Photosynthetic acclimation to light in woody and herbaceous species: a comparison of leaf structure, pigment content and chlorophyll fluorescence characteristics measured in the field

Acclimation of foliage photosynthetic properties occurs with varying time kinetics, but structural, chemical and physiological factors controlling the kinetics of acclimation are poorly understood, especially in field environments. We measured chlorophyll fluorescence characteristics, leaf total carotenoid (Car), chlorophyll (Chl) and nitrogen (N) content and leaf dry mass per area (LMA) along vertical light gradients in natural canopies of the herb species, Inula salicina and Centaurea jacea, and tree species, Populus tremula and Tilia cordata, in the middle of the growing season. Presence of stress was assessed on the basis of night measurements of chlorophyll fluorescence. Our aim was to compare the light acclimation of leaf traits, which respond to light availability at long (LMA and N), medium (Chl a/b ratio, Car/Chl ratio) and short time scales (fluorescence characteristics). We found that light acclimation of nitrogen content per unit leaf area (N(area)), chlorophyll content per unit dry mass (Chl(mass)) and Chl/N ratio were related to modifications in LMA. The maximum PSII quantum yield (F(v) /F(m)) increased with increasing growth irradiance in I. salicina and P. tremula but decreased in T. cordata. Leaf growth irradiance, N content and plant species explained the majority of variability in chlorophyll fluorescence characteristics, up to 90% for steady-state fluorescence yield, while the contribution of leaf total carotenoid content was generally not significant. Chlorophyll fluorescence characteristics did not differ strongly between growth forms, but differed among species within a given growth form. These data highlight that foliage acclimation to light is driven by interactions between traits with varying time kinetics.     

Light and VPD gradients drive foliar nitrogen partitioning and photosynthesis in the canopy of European beech and silver fir

While foliar photosynthetic relationships with light, nitrogen, and water availability have been well described, environmental factors driving vertical gradients of foliar traits within forest canopies are still not well understood. We, therefore, examined how light availability and vapour pressure deficit (VPD) co-determine vertical gradients (between 12 and 42 m and in the understorey) of foliar photosynthetic capacity (Amax), 13C fractionation (∆), specific leaf area (SLA), chlorophyll (Chl), and nitrogen (N) concentrations in canopies of Fagus sylvatica and Abies alba growing in a mixed forest in Switzerland in spring and summer 2017. Both species showed lower Chl/N and lower SLA with higher light availability and VPD at the top canopy. Despite these biochemical and morphological acclimations, Amax during summer remained relatively constant and the photosynthetic N-use efficiency (PNUE) decreased with higher light availability for both species, suggesting suboptimal N allocation within the canopy. ∆ of both species were lower at the canopy top compared to the bottom, indicating high water-use efficiency (WUE). VPD gradients strongly co-determined the vertical distribution of Chl, N, and PNUE in F. sylvatica, suggesting stomatal limitation of photosynthesis in the top canopy, whereas these traits were only related to light availability in A. alba. Lower PNUE in F. sylvatica with higher WUE clearly indicated a trade-off in water vs. N use, limiting foliar acclimation to high light and VPD at the top canopy. Species-specific trade-offs in foliar acclimation to environmental canopy gradients may thus be considered for scaling photosynthesis from leaf to canopy to landscape levels.     

Ecophysiology of exotic and native shrubs in Southern Wisconsin

Summary We compared seasonal trends in photosynthesis of two naturalized exotic shrubs (Rhamnus cathartica and Lonicera X bella) and two native shrubs (Cornus racemosa and Prunus serotina) in open and understory habitats in southern Wisconsin. We examined the relationships between resource availability and leaf photosynthetic performance in these four species. All four species had similar relationships between leaf nitrogen (N) content and photosynthetic rate, but the species differed in absolute leaf N content and therefore in photosynthetic rates. Maximum daily photosynthetic rates of all species were significantly correlated with leaf N content in the open habitat, but not in the understory, where low light availability was the major limitation to photosynthesis. Extended leaf longevity was important in the forest understory because it allowed shrubs to take advantage of high light availability at times when the overstory canopy was leafless. Early leaf emergence was more important than late senescence: from 27% to 35% of the annual carbon gain of P. serotina, R. cathartica, and L. X bella occurred prior to leaf emergence of C. racemosa, the species with the shortest leaf life span. Extended leaf longevity of exotic shrubs may help explain their persistence in the understory habitat, but it contributed relatively less to their annual carbon gain in the open habitat.     

