The Physiological And Ecological Responses Mechanisms Of Isoetes Sinensis And Brasenia Schreberi In Different Habitats

Isoetes sinensis and Brasenia schreberi had been listed as the national first-grade protected plant in China.And it was investgated that they had been in imminent danger due to rapid loss of their natural community and the number of populations.The main cause was human activities which led to the loss of wild habitat and suitable habitat changes.At present,some measures had been taken to protect endangered plants,such as in-situ conservation and ex-situ conservation.Hydroponic culture was conducted to study the effect of different pH values(the nutrient solution initial pH treatments as 6.4,6.6,6.8,7.0 and 7.2 of five gradients cultivation),nutritional conditions(the control,medium nutritional condition and high nutritional condition of three nutritional models cultivation)and light conditions(the full light condition,70%of light condition and 40%of light condition for three light patterns cultivation)on the growth of them,the paper examined the changing rule of physiological and biochemical characteristics and photosynthetic fluorescence characteristics.This paper measured the chlorophyll content,osmotic adjusttment substance content,malondialdehyde content,protective enzyme activity and photosynthetic system of the leaves of them.The aim of these studies were to observe the adaptability of the ecological environment factors such as pH,N and P concentration and light,in order to provide the important theoretical basis for the protection and habitat selection of Isoetes sinensis and Brasenia schreberi.The main results were as follows:(1)The chlorophyll content of the leaves of Isoetes sinensis increased and then decreased but other physiological and biochemical indexes including soluble sugar content,malondialdehyde(MDA)content,proline(PRO)content,peroxidase(POD)activities and catalase(CAT)activities gradually decreased at the beginning then increased as pH increased.The highest chlorophyll content was detected in the pH = 6.6 treatment,and the soluble sugar content,MDA content,PRO content,POD activities and CAT activities were the lowest.Among the photosynthetic fluorescence characteristics,the PSII maximal quantum yield(Fv/Fm),PSII effective quantum yield(Yield),photochemical quenching(qP),higher potential maximum relative electron transfer rates(Pm),initial slope of rapid light curve(a)and half-starved value of light intensities(Ik)gradually increased and then decreased as pH increased,while non-photochemical quenching(qN)decreased and then increased.The lowest qN was detected in the pH = 6.6 treatment,Fv/Fm,Yield,qP,Pm,a and Ik were the highest.Our results show that the partial acid water is more suitable for the growth of Isoetes sinensis.And it had been stressed in the alkaline acid water.(2)The chlorophyll content of the leaves of Brasenia schreberi decreased but other physiological and biochemical indexes including soluble sugar content,MDA content,PRO content,POD activities and CAT activities gradually increased as pH increased.The highest chlorophyll content was detected in the pH = 6.4 treatment,and the soluble sugar content,MDA content,PRO content,CAT activities and POD activities were the lowest.Among the photosynthetic fluorescence characteristics,Fv/Fm,Yield,qP,Pm,a and Ik gradually decreased as pH increased,while qN increased.The lowest qN was detected in the pH = 6.4 treatment,Fv/Fm,Yield,qP,Pm,a and Ik were the highest.Our results show that the partial acid water is more suitable for the growth of Brasenia schreberi.And it had been stressed in the alkaline acid water.(3)The chlorophyll content of the leaves of Isoetes sinensis decreased but other physiological and biochemical indexes including soluble sugar content,MDA content,PRO content,CAT activities gradually increased as N and P concentrations increased.And POD activities increased at the beginning then decreased.Among the photosynthetic fluorescence characteristics,Fv/Fm Yield,qP,Pm,a and Ik gradually decreased,while qN increased.We could conclude that Isoetes sinensis had a better tolerance to the stress of the medium nutritional condition but poor tolerance to the stress under the high nutritional condition with comparatively obvious physiological injury as N and P concentrations increased.The ability of osmotic adjustment and antioxidant capacity increased,but the photosynthesis capacity decreased with the high nutritional condition.The higher nitrogen and phosphorus could inhibit the physiological activities of Isoetes sinensis,and thus affected its growth.In terms of the possibility that one of most important factors of endangerment of Isoetes sinensis attributes to the eutrophication water.(4)The chlorophyll content of the leaves of Brasenia schreberi increased and then decreased but other physiological and biochemical indexes including MDA content,PRO content,CAT and POD activities gradually decreased at the beginning then increased as N and P concentrations increased.And the soluble sugar content decreased.Among the photosynthetic fluorescence characteristics,Fv/Fm,Yield,qP,Pm,a and Ik gradually increased and then decreased with N and P concentrations increased,while qN decreased and then increased.We could conclude that Brasenia schreberi had good growth in the commonly used N and P concentrations,and it was well adapted to the medium nutritional condition.The ability of osmotic adjustment and antioxidant capacity increased,but the photosynthesis capacity decreased and affected its growth with the control condition because the N and P concentration was too low.So that Brasenia schreberi can be planted in eutrophic wetlands and lakes and beneficial in Brasenia schreberi growth.(5)The chlorophyll content of the leaves of Isoetes sinensis increased and then decreased but other physiological and biochemical indexes including soluble sugar content,MDA content,PRO content,POD activities and CAT activities gradually decreased at the beginning then increased with the decreasing light intensity.Among the photosynthetic fluorescence characteristics,Fv/Fm,Yield,qP,Pm,a and Ik gradually increased and then decreased,while qN decreased and then increased.The suitable light intensity for physiological and photosynthesis of Isoetes sinensis is about 70%of full light.In general,moderate shading should improve the carbon assimilation capacity of Isoetes sinensis,stimulate the accumulation of photoproduct and beneficial in Isoetes sinensis growth.(6)The physiological and biochemical characteristics of the leaves of Brasenia schreberi including the chlorophyll content,soluble sugar content,MDA content,PRO content,POD activities and CAT activities gradually increased with the decreasing light intensity.Among the photosynthetic fluorescence characteristics,Fv/Fm,qP,Pm,a and Ik gradually decreased with the decreasing light intensity,while qN increased.And Yield decreased and then increased.The suitable light intensity for physiological and photosynthesis of Brasenia schreberi is full light.In sum,strong light was beneficial,but weak light radiations were adverse to Brasenia schreberi growth.