Seasonal evolution of soil organic matter, glomalin and enzymes and potential for C storage after land abandonment and renaturalization processes in soils of NE Spain

Rates of recovery of soil organic matter (SOM) in abandoned fields of Mediterranean Spain are affected by spontaneous succession in the vegetation, the occurrence of periodic wildfires and lack of forest management. Soil organic matter has a relevant role together with the renaturalization process of shallow soil under vines (V) and olive groves (OL), cork oak (S) and pine (PI) trees, pasture (PR), Cistus (MC) and Erica (MB) scrub in abandoned areas of NE Spain that are sensitive to fire. Physical, chemical, biological and biochemical properties of the soil determined season by season warned against its fragility. Pyrolysis-GC products showed in general moderate to strong positive and negative correlation with soil organic carbon (OC), easily extractable glomalin (EE-GRSP) and total glomalin (GRSP), β-glucosidase and protease, which strengthens the hypothesis that both less and more recalcitrant SOM fractions might be inferred and so there is a scale of potential carbon storage in the environments studied. Recently abandoned V and OL soil had small OC contents (mean 2.51 ± 0.25 and 15.26 ± 1.39 g kgâ^' 1) and GRSP (mean 1.04 ± 0.22 and 2.84 ± 0.53 g kgâ^' 1) and large contents of aromatic compounds. By contrast, PR and MB soil had large OC (mean 36.24 ± 0.75 and 37.66 ± 2.38 g kgâ^' 1) and GRSP (mean 4.85 ± 0.87 and 3.88 ± 0.76 g kgâ^' 1) content and smaller contents of aromatic compounds. This suggested a renewal of active OC in older soil. In fact, EE-GRSP and GRSP of more organic soil were positively correlated with the mineralization indices N/O (Furfural/Pyrrole) and O/Y (Pyrrole/Phenol) from active organic compounds (P < 0.05 and P < 0.01 respectively), and negatively correlated (P < 0.05) with the humification index B/E3 (Benzene/Toluene) from recalcitrant organic compounds. Principal component analysis (PCA) identified those environments where soil renaturalization is better. Our findings might indicate the potential for carbon storage in different abandoned shallow soil environments under renaturalization in Mediterranean climate conditions.