Soil CO2 respiration (Rs) tends to increase with short-term experimental warming around the world, which indicates an alarming potential for positive soil carbon-climate change feeds. However, Rs is often observed to either return to baseline or become lower than ambient soils in the longer term ( >3 years), pointing to ecosystem resiliency. The vast majority of experimental warming experiments are found in temperate regions, therefore we know very little about the response and resiliency of Rs to warming in tropical ecosystems. Climate, vegetation type, and the size of standing carbon stocks play an important role in the magnitude and direction of warming effects of Rs. However, the temperate bias in the number of warming experiments globally limits our ability to fully understand the factors mediating the effects of experimental warming on Rs. Our study, an OTC warming experiment part of the International Paramo and Puna Experimental Network (IPPEX), is located in the páramo of Chirripó National Park in Costa Rica. We monitored Rs, soil temperature, soil moisture, and air temperature in response to warming over the course of 4.5 months, spanning the wet and dry seasons.
Contrary to increases in Rs commonly observed in response to short-term experimental warming in temperate ecosystems, we found that an increase in soil temperature of about 1.0°C (with a an increase in air temperature of over 3°C) generally reduced Rs after just 1 year in a tropical alpine ecosystem (treatment: t=-1.7, p=0.09), with the most marked difference in the wet season. We also observed high spatial and temporal heterogeneity in response to warming (location: t=5.5, p< 0.001; time of day: t=2.6, p=0.01; month of year: t=5.2, p< 0.001). In addition to Rs and microclimate data, we will present pending results (including carbon and nitrogen pools and vegetation cover) that will help elucidate the factors driving the warming-induced reduction in Rs as well as the factors driving spatial and temporal variability in the response. Warming experiments in the tropics (such as this one) are essential to determine whether the drivers and patterns of Rs response to warming hold across biomes.