Photosynthetic and transpiration (E) rates, stomatal conductance, and leaf nitrogen content were surveyed for Myrica gale var. tomentosa, a N2-fixing wetland shrub, Betula platyphylla var. japonica, and Rhododendron japonicum in Ozegahara moor, an oligotrophic moor in Central Japan. Net photosynthetic rate saturated with irradiance (Pmax) of M. gale was 15.2-16.5 μmol(CO2) m-2 s-1, higher than those of the other species throughout the growing season. Pmax was positively correlated with leaf N content among the three species. The large leaf N content in M. gale was due to N2-fixation in root nodules. In a comparison of M. gale in two habitats, Pmax, leaf N content, and root nodule development were larger in the wetter habitat. M. gale showed high E and no midday depression of Pmax even under high irradiance and large vapour pressure deficit between leaves and ambient air on a midsummer day. These traits of photosynthesis and water relations were associated with the dominance of this shrub in wetter sites such as stream sides and hollows. and K, Maeda ... [et al.].
Sun-and shade-adapted plants of Ailanthus altissima utilized thermal-dissipative photoprotection (NPQ) across a range of photosynthetic photon flux densities (PPFD), with higher NPQ and lower maximum quantum yield of photosystem 2 photochemistry (Fv/Fm) in sun-adapted individuals, suggesting increased engagement of antennae-based quenching. Photosynthetic quantum requirements (Qreq; number of photons per CO2) were similar in sun and shade plants, but were low and comparable to forest understory species. Diurnal measurements showed that PPFDs in both habitats were consistently above photosynthetic compensation irradiance, and frequently exceeded saturating values. In addition, sun- and shade-adapted individuals possessed stomata that tracked short-term fluctuations in PPFD. Thus A. altissima may be unique in that it couples high, shade-plant like photosynthetic efficiency with high photosynthetic capacity in high-irradiance, while stomatal attributes that optimize water use efficiency are maintained in the shade. These features may contribute to success of A. altissima in establishing in disturbance-prone urban systems, and facilitate its spread into more PPFD-limited and competitive natural ecosystems.