穿透雨减少下锐齿栎叶片光合色素季节动态及其反射光谱响应

通过林地穿透雨排除的方法模拟降雨减少,测定河南宝天曼自然保护区锐齿栎叶片光合色素含量与反射光谱的季节变化,对减雨处理造成的光合色素变化及其反射光谱的变化进行了定量分析,并探讨了水分控制条件下反射光谱对叶片光合色素变化的响应机制.结果表明: 锐齿栎叶片的光合色素含量和色素比率均呈现明显的季节变化.减雨样地与对照样地叶片的光合色素含量和比率在生长季的各个时期存在差异,其中,叶片叶绿素b(Chl b)含量的差异显著,说明Chl b对减雨处理的敏感性最高,叶片类胡萝卜素(Car)含量的差异较小,说明Car对减雨处理的敏感性相对较弱.550 nm处的光谱反射率对色素季节变化的响应最敏感,以其构造的简单比值指数(SR_750,550)与叶片Chl a、Chl b、总Chl和Car含量的正相关关系显著,光化学反射指数(PRI)与叶片Car/Chl的负相关关系显著.550 nm处的光谱反射率对减雨处理造成的色素变化响应最为敏感.SR_750,550对减雨处理造成的叶片Chl a、Chl b和总Chl的含量变化表现敏感(P<0.01),对Chl a/b的变化不敏感.PRI对减雨处理造成的叶片Car/Chl变化表现敏感(P<0.01).     

四种热带雨林树种光合和形态解剖特征对不同生长光强的适应

研究了西双版纳热带雨林2种喜光树种中平树(Macaranga denticulata)、倒樱木(Pnravallaris macrophylla)和2种耐荫树种云南肉豆蔻(Myristica yunnanensis)、金丝李(Garcinia paucinervis)幼苗叶片光合和形态解剖特征对3种不同生长光强(5％、25%和50％相对光强)的适应。研究结果表明,与强光下相比,弱光下生长的4种植物最大净光合速率、光饱和点、光补偿点、暗呼吸速率、叶绿素a／b、叶片和栅栏组织厚度、气孔密度和比叶重都降低,而海绵组织／栅栏组织和叶绿素含量升高。在相同光强下,与2种耐荫树种相比,2种喜光树种有较大的最大净光合速率、暗呼吸速率、气孔密度和较低的叶绿素含量。在不同光强下,4种植物均表现出了对光适应有利的生理和形态解剖可塑性,而喜光树种比耐荫树种有较大的生理和形态可塑性,表明喜光树种具有比耐荫树种对强光有更强的适应能力。4种植物的生理指标的可塑性均大于叶片解剖结构的可塑性。     

生长光强对六个橡胶树品种幼苗光合特性的影响

研究了6个橡胶树品种幼苗(适应1年后)在不同生长光强(100%、50%、25%和5%自然光)下的叶片光合系统对光强和CO2浓度的响应特性。结果表明,6个橡胶树品种对不同的光环境均表现出较强的适应性。在不同生长光强下,橡胶树幼苗叶片的最大光合速率(Pmax)、光补偿点(LCP)、暗呼吸速率(Rd)、磷酸丙糖利用速率(TPU)、最大羧化速率(Vcmax)和最大电子传递速率(Jmax)以及叶绿素含量(Chl)均有显著差异(P<0.05),而光饱和点(LSP)和AQY(表观量子效率)则无显著差异。相同生长光强下,6个橡胶树品种间叶片的最大光合速率(Pmax)、暗呼吸速率(Rd)、磷酸丙糖利用速率(TPU)、最大电子传递速率(Jmax)和叶绿素含量(Chl)有显著差异(P<0.05),其光补偿点(LCP)、最大羧化速率(Vcmax)和表观量子效率(AQY)则无显著差异。综合比较各参数,RRIM600、云研77-4和PR107适宜于相对光强为100%~50%的植胶环境,而云研77-2、GT1和热研523适宜于相对光强为50%~25%的植胶环境。     

Differences in pigment composition, photosynthetic rates and chlorophyll fluorescence images of sun and shade leaves of four tree species.

