Belowground responses to elevation in a tropical montane cloud forest

Background/Question/Methods

Tropical montane cloud forests (TMCF) are high elevation forests characterized by persistent low-level cloud cover and are biodiversity hot spots within the tropics. They are natural laboratories that represent shifts in temperature and moisture. While many studies have investigated aboveground properties and communities in TMCF, little exploration has been done belowground. Moreover, there are vast knowledge gaps in how soil microbes respond to changes in elevation. These gaps limit our understanding of the climatic controls over microbial communities and the mechanisms by which elevation structures these communities and processes. The overall objective of this work was to characterize belowground properties in a TMCF. We established an elevation transect on the Pacific slope of the Cordillera de Tilarán within the Monteverde Cloud Forest Reserve (10º18´N, 84º47´W) in Monteverde, Costa Rica. We measured belowground properties such as soil temperature, moisture content, pH, and basal respiration. We also measured amounts of inorganic N and C:N ratios.

Results/Conclusions

Soil temperature decreased (r²=0.8554, p<0.001) and soil moisture increased (r²=0.2117, p=0.05) with increasing elevation. Soil C:N ratios also increased with increasing elevation (r²=0.7313, p<0.001). There were no significant relationships between elevation and soil pH, basal respiration, and rates of mineralization. Significant relationships between elevation and soil temperature and moisture content show that there are temperature and moisture shifts needed to determine the climatic controls over microbial communities. The relationship between elevation and soil C:N may coincide with shifts in bacterial and fungal diversity, as soils with high C:N ratios tend to be fungal dominant. We are currently using high-throughput DNA sequencing to examine this possibility. Climate change is exposing TMCF to drier and warmer conditions due to the rise of the cloud layer. Elevation gradients like these are important tools in understanding responses to climate change at larger scales than is possible through traditional ecological experiments. Overall, this elevation gradient can be a powerful tool to understanding belowground responses to climate change in TMCF.