Abstract
Terrestrial carbon sequestration is constrained by the supply of soil phosphorus (P). Climate and bedrock are two key independent drivers of soil P supply. Their potential interactions with soil P supply remains poorly understood. To address this issue, we examined the P status of subtropical forests in southern China along two adjacent elevational gradients with contrasting bedrock types (granite vs. slate). The results show that the P concentration of granite was significantly lower than that of slate. Accordingly, the P concentration of mineral soil, litter, and fine-root P on the granite was significantly lower than that on the slate. In contrast, their ratios to the bedrock P concentration were higher in the granite transect than in the slate transect. Moreover, we found a stronger nutrient uplift effect on P in the P-poor transects. Although bedrock P concentrations were constant along elevation, topsoil total P, soil labile inorganic P (Pi), soil labile organic P (Po), and soil moderately labile Pi concentrations showed a significant increasing trend with elevation on both transects. Multivariate linear regression models revealed that bedrock P explained more variation of plant and soil P than did climate. Soil moderately labile Po concentration showed contrasting elevational patterns on different bedrock types, which indicated an interactive effect between bedrock P concentration and climate on the soil moderately labile Po concentration. The Pearson correlation analysis indicated that plant and soil P measures were more tightly coupled in the P-poor transect than in the P-rich transect. These results indicate that the P status of subtropical forests is determined predominantly by the bedrock P concentration and by its interaction with climate. Our results suggest that predictions of ecosystem P status and its responses to climate change can be improved significantly by incorporating local-scale parent material properties into the modeling frameworks.
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