Soil Carbon and Microbial Functioning Reveal Multidimensional Patterns Across a Cedrus libani Afforestation Chronosequence in Mediterranean Karst

Afforestation assessments in Mediterranean karst regions often focus on vegetation and soil carbon, paying less attention to microbial activity. We examined the surface soil properties of a four-site Cedrus libani chronosequence in southern Turkey. In October 2024, topsoil (0–10 cm deep) was sampled at one degraded reference site and three plantation sites aged approximately 9, 14 and 24 years (15 samples were taken from each site). The afforested sites generally exhibited higher levels of soil organic carbon, total nitrogen, aggregate stability and microbial biomass carbon (MBC). Mean MBC ranged from 288 to 536 mg C kg−1 at afforested sites versus 180 mg C kg−1 at the reference site. Basal respiration was lower (0.30–0.36 versus 0.96 µg CO2-C g−1 h−1), as was biomass-specific respiration (qCO2: 0.54–1.39 versus 5.41 mg CO2-C g−1 MBC h−1). The microbial quotient did not differ significantly. The pooled MBC–respiration association was weak, whereas the site-adjusted association was positive. Multivariate patterns and the non-monotonic ordering of sites highlighted edaphic heterogeneity. As plantation age was completely confounded with site identity, these single-campaign observations cannot establish causal temporal effects. Nevertheless, integrating structural, chemical and microbial indicators provides complementary information for characterizing soil conditions across these karst sites.