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To explore the effect of monoculture and mixture sowing artificial grassland on the photosynthetic characteristics of Leymus chinensis and Medicago sativa , we determined the diurnal variation of photosynthetic properties of L. chinensis and M. sativa under different treatments. The results showed that the diurnal changes of net photosynthetic rate, blade temperature and transpiration rate of L. chinensis and M. sativa showed 'unimodal type' in monoculture, the stomatal conductance of M. sativa showed 'unimodal type', and the stomatal conductance and water use efficiency of L. chinensis showed 'bimodal type'. Under the mixed sowing treatment, the diurnal changes of net photosynthetic rate, blade temperature and transpiration rate of L. chinensis and M. sativa showed 'unimodal type', the stomatal conductance and water use efficiency of L. chinensis showed 'unimodal type', and the stomatal conductance of M. sativa showed 'bimodal type'. The peak photosynthetic rate of L. chinensis under mixture was signi-ficantly higher than that under monoculture, being 17.72 and 13.65 μmol CO 2 ·m -2 ·s -1 , respectively. Under monoculture and mixture sowing treatments, the chlorophyll content of L. chinensis was higher than that of M. sativa , nitrogen content of the leaves of L. chinensis was lower than that of M. sativa , and the nitrogen content in the leaves of mixture sowing L. chinensis was significantly higher than that of monoculture sowing L. chinensis , which were 27.60 and 22.55 g·kg -1 , respectively. Net photosynthetic rates of L. chinensis and M. sativa were significantly positively correlated with stomatal conductance and transpiration rate, and significantly negatively correlated with intercellular CO 2 concentration under different planting methods. Net photosynthetic rate of M. sativa was significantly positively correlated with blade temperature and water use efficiency. In summary, mixed sowing was beneficial to enhance nitrogen content of L. chinensis . Our results provided a theoretical basis for the response of the photosynthetic characteristics of forage to planting mode of artificial grassland.

We examined the responses of physiological and leaf anatomic structural characteristics of six Helleborus orientalis cultivars to different degrees of drought stress. A membership function was used to evaluate drought resis-tance and identify physiological and leaf anatomical indicators that exhibited a stronger correlation with drought tolerance. The results showed that leaf thickness, leaf area per unit mass and soluble protein levels of the six cultivars significantly decreased with the increases of drought stress. Net photosynthetic rate, stomatal conductance, and transpiration rate of leaves increased first and then decreased, while the intercellular CO 2 concentration decreased. The relative electrical conductivity, MDA, and H 2 O 2 contents of leaves were increased. Soluble saccharide and proline contents, and antioxidant enzyme activities were first elevated and then decreased. With the increases of drought stress, the ratio of palisade tissue thickness to sponge tissue thickness and stomatal density increased. Key indicators and relativities in evaluating drought resistance of those cultivars were proline, soluble sugars, and the ratio of palisade tissue thickness to sponge tissue thickness. H. orientalis 'Anemone Red' and H. orientalis 'Ane-mone Red spotted' had better drought resistance, which could be the excellent parental materials for the cultivation of new drought-resistant cultivars in the future.

We took 5-year-old Pinus koraiensis seedlings under natural secondary forests with canopy densities of 0.2-0.3, 0.4-0.6, and 0.7-0.9 at Laoshan Plantation Experimental Station in Maoershan Experimental Forest Farm of Northeast Forestry University as monitor object, and P. koraiensis seedlings under full-light environment as control (CK), to investigate the photosynthetic characteristics and the anatomical structure of P. koraiensis needles in response to the changes of canopy densities. The results showed that the height and diameter of P. koraiensis seedlings tended to decrease while specific leaf area increased with the increases of canopy densities. The total biomass of P. koraiensis seedlings under different canopy densities ranked in an order of 0.4-0.6＞CK＞0.7-0.9＞0.2-0.3. Photosynthetically active radiation (PAR) was significantly and positively correlated with leaf biomass, stem biomass, and root biomass. The net photosynthetic rate, transpiration rate, and intercellular CO 2 concentration of P. koraiensis seedlings showed a decreasing trend with the increases of canopy densities, while the stomatal conductance showed an increasing trend. Net photosynthetic rate and chlorophyll a/b showed a significant positive correlation with PAR. Stomatal density showed a gradual decreasing trend with the increases of canopy densities, and the needle cross-sectional area, mesophyll tissue area, xylem area, and phloem area of P. koraiensis seedlings under canopy density 0.4-0.6 were significantly higher than those in other treatments. P. koraiensis seedlings with stronger photosynthetic abilities and higher needle anatomy parameters under canopy density 0.4-0.6, and were able to maintain strong competitiveness in this habitat. Those results indicated that 5-year-old P. koraiensis seedlings need certain shading environment.

5-hydroxytryptamine (5-HT) participates in plant growth and development, and can also delay senescence and cope with abiotic stress. To explore the role of 5-HT in regulating the abilities of mangrove in cold resis-tance, we examined the effects of cold acclimation and the spraying of p-chlorophenylalanine (p-CPA, 5-HT synthesis inhibitor) on leaf gas exchange parameters and CO 2 response curves (A/Ca), as well as the endogenous phytohormone content levels in the mangrove species Kandelia obovata seedlings under low temperature stress. The results showed that low temperature stress significantly reduced the contents of 5-HT, chlorophyll, endogenous auxin (IAA), gibberellin (GA), and abscisic acid (ABA). It weakened the CO 2 utilization abilities of plants and reduced net photosynthetic rate, which ultimately reduced carboxylation efficiency (CE). Under low temperature stress, exogenous p-CPA reduced the contents of photosynthetic pigments, endogenous hormones, and 5-HT in the leaves, which aggravated the damages caused by low temperature stress on photosynthesis. By enhancing cold acclimation abilities, the endogenous IAA content in the leaves could was reduced under low temperature stress, promoted the production of 5-HT, improved the contents of photosynthetic pigments, GA, and ABA, as well as enhanced photosynthetic carbon assimilation abilities, which would increase photosynthesis in the K. obovata seedlings. Under cold acclimation conditions, the spraying of p-CPA could significantly inhibit the synthesis of 5-HT, promote the production of IAA, and reduce the contents of photosynthetic pigments, GA, ABA, and CE, which would weaken the effects of cold acclimation by improving the cold resistance of mangroves. In conclusion, cold acclimation could improve the cold resistance abilities of K. obovata seedlings by regulating photosynthetic carbon assimilation capacity and the contents of endogenous phytohormone. 5-HT synthesis is one of the necessary conditions for improving the cold resistance abilities of mangroves.

Uncovering the variations of short-term water-use efficiency (WUE p ) at whole-plant level in response to CO 2 concentration ( C a ) and soil water content (SWC) can improve the understanding of plant survival strategies under climate change. In this study, Platycladus orientalis saplings were cultured in simulated climate chambers.There were totally 15 treatments, including C a of 400 ( C 400 ), 600 ( C 600 ) and 800 ( C 800 ) μmol·mol -1 and SWC of 35%-45% field water holding capacity (FC), 50%-60%FC, 60%-70%FC, 70%-80%FC and 95%-100%FC. The WUE p was measured by mini-lysimeters, weighting method, and static assimilation chamber. The results showed that both daytime (0.12-1.87 mol·h -1 ) and nighttime transpiration rates (0.01-0.16 mol·h -1 ) at whole-plant level reached the maximum at C 400 ×70%-80%FC, while the whole-plant daytime net photosynthetic rate (2.12-22.10 mmol·h -1 ) reached the maximum at C 800 ×70%-80%FC. In contrast, nighttime respiration rate (0.84-4.41 mmol·h -1 ) increased with increasing SWC, but decreased with increasing of C a , reaching the maximum at C 400 ×95%-100%FC. For WUE p (5.37-24.35 mmol·mol -1 ), it reached the maximum at C 800 ×50%-60%FC, indicating that plants could use less water and fixed more carbon by adjusting adaptation strategies under high C a and drought conditions. In addition, leaf instantaneous water-use efficiency was a good predictor of WUE P when the canopy structure was similar.

