PLANT-AND MICROBIAL-DERIVED BIOMARKERS IN COASTAL PLAIN SOILS CULTIVATED WITH EUCALYPTUS AND ACÁCIA

http://dx.doi.org/10.5902/198050987554<br /><br />Changes in the management system for the cultivation of different forest populations and the use of crop rotation can lead to changes in the quality of soil organic matter (SOM) and vegetable residue deposition. This study evaluated the stage of decomposition and the contribution of plant and microbial compounds of microbial origin for SOM through biomarkers, such as phenols-derived lignin, carbohydrates and amino sugars in monoculture of eucalyptus of short-cycle (Eucalyptus urograndis) (seven years) compared to crop rotation system with acacia (Acacia mangium Willd.) after eucalyptus monoculture; monoculture of eucalyptus of long-cycle (24 years) and native vegetation (Atlantic Forest), as a condition of the original soil of the north coast of Espírito Santo state. To do so, it was estimated in samples of soil and litter the content of total organic C (TOC), total N (TN) and the contents of lignin-derived phenols (VSC), the carbohydrates and the amino sugars derived from soil microbial activity and relationships acids and aldehyde groups vanilil ((Ac/Al)vanilil) and syringyl ((Ac/Al)syringyl) of the lignin, relations hexoses/pentoses (H/P) of the carbohydrates,  glucosamine/muramic acid (Gluc/Ac. Mur) and glucosamine/galactosamine (Gluc/Gal) of the amino sugars. The results indicated that litter of the monoculture of eucalyptus short-cycle has greater deposition of dry matter, lignin content (VSC) and carbohydrates, C/N and VSC/N ratio; similar proportion of coarse litter, fine litter and C content and; lower N content in comparison to the crop rotation system with acacia. In the soil, acacia cultivation increases C, N and carbohydrates content, enlarge the acid/aldehyde ratio of vanilil grouping and the glucosamine/muramic acid ratio of amino sugars derived from microbial activity. The increase in time of eucalyptus cultivation (24 years) increased C content and decreased the VSC/N ratio in SOM compared to the monoculture of eucalyptus short-cycle, but still having C and N content lower than in soil of acacia and native forest. The smallest Ac/Al ratio of phenol derived from lignin in soils cultivated with eucalyptus (in long and short-cycle) indicates that the SOM is in lower stage of decomposition (oxidation) than in the soil cultivated with acacia, and that under native forest. In the soils under acacia, followed by that of eucalyptus short-cycle, the highest glucosamine/muramic acid ratio suggested a greater contribution of fungi in SOM cycling, whereas in the native forest and eucalyptus long-cycle soils there is greater abundance of bacteria-derived compounds. In this sense, there was recovery in the quality of the soil cultivated with eucalyptus long-cycle and rotated with acacia in respect to the monoculture eucalyptus short-cycle.