The differential pigment composition and photosynthetic activity of sun and shade leaves of deciduous (Acer pseudoplatanus, Fagus sylvatica, Tilia cordata) and coniferous (Abies alba) trees was comparatively determined by studying the photosynthetic rates via CO(2) measurements and also by imaging the Chl fluorescence decrease ratio (R(Fd)), which is an in vivo indicator of the net CO(2) assimilation rates. The thicker sun leaves and needles in all tree species were characterized by a lower specific leaf area, lower water content, higher total chlorophyll (Chl) a+b and total carotenoid (Cars) content per leaf area unit, as well as higher values for the ratio Chl a/b compared to the much thinner shade leaves and needles that possess a higher Chl a+b and Cars content on a dry matter basis and higher values for the weight ratio Chls/Cars. Sun leaves and needles exhibited higher rates of maximum net photosynthetic CO(2) assimilation (P(Nmax)) measured at saturating irradiance associated with higher maximum stomatal conductance for water vapor efflux. The differences in photosynthetic activity between sun and shade leaves and needles could also be sensed via imaging the Chl fluorescence decrease ratio R(Fd), since it linearly correlated to the P(Nmax) rates at saturating irradiance. Chl fluorescence imaging not only provided the possibility to screen the differences in P(N) rates between sun and shade leaves, but in addition permitted detection and quantification of the large gradients in photosynthetic rates across the leaf area existing in sun and shade leaves.     

Ecophysiological significance of leaf traits in Cypripedium and Paphiopedilum

There is a close phylogenetic relationship between Paphiopedilum and Cypripedium, but these two genera diverge considerably in terms of their leaf traits. To understand the evolution and the ecophysiological significance of leaf traits, we investigated the leaf traits of three Paphiopedilum species and three Cypripedium species in southwestern China. Cypripedium tibeticum and C. flavum showed a significantly higher light-saturated photosynthetic rate (P(max) ), stomatal conductance (g(s) ), photosynthetic nitrogen utilization efficiency (PNUE) and specific leaf area (SLA), but lower ratio of leaf carbon to nitrogen content (C/N) and leaf construction cost (CC) than Paphiopedilum. These leaf traits of Cypripedium suggest its high resource use efficiency and high growth rate reflecting adaptation to a short growing period and abundant soil nutrients and water in alpine habitats. Conversely, the low P(max) , g(s) , PNUE, SLA and the ratio of chlorophyll a to chlorophyll b (Chl a/b), but high leaf nitrogen investment in light-harvesting component (P(L) ), CC and C/N in Paphiopedilum indicate its adaptation to a low light, nutrient-poor and limited soil water habitats in karst areas. As a sympatric species of Paphiopedilum, although C. lentiginosum retained the phylogenetic leaf traits of Cypripedium, such as high mass-based light-saturated photosynthetic rate (P(max-M) ), g(s) and PNUE, it had some similar leaf traits to those of Paphiopedilum, such as low mesophyll conductance (g(m) ) and Chl a/b, and high P(L) , which reflected an adaptation to the same habitat. Our results show that the evolution of the leaf traits of Paphiopedilum and Cypripedium are shaped by both phylogeny and environment.     

沙木蓼和沙枣对地下水位变化的生理生态响应I.叶片养分、叶绿素、可溶性糖和淀粉的变化

 在甘肃民勤沙生植物园内利用植物蒸腾耗水量观测场,研究了两种优势旱生植物沙木蓼(Atraphaxis frutescens)和沙枣(Elaeagnus angustifolia)叶片中的叶绿素、可溶性糖、淀粉和N、P、K含量等对不同地下水深度(1～3.4 m)的响应。结果表明：1) 1.4 m、2.4 m和3.4 m 3种不同的地下水深度处理,产生了3种差异显著的土壤水分梯度;2) 地下水深度的变化导致了这两种旱生植物叶绿素a、叶绿素b、叶绿素总量、叶绿素a与叶绿素b的比值等的显著变化(p<0.01);3) 地下水深度的增加引起了两种植物叶片可溶性糖含量的升高和淀粉含量的降低;4) 地下水深度的增加引起了两种植物叶片中N、P、K含量的降低;5) 不同的地下水深度引起沙枣和沙木蓼叶绿素a、叶绿素b、叶绿素总量、叶绿素a与叶绿素b的比值、N、P、K含量、可溶性糖和淀粉增加或减少的程度不同。沙枣是非豆科固氮植物,两者的差异是否与固氮作用相关还有待于进一步研究。     