Photosynthesis and respiration are two important components of net ecosystem exchange (NEE). NEE can be directly observed by eddy covariance (EC) technique, and statistically separated into ecosystem assimilation and respiration based on the statistical flux partitioning of temperature response function or light-response curves. However, these methods would result in auto-correlation between assimilation and respiration, and overestimate daytime respiration. Recently-developed isotope ratio infrared spectroscopy permits high-resolution measurement of atmospheric CO 2 and its stable carbon isotope composition (δ 13 C) under field conditions, and achieves diurnal and seasonal partitioning of ecosystem photosynthesis and respiration by matching with NEE measurements from EC. We expounded the fundamental theories and assumptions of isotopic flux partitioning of ecosystem photosynthesis and respiration, elaborated the development and application advance of techniques in isotopic flux measurement, summarized the advance of isotopic flux partitioning to provide new insight into the assimilation and respiration processes, and prospected the uncertainty of isotopic flux partitioning theory and the necessity of comparative researches of various methods.

Exploring the impacts of CO 2 and soil water availability on the photosynthetic performance and water use efficiency of three green manure plants could provide theoretical basis for the adaptive management of grassland ecosystems under future climate change. An experiment was conducted in an artificial climate chamber with precisely controled CO 2 concentrations of 400 (natural atmospheric) and 800 μmol·mol -1 (doubled), and four water treatments, 80% field water holding capacity (FC) (full irrigation control group), 55%-60% FC (mild water deficit), 35%-40% FC (moderate water deficit), <35% FC (severe water deficit) to investigate the impacts of increasing CO 2 concentration and water deficit on chlorophyll content, gas exchange variables, and water use efficiency (WUE) of oilseed rape ( Brassica napus ), white clover ( Trifolium repens ), and alfalfa ( Medicago sativa ). The results showed that under the same CO 2 concentration, when soil moisture was less than 40% FC, the chlorophyll content and gas exchange parameters of three plants were significantly decreased. The treatment of 55%-60% FC did not alter the total chlorophyll content of three species, but reduced the photosynthetic rate ( P n ) and transpiration rate ( T r ) of white clover and alfalfa by 6%-25% and did not affect their WUE. Compared with atmospheric CO 2 concentration, the doubled CO 2 concentration significantly decreased the P n of oilseed rape by 21.5% under the full irrigation treatment, increased the P n of three species under mild water deficit, increased the P n of oilseed rape and alfalfa under moderate water deficit, but only improved the P n of alfalfa under severe water deficit. The doubled CO 2 concentration significantly increased WUE of white clover and alfalfa under all water deficit conditions, but only increased WUE of oilseed rape under mild water deficit. Increasing CO 2 concentration and water deficit significantly interacted to affect P n of three species and the WUE of oilseed rape. In summary, the three species differed in their responses to doubled atmospheric CO 2 concentration and different levels of water deficit. Our results suggested that elevated CO 2 concentration could improve the adverse effects of mild water deficit on photosynthetic performance and WUE of three species, but only improve the photosynthetic performance of alfalfa under severe water deficit.

To explore the photosynthetic adaptation of Phoebe bournei to different light conditions, two-year-old P. bournei seedlings were grown under three light regimes (full light, shading rate 50% and 78% of full light). The chlorophyll contents, leaf gas exchange and chlorophyll fluorescence of P. bournei were measured after six-month treatment. The results showed that the contents of chlorophyll a, chlorophyll b, chlorophyll (a+b) and carotenoids in leaves were in a descending order of shading rate 78% > shading rate 50% > full light. There was no significant difference of chlorophyll a/b between natural and shade treatments. The shading treatment reduced light compensation point (LCP), but increased light saturation point (LSP) and apparent quantum yield (AQY), suggesting that plants could utilize both the weak light and the high light. Maximum net photosynthetic rate (P n max ), dark respiration rate (R d ), and maximum electron transfer rate (J max ) increased under the shading treatment. There was significant difference between natural and shade treatment in net photosynthetic rate (P n ), stomatal conductance to CO 2 (g sc ), intercellular CO 2 concentration (C i ), and mesophyll conductance (g m ). P n and g m of different light regimes were sorted from the highest to the lowest as shading rate 78% > shading rate 50% > full light. g sc under shading rate 78% was higher than that under full light. C i under shading rate 50% and 78% were lower than that under full light. Actual photochemical efficiency of PS2 (F v '/F m '), quantum yields of PS2 (Φ PS2 ), and electron transport rate (J) of P. bournei leaves were significantly higher under shading rate 78% than those under shading rate 50% and full light. In conclusion, P. bournei could increase P n by increasing chlorophyll content, AQY, J, g sc , and g m under shade condition.

Hydroponic experiment was carried out on M9T337 seedlings using 15 N and 13 C isotope tracer technology to study the effects of different potassium supply levels (K 0 , K 1 , K 2 , K 3 and K 4 were equivalent to 0, 3, 6, 9 and 12 mmol·L -1 , respectively) on the growth, photosynthetic characteristics and 15 N and 13 C absorption and utilization of M9T337 seedlings. The results showed that dry mass, root length, root surface area, number of tips and root activity of M9T337 seedlings under the K 2 level were significantly higher than those under other levels. The net photosynthetic rate (P n ) of leaves increased at low K + concentration and then decreased with the increases of potassium supply level, and reached the maximum value at K 2 treatment (15.5 μmol CO 2 ·m -2 ·s -1 ). At the 30th day after treatment, the activities of nitrate reductase (NR) and carbon metabolism enzyme were highest in K 2 treatment, and lowest in K 0 treatment. With the increases of potassium application rate, the 13 C accumulation of seedlings were first increased and then decreased, with the 13 C distribution rate of each organ being the most balanced at K 2 treatment. There were significant differences in 15 N uptake and utilization rate among treatments. 15 N uptake and utilization rates of seedlings under K 2 treatment were the highest, which were 16.1 mg and 17.9%, respectively. Therefore, too low or too high potassium supply could inhibit seedling root growth and leaf photosynthesis, which was not conducive to carbon and nitrogen absorption. Appropriate potassium supply could improve root activity and net photosynthetic rate, enhance nitrate reductase (NR) and carbon metabolic enzyme activity, and promote carbon and nitrogen metabolism.

We examined the effects of nitrogen, soil microbe and their interactions on biomass allocation, growth and photosynthesis of Fraxinus mandschurica, a typical tree species in Changbai Mountain, through outdoor control experiments. In June 2017, an experiment with two-factor randomized block design was carried out. There were four treatments: control (F), nitrogen addition (FN), sterilization (FS), sterilization and nitrogen addition (FSN), six repetitive blocks, three repetitions per block, including 18 repetitions of each treatment. In mid-August 2018, we measured photosynthetic parameters and then harvested seedlings to measure biomass and growth parameters in September. The results showed that compared with F, FN significantly increased total biomass by 14%, basal diameter by 9%, chlorophyll content, net photosynthetic rate (P n ), stomatal conduc-tance (g s ), transpiration rate (T r ) by 75%, 318%, 231%, 227% respectively. FS significantly increased total biomass by 13%, basal diameter by 9% and chlorophyll content, P n , g s and T r increased by 34%, 213%, 120% and 115%, respectively. FSN increased total biomass by 23%, basal diameter by 14%, chlorophyll content, P n , g s and T r increased by 81%, 672%, 312% and 273%, respectively. Nitrogen, soil microbe and their interactions had significant effects on biomass, growth and photosynthesis of F. mandschurica seedlings. Soil microbe would regulate the response of F. mandschurica seedlings to nitrogen.

In two growing seasons of wheat (2016-2018), a field trial with Jimai 22 as test mate-rial was conducted in Shijiawangzi Village, Yanzhou City, Shandong Province. Under three nitrogen levels of 150 (N 1 ), 180 (N 2 ) and 210 (N 3 ) kg·hm -2 , two irrigation-fertilization methods were designed at jointing as border irrigation and broadcasting of fertilizer (W 1 ), micro spraying irrigation and water-fertilizer integration (W 2 ), to examine the effects of irrigation-fertilization methods on water use, photosynthetic characteristics, and dry matter accumulation and transport of wheat. The results showed that under the same nitrogen level, seven days average soil evaporation of W 2 treatment in filling period was significantly lower than that of W 1 treatment, and that soil water consumption in the 60-160 cm soil layer was significantly higher than that in W 1 treatment. The flag leaf net photosynthetic rate, stomatal conductance and transpiration rate of W 2 treatment were signi-ficantly higher than W 1 treatment from 14 to 28 days after anthesis. The amount of dry matter in anthesis and maturity stage and the allocation to grain of post-anthesis assimilates of W 2 treatment were significantly higher than those in W 1 treatment. There was no difference in total water consumption between W 2 and W 1 treatments. Grain yield, water use efficiency and nitrogen use efficiency of W 2 treatment were significantly higher than W 1 treatment. The highest grain yield, water use efficiency and nitrogen use efficiency were obtained at the nitrogen level of 210 kg·hm -2 . By comprehensive considerations, under the same nitrogen level, treatment of micro spraying irrigation and water-fertilizer integration was better than border irrigation and broadcasting of fertilizer. The W 2 N 3 treatment under the nitrogen level of 210 kg·hm -2 and with the application of micro spraying irrigation and water-fertilizer integration at jointing was the optimal treatment to save water and fertilizer.

