Dark Respiration Rate Research Articles

Photosynthetic Physiology Comparisons between No Tillage and Sod Culture of Citrus Farming in Different Seasons under Various Light Intensities

Sod culture (SC) and no tillage (NT) are modern orchard management systems, and are two different bases for the sustainable development and production of citrus orchards in Taiwan. However, there is no information about the efficiency of either NT or SC on the photosynthetic physiology of farmed citrus under different seasons and varying light intensities. The objective of this study was to clarify the impacts of SC and NT under eco-friendly farming management on the photosynthetic apparatus of an important plantation citrus species in response to varying light intensities over the seasons. The results showed that Rd (dark respiration rate of CO2), Qy (light quantum yield of CO2), LCP (light compensation point), Amax (maximum net assimilation of CO2), and Fv/Fm values of citrus plants under SC were somewhat higher under NT in the same season, particularly in the fall and in winter. As light intensity increased from 200 to 2000 μmol photon m−2 s−1 PPFD, higher Pn (net photosynthesis rate), Gs (stomatal conductance), ETR (electron transport rate), NPQ (non-photochemical quenching), and Fv/Fm (potential quantum efficiency of PSII) values were observed in spring and summer compared to the fall and winter, and increasing NPQ and decreasing Fv/Fm values were observed in all seasons. Positive and significant correlations were shown between the Pn and Gs under NT and SC in all seasons with all light illuminations, whereas significant and negative relationships were observed between the ETR and NPQ under NT in fall and winter at 1200~2000 PPFD. In short, ETR was useful for non-destructive estimations of Pn and NPQ since these indices were significantly and positively correlated with ETR in citrus leaves exposed to 0~1200 PPFD in all seasons and 1200~2000 PPFD in spring, the fall, and winter, providing a quick means to identify the physiological condition of plants under various seasons and tillages. The precise management of photosynthetic parameters such as ETR in response to light irradiances under varied seasons also provides implications for sustainable citrus production for tillage cropping systems in future higher CO2 and potentially wetter or drier environments. The tillages may hold promise for maximizing the economic efficiency of the growth and development of citrus plants grown in the field.

Growth and physiological acclimation to shade in young plants of Adesmia bijuga Phil., a critically endangered species in central Chile

Adesmia bijuga Phil. is an endemic and endangered shrub species of central Chile. Its potential shade intolerance is one of the leading hypotheses for its vigor loss when the species grows beneath closed canopies. The objective of this study was to assess the growth and physiological acclimation to the shade of young plants of A. bijuga. A nursery experiment was established with three light levels based on the interception of photosynthetic active radiation (PAR) (TRT0: control at full sun; TRT60: 60% shaded; TRT90: 90% shaded), and maintained for 71 days during the summer season. Growth and leaf morpho-physiological responses were evaluated at the beginning, at the middle, and at the end of the experiment. The shading treatment increased plant height (H), live crown percentage (Lcrown), and specific leaf area (SLA) compared to the control treatment at full sun. However, light-saturated photosynthetic rate (Amax), dark respiration rate (Rd), and light compensation point (Γi) were higher in TRT60 than in the other treatments, while no differences were found among treatments for the apparent quantum yield (α). At this stage of plant development, our results suggest high acclimation plasticity of A. bijuga to light levels; however, a semi-shade environment (i.e., TRT60) favored a better performance of the species.

Differential effects of acid rain on photosynthetic performance and pigment composition of the critically endangered Acer amplum subsp. catalpifolium

