Changes In Net Photosynthetic Rate Research Articles

Photosynthetic characteristics of Leymus chinensis and Medicago sativa in artificial grassland

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 CO2·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 CO2 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.

The Synergistic Mechanism of Photosynthesis and Antioxidant Metabolism between the Green and White Tissues of Ananas comosus var. bracteatus Chimeric Leaves.

Ananas comosus var. bracteatus (Ac. bracteatus) is a typical leaf-chimeric ornamental plant. The chimeric leaves are composed of central green photosynthetic tissue (GT) and marginal albino tissue (AT). The mosaic existence of GT and AT makes the chimeric leaves an ideal material for the study of the synergistic mechanism of photosynthesis and antioxidant metabolism. The daily changes in net photosynthetic rate (NPR) and stomatal conductance (SCT) of the leaves indicated the typical crassulacean acid metabolism (CAM) characteristic of Ac. bracteatus. Both the GT and AT of chimeric leaves fixed CO2 during the night and released CO2 from malic acid for photosynthesis during the daytime. The malic acid content and NADPH-ME activity of the AT during the night was significantly higher than that of GT, which suggests that the AT may work as a CO2 pool to store CO2 during the night and supply CO2 for photosynthesis in the GT during the daytime. Furthermore, the soluble sugar content (SSC) in the AT was significantly lower than that of GT, while the starch content (SC) of the AT was apparently higher than that of GT, indicating that AT was inefficient in photosynthesis but may function as a photosynthate sink to help the GT maintain high photosynthesis activity. Additionally, the AT maintained peroxide balance by enhancing the non-enzymatic antioxidant system and antioxidant enzyme system to avoid antioxidant damage. The enzyme activities of reductive ascorbic acid (AsA) and the glutathione (GSH) cycle (except DHAR) and superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were enhanced, apparently to make the AT grow normally. This study indicates that, although the AT of the chimeric leaves was inefficient at photosynthesis because of the lack of chlorophyll, it can cooperate with the GT by working as a CO2 supplier and photosynthate store to enhance the photosynthetic ability of GT to help chimeric plants grow well. Additionally, the AT can avoid peroxide damage caused by the lack of chlorophyll by enhancing the activity of the antioxidant system. The AT plays an active role in the normal growth of the chimeric leaves.

Diurnal and Seasonal Variations in the Photosynthetic Characteristics and the Gas Exchange Simulations of Two Rice Cultivars Grown at Ambient and Elevated CO2.

Investigating the diurnal and seasonal variations of plant photosynthetic performance under future atmospheric CO2 conditions is essential for understanding plant adaptation to global change and for estimating parameters of ecophysiological models. In this study, diurnal changes of net photosynthetic rate (Anet), stomatal conductance (gs), and photochemical efficiency of PSII (Fv′/Fm′) were measured in two rice cultivars grown in the open-top-chambers at ambient (∼450 μmol mol–1) and elevated (∼650 μmol mol–1) CO2 concentration [(CO2)] throughout the growing season for 2 years. The results showed that elevated (CO2) greatly increased Anet, especially at jointing stage. This stimulation was acclimated with the advance of growing season and was not affected by either stomatal limitations or Rubisco activity. Model parameters in photosynthesis model (Vcmax, Jmax, and Rd) and two stomatal conductance models (m and g1) varied across growing stages and m and g1 also varied across (CO2) treatments and cultivars, which led to more accurate photosynthesis and stomatal conductance simulations when using these cultivar-, CO2-, and stage- specific parameters. The results in the study suggested that further research is still needed to investigate the dominant factors contributing to the acclimation of photosynthetic capacity under future elevated CO2 conditions. The study also highlighted the need of investigating the impact of other environmental, such as nitrogen and O3, and non-environmental factors, such as additional rice cultivars, on the variations of these parameters in photosynthesis and stomatal conductance models and their further impacts on simulations in large scale carbon and water cycles.

Close relationship between the state of the oxygen evolving complex and rice cold stress tolerance

The results of the present work suggested a relationship between the growth stability and functional/structural parameters associated to the primary photochemistry and oxygen evolving complex (OEC) in tolerant rice plants under suboptimal low temperatures (SLT) stress. This was concluded from the absence of changes in net photosynthetic rate and in fraction of reaction centers to reduce quinone A, and very small changes in P680 efficiency to trap and donate electrons to quinone A and in fraction of active OEC in tolerant plants under cold stress but not in sensitive plants. The SLT stress also induced OEC activity limitations in both genotypes, but in a greater extent in sensitive plants. However, an assay using an artificial electron donor to replace OEC indicated that the P680+ capacity to accept electrons was not altered in both genotypes under SLT stress from the beginning of the stress treatment, suggesting that the OEC structure stability is related to rice SLT tolerance to sustain the photosynthesis. This hypothesis was also supported by the fact that tolerant plants but not sensitive plants did not alter the gene expression and protein content of PsbP under SLT stress, an OEC subunit with a role in stabilizing of OEC structure.

