Impact of nitrogen inputs on multiple facets of plant biodiversity in mountain grasslands: does nutrient source matter?

Questions: What is the impact of nitrogen (N) inputs on the vegetation of mountain permanent grasslands? Beyond the effect of fertilizer quantity (total and available N supply), is there a specific effect of fertilizer quality (the various N sources) on the multiple biodiversity facets of plant communities? Location: Jura Mountains (France). Methods: Based on a vegetation and agronomic survey of 29 mown grasslands, we considered taxonomic, phylogenetic and multi-trait functional diversity indices as well as community-weighted means of seven functional traits (CWMs) including CSR strategies. Using partial redundancy analysis (pRDA) and Spearman correlations, we assessed the response of these biodiversity metrics to (1) the medium-term total N input and the short-term available N input of any origin, and (2) the relative contribution of industrial fertilizers, solid manure, liquid manure, livestock restitutions and atmospheric deposition to the amount of available N added to the soil during the year preceding vegetation sampling. Results: We report significant negative rank correlations between total or available N input and two diversity metrics: species richness and functional richness. Among CWMs, high N inputs were positively correlated with specific leaf area (SLA), competitive and ruderal strategies, and negatively with seed mass and stress-tolerant strategy. Results also revealed various trends according to the N source: when the proportion of available N from livestock restitutions was high, plant communities showed higher taxonomic and phylogenetic diversity and lower leaf dry matter content. In contrast, communities receiving mainly industrial fertilizers showed lower taxonomic and phylogenetic diversity and higher SLA. Moreover, pRDA suggested contrasting impacts of the main N source on life strategies: R strategy appeared more favoured by a high proportion of industrial fertilizers, while C strategy was enhanced by liquid or solid manure. Conclusions: Our observations support the common finding that a high N supply impacts plant functional composition and is associated with a decrease in species richness through the loss of stress-tolerant species. In addition, they show that biodiversity patterns mostly depend on fertilizer origin. In particular, industrial fertilizers appear to be the most detrimental sources of nutrients for both taxonomic and phylogenetic diversity in mountain grasslands.

Impact of management type and intensity on multiple facets of grassland biodiversity in the French Jura Mountains

François Gillet

Questions(1) Does grassland vegetation differ in its taxonomic, phylogenetic and functional alpha diversity between strictly grazed parcels (SGP) and mowed-and-grazed parcels (MGP)? (2) Do we observe differences in the responses of functional diversity (reflecting differences in the interspecific variation of a trait in the plant community) and community-weighted mean trait values (CWMs, reflecting the characteristics of the dominant species)? (3) How do diversity and CWM patterns respond to disturbance and fertilization gradients measured by agronomic descriptors in both parcel types? LocationFrench Jura Mountains. MethodsWe compared taxonomic, phylogenetic and functional diversities (based on Rao quadratic entropy) and CWMs between the two management types (SGP and MGP). We then used agronomic variables, describing both defoliation regime and fertilization intensity over the past 10yrs to explain diversity indices and CWMs in a partial redundancy analysis (pRDA). ResultsTaxonomic and phylogenetic diversities were higher in SGP than in MGP, as well as functional diversity computed for qualitative traits (clonal growth organs and leaf distribution along the stem). Contrary to expectations from literature, we found higher CWM for leaf dry matter content (LDMC) in intensively and regularly cut grasslands compared to only grazed grasslands, which can be explained by the higher dominance of grass species in hay meadows. In addition, constrained ordination revealed that taxonomic, phylogenetic and some functional diversity metrics were negatively affected by defoliation intensity (mowing frequency), while most CWMs were mainly influenced by fertilization intensity, either by the available N input or by the role of commercial inorganic fertilizers, depending on the trait considered. ConclusionsOur study revealed consistent patterns between the various facets of biodiversity in grasslands according to the main management regime. Taking agronomic gradients into account suggests the importance of considering both CWMs and functional diversity, which respond variously to agricultural practices. Conservation of high diversity in grasslands, whatever the facet considered, implies keeping some parcels exclusively grazed and limiting N inputs, especially those from inorganic commercial fertilizers.

