In a new study published in the journal Plant and Soil, researchers from the Chinese Academy of Sciences (CAS) have revealed that mixed larch-broadleaf forests exhibit a stronger resistance to soil acidification—a decrease in the pH of soil—compared to pure larch forests. This discovery suggests that mixed forests, which contain a variety of tree species, could be a more effective forest management strategy to combat soil acidification.

Human activities such as burning fossil fuels and using chemical fertilizers have led to high levels of nitrogen deposition, the transfer of nitrogen from the atmosphere to the Earth's surface, across many regions globally; this process may cause soil acidification and plant nutrient imbalance. While air pollution control measures are implemented, overall levels of nitrogen deposition remain relatively high in some parts of China. Previous research has primarily focused on nitrogen-deficient temperate forests, leaving the response of nitrogen-rich forest ecosystems and the regulatory role of tree species composition unclear.

The Stable Isotope Ecology Team from CAS' Institute of Applied Ecology conducted the new study by establishing simulated nitrogen deposition experiments in larch (Larix Kaempferi) forests and mixed larch-broadleaf forests in Qingyuan County, Liaoning. Over four years, they analyzed the effects of nitrogen addition on soil and tree leaves.

The researchers found that nitrogen addition increased the nitrate nitrogen content of larch forest soil, decreased the exchangeable base cations and pH in the litter layer and mineral soil surface, and increased the soil exchangeable hydrogen and aluminum ions, leading to soil acidification in these layers. 

The researchers also found that nitrogen addition reduced the carbon-to-nitrogen ratio of larch needles in the pure larch forests.

Unlike larch forests, the mixed forest showed no significant changes in soil inorganic nitrogen content, pH, or nutrient content in the leaves of dominant tree species due to nitrogen addition.

The study, titled "Higher resistance of larch-broadleaf mixed forests than larch forests against soil acidification under experimental nitrogen addition," provides valuable insights into the management of forest ecosystems. The findings suggest that in the northeastern regions of China, establishing mixed forests could be a better forestry management practice to prevent soil acidification under conditions of increased nitrogen deposition. By understanding the traits of different forest tree species, we can better manage our forest ecosystems to address environmental challenges.