Effects of Long-Term Periodic Submergence on Photosynthesis and Growth of Taxodium distichum and Taxodium ascendens Saplings in the Hydro-Fluctuation Zone of the Three Gorges Reservoir of China.

Responses of bald cypress (Taxodium distichum) and pond cypress (Taxodium ascendens) saplings in photosynthesis and growth to long-term periodic submergence in situ in the hydro-fluctuation zone of the Three Gorges Dam Reservoir (TGDR) were studied. Water treatments of periodic deep submergence (DS) and moderate submergence (MS) in situ were imposed on 2-year-old bald cypress and pond cypress saplings. The effects of periodic submergence on photosynthesis and growth were investigated after 3 years (i.e. 3 cycles) compared to a control (i.e. shallow submergence, abbreviated as SS). Results showed that pond cypress had no significant change in net photosynthetic rate (Pn) in response to periodic moderate and deep submergence in contrast to a significant decrease in Pn of bald cypress under both submergence treatments, when compared to that of SS. Ratios of Chlorophyll a/b and Chlorophylls/Carotenoid of pond cypress were significantly increased in periodic moderate submergence and deep submergence, while bald cypress showed no significant change. Diameter at breast height (DBH) and tree height of both species were significantly reduced along with submergence depth. Relative diameter and height growth rates of the two species were also reduced under deeper submergence. Moreover, bald cypress displayed higher relative diameter growth rate than pond cypress under deep submergence mainly attributed to higher productivity of the larger crown area of bald cypress. When subjected to deep subergence, both species showed significant reduction in primary branch number, while in moderate submergence, bald cypress but not pond cypress showed significant reduction in primary branch number. These results indicate that both bald cypress and pond cypress are suitbale candidates for reforestation in the TGDR region thanks to their submergence tolerance characteristics, but bald cypress can grow better than pond cypress under deep submergence overall.

