| dc.description.abstract | Global change driven by human activities and its impact on the world ecosystems' properties and functioning has been the object of many scientific studies done to date. However, soils ecosystems' response to global change has not received sufficient attention, despite the big portion of the global biodiversity that they host and the essential ecosystem functions and services that derive from them. Soil food webs carry out the decomposition and the regulation of nutrient cycling in belowground systems, which are determinant functions for soil quality. The present study focuses on soil food webs structure and functioning as affected by four global change agents: elevated CO2 concentrations, nitrogen addition, warming and reduced precipitation; in a long-term grassland experiment.
Soil structure and functioning was determined by analyzing the decomposition and activity mediated by the microbial community and the structure and functional diversity of the nematode community as a representative of higher trophic levels. Microbial biomass and nematode densities were measured in consecutive years to assess the consistency of soil biota responses to the treatments. They varied through time on their response to global change agents. However, microbial biomass always tended to decrease, whereas nematode density tended to increase under global change. An extracellular enzyme analysis of enzymes involved in the carbon, nitrogen and phosphorous cycles in 2015 was performed. The activity of all enzymes relative to the microbial biomass increased under global change, and all of them were affected by the significant interaction between nitrogen, temperature and precipitation. Nematode community from 2014 was studied by its biodiversity and by calculating nematode functional indices. Nematode richness and diversity increased whereas evenness decreased. All the nematode functional indices were affected by the significant interaction between precipitation and temperature, indicating a degraded food web with a higher resource availability to primary consumers, and a bacterial-dominated decomposition under elevated temperature and reduced precipitation. Opportunistic nematode became more dominant whereas K-strategist presented a loss in density.
These results indicate that, despite the context-dependency of soil ecosystems response to global change, soil quality decreased. Soil food webs under global change in this experiment were representatives of a disturbed and stressed system with less trophic links, and where carbon, nitrogen and phosphorous cycles' stoichiometry was altered. | |
