Abstract
To evaluate the relative importance of photosynthetic versus morphological adaptations of submersed macrophytes to low light intensity in lakes, rapid light curves (RLCs), morphological parameters, relative growth rate (RGR), clonal reproduction and abundance of two submersed macrophytes (Potamogeton maackianus and Vallisneria natans) were examined under 2.8%, 7.1%, 17.1% and 39.5% ambient light in a field and outdoor experimental study. The plants increased their initial slope of RLCs (α) and decreased their minimum saturating irradiance (Ek) and maximum relative electron transport rate (ETRm) of RLCs under low light stress, but V. natans was more sensitive in RLCs than P. maackianus. Accordingly, the RGR, plant height and abundance of P. maackianus were higher in the high light regimes (shallow water) but lower in the low light regimes than those of V. natans. At the 2.8% ambient light, V. natans produced ramets and thus fulfilled its population expansion, in contrast to P. maackianus. The results revealed that P. maackianus as a canopy-former mainly elongated its shoot length towards the water surface to compensate for the low light conditions, however, it became limited in severe low light stress conditions. V. natans as a rosette adapted to low light stress mainly through photosynthetic adjustments and superior to severely low light than shoot elongation.
Highlights
We hypothesized that 1) P. maackianus and V. natans have different low light adaptive strategies as they differ in growth form, potentially leading to a trade-off between physiological and morphological responses to low light stress; 2) P. maackianus as a canopy former might alleviate the low light stress by elongating its shoot length towards the water surface, while V. natans, being a rosette with low shoot elongation capacity rather, relies on photosynthetic adjustments to cope with the low light stress; 3) photosynthetic adjustments would become more important in determining plant abundance in deep water due to the lower carbon requirement compared with shoot elongation
The photosynthetic Rapid light curve (RLC) and their parameters (α, Ek and ETRm) of V. natans and P. maackianus were significantly affected by the experimental light regimes (Figs 2 and 3, F = 5.42, 6.65 and 8.76 for α, Ek and ETRm, respectively, and p < 0.05 for all)
The average ETRm values of P. maackianus were 29.9, 50.2, 53.7, and 44.1 μmol m−2 s−1 in the I1 to I4 light regimes, respectively, and higher than the 27.8, 33.7, 39.9, and 35.6 μmol m−2 s−1 of V. natans, for the I2 and I3 light regimes (Fig. 3B). Both species had increased αwhen the light availability decreased, with the highest value occurring in the I1 treatment; the average αvalue in the I1, I2, and I3 treatments of V. natans increased by 36.5% as compared to I4 treatment and the average αvalue in the I1, I2, and I3 treatments of P. maackianus increased by only 26.3% as compared to I4 treatment (Fig. 3C)
Summary
Morphological parameters, relative growth rate (RGR) and clonal reproduction provide information on the ecological adaptation of submersed macrophytes to various light regimes, because the survival, fulfillment of life history and population expansion of the plants require extra photosynthetic carbohydrate supply than those using for leaf maintenance alone[12]. Hara (rosette) grow well in waters with medium turbidity They can both be dominant in such an environment despite their different growth forms[13], indicating that their low light adaptive strategies differ significantly. P. maackianus and V. natans were cultured at various experimental light regimes with the aim to explore their low light adaptive strategies by measuring the RLC, morphological parameters, RGR and clonal reproduction and relating our findings to their abundance in two Chinese lakes.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
