Chlorophyll a fluorescence, water potential (Ψs), and root system of Juniperus oxycedrus ssp. macrocarpa, Juniperus phoenicea ssp. turbinata, and Pinus pinea were studied in Mediterranean coastal dunes of SW Spain during summer drought and after fall rains in 1999, the driest year in the 90's. A strong and reversible depression in the photochemical efficiency of photosystem 2 of the three species was recorded, which happened concomitantly with the diurnal increase and decrease in radiation. J. phoenicea, with superficial root system, was the most affected species by summer drought. It showed high rates of down-regulation of photosynthesis by photoinhibition and positive correlation between Ψs and Fv/Fp, with Ψs lower than -7 MPa. However, it tolerated this high stress, showing a fast recovery of its physiological state after fall rains. On the other hand, J. oxycedrus and P. pinea, both with deep root systems, kept their Ψs values up to -3 MPa, showing lower stress during summer drought. On the other hand, J. oxycedrus and J. phoenicea were more sensible to changes in edaphic water content than P. pinea. These specific responses to summer drought would be determined by their root distributions and stomatal control of transpiration, conditioning the efficiency in getting and using the available water resources. Ecophysiological responses indicate that these species are well-adapted to long periods of drought in Mediterranean climate areas, developing different strategies: J. phoenicea tolerates high stress with a fast recovery after fall rains, while J. oxycedrus and P. pinea are less affected by summer drought since their deep root systems would allow them to reach deep water resources. and J. M. Castillo ... [et al.].
Sparse-elm grassland is the remarkable landscape of Hunshandak Sandland in Inner Mongolia Autonomic Region of China. Maximum quantum efficiency (Fv/Fm) of 99 native plant species (85 grasses, 11 shrubs, and 3 trees) of different plant functional Types (PFTs) distributed in fixed sand dune, lowland, and wetland was investigated. Deep-rooted plant species (tree, shrub, and perennial grass) had higher Fv/Fm values than the shallow-rooted species (annual grasses), suggesting that soil drought is the major environmental stress. Annual C4 grasses had higher Fv/Fm values than annual C3 or CAM ones, indicating that C4 photosynthesis is more ecologically adaptive than CAM and C3 grasses. According to the habitats with annual C3 grass distribution, Fv/Fm values were in the order of fixed dune>lowland>wetland, suggesting that salt and pH value may enhance irradiance or heat stress for those distributed in pickled and watery habitats. Based on such characteristics, Ulmus pumila, Salix gordejevii, Caragana microphylla, Agriophyllum pungens, and Agropyron cristatum are recommended as ideal species for ecological restoration in degraded sand-land ecosystems. and Yong-Geng Li ... [et al.].