Tropical montane cloud forests (TMCF) are high-elevation forests covered with a dense cloud layer. Clouds add moisture to these forests allowing high levels of biodiversity to reside there, especially within the canopy. The biodiversity of epiphytes in the canopy is another defining characteristic of TMCF. Organic material gets trapped in these epiphytes, and it decomposes forming canopy soil. We know that tropical ecosystems contribute greatly to global C cycling, but there is a large amount of C within the canopy that is not accounted for. Moreover, we do not know how soil fungi differ between canopy and terrestrial soils. Here, we compare soil fungal communities and extracellular enzyme activity (EEA) in these two soils types. This work was conducted along two elevation gradients in the Monteverde Cloud Forest Reserve (10º18´N, 84º47´W) in Monteverde, Costa Rica. Fungal diversity was measured using high-throughput sequencing and a primer set targeting the fungal ITS region. We measured EEA of C-degrading enzymes, including α-glucosidase (AG; starch degrading), β-glucosidase (BG; cellulose degrading), cellobiohydrolase (CBH; cellulose degrading), and β-xylosidase (BX; hemicellulose degrading).
Results/Conclusions
Soil temperature was higher in canopy soils during the dry season (P = 0.01). Soil moisture differed between the two soil types during both seasons, but the pattern varied seasonally. Canopy soils were drier than terrestrial soils during dry season (P = 0.005), but wetter than terrestrial soils during the wet season (P < 0.001). Moreover, canopy soils had higher C:N ratios during both seasons (P < 0.001). During the wet season, EEA of AG, BG, CBH, and BX was higher in canopy soils (P (AG, CBH, BX) < 0.001; P (BG) = 0.002). This pattern continued during the dry season as AG, BG, CBH, and BX activities were higher in canopy soils (P < 0.001). Fungal communities differed between canopy and terrestrial soils during the wet (P = 0.012) and dry (P = 0.014) seasons. Climate change is exposing TMCF to drier and warmer conditions. Elevation gradients are important tools in understanding how soil fungi may respond to climate change in their natural environment. Canopy soils are especially vulnerable due to the greater environmental stress that occurs up in the canopy. It is important that we determine what functional roles fungi are fulfilling, and what their roles may be in C cycling.