Study On The Chlorophyll Fluorescence Characteristics Of Aquatic Plants In Huixian Karst Wetland Of Guilin

Aquatic plant plays a significant role in energy flowing and nutrient cycling of wetland ecosystem. To study the photosynthetic characteristics of aquatic plants matters to the protection and restoration of ecosystem in Huixian karst wetland. In this thesis, we studied chlorophyll fluorescence characteristics of19species of aquatic plants in Huixian karst wetland by usingDIVING-PAM.19species of aquatic plants included6species of submerged plants: Vallisneria denseserrulata, Ceratophyllum oryzetorum, Myriophyllum verticillatum, Hydrilla verticillaia, Potamogeton malaianus, Limnophila sessiliflora,10species of emergent plants: Phragmites australis, Phramites karka, Cladium chinense, Typha angustata, Acorus calamus, Zizania latifolia, Polygonum hydropiper, Ludwigia prostrate, Nelumbo nucifera, Hygrophila salicifolia, and3species of floating plants:Ludwigia adscendens, Eichhornia crassipes, Alternanthera philoxeroides. The results were as follows.First, we measured the chlorophyll fluorescence induction curves of19species of aquatic plants in situ and found the Fv/Fm(maximal quantum yield of PS Ⅱ in the dark) showed significant differences. The Fv/Fm of6spices of submerged plants, and A. calamus, Z. latifolia, H. salicifolia were lower than0.8. The rest aquatic plants’Fv/Fm were larger than0.8, so they shall be in good physical status, and had obvious potential photosynthetic capacity.The Y (effective quantum yield), the rETR (relative electronic transfer rate) and the qP (photochemical quenching) of the19species of aquatic plants from the induction curves showed the same variation trend, rising and then to keep steady state as the time changed. And the NPQ (non-photochemical quenching) of H. verticillata, P. malaianus, C. chinense, T. angustata, A. calamus, N. nucifera and L. adscendens kept the high quantities after rising and did not dropt, while the rest aquatic plants’NPQ were rising and then downing to the steady state.Secondly, we compared the fitting parameters, rETRmax (maximal relative electron transport rate), a (initial slop of RLC) and EK(half-saturation light intensity) by fitting the rapid light curves of the aquatic plants under the condition of light adaptation and dark adaptation in situ. The results showed that rETRmaxof19species of aquatic plants under the condition of light adaptation were larger than under the condition of dark adaptation, this illustrated the increasing of the maximum photosynthesis rate after light adaptation. The a of C. oryzetorum and H. verticillata under the condition of light adaptation were lower than under the condition of dark adaptation, this illustrated the decreasing of the light use efficiency after light adaptation, while the rest17species of aquatic plants’light use efficiency increased, because their a were larger under the condition of light adaptation. The EK of N. nucifera under the condition of light adaptation was lower than under the condition of dark adaptation, this illustrated the decreasing of intensive-light tolerant capacity after light adaptation, and the rest18species of aquatic plants’ EK were larger under the condition of light adaptation, therefore their intensive-light tolerant capacity increased after light adaptation.Under the condition of dark adaptation, Potamogeton malaianus and Ceratophyllum oryzetorum had stronger intensive-light tolerant capacity and higher maximum photosynthesis rates than other stutied submerged plants. N. nucifera and A. calamus had larger EK and maximum photosynthesis rate, and C. chinense had lower EK and potential maximum photosynthetic raie but highest light use efficiency, compared with other studied emergent plants. E. crassipes and A. philoxeroides had larger rETRmax、a and EK, among the3species of floating plants, so they had stronger photosynthetic capacity than L. adscendens.Under the condition of light adaptation, P. malaianus and C. oryzetorum had stronger intensive-light tolerant capacity and higher potential maximum photosynthetic rate but lower light use efficiency than Vallisneria denseserrulata, M. verticillatum, H. verticillata and L. sessiliflora. L. sessiliflora had higher light use efficiency but lower intensive-light tolerant capacity and maximum photosynthesis rate than other stutied submerged plants. The species of emergent plants, which had larger EK, had larger rETRmax, while the species had higher light use efficiency, it would have lower rETRmax. E. crassipes had the largest rETRmax、a and EK among the3species of floating plants, and L. adscendens had the lowest rETRmax and EK.Thirdly, we studied the diurnal variations of chlorophyll fluorescence of the19species of aquatic plants in sunny days. The results showed that the diurnal variation process of PAR (photosynthetic active radiation) was fit to the single peak curve, being largest at12:30or14:30and much lower in the morning and evening. As the PAR changed, the diurnal variations of NPQ showed the same performance with PAR. The diurnal variations of rETR of C. oryzetorum, M. verticillatum, L. sessiliflora, C. chinense, P. hydropiper, L. prostrate, N. nucifera and E. crassipes were fit to single peak curves, and the rest11species of aquatic plants’ were fit to the twin peaks curves. The Y and qP of19species of aquatic plants were lowest at12:30or14:30and much larger in morning and evening, while the NPQ of the studied aquatic plants were largest at noon and lower at moring and evening.