Accumulation Characteristics Of N And P In Soils Under Different Vegetations In Coastal Wetland

Nitrogen (N) and phosphorus (P) in soil are closely related to the community succession and stability of wetland ecosystems. Nevertheless, they are so poorly understood about how the vegetation affects the accumulation forms of N, P in soil and whether there is fertile island effect of Phragmites australis (Cav.) Trin. ex Steud in coastal wetland. To understand the accumulation forms of N, P and the C:N:P in soil under different vegetations and the possibilitiy of fertile island effects of P. australis (Cav.) Trin. ex Steud better, the physical and chemical properties, N, P in soil under Phragmites australis (Cav.) Trin. ex Steud, Cyperus rotundus L. and Typha angustifolia L. of Yuehu Lake in Shandong were studied in the present work. The results were showed as follows.1) The soil bulk density ranged from 1.06 to 1.53 g/cm3. The result indicated soil bulk density changed as different vegetations and quarters. In spring, the soil bulk density under T.angustifolia was 1.06 ± 0.25 g/cm3, which was significantly lower than that of P.australis (Cav.) Trin. ex Steu (1.40 ± 0.25 g/cm3) and C. rotundus L. (1.51 ± 0.17 g/cm3) (p<5%).In summer, the result was the opposite of that in spring. Soil bulk density increased with soil depth. The organic matters contents in soil showed the same trend in spring and autumn, which was that the organic matters contents under Typha angustifolia L. was significantly higher than that of P.australis (Cav.) Trin. ex Steud and C.rotundus L. (p< 5%). Water contents in soil ranged from 8.43% to 38.96% and it showed a same trend in all the quarters, water contents in soil under T. angustifolia were significantly higher than that of P.australis (Cav.) Trin. ex Steud and C.rotundus L. (p< 5%). As a whole, the water and organic matters contents were at 0-10cm more than that at 10-20cm.2) Organic nitrogen(ON) and organic phosphorus(OP) are the major component in the form of N and P, which accounted for 94.67% of total nitrogen (TN) and 97.16% of total phosphorus (TP) in soil, respectively. Inorganic phosphorus (IP) contents were similar to TP contents in soil under different vegetations, which had the same trend. IP and TP contents in soil under T.angustifolia are significantly higher than that of P.australis (Cav.) Trin. ex Steud and C.rotundus L. (p< 5%). There were cumulative effects of IP and TP at 0-2cm in soil under C.rotundus L.and at 10-20cm in soil under T.angustifolia. There was no significant difference of inorganic nitrogen (IN) contents and TN contents in soil under vegetation types. The trend of exchangeable nitrogen (Ex-P) contents and exchangeable phosphorus (Ex-N) content under different vegetations would be differed depending on the quarter. In spring and summer, Ex-P contents in soil under T.angustifolia was the minimum one in all the vegetation types.In autumn and winter, it was the soil underP. austral is (Cav.) Trin. ex Steud, which got the minimum one (p< 5%). The difference of Ex-N contents in soil was more significant in summer and winter. In summer, the order of Ex-N contents in soil under vegetation was C.rotundus L.>T. Angustifolia>P. australis (Cav.) Trin. ex Steud (p< 5%). In winter, the order of Ex-N contents in soil under vegetation was T. Angustifolia>C. rotundus L.>P. australis (Cav.) Trin. ex Steud (p< 5%)3) In spring, summer and winter, the ratio of Ex-N/Ex-P in soil under P. australis (Cav.) Trin. ex Steud was 15.20 ± 6.31,7.31 ± 2.44 and 36.76 ± 9.24, respectively, which were significantly lower than that of T.angustifolia and C.rotundus L. (p< 5%).In addition, except the ratio of Ex-N/Ex-P in soil under P.australis (Cav.) Trin. ex Steud in spring and summer, all the ratio of Ex-N/Ex-P in soil were greater than 16 and the growth of vegetation was limited by P. All the ratio of C/N in soil under vegetation was greater than 25, indicating fast microbial decomposition of organic matter faster and conducive accumulation of N.4) The effective range of P.australis (Cav.) Trin. ex Steud to water content sand the ratio of C/N in soil were from 0-2m,reflected in the 16-18cm,6-8cm,respectively. The effective range of P.australis (Cav.) Trin.exSteudto to organic matters contents in soil was from 0-0.5m; to Ex-N, TN contents and the ratio of Ex-N/Ex-P, TN/TP in soil were 0.5m, reflected in the 12-14cm; to IN, IP contents in soil were 1.5m, reflected in the 14-18cm.In addition, P. australis (Cav.)Trin.ex Steud can increase the organic matters, Ex-P, IN, TN content and reduce the water, Ex-N, IP, TP contents in soil. From the trend of water contents and the ratio of C/N in soil between the P.australis (Cav.) Trin. ex Steud and barren, we can see that the result was the opposite of fertile island effect of P. australis (Cav.) Trin. ex Steud in coastal wetland.