Acer amplum subsp. catalpifolium is a critically endangered, native deciduous broad-leaved tree species mainly distributed in the rainy zone of west China. Acid rain is a frequent phenomenon in this region and its impact on regional forests, especially for susceptible species have major implications on community stability and biodiversity conservation. To understand the basic physiological responses of A. amplum subsp. catalpifolium to acid rain, a simulation experiment spanning 18 months was conducted. The aim is to determine the effects of acidity levels (pH 2.5, 3.5, and 4.5), chemical composition (H2SO4: HNO3 ratio of 7.5:1 and 5:4.1, respectively), and deposition patterns (soil addition and leaf spraying modes) on photosynthetic performance and stress status of A. amplum subsp. catalpifolium The results showed that simulated acid rain can enhance the peak photosynthetic rate (Pn) and stomatal conductance (Cs) in the diurnal variation of A. amplum subsp. catalpifolium under soil addition mode, and it is attributed to the increased net photosynthetic rate at the light saturation point (Amax), net photosynthetic rate at saturating CO2 concentration (Pmax) and various chlorophyll fluorescence parameters (ΦPSII, Fv/Fm, Fv/F0, and qP). On the contrary, the photosynthetic performance of A. amplum subsp. catalpifolium was significantly inhibited by acid rain under leaf spraying mode, with increased dark respiration rate (Rd) and photorespiration rate (Rp). The reduction levels in Amax and Pmax was higher in the nitric based acid rain compared to sulfuric acid dominant acid rain. In general, improved nutrient availability brought about by acid rain on soil promoted the photosynthetic performance of A. amplum subsp. catalpifolium. Meanwhile, acid rain in direct contact with the leaves negatively affects leaf performance and chemical makeup. Therefore, acid rain patterns (such as fog or snow) in direct contact with leaves should be accounted for in the protection of A. amplum subsp. catalpifolium.

Effects of Throughfall Exclusion on Photosynthetic Traits in Mature Japanese Cedar (Cryptomeria japonica (L. f.) D. Don.)

As climate change progresses, it is becoming more crucial to understand how timber species respond to increased drought frequency and severity. Photosynthetic traits in a 40-year-old clonal Japanese cedar (Cryptomeria japonica) plantation were assessed under artificial drought stress using a roof to exclude rainfall and a control with no exclusion. C. japonica is a commercial tree that is native to Japan and has high growth on mesic sites. The maximum carboxylation rate (Vcmax), maximum electron transfer rate (Jmax), and dark respiration rate (Rd) in current-year shoots in the upper canopy were determined from spring to autumn over two growing seasons. In addition, the photosynthetic rate at light saturation (Pmax), stomatal conductance (gs), and intrinsic water use efficiency (WUEi) were measured in the morning and afternoon during the same period. Leaf mass per unit area (LMA) and nitrogen concentration (N) were also measured. The values of Vcmax, Jmax, Rd, N, and LMA did not differ between the two plots. By contrast, significantly lower Pmax and gs and higher WUEi were found in the drought plot, and the reduction in Pmax was accompanied by low gs values. Midday depressions in Pmax and gs were more pronounced in the drought plot relative to the control and were related to higher WUEi. Under drought conditions, mature Japanese cedar experienced little change in photosynthetic capacity, foliar N, or LMA, but they did tend to close the stomata to regulate transpiration, thus avoiding drought-induced damage to the photosynthetic machinery and improving WUEi.

Succinic acid inhibits photosynthesis of Microcystis aeruginosa via damaging PSII oxygen-evolving complex and reaction center.

To elucidate the mechanism of succinic acid (SA) inhibition of Microcystis aeruginosa, the chlorophyll fluorescence transients, photosynthesis, photosynthetic electron transport activity, and gene expression of M. aeruginosa were evaluated under various doses of SA. The results demonstrated that, after treatment with 60 mg L-1 SA for 1 h, the chlorophyll fluorescence transients and related parameters changed significantly, indicating that the function and structure of photosynthetic apparatuses of Microcystis were seriously damaged. The initial quantum efficiency α, maximum net photosynthetic rate Pnmax, dark respiration rate Rd, and gross photosynthetic rate decreased to 57%, 49%, 49%, and 46%, respectively, relative to the control. Furthermore, photosystem II (PSII) activity (H2O→p-BQ) and the electron transport activity of H2O→MV and DPC→MV significantly decreased. Real-time PCR analysis revealed that, following incubation with 60 mg L-1 SA for 24 h, the expression level of core protein genes (psbA, psaB, psbD, and psbO) of the photosynthesis centers photosystem I (PSI) and PSII decreased significantly. However, the transcription of gene nblA encoding phycobilisome degradation protein was elevated. The downregulation of the rbcL gene, which encodes the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), resulted in the suppression of CO2 fixation and assimilation. High concentration (60 mg L-1) of SA resulted in damage to oxygen-evolving complex (OEC) and reaction center of PSII, blocking photosynthetic electron transport, thereby lowering the rate photosynthesis and inhibiting the growth of Microcystis. We concluded that inhibition of photosynthesis is an important mechanism of SA inhibition in M. aeruginosa.

