Comparing Indicators of Carbon Cycling Under Different Climatic Regions of Iran

Abstract

ABSTRACT Dissolved organic carbon (DOC) and soil respiration (SR) are essential in carbon cycling and storage. Consequently, proper soil management requires knowledge of factors influencing DOC and SR in soil. The main objective is to identify the most critical indicators that control DOC and SR in the major climatic regions of Iran. The carbon cycling of sixteen pedons from six study sites with different soil moisture and temperature regimes was measured. Soil samples were collected from various genetic horizons to assess their physicochemical properties. Stepwise multiple linear regression (MLR) models were conducted on all horizons and B horizon properties (representing the subsoil) to identify the strongest correlation with DOC and SR. The MLR model revealed that organic carbon (OC) was negatively affected by pH, electrical conductivity (EC), amorphous and crystalline iron oxide contents in all horizons (R2 = 0.69), EC, and cation exchange capacity (CEC) in B horizons (R2 = 0.62). On the other hand, SR was negatively affected by pH, EC, soil water content, and clay contents in all horizons (R2 = 0.67), and calcium carbonate equivalent (CCE), pH, and sodium adsorption ratio in B horizons (R2 = 0.67). The most important indicators associated with carbon cycling included EC and pH in the different soil types of Iran. This study contributes to improving crop yield and mitigating soil degradation, mainly by controlling and managing salinity and pH threats for soil fertility to increase carbon storage in such climatic regions.