Temporal And Spatial Patterns Of Phosphorus Fractions In Forest Soils Along An Urban-suburban-rural Gradient In Nanchang City

Soil phosporus (P) is not only one of the major limiting factors affecting plant growth, but also a potential source of environmental pollution. We know a little that P cycling and accumulation is influenced by the urbanization, a global problem. Soils in shrubs, Pinus massoniana, P. elliottii, conifer and broadleaf mixed, everygreen broadleaved, Phyllostachys edulis forests in the mid-subtropical region along an urban-rural gradient in Nanchang city, southern China, were analyzed for total P and P fractions using the modified Hedley P sequential fractionation method, while the seasonal variation of foliar P concentrations and resorption efficiency were studied in P. elliottii forests. The main results are as follows:(1) In general, soil total P and all P fractions concentration were highest in urban, lowest in rural under 39 sites in six forest types along an urban-rural gradient in Nanchang City, the result indicates that urbanization increase with the addition of P in urban soils.(2) Mean values of topsoil all P fractions in five typical forest successional stages(shrubs, Pinus massoniana, conifer and broadleaf mixed, everygreen broadleaved, Phyllostachys edulis forest) along an urban-rural gradient in Nanchang City were analyzed, our findings suggest that the relative abundance of HCl-P in urban forest soils (36%) was the highest among five P fractions, with NaOH-P as the dominant form in suburban (41%) and rural soils (50%); but the annual mean values of all fractions in P. elliottii forest show that NaOH-P is the dominant among five fractions in urban, suburban and rural (52%,58% and 53%, respectively). It can be seen that soil P fractions input is different among all the forests along urban-rural gradient, extraneous P input has spatial heterogeneity.(3) In five typical forest along urban-rural gradient in Nanchang City, mean values of soil all P fractions is higher in shrub and Ph. edulis forest than P. massoniana, conifer and broadleaf mixed, everygreen broadleaved forest, shrub and Ph. edulis forest are intensively anthropogenic disturbed. This means that anthropogenic disturbances can be an important factor for P accumulation, while increases in soil P pool and its availability were not significantly increased by the biological process of forest succession.(4) Leaves in 9 sites of P. elliottii forest an urban-rural gradient in Nanchang city, were analyzed for P concentration and its resorption efficiency and proficiency. The findings show mean values of leaf P concentration is higher in urban (0.94 g kg-1) and suburban (1.03 g kg-1) than rural (0.78 g kg-1), while PRE is lower in urban(75%) and suburban (74%) than rural (84%). These results suggest that urbanization affects plants P absorbability and availability.On the whole, urbanization would lead to soil total P and all P fractions accumulation which affect the cycle of P and plant absorbability in urban forest systems. Therefore, it is necessary to control anthropogenic disturbances and decrease extraneous P input in order to ensure the health of the forest ecological systems.