Linking Soil Acidity to P Fractions and Exchangeable Base Cations under Increased N and P Fertilization of Mono and Mixed Plantations in Northeast China

• Main Authors: Nowsherwan Zarif, Attaullah Khan, Qingcheng Wang
• Format: Article
• Language: English
• Published: MDPI AG 2020-11-01
• Series: Forests
• Subjects: temperate region; nitrogen; phosphorus; simulated atmospheric deposition; P fractions; soil Acidification
• Online Access: https://www.mdpi.com/1999-4907/11/12/1274

Atmospheric N deposition is increasing worldwide, especially in China, significantly affecting soil health, i.e., increasing soil acidification. The northern region of China is considered to be one of the N deposition points in Asia, ranging from 28.5 to 100.4 N ha⁻¹yr⁻¹. Phosphorus (P) is the limiting factor in the temperate ecosystem and an important factor that makes the ecosystem more susceptible to N-derived acidification. However, it remained poorly understood how the soil acidification process affects soil P availability and base cations in the temperate region to increased N deposition. To address this question, in May 2019, a factorial experiment was conducted under N and P additions with different plantations in Maoershan Experimental Forest Farm, Northeast China, considering species and fertilization as variables. The effective acidity (EA) increased by N and NP fertilizations but was not significantly affected by P fertilization. Similarly, the pH, base saturation percentage (BS%), calcium (Ca²⁺), and magnesium (Mg²⁺) were decreased under N addition, while the Al:Ca ratio increased, whereas NaHCO₃ inorganic phosphorus (Pi) and NaOH organic phosphorus (Po) significantly decreased under N enrichments. However, NaOH Pi increased in N-enriched plots, while H₂O Pi and NaHCO₃ Pi increased under the P addition. Thus, the results suggest that the availability of N triggers the P dynamics by increasing the P uptake by trees. The decrease in base cations, Ca²⁺, and Mg²⁺ and increase in exchangeable Fe³⁺ and Al³⁺ ions are mainly responsible for soil acidification and lead to the depletion of soil nutrients, which, ultimately, affects the vitality and health of forests, while the P addition showed a buffering effect but could not help to mitigate the soil acidity.