Provenance variation in morphology and leaflet anatomy of Parkia biglobosa and its relation to drought tolerance

Abstract

Measurements of morphological and anatomical characteristics made on 4-month-old seedlings from five provenances of Parkia biglobosa (Jacq.) Benth., grown in a tropical greenhouse under controlled conditions, showed significant differences between the northern provenances, which represented the Sudan savanna zone, and the southern provenances which represented the forest zone of the species distribution. Seedlings of provenances from the savanna zone showed more xerophytic characteristics than those from the forest zone. They were smaller in height, with a greater number of smaller leaflets per pinnae, a lower specific leaflet mass, smaller palisade and guard cells and a lower ratio of palisade:non-palisade tissue. There were also significant differences in the same characteristics, except palisade cell length, between provenances from the easterly and westerly extremes of the species range. Stomatal conductance measured after 2 weeks of droughting also showed that provenances from the savanna zone had higher values, indicating greater physiological activity and reduced stress, compared with provenances from the forest zone. Multivariate discriminant analysis of the morphological and anatomical characteristics showed that 98% of the seedlings were classified correctly with respect to provenance. The squared distances between provenances were closely related to the geographical distances between locations. Yet, not all variation in leaf anatomy could be explained by the difference in climatic conditions from north to south. Also drought tolerance was not always related to morphological and anatomical features. It is possible that clinal variation within the species from east to west may be interacting with climatic differences from north to south.