Effects Of Hydrological Alteration On Plants Decomposition

Decomposition of aquatic macrophytes can substantially regulate the recycling of nutrierts.The study on the decomposition of aquatic macrophytes in the lake had an important significance for understanding the eutrophication,biological sedimentation,nutrition balance and so on.In the thesis,we studied the decomposition rate and nutrient dynamics of three life forms of aquatic macrophytes and the responses of mixed floating and submerged macrophytes.decomposition to nitrogen(N)and phosphorus(P)availability.Besides,we also studied the role of duration,and frequency of inundation in controlling leaf litter decomposition in the natural Baoxing River corridor,located in southwestern China.The results were mainly as follows:1.There existed greater differences in the C,N,P,Lignin,cellulose,hemicellulose content,C/N,C/P,while no differences in the polyphenol content,between the three life forms of aquatic macrophytes.Decomposition was fastest in Floating-leaved plants,slowest in emerged plants,and intermediate in submerged plants.The same life form of aquatic macrophytes had different decomposition rate,which decreased in the order of Nelumbo nucifera,Hydrochar is dubia,Trapa matans,Nymphoides peltatum,Vallisneria natans,Myriophyllum spicalum,Polamogeton maackianus,Typha angustifolia,Phragmites communis.The decomposition rate of aquatic macrophytes was significantly positively correlated with initial N(P<0.05,r = 0.797)and P content(P<0.01,r =0.929),negatively correlated with initial C/P(P<0.01,r=-0.821),C/N(P<0.05,r =-0.650)and cellulose content(P<0.05,r =-0.690).Net N and P release was observed in all aquatic plant species over 150 days of decomposition.Floating-leaved plants had the highest N and P release rate,followed by submerged plants,and emerged plants.The same life form of aquatic macrophytes had different N and P release rate.The N release rate decreased in the order of N.nucifera,H.dubia,N.peltatum,T.matans,V.natans,P.communis,M.spicatum,T.angustifolia,and P.maackianus.The P release rate decreased in the order of N.nucifera,H.dubia,N.peltatum,V.natans,T.matans,P.communis,T.angustifolia,M.spicatum,and P.maackianus.2.Decomposition was fastest in Nymphoides peltatum,slowest in Potamogeton crispus,and intermediate in the mixture of them.Increase in P-availability alone increased the decomposition rate of the three aquatic plants,whereas the impact of increase N-availability was insignificant.The observed decomposition rate of the mixture was 0.9%,1.3%(P<0.05)higher than the expected,which indicating that there was synergistic effects of the mixture with increase P-availability and both N-and P-availability.In contrast,there was no significant mixing effect with increase N-availability.Increase in P-availability increased the N and P release of the three aquatic plants,the impact of increased N-availability was insignificant,except for the impact on N content of P.crispus(P = 0.021).Increase both N-and P-availability increase P release of Single species,N and P release of the mixture.The remaining percentage of N and P of N.peltatum and P.crispus were lower than that of P.crispus.There was synergistic effect on N and P release in the mixture during the early stages of decomposition under high P.Afterwards,there was no significant mixing effect.There was no significant mixing effect during the decomposition under low P.Our results indicated that P-availability has stronger effects on litter decomposition than N-availability.There was no significant effect on decomposition rate with Increase both N-and P-availability,while there was significant effect on N and P dynamics,especially for P.The effects of mixing rely on P.3.How do frequency and duration of inundation affect fundamental ecosystem processes such as leaf litter decomposition?Along the natural Baoxing River corridor,located in southwestern China,we employed in situ experiments to separate effects of different inundation components on breakdown rates of Alnus cremastogyne,Houpoea officinalis is and the mixture of them.We used a litter-bag method with two different mesh sizes to investigate how microorganisms and macroinvertebrates influence leaf breakdown rates.Eleven treatments,each representing a specific combination of duration and frequency of inundation,were deployed to mimic complex inundation patterns.After 60 days of exposure,leaf litter had the highest decomposition rate in permanent wet condition and the lowest decomposition rate in permanent dry condition.Duration of inundation was the main inundation component that controlled leaf breakdown rates.Leaf breakdown was significantly faster in coarse mesh bags than in fine ones.In fine mesh bags,the observed mass remaining was lower than the expected after 45,30 and 15 days,which indicating that the occurrence of synergistic effect,whereas there was no significant mixing effect in permanent wet and wet condition.In coarse mesh bags,there was no significant mixing effect.Frequency,duration and the interaction term of both,but not mesh size significantly influenced microbial respiration.Frequency and mesh size significantly influenced microbial biomass carbon,but not duration and the interaction term of both frequency and duration significantly influenced microbial biomass carbon.Our study suggests that modifications of the inundation regime will directly modify established decomposition processes.Factors reducing duration of inundation will decelerate leaf breakdown rates,whereas frequency has no significant influence on leaf breakdown rates.Macroinvertebrates accelerate litter decomposition rates and play a role in mixing effects.