Crop productivity depends on photosynthetic source capacity. Appropriate nitrogen (N) fertilizer management is beneficial for improving growth, photosynthetic capacity and thereby increasing crops yield. A two-year pot experiment was conducted with four N treatments, i.e., conventional basal application 100 kg N·hm -2 as control (FP), a total of 80 kg N·hm -2 applied either 100% at basal application (JS), 100% at tuber initiation stage (35 d after transplant, KS), 50% at basal application and 50% at tuber initiation stage (35 d after transplant, FS), to examine the effects of reduced nitrogen fertilizer combined with application methods on the photosynthesis and chlorophyll fluorescence characteristics of sweetpotato (Ipomoea batatas) during summer 2016 and 2017. The results showed that the conventional basal application of a reduced N rate decreased photosynthesis of sweetpotato during the final growth phases compared to conventional application, dressing application relatively delayed late-season leaf senescence as indicated by the increased net photosynthetic rate (P n ), stomatal conductance (g s ), intercellular CO 2 concentration (C i ) and chlorophyll (Chl a+b) content during tuber expansion period. Split application of N fertilizer had noticeably higher P n , g s , C i and Chl a+b than other treatments. Furthermore, split application of N fertilizer had a significantly higher photochemical efficiency of photosystem 2 (F v /F m ), quantum yield of electron transport (Φ PS2 ), and photochemical quenching co-efficient (q P ), but lower initial fluorescence (F o ) and non-photochemical quenching coefficient (NPQ) during tuber expansion period. The improved photosynthesis by split N was due to both increased F v /F m with higher electron transfer rate and reduced thermal dissipation of light energy in the tuber expansion period. Results were consistent between two sweetpotato cultivars across years. The results indicated that one-time fertilization at basal or tuber initiation stage were not conducive to sweetpotato leaf photosynthesis. The split N application was more beneficial in terms of delaying late-season leaf senescence, extending leaf function period, enhancing photosynthesis and biomass production under reduced N application rate, which would be beneficial for sweetpotato yield.

Weedy rice is an important germplasm source of rice, which has the characteristics of cold-, drought-, and barren tolerance. Taking 88 accessions of weedy rice and 4 varieties of cultivated rice in northern China as test materials, this paper studied the photosynthetic characteristics (photosynthetic rate, transpiration rate, and stomatal conductance), water physiological characteristics, and their interrelationships of weedy rice in northern China. There existed greater differences in the photosynthetic and water physiological characteristics among the weedy rice accessions, possessing abundant diversity. The photosynthetic rate of the accessions was from 12.47 micromol CO2 x m(-2) x s(-1) to 28.67 micromol CO2 X m(-2) x s(-1), and the instantaneous water use efficiency was from 1.39 mg x g(-1) to 3.40 mg x g(-1). Among the photosynthetic parameters, intercellular CO2 concentration had the smallest variable coefficient, while stomatal conductance had the largest one. The photosynthetic rate had significant conic relationships with transpiration rate and stomatal conductance, and had a linear relationship with intercellular CO2 concentration. The significant conic relationships also existed between the instantaneous water use efficiency and the transpiration rate and stomatal conductance. The excellent features of weedy rice could be used to improve the cultivated rice varieties.

By using aeroponics culture system, this paper studied the effects of elevated rhizosphere CO2 concentration on the leaf photosynthesis and the fruit yield and quality of muskmelon during its anthesis-fruiting period. In the fruit development period of muskmelon, as compared with those in the control (350 microL CO2 x L (-1)), the leaf chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), and the maximal photochemical efficiency of PS II (Fv/Fm) in treatments 2500 and 5000 microL CO2 x L(-1) decreased to some extents, but the stomatal limitation value (Ls) increased significantly, and the variation amplitudes were larger in treatment 5000 microL CO2 x L(-1) than in treatment 2500 microL CO2 x L(-1). Under the effects of elevated rhizosphere CO2 concentration, the fruit yield per plant and the Vc and soluble sugar contents in fruits decreased markedly, while the fruit organic acid content was in adverse. It was suggested that when the rhizosphere CO2 concentration of muskmelon during its anthesis-fruiting period reached to 2500 microL x L(-1), the leaf photosynthesis and fruit development of muskmelon would be depressed obviously, which would result in the decrease of fruit yield and quality of muskmelon.

Taking the drought-sensitive Dactylis glomerata line "01998" and drought-tolerant cultivar "Baoxing" as test materials, a pot experiment was conducted to study the effects of drought stress on the seedlings root growth, physiological characteristics, and leaf photosynthesis, aimed to approach the differences in the drought-tolerance mechanism of different D. glomerata lines (cultivars). Under drought stress, the root vitality and root number of "01998" and "Baoxing" presented a trend of increased first and decreased then. When the soil relative moisture content decreased to 30%, the root vitality and root number of "01998" and "Baoxing" increased significantly and reached the maximum. Drought stress decreased the relative water content, leaf chlorophyll content, net photosynthesis, transpiration, and stomatal conductance, but increased the electric conductivity and intercellular CO2 concentration of "01998" and "Baoxing". Under drought stress, the leaf area per plant of both "01998" and "Baoxing" decreased, and the underground and aboveground plant biomass of "01998" decreased while that of "Baoxing" had less change.

By using eddy covariance technique, this paper measured the net ecosystem CO2 exchange (NEE) in a reed (Phragmites australis) wetland in the Yellow River Delta of China during the growth season of 2011, and investigated the variation patterns of the NEE and related affecting factors. The average diurnal variation of the NEE in different months showed a U-type curve, with the maximum net CO2 uptake rate and release rate being (0.44 +/- 0.03) and (0.16 +/- 0.01) mg CO2 x m(-2) x s(-1), respectively. The NEE, ecosystem respiration (R(eco)), and gross primary productivity (GPP) were all higher in vigorous growth season (from July to September) and lower in early growth season (from May to June) and late growth season (from October to November). Both R(eco) and NEE reached their maximum values in August, while GPP reached its peak value in July. During the growth season, the ecosystem CO2 exchange was mainly dominated by photosynthetic active radiation (PAR), soil temperature (T(s)), and soil water content (SWC). There was a rectangular hyperbolic relationship between the daytime NEE and PAR. The nighttime ecosystem respiration (R(eco,n)) was exponentially correlated with the T(s) at 5 cm depth, and the temperature sensitivity of the ecosystem respiration (Q10) was 2.30. SWC and T(s) were the main factors affecting the R(eco,n). During the entire growth season, the reed wetland ecosystem in the Yellow River delta was an obvious carbon sink, with the total net carbon sequestration being 780.95 g CO2 x m(-2).

Taking stay-green sorghum (B35) and non-stay green sorghum (Sanchisan) as test materials, a pot experiment was conducted to study their leaf osmotic adjustment and chloroplast ultrastructure at flowering and filling stages under impacts of drought stress (45% -50% of maximum field capacity). For the two sorghum lines, drought stress caused the reduction of their leaf free water content and relative water content, and increased the leaf bound water content, water saturation deficit, and electrical conductivity, with the increment or dement being larger for Sanchisan than for B35. Drought stress increased the leaf soluble sugar content and proline content, with the increment of the soluble sugar content being larger for Sanchisan and the increment of the proline content being larger for B35, while decreased the leaf soluble protein content, with the decrement being larger for Sanchisan than for B35. The chloroplast ultrastructure of both B35 and Sanchisan under drought stress was damaged to some extent, but the damaged degree was obviously lower for B35 than for Sanchisan. The findings indicated that stay-green sorghum had a greater adaptation to drought stress through stronger osmotic adjustment.

