Net primary productivity allocation and cycling of carbon along a tropical forest elevational transect in the Peruvian Andes

Abstract

The net primary productivity, carbon (C) stocks and turnover rates (i.e. C dynamics) of tropical forests are an important aspect of the global C cycle. These variables have been investigated in lowland tropical forests, but they have rarely been studied in tropical montane forests (TMFs). This study examines spatial patterns of above- and belowground C dynamics along a transect ranging from lowland Amazonia to the high Andes in SE Peru. Fine root biomass values increased from 1.50 Mg C ha⁻¹ at 194 m to 4.95 ± 0.62 Mg C ha⁻¹ at 3020 m, reaching a maximum of 6.83 ± 1.13 Mg C ha⁻¹ at the 2020 m elevation site. Aboveground biomass values decreased from 123.50 Mg C ha⁻¹ at 194 m to 47.03 Mg C ha⁻¹ at 3020 m. Mean annual belowground productivity was highest in the most fertile lowland plots (7.40 ± 1.00 Mg C ha⁻¹ yr⁻¹) and ranged between 3.43 ± 0.73 and 1.48 ± 0.40 Mg C ha⁻¹ yr⁻¹ in the premontane and montane plots. Mean annual aboveground productivity was estimated to vary between 9.50 ± 1.08 Mg C ha⁻¹ yr⁻¹ (210 m) and 2.59 ± 0.40 Mg C ha⁻¹ yr⁻¹ (2020 m), with consistently lower values observed in the cloud immersion zone of the montane forest. Fine root C residence time increased from 0.31 years in lowland Amazonia to 3.78 ± 0.81 years at 3020 m and stem C residence time remained constant along the elevational transect, with a mean of 54 ± 4 years. The ratio of fine root biomass to stem biomass increased significantly with increasing elevation, whereas the allocation of net primary productivity above- and belowground remained approximately constant at all elevations. Although net primary productivity declined in the TMF, the partitioning of productivity between the ecosystem subcomponents remained the same in lowland, premontane and montane forests.