Abstract
The study estimates the parameters of the photosynthesis–irradiance relationship (PN/I) of a sedge-grass marsh (Czech Republic, Europe), represented as an active “green” surface—a hypothetical “big-leaf”. Photosynthetic parameters of the “big-leaf” are based on in situ measurements of the leaf PN/I curves of the dominant plant species. The non-rectangular hyperbola was selected as the best model for fitting the PN/I relationships. The plant species had different parameters of this relationship. The highest light-saturated rate of photosynthesis (Asat) was recorded for Glyceria maxima and Acorus calamus followed by Carex acuta and Phalaris arundinacea. The lowest Asat was recorded for Calamagrostis canescens. The parameters of the PN/I relationship were calculated also for different growth periods. The highest Asat was calculated for the spring period followed by the summer and autumn periods. The effect of the species composition of the local plant community on the photosynthetic parameters of the “big-leaf” was addressed by introducing both real (recorded) and hypothetical species compositions corresponding to “wet” and “dry” hydrological conditions. We can conclude that the species composition (or diversity) is essential for reaching a high Asat of the “big-leaf ”representing the sedge-grass marsh in different growth periods.
Highlights
The study estimates the parameters of the photosynthesis–irradiance relationship (PN/I) of a sedgegrass marsh (Czech Republic, Europe), represented as an active “green” surface—a hypothetical “big-leaf”
Knowledge of the photosynthetic parameters of individual dominant plant species based on in situ measurements makes it possible to determine the functional contributions of these species to the photosynthesis of the whole ecosystem characterised as a green “big-leaf ” surface
The highest daily average amount of incident photosynthetically active radiation (PAR) was recorded in summer 8.7 MJ m−2 d−1
Summary
The study estimates the parameters of the photosynthesis–irradiance relationship (PN/I) of a sedgegrass marsh (Czech Republic, Europe), represented as an active “green” surface—a hypothetical “big-leaf”. The P N/I curves are fitted to daytime NEE measurements, and respiration is estimated from the intercept of the ordinate[7] This approach allows assessing photosynthetic parameters of a whole plant community as those of a “big-leaf ”, without any knowledge of individual contributions of dominant plant species forming this community. The aims of our study are as follows: (1) individual estimation of the parameters of the photosynthesis–irradiance relationship ( PN/I curve) of five dominant plant species of the sedge-grass marsh community, based on in situ measurements. We expected that the wetland plant species studied will differ in values of their photosynthetic parameters, i.e., apparent quantum use efficiency (α), light-saturated rate of photosynthesis (Asat), rate of dark respiration (Rd) and compensation point (Icomp) These parameters will change during the individual periods of growth, reflecting changing in situ conditions (e.g., position of water table). These differences show the involvement of individual plant species in carbon cycling in the sedge-grass marsh ecosystem
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