Effects of functional and phylogenetic diversity on the temporal dynamics of soil N availability

[Purpose]: Plant species diversity is expected to affect multiple ecosystem functions, such as soil nitrogen (N) availability. However, this effect may be related to the ecological differentiation between coexisting species, often expressed as either functional diversity (FD; diversity in traits) or phylogenetic diversity (PD; diversity in phylogenetic ancestry) within plant communities. Evidence for the independent and combined role of FD and PD on ecosystem functions is generally missing, as measures of FD and PD are usually confounded in empirical studies. [Methods]: To solve this challenge we used an ad-hoc designed biodiversity experiment, with sown meadow plant communities forming independent combinations of FD and PD (low/low, low/high, high/low, high/high values, plus monocultures) and used ion-exchange membranes to monitor changes in soil N (i.e. NH4+-N and NO3−-N) availability through time (four sampling times per year; i.e. seasonality). [Results]: Our results showed a positive diversity effect for soil NH4+-N, with mixture communities yielding higher levels of NH4+-N than the corresponding monocultures. Within mixtures, communities with combinations of both high FD and PD showed the highest NH4+-N availability. Most importantly, although seasonality strongly affected soil N availability, diversity effects were generally consistent through time in the case of NH4+-N. In addition to these diversity effects, communities with higher proportion of nitrogen-fixing species also showed higher soil N availability. [Conclusions]: Plant communities composed of species with larger ecological differences can sustain high levels of available NH4+-N throughout the year, suggesting a stimulation of decomposition processes via the coexistence of plants with multiple strategies.The study was supported by a British Ecological Society Small Research Grants (SR16/1364), by the Young Researchers R&D Project. Ref. M2165 – INTRANESTI – fnanced by Community of Madrid and Rey Juan Carlos University and by the Czech Science Foundation grant GA16-15012 S. E.V. was funded by the 2017 program for attracting and retaining talent of Comunidad de Madrid (no. 2017‐T2/ AMB‐5406). CPC was supported by the Estonian Research Council (project PSG293). J.D. acknowledges support from the Fundação para a Ciência e a Tecnologia (IF/00950/2014 and 2020.03670.CEECIND) and the R&D Unit Center for Functional Ecology - Science for People and the Planet (CFE), with reference UIDB/04004/2020, fnanced by FCT/MCTES through national funds (PIDDAC)