In an era of significant and rapid environmental change, understanding controls on carbon (C) and nutrient cycling is of immense importance. Tropical forests are biogeochemical engines that drive C cycling at the global-scale. They account for approximately one third of the World’s soil C pool, and exhibit the highest soil respiration rates globally. These highly productive systems are often found on highly weathered soils where phosphorous (P) is typically considered the primary factor limiting various processes related to C cycling, such as forest productivity and the rate of soil C loss via soil respiration. It follows that the long-term stability of C stocks in tropical forests could depend, in part, on the availability of this nutrient. Nevertheless, the spatial and temporal patterns of P availability are poorly resolved, and this constrains our ability to consider this control of P. Here, we review our current understanding of the interactions between seasonal rainfall patterns and biotic and abiotic controls on temporal patterns of soil P availability in tropical forests, including the wet to dry season transition. We will also offer methodological recommendations that should be considered when assessing available P pools in field settings.
Results/Conclusions
Emerging research from multiple tropical forest sites suggests that the available soil P pool is highly dynamic, even in relatively a-seasonal tropical forests. Soil P availability and soil moisture availability tend to be correlated; however, the direction of the relationship among P and moisture is not consistent across tropical forest sites and soil attributes beyond moisture maintain significant control. In the acidic, iron (Fe) rich wet tropical forest soils, microbial demand, in addition to soil sorption capacity, can determine the partitioning of available P into biological vs. geochemical sinks across a range of time scales. Data from tropical dry forests also show strong seasonal patterns, which are also very likely related to biological demand and mineralization dynamics. Taken together, these data suggest that the dominant controls on the fate of newly available P is likely to vary across tropical forest sites depending on the level of P availability, aspects of soil chemistry, and the strength of biological demand. Research that evaluates the importance of Fe-P dynamics and plant/microbial competition might enable further insight into controls on soil P availability and related controls on C cycling in tropical forests.