The photosynthetic and chlorophyll fluorescence parameters were studied in Ziziphus jujuba var. spinosus under different soil water gradients obtained by irrigation and natural water consumption. We used the rectangular hyperbola model, the nonrectangular hyperbola model, the exponential model, and the modified rectangular hyperbola model to fit our data and evaluate them quantitatively. Based on the relationship among the parameters, the effects of the availability of soil water on photosynthesis were elucidated. The results showed that: (1) The relationship between water content and photosynthetic parameters were fitted best by the modified rectangular hyperbola model, followed by the nonrectangular hyperbola model, the exponential model, and the rectangular hyperbola model. The modified rectangular hyperbola model fitted best the maximum net photosynthetic rate (PNmax) and the light-saturation point (LSP), while the nonrectangular hyperbola model fitted best the dark respiration rate (R D ), the apparent quantum yield (AQY), and the light-compensation point (LCP). (2) The main reason for the net photosynthetic rate (P N ) decline was that it reached a stomatal limit when the soil relative water content (RWC) was greater than 25% and it reached a nonstomatal limit when the RWC was lesser than 25%. Under these conditions, the photosynthetic apparatus of Z. jujuba was irreversibly damaged. (3) P max , R D , AQY, and LSP increased first and then decreased, while LCP increased contrary to the RWC. The P N light-response parameters reached optimum when the RWC was 56-73%. (4) The quantum yield of PSII photochemistry reached a maximum when RWC was 80%. Nonphotochemical quenching decreased rapidly, and the minimum fluorescence in the dark-adapted state increased rapidly when RWC was lesser than 25%. Under these conditions, PSII was irreversibly damaged. (5) The RWC range of 11-25% resulted in low productivity and low water use efficiency (WUE). The RWC range of 25-56% resulted in moderate productivity and moderate WUE, and the RWC range of 56-80% resulted in high productivity and high WUE. The RWC range of 80-95% resulted in moderate productivity and low WUE. In summary, photosynthesis of Z. jujuba was physiologically adaptable in response to water stress in sand formed from seashells. The photosynthetic and physiological activity was maintained relatively high when the RWC was between 56 and 80%; Z. jujuba seedlings grew well under these conditions. Additional key words: chlorophyll fluorescence, light-response model; photosynthetic productivity; relative water content. ---Received 5 October 2013, accepted 11 March 2014. +Corresponding author; fax:+865388249164, e-mail: zhsy@sdau.edu.cn Abbreviations: AQY -apparent quantum yield; Ci -intercellular CO2 concentration; E -transpiration rate; EM -exponential model FC -field capacity; Fm -maximum fluorescence of the dark-adapted state; Fm' -maximuml fluorescence yield; F0 -minimum fluorescence yield of the dark-adapted state; Fs -steady-state fluorescence; Fv/Fm...

As a common waterfront and wet environment tree species, Salix babylonica shows a great potential for restoration of contaminated water or soil environments, such as phenol-polluted water. However, studies on such remediation effects have not been carried out yet. The objective of this study was to investigate the effects of phenols on photosynthesis of S. babylonica. Photosynthetic and chlorophyll fluorescence parameters of S. babylonica cuttings were determined in hydroponic experiment, where six phenol concentrations was used (0, 50, 100, 200, 400, and 800 mg L -1 ). Phenol presence inhibited photosynthesis of S. babylonica significantly, as the net photosynthetic rate (P N ), light-saturated net photosynthetic rate, apparent quantum yield, maximal quantum yield of PSII photochemistry, and effective quantum yield of PSII photochemistry declined significantly. The higher the concentration of phenol solution, the greater inhibition of photosynthesis occurred. Our data indicated that nonstomatal limitation was responsible for the reduction of P N . S. babylonica should be used to remediate phenol-contaminated water, when the concentration of phenol solution is lower than 200 mg L -1 . Otherwise, the efficiency of photosynthesis of S. babylonica would decrease markedly. However, further study is needed to determine the maximum concentration of phenol that S. babylonica can tolerate to maintain normal photosynthetic activity.

As a common tree species in northern China, Populus × euramericana "Neva" has an important practical value for the study of continuous cropping obstacles in poplar cultivation. Plant allelopathy is the main reason for continuous cropping obstacles, which are caused by allelochemicals, such as para-hydroxybenzoic acid (p-HB). The objective of this study was to investigate the effects of p-HB on the photosynthesis of poplar. Photosynthetic parameters of Populus × euramericana "Neva" poplar were determined in a pot culture experiment where five p-HB concentrations were used (0, 1, 2, 4, and 6 mmol L −1 ). Each seedling was treated with 4 L of p-HB solution every seven days, ten times in total. p-HB inhibited the photosynthesis of poplar significantly, as shown by a clear decline in the net photosynthetic rate. Our results indicated nonstomatal limitation responsible for the photosynthesis reduction.

The photosynthetic parameters in leaves of three-year-old seedlings of Fraxinus rhynchophylla L. were studied under different soil water conditions and CO 2 concentrations ([CO 2 ]) with a LI-COR 6400 portable photosynthesis system. The objective was to investigate the response of photosynthesis and stomatal conductance (g s ) to various [CO 2 ] and soil water conditions, and to understand the adaptability of F. rhynchophylla to such conditions. The results showed that the soil water content (RWC) required to maintain high photosynthetic productivity in F. rhynchophylla was 49.5-84.3%; in this range, net photosynthetic rate (P N ) rose with [CO 2 ] increasing from 500 to 1,400 µmol mol -1 . Outside this RWC range, P N decreased significantly. The apparent maximum photosynthetic rate (P max,c ) and carboxylation velocity (V c ) increased with increasing RWC and remained relatively high, when RWC was between 49.5 and 96.2%. CO 2 compensation points and photorespiration rate exhibited a trend opposite to that of P max,c and V c , indicating that moderate water stress was beneficial for increasing plant assimilation, decreasing photorespiration, and increasing production of photosynthates. g s declined significantly with increasing [CO 2 ] under different water supplies, but the RWC range maintaining high g s increased. g s reached its maximum, when RWC was approximately 73% and then decreased with declining RWC. The maximal g s was found with increasing RWC. Thus, based on photosynthetic characteristics in artificial, vegetation construction in semiarid loess hill and gully area, F. rhynchophylla could be planted in habitats of low soil water content.

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 (P N ) and water use efficiency (WUE). Using a Li-6400 portable photosynthesis system, we measured light response of P N , 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 plant's light compensation point decreased and its light saturation point (LSP), apparent quantum yield, and maximum P N increased. When MWC was at 17.6%, the low and high light use efficiency of Z. jujuba was all maximal. P N obviously increased with increasing MWC (9.2-17.6%). However, P N decreased when MWC was too high or low. When PAR ranged from 800 to 1200 mmol m 22 s 21 , P N and WUE were higher and the LSPs of P N and WUE ranged between 706 and 1209 mmol m 22 s 21. 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,.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 mmol m 22 s 21.