Wiley-Blackwell2014

Contrasted taxonomic, phylogenetic and functional diversity patterns in semi-natural permanent grasslands along an altitudinal gradient

François Gillet

Background and aims - Recent methodological and theoretical advances in community ecology have allowed more robust exploration of complementary facets of biodiversity in plant communities. Focusing on semi-natural permanent grasslands of the French Jura Mountains, we assessed how taxonomic, phylogenetic and functional diversity metrics vary among three phytosociological vegetation units. Methods - We selected a sample of 135 releves out of a phytosociological database, depicting three phytosociological orders (Brometalia erecti, Arrhenatheretalia elatioris and Trifolio repentis-Phleetalia pratensis) and including 381 vascular plant species. We built a phylogenetic tree based on sequences of two genes encoding chloroplast proteins, from which we computed phylogenetic diversity metrics that we compared to various taxonomic, single-trait and multi-trait functional metrics, including community-weighted means of functional traits (CWMs). Key results - Most diversity metrics and CWMs significantly differed among vegetation units. Within each facet of biodiversity, the different metrics showed complementary results. Moreover, even when considering diversity metrics comparable in mathematical terms, i.e. based on Rao quadratic entropy, the results were largely non-redundant among the facets of biodiversity. Phylogenetic diversity and multi-trait functional diversity show opposite responses to vegetation units, as well as a low phylogenetic signal. These two results suggest that phylogenetic diversity cannot be used as a simple proxy for functional diversity. Conclusion - This study highlights the importance of taking into consideration different facets for a better understanding of biodiversity. In particular, phylogenetic and functional facets appear highly informative, and could thus be used in addition to taxonomic diversity metrics as indicators of conservation value.

Soc Royal Botan Belgique2014

Contrasting processes drive alpha and beta taxonomic, functional and phylogenetic diversity of orthopteran communities in grasslands

Bertrand Fournier, François Gillet

Taxonomic, functional and phylogenetic diversities can respond differently to biotic and abiotic filters. However, biodiversity management tends to focus on a single index, generally taxonomic diversity, assuming a strong positive correlation among biodiversity components across scales. This can result in a mismanagement of functional and phylogenetic diversities with negative consequences for ecosystem functioning and long-term maintenance of services. Understanding the relationships among biodiversity components, how they change across scales and which their main drivers are can lead to more sustainable management of biodiversity and its associated ecosystem services and functions. We used an integrative approach of biodiversity where we investigated alpha and beta taxonomic (TD), functional (FD) and phylogenetic (PD) diversity of orthopteran communities as well as species and functional traits composition and their associated drivers at the local and landscape scales in permanent mesic grasslands of the French Jura Mountains. We assessed whether orthopteran TD, FD and PD were positively correlated. We also determined the drivers of TD, FD and PD and their changes across scales and among indices using data related to soil, agricultural practices, elevation, and biotic interactions with plants. Our results showed that (i) elevation was a strong driver of orthopteran community trait composition, (ii) orthopteran alpha TD, FD and PD were correlated among themselves and increased with plant species richness, and (iii) local beta diversity was not correlated with alpha diversity. Beta diversity had different drivers at local and landscape scale: it was influenced by soil chemistry and texture at the local scale and increased with the difference in elevation among plots at the landscape scale. This study evidences distinct processes driving alpha and beta diversity of orthopteran communities at both the local and landscape scales. It supports the hypothesis that less intensive agricultural practices enhance orthopteran diversity and highlights the importance to consider beta diversity at both local and landscape scale when designing and assessing the management regimes of grassland ecosystems. Prioritizing the importance of the different biodiversity components and spatial scales constitutes an important challenge for sustainable grassland management.

Elsevier Science Bv2017

Impact of management type and intensity on multiple facets of grassland biodiversity in the French Jura Mountains

François Gillet

Wiley-Blackwell2014

Contrasted taxonomic, phylogenetic and functional diversity patterns in semi-natural permanent grasslands along an altitudinal gradient

François Gillet

Soc Royal Botan Belgique2014

Contrasting processes drive alpha and beta taxonomic, functional and phylogenetic diversity of orthopteran communities in grasslands

Bertrand Fournier, François Gillet

Elsevier Science Bv2017