Effect of Urban Tree Species on Soil Physicochemical Properties in Harbin, Northeastern China, and Afforestation Implications
LU Jia-Li, SHEN Guang, WANG Qiong, REN Man-Li, PEI Zhong-Xue, WEI Chen-Hui, WANG Wen-Jie
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Owing to diversified urban tree species in Northeast China, their possible impact on soil fertility and salinity-alkalinity and different patterns on soil profile are significant for appropriate species selection, and data from long-term permanent plots are very limited. Eight species(Fraxinus mandschurica, Juglans mandshurica, Picea spp., Pinus spp., Populus spp., Ulmus pumila, Phellodendron amurense, Larix gmelinii) were selected from the long-term plots in Harbin Experimental Forest Farm of Northeast Forestry University and Harbin Botanical Garden, and samples from 0-20, 20-40 and 40-60 cm soils were collected for measuring nine parameters of soil pH, electrical conductance(EC), soil organic carbon(SOC), alkali-hydrolyzed nitrogen(AN), total nitrogen(TN), available phosphorus(AP), total phosphorus(TP), available potassium(AK) and total potassium(TK). By a multivariate analysis of variance, tree species can significantly influence most of soil parameters at the same soil conditions, and different soil depth had significant differences. 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). Our findings highlights that 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 should be chosen 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. In the case of roadsides usually affected by high saline-alkali degrees from winter snow-melting, species with less saline-alkali declining ability should be avoided in afforestation practices.