Photosynthetic stimulation under long-term CO2 enrichment and fertilization is sustained across a closed Populus canopy profile (EUROFACE)

The long-term response of leaf photosynthesis to rising CO2 concentrations [CO2] depends on biochemical and morphological feedbacks. Additionally, responses to elevated [CO2] might depend on the nutrient availability and the light environment, affecting the net carbon uptake of a forest stand. After 6 yr of exposure to free-air CO2 enrichment (EUROFACE) during two rotation cycles (with fertilization during the second cycle), profiles of light, leaf characteristics and photosynthetic parameters were measured in the closed canopy of a poplar (Populus) short-rotation coppice. Net photosynthetic rate (A(growth)) was 49% higher in poplars grown in elevated [CO2], independently of the canopy position. Jmax significantly increased (15%), whereas leaf carboxylation capacity (Vcmax), leaf nitrogen (N(a)) and chlorophyll (Chl(a)) were unaffected in elevated [CO2]. Leaf mass per unit area (LMA) increased in the upper canopy. Fertilization created more leaves in the top of the crown. These results suggest that the photosynthetic stimulation by elevated [CO2] in a closed-canopy poplar coppice might be sustained in the long term. The absence of any down-regulation, given a sufficient sink capacity and nutrient availability, provides more carbon for growth and storage in this bioenergy plantation.     

沙木蓼和沙枣对地下水位变化的生理生态响应Ⅰ.叶片养分、叶绿素、可溶性糖和淀粉的变化

在甘肃民勤沙生植物园内利用植物蒸腾耗水量观测场,研究了两种优势旱生植物沙木蓼（Atraphaxis frutescens)和沙棘（Elaeagnus angustifolia)叶片中的叶绿素、可溶性糖,淀粉和N、P、K、含量等对不同地下水深度（1－3．4m）的响应。结果表明：1）1.4m,2.4m和3．4m 3种不同地的地下水深度处理,产生了3种差异显著的土壤水分梯度;2）地下水深度的变化导致了这两种旱生植物叶绿素a、叶绿素b、叶绿素总量、叶绿素a与叶绿素b的比值等的显著变化（P＜0．01）;3）地下水深度的增加引起了两种植物叶片可溶性糖含量的升高和淀粉含量的降低;4）地下水深度的增加引起了两种植物叶片中N、P、K含量的降低;5）不同的地下水深度引起沙棘和沙木蓼叶绿素a、叶绿素b、叶绿素总量、叶绿素a与叶绿素b的比值、N、P、K含量,可溶性糖和淀粉增加或减少的程度不同。沙棘是非豆科固氮植物,两者的差异是否与固氮作用相关还有待于进一步研究。     

CO2 浓度升高对两种沈阳城市森林树种光合特性的影响

利用开顶式气室, 研究了CO2浓度升高条件下城市森林主要树种油松(Pinus tabulaefomis)和银杏(Ginkgo biloba)主要光合特性的变化。结果表明, 整个生长季, CO2浓度升高(700 mmol.mol-1)条件下2树种叶片的净光合速率、可溶性糖、淀粉和可溶性蛋白含量均接近或高于相应对照(自然CO2浓度)值, 但不同树种增加的幅度不同; 而2树种的叶绿素含量和Chl a/Chl b值对CO2浓度升高反应不一, 表现为CO2浓度升高条件下油松的叶绿素含量较对照值高, Chl a/Chl b值降低, 银杏的叶绿素含量为前期升高, 后期降低, Chl a/Chl b值变化与之正好相反, 说明城市森林组成树种对CO2浓度升高的响应具有复杂性。CO2浓度升高条件下, 两树种均未发生光合适应现象。     

