Rapid response of leaf photosynthesis in two fern species Pteridium aquilinum and Thelypteris dentata to changes in CO2 measured by tunable diode laser absorption spectroscopy

Abstract

We investigated stomatal conductance (gs) and mesophyll conductance (gm) in response to atmospheric CO2 concentration [CO2] in two primitive land plants, the fern species Pteridium aquilinum and Thelypteris dentata, using the concurrent measurement of leaf gas exchange and carbon isotope discrimination. [CO2] was initially decreased from 400 to 200 μmol mol−1, and then increased from 200 to 700 μmol mol−1, and finally decreased from 700 to 400 μmol mol−1. Analysis by tunable diode laser absorption spectroscopy (TDLAS) revealed a rapid and continuous response in gm within a few minutes. In most cases, both ferns showed rapid and significant responses of gm to changes in [CO2]. The largest changes (quote % decrease) were obtained when [CO2] was decreased from 400 to 200 μmol mol−1. This is in contrast to angiosperms where an increase in gm is commonly observed at low [CO2]. Similarly, fern species observed little or no response of gs to changes in [CO2] whereas, a concomitant decline of gm and gs with [CO2] is often reported in angiosperms. Together, these results suggest that regulation of gm to [CO2] may differ between angiosperms and ferns.