Nitrogen deposition does not always induce soil acidification in tropical forests

Anthropogenic nitrogen (N) deposition rates have rapidly increased at the global scale, which has become an environmental issue that receives wide-spread concerns. It is well documented that elevated N deposition often exacerbates soil acidification in tropical/subtropical forests, characterized by the decreases in soil pH values and acidic cations (such as Ca²⁺ and Mg²⁺) concentrations, and the increased release of acidic cation (such as Al³⁺ and Fe³⁺). However, these observations were mainly derived from natural forests, and relatively few studies have been conducted in tropical plantations, in which tree species are few and ecosystem structures are relatively simple.

In order to address whether long-term N addition affects soil acidity of tropical plantations, Dr. Juan Huang and others from the research group of Ecosystem Management (Principal Investigator: Dr. Jiangming Mo) of South China Botanical Garden, Chinese Academy of Sciences, carried out a 7-year study in two plantations (Eucalyptus urophylla (EU) and Acacia auriculiformis (AA) plantations), which has been experienced long-term N addition since 2010. The results showed that long-term N addition did not affect soil acidity in the two plantations, with no significant changes in soil pH values and exchangeable non-acidic and acidic cations concentrations. Long-term N deposition did not significantly affect the plant and total soil N concentrations, but significantly increased the soil nitrous oxide emission rates and total dissolved N concentrations in the soil solutions. Their findings indicate that most of the added N was lost via leaching and emissions, such that long-term N addition did not exacerbate soil acidification in broadleaf plantations, thereby providing novel insight into the effects of atmospheric N deposition on forest ecosystems. Overall, their study suggests that long-term N deposition does not always lead to soil acidification in tropical forests.

This study, entitled “Long-term nitrogen deposition does not exacerbate soil acidification in tropical broadleaf plantations”, was published online in Environmental Research Letters.（https://iopscience.iop.org/article/10.1088/1748-9326/ac30bd）

Figure 1. Changes in soil pH at 0-10 cm depth of EU (a) and AA (b) plantations across 7 year of N addition.