Differences in light usage among three fern species of genus <Emphasis Type="Italic">Blechnum</Emphasis> of contrasting ecological breadth in a forest light gradient

In Chilean evergreen temperate forest, fern species of the genus Blechnum occur in diverse microhabitats in a light gradient. We hypothesized that differences in the habitat preferences of three co-occurring Blechnum species would be associated with differences in the magnitude of responses of light capture [chlorophyll (Chl) content] and use (photosynthetic capacity and performance) to light availability. We measured the abundance, chlorophyll content, photosynthetic capacity (A), and photosynthetic performance (chlorophyll fluorescence of photosystems I and II) of juvenile individuals of each species growing in different light levels in the field. While Blechnum magellanicum covers a broad light environments range, B. mochaenum is restricted to shade, and B. penna-marina occupies full sun sites. Despite significant interspecific differences in average total chlorophyll content, this trait did not differ among species along the light gradient. There was significant interspecific variation in both the mean value and the plasticity of Chl a:Chl b ratio and A to light availability. While B. penna-marina showed a flatter reaction norm (lower response) of Chl a:Chl b ratio to light availability than its two congeners, B. mochaenum showed a lower response of A to light availability. B. penna-marina and B. magellanicum individuals from open sites had higher light saturation points of the electron transport rate (ETR) of both photosystems (ETR_LSP I and II) and photochemical quenching (qL and NA) than the shade restricted B. mochaenum. Additionally, non-photochemical quenching values for both photosystems (NPQ and ND) were higher in ferns species occurring in shaded sites. The adjustment of the photosynthetic capacity and performance to light availability appears to be an important mechanism of acclimation in these three Blechnum species that differ in their habitat preferences across a light gradient.     

Effect of fruit load and girdling on leaf photosynthesis in Mangifera indica L

Leaf nitrogen concentration (Nm), mass-to-area ratio, amount of nitrogen per unit leaf area (Na), non-structural carbohydrate concentration (TNCa), maximal rate of carboxylation (Vcmax), light-saturated rate of photosynthetic electron transport (Jmax), dark respiration (Rd), net photosynthetic assimilation (Anet), quantum yield of photosystem II (PhiPSII), and intercellular CO2 concentration (Ci) were measured in Mangifera indica L. leaves on three types of fruit-bearing branches (non-girdled, NG; girdled with high (HFL) and low (LFL) fruit load), experiencing similar light exposure. TNCa, Vcmax/Na, Jmax/Na, Rd/Na, Ci, and the initial quantum yield of photosynthetic electron transport (alpha) were similar in both HFL and NG treatments, but Nm, Na, and photosynthetic capacity parameters (Vcmax and Jmax) were lower in the HFL than in the NG treatment. The strong depressing effect of girdling on leaf nitrogen concentration cannot therefore be attributed to a change in TNCa. By contrast, Na and TNCa were lower and higher, respectively, in the LFL than in the HFL treatment, suggesting that carbohydrate content may become the driving force behind photosynthetic acclimation to changing source-sink relationships, like the ones resulting from the presence of developing fruits. Vcmax/Na and Jmax/Na were lower in the LFL than in the HFL treatment, while Rd/Na, Ci, and alpha were not affected by fruit load. It is concluded that girdling and high fruit load affect photosynthesis permanently by decreasing and increasing, respectively, leaf nitrogen concentration. Fruit load, moreover, may have an additional effect on photosynthetic capacity by affecting the relationship between Vcmax and Jmax, and Na.     

Photosynthetic rates in relation to leaf phosphorus content in pioneer versus climax tropical rainforest trees

In Guyana dense rainforest occurs on intensely weathered acid soils, low in soil phosphorus. To investigate whether low P availability limits photosynthesis of trees growing on these soils more than N does, leaf P and N content, and their relationship with the photosynthetic capacity (A _sat, mol CO₂ m^-2 s^-1) were studied for nine pioneer and climax tree species in a range of light climates. Light environment was described using hemispherical photographs. For both pioneer and climax species, leaf P content (r ²=0.71 and 0.23, respectively) is a more important determinant of A _sat than leaf N content (r ²=0.54 and 0.12, respectively). Pioneer species have a higher leaf P and N content than climax species. At similar P or N content, pioneers have a higher A _sat than climax species. The saplings studied had a relatively high A _sat, considering their low P concentration (15–30 mol P g^-1). All species studied had a constant leaf P and N concentration and photosynthetic capacity across light climates, because specific leaf mass (g m^-2) increased similarly with light availability. This acclimation to a change in light environment makes a possible limitation of A _sat by P or N independent of light environment.     