模拟增温条件下接种AMF对夏蜡梅幼苗生长与光合生理特性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 模拟增温条件下接种AMF对夏蜡梅幼苗生长与光合生理特性的影响 DOI: 10.5846/stxb201501220177 作者: 作者单位: 台州学院生态研究所,台州学院生态研究所,台州学院生态研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（31400423）；浙江省自然科学基金（LQ14C030001）；台州学院生态学浙江省重点学科开放课题（EKD2013-07） Effects of AMF inoculation on growth and photosynthetic physiological characteristics of Sinocalycanthus chinensis under conditions of simulated warming Author: Affiliation: Taizhou University,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:全球变暖已对植物尤其是珍稀濒危植物产生重要影响。AMF对植物应对气候变化具有重要意义，但是在濒危植物应对气候变暖过程中发挥的作用并不清楚。以濒危植物夏蜡梅（Sinocalycanthus chinensis）一年生幼苗为对象，研究人工模拟增温条件下接种AMF对其生长、形态建成、光合生理、抗氧化酶活性和膜脂过氧化程度、营养物质积累和叶绿素相对含量的影响。实验共4个处理：模拟增温条件下添加AMF（AMF+SW）、添加AMF（AMF）、模拟增温（SW）和对照（CK）。结果表明：（1）接种AMF对幼苗株高、叶宽长比、总根长、根平均直径、根尖总数、比根长和比根表面积有显著影响。（2）AMF+SW条件下幼苗光合日进程呈现出明显"双峰"曲线，AMF显著提高叶片日均净光合速率（Pn）；光合有效辐射大于50 μmol m-2 s-1时，AMF+SW和AMF处理的Pn、最大净光合速率Pnmax和呼吸速率Rd显著高于CK；胞间CO2浓度大于100 μmol CO2/mol时，AMF+SW与AMF处理的Pn、AMF+SW处理的初始羧化效率（α）及AMF处理的光合能力（Amax）显著高于CK，而AMF+SW和AMF处理的CO2补偿点均低于CK。（3）AMF处理的叶可溶性糖显著高于其它处理，AMF+SW和AMF处理的叶可溶性蛋白显著高于CK。因此，AMF能显著促进夏蜡梅幼苗的形态建成和光合作用；在模拟增温条件下，接种AMF对夏蜡梅光合生理具有显著影响。 Abstract:The global climate warming is affecting ecosystems, especially endangered plant species whose distribution is mostly restricted to few areas. Arbuscular mycorrhizal fungi (AMF) form symbiotic associations with many plant species, supplying mineral nutrients to their host plants. Sinocalycanthus chinensis is a national second-class protected plant species, distributed in only a few areas in Zhejiang and Anhui provinces in China. Preliminary investigation has revealed higher infection rate of natural populations of S. chinensis by AMF. The role of AMF in S. chinensis under global warming has remained unknown. To reveal the effects of AMF on S. chinensis under the conditions of global climate warming, the pot experiment was conducted with one-year-old S. chinensis seedlings inoculated with AMF (inoculation of rhizosphere soil at a rate of 5%, v/v; soil without AMF was used as control) and temperature increase was simulated by an electric radiant infrared heater (+ 2℃ measured around the leaves; normal temperature was used as control). Growth rate, morphogenesis, photosynthetic physiological characteristics, antioxidant activities, membrane lipid peroxide level, nutrient content of S. chinensis seedlings were compared under four treatments: AMF, simulated warming (SW), both AMF inoculation and simulated warming (AMF + SW), and control (CK). The results showed that: (1) AMF inoculation had a significant positive effect on plant height and average root diameter, and a negative effect on the width-to-length ratio of mature leaves, total root length, total number of root tips, special root length (root length/root biomass), and special root surface area (root surface area/root biomass). Double-factor variance analysis showed that the average root diameter and total number of root tips was significantly correlated with AMF and SW. This showed that symbiotic association between AMF and S. chinensis may modify the nutrient absorption strategy of S. chinensis through modification in root morphology. (2) The diurnal change in net photosynthetic rate (Pn) of leaves in S. chinensis seedlings under AMF + SW treatment had a typical bimodal curve that was determinately regulated by stomatal conductance. AMF affected significantly the daily mean Pn. After fitting the photosynthesis light response using modified models of rectangular hyperbola, we found that Pn in plants with AMF + SW and AMF treatments were distinctly higher than that of CK when light intensity was more than 50 μmol m-2 s-1. The double-factor variance analysis showed that AMF significantly affected the daily mean Pn, maximum net photosynthetic rate, light saturation point (LSP), and dark respiration rate, whereas SW had a significant effect on LSP. Fitting of the CO2 response by using modified models of rectangular hyperbola revealed that Pn in plants under AMF + SW and AMF treatments was significantly higher than that in the CK with increasing the concentration of CO2. Initial carboxylation efficiency under AMF + SW treatment and photosynthetic capacity under AMF treatment were significantly higher than that of the CK. The CO2 compensation point after the treatment by AMF + SW or AMF was significantly lower than that of the CK. (3) The content of soluble sugars in leaves after the treatment with AMF was significantly higher than that in other treatments. The content of soluble proteins in leaves of plants treated with AMF + SW or AMF was distinctly higher than that of the CK. The double-factor variance analysis showed that SW and AMF + SW interaction had significant effect on the content of soluble sugars in leaves, and both AMF and SW had significant effect on the content of soluble proteins in leaves. The results provided the theoretical foundation for conservation and artificial cultivation of S. chinensis under conditions of global climate change. 参考文献 相似文献 引证文献

Physiological response of wheat varieties to elevated atmospheric CO<sub>2</sub> and low water supply levels

In the phytotron experiment, the effect of elevated atmospheric CO2 (EC, 750 μmol mol−1) on the drought tolerance was studied in two winter varieties (Mv Mambo, tolerant; Mv Regiment, moderately tolerant) and in one spring variety of wheat (Lona, sensitive to drought). Changes in net photosynthetic rate (P N), stomatal conductance, transpiration, wateruse efficiency, effective quantum yield of photosystem II, and activities of glutathione reductase (GR), glutathione-Stransferase (GST), guaiacol peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) were monitored during water withdrawal. Drought caused a faster decline of P N at EC, leading to the lower assimilation rates under severe drought compared with ambient CO2 (NC). In the sensitive variety, P N remained high for a longer period at EC. The growth at EC resulted in a more relaxed activation level of the antioxidant enzyme system in all three varieties, with very low activities of GR, GST, APX, and POD. The similar, low values were due to decreases in the varieties which had higher ambient values. A parallel increase of CAT was, however, recorded in two varieties. As the decline in P N was faster at EC under drought but there was no change in the rate of electron transport compared to NC values, a higher level of oxidative stress was induced. This triggered a more pronounced, general response in the antioxidant enzyme system at EC, leading to very high activities of APX, CAT, and GST in all three varieties. The results indicated that EC had generally favourable effects on the development and stress tolerance of plants, although bigger foliage made the plants more prone to the water loss. The relaxation of the defence mechanisms increased potentially the risk of damage due to the higher level of oxidative stress at EC under severe drought compared with NC.