A pot experiment was conducted to study the effects of different water treatments (normal irrigation, light drought, moderate drought, and severe drought) on the growth, gas exchange, chlorophyll fluorescence characteristics, and active oxygen metabolism of poplar ( Populus x euramericana cv. 'Neva') seedlings in the experimental nursery of Shandong Forestry Academy from April to October, 2011. As compared with those under normal irrigation, the growth of the seedling' s basal diameter under light, moderate, and severe drought stress decreased by 12.8%, 44.5%, and 65.6%, and the height growth decreased by 12.2%, 43.1%, and 57.2%, respectively. With the increasing extent and duration of drought stress, the maximal photochemical efficiency of PS II , quantum yield, photochemical quenching coefficient, net photosynthetic rate, and stomatal conductance of the seedling leaves decreased gradually under light drought stress, while decreased rapidly under both moderate and severe drought stress. The non-photochemical quenching coefficient increased significantly under light drought stress, but decreased after an initial increase under moderate and severe drought. The leaf superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities under drought stress decreased after an initial increase, but definite differences existed in the responses of the three enzymes to drought stress and reactive oxygen. The leaf relative electric conductivity and malondialdehyde (MDA) content under drought stress increased significantly, plasma membrane was damaged, and massive ions leaked out. The most serious damage of plasma membrane was found under severe stress. Under light drought stress, the seedlings had higher photosynthetic efficiency and stronger oxidative enzyme defense system; under moderate and severe drought stress, the photosynthetic efficiency decreased significantly, and the oxidative enzyme defense system was damaged remarkably.

Photosynthesis is one of the vital physiological processes easily affected by environmental changes. As a plant group growing in specific low temperature and strong irradiance environment, the photosynthetic apparatus of alpine plants have developed special morphologically and physiologically mechanisms in adapting to this extreme adverse environment. However, due to the high heterogeneity of habitats, there exist great differences in the photo-protection and adaptation mechanisms among different alpine plants. This paper reviewed the recent researches about the morphology and ultramicro-anatomical structure of the chloroplasts in photosynthetic apparatus of alpine plants and the photo-protection and adaptation mechanisms of the plants, and proposed the further research directions on the physiological adaptation of the photosynthesis of alpine plants.

Different genotypes wheat cultivars (spring wheat Yangmai 18, semi-spring wheat Zhengmai 9023, and semi-winter wheat Yannong 19) were chosen to study their photosynthetic and chlorophyll fluorescence characteristics at tillering and stem elongation stages under low temperature stress. After treated with low temperature (-10 degrees C at night) at tillering stage for 2 days, the net photosynthetic rate (Pn), stomata conductance (g(s)), maximum quantum yield of PSII (Fv/Fm), photochemical quenching (q(P)), non-photochemical quenching coefficient (NPQ), and acyclic photosynthetic electron transfer rate of PSII (ETR) of Yannong 19 were significantly higher than those of Yangmai 18 and Zhengmai 9023, the g(s), Fv/Fm, qP, and NPQ of Zhengmai 9023 were significantly higher than those of Yangmai 18, while the intercellular CO2 concentration (Ci) of Yannong 19 was significantly lower than that of Zhengmai 9023 and Yangmai 18. In addition, the minimal fluorescence (Fo) of Yangmai 18 was significantly higher than that of Zhengmai 9023 and Yannong 19. Similarly, after treated with low temperature (0 degrees C at night) at stem elongation stage for 3 days, the Pn, g(s), qP, and Fv/Fm of Yannong 19 were significantly higher than those of Yangmai 18 and Zhengmai 9023, and the NPQ and ETR of Yannong 19 were significantly higher than those of Yangmai 18. In addition, the Pn, g(s), Fv/Fm, and qP of Zhengmai 9023 were significantly higher than those of Yangmai 18, the Fo of Zhengmai 9023 was significantly higher than that of Yannong 19, and the Ci and Fo of Yangmai 18 were significantly higher than those of Zhengmai 9023 and Yannong 19. It was suggested that under low temperature stress at tillering and stem elongation stages, semi-winter wheat Yannong 19 had the highest photosynthetic activity and the best self-protection mechanism, followed by semi-spring wheat Zhengmai 9023, and spring wheat Yangmai 18.

In 2010-2011, a field experiment was conducted in Northeast China to evaluate the effects of different tillage patterns on the temperature and moisture in topsoil layer and the leaf photosynthesis and chlorophyll fluorescence of maize. The effects of tillage patterns on the soil temperature and moisture mainly manifested at sowing-jointing stage. In treatments flat planting with ridging at early jointing stage (PL) and flat planting without ridging (PP), the soil moisture content at the depth of 0-40 cm was significantly higher than that in treatment ridge planting (LL), with the increment being 5.6% and 5.2%, 4.6% and 7.3%, and 3.9% and 4.8% at emergency, seedling, and jointing stages, respectively. The minimum temperature at the soil depth 5 cm at seedling stage in PL and PP was 1.4 and 1.3 degrees C higher than that in LL, respectively. Due to the improvement of soil water and thermal conditions, the leaf photosynthetic rate (Pn) and transpiration rate (Tr) at jointing stage in PL and PP were significantly higher than those in LL, whereas the PS II potential activity (Fv/Fo) and PS II maximal photochemical efficiency (Fv/Fm) had no significant differences among the treatments, indicating that the stomatal factors such as stomata conductivity and stomata limitation were the main factors inducing the photosynthesis differences among the treatments. Furthermore, the Pn and Tr at grain filling stage in LL and PL were higher than those in PP, mainly due to the high water-logging risk in PP in strong rainfall season. Consequently, treatment PL could promote maize photosynthesis through improving soil water and thermal conditions, and further, increase maize grain yield.

Leaf area index is a key indicator of leaf area change of crop population, and also, an important parameter for studying crop photosynthesis, transpiration, and biomass formation, etc. How to establish an optimum leaf area index (LAI) dynamic model with the minimum field observation data is of great significance for accurately simulating crop growth and yield. Based on the field experiment data of various spring maize varieties from the Jinzhou Agricultural Ecosystem Research Station in Northeast China in 2005-2011, in combination with the universal maize LAI dynamic model, this paper discussed the optimum field observation data for accurately simulating the dynamics of maize LAI. It was suggested that for the accurate simulation of the dynamics of maize LAI, the field observation should be no less than 3 years, with at least 4 times observation during the growth period each year. The proper four observation times during maize growth period were suggested as about 20 d after seedling emergence for the first observation, and monthly thereafter for the other three observations. This study could provide reference for conducting an effective observation on leaf area index and its dynamic modeling.

The source and sink effect of terrestrial plants is one of the hotspots in terrestrial ecosystem research under the background of global change. Dark respiration of terrestrial plants accounts for a large fraction of total net carbon balance, playing an important role in the research of carbon cycle under global climate change. However, there is little study on plant dark respiration. This paper summarized the physiological processes of plant dark respiration, measurement methods of the dark respiration, and the effects of plant biology and environmental factors on the dark respiration. The uncertainty of the dark respiration estimation was analyzed, and the future hotspots of related researches were pointed out.

Taking cold-resistant maize variety Fengdan 3 and cold-sensitive maize variety Zhengdan 958 as test materials, field experiments were conducted in I, II, and III accumulated temperature zones in Heilongjiang Province of Northeast China to study the effects of different accumulated temperature on the photosynthetic performances of different types of cold-resistant spring maize varieties during their grain-filling period. In the three accumulated temperature zones, the tasseling and maturing periods of Fengdan 3 and Zhengdan 958 were prolonged in the order of I > II > and III, and the grain bulk density decreased in the same order. The RuBPCase and PEPCase activities of Fengdan 3 and Zhengdan 958 leaves had different temperature sensitivity. For Fengdan 3, its leaf RuBPCase and PEPCase activities were high in early grain filling period (0-20 days after anthesis), and the variety could ripen in temperature-limited region. For Zhengdan 958, its leaf RuBPCase and PEPCase activities were high within 0-10 days and 40-60 days after anthesis but not sensitive to the active accumulated temperature during 10-40 days after anthesis, and the variety could not ripen in temperature-limited region. The photosynthetic rates of the two varieties were significantly positively correlated with the active accumulated temperature during 0-10 days and 30-40 days after anthesis. The effects of the accumulated temperature in the three zones on the photosynthetic performances were significant at both early and later grain filling stages. For the same varieties, the higher the active accumulated temperature in grain filling period, the higher the grain yield. Zhengdan 958 had higher yield than Fengdan 3.

