Organic residues (compost) can be used as growth medium but may contain phytotoxic ions that, combined with a water deficit may alter the behavior of plants. The experiment was carried out in a growth chamber with Cistus albidus in a commercial substrate, C (sphagnum peat, coconut fiber and perlite, 8:7:1) and a mixture of compost substrates, Cp (slurry compost, coconut fiber and perlite, 3:6:1). Plants were grown in pots under well-watered, maintaining values of Ψl around -0.9 MPa (WW) and water-stressed (WS) conditions, where the irrigation was removed until reached values of Ψl around -3.0 MPa (water stress period), after then, water was re-established in all plants (recovery period). Although, the well-watered plants had a leaf water potential (Ψl) around -0.9 MPa, stomatal conductance (gs) was 125 mmol m-2s-1 in the commercial substrate and 30 mmol m-2s-1 in compost. The time taken to reach the threshold value at which water stress occurs was 13 days in the commercial substrate and 53 days in compost. Water-stressed plants in the commercial substrate had significantly lower values of Ψl and gs than well-watered. Plants in compost maintained values of gs similar in both irrigation treatments (WW and WS) and accumulated less biomass than those that grown in commercial. The water stress in compost led an increase in the adaxial epidermis, parenchyma and mesophyll, whereas water stress in commercial the proportions of the different tissues decreased. Higher lipid peroxidation values were found in plants grown in both substrates under water stress. The recovery time of the plants, until manage Ψl values around -0.9 MPa, depended on the type of substrate. The restoration of irrigation in commercial substrate act as a new stress, as reflected in the photochemical mechanisms.
Keywords: Chlorophyll fluorescence; Lipid peroxidation; Mineral content; Osmotic stress; Substrate; Water relations.
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