吉林不同生境防风夏季光合特性

PDF HTML阅读 XML下载 导出引用 引用提醒 吉林不同生境防风夏季光合特性 DOI: 10.5846/stxb201208081122 作者: 作者单位: 吉林农业大学,中国科学院东北地理与农业生态研究所,吉林农业大学,吉林农业大学,吉林省和龙市科学技术情报研究所,吉林农业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（31300270）；国家科技支撑计划项目（2011BAI03B01-02）；教育部博士点新教师基金（20112223120004）；吉林省科技发展计划项目（20130522048JH） Photosynthetic characteristics of Saposhnikovia divaricata in different habitats in summer Author: Affiliation: College of Chinese Medicinal Materials,Jilin Agricultural University,Northeast Institute of Geography and Agroecology,Chinese Academy of Sciences,College of Chinese Medicinal Materials,Jilin Agricultural University,College of Chinese Medicinal Materials,Jilin Agricultural University,Helong Institute of Scientific and Technical Information of Jilin Province,College of Chinese Medicinal Materials,Jilin Agricultural University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用LCpro+全自动便携式光合仪同时测定了长春、长岭和白城3个生境防风的光合作用及环境因子，研究不同生境防风净光合速率、蒸腾速率及水分利用效率等日变化特征及其与生态因子之间关系，并采用通径分析法分析各环境因子对防风净光合速率的直接和间接影响，探讨防风的光合生理规律，为进一步研究防风的光合生理提供依据。结果表明，各环境因子之间存在相互作用，在影响防风光合作用的环境因子中，光合有效辐射（PAR）是驱动因子，它的变化驱动了大气温度（Ta）、叶片温度（Tl）变化，Ta升高引起空气密度的变化是午间相对湿度（RH）和大气浓度CO2（Ca）降低的一个重要原因。环境因子中对Pn直接作用由大到小长春为Tl >Ta > PAR >Ca >RH ，长岭为PAR >Tl > RH > Ca >Ta，白城为Ta >Tl >RH > PAR >Ca。长春、长岭PAR与Pn相关系数最大，而白城地区Ca与Pn相关系数最大，说明防风叶片对不同环境因子的反应有所不同。8月份3个地区防风净光合速率日变化均呈双峰型曲线，具有明显的光合"午休"现象。长春、长岭地区防风光合"午休"现象主要由气孔因素引起，白城地区防风光合"午休"现象主要由非气孔因素引起的。3个生境防风的Pn与Gs之间均呈显著的正相关关系，白城的Gs比长春、长岭地区的低44%左右，这是防风为适应高温干旱的环境而形成的生理反应。不同生境土壤含水量间差异显著，白城地区土壤水分含量很低，只有20.35%，仅是长春土壤含水量的56.50%，而空气温度较高，强辐射使气孔叶片蒸腾失水加剧，导致叶片含水量也很低，仅仅为56.60%，高温干旱使防风叶温升高，防风磷酸化、电子传递、酶活性等受到抑制，导致光合速率降低。因此，白城地区长期高温胁迫是限制防风Pn的主要原因。 Abstract:Photosynthesis of Saposhnikovia divaricata (Turcz.) Schischk. and environmental factors were measured by using LCPro+ portable photosynthesis system in Changchun, Changling and Baicheng, the diurnal changes in net photosynthetic rate (Pn), transpiration rate (E) and water use efficiency (WUE) of S. divaricata and their relationships with environmental factors were studied, and direct and indirect effects of environmental factors on net photosynthetic rate were calculated through the path analysis in different habitats in order to discuss photosynthetic physiology rule of S. divaricata . This knowledge could provide basis for further study the photosynthetic physiology of S. divaricata . The results showed that there were significant interactions among environmental factors, variation of photosynthetically active radiation (PAR) triggered the fluctuations of air temperature (Ta) and leaf temperature (TL), and Ta was closely related to the air density, which had significant impacts on the air CO2 concentration (Ca) and relative humidity (RH), the reduce of air density affected by increase of Ta was the one of important causes, which decreased the RH and Ca at noon. Environmental factors driven intrinsically by PAR superposed an integrative effect on Pn. And the responses of the species to the environmental factors were different in different habitats, and the direct effects of environmental factors in three different habitats were of the order: Tl >Ta > PAR >Ca >RH in Changchun, PAR >Tl >RH >Ca >Ta in Changling and Ta >Tl >RH > PAR >Ca in Baicheng. The correlation coefficients between PAR and Pn were the biggest in Changchun and Changling, but Ca and Pn was the biggest in Baicheng. The diurnal changes in Pn of the species in different habitats were similar and could be expressed as two-hump curves, reflecting a significant middy depression at noon. The decrease in Pn during midday was mainly resulted from stomatal limitation in Changchun and Changling, but non-stomatal limitation occurred in Baicheng. There were significant positive correlations between Pn and Gs in three ecological regions, Gs in Baicheng was about 44% lower than in Changchun and Changling, this was a physiological reaction in order to response to high temperature and drought in Baicheng. The soil water content differed significantly in different habitats, it was only 20.35% in Baicheng, and that was 56.50% of that in Changchun, but air temperature in Baicheng was high, leaf water content was only 56.60%, which resulted from leaf strong transpiration and water loss affected by intense radiation. So the net photosynthetic rate decreased because of that the phosphorylation, electron transfer and enzyme activities of S. divaricata were restrained by high leaf temperature. So heat-stress was one of critical factors constraining Pn in Baicheng. 参考文献 相似文献 引证文献

