A Preliminary Study On Afforestation Tree Species Selection Based Tree Species Effects On Soil Properties

Owing to diversified urban tree species in Northeast China, their possible impact on soil indicators and different patterns on soil profile are significant for appropriate species selection. Different species(Fraxinus mandschurica, Pinus sylvestris var. mongolica, Populus spp., Ulmus pumila, Larix gmelinii et al.) were selected from Harbin Forest Farm and Xiushui, Maoershan Forest Farm, and samples from 0-20 cm,20-40 cm and 40-60cm soils were collected for measuring 17 parameters of root density, soil pH, electrical conductance(EC), total nitrogen (TN),total phosphorus(TP),total potassium (TK),alkali-hydrolyzed nitrogen (AN), available phosphorus(AP), available potassium (AK), Glomalin Related Soil Protein (GRSP) including easily extracted GRSP (EEG) and Total GRSP (TG), soil bulk density, soil specific gravity, soil porosity, soil specific surface area, soil organic carbon (SOC) and organic carbon mineralization rate. The main conclusions were as follows:(1) Based on multiple comparison results, all tested parameters were standardized as scores, and comprehensive scores for soil fertility maintaining ability(SOC, N, P, K and its effective state) and for reducing soil saline-alkali degree(pH and EC) were respectively computed from above soil parameters. Much higher comprehensive scores in soil fertility maintaining ability were observed in different soil layers in species of Ulmus pumila(scores at 38),while lowest scores were generally found in Populus spp.(scores at 26.5). In the case of reducing soil saline-alkali ability, Phellodendron amurense and Larix gmelinii had higher scores (>15), while Juglans mandshurica had the lowest scores(7.5). When we divided trees into evergreen and deciduous species, no differences were found in fertility maintaining ability and saline-alkali declining ability (less than 15.6% differences). Species selections for urban afforestation are important for tough site improvement. In the site of downtown with infertile soil and high saline-alkali degree, some species with high soil fertility maintaining and salinity-alkalinity declining capacity should be chose for their successful survival, while in fertile sites, such as river banks and wetlands, some species with high nutrient consumption and high growth rate could be selected for fast forest function rehabilitation.(2) Although there are great differences in soil between different locations, there are consistent betwen tree species difference. Through comprehensive analysis, standardized comprehensive score of two forest farm related indicators were most display that Fraxinus spp. had the highest scores of soil physical properties maintenance ability. In other words, Fraxinus spp. plantation had better soil physical properties maintenance ability, and mainly depended on decreased soil bulk density to achieve. The highest scores of soil carbon sequestration ability were also Fraxinus spp.. Two study locations had similar results. That was mainly related to its higher root density. Comprehensive soil fertility maintaining ability(N, P, K and its effective state and fungal metabolic product Glomalin Related Soil Protein), inter-species differences ranking between different locations were different. Through reducing soil salinity ability (pH and EC), Pinus sylvestris var. mongolica had the highest scores. The effects of different vegetation types on soil were not same in different locations and different soil depth, but there were regularity on the whole, especially soil physical properties and soil carbon sequestration ability.(3) Tree species can significantly influence most of soil parameters at the same soil conditions, and different soil depth had significant differences. Inter-species differences between most of the measured indicators were consistent in 0-60cm soil layers, including Harbin forest farm 10 indicators, Xiushui forest farm 13 indicators and Maoershan forest farm all 17 indicators. The reason for inter-species differences between most of the measured indicators were not consistent in different soil layers was soil pH, EC, soil bulk density, AP.TP.TK.