Spontaneous urban vegetation as an indicator of soil functionality and ecosystem services

Questions: Our study focused on spontaneous vegetation in urban greenspaces in a Mediterranean city with the aim of relating plant community properties with ecological services along soil disturbance gradients. We asked which plant communities have the greatest plant biodiversity and soil carbon storage and the best-performing nutrient cycles and water regulation.Location: Madrid City (Central Spain).Methods: We studied four types of plant communities following soil disturbance gradients: vegetation on trampled soils, roadside vegetation, annual grasslands and perennial forbs. Regarding vegetation, we studied plant composition and productivity, plant diversity, plant growth forms and functional groups. Regarding soils, we determined soil organic carbon (TOC), available nutrients, the activity of seven enzymes relating to the main macronutrient cycles, and physical properties such as bulk density (BD) and soil water-holding capacity (WHC). We used one-way ANOVA to determine the influence of the plant community type on both soil and vegetation variables. Canonical correspondence analysis was performed to interpret the relationships between plant species assemblages with environmental gradients.Results: Perennial forbs showed greater biomass and developed on soils with the greatest TOC and available phosphorus. Annual grasslands displayed the highest plant diversity. Roadside vegetation developed on soils with higher phenoloxidase activity when compared to vegetation on trampled soils and annual grasslands. Vegetation on trampled soils developed on soils with lower WHC, lower beta-glucosidase, arylamidase and phosphatase activities and higher BD when compared to perennial forbs. Plant community distribution followed gradients most significantly associated with soil organic matter content, soil compaction and nutrient cycling performance.Conclusions: We conclude that plant communities are good indicators of ecosystem function and services which are unevenly distributed throughout urban habitats. The management in Mediterranean unmaintained urban greenspaces should be aimed at avoiding soil compaction to promote biodiversity, carbon storage and water regulation.