Effects of Foliage Spraying with Sodium Bisulfite on the Photosynthesis of Orychophragmus violaceus

Sulphurous acid derived from sulfur dioxide (SO2) emission leads to the pollution of irrigation water and the inhibition of plant growth. The safe concentration threshold of NaHSO3 in plants should be clarified to promote agricultural production. In this study, Orychophragmus violaceus seedlings were used as experimental materials and five NaHSO3 concentrations (i.e., 0, 1, 2, 5, 10 mmol·L−1) were simultaneously sprayed on the leaf surface of different seedlings separately. Leaf physiology responses under different concentrations were analyzed. The NaHSO3 did not promote photosynthesis in O. violaceus under the 1 and 2 mmol·L−1 treatments. It was conducive to the net photosynthetic rate (PN), photorespiration rate (Rp), chlorophyll content, actual photochemical quantum yield (YII) and photochemical quenching (qP) under the 5 mmol·L−1 treatment. However, quantum yield of regulated energy dissipation (YNPQ) and nonphotochemical quenching (NPQ) were inhibited. Under the 10 mmol·L−1 treatment, PN, chlorophyll content, YII, qP, dark respiration rate (Rd) and electron transport rate (ETR) showed significant decreases, while the photorespiration portion (Sp) significantly increased. Our results demonstrated that NaHSO3 provided a sulfur source for plant growth and interfered with the redox reaction of the plant itself, and its role as a photorespiratory inhibitor might be masked.

Impact of the facultative parasitic weed Rhamphicarpa fistulosa (Hochst.) Benth. on photosynthesis of its host Oryza sativa L.

Rhamphicarpa fistulosa is a facultative root parasitic annual forb, of the family Orobanchaceae that is native to sub-Saharan Africa. Parasitism results in yield reductions by the host plants but it is not known how exactly R. fistulosa affects its host or how the host responds physiologically. In three pot experiments, we investigated whether and when the parasite affects photosynthesis of rice, whether the level of impact was parasite density dependent and explored mechanisms underlying the response of rice photosynthesis to parasitism. Photosynthesis and related parameters were measured at a range of light use intensities. Host photosynthesis was negatively affected while light use efficiency was negatively affected only later on in the growth process. Except for dark respiration rates, which were never affected by parasite infection, suppression of host photosynthesis at light saturation, the initial light-use efficiency, chlorophyll content, specific leaf area and shoot weight were parasite density dependent with a stronger effect for higher parasite densities. Only at 56 days after sowing, the slope of the linear relationship between light adapted quantum efficiency of PSII electron transport (ΦPSII) and the quantum yield of CO2 assimilation (ΦCO2) of infected plants was less than those of un-infected plants. There was a considerable time lag between the parasite’s acquisition of benefits from the association, in terms of growth (previously observed around 42 DAS), and the reduction of host photosynthesis (around 56 DAS). Expression of relative reductions in host growth rates started at the same time as the relative suppression of host photosynthesis. This indicated that R. fistulosa affects host growth by first extracting assimilates and making considerable gains in growth, before impacting host photosynthesis and growth.

The legacy effects of PM2.5 depositon on Nerium Oleander L

Green plants have the capability to retain atmospheric particulate matter (PM) on their leaves, which can effectively reduce PM pollution, especially in the urban settings. Some studies reported that the periodic PM pollution could change plant retaining PM capacity, which, indeed, was the reason of physiological responses. In advancing the previous studies, we selected Nerium oleander L. to measure PM retention on leaf surface in a controlled environment by the following periods: initial pollution period (S1), recovery period (R), and secondary pollution period (S2) for a total of 12 weeks. The experimental design was one elevated pollution treatment (166 μg m−3) and one ambient control (28 μg m−3) with three replications. Results showed that during S2, the total retention decreased by 8.87 μg cm−2, which was about 10.4% significant lower than in S1. During the third week, the ascorbic acid content (ASA) in S1 was 6.71 mg g−1 significantly lower than that in S2 in the treatment. The total chlorophyll (Chl T) of the treatment decreased continuously and significantly by 33.8% in S1, but showed no similar trend in S2. The net photosynthetic rate of the treatment was significantly lower than that of the control, and the plants in the treatment showed a consistently high dark respiration rate than that in the control. The correlations between PM retention and ASA, Chl T and RWC were weaker in S1 than that in S2. In addition, air pollution tolerance index (APTI) showed a significant decline in plant pollution tolerance in the treatment during the third week.

