Jingkuan Sun

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 (RD), 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 (R2) greater than 0.996. There were significant differences in the photosynthetic capacity, AQY, RD, 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 ( Pn ) and WUE had evident threshold responses to the variations of soil moisture to maintain high efficient water use. The relative moisture content (Wr) 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 Pn 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.

Threshold effects of photosynthetic efficiency parameters of wild jujube in response to soil moisture variation on shell beach ridges, Shandong, China

To investigate the threshold effects of photosynthetically active radiation (PAR) and soil mass water content (MWC) on photosynthetic efficiency parameters of Ziziphus jujuba Mill var. spinosa and to understand the adaptability of Z.jujuba to light and soil moisture variation, we determined optimal MWC and PAR for Z. jujuba which maintained higher net photosynthetic rate (PN) and water use efficiency (WUE). Using a Li-6400 portable photosynthesis system, we measured light response of PN, transpiration rate (E), WUE, and other gas-exchange parameters of 3-year-old Z. jujuba shrubs in a range of soil moisture conditions. The results showed that the leaf photosynthetic rate and WUE of Z. jujuba had a significant response to MWC and PAR. Given increases in the MWC (7.1–17.6%), the plants light compensation point decreased and its light saturation point (LSP), apparent quantum yield, and maximum PN increased. When MWC was at 17.6%, the low and high light use efficiency of Z. jujuba was all maximal. PN obviously increased with increasing MWC (9.2–17.6%). However, PN decreased when MWC was too high or low. When PAR ranged from 800 to 1200 μmol m− 2 s− 1, PN and WUE were higher and the LSPs of PN and WUE ranged between 706 and 1209 μmol m− 2 s− 1. These data indicate that Z. jujuba possessed higher adaptability to light conditions. Based on photosynthetic efficiency parameters, the soil moisture availability and productivity of Z. jujuba were classified and evaluated. For Z. jujuba woodland, MWC < 9.2% and MWC>21.5% resulted in low productivity and medium WUE, 19.8–21.5% of MWC resulted in medium productivity and low WUE, 9.2–11.2% of MWC resulted in medium productivity and medium WUE, and 11.2–19.8% of MWC resulted in high productivity and high WUE. The optimum high productivity and high WUE of MWC were at 17.6%, and the corresponding optimum PAR was 1209 μmol m− 2 s− 1.

Soil-water interacting use patterns driven by Ziziphus jujuba on the Chenier Island in the Yellow River Delta, China

ABSTRACT The determination of water use patterns of plants in a coastal ecosystem is critical to our understanding of local eco-hydrological processes and predicting trends in ecological succession under the background of global climate change. The water use patterns of Ziziphus jujuba, the dominant species on the Chenier Island in the Yellow River Delta, were examined following summer rainfall events. Stable oxygen isotope analysis was employed to analyze the effects of rainfall on the stable isotopic composition in potential water sources in Z. jujuba. The IsoSource model was used to estimate the contributions of potential water sources for xylem water in Z. jujuba. The results showed heavy rainfall could recharge both soil and groundwater but contributed little to the δ18O values in deep soil water (60–100 cm) and groundwater. Light rainfall had an effect only on surface soil water (0–40 cm). Z. jujuba mainly absorbed deep soil water on non-rainy days. Rainwater became the predominant water source for Z. jujuba during and immediately after heavy rainfall. Switching the plant’s main water source between deep soil water and rainwater provided Z. jujuba with a competitive advantage and improved the water use efficiency of Z. jujuba in this coastal ecosystem.

Response of stem sap flow and leaf photosynthesis in Tamarix chinensis to soil moisture in the Yellow River Delta, China

Soil moisture is the main limiting factor for vegetation growth at shell ridges in the Yellow River Delta of China. The objective of this study was to explore the soil moisture response of photosynthetic parameters and transpiration in Tamarix chinensis Lour., a dominant species of shell ridges. Leaf photosynthetic light-response parameters and sap flow were measured across a gradient of relative soil water content (RWC), from drought (23%) to waterlogging (92%) conditions. Leaf photosynthetic efficiency and stem sap flow of T. chinensis showed a clear threshold response to soil moisture changes. Leaf net photosynthetic rate, water-use efficiency (WUE), light-saturation point, apparent quantum yield, maximum net photosynthetic rate, and dark respiration rate peaked at moderately high RWC, decreasing towards high and low values of RWC. However, peak or bottom RWC values substantially differed for various parameters. Excessively high or low RWC caused a significant reduction in the leaf photosynthetic capacity and WUE, while the high photosynthetic capacity and high WUE was obtained at RWC of 73%. With increasing waterlogging or drought stress, T. chinensis delayed the starting time for stem sap flow in the early morning and ended sap flow activity earlier during the day time in order to shorten a daily transpiration period and reduce the daily water consumption. The leaf photosynthetic capacity and WUE of T. chinensis were higher under drought stress than under waterlogging stress. Nevertheless, drought stress caused a larger reduction of daily water consumption compared to waterlogging, which was consistent with a higher drought tolerance and a poor tolerance to waterlogging in this species. This species was characterized by the low photosynthetic capacity and low WUE in the range of RWC between 44 and 92%. The RWC of 49–63% was the appropriate range of soil moisture for plant growth and efficient physiological water use of T. chinensis seedlings.

Influences of micro-geomorphology on the stoichiometry of C, N and P in Chenier Island soils and plants in the Yellow River Delta, China

Studies have indicated that consistent or well-constrained (relatively low variability) carbon:nitrogen:phosphorus (C:N:P) ratios exist in large-scale ecosystems, including both marine and terrestrial ecosystems. Little is known about the C, N and P stoichiometric ratios that exist in the soils and plants of Chenier Island in the Yellow River Delta (YRD). We examined the distribution patterns and relationships of C, N and P stoichiometry in the soils and plants of Chenier Island, as well as the potential influences of the island’s micro-geomorphology. Based on a study of four soil profile categories and Phragmites australis and Suaeda heteroptera plant tissues, our results showed that micro-geomorphology could leave a distinct imprint on the soil and plant elemental stoichiometry of Chenier Island; significant variation in the atomic C:N:P ratios (RCNP) existed in soils and plants, indicating that the RCNP values in both the soil and plants are not well constrained at the Chenier Island scale. RCN and RCP in Chenier Island soils were high, whereas the RNP values were comparatively low, indicating that the ecosystems of Chenier Island are nutrient-limited by N and P. However, the RNP values in P. australis and S. heteroptera plant tissues were high, suggesting that the plants of Chenier Island are nutrient-limited by P. Finally, we suggest that soil and plant N:P ratios may be good indicators of the soil and plant nutrient status during soil development and plant growth, which could be a useful reference for restoring the degraded soils of Chenier Island.