data for conifers and angiosperms and the experimental study on cycads.
In their tests, leaf light-saturated net photosynthetic rate per leaf area in the favorable season was positively correlated with the absolute or relative (percentage) decline of leaf light-saturated net photosynthetic rate per leaf area in the unfavorable season.
They resolved a possible mechanism based on biomechanics and nitrogen allocation; cycads with high leaf toughness (leaf mass per area) and higher investment in leaf construction than in physiological function (C/N ratio) tended to have lower warm season photosynthesis but less depression in the cool season.
Their study provides strong evidence for a general tradeoff across species between light-saturated photosynthetic rate in the favorable season, and the ability to maintain photosynthesis in the relatively unfavorable season.