Heating rate modulates the metabolic response of the staghorn coral Acropora cervicornis (Lamarck, 1816)

Corals are relatively stenothermic organisms and highly sensitive to thermal stress. To understand how heating rate modulates the holobiont response to thermal challenge, we compared the effects of acute heat shock and cumulative thermal exposures on Acropora cervicornis from Southeast Florida (26° 06 N, 80° 05 W). In March of 2017, maximum dark-adapted yield of photosystem II (FV/FM), rates of dark respiration (R), and rates of gross photosynthesis (Pg) were measured at temperatures spanning 25–36 °C. Thermal performance curves of each response variable were constructed as a function of temperature and thermal dose (i.e., degree heating minutes). Acute exposure (i.e., instantaneously increasing temperature by between 2.5 and 10 °C) resulted in a more marked decline in physiology despite a lower thermal dose, compared to the cumulative exposure (2.5 °C h−1). Apparent deficits in coral holobiont metabolism were observed as a function of both temperature and thermal dose, but examination of holobiont metabolism in a dose-context revealed more pronounced differences between acute and cumulative exposures. Subtle physiological differences may be more easily identified and better cross-study comparisons of cnidarian thermal tolerance may be achieved by placing temperature exposures in degree heating times. In addition, the ratio of daily Pg:R fell below 1 when temperatures exceeded 32 °C, corroborating prior observations that Pg:R may be a means of identifying physiological deficits in advance of visual signs of dysbiosis, such as bleaching.

Use of rapid light curves to evaluate photosynthetic changes in turfgrasses exposed to low‐light conditions

AbstractShade is a widespread issue for turf areas that reduces turf quality, and the lack of light to drive photosynthetic processes is one major factor responsible for these declines. Maintaining a positive carbon balance is essential for plant survival under low‐light conditions, but large‐scale screening for photosynthetic performance can be a difficult task. Chlorophyll fluorescence rapid light curves (RLC) were used to understand difference in photosynthetic processes of hybrid bermudagrass ‘Tifway’ (Cynodon dactylon (L,) Pers. × C. transvaalensis Burtt Davy) and Japanese lawngrass ‘El Toro’ (Zoysia japonica Steud.) to high‐light (800 µmol m–2 s–1) and low‐light (200 µmol m–2 s–1) treatments in controlled environment studies. Measurement of maximum potential quantum yield (Fv/Fm) did not change over the course of the study but were significantly greater in El Toro. Tifway grown under high‐light treatment had greater maximum photosynthesis, and dark respiration rates compared to El Toro. The RLCs demonstrated that compared to hybrid bermudagrass in the low‐light treatment, Japanese lawngrass was more efficient at harvesting light at lower irradiance levels, but also reached saturation of light harvesting at lower irradiance levels. Differences in rapid light curves among plants grown under high‐light or low‐light treatments may be due to differences in photoacclimation. While rapid light curves should not be seen as a replacement for traditional light response curves based on CO2 flux, they did provide valuable information about acclimation of photosynthetic systems and warrant further testing in real‐world conditions.

Photosynthetic rate and chlorophyll fluorescence of barley exposed to simulated acid rain.

Acid rain is considered one of the most serious plant abiotic stresses. Photosynthesis is the basis of crop growth and development. The effect of acid rain on barley photosynthesis remains unclear. A glasshouse experiment was conducted, and the photosynthetic rate, chlorophyll (Chl) fluorescence, and pigment content of barley were measured in simulated acid rain (SAR) under pH 6.5, 5.5, 4.5, and 3.5. The results showed that net photosynthetic rate, maximal photosynthetic rate, and light saturation point decreased and the light compensation point, and dark respiration rate increased with increasing acidity. The results suggested that photosynthesis in barley plants was inhibited by SAR stress. The Chl content and stomatal conductance declined in parallel with the reduced net photosynthetic rate when barley plants were under SAR stress conditions. This indicated that non-stomatal factors may contribute to reduced photosynthesis under acid rain stress. Acid rain had greater effects on the photosynthesis of the acid rain-sensitive plant Zhepi 33 than on non-sensitive Kunlun 12. A significant difference in parameters such as the maximal fluorescence, variable fluorescence, and active PSII reaction centers was found among the SAR treatments and may be used to evaluate the sensitivity of plants to acid rain stress. The visualization model showed that the photosynthetic reaction centers were inactivated in acid rain stressed barley plants. These findings are valuable for the evaluation of the plant sensitivity to acid rain stress and may be used for the detection and monitoring of acid rain effects on plants in the future.

