Characteristics Of Soil Nitrogen Mineralization Of Different Urban Forests In Karst Areas

Soil nitrogen mineralization is one important part of nitrogen cycle, while the research based on it can provide reference for improve technology of nitrogen using, and it can also provide theoretical and practical basis for sustainable management of urban forests in Karst areas. The research has important practical significance for the forest management.Four typical forest ecosystem(Locust+Chinese catalpa, Sawtooth oak, Pinus massonian, Shrub)were selected as the research object in Guiyang city of Guizhou province, the process and characteristic of soil mineralization had been studied by using resin-eore technique from November2011to January2013. The results showed that:(1) The seasonal contents of ammonium and nitrate nitrogen in soil have significant difference between the four forest ecosystems(P<0.05). The order of ammonium nitrogen content is as follows:July>October> April>January, the order of nitrate nitrogen content is:April>July>October>January. The available nitrogen content is:Locust+Chinese catalpa>Sawtooth oak> Pinus massonian>Shrub(Except April). Ammonium nitrogen is the main existence form of available nitrogen, and the proportion of four forests are82.96%～90.21%、84.66%～90.50%、83.89%～90.21%、84.64%～90.63%.(2) The net ammonium amount and net ammonifying rate of four forests are all have significant difference(P<0.05). The order of Locust+Chinese catalpa and Sawtooth oak is April>July>October>January, Pinus massonian and Shrub is April>July> January>October. The net nitrification amount and rate are all have significant difference(P<0.05), and they have the same order is July>April> October>January. The total net nitrogen mineralization amount and rate all have significant difference(P<0.05), and they have the same order is uly>April> October>January. The soil nitrogen mineralization has obvious seasonal dynamics.(3) Being incubated for30days,60days and90days, the net nitrogen mineraization amount have significant difference between the four forest types(P<0.05), each of which is4.15±0.23mg·kg-1、3.54±0.24mg·kg-1、10.45±1.12mg·kg-1in Locust+Chinese catalpa community,3.17±0.48mg·kg-1、6.59 ±0.51mg·kg-1、8.49±0.87mg·kg-1Sawtooth oak community,1.48±0.11mg·kg-1、2.59±0.12mg·kg-1、7.65±1.01mg·kg-1in Pinus massonian community,3.02±0.43mg·kg-1、3.45±0.45mg·kg-1、5.22±0.47mg·kg-1in Shrub community.(4) The average tempreture(5cm depth) and moisture have great effect on nitrogen mineralization rate. The order of soil temperature on the impact of nitrogen mineralization rates is Locust+Chinese catalpa, Sawtooth oak, Pinus massonian, Shrub, the order of soil moisture on the impact of nitrogen mineralization rates is Locust+Chinese catalpa, Sawtooth oak, Pinus massonian, Shrub.(5) The net soil nitrogen mineralization show a significant linear relationship with soil organic matter; The net soil nitrogen mineralization and show a significant linear negative correlation with C/N ratio; The net soil nitrogen mineralization show a significant linear positive correlation with soil pH value.