Nitrogen Fixing Legumes in the Plant Communities

Abstract

Problems statement: Numerous authors have used energetic to explain the ecological success of N-fixing plants. Legume biodiversity assessment, species dynamics, nitrogen fixation monitoring and environment impact assessment of these ecological events in Al-Hassa Oasis, Saudi Arabia are rare and need to be continuous and more frequent. Approach: Thus the objectives of this study were to analyze legume abundance within and outside Al-Hassa Oasis and relate it to the distribution of the different genera. Results: Thirty two legume plant species from 20 genera have been recorded within and outside the Oasis. The largest genera were Cassia (4 species), Indigofera (4) and Acacia (3). Annual herbs were the dominant growth form (34% of species recorded), followed by shrubs (28%), perennial herbs (19%) and trees (19%). Eighteen alien plant species were recorded (maybe an underestimated number). The nitrogen fixation of the legume plant species in Al-Hassa Oasis was estimated/analyzing the fixing potentiality of these species and nonfixing reference species (Panicum turgidum) using the ¹⁵N natural abundance method. Species with great nitrogen fixing capacity in Al-Hassa include: Medicago sativa, Vicia faba, Vicia sativa, Melitotus indicus, Dolicus lablab, Melitotus alba and Cliforia ternate. The mean biological fixation contribution of most of the recorded legume plants were high, varying from 3.9% (Indigofera argentea) to 64.6% (Medicago sativa). Conclusion: Al-Hassa Oasis is richer than expected based on its location within the desert zone. This study confirms the importance of the Oasis for national flora conservation in the Kingdom. results showed a good potential for use of the 15N natural abundance methodology for evaluating the nitrogen fixation ability of the legume plants under field conditions as well as for the estimation of %Ndfa.