Abandoned pastures and restored savannahs have distinct patterns of plant-soil feedback and nutrient cycling compared with native Brazilian savannahs.

Around 40% of the original Brazilian savannah territory is occupied by
pastures dominated by fast-growing exotic C4 grasses, which impact
ecosystem nutrient cycling. The restoration of these areas depends on the
re-establishment of soil processes. We assessed how restoration of
abandoned pastures through direct seeding of native species and
land-management practices (burning and ploughing) affect soil nutrient
cycling dynamics compared to native savannahs. We compared the activity of
soil enzymes related to carbon (C), nitrogen (N) and phosphorus (P)
cycling, as well as soil microbial biomass and soil chemical properties,
such as pH and the concentration of N, P, potassium (K) and soil organic
matter, among abandoned pastures, native savannah and restored areas.
Abandoned pastures had faster nutrient turnover than native savannah,
dominated by slow-growing native species. This pattern was evident from
the overall higher biomass-specific enzyme activity in abandoned pastures
than in native savannah. Compared with native savannah, restored areas had
similar levels of soil enzyme activity, but lower microbial biomass and
soil organic matter. Synthesis and application: The low enzyme activity in
restored areas was likely related to a reduced soil organic carbon
concentration due to practices such as burning and ploughing, rather than
plant-soil feedback. The lower immobilization of nutrients in microbial
biomass and lower retention of nutrients in restored areas, compared with
native savannah, is expected to favour the re-establishment of
fast-growing exotic species. Furthermore, the modifications of soil
chemical and microbial properties related to abandonment of pastures did
not influence restoration outcomes, because land-management practices
applied prior to direct seedling had a major impact on the soil microbial
community and soil fertility. Therefore, restoration of abandoned pastures
should consider a greater focus on restoring soil carbon and nutrient
cycling.