Appraisal of different land use systems for heterotrophic respiration in a Karst landscape

Soil respiration, particularly heterotrophic respiration (RH), is a potent source of carbon dioxide (CO₂) in the atmosphere. The current research focuses on the evaluation of RH for six land use systems including sloping cropland (SC), shrub land (SD), grassland (GD), shrub & grassland (SGD), newly abandoned cropland (NC) and afforested forest (AF). Heterotrophic respiration showed a diverse seasonal pattern over a year long period that was affected by various soil properties and climatic variables across the six land use systems in a subtropical Karst landscape. The lowest RH scores were found in the SD site (annual cumulative soil CO₂ flux: 2447 kg C ha^-1), whereas the maximum heterotrophic respiration occurred in the SF site (annual cumulative soil CO₂ 13597 kg C ha^-1). The values of RH were: SC site: 3.8-191.5 mg C m^-2 h^-1, NC site: 1.04-129 mg C m^-2 h^-1, GD site: 3.6-100.7 mg C m^-2 h^-1, SGD site: 0.3-393.5 mg C m^-2 h^-1, SD site: 3-116 mg C m^-2 h^-1, and SF site: 10.6-398.2 mg C m^-2 h^-1. Highly significant (p ≤ 0.01) and positive correlations between RH rate and soil temperature were found for the studied land use types (correlation coefficients as follows; SC: 0.77, NC: 0.61, GD: 0.283, SGD: 0.535, SD: 0.230, SF: 0.85). However, water filled pore space (WFPS), NH₄⁺, NO₃^-, dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) concentrations showed varied (positive and negative) correlations with RH. The overall results show that soil temperature can be considered as the most limiting factor for RH among all the sites studied in the present research. In these environments, soil heterotrophic respiration significantly correlated with soil temperature, highlighting the significance of climate on heterotrophic respiration.