Abstract:

Objective: Under altered precipitation patterns driven by global climate change, this study investigates the effects of throughfall reduction on soil macrofaunal communities in Quercus mongolica (Mongolian oak) forests of the Sanjiang Plain. The focus is on analyzing the changes in community composition, diversity, and trophic structure, providing a scientific basis for accurately predicting the potential impacts of climate change on biodiversity within the ecological function zone of Northeast China. Method: A throughfall reduction experiment was conducted at the Heilongjiang Fuyuan Forest Ecosystem Observation and Research Station from July to September 2024. Polyethylene permeable (PEP) membranes were utilized to intercept throughfall, achieving a 50% interception rate in the treatment group while maintaining natural throughfall conditions in the control group. Three pairs of treatment-control plots, each measuring 20 m by 20 m, were randomly established. To verify treatment efficacy, soil water content in the 0–10 cm layer was measured using the oven-drying method. Results showed that soil water content in the treatment group was on average 22.29% lower than in the control group, confirming that throughfall interception effectively achieved the experimental objective. Subsequently, both pitfall trapping and hand-sorting methods were employed to assess the composition and abundance of soil macrofauna. Furthermore, multiple soil physicochemical parameters were assessed, including soil organic matter, pH value, and soil fertility indicators such as total nitrogen, ammonium nitrogen, nitrate nitrogen, total phosphorus, and available phosphorus. The effects of throughfall reduction on the community composition, diversity, and trophic structure of soil macrofauna in Mongolian oak forests at the Sanjiang Plain were then analyzed. Result: 1) During the study period, a total of 23 953 soil macrofauna individuals were collected, belonging to 4 classes, 13 orders, and 34 families. The Formicidae family was the dominant group, accounting for 77.77% of the total. There were no significant differences in the community composition of soil macrofauna under throughfall reduction conditions compared to the control group. 2) The reduction in throughfall significantly increased the abundance of soil macrofauna and the Simpson dominance index (P<0.01), while significantly decreasing the Shannon-Wiener diversity index and Pielou evenness index (P<0.001). It had no significant effect on the richness of functional groups. Simultaneously, it significantly increased both the abundance and richness of carnivorous groups as well as the abundance of omnivorous groups (P<0.05). 3) Under throughfall reduction conditions, the soil macrofaunal community was predominantly influenced by available phosphorus, ammonium nitrogen, and soil organic matter. 4) The decrease in throughfall predominantly affected soil organic matter, pH value, and soil fertility indicators (such as total nitrogen, ammonium nitrogen, nitrate nitrogen, total phosphorus, and available phosphorus) through alterations in soil water content. Additionally, it had no discernible direct or indirect effects on the trophic structure of soil macrofauna. Conclusion: Throughfall reduction treatment increases the abundance of soil macrofauna in the Mongolian oak forest in the Sanjiang Plain while concurrently suppressing its diversity. This suppression, in turn, influences the availability of soil organic matter, pH value, and soil fertility for soil macrofauna. The projected future decline in throughfall in China’s Sanjiang Plain may lead to decoupled responses between soil physicochemical properties and soil macrofauna in Mongolian oak forests. Such disconnection could simplify the structure of soil macrofaunal communities, ultimately compromising the diversity and stability of these communities.

Key words: throughfall reduction, Sanjiang Plain, Quercus mongolica forest, soil macrofauna, community structure