Morphological development and photosynthetic acclimation of Panax ginseng seedlings to irradiation by light-emitting diodes (LEDs)

To determine the optimal light intensity and enable plants to cope with various environmental stresses in plant factories, the morphological and photosynthetic characteristics of ginseng seedlings, including the secondary metabolites, were investigated under six light intensities: 25, 50, 75, 100, 125, and 150 μmol m−2 s−1. The shoot length increased with lower light intensity up to 75 μmol m−2 s−1, and the leaf area and specific leaf weight were greatest at 100 and 75 μmol m−2 s−1, respectively. Stomata frequency was higher from 100 μmol m−2 s−1 with higher light intensity, and single stomatal pore length also increased at 150 μmol m−2 s−1. Net photosynthetic rate at light saturation and net photosynthetic rate in growth condition increased sequentially up to 100 μmol m−2 s−1 before rapidly decreasing at 150 μmol m−2 s−1. The dark respiration rate and light compensation point were significantly high at 150 μmol m−2 s−1 only. Fv/Fm and chlorophyll content statistically differed from 63 and 84 days after seedling stand, respectively. Thus, the leaves withered to death with higher light intensity. The ginsenoside content in the roots significantly increased according to the light intensity, and the panaxadiol/panaxatriol (PT) ratio tended to decrease as the PT-type ginsenosides increased further. Taken together, the range of 75–100 μmol m−2 s−1 was found to be beneficial for growth, photosynthetic acclimation response, and total accumulated ginsenosides of ginseng seedlings.

Light Intensity Influence on Growth and Photosynthetic Characteristics of Horsfieldia hainanensis

Due to both anthropogenic and natural causes, the number of Horsfieldia hainanensis has been decreasing each year in the Tongza Branch nursery (109.534 525°E, 18.763 516°N) of the Hainan Academy of Forestry, China. Consequently, the protection of H. hainanensis is urgent, as is that of most rare tree species. To develop a more comprehensive understanding of the H. hainanensis growth environment, we took 3-year-old H. hainanensis saplings as the research object. We controlled the light intensity by setting different shade amounts to explore the growth and photosynthetic characteristics of H. hainanensis under different light intensities. We found that shade can promote growth and increase the contents of certain substances. Light transmittance of 44.41% can increase plant height (by 29.545%) and biomass (by 66.676%). Light transmittance of 16.19% can increase the pigment content; Chl increased by 40.864%, Chl a increased by 38.031%, and Chl b increased by 48.412%. Light transmittance of 7.30% can increase the soil plant analysis development (SPAD) value of each part of the leaf; the leaf base increased by 41.000%, the leaf margin increased by 32.574%, the blade tip increased by 49.003%, and the leaf average increased by 40.466%. The specific leaf area can reduce the specific leaf weight. We also found that compared to full light, reducing the light transmittance can increase the total chlorophyll (Chl), chlorophyll A (Chl a), and chlorophyll B (Chl b) contents, and the Chl-SPAD-leaf base, leaf edge, leaf tip, average content, and light-saturated net photosynthetic rate. This can in turn reduce the apparent quantum efficiency (AQY), light compensation point (LCP), and dark respiration rate (Rd). In addition, we found a strong correlation between seven of the photosynthetic pigment indicators (Chl, Chla, Chl b, Chl-SPAD-leaf base, leaf margin, leaf tip, and mean) and the three photosynthesis physiological parameters (AQY, LCP, and Rd). The light transmittance of 44.41% (one layer of shading net) treatment group was conducive to the growth of H. hainanensis and photosynthetic characteristic improvement. Therefore, our light transmittance selection of approximately 44.4% is significant for the natural return of H. hainanensis.

Metabolome and Transcriptome Analyses Reveal the Regulatory Mechanisms of Photosynthesis in Developing Ginkgo biloba Leaves.