Post-Anthesis Photosynthetic Assimilation and the Changes of Carbon and Nitrogen in Different Varieties of Spring Maize

Dry matters production after anthesis is very important for maize yield.To further clear its role in super high yield con-dition(high density with ample water and fertilizer supply),we compared yield components in three cultivated varieties,including Denghai661(DH661),Zhongdan 909(ZD909) and 970.According to the theory of yield performance,the post-anthesis yield performance parameters were analyzed.The changes of net photosynthetic rate,the contents of chlorophyll,soluble sugar,starch,total C and N were measured in the ear leaf.The results showed that there were significant differences in the yield among three varieties.Varieties with higher yield(DH661 and ZD909) had higher kernel weight per ear,while DH661 had more grains per ear(466.7) and ZD909 had higher 1000-kernel weight(392.7 g).The post-anthesis dry matter production and its partitive ratios in grains were both higher in the two varieties with higher yield.Yield performance analysis showed that the mean leaf area index(mLAI) and leaf area duration(LAD) were significantly and positively correlated with post-anthesis dry matter production and yield.The chlorophyll,total carbon and total nitrogen content decreased slowly and C/N ratio increased slowly in the two varieties with higher yield.The net photosynthetic rate(Pn) was relatively higher in the ear leaves in the whole grain filling stage.The photosynthate not only supplied to kernels but also stored as starch in leaves at the early phase of grain filling.Only when Pn de-clined at late phase of grain filling the accumulated starch began to degrade for the kernel filling.These results indicated that the balance between carbon and nitrogen metabolism,and slowing down the photosynthate decrease in ear leaf are responsible for maintaining higher mLAI and LAD,resulting in higher yield.

Expression of the genes encoding rubisco and rubisco activase in cucumber leaves

Diurnal changes in the gene expressions and activities of Rubisco and Rubisco activase (RCA) in different position of leaves of cucumber were investigated. The results showed the diurnal variations of the mRNA abundance of rbcL, activities of Rubisco and RCA in 4th apical leaf which gave a single-peak curve, which was similar to the Pn curve on a sunny day. However, the mRNA abundance of rbcS and CsRCA showed a double-peak pattern in diurnal changes. The mRNA abundance of rbcL and the activities of Rubisco and RCA were the highest in the 4th and 8th apical leaves, lower in 12th, and the lowest in the 1st leaves. The mRNA abundance of rbcS in 4th to 8th leaves was also found to be the highest, but that in 12th leaves was lower than that in 1st leaves. The mRNA abundance of CsRCA increased successively as leaf position declined. Different position of leaves showed the same changing patterns in Pn as compared to the activity patterns of Rubisco and RCA. These data indicated that the mRNA expression of rbcL and the activities of Rubisco and RCA in cucumber leaves are involved in diurnal changes of net photosynthetic rate. Key words: Photosynthetic rate, gene expression, diurnal variation, leaf-position, Cucumis sativus L.

Effects of Potassium Fertilizer on Diurnal Change of Photosynthesis in Stevia Rebaudiana Bertoni

The effects of potassium fertilizer on diurnal change of photosynthesis in Stevia rebaudiana Bertoni had been studied. Diurnal changes of net photosynthetic rate (Pn) and environmental and physiological traits in leaves of Stevia rebaudiana Bertoni were measured using LI-6400 portable photosynthesis system. The results showed that optimal potassium fertilizer can increased chlorophyll content and improved photosynthesis rate and decreased the chlorophyll a/b ratio. At the same time, midday depression of photosynthesis abated or disappeared.

