Seasonal changes in soil carbon storage capacity and glomalin-related soil protein under different agricultural activities, abandonment, and wildfire occurrence in Mediterranean region

Abstract

Agricultural practices can directly affect soil environmental conditions and consequently soil ecosystems and fertility. Soils under different agricultural practices like tillage and grazing were studied and compared to other soils affected by wildfire and different ages of abandonment. Atmospheric CO2, soil C-CO2 loss, soil temperature, soil moisture, bulk density, soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), Redfield ratios of C:N:P, easily exactable and total glomalin-related soil protein (GRSPEE and GRSPT), and morphology, quantity, and stability of soil aggregates (WSA) were seasonally analyzed. Statistical significance checked using the two-factor ANOVA. Intense tillage and wildfire occurrence revealed a deficiency in soil nutrients and fertility more than grazing practices. Steady soil fertility conditions occurred in soils preserved by fire and ancient abandonment. The GRSP seasonal means varied significantly among all soils because of land-use effects. GRSPT, SOC, TN, and TP increased from winter to spring and reached the highest values in summer then decreased again in autumn. GRSP was positively correlated (P < 0.01) with atmospheric CO2, SOC, TN, and TP with high peaks in summer indicating the dependent GRSP production on plant nutrients acquisition as well as soil carbon pools. Moreover, the correlation between GRSP and emitted C-CO2 may indicate the contribution of GRSP fractions to the labile as well as the stable SOC fractions. The GRSPEE showed rapidly transformed into stable forms in more fertile and better-structured soils than in less fertile soils with vulnerable soil structures. In conclusion, the stoichiometric balance of soil nutrients, aggregate stability, and stabilized GRSP pools improved relatively across the seasonal rhythms from winter to summer. Moreover, environmental soil conditions developed to preserve organic carbon in soils with long abandonment than in mid abandonment, while the worst conditions were in the vulnerable soils intensively mismanaged and devastated by fire