RESUMO
Heat and drought stresses have become more frequent and intense in the Mediterranean, strongly influencing arable crop phenology, growth, and grain yield. Agroforestry systems can effectively buffer the adverse climate conditions and stabilize or even increase crop yield under climate change. However, the positive effects of agroforestry remain uncertain due to the possible intense competition between trees and crops, especially for legume crops that have been less studied than cereals in such context. This study aimed to assess the response of the phenology, growth, grain yield, and yield-related traits of chickpea (Cicer arietinum), faba bean (Vicia faba), and lentil (Lens culinaris) to olive-based agroforestry (AFS) as compared to sole crops system (SCS) in the South of the Mediterranean. We conducted a field experiment during two growing seasons marked by an intense drought, either at the beginning (year 1) or at the end (year 2) of the crop cycle. Crop growth and yield were lower in year 1 than in year 2, reflecting the adverse growing conditions caused by the early drought. They were also lower in AFS than in SCS for both years, indicating that trees had competitive effects on crops. In year 1, the yield loss of grains in AFS was 66 % for lentil, 47 % for chickpea, and 43 % for faba bean compared to SCS, confirming the greater shade sensitivity of lentil. In year 2, the reduction was significantly smaller and was about 46 %, 34 %, 38 % for lentil, chickpea and, faba bean, respectively. The number of pods and grains were the most affected yield components by agroforestry and drought timing across the three legumes crops. Similar responses were found when comparing crops at different distances to trees within the AFS field. Crops generally had lower biomass and yield, explained by fewer pods and grains, on the northern side of trees compared to the southern side of trees or the middle of tree inter-rows, causing significant spatial heterogeneity in crops. However, lentil and chickpea had a positive response to shade during the early drought year while a negative response during the late drought year, suggesting that the benefits of the microclimate created by olive trees express depending on drought timing and crop physiology. Our study supports legume integration into AFS, suggesting that chickpea should be considered during high-stress conditions, while faba bean should be preferred during low-stress conditions.
RESUMO
Rhizobia are symbiotic nitrogen-fixing bacteria in root nodules of legumes. In Morocco, faba bean (Vicia faba L.), which is the main legume crop cultivated in the country, is often grown in marginal soils of arid and semi-arid regions. This study examines the phenotypic diversity of rhizobia nodulating V. faba isolated from different regions in Morocco for tolerance to some abiotic stresses. A total of 106 rhizobia strains isolated from nodules were identified at the species level by analysing 16S rDNA. Additionally, for selected strains recA, otsA, kup and nodA fragments were sequenced. 102 isolates are likely to belong to Rhizobium leguminosarum or R. laguerreae and 4 isolates to Ensifer meliloti. All strains tolerating salt concentrations of 428 or 342mM NaCl as well as 127 or 99mM Na2SO4 were highly resistant to alkaline conditions (pH 10) and high temperature (44°C). Three strains: RhOF4 and RhOF53 (both are salt-tolerant) and RhOF6 (salt-sensitive) were selected to compare the influence of different levels of salt stress induced by NaCl on growth and on trehalose and potassium accumulation. We find a direct correlation between the trehalose contents of the rhizobial strains and their osmotolerance.