Atributos físicos, químicos e biológicos do solo como indicadores de recuperação de áreas de mata ciliar na ecoregião de Cerrado em Minas Gerais

Abstract

Riparian Forests refer to forest patches located at the margins of water bodies, connecting terrestrial and aquatic ecosystems. The roles of such riparian buffers are related to reduction of nutrient losses as well as the anchoring and soil stabilizing effect promoted by plant root system and soil organic matter, resulting in erosion prevention. Riparian forest are commonly subjected to flooding events which , although being a key-process for terrestrial-aquatic ecosystems interface, may result in significant changes in soil physical, chemical and biological properties. This study evaluated two riparian forests under restoration located within the Cerrado biome and subjected to periodic flooding conditions: the first located at Velhas River basin and the second at Uberaba river basin. The former was restored with native species belonging to the Cerrado biome while the latter was cultivated by local landowners with Syzygium cumini (jambolão) under monoculture. The aim of this study was to assess the restoration of both riparian sites by using soil physical, chemical and biological properties, particularly those involved in C and N biogeochemical cycles, as restoration indicators. Each study area was composed of an experimental site (ES) under restoration which was compared with a preserved site (PS) and a disturbed site (DS) located within the same water body. In the Velhas River basin experimental site, 6 year after restoration, it was found a high soil pH and P content. The evaluation of parameters as soil cation exchange capacity (CEC), sum of bases (SB) and base saturation (BS) indicates the recovery of soil fertility in ES. However, other parameters as total nitrogen (TN), nitrate (NO3-), humic and fulvic acids (HA, FAs) revealed that ES is in an intermediate stage of restoration as compared to the reference sites. It was particularly influenced by the high soil NH4+ content and deficient nitrate production observed in both ES and DS, following this order: DS >ES. Such ammonium accumulation was not registered in PS. The soil microbial communities as assessed by the Phospholipid derived fatty acids (PLFA) and Temperature Gradient Gel Electrophoresis (TGGE) techniques showed that both the mineralization and denitrification were inhibited in ES and especially in DS (DS>ES). In contrast, in the PS it was observed a complete N biogeochemical cycle that prevented ammonium accumulation. The soil ammonium accumulation in ES and DS (DS>ES) was attributed to the swage discharge which the river is subjected and the effect of flooding. Thus, the increase of denitrification in ES suggests that this site is evolving towards the condition of PS, showing evidence of increase of resilience to the impact. In relation to the 15 years old site under restoration with a single exotic species in the Uberaba river basin, parameters as exchangeable bases and soil fertility (CEC, SB e BS) put it in an intermediate stage of restoration. It was found similarities between ES and PS in relation to soil aggregation and porosity but the chemical composition of the soil organic matter (SOM) was different. While ES showed a high FA and aliphatic compounds, the PS produced a more aromatic humic acid. These results suggest that, although some ecosystems properties related to soil aggregation and porosity have been restored under a single plantation with an exotic species, the qualitative differences in SOM do not allow to conclude that the soil properties of this plantation is fully restored. Overall, these results show that soil physical as well as C and N biogeochemical parameters can be considered suitable indicators of riparian forest restoration in light of different environmental impacts and conditions they are subjected.