Abstract
In order to raise a healthy pond cypress forest under wetland conditions, a study on tree growth and nutrient properties in different water table sites was performed in a 17-year-old pond cypress wetland plantation which was located in the Lixiahe region of the Jiangsu province in China. Based on the investigation of the water table, the study sites were divided into three groups : high, middle, and low. The sites were flooded for about 6, 1, and 0 months per year, respectively. The depth of the mean water tables for one year was -2±12, -15±13, and -37±12 cm, respectively. The stem volume of the pond cypress located in the high, middle and low water tables was 45±8, 142±16, and 187±24m3ha-1, respectively, and the above-ground biomass was 33, 73, and 114 Mgha-1, respectively. The ratios of the above-ground and below-ground biomass decreased from 2.7 to 1.5 with the increase in the water table. The growth of the pond cypress was seriously inhibited when the depth of the mean water table was higher than -10cm, or the flooding period was longer than 1.5 months in one year. Compared to the middle and low water table sites, the soil pH in the high water table site increased by 0.5 to 1.1 units, but the total C and the total N contents decreased by 30%. The concentrations of exchangeable K, Ca, Mg, Na and total Fe in the soil were the lowest in the high water table site and the highest in the low water table site. The concentrations of NO3-N in the soil were not detected when the sites were flooded. Nutrient concentrations in leaves were not significantly influenced by the differences in the water table conditions except for an increase of Mn in the high water table. In the case of roots, N and Ca concentrations were higher, and Fe, Mn and Na concentrations were lower in the low water table site than in the other water table sites.
