Patterns of soil properties and respiration along an elevation gradient in the Luquillo Mountains of Northeastern Puerto Rico

As an important component in global carbon cycle, soil respiration is one of the primary paths to release carbon fixed by vegetation to the atmosphere. Early studies of soil respiration focused on its relations with environmental conditions and terrestrial ecosystem structure and function. With the continuous climate changes, the study of soil respiration in the context of global climate change becomes a hot topic. The Luquillo Experimental Forest (LEF) is a typical tropical montane forest with distinct altitudinal variations in plant community distribution, which provides a natural environmental gradient to study factors driving long-term changes in tropical forest ecosystems, as well as the ecosystem responses to the accumulated effects of both natural and human disturbances. We first analyzed the soil physical and chemical properties along the elevation gradient, and then conducted a soil translocation experiment to measure the responses of soil organic carbon (SOC) and soil respiration rate to climatic changes. As the results shown, soil properties, especially soil organic matter (SOM) content varied significantly along the elevation gradient with the altered temperature and precipitation. Soil cores translocated from the top to the down site showed increased soil respiration and decreased soil C content at the end of the experiment, which is mostly influenced by the increased temperature. While soil cores translocated from the down site to the top showed increased soil respiration and decreased soil C content, which may be mostly influenced by the increased soil moisture. Therefore, both soil respiration rate and soil C content changed with climate conditions. The predicted climate changes in the Caribbean region, warmer and drier, might bring significant impacts on C sequestration in tropical forests.