Diurnal changes in net photosynthetic rate of Pueraria lobata and its impact factors

In order to identify the relationship between diurnal changes in the net photosynthetic rate (Pn) of Pueraria lobata and environmental factors, diurnal changes in the Pn of leaves of two P. lobata cultivars were measured using a CIRAS-1 portable photosynthesis measurement system (PP-Systems, UK). The results show that diurnal changes in Pn of both cultivars could be interpreted as double-peak curves, indicating the occurrence of an obvious midday depression. Further analyses indicate that the correlation between Pn and stomatal conductance was positive and extremely significant (p < 0.01). The correlations of Pn with intercellular CO2 concentration and transpiration rate were positive and significant (p < 0.05), while the correlations of Pn with air and leaf temperatures were negative and significant (p < 0.05). The results indicate that among the factors affecting photosynthetic properties, some can be grouped as stomatal limitations while others are non-stomatal limitations.

Patchy stomatal behavior during midday depression of leaf CO2 exchange in tropical trees

We investigated effects of heterogeneous stomatal behavior on diurnal patterns of leaf gas exchange in 10 tree species. Observations were made in middle and upper canopy layers of potted tropical rainforest trees in a nursery at the Forest Research Institute Malaysia. Measurements were taken from 29 January to 3 February 2010. We measured in situ diurnal changes in net photosynthetic rate and stomatal conductance in three leaves of each species under natural light. In both top-canopy and sub-canopy species, midday depression of net assimilation rate occurred in late morning. Numerical analysis showed that patchy bimodal stomatal behavior occurred only during midday depression, suggesting that the distribution pattern of stomatal apertures (either uniform or non-uniform stomatal behavior) varies flexibly within single days. Direct observation of stomatal aperture using Suzuki's Universal Micro-Printing (SUMP) method demonstrated midday patchy stomatal closure that fits a bimodal pattern in Shorea leprosula Miq., Shorea macrantha Brandis. and Dipterocarpus tempehes V.Sl. Inhibition of net assimilation rate and stomatal conductance appears to be a response to changes in vapor pressure deficit (VPD). Variable stomatal closure with increasing VPD is a mechanism used by a range of species to prevent excess water loss from leaves through evapotranspiration (viz., inhibition of midday leaf gas exchange). Bimodal stomatal closure may occur among adjacent stomata within a single patch, rather than among patches on a single leaf. Our results suggest theoccurrence of patches at several scales within single leaves. Further analysis should consider variable spatial scales in heterogeneous stomatal behavior between and within patches and within single leaves.

Intraspecific variation in sensitivity to ultraviolet-B radiation in endogenous hormones and photosynthetic characteristics of 10 wheat cultivars grown under field conditions

Field studies were conducted to determine the potential of altering endogenous hormones and photosynthetic characteristics and intraspecific variation in sensitivity of 10 wheat ( Triticum aestivum) cultivars (four tolerant, two middle sensitive and four sensitive) to enhanced ultraviolet-B (UV-B, 280–315 nm) radiation under field conditions. The supplemental UV-B radiation was 5.00 kJ m − 2, simulating a depletion of 20% stratospheric ozone. Responses were cultivar-specific. Out of the 10 tested wheat cultivars, six showed significant decrease in IAA content. UV-B radiation significantly increased ZR content in two wheat cultivars and significantly decreased in five cultivars. ABA content of three wheat cultivars was increased significantly, while that of five cultivars was decreased significantly. UV-B radiation significantly increased the stomatal conductance of three cultivars, and significantly decreased that of four cultivars. Intercellular CO 2 concentrations were significantly increased in five cultivars and significantly decreased in one cultivar (Mianyang 20). Transpiration rate of three cultivars significantly increased, while that of three cultivars significantly decreased. UV-B radiation significantly decreased the net photosynthetic rate of six cultivars. Intraspecific differences were found for the different measured parameters. For seven measured parameters, UV-B radiation had significant effects on five wheat cultivars, while no effect on the others. Significant correlations were observed between net photosynthetic rate and stomatal conductance, intercellular CO 2 concentrations and transpiration rate in eight cultivars. UV-B radiation might change stomatal conductance, intercellular CO 2 concentrations and transpiration rate, thus resulting in changes in net photosynthetic rate.

