Correlations Between Seed Set and Physiology

In wild plant species, there are few studies that have directly linked physiological rates to fitness. Here, we explore relationships between plant physiology and plant fitness in two wild annual species in the family Clarkia, Clarkia unguiculata and Clarkia xantiana. Because fruits are carbon sinks, we expect that plants that are photosynthesizing at higher rates would have higher fitness. In addition, because there is a morphological constraint in which stoma that control carbon uptake also permits water loss, plants that have higher photosynthetic rates are expected to have higher transpiration rates. Therefore, higher transpiration rates should also be correlated with higher fitness. The ratio of carbon gain to water loss is an indicator of how efficient plants are with their water (WUE_i). WUE is a little more difficult to predict because there are two plausible scenarios. The first being that plants with high WUE could have higher fitness because they are more water efficient in a water-limited environment. On the other hand, plants with low WUE may be taking advantage of water resources available early in the season. Plant fitness was estimated using seed set, measured from one fruit per plant. For C. xantiana, transpiration was positively correlated with seed set; plants with higher transpiration rates had higher seed set. Then, for C. unguiculata, WUE was positively correlated with seed set. Future work in which we control for position at which the fruit was formed, may decrease ontogenetic noise and thus reveal patterns hidden in the present study.