Photosynthetic and water use characteristics in three natural secondary shrubs on Shell Islands, Shandong, China

Ziziphus jujuba var . spinosa Hu, Periploca sepium Bunge, and Securinega suffruticosa (Pall.) Rehd are mainly natural secondary shrubs on Shell Islands of the Yellow River Delta. The physiological characteristics of leaves of the 3-year-old shrub species, including photosynthesis, apparent quantum yield (AQY), dark respiration rate (R D), light compensation point (LCP), light saturation point (LSP), transpiration rate (E), and water use efficiency (WUE) and so on, were studied by using a Li-Cor6400 portable photosynthesis system. The results showed that the modified rectangular hyperbola model could simulate the photosynthesis–light response curves better, with a compound correlation coefficient (R ²) greater than 0.996. There were significant differences in the photosynthetic capacity, AQY, R D, LCP, LSP, E , and WUE among the three shrub species. The three shrub species displayed different photosynthetic ability in the same environment; the photosynthetic capacity of Z. jujuba was 1.49 times that of S. suffruticosa . Z. jujuba had the highest ability to use low light, and its AQY was 0.058, and that of other two species was among ordinary species. The consumption of photosynthetic products of S. suffruticosa was highest and it had the most active physiological metabolism. Z. jujuba had higher shade tolerance, while these three species were photophilous. The sequence of water-consuming ability by transpiration was in the order of Z. jujuba > P. sepium>S. suffruticosa . The water-consuming ability of P. sepium and S. suffruticosa did not show significant correlation with meteorological factors. P. sepium had the highest WUE, followed by Z. jujuba , and S. suffruticosa had the least. The net photosynthetic rate (P ₙ) and WUE had evident threshold responses to the variations of soil moisture to maintain high efficient water use. The relative moisture content (W ᵣ) of Z. jujuba , P. sepium , and S. suffruticosa was within the range of 36.18–68.89%, 42.31–81.76%, and 46.87–91.62%, respectively, in which three natural secondary shrubs had higher levels of P ₙ and WUE . In summary, P. sepium had higher development potential, and Z. jujuba had physiological characteristics of higher photosynthetic ability, transpiration, and WUE, and is the most suitable shrub species for afforestation.