Taking the two-year old potted Prunus sibirica seedlings as test materials, and using CIRAS-2 photosynthetic system, this paper studied the CO2 response process of P. sibirica photosynthesis in semi-arid loess hilly region under eight soil moisture conditions. The CO2 response data of P. sibirica were fitted and analyzed by rectangular hyperbola model, exponential equation, and modified rectangular hyperbola model. Meanwhile, the quantitative relationships between the photosynthesis and the soil moisture were discussed. The results showed that the CO2 response process of P. sibirica photosynthesis had obvious response characteristics to the soil moisture threshold. The relative soil water content (RWC) required to maintain the higher photosynthetic rate (P(n)) and carboxylation efficiency (CE) of P. sibirica was in the range of 46.3%-81.9%. In this RWC range, the photosynthesis did not appear obvious CO2 saturated inhibition phenomenon. When the RWC exceeded this range, the photosynthetic capacity (P(n max)), CE, and CO2 saturation point (CSP) decreased evidently. Under different soil moisture conditions, there existed obvious differences among the three models in simulating the CO2 response data of P. sibirica. When the RWC was in the range of 46.3%-81.9%, the CO2 response process and the characteristic parameters such as CE, CO2 compensation point (see symbol), and photorespiration rate (R(p)) could be well fitted by the three models, and the accuracy was in the order of modified rectangular hyperbola model > exponential equation > rectangular hyperbola model. When the RWC was too high or too low, namely, the RWC was > 81.9% or < 46.3%, only the modified rectangular hyperbola model could well fit the CO2 response process and the characteristic parameters. It was suggested that when the RWC was from 46.3% to 81.9%, the photosynthetic efficiency of P. sibirica was higher, and, as compared with rectangular hyperbola model and exponential equation, modified rectangular hyperbola model had more applicability to fit the CO2 response data of P. sibirica photosynthesis under different soil moisture conditions.

This paper studied the effects of 2,4-epibrassinolide (EBR) on the photosynthesis and antioxidant system of cucumber seedling leaves under NaCl stress. As compared with the control, NaCl stress increased the leaf superoxide anion production rate, hydrogen peroxide content, malondialdehyde content, and cell membrane permeability while decreased the leaf net photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO2 concentration significantly, and inhibited the seedlings growth significantly. Applying EBR could increase the activities of leaf superoxide dismutase, peroxidase, and catalase, decrease the leaf superoxide anion production rate, hydrogen peroxide content, malondialdehyde content, and cell membrane permeability, make the leaves keep a higher photosynthetic rate, and thus, promote the seedlings growth, being able to effectively alleviate the damage of NaCl stress.

By using polyethylene glycol (PEG-6000) solution to regulate the water potential of tomato (Lycopersicon esculentum) rhizosphere to simulate water stress, this paper studied the dynamic changes of net photosynthetic rate, dark respiratory rate and CO2 compensatory concentration of detached tomato leaves in the process of photosynthetic induction. Under 1000 micromol m-2 s-1 of light induction, the time required to reach the maximum net photosynthetic rate of water-stressed tomato leaves was shortened by 1/3, while the stomatal conductance was increased by 1.5 times, as compared to the non-stress control. Also, the light saturation point (LSP) of water-stressed tomato leaves was lowered by 65% to 85%, and the light compensation point (LCP) was increased by 75% to 100%, suggesting that the effective range of light utilized by tomato leaves was reduced. Furthermore, water stress decreased the maximum photosynthetic capacity of tomato leaves by 40%, but increased the dark respiration rate by about 45% . It was suggested that rapid water stress made the stomata of tomato leaves quickly opened, without initial photosynthetic induction stage. In conclusion, water stress could induce the decrease of plant light-energy use efficiency and potential, being the main reason for the decrease of plant productivity, and stomatal regulation could be the main physiological mechanism of tomato plants to adapt to rapid water stress.

Biological soil crust (biocrust) is a compact complex layer of soil, which has photosynthetic activity and is one of the factors affecting the CO2flux of soil-atmosphere interface. In this paper, the soil CO, flux under the effects of biocrust at different succession stages on the re-vegetated grassland in the hilly region of Loess Plateau was measured by a modified LI-8100 automated CO, flux system. Under light condition, the soil CO2 flux under effects of cyanobacteria crust and moss crust was significantly decreased by 92% and 305%, respectively, as compared with the flux without the effects of the biocrusts. The decrement of the soil CO, flux by the biocrusts was related to the biocrusts components and their biomass. Under the effects of dark colored cyanobacteria crust and moss crust, the soil CO2 flux was decreased by 141% and 484%, respectively, as compared with that in bare land. The diurnal curve of soil CO2 flux under effects of biocrusts presented a trend of 'drop-rise-drop' , with the maximum carbon uptake under effects of cyanobacteria crust and moss crust being 0.13 and -1.02 micromol CO2.m-2.s-1 and occurred at about 8:00 and 9:00 am, respectively, while that in bare land was unimodal. In a day (24 h) , the total CO2 flux under effects of cyanobacteria crust was increased by 7.7% , while that under effects of moss crust was decreased by 29.6%, as compared with the total CO2 flux in bare land. This study suggested that in the hilly region of Loess Plateau, biocrust had significant effects on soil CO2 flux, which should be taken into consideration when assessing the carbon budget of the 'Grain for Green' eco-project.

Three water treatments (control, CK; continuous flooding, CF; and periodic flooding, PF) were installed to simulate the soil moisture change of the riparian zone in the Three Gorges Reservoir (TGR) region of China to study the physiological and ecological adaptation mechanisms of the native plant species Pterocarya stenoptera seedlings to the soil moisture change. All the water treatments had significant effects on the photosynthesis, biomass accumulation, and growth of the P. stenoptera seedlings. As compared with those in CK, the seedling's net photosynthetic rate (Pn) and stomatal conductance (gs) in treatments CF and PF were significantly lower while the intercellular carbon dioxide concentration was significantly higher, and the Pn and gs in CF and PF declined initially followed by a gradual recovery or tended to be stable. With the extension of treatment time, the total biomass and root-, stem-, and leaf biomass, plant height, and basal diameter in CF and PF all presented an increasing trend. Throughout the experimental period, the total biomass, root- and leaf biomass, and plant height in CF and PF and the stem biomass in PF were significantly lower than those in CK, whereas the stem biomass in CF had no significant difference with that in CK, though the basal diameter in CF was significantly higher than that in CK. It was suggested that the P. stenoptera seedlings had the physiological and ecological characteristics of tolerating flooding rather than flooding-drought alteration.

Taking the Arachis hypogaea cv. 'Qinghua 7' as test material, a field experiment was conducted to study the effects of different cultivation modes on the leaf photosynthetic characteristics and yield of summer-sowing peanut after wheat harvest. As compared with conventional cultivation mode, high-yield protective cultivation mode promoted the leaf growth, significantly improved the leaf area index (LAI), and maintained a longer time of high LAI and chlorophyll content. Meanwhile, the net photosynthetic rate, stomatal conductance, and transpiration rate of functional leaves under high-yield protective cultivation mode were higher while the intercellular CO2 concentration was lower, which induced the photosynthetic efficiency of functional leaves being significantly improved. Therefore, under high-yield protective cultivation mode, the yield per peanut plant was higher, the pod yield increased significantly, and the economic coefficient improved obviously. Both film mulching and straw returning could also improve the leaf photosynthesis of summer-sowing peanut, and increase the peanut yield. It was suggested that high-yield protective cultivation mode could effectively alleviate the adverse factors of summer-sowing peanut, such as the short growth period and lower productivity per plant, being a practical high-yield cultivation mode of summer-sowing peanut.

Abstract: In this study, same amount of potassium (240 kg . hm-2) was applied as basal dressing (treatment 1) and as 1/2 basal dressing + 1/2 top-dressing at day 75 after planting (treatment 2), aimed to investigate the effects of potassium fertilization period on the photosynthetic characteristics of edible sweetpotato and the starch accumulation in storage root. As compared with treatment 1, treatment 2 improved the leaf photosynthetic rate and sucrose-phosphate synthase activity and the storage root's adenosine diphosphate glucose pyrophosphortlase activity, enhanced the starch accumulation rate in storage root (with an average increment of 6. 7%), and increased the root tuber yield significantly by 8. 2%. Both of the potassium fertilization treatments improved the synthesis of sucrose in leaf and the transformation from sucrose to starch in storage root, as compared with no potassium fertilization.

