Convergence Of A Specialized Root Trait In Plants From Nutrient-impoverished Soils: Phosphorus-acquisition Strategy In A Nonmycorrhizal Cactus.

In old, phosphorus (P)-impoverished habitats, root specializations such as cluster roots efficiently mobilize and acquire P by releasing large amounts of carboxylates in the rhizosphere. These specialized roots are rarely mycorrhizal. We investigated whether Discocactus placentiformis (Cactaceae), a common species in nutrient-poor campos rupestres over white sands, operates in the same way as other root specializations. Discocactus placentiformis showed no mycorrhizal colonization, but exhibited a sand-binding root specialization with rhizosheath formation. We first provide circumstantial evidence for carboxylate exudation in field material, based on its very high shoot manganese (Mn) concentrations, and then firm evidence, based on exudate analysis. We identified predominantly oxalic acid, but also malic, citric, lactic, succinic, fumaric, and malonic acids. When grown in nutrient solution with P concentrations ranging from 0 to 100 μM, we observed an increase in total carboxylate exudation with decreasing P supply, showing that P deficiency stimulated carboxylate release. Additionally, we tested P solubilization by citric, malic and oxalic acids, and found that they solubilized P from the strongly P-sorbing soil in its native habitat, when the acids were added in combination and in relatively low concentrations. We conclude that the sand-binding root specialization in this nonmycorrhizal cactus functions similar to that of cluster roots, which efficiently enhance P acquisition in other habitats with very low P availability.

Nossa notação m' na prova de Rorschach: ampliação e restrição do fator m de Klopfer

Klopfer's differentiation of movement scores, among which inanimate movement integrating the minor movements group, was no doubt opportune and needed. Their peculiar meaning has been clearly stressed and enriched by Piotrowski in his reformulation of Rorschach variables. It is our belief that Rorschach himself would take such step. Our criteria for scoring this determinant are somewhat different of both Klopfer's and Piotrowski's. On the one hand, masks, facial traits, emotional expressions, body parts in motion are not entered there. On the other, we score as such human or animal movement, provided this does not originate in the blot shape directly, but in the subjective reaction against the sensed muscular tension. Basic requirement for this scoring is the kinesthetic component, as for Mever since Rorschach's elaboration; and common trait distinctive for any response to be so scored ? be it an abstraction, an inanimate object, an animal or human being ? must be the subjective way of feeling the movement: (a) intention, blocking, struggle for achieving, for instance, or (b) activity of nature elements. Due to this subjective meaning we use the symbol m'intead of mfor this category. We already find these two kinds (a) and (b) of movement responses in Rorschach's text, respectively in the Examplesand in his posthumous Contribution.Either may point to a flight from emotional stress or to outstanding mental ability.