Radiocarbon has been applied as a tracer to study carbon dynamics in different types of tropical soils, under paddy and non-paddy management on Java, Indonesia. The 14C concentrations were measured in samples of total organic carbon as well as in alkali-soluble humic acids, insoluble humin, and plant remains (roots, seeds, leaves) obtained from three sites with Andosols, Alisols, and Vertisols at different altitudes. In addition, the abundance and distribution of plant macrofossils in the soil column and organic δ13C values were determined. The results obtained so far are compared with those from a chronosequence of Cambisols in China. They indicate the input of fresh plant materials into the subsoil directly via roots and/or by soil cracks and bioturbation of aboveground litter. The total organic C and 14C concentrations show the usual decrease with increasing depth in paddy and non-paddy soils, reflecting the influence of direct input as well as the downward redistribution of organic material as particulates or dissolved organic carbon (DOC) depending on soil type (pedogenesis, plough-pan formation, drying cracks), crop type and management, and climatic factors. A disturbance of the Andosol around 0.4 m depth and a change in profile properties around 0.63 m in the Alisol limit the general conclusions.

Solar irradiance and precipitation are the most likely drivers of the seasonal variation of net primary productivity (NPP) in tropical forests. Since their roles remain poorly understood, we use litter traps, dendrometer bands and census data collected from one hectare permanent plots to quantify the seasonality of above-ground NPP components and weather parameters in 13 sites distributed along a 2800-m altitudinal gradient ranging from lowland Amazonia to the high Andes. We combine canopy leaf area index and litterfall data to describe the seasonality of canopy production. We hypothesize that solar irradiance is the primary driver of canopy phenology in wetter sites, whereas precipitation drives phenology in drier systems. The seasonal rhythm of canopy NPP components is in synchrony with solar irradiance at all altitudes. Leaf litterfall peaks in the late dry season, both in lowland (averaging 0.54 ± 0.08 Mg C ha y−1, n = 5) and montane forests (averaging 0.29 ± 0.04 Mg C ha y−1, n = 8). Peaks in above-ground coarse woody NPP appears to be triggered by the onset of rainfall in seasonal lowland rain forests (averaging 0.26 ± 0.04 Mg C ha y−1, n = 5, in November), but not in montane cloud forests.

A model was used to simulate primary production of benthic microbial mats in Lake Hoare, southern Victoria Land, Antarctica, and to compare potential benthic to planktonic production. Photosynthetic and respiratory characteristics of mats from five depths in the lake were extrapolated across depth, surface area and time, to estimate whole-lake, annual net primary production. Variation in under-ice light regimes resulting from changes in ice thickness and transparency, and light extinction in the water column was examined, and an uncertainty analysis of key model parameters performed. Daily mat production estimates were 0.98–37.83 mg C m−2 d−1, depending on depth and PAR, whereas in situ production of phytoplankton averaged 15% of this. Annual patterns of mat production achieved maximum rates of 15–16 g C m−2 y−1 at 10 m depth when ≥ 5% of ambient PAR was transmitted through the ice covering the lake; observed transmittance values were usually ≤ 5%. Increasing underwater PAR had little effect above 5–7% transmittance, as photosynthesis became saturated at this level. Uncertainties in estimates of maximum photosynthetic rate (Pmax), initial slope of photosynthetic-light response (α) and maximum respiration rate (Rmax) explained 72–99% of uncertainty in model behaviour; Pmax was increasingly important at high light levels whereas α was more important at low light levels, however Rmax exerted the greatest influence under most conditions.