Taking the tomato (Solanum lycopersicum) cultivar "Kuiguan108" as test object, a comparative study was made on the effects of outer type and built-in type straw bio-reactors on the CO2 concentration, air relative humidity , air vapor pressure deficit in the solar greenhouse during the tomato growth over autumn-delayed cultivation as well as the effects of the bio-reactors on the tomato growth and photosynthetic performance. As compared with that in CK, the average CO2 concentration in the greenhouse with outer type straw bio-reactor at 9:30-11:30 and 14:30-15:00 on sunny days was increased significantly by 207. 3 and 103 micromol . mol-1 , respectively, and the ave-rage CO2 concentration in the greenhouse with built-in straw bio-reactor at 9:30-11:30 on sunny days was raised by 19.0 micromol . mol-1. Both the outer type and the built-in type straw bio-reactors promoted the tomato plant height growth and early flowering, enhanced the plant net photosynthetic rate and the yield per plant and per unit area significantly, and decreased the plant transpiration rate at the stages of vegetative growth and fruit- bearing significantly. Nevertheless, as compared with built-in type straw bio-reactor, outer type straw bio-reactor was more suitable for the autumn- delayed cultivation of tomato in solar greenhouse.

Three light intensities (100% , 56.2%, and 12.5%) were installed to simulate the light regimes of opening field (cutting blank), forest gap, and understory, respectively, aimed to understand the effects of different light regimes on the seedling growth, photosynthetic characteristics, and biomass accumulation and allocation of alien species Alnus formosana and native species A. cremastogyne. Low light regime limited the seedling growth of the two alder species, while the light regime of forest gap was more favorable for the growth, in comparison with that of the opening field. Regardless of the light regimes, A. formosana seedlings had higher specific leaf area (SLA), relative growth rate (RGR) , leaf area, leaf length, leaf width, plant height, and basal diameter, but smaller leaf number, leaf area ratio (LAR), and petiole length. Under low light regime, A. formosana seedlings had higher maximum net photosynthetic rate (Pn max), light saturation point (LSP), and apparent quantum yield (AQY), but smaller light compensation point (LCP) and dark respiration rate (Rday). With the decrease of light intensity, A. formosana seedlings had much higher root mass ratio (RMR) and much lower leaf mass ratio (LMR), implying that more carbon was allocated and stored to the roots rather than new leaves, whereas the A. cremastogyne seedlings were in adverse, i.e. , more carbon was allocated to the above-ground parts, which might increase the risk of animal feeding and mechanical damage.

Taking different genotype cotton varieties as test materials, a soil column culture experiment was conducted to study the effects of water and nitrogen management modes on the photosynthetic characters and yield formation of cotton with under-mulch drip irrigation in Xinjiang, Northwest China. Under the management mode W4N2, i.e., pre-sowing irrigation + limited drip irrigation before full-flowering + abundant drip irrigation after full-flowering in combining with basal 20% N + topdressing 80% N, the chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (gs) , actual photochemical efficiency of photosystem II (Psi PSII), and photochemical quenching coefficient (qp) at full-flowering stage all decreased significantly, the non-photochemical quenching (NPQ) increased, and the aboveground dry matter accumulation was inhibited, as compared with those under common drip irrigation. From full-flowering stage to boll-opening stage, the chlorophyll content, gs, Pn, Psi PSII, and qp increased with increasing water and nitrogen supply, and the aboveground dry matter accumulation was enhanced by compensation, which benefited the translocation and distribution of photosynthates to seed cotton. Under the fertilization mode of basal 20% N + topdressing 80% N, the seed cotton yield of Xinluzaol3 was the highest in treatment pre-sowing irrigation + common drip irrigation (W3), but that of Xinluzao43 was the highest in treatment pre-sowing irrigation + limited drip irrigation before full-flowering + abundant drip irrigation after full-flowering (W4). It was concluded that under the condition of pre-sowing irrigation, to appropriately decrease the water and nitrogen supply before full-flowering stage and increase the water and nitrogen supply at middle and late growth stages could extend the active photosynthesis duration and promote the photosynthates allocation to reproductive organ, which would fully exploit the yield-increasing potential of cotton with under-mulch drip irrigation.

To explore the invasion mechanisms of Conyza canadensis and develop effective control measures, this paper studied the photosynthetic characteristics of the invasive plant and its main associated plants Ixeris chinensis and Commelina communis. The light saturation point and light compensation point of C. canadensis were 1634.00 and 23.84 micromol x m(-2) x s(-1), respectively, which were between those of the two associated plants. The maximum net photosynthetic rate of C. canadensis below light saturation point was 28.12 micromol x m(-2) x s(-1), being much higher than that of the two associated plants. The apparent quantum yield of C. canadensis was 0.06, equal to that of I. chinensis but higher than that of C. communis. The CO2 saturation point and CO2 compensation point of C. canadensis were 834.00 and 23.69 micromol x mol(-1), respectively. The maximum net photosynthetic rate of C. canadensis below CO2 saturation point was 31.97 micromol x m(-2) x s(-1), which was between that of the two associated species. The carboxylation efficiency of C. canadensis was 0.078, being higher than that of the two associated species. The variations of photosynthetically active radiation and CO2 concentration had little effects on the stomatal conductance and transpiration rate of the three plants, but significantly affected their water use efficiency. C. canadensis had higher photosynthetic rate and material accumulation capability, and its high productivity could be one of the important factors for its successful invasion.

This paper studied the community characteristics of two sand-fixing plants (Artemisia ordosica and Caragana korshinskii) under different configuration modes (1 m x 1 m and 2 m x 2 m) in the Shapotou region of Northwest China as well as the water relation, gas exchange, and their adjustment mechanisms of the plants under natural and artificial precipitation conditions. With the variation of soil water content, the physiological water consumption and growth characteristics of A. ordosica differed from those of C. korshinskii. A. ordosica presented obvious fluctuation in the stomatal conductance, water potential, transpiration rate, photosynthetic rate, and rapid growth, and had higher water consumption than C. korshinskii. However, the variations of the above-mentioned indices of C. korshinskii were relatively slow and more constant. The C. korshinskii had a lower photosynthetic rate but a very high accumulated biomass over years than A. ordosica. The response procedures and adjustment mechanisms of the two plants under water stress differed, with a water-conserving mechanism for A. ordosica and a water-saving mechanism for C. korshinskii. In extremely drought years, the C. korshinskii had stronger capabilities of water-saving and stress tolerance than A. ordosica. It was suggested that the selection of sand-fixing plants should have a view to the benefits in water saving and sand fixation, and also, to the stability of sand-fixing forest.

In this study, measurements were made on the leaf water potential (psi1), stomatal conductance (g(s)), transpiration rate, leaf area index, and sapwood area of mature Acacia mangium, aimed to understand the relationships of the leaf hydraulic conductance (K1) with the leaf water use and photosynthetic characteristics of the A. mangium in wet season (May) and dry season (November). The ratio of sapwood area to leaf area (A(sp)/A(cl)) of the larger trees with an average height of 20 m and a diameter at breast height (DBH) of 0.26 m was 8.5% higher than that of the smaller trees with an average height of 14.5 m and a DBH of 0.19 m, suggesting that the larger trees had a higher water flux in their leaf xylem, which facilitated the water use of canopy leaf. The analysis on the vulnerability curve of the xylem showed that when the K1 decreased by 50%, the psi1 in wet season and dry season was -1.41 and -1.55 MPa, respectively, and the vulnerability of the xylem cavitation was higher in dry season than in wet season. The K1 peak value in wet season and dry season was 5.5 and 4.5 mmol x m(-2) x s(-1) x MPa(-1), and the maximum transpiration rate (T(r max)) was 3.6 and 1.8 mmol x m(-2) x s(-1), respectively. Both the K1 and T(r max), were obviously higher in wet season than in dry season. Within a day, the K1 and T(r), fluctuated many times, reflecting the reciprocated cycle of the xylem cavitation and refilling. The leaf stomatal closure occurred when the K1 declined over 50% or the psi1 reached -1.6 MPa. The g(s) would be maintained at a high level till the K1 declined over 50%. The correlation between the hydraulic conductance and photosynthetic rate was more significant in dry season than in wet season. The loss of leaf hydraulic conductance induced by seasonal change could be the causes of the decrease of T(r) and CO2 gas exchange.

