title: Ecophysiological and anatomical mechanisms behind the nurse effect: which are more important? A multivariate approach for cactus seedlings.
abstract: BACKGROUND
  Cacti establish mostly occurs under the canopy of nurse plants which provide a less stressful micro-environment, although mechanisms underlying this process are unknown. The impact of the combination of light and watering treatments on Opuntia streptacantha (Cactaceae) seedlings was examined.
  
  
  RESULTS
  Ecophysiological [titratable acidity, osmotic potential ('solute potential', Ψs ), relative growth rate (RGR) and their components (NAR, SLA, and LWR)], anatomical (chloroplast density, chloroplast frequency, and cell area), and environmental [photosynthetic photon flux density (PPFD) and air temperature] sets of variables were analyzed, assessing relationships between them and measuring the intensity of the relationships. Three harvests were carried out at days 15, 30, and 45. Ψs and acidity content were the most important responses for seedling establishment. The main anatomical and environmental variables were chloroplast density and water availability, respectively. Opuntia streptacantha seedlings establish better in the shade-watering treatment, due to higher Ψs and acidity, unaffected chloroplasts, and lower PPFD. In addition, the chloroplasts of cells under high-light and non-watering treatment were clumped closer to the center of the cytosol than those under shade-drought, to avoid photoinhibition and/or to better distribute or utilize the penetrating light in the green plant tissue.
  
  
  CONCLUSIONS
  Opuntia seedlings grow better under the shade, although they can tolerate drought in open spaces by increasing and moving chloroplasts and avoiding drastic decreases in their Ψs . This tolerance could have important implications for predicting the impact of climate change on natural desert regeneration, as well as for planning reforestation-afforestation practices, and rural land uses.
authors: Facultad de Agronomía y Veterinaria, Universidad Autónoma de San Luis Potosí, Soledad de Graciano Sánchez, México.
authors: Pablo
authors: P
authors: Delgado-Sánchez
authors: Laura
authors: L
authors: Yáñez-Espinosa
authors: Juan Francisco
authors: JF
authors: Jiménez-Bremont
authors: Leonardo
authors: L
authors: Chapa-Vargas
authors: Joel
authors: J
authors: Flores
mesh_terms: D000388:Air; D029421:Cactaceae / Q000033:anatomy & histology* / Q000502:physiology*; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D016002:Discriminant Analysis; D004777:Environment; D006863:Hydrogen-Ion Concentration; D008027:Light; D015999:Multivariate Analysis; D009995:Osmosis; D010788:Photosynthesis / Q000187:drug effects / Q000528:radiation effects; D036226:Seedlings / Q000502:physiology*; D013696:Temperature; D014867:Water / Q000494:pharmacology
chemical_list: D014867:Water