Ginkgo (Ginkgo biloba L.) is a deciduous tree species with high timber, medicinal, ecological, ornamental, and scientific values, and is widely cultivated worldwide. However, for such an important tree species, the regulatory mechanisms involved in the photosynthesis of developing leaves remain largely unknown. Here, we observed variations in light response curves (LRCs) and photosynthetic parameters (photosynthetic capacity (Pnmax) and dark respiration rate (Rd)) of leaves across different developmental stages. We found the divergence in the abundance of compounds (such as 3-phospho-d-glyceroyl phosphate, sedoheptulose-1,7-bisphosphate, and malate) involved in photosynthetic carbon metabolism. Additionally, a co-expression network was constructed to reveal 242 correlations between transcription factors (TFs) and photosynthesis-related genes (p < 0.05, |r| > 0.8). We found that the genes involved in the photosynthetic light reaction pathway were regulated by multiple TFs, such as bHLH, WRKY, ARF, IDD, and TFIIIA. Our analysis allowed the identification of candidate genes that most likely regulate photosynthesis, primary carbon metabolism, and plant development and as such, provide a theoretical basis for improving the photosynthetic capacity and yield of ginkgo trees.

Quantifying light response of photosynthesis: addressing the long-standing limitations of non-rectangular hyperbolic model

Light intensity (I) fluctuates rapidly and is the most important environmental factor affecting photosynthesis. Accurate characterization of light-response curve of leaf-scale photosynthesis (PN-I curve) is fundamental for understanding PN-I relations at the whole-plant and ecosystem scales. A robust PN-I model should be accurate in reproducing PN-I curves over light-limited, light-saturated, and photoinhibitory I levels, and ideally returning key quantitative traits defining the curves, including initial slope of increase (&alpha;), dark respiration rate (RD), the maximum net photosynthetic rate (PNmax), and the corresponding saturation intensity (Isat). We need to improve a model reproduction of (1) PN-I responses over low I levels and (2) the widely reported decline of PN at photoinhibitory I levels. Our observation-modelling comparison, shown by the widely used non-rectangular hyperbolic model, led to (1) underestimation of RD, (2) overestimation of PNmax, and (3) failure in reproducing the photoinhibitory response when I surpassed the cultivar-specific Isat. In contrast, our model addressed the above limitations extremely well. The results highlighted the accuracy and robustness of our model, especially in (1) returning key traits defining the curve and (2) reproducing the curve over both low [i.e., 0-50 &mu;mol(photon) m-2 s-1] and photoinhibitory I levels (i.e., beyond Isat).

Three new methods indicate that CO2 concentration affects plant respiration in the range relevant to global change.

Short-term responses of plant dark respiration to carbon dioxide concentration ([CO2]) in the range anticipated in the atmosphere with global change remain controversial, primarily because it is difficult to convincingly eliminate the many possible sources of experimental error in measurements of carbon dioxide or oxygen exchange rates. Plant dark respiration is a major component of the carbon balance of many ecosystems. In seedlings without senescent tissue, the rate of loss of dry mass during darkness indicates the rate of respiration. This method of measuring respiration was used to test for [CO2] effects on respiration in seedlings of three species with relatively large seeds. The time it took respiration to exhaust substrates and cause seedling death in darkness was used as an indicator of respiration rate in four other species with smaller seeds. The third method was measuring rates of CO2 exchange in excised petioles sealed in a cuvette submerged in water to prevent leaks. Petioles were utilized as the plant tissue type with the most reliable rates of respiration, for excised tissue. The rate of loss of dry mass in the dark decreased with increasing [CO2] in the range of 200-800 μmol mol-1 in all three large-seeded species. The seedling survival time in the dark increased with [CO2] in the same concentration range in all four of the smaller-seeded species. Respiration rates of excised petioles of several species also decreased over this [CO2] range. The data provide new evidence that the rate of dark respiration in plant tissue often decreases with increasing [CO2] in the 200-800 μmol mol-1 range.

Rising nutrient nitrogen reverses the impact of temperature on photosynthesis and respiration of a macroalga Caulerpa lentillifera (Ulvophyceae, Caulerpaceae)

