Ecological aspects and relationships of the emblematic Vachellia spp. exposed to anthropic pressures and parasitism in natural hyper-arid ecosystems: ethnobotanical elements, morphology, and biological nitrogen fixation

Bryan Vincent (1) , Julie Bourillon (1) , Karine Gotty (1) , Hassan Boukcim (2) , Marc-André Selosse (3, 4, 5) , Aurélie Cambou (6) , Coraline Damasio (1) , Mathis Voisin (1) , Stéphane Boivin (1) , Tomáš Figura (3, 4, 7) , Jérôme Nespoulous (2) , Antoine Galiana (1) , Kenji Maurice (1) , Marc Ducousso (1)

1 UMR LSTM - Laboratoire des symbioses tropicales et méditerranéennes
2 Valorhiz
3 ISYEB - Institut de Systématique, Evolution, Biodiversité
4 Department of Plant Taxonomy and Nature Conservation
5 IUF - Institut universitaire de France
6 UMR Eco&Sols - Ecologie fonctionnelle et biogéochimie des sols et des agro-écosystèmes
7 Naturalis Biodiversity Center [Leiden]

AlUla region in Saudi Arabia has a rich history regarding mankind, local wildlife, and fertility islands suitable for leguminous species, such as the emblematic Vachellia spp. desert trees. In this region, we investigated the characteristics of desert legumes in two nature reserves (Sharaan and Madakhil), at one archaeological site (Hegra), and in open public domains et al. Ward and Jabal Abu Oud. Biological nitrogen fixation (BNF), isotopes, and N and C contents were investigated through multiple lenses, including parasitism, plant tissues, species identification, plant maturity, health status, and plant growth. The average BNF rates of 19 Vachellia gerrardii and 21 Vachellia tortilis trees were respectively 39 and 67%, with low signs of inner N content fluctuations (2.10-2.63% N) compared to other co-occurring plants. The BNF of 23 R. raetam was just as high, with an average of 65% and steady inner N contents of 2.25 +/- 0.30%. Regarding parasitism, infected Vachellia trees were unfazed compared to uninfected trees, thereby challenging the commonly accepted detrimental role of parasites. Overall, these results suggest that Vachellia trees and R. raetam shrubs exploit BNF in hyper-arid environments to maintain a high N content when exposed to parasitism and grazing. These findings underline the pivotal role of plant-bacteria mutualistic symbioses in desert environments. All ecological traits and relationships mentioned are further arguments in favor of these legumes serving as keystone species for ecological restoration and agro-silvo-pastoralism in the AlUla region.

Mots clés: Hyper-arid desert; Mistletoe; Mutualism; 15 N natural abundance; Retama raetam; Vachellia gerrardii; Vachellia tortilis subsp. raddiana; Witch broom

Domaines: Biodiversité et Ecologie; Science des sols

Bryan Vincent, Julie Bourillon, Karine Gotty, Hassan Boukcim, Marc-André Selosse, et al.. Ecological aspects and relationships of the emblematic Vachellia spp. exposed to anthropic pressures and parasitism in natural hyper-arid ecosystems: ethnobotanical elements, morphology, and biological nitrogen fixation. Planta, 2024, 259, pp.132. ⟨10.1007/s00425-024-04407-0⟩. ⟨hal-04577814⟩