Large seasonal variation of soil respiration in a secondary tropical moist forest in Puerto Rico

Omar Gutiérrez Del Arroyo; Tana E Wood

doi:10.1002/ece3.7021

Large seasonal variation of soil respiration in a secondary tropical moist forest in Puerto Rico

Ecol Evol. 2020 Dec 10;11(1):263-272. doi: 10.1002/ece3.7021. eCollection 2021 Jan.

Authors

Omar Gutiérrez Del Arroyo^{1

2

3}, Tana E Wood²

Affiliations

¹ Department of Biology University of Puerto Rico Río Piedras Puerto Rico.
² USDA Forest Service International Institute of Tropical Forestry Rio Piedras Puerto Rico.
³ Department of Environmental Science, Policy, and Management University of California Berkeley California.

Abstract

Tropical forests are the largest contributors to global emissions of carbon dioxide (CO₂) to the atmosphere via soil respiration (R _s). As such, identifying the main controls on R _s in tropical forests is essential for accurately projecting the consequences of ongoing and future global environmental changes to the global C cycle. We measured hourly R _s in a secondary tropical moist forest in Puerto Rico over a 3-year period to (a) quantify the magnitude of R _s and (b) identify the role of climatic, substrate, and nutrient controls on the seasonality of R _s. Across 3 years of measurements, mean R _s was 7.16 ± 0.02 μmol CO₂ m^-2 s^-1 (or 2,710 g C m^-2 year^-1) and showed significant seasonal variation. Despite small month-to-month variation in temperature (~4°C), we found significant positive relationships between daily and monthly R _s with both air and soil temperature, highlighting the importance of temperature as a driver of R _s even in warm ecosystems, such as tropical forests. We also found a significant parabolic relationship between mean daily volumetric soil moisture and mean daily R _s, with an optimal moisture value of 0.34 m³ m^-3. Given the relatively consistent climate at this site, the large range in mean monthly R _s (~7 μmol CO₂ m^-2 s^-1) was surprising and suggests that even small changes in climate can have large implications for ecosystem respiration. The strong positive relationship of R _s with temperature at monthly timescales particularly stands out, as moisture is usually considered a stronger control of R _s in tropical forests that already experience warm temperatures year-round. Moreover, our results revealed the strong seasonality of R _s in tropical moist forests, which given its high magnitude, can represent a significant contribution to the seasonal patterns of atmospheric (CO₂) globally.

Keywords: litterfall; moisture; nutrients; seasonality; soil respiration; temperature; tropical forests.