Both temperature and nutrient nitrogen are rising in worldwide aquatic ecosystems. To explore their interactive impacts on algal physiology, we measured the growth, cell components, photosynthesis, and dark respiration of a farmed green alga, Caulerpa lentillifera, under a matrix of temperatures (low, 22 °C; high, 27 °C) and nitrogen concentrations (low, 47 μmol L−1; medium, 188 μmol L−1; high, 750 μmol L−1). The relative growth rate (RGR) was less than 1.0% day−1 at low temperature, which was ~ eightfold higher at high temperature, with no significant effect of nitrogen. Pigment contents of chlorophyll a (Chl a) and carotenoids (Car) and soluble protein content increased with increasing nitrogen levels. High temperature reduced Chl a content under lower nitrogen and enhanced Car contents under higher nitrogen, but had a limited effect on proteins. Photosynthetic parameters, i.e., light-utilized efficiency (α) and maximum photosynthetic rate (Pmax), and dark respiration rate (Rd) increased with increasing nitrogen levels at low temperature. High temperature enhanced the α, Pmax, and Rd under low nitrogen, but reduced them under high nitrogen. Moreover, high temperature lowered both superoxide dismutase (SOD) and catalase (CAT) contents, indicating the beneficial effects on metabolism of C. lentillifera and thus the growth. In addition, our results indicate that the temperature-caused effects on photosynthesis and respiration of C. lentillifera are reversed by increased nitrogen levels.

古尔班通古特沙漠白梭梭枝干光合及其影响因素

植物枝干光合（P_g）固定其自身呼吸所释放的CO₂，有效减少植物向大气的CO₂排放量。以古尔班通古特沙漠优势木本植物白梭梭（Haloxylon persicum）为研究对象，利用LI-COR 6400便携式光合仪与特制光合叶室（P-Chamber）相结合，观测白梭梭叶片、不同径级枝干的光响应及光合日变化特征；同时监测环境因子（大气温湿度、光合有效辐射、土壤温度及含水量等）与叶片/枝干性状指标（叶绿素含量、含水量、干物质含量、碳/氮含量等），揭示叶片/枝干光合的主要影响因子；采用破坏性取样，量化个体水平上叶片与枝干的总表面积，阐明枝干光合对植株个体碳平衡的贡献。研究结果显示：（1）白梭梭叶片叶绿素含量是枝干叶绿素含量的12-16倍，各径级枝干叶绿素含量差异不显著；（2）枝干光饱和点低于叶片，枝干不同径级（由粗至细），暗呼吸速率和枝干光合逐渐减小；（3）光合有效辐射、土壤含水量和空气温湿度是影响叶片光合的主要因子，对枝干光合无显著影响；（4）枝干光合可以固定其自身呼吸产生CO₂的73%，最高可达90%，枝干光合固定CO₂约占个体水平固碳量的15.4%。研究结果表明，忽视枝干光合的贡献来预测未来气候变化背景下荒漠生态系统碳过程，可能存在根本性缺陷，并且在估算枝干呼吸时，需要考虑枝干是否存在光合作用，以提高枝干呼吸的准确性。;Stem photosynthesis reassimilates CO₂ that released from their own respiration, which effectively reduces the CO₂ efflux to the atmosphere. In this study, Haloxylon persicum, the dominant woody plant in Gurbantunggut Desert, was selected as the research object. A portable LI-6400 photosynthesis system combined with P-Chamber was used to observe the light response and diurnal photosynthetic characteristics of leaves and stems. The environmental factors, including temperature and humidity, photosynthetically active radiation, soil temperature and water content, and leaf or stem traits (chlorophyll content, water content, dry matter content, carbon or nitrogen content, etc.) were monitored to reveal the main influencing factors of leaf or stem photosynthesis. The destructive sampling was used to quantify the total surface area of leaves and stems to clarify the contribution of stem photosynthesis to individual carbon balance. The results showed that:(1) the chlorophyll content of the leaves was 12-16 times than that of stems in H. persicum, and there was no significant difference in chlorophyll content among different diameter stems. (2) The light saturation point of the stems was lower than that of the leaves, and the dark respiration rate and photosynthesis of different diameter classes (from coarse to fine) of stems gradually decreased. (3) The photosynthetic effective radiation, soil moisture and air temperature and humidity were the main factors affecting leaf photosynthesis, but had no significant effect on stem photosynthesis. There was a strong correlation between stem photosynthesis and stem. (4) Stem photosynthesis fixed 73% of CO₂ produced by its own respiration, and the highest rate reached 90%, photosynthetic CO₂ fixation in stems accounted for about 15.4% of individual level carbon fixation. The results of this study show that there may be a fundamental defect in ignoring the contribution of stem photosynthesis to predict the carbon process of desert ecosystem under the background of future climate change. When estimating the stem respiration, it is necessary to consider whether there is stem photosynthesis to improve the accuracy of branch respiration.

