Temporal Variability of Soil Respiration in Experimental Tree Plantations in Lowland Costa Rica

The principal objective of this study was to determine if there is consistent temporal variability in soil respiration from different forest plantations in a lowland tropical rainforest environment. Soil respiration was measured regularly over 2004 to 2010 in replicated plantations of 15- to 20-year-old evergreen tropical trees in lowland Costa Rica. Statistically significant but small differences in soil respiration were observed among hours of the day; daytime measurements were suitable for determining mean fluxes in this study. Fluxes varied more substantially among months, with the highest average emissions (5.9 μmol*m-2*s-1) occurring in September and low emissions (3.7 μmol*m-2*s-1) occurring in January. Three of the six tree species had significantly increasing rates of soil respiration across 2004-2010, with fluxes increasing at an average of 0.09 μmol*m-2*s-1 per year: the three other species had no long-term trends. It was hypothesized that there would be a tradeoff between carbon allocation aboveground, to produce new leaves, and belowground, to sustain roots and mycorrhizae, but the relationship between canopy leaf fall-a surrogate for canopy leaf flushing-and soil respiration was significantly positive. The similarities observed among temporal trends across plantation types, and significant relationships between soil respiration, soil water content and soil temperature, suggest that the physical environment largely controlled the temporal variability of soil respiration, but differences in flux magnitude among tree species were substantial and consistent across years.