Hidden belowground plant diversity buffers against species loss during land‐use change in species‐rich grasslands

QUESTIONS: Theory suggests that while plant diversity of grasslands decreases in response to increased competition for light, many plant species persist below‐ground even in the temporary absence of shoots. Thus, we hypothesized that below‐ground, diversity is less affected by increased competition during land‐use change compared to above‐ground. LOCATION: Species‐rich, oligotrophic grasslands in the Železne hory Mts, eastern Bohemia, Czech Republic. METHODS: We quantified above‐ and below‐ground plant richness (roots and rhizomes, seed and bud bank) in grasslands subjected to seven years of experimental abandonment and fertilization. We used conventional species identification to measure richness above‐ground and 454 sequencing of the chloroplast trnL (UAA) gene to measure richness of roots and rhizomes; additionally, we used the shoot emergence method to measure soil seed and bud bank richness. RESULTS: While above‐ground richness decreased with abandonment and fertilization, below‐ground richness remained less affected or even increased compared to the control (traditional mowing). Overall, compared to above‐ground the proportion of plant species found only below‐ground as roots and rhizomes increased, particularly in the abandonment with fertilization treatment. CONCLUSIONS: Below‐ground plant diversity could potentially buffer against biodiversity losses during short‐term land‐use change. Our findings highlight that measuring the complete plant species diversity improves our understanding of processes that underlie plant diversity and coexistence and refine predictions of vegetation responses to biodiversity threats.