Leaf gas exchange and bean quality fluctuations over the whole canopy vertical profile of Arabic coffee cultivated under elevated CO2

Leaves in different positions respond differently to dynamic fluctuations in light availability, temperature and to multiple environmental stresses. The current hypothesis states that elevated atmospheric CO2 (e[CO2]) can compensate for the negative effects of water scarcity regarding leaf gas exchanges and coffee bean quality traits over the canopy vertical profile, in interactions with light and temperature microclimate during the two final stages of berry development. Responses of Coffea arabica L. were observed in the 5th year of a free air CO2 enrichment experiment (FACE) under water-limited rainfed conditions. The light dependent leaf photosynthesis curves (A/PAR) were modelled for leaves sampled from vertical profile divided into four 50-cm thick layers. e[CO2] significantly increased gross photosynthesis (AmaxGross), the apparent quantum yield efficiency, light compensation point, light saturation point (LSP) and dark respiration rate (Rd). As a specific stage response, considering berry ripening, all parameters calculated from A/PAR were insensitive to leaf position over the vertical profile. Lack of a progressive increase in AmaxGross and LSP was observed over the whole canopy profile in both stages, especially in the two lowest layers, indicating leaf plasticity to light. Negative correlation of Rd to leaf temperature (TL) was observed under e[CO2] in both stages. Under e[CO2], stomatal conductance was also negatively correlated with TL, reducing leaf transpiration and Rd even with increasing TL. This indicated coffee leaf acclimation to elevated temperatures under e[CO2] and water restriction. The e[CO2] attenuation occurred under water restriction, especially in A and water use efficiency, in both stages, with the exception of the lowest two layers. Under e[CO2], coffee produced berries in moderate- and high light level layers, with homogeneous distribution among them, contrasted to the heterogeneous distribution under actual CO2. e[CO2] led to increased caffeine content in the highest layer, with reduction of chlorogenic acid and lipids under moderate light and to raised levels of sugar in the shaded low layer. The ability of coffee to respond to e[CO2] under limited soil water was expressed through the integrated individual leaf capacities to use the available light and water, resulting in final plant investments in new reproductive structures in moderate and high light level layers.

Effects of high temperature on photosynthetic physiological characteristics of strawberry seedlings in greenhouse and construction of stress level.

Strawberry variety 'Benihoppe' was used as the experimental material. The temperature treatments were set at 32 ℃/22 ℃, 35 ℃/25 ℃, 38 ℃/28 ℃ and 41 ℃/31 ℃ (daily maximum temperature/daily minimum temperature), and the stress days lasted for 2, 5, 8 and 11 d, with 28 ℃/18 ℃ as the control. We measured the photosynthetic characteristics, chlorophyll fluorescence characteristics, reactive oxygen species, protective enzyme activity and membrane lipid peroxidation of strawberry under different high temperature treatments. The key indices were extracted by principal component analysis. The high temperature stress index (Z) was defined to divide the high temperature stress grade. The results showed that 1) with the aggravation of high temperature stress and the extension of stress time, chlorophyll a (Chl a), chlorophyll b (Chl b), carotenoid (Car), light saturation point (LSP), maximum net photosynthetic rate (Pmax), apparent quantum efficiency (AQE) and maximum photochemical efficiency (Fv/Fm) decreased, while light compensation point (LCP) and dark respiration rate (Rd) increased. 2) High temperature hindered the energy transfer of thylakoid in PSⅡ center (ΔWOK＞0), and accelerated the reduction rate of PSⅠ terminal electron receptor pool. On the 11th day of the stress, except that under 32 ℃, all other oxygen evolution complexes (OEC) were inactivated. 3) The content of reactive oxygen species (H2O2 Content and O2-· production rate) and malondialdehyde (MDA) increased with the stress days under different high temperature treatments. 4) The protective enzyme activities and soluble protein content increased first and then decreased with stress duration. 5) Based on principal component analysis (PCA) and combined with the difficulty of index acquisition, Chl a, Pmax, Fv/Fm and MDA were extracted as the key indices, and Z value was calculated. Five high temperature stress grades were divided which were normal (0<Z≤1), mild (1<Z≤2), moderate (2<Z≤3), severe (3<Z≤4) and extra severe (4<Z). The results would be helpful for the prevention of strawberry high temperature disaster and the optimization of microclimate environment.