Mycorrhizal inoculation on compost substrate affects nutritional balance, water uptake and photosynthetic efficiency in Cistus albidus plants submitted to water stress

The use of composted manure as alternative substrate can be suitable to produce ornamental potted plants. However, under water stress this substrate can result an additional stress for plants due to its physicochemical properties. In these conditions, mycorrhizae application can improve water and nutrients efficiency. The experiment was carried out in a growth chamber with a first phase (I) in which both inoculated and non-inoculated Cistus albidus L. plants at two substrates (commercial and mixtures of composted manure) were well irrigated and a second phase (II) in which the plants were submitted to water stress. Glomus iranicum (Blaszk., Kovacs & Balazs) var. tenuihypharum sp. nova was well established in cistus roots, but water stress hindered mycorrhizal proliferation in compost, which resulted in plants with smaller leaf and root biomass. The plants in compost had the highest Cl, K, Na, P and Zn contents in leaf; mycorrhizae reduced the Na and increased phosphorus, especially when the substrate was well-watered. Water stress decreased leaf water potential (psi(1)) and mycorrhizae induced higher psi(1) values in both substrates. Compost induced leaf osmotic adjustment, lower gas exchange and photochemical quenching parameters (F-v/F-m, Y(II)) values. Mycorrhizal plants had higher Y(II) and qP values than non-inoculated plants. Compost decreased relative chlorophyll content in both phases, but in inoculated plants these values increased under water stress. C. albidus plants growing in compost maintain a good nutritional balance and efficient osmotic regulation. Under water stress, plants suffer more stress than plants in commercial substrate, as reflected by the lipid peroxidation and P-n values.