Urbanization in China drives soil acidification of Pinus massoniana forests

Abstract

Soil acidification instead of alkalization has become a new environmental issue caused by urbanization. However, it remains unclear the characters and main contributors of this acidification. We investigated the effects of an urbanization gradient on soil acidity of Pinus massoniana forests in Pearl River Delta, South China. The soil pH of pine forests at 20-cm depth had significantly positive linear correlations with the distance from the urban core of Guangzhou. Soil pH reduced by 0.44 unit at the 0–10 cm layer in urbanized areas compared to that in non-urbanized areas. Nitrogen deposition, mean annual temperature and mean annual precipitation were key factors influencing soil acidification based on a principal component analysis. Nitrogen deposition showed significant linear relationships with soil pH at the 0–10 cm (for ammonium N (-N), P < 0.05; for nitrate N (-N), P < 0.01) and 10–20 cm (for -N, P < 0.05) layers. However, there was no significant loss of exchangeable non-acidic cations along the urbanization gradient, instead their levels were higher in urban than in urban/suburban area at the 0–10 cm layer. Our results suggested N deposition particularly under the climate of high temperature and rainfall, greatly contributed to a significant soil acidification occurred in the urbanized environment.

Responses of Inorganic Nitrogen of Forest Soils to Urbanization in Pearl River Delta, South China

“…3, 4) distance had correlations with soil chemical properties [40]. In this region, distance also had linear relationships with soil pH [34] and organic carbon [35] and atmospheric N deposition [7]. However, soil nitrate N in PF did not indicate significant linear relationship with the distance near to the urban core (Fig.…”

“…In this region, it has a warm and humid climate with annual precipitation ranging from 1566 to 2133 mm and mean annual air temperature from 19.65 to 22.22 °C. Obvious environment gradients caused by urbanization occurred in this region, including: (1) higher air temperature in the core of PRD than in its surroundings [31,32], (2) higher annual average precipitation in urban areas than in its soundings [33], (3) higher N deposition [7] and lower soil pH [34] in urbanized areas than in rural areas.…”

“…The detailed description of this design can see [35] and [7,34]. Fourteen sites were chosen for the study.…”

“…So the two forest types have experienced urbanization since 1978 and exhibited typical responses of the forests in this region. The forest soils were lateritic red earth [34,35].…”

“…Data of atmospheric inorganic N deposition (including NH 4 + -N and NO 3 --N deposition) and soil pH in PF derived from [7] and [34], respectively. Data of stage age, mean annual temperature and mean annual precipitation of each site were collected from the records of the bureau meteorology.…”