DAILY AND SEASONAL VARIATION OF SOIL RESPIRATION IN A SEASONAL SEMIDECIDUAL ATLANTIC FOREST FRAGMENT AND A RESTORATION SITE IN SOUTHERN BRAZIL

Abstract

Forest soils have a large capacity of stocking and cycling carbon, incorporated by organic matter and evaded by roots and soil microbiota as CO₂. Soil respiration can indicate ecosystem processes, but little is known about the successional, seasonal and diurnal variation in CO₂ flux. This study presents estimations of soil CO₂ efflux in a seasonal Atlantic forest fragment (FF) and an adjacent 15 years-old restoration site (RS), in two seasons (winter-dry and summer-rainy), during 24-hour periods, in southern Brazil. Measurements were performed with an infrared gas analyser at 2-hour intervals. Respiration rates were 50% higher in the rainy season, both in FF (261, against 135 mg m^-2 s^-1 in the dry season) and RS (237 and 127 mg m^-2 s^-1), indicating that higher humidity and temperature promoted higher soil biota activity. The soil respiration was higher at FF only in the dry season, revealing that this environment may be less sensitive to water limitation. Greater overnight respiration was observed in the dry season for both sites, likely reflecting more intense microbial metabolism at night in this season. There was no rainy season diurnal variation. Seasonal and daily variation suggests that soil respiration in the RS is more sensitive to warmer and dryer conditions.