| Under the context of the increasingly prominent environmental problems,the growth of plants is often affected by environmental changes.Plants can resist the external environmental changes by adjusting their own traits,which is so called environmental adaptive strategies.Coastal wetland is between the terrestrial ecosystem and the marine ecosystem,and the interaction between fresh and salt water is obvious,creating a unique habitat and biogeochemical cycle model.In this paper,Kandelia candel in the coastal wetland of Fujian Province,a typical mangrove tree species,was selected to study the adaptive mechanisms of its foliar and photosynthetic functional traits,analyze the nutrient element content,caloric value traits and the adsorption of soil P in different organs,explain environmental adaptive strategies of dominant plants in wetland community,and explore adaptive strategies of functional traits of plants in Coastal wetland to resist environmental stress.The study provides theoretical guidance for the conservation and application of Kandelia candel in a global context.The results showed were:(1)The experiments were conducted to compare the functional traits of uneven-aged leaves of Kandelia candel plantation and natural forest.The results showed were:1)The MLA,SLA and LDMC of current-year leaves in two habitats of Kandelia candel forests were all higher than those of former-year leaves,the values were 38.4 cm2>36.0 cm278.9m2·kg-1>67.5 m2·kg-1,258.7 mg·g-1>193.8 mg·g-1,respectively.2)The MLA of both current-year and former-year leaves of the plantation were all higher than those of the natural forest,the values were 40.7 cm2>36.1 cm2,37.5 cm2>34.4 cm2,respectively.The SLA of current-year leaves in the plantation was lower than those of the natural forest(78.4 m2·kg-1<79.4 m2·kg-1),while former-year leaves showed a contrasting trend(71.0 m2·kg-1>64.0 m2·kg-1).The LDMC of both current-year and former-year leaves of the plantation were higher than those of the natural forest,the values were 344.4 mg·g-1>173.0 mg·g-1,225.6 mg·g-1>162.0 mg·g-1,respectively.The trade-off between light resources acquisition and material storage to construct leaf organs of uneven-aged leaves is the result of the adaptive evolution of plants in their own habitats.The Kandelia candel can adjust strategies to tackle environmental stress,and has strong environment adaptability.Therefore,Kandelia candel is suitable to be planted as the coastal shelter forest tree species.(2)Photosynthetic characteristics of uneven-aged leaves of Kandelia candel in two different habitats were measured.The results showed were:1)The net photosynthetic rate,transpiration rate,stomatal conductance and intercellular CO2 concentration of former-year leaves were all higher than those of current-year leaves,and former-year leaves had stronger photosynthetic capacity.2)The chlorophyll a,chlorophyll b,chlorophyll a and b,and carotenoids of former-year leaves were all greater than those of current-year leaves,but the chlorophyll a/b showed an inverted trend.3)The maximum fluorescence(Fm)and maximum photochemical quantum yield(Fv/Fm)of current-year leaves of Kandelia candel were lower than those of former-year leaves.However,the fluorescence yield of leaves(F0)was the opposite of the former.4)The correlation analysis showed that there was a significant correlation among the photosynthetic functional traits of uneven-aged leaf of Kandelia candel(P<0.01).Therefore,Kandelia candel has good adaptability to external environmental changes.(3)The calorific value functional traits of Kandelia candel forest in different habitats were determined.The results showed were:1)The average gross caloric value(GCV)and ash-free caloric value(AFCV)of leaves of the Kandelia candel in different habitats were higher than those of roots(18.28 KJ·g-1>10.57 KJ·g-1,20.32 KJ·g-1>13.06 KJ·g-1),which meant that there were more high-energy organic substances in the leaves than in other organs.2)The average ash content was highest in roots(197.2%)and lowest in trunks(70.1%),indicating that plant roots contained more mineral elements.3)The gross caloric value(GCV)and ash-free caloric value(AFCV)of the natural forest were higher than those of the plantation(16.17 KJ·g-1>14.13 KJ·g-1,17.66 KJ·g-1>13.71 KJ·g-1),while ash content(AC)showed an inverted trend(86.62 g·kg-1<136.76 g·kg-1).The correlation analysis showed that there was a significant negative correlation between ash content(AC)and organic carbon(OC),ash-free caloric value(AFCV),gross caloric value(GCV)(P<0.01).There was a significant positive correlation between gross caloric value(GCV)and ash-free caloric value(AFCV)(P<0.01).The study indicated that changes in calorific value can comprehensively reflect the adaptation strategies of plants to the environment,providing a theoretical basis for further introduction and application of mangrove plants in the future.(4)The contents of C,N and P of different organs of Kandelia candel forest in different habitats were measured.The results showed were:1)The contents of C in different organs were:leaf(381.4 mg·g-1)>trunk(372.9 mg·g-1>branch(364.4 mg·g-1)>root(263.9 mg·g-1).The contents of N were:leaf(72.0 mg·g-1)>branch(21.7 mg·g-1)>trunk(16.6 mg·g-1)>root(12.3 mg·g-1).P contents were:leaf(1.25 mg·g-1)>branch(1.15 mg·g-1)>trunk(1.0 mg·g-1)>root(0.95 mg·g-1).2)C:N ratios were expressed as root(123.2)>trunk(87.9)>branch(50.6)>leaf(18.4).C:P ratios were:trunk(444.4)>branch(388.0)>leaf(336.5)>root(263.4).N:P ratios were:leaf(62.1)>branch(19.8)>trunk(18.4)>root(11.7).3)The N:P mean value of each organ of the Kandelia candel was 28.0,which was significantly greater than N:P mean value in the Chinese region(18.0),N:P mean value in the global scale(13.8),and the threshold of P restriction in plant growth(16.0),which indicated that the growth of coastal wetland plants was generally limited by P.Therefore,it is suggested that P fertilizer should be appropriately increased in the management of the Kandelia candel forest to increase the biological productivity.(5)Phosphorus adsorption characteristics of rhizosphere soils of Kandelia candel in different habitats were studied.The results showed were:1)The root activity of Kandelia candel could promote the adsorption of phosphorus in rhizosphere soil,and the promoting ability was related to exogenous phosphorus concentration.2)In the range of normal exogenous phosphorus concentration,the rhizosphere and nonrhizosphere soil thermostatic adsorption data could be well fitted to Langmuir model and Freunidch isotherm adsorption model by the onedimensional linear regression equation,in which the Freunidch model was better fitted.3)The phosphorus adsorption capacity parameters Kd and Kf in the rhizosphere soil in two models were significantly larger than those in the non-rhizosphere soil.4)The correlation analysis showed that the effect of organic matter content on the adsorption of phosphorus in rhizosphere and non-rhizosphere soil of Kandelia candel was significant.The study indicated that the activation of soil phosphorus by root activity can promote the bioavailability of phosphorus in soil,and improve the growth of forest trees. |
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