Text by Tiina Tosens
Mesophyll conductance is an important limiter of photosynthesis. It is generally thought to be especially important in evolutionarily older plant groups. However, very little research has been conducted in this field with more basal plant species. Until now! An international group of scientists studied the photosynthetic capacity of 35 species of ferns and fern allies with interesting and novel results. Importantly, low mesophyll conductance was the main reason for lower photosynthesis in these plants.
What is more, the frond anatomy was studied in all the species and we found that lower mesophyll conductance depends largely on their thick cell walls and a low number of chloroplasts exposed to intercellular air spaces. Studying these evolutionarily more basal plants is important as they may hold answers to questions regarding our environment though this century. These genera have once dominated our planet and thrived in conditions similar to today, but also the climate predicted for the next 100 years. Furthermore, they have successfully persisted after the rise of angiosperms with more than 10 000 species still in existance.
Full citation: Tosens, T., Nishida, K., Gago, J., Coopman, R. E., Cabrera, H. M., Carriquí, M., Laanisto, L., Morales, L., Nadal, M., Rojas, R., Talts, E., Tomas, M., Hanba, Y., Niinemets, Ü. and Flexas, J. (2015), The photosynthetic capacity in 35 ferns and fern allies: mesophyll CO2 diffusion as a key trait. New Phytologist doi:10.1111/nph.13719 (link to full text)
- Ferns and fern allies have low photosynthetic rates compared with seed plants. Their photosynthesis is thought to be limited principally by physical CO2 diffusion from the atmosphere to chloroplasts.
- The aim of this study was to understand the reasons for low photosynthesis in species of ferns and fern allies (Lycopodiopsida and Polypodiopsida). We performed a comprehensive assessment of the foliar gas-exchange and mesophyll structural traits involved in photosynthetic function for 35 species of ferns and fern allies. Additionally, the leaf economics spectrum (the interrelationships between photosynthetic capacity and leaf/frond traits such as leaf dry mass per unit area or nitrogen content) was tested.
- Low mesophyll conductance to CO2 was the main cause for low photosynthesis in ferns and fern allies, which, in turn, was associated with thick cell walls and reduced chloroplast distribution towards intercellular mesophyll air spaces.
- Generally, the leaf economics spectrum in ferns follows a trend similar to that in seed plants. Nevertheless, ferns and allies had less nitrogen per unit DW than seed plants (i.e. the same slope but a different intercept) and lower photosynthesis rates per leaf mass area and per unit of nitrogen.