Effects Of Typical Forest Communities And Wetland Communities On Soil Ecological Characteristics In Tianjin

1. Litter decomposition is an important component of process of nutrient cycling in terrestrial ecosystems. Forest litter provides the main of material for the soil nutrients and affects the soil physicochemical properties. Currently, numerous studies have focused on the major influence factors, the element dynamics and soil quality status in the litter decomposition process in different climatic zones. However, there are a few studies about the nutrient dynamics of litter and soil nutrients in north area of warm temperate zones, especially close to temperate zones. Through nutrients in soils of Quercus variabilis forest, Juglans mandshurica forest and Quercus aliena forest in Baxian Mountain National Nature Reserve in Tianjin were measured as affected by different litter treatments:fresh litter, half-decomposed litter and soils and provided evidence for the process of forest nutrients cycling in north area of warm temperate zones. The results showed that:(1) In the fresh litter, C content was highest in the Quercus aliena forest (486.1g·kg-1) and lowest in the Quercus variabilis forest (447.5g·kg-1), N and P contents were highest in the Juglans mandshurica forest (17.9and1.2g·kg-1) and lowest in the Quercus aliena forest (13.2and0.8g·kg-1). In the half-decomposed litter, C and P contents were not significantly different among three different forests; N content was highest in the Quercus aliena forest (17.1g·kg-1) and lowest in the Quercus variabilis forest (10.5g·kg-1). The contents of C, N and P in the soils varied with different forests:Quercus aliena forest> Juglans mandshurica forest> Quercus variabilis forest.(2) In the fresh litter, C/N and C/P of Juglans mandshurica forest were significantly less than those of Quercus aliena forest and Quercus variabilis forest; in the half-decomposed layer, C/N and C/P among three forest types were not significantly different. From the fresh layer to the half-decomposed layer of litter, C/N and C/P were decreased by17%and11%in Quercus variabilis forest, and decreased by19%and35%in Quercus aliena forest, but there were not significant differences in Juglans mandshurica forest.(3) The mineral element content in the fresh litter tended to decrease from Juglans mandshurica forest, to Quercus variabilis forest, and Quercus aliena forest; pH increased with increasing the mineral element content. The order of total content of mineral element was Quercus variabilis forest> Quercus aliena forest> Juglans mandshurica forest.(4) The content of C in the soil have no significant correlation with that in the fresh litter, but have approximate significant correlation with that in the half-decomposed litter (p=0.053). The content of N in the soil had no significant correlation with that in the fresh litter, but had a significant positive correlation with that in the half-decomposed litter (p<0.01). It indicated that soil nutrients were more significantly influenced by the half-decomposed litter than the fresh litter.2. The coastal wetlands of Tianjin played an influential role in complementing groundwater and purifying land source pollution entering the sea. Recently, under people’s long-term and high-strength exploitation’s influence, the coastal wetland ecosystem is facing serious problem such as the ecological environment worsening. Through salinity (EC), bulk density, pH, organic carbon density and nitrogen in different soil depths of Phragmites australis community, Suaeda glauca community and Aeluropus sinensis community in coastal wetland were measured, then provided the reference for recovering the ecological function of coastal wetland in this paper.The main conclusions are as follows:(1)0-30cm soils in three communities, salinity was the highest in the Aeluropus sinensis community and lowest in the Phragmites australis community, bulk density was highest in the Aeluropus sinensis community and lowest in the Phragmites australis community, pH was highest in the Suaeda glauca community and lowest in the Phragmites australis community.(2) In three communities, organic carbon density in soils was highest in the Phragmites australis community (7.06kg-m"2), followed by Aeluropus sinensis community (6.38kg-m") and lowest in the Suaeda glauca community (5.70kg-m"). Organic carbon density all decreased with the soil depth and the highest values appeared in the surface layer (0-10cm) in three communities. (3) In the soils (0-30cm) of three communities, the order of total nitrogen content and NH4+-N content were Phragmites australis community>Suaeda glauca community>Aeluropus sinensis community, the content of NO3--N was highest in the Suaeda glauca community and lowest in the Aeluropus sinensis community.(4) In soils, organic carbon density and total nitrogen had a negative significant correlation with bulk density and pH, NH4+-N had a significant positive correlation with organic carbon density and total nitrogen, and NO3--N only had a significant positive correlation with organic carbon density and no significant correlation with other factors.