Short-Term Effects of Tunnel Construction on Soil Organic Carbon and Enzyme Activity in Shrublands in Eastern Tibet Plateau

Soil is the largest carbon pool, and our understanding of soil organic carbon (SOC) has been enhanced due to its role in mitigating climate change. However, fundamental uncertainty remains about the quantitative importance of tunnel excavation, one of the most common practices for road construction in mountainous areas, on the SOC dynamics. Therefore, the short-term effects of tunnel construction on SOC and its fraction, soil microbial carbon, and soil enzyme activity within 0–20 cm in two shrublands (dominated by Quercus aquifolioides and mixed with Q. aquifolioides, Rhododendron phaeochrysum and Betula platyphylla, respectively) in Eastern Tibet Plateau were investigated. The results showed that, regardless of vegetation type, SOC, dissolved organic carbon, and easily oxidizable carbon were 27.14 ± 2.87, 6.70 ± 0.74, and 0.29 ± 0.10 g kg−1 for tunnel-affected area of Q. aquifolioides and 47.96 ± 17.89, 11.19 ± 2.92, and 0.24 ± 0.04 g kg−1 for the mixture of Q. aquifolioides, R. phaeochrysum, and B. platyphylla, respectively. The values were not significantly different from those of tunnel unaffected areas (p > 0.05). Similarly, soil enzymes (except cellulase) were not significantly different between tunnel-affected and unaffected areas (p > 0.05), indicating that tunnel construction had a minor impact on the SOC fractions and soil enzymes in the early stage. The unchanged SOC and enzyme activities may be associated with no changes in vegetation production and soil water content in tunnel-affected areas. However, vegetation type had a significant impact on SOC and its fractions and soil enzymes (p < 0.05), demonstrating the importance of vegetation control on the SOC fraction and soil enzymes. This study would be one of the earliest studies to explore the effects of tunnel construction on soil carbon dynamics based on field experiment, which could provide a new concept on environmental sustainability during tunnel construction. However, a long-term study is encouraged to detect the effects of tunnel construction SOC and soil enzymes in the future.