Comparative studies on physiological and biochemical adaptation of Taxodium distichum and Taxodium ascendens seedlings to different soil water regimes

Responses of baldcypress (Taxodium distichum) and pondcypress (Taxodium ascendens) seedlings in leaf gas exchange and root metabolism to a wide range of hydrological regimes were studied. Four water treatments included control (C), mild drought (MD), wet soil (WS) and flooding (FL). Both species showed no significant change in net photosynthetic rate (Pn) in response to flooding in contrast to significant reduction in Pn under mild drought conditions. In baldcypress, Pn was also maintained at control level compared to significant increase of Pn in pondcypress when subjected to the wet soil treatment. In flooding, both species showed significant increase in contents of malate and shikimate in their lateral roots and further in total roots, as compared to control. However, different adaptation to flooding was demonstrated in their taproots in contents of malate and shikimate. Furthermore, baldcypress seedlings showed significant reductions in lateral and total root biomass, in contrast with no significant change in that of pondcypress seedlings in response to flooding. In wet soil, no significant effects were revealed in contents of malate and shikimate in roots (including different root portions) of baldcypress seedlings in contrast to significant increase of their contents in lateral roots of pondcypress seedlings. No significant effects on root biomass were detected in either baldcypress or pondcypress seedlings in response to wet soil. When subjected to mild drought, baldcypress seedlings displayed no significant change in contents of malate and shikimate in roots, whereas pondcypress seedlings exhibited significant reduction in content of shikimate in lateral roots and total roots. In addition, root biomass of baldcypress seedlings showed no significant change, while lateral and total root biomass of pondcypress seedlings demonstrated significant increase when mild drought was imposed. These findings indicate that baldcypress and pondcypress appear to be promising candidates for reforestation in the Three Gorges Reservoir region due to their characteristics of water-tolerance and mild drought endurance. However, pondcypress is more resilient than baldcypress to the continuum of water availability conditions expected in the Three Gorges Reservoir region.

Midday depression of photosynthesis is related with carboxylation efficiency decrease and D1 degradation in bayberry ( Myrica rubra) plants

Diurnal patterns of photosynthesis in two-year-old Myrica rubra young trees under natural conditions were studied by measuring gas exchange, chlorophyll fluorescence parameters and D1 protein. When measured on a clear day, the diurnal changes of net photosynthetic rate ( P n), stomatal conductance ( G s) and apparent quantum yield (AQY) show two daily maxima; the maximum value occurred at about 09:00 h, then declined, and reached the lowest values at about 13:00 h then increased to reach the second maxima at about 15:00 h. However, with the consistent decline of P n and G s in the afternoon, the ratio of intercellular CO 2 concentration ( C i) to atmospheric CO 2 concentration ( C a) increased. In addition, carboxylation efficiency (CE) and RUBP regeneration declined as the afternoon progressed. In the morning, the maximum yield of fluorescence after dark adaptation ( F m) and maximal photochemical efficiency of PSII ( F v/ F m) decreased continuously until it reached its minimum at 13:00 h, while the reverse occurred in the later afternoon. The quantum yield of PSII ( Φ PSII) declined after 09:00 h; in contrast, initial fluorescence ( F o) increased. A decrease in the rate of Q A reduction and an increase in inactive PSII reaction centers was observed as the day progressed. Non-photochemical quenching (qN) and its slow-relaxing (qS) component increased at about midday, while the fast-relaxing component (qF) declined. The amount of inactive PSII centers was significantly enhanced, while F v/ F m, Φ PSII, qS and rate of Q A reduction were significantly reduced by DTT (dithiothreitol), an inhibitor of the xanthophyll cycle. The D1 protein was significantly degraded at 13:00 h relative to that at 09:00 h during the course of the day. These results suggest that stomatal and non-stomatal limitations, which decreased carboxylation and photochemical efficiency, may cause the midday depression; and that non-stomatal limitations may be due to the decrease in RuBPCase activity and degradation of D1 protein, which causes decreased photoprotection at midday.

Midday depression of leaf CO2 exchange within the crown of Dipterocarpus sublamellatus in a lowland dipterocarp forest in Peninsular Malaysia

We observed diurnal and seasonal patterns of leaf-scale gas exchange within the crown of a Dipterocarpus sublamellatus Foxw. tree growing in a lowland dipterocarp forest at Pasoh, Peninsular Malaysia. Observations were carried out nine times over 6 years, from September 2002 to December 2007. Observation periods included both wet and mild-dry periods, and natural and saturated photosynthetic photon flux density (PPFD) light conditions. In situ measurements of the diurnal change in net photosynthetic rate and in stomatal conductance were carried out on canopy leaves of a 40-m-tall D. sublamellatus tree, which was accessed from a canopy corridor. A diurnal change in electron transport rate was observed under saturated PPFD conditions. The maximum net assimilation rate was approximately 10 micromol m(-2) s(-1). There was a clear inhibition of the net assimilation rate coupled with stomatal closure after late morning and this inhibition occurred year-round. Although the electron transport rate decreased alongside this inhibition, it sometimes followed on. Numerical analysis showed that the main factor in the inhibition of the net assimilation rate was patchy bimodal stomatal closure, which occurred in both mild-dry and wet periods. The midday depression occurred year-round, though there are fluctuations in soil moisture during the mild-dry and wet periods. The magnitude of the inhibition was not related to soil water content but was related to vapor pressure deficit (VPD): that is, whether the days were sunny and hot or cloudy and cool. On cloudy, cool days in the wet period, the net photosynthesis was only moderately inhibited, but it still decreased in the afternoon and was coupled with patchy stomatal closure, even in quite moderate VPD, leaf temperature and PPFD conditions. Our results suggest that patchy stomatal closure signaled by the increase in VPD, in transpiration and by circadian rhythms, was the key factor in constraining midday leaf gas exchange of the D. sublamellatus canopy leaves.

