Differences in Soil Respiration across a Successional Gradient in a Tropical Dry Forest from Northwestern Mexico

Abstract:

Soil respiration (R_s) is an important component of the carbon (C) cycle due to the significant CO₂ efflux to the atmosphere as a result of the metabolism and respiration from plants (i.e., roots) and microorganisms (i.e decomposers). Tropical dry forests (TDF) from northwestern Mexico are seasonally dry; thus, the peak of R_s rates occur during the wet season, usually influenced by the North American Monsoon System. However, the relative importance of the controlling biophysical mechanisms and flux magnitudes along successional gradients are still poorly understood. In this study, we present the analysis of three years (2015 to 2017) of systematic quasi-monthly measurements of R_s with static chambers in TDF sites with different land uses: an old-growth (OG), a mid-succession (MS), and an early succession (ES). During the study period, R_s magnitudes from the dry season were similar among sites (between 0.96-1.31 µmol CO₂ m^-2 s^-1). In contrast, during the wet season, R_s rates in OG were consistently higher than in MS and ES, reaching rates of 10.19 µmol CO₂ m^-2 s^-1. We identified by the end of wet season that R_s rates in OG were sustained by a longer time period, while in MS and ES, R_s decreased according to the moisture availability in the system. A preliminary statement about why R_s among study sites is highly variable (particularly in OG) are biophysical factors and biological processes related to features in the microbiota, substrate availability (i.e. litterfall) and decomposition rates, as well as, the influence of the antecedent moisture, instead of temperature.