To understand the mechanisms of soil respiration and accurately estimate its magnitude are the crucial basis of evaluating global carbon balance. However, the previously built soil respiration forecast models usually neglect the physiological processes that photosynthesis supplies substrates for rhizospheric respiration, leading to the defect in evaluating the mechanisms of soil respiration. This paper summarized the research progress on the mechanisms of photosynthetic regulation and control of soil respiration, introduced the related main research methods, and discussed the existing problems and research hotspots.

A pot experiment was conducted to study the effects of partial root excision on the growth of two maize cultivars (Zhengdan 958 and Denghai 9) throughout their growth period and the photosynthesis and leaf antioxidant enzyme activities at grain-filling stage under salt stress. Four treatments were installed, i. e., control (no salt), low salt (0.2% NaCl), moderate salt (0.4% NaCl), and high salt (0.6% NaCl). Under low salt stress, the grain yield of Zhengdan 958 and Denghai 9 with partial root excision was increased by 13.1% and 31.4%, respectively, as compared with that of the cultivars with no root excision. At jointing stage, the growth of the cultivars with partial root excision was restrained, the root- and shoot dry masses under the same salt stresses being lesser than those of the cultivars with no root excision, but the growth under the conditions of no salt and low salt recovered quickly. At milk-ripe stage and under no salt and low salt conditions, the root- and shoot dry masses, leaf area, total root length, total root surface area, root activity, leaf chlorophyll content, and ear leaf net photosynthetic rate, stomatal conductance, transpiration rate, and CAT and POD activities of the cultivars with partial root excision were significantly larger than those of the cultivars with no root excision, while the shoot diameter and ear leaf MDA content were in adverse. Moderate and high salt stresses had greater effects on the cultivars with partial root excision. The root- and shoot dry masses, root morphology, and photosynthesis indices of the cultivars with partial root excision were smaller than those of the cultivars with no root excision, so did the grain yields. Throughout the growth period of the cultivars, the growth of the cultivars with partial root excision depended on the salt concentration, i. e., was promoted under no and low salt, and inhibited under moderate and high salt conditions.

This study analyzed the sensitivities of three vegetation biochemical parameters [chlorophyll content (Cab), leaf water content (Cw), and leaf area index (LAI)] to the changes of canopy reflectance, with the effects of each parameter on the wavelength regions of canopy reflectance considered, and selected three vegetation indices as the optimization comparison targets of cost function. Then, the Cab, Cw, and LAI were estimated, based on the particle swarm optimization algorithm and PROSPECT + SAIL model. The results showed that retrieval efficiency with vegetation indices as the optimization comparison targets of cost function was better than that with all spectral reflectance. The correlation coefficients (R2) between the measured and estimated values of Cab, Cw, and LAI were 90.8%, 95.7%, and 99.7%, and the root mean square errors of Cab, Cw, and LAI were 4.73 microg x cm(-2), 0.001 g x cm(-2), and 0.08, respectively. It was suggested that to adopt vegetation indices as the optimization comparison targets of cost function could effectively improve the efficiency and precision of the retrieval of biochemical parameters based on PROSPECT + SAIL model.

A pot experiment was conducted to study the variations of the photo-physiological characteristics of native bluestem (Bothriochloa ischaemum) in loess hilly-gully region under different soil moisture condition (80% and 40% field capacity) and different atmospheric CO2 concentration (375 micromol x m(-2) x s(-1) and 750 micromol x m(-2) x s(-1). The results showed that drought stress decreased the maximum photosynthetic rate (Pn max), apparent quantum efficiency (AQE), stomatal conductance (ga), transpiration rate (Tx), maximum photochemical efficiency (F/Fm), potential photochemical efficiency (Fv/Fo), and photosynthetic pigments contents, and increased the malondialdehyde (MDA) and proline (Pro) contents. Under sufficient moisture condition, elevated CO2 concentration didn't change the P n max and the, MDA and Pro contents significantly; under drought stress, elevated CO2 improved the maximal fluorescence (Fm), Fv/Fm, Fv/Fo, photosynthetic pigments contents, and AQE, and the Pn max under elevated CO2 was increased significantly by 23.3%, and the MDA and Pro contents were decreased significantly, as compared with those under ambient CO2 concentration. All the results suggested that elevated CO2 concentration had definite compensation effect on the photosynthetic reduction of B. ischaemum induced by drought stress, and alleviated the damage of drought stress on B. ischaemum.

From June 2010 to July 2011, a pot experiment was conducted to explore the effects of nitrogen deposition on the leaf physiological and ecological characteristics of Lindera aggregate seedlings. Three levels of NH4NO3, i. e., low-N (2 g x m(-2) x a(-1)), medium-N (8 g x m(-2) x a(-1)), and high-N (32 g x m(-2) x a(-1)) , were added to simulate nitrogen deposition, and the seedling leaf photosynthesis, relative chlorophyll content, chlorophyll fluorescence parameters, membrane lipid peroxidation, and antioxidant enzyme activities were determined. After one-year treatment, the daily mean values of the net photosynthetic rate (P)n)) and the maximum net photosynthetic rate (P(n max)) at low, medium and high levels of NH4 NO3 addition were 47.0%, 117.8% and 41.2%, and 82.6%, 191.3% and 152.2% higher than those of the control (no NH4 NO3 addition), respectively, with the highest values at medium level of NH4NO3 addition. The intercellular CO2 concentration, daily mean stomatal conductance, light saturation point, and apparent quantum yield in the three treatments of NH4NO3 addition were all higher than those of the control, and the dark respiration rate was the highest in treatment high-N. The relative chlorophyll content was the highest in treatment medium-N, followed by in treatment high-N, and had no significant difference between treatment low-N and the control. The chlorophyll fluorescence parameters varied with the levels of NH4NO3 addition. The PS II primary chemical efficiency (F(v)/F(m)) and PS II potential activity (F(v)/F(o)) were the lowest in treatment high-N, the superoxide dismutase activity was higher in nitrogen addition treatments than in the control, and the peroxidase activity, malonydialdehyde content, and membrane permeability were the highest in treatment high-N. All the results suggested that nitrogen deposition enhanced the photosynthetic ability of L. aggregata seedlings, with the most obvious effects in treatment medium-N, and altered the other physiological traits of the seedlings to different degrees.

With five temperature gradient treatments, this paper studied the effects of high temperature stress on the photosynthetic parameters and chlorophyll fluorescence characteristics of four Xinjiang hybrid hazels. When the temperature gradually raised from 25 degrees C to 45 degrees C, the net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, water use efficiency and light use efficiency of the hybrid hazels decreased gradually, and the decrement was the largest at 35 degrees C - 45 degrees C. The actual photochemical efficiency of photosystem II, electron transport rate, and photochemical quenching coefficient increased slowly with increasing temperature, but decreased sharply when the temperature was raised to >35 degrees C. The water consumption for transpiration and the heat dissipation also increased with increasing temperature. Among the four hybrid hazels, Xinzhen No. 3 had higher tolerance against high temperature in photosynthesis, belonging to heat-resistant cultivar.

Taking 4-, 11-, 25-, and 37- year old Salix cheilophila stands on the alpine sandy land of Gonghe basin in Qinghai of West China as test objects, a laboratory test was conducted on their relative water deficit, water holding ability, specific leaf area (SLA), leaf mass-based nitrogen concentration (N(mass)) and phosphorous concentration (P(mass)), and N(mass)/P(mass), aimed to understand the variation patterns of the water physiological characteristics and leaf traits of different aged S. cheilophila on alpine sandy land. No significant difference was observed in the relative water deficit of the four stands. The daily mean value of water potential of the 37-year old stand was significantly lower, as compared with that of the other three stands, and the 4- and 11-year old stands had a significantly lower daily mean water potential than the 25-year old stand. The water loss rate of the 4-year old stand was significantly lower than that of the other three stands, and the 25-year old S. cheilophila stand had a significantly lower water loss rate than the 11-year old stand. The 4-year old stand also had a significantly lower SLA than the other three stands, implying its higher water use efficiency. The N(mass) of the 11-year old stand was significantly higher than that of the other three stands, and the 25-year old stand had a significantly higher N(mass) than the 37-year old stand, implying that the 11- and 25-year old stands had a higher photosynthetic capacity. The P(mass) of the 11-year old stand was significantly higher than that of the 25- and 37-year old stands, and the 4-year old stand had a significantly higher P(mass) than the 25-year old stand. The N(mass)/P(mass) of the four stands was 5.16-6.28, and the 25-year old stand had a significantly higher N(mass)/P(mass) than the 4- and 11-year old stands. The N(mass) of the four stands was significantly positively correlated with P(mass) the P(mass) was highly significantly negatively correlated with N(mass)/P(mass) and significantly nega- tively correlated with stand age, and the N(mass)/P(mass) was significantly positively correlated with stand age. It was suggested that S. cheilophila at its different developmental stages could have different ecological adaptive strategies.