Maintenance of a high photosynthetic performance is linked to flooding tolerance in citrus

Citrus trees have been considered as flooding-sensitive although important differences in tolerance among species have been reported. The tolerance to flooding has been linked to optimal photosynthetic performance in other woody plants. To test whether there was a relationship between photosynthetic performance and flooding tolerance, leaf damage, chlorophyll content, net photosynthetic rate, stomatal conductance, the ratio of internal to ambient CO 2 concentration ( C i/ C a), water use efficiency and chlorophyll fluorescence parameters were studied in leaves of three citrus genotypes differing in their tolerance to flooding during continuous substrate flooding and alternate cycles of flooding and recovery. In Cleopatra and Citrumelo genotypes, marked reductions in net photosynthetic rate and stomatal conductance as well as increases in C i/ C a in response to flooding stress were observed although with differences in the magnitude of the variation. In contrast, in Carrizo, a relatively flooding-tolerant genotype, there were no changes in net photosynthetic rate or in C i/ C a and only a slight decrease in stomatal conductance occurred in response to flooding. Significant correlation between net photosynthetic rate and chlorophyll fluorescence parameters during flooding indicated a biochemical impairment of photosynthetic activity. This effect was apparently linked to damage in the PSII light-harvesting complexes induced by flooding and a subsequent effect on PSII to PSI electron flow that may alter the redox status in cells. Such biochemical impairment could lead to an increase in oxidative damage in Cleopatra and Citrumelo. The maintenance of good photosynthetic performance together with mechanisms to adjust electron flow in the photosynthetic apparatus could be linked to flooding tolerance in these woody plants.

Study on the Diurnal Changes of Net Photosynthetic Rate and the Impact Factors of Stevia rebaudiana Bertoni in Autumn

Study on the Diurnal Changes of Net Photosynthetic Rate and the Impact Factors of Stevia rebaudiana Bertoni in Autumn

Photosynthesis responses of endemic shrubs of Taklimakan Desert to adverse temperature, humidity and radiation

Under the native habitat conditions, the seasonal gas exchange characteristics of two natural endemic plant species, Calligonum taklimakanensis B.R. Pan & G.M. Shen and Tamarix taklamakanensis M.T. Liu, which are located in the hinterland of the Taklimakan Desert, are measured and compared by Li-6400 photosynthesis system. The results indicate that temperature (°C), solar radiation (PAR), soil water content (SWC), and other environmental factors have obvious seasonal variations and the gas exchange characteristics of two plants have different changes in different growing seasons. For C. taklimakanensis, both in July and September, its daily changes of net photosynthetic rate tend to be obvious double peak curve, but in July its peak appeared earlier. Besides its maximum net photosynthetic rate (Pmax), apparent quantum efficiency (Φ), range of effective photosynthetic radiation significantly less than that in September. Moreover, its water use efficiency (WUE) in July was also lower than that in September due to the higher transpiration rate (Tr). For T. taklamakanensis, although its daily change of net photosynthetic rate is a single peak curve in September, its peak time has not changed, and except that its WUE is higher in September like C. taklimakanensis, the maximum net photosynthetic rate (Pmax), apparent quantum efficiency (Φ), light saturation point, and range of effective photosynthetic radiation has not changed or slightly declined. That is to say C. taklimakanensis select a season that habitat was better (like September) to progress relative effectively photosynthesis accumulation, in contrast, T. taklamakanensis still keep a relatively stable photosynthesis rate in different growth seasons. The difference of gas exchange characteristics of the two plants in different seasons shows that adaptation strategies of the two plants to extreme conditions in desert are different. Besides, both the higher photosynthetic accumulation rate and the higher water use efficiency in September also indicate that these two endemic desert shrubs possess the abilities and strategies to make the best of limited natural resources.