By using a free-air controlled enrichment (FACE) system, this paper studied the effects of elevated atmospheric ozone (O3) concentration (150% of ambient O3) on the flag leaf photosynthetic pigment contents of wheat varieties Yannong 19, Yangmai 16, Jiaxin 002, Yangmai 15, and Yangfumai 2. For the test varieties, no significant differences were observed in the flag leaf chlorophyll a, chlorophyll b, chlorophyll (a+b), and carotenoid contents between treatments elevated O3 concentration and ambient O3 at booting and anthesis stages, but the photosynthetic pigment contents in treatment elevated O3 concentration all decreased after anthesis, with a significant decrease of chlorophyll a, chlorophyll b, and chlorophyll (a+b) contents, which indicated that elevated O3 had minor effects on the synthesis of photosynthetic pigments but accelerated their decline process. Different wheat varieties had genetic difference in the responses of flag leaf photosynthetic pigment contents to elevated O3, among which, Yangmai 15 and Jiaxin 002 had better tolerance to ozone stress. The flag leaf chlorophyll a, chlorophyll b, and chlorophyll (a+b) contents at grain-filling stage (about 21 days after anthesis) had a significant positive correlation with the 1000-grain mass.

Taking one-year old sand-cultured Kyoho (Vitis vinifera x Vĩtis labrusca) grapevines as test materials, this paper studied the effects of spraying acetochlor on the grape leaves photosynthetic and fluorescence characteristics and chloroplast ultra-structure. On the 13th day after spraying acetochlor, the net photosynthesis rate and stomatal conductance of upper-node leaves decreased significantly, so as the maximal photochemistry of PSII and the quantum yield of PSII electron transport. The relative variable fluorescence in the J step and K step of the chlorophyll fluorescence transients had an obvious increase, while the performance index (PI(ABS)) had a marked decrease. The damages to the PSII reaction center and oxygen-evolving complex of upper-node leaves were more severe, as compared to middle-node leaves, but the damage degree was alleviated along with treatment time. On the 60th day after spraying acetochlor, the differences in the photosynthetic and chlorophyll fluorescence parameters between upper- and middle-node leaves diminished. The responses of bottom-node leaves appeared later than those of the upper- and middle-node leaves. The damage of PSII reaction center and oxygen-evolving complex, the rise of relative variable fluorescence in the J step and K step, and the decline of PI(ABS) of bottom-node leaves were much greater than those of the upper- and middle-node leaves. On the 60th day after spraying acetochlor, the leaf sugar and starch contents increased, but the pigments in the upper- and middle-node leaves decreased significantly, the chloroplast membrane was impaired, the size of chloroplasts decreased, and the lamellae became fuzzy or the gap between lamellae increased. As a whole, acetochlor could be transmitted to the aboveground part of grapevine, and result in the damage of leaf photosynthetic apparatus and the decrease of PSII activity and photosynthetic rate.

This paper studied the variations of leaf photosynthesis gas exchange, chlorophyll fluorescence, and free amino acid contents of Heyedysarum scoparium under the stress of different concentration NaCl, aimed to understand the effects of salt stress on the leaf physiological characteristics and free amino acid metabolism of the plant. Under mild salt stress, the photo-damage of the leaf photosystem II was avoided via the dissipation of excess excitation energy, and stomatal limitation was the main factor reducing the photosynthesis rate. With the increase of salt stress, the leaf photoprotection was not sufficient to avoid oxidative damage, and thus, the damage to photosystem II happened. Under the stress of 200 mmol NaCl x L(-1), non-stomatal limitation was the main factor responsible for the inhibition of photosynthesis. The accumulation and metabolism of major free amino acids in H. scoparium leaves varied under salt stress. Under mild salt stress, the major free amino acids such as proline, glutamate, aspartate, and alanine had a significant accumulation, but with the further increase of salt stress, the aspartate and alanine contents in H. scoparium leaves decreased, while the synthesis and accumulation of praline increased.

Taking Rumex K-1 leaves as test materials, this paper studied the role of mitochondrial alternative oxidase (AOX) pathway in photoprotection under different light intensities. Under low light intensity (200 micromol x m(-2) x s(-1)), and after treated with salicylhydroxamic acid to inhibit the AOX pathway, the leaf actual photochemical efficiency of PS II, linear electron transport rate of photosynthesis, and photosynthetic O2 evolution rate all decreased significantly while the non-Q(B) reducing reaction center had a significant increase, indicating that under low light, the photoinhibition was aggravated while the scavenging enzymes of reactive oxygen species (ROS) increased, which avoided the over-accumulation of ROS and partially alleviated the photoinhibition of Rumex K-1 leaves. Under high light intensity (800 micromol x m(-2) x s(-1)), the inhibition of AOX pathway caused more severe photoinhibition, and the increased activities of ROS scavenging enzymes were insufficient to prevent the over-accumulation of ROS. This study demonstrated that AOX pathway played an important role in the photoprotection in Rumex K-1 leaves under both high and low light intensities, and the role of AOX pathway in photoprotection under high light could be irreplaceable by the other photoprotection pathways in chloroplast.

A field experiment was conducted to investigate the yield traits, leaf photosynthetic rate, chlorophyll fluorescence parameters, chlorophyll content (Chl), and leaf area index (LAI) of eight new big-spike wheat lines, with multiple-spike cultivar Xinong 979 (Triticum aestivum cv. Xinong 979) as the control. The eight new lines had significantly higher kernel numbers per spike, kernel qualities, and 1000-grain mass but lower spike numbers per unit area, and the lines 2036, 2037, 2038, and 2040 had significantly higher yields than the control. The average net photosynthetic rate (P(n)) of the eight new lines had no significant difference with that of the control, but the PS II maximum energy conversion efficiency, PS II actual photochemical efficiency, photochemical quenching coefficient, and PS II reaction center activity of the lines were higher than those of the control. The leaf Chl of the lines 2037, 2040, 2039, 2038 and 2036 were 17.5%, 19.1%, 15.3%, 13.9%, and 7.9% higher than those of the control, and their LAI was significantly higher than that of the control and declined slowly in late growth period.

By the method of Granier' s thermal dissipation probe, the stem sap flow density of four dominant tree species (Pinus massoniana, Castanopsis chinensis, Schima superba, and Machilus kwangtungensis) in a mixed conifer-broadleaf forest in Dinghushan Reserve of South China was continuously measured in the dry season (November) and wet season (July) in 2010, and the environmental factors including air temperature, relative humidity, and photosynthetically active radiation (PAR) were measured synchronically, aimed to study the characteristics of the stem sap flow of the tree species in response to environmental factors. During the dry and wet seasons, the diurnal changes of the stem sap flow velocity of the tree species all presented a typical single-peak curve, with high values in the daytime and low values in the nighttime. The average and maximum sap flow velocities and the daily sap flow flux of broad-leaved trees (C. chinensis, S. superba, and M. kwangtungensis) were significantly higher than those of coniferous tree (P. massoniana), and the maximum sap flow velocity of P. massoniana, C. valueschinensis, S. superba, and M. kwangtungensis was 29.48, 38.54, 51.67 and 58.32 g H2O x m(-2) x s(-1), respectively. A time lag was observed between the sap flow velocity and the diurnal variations of PAR, vapor pressure deficiency, and air temperature, and there existed significant positive correlations between the sap flow velocity and the three environmental factors. The PAR in wet season and the air temperature in dry season were the leading factors affecting the stem sap flow velocity of the dominant tree species.