羊草草原群落6种植物叶片功能特性对氮素添加的响应

 该文比较了羊草草原群落中包括建群种和优势种在内的6种植物,羊草（Leymus chinensis）、西伯利亚羽茅（Achnatherum sibiricum）、大 针茅（Stipa grandis）、 冰草（Agropyron cristatum）、糙隐子草（Cleistogenes squarrosa）和黄囊苔草（Carex korshinskyi）的比叶 面积(Specific leaf area, SLA)、叶片含氮量和叶绿素含量等叶片功能特性( Leaf functional trait)对氮素添加的响应,旨在探讨草原生态 系统中,不同物种对氮素可利用性改变的响应和适应对策。结果表明：随着氮素添加量的增加,物种对光资源的竞争增强,不同物种在光资源 的竞争策略和竞争力间存在着显著的差异。羊草通过提高SLA、单位质量叶片的叶绿素含量和含氮量,使单位面积叶片含氮量和叶绿素含量均呈 线性提高,进而增强了其对光的竞争力。西伯利亚羽茅主要通过提高SLA增加光合总面积,来增强自身的光竞争力。冰草在SLA和单位质量叶片 的叶绿素和氮含量均有一定的可塑性,但对光的竞争力明显弱于羊草和西伯利亚羽茅。大针茅和黄囊苔草对SLA的调节能力较低,加之大针茅 SLA较低,而黄囊苔草处于群落的下层,这两种植物的光竞争力较弱。糙隐子草具有较高的SLA,对单位质量叶片叶绿素和氮含量的调节能力相 对较强,其光竞争力高于黄囊苔草。同时,糙隐子草叶片叶绿素a与叶绿素b的比值沿氮素添加梯度显著降低,进一步证实氮素添加改变了群落 的光环境。     

Differences in photosynthetic activity, chlorophyll and carotenoid levels, and in chlorophyll fluorescence parameters in green sun and shade leaves of Ginkgo and Fagus

The differences in pigment levels and photosynthetic activity of green sun and shade leaves of ginkgo (Ginkgo biloba L.) and beech (Fagus sylvatica L.) are described. Sun leaves of both tree species possessed higher levels in chlorophylls (Chl) and carotenoids on a leaf area basis, higher values for the ratio Chl a/b and lower values for the ratio Chl/carotenoids (a+b)/(x+c) in comparison to shade leaves. The higher photosynthetic rates P(N) of sun leaves (ginkgo 5.4+/-0.9 and beech 8.5+/-2.1 micromol m(-2)s(-1)) were also reflected by higher values for the Chl fluorescence decrease ratios R(F)(d) 690 and R(F)(d) 735. In contrast, the shade leaves had lower P(N) rates (ginkgo 2.4+/-0.3 and beech 1.8+/-1.2 micromol m(-2)s(-1)). In both tree species the stomatal conductance G(s) was significantly higher in sun (range: 70-19 1 mmol m(-2)s(-1)) as compared to shade leaves (range: 5-55 mmol m(-2)s(-1)). In fact, at saturating light conditions there existed a close correlation between G(s) values and P(N) rates. Differences between sun and shade leaves also existed in several other Chl fluorescence ratios (F(v)/F(m), F(v)/F(o), and the stress adaptation index Ap). The results clearly demonstrate that the fan-shaped gymnosperm ginkgo leaves show the same high and low irradiance adaptation response as the angiosperm beech leaves.     

弱光胁迫对玉米产量及光合特性的影响

通过在玉米授粉前0～14d、授粉后1～14d、授粉后15～28d3个时期分别进行遮光处理,研究了弱光胁迫对两个玉米品种费玉3号和泰玉2号产量及光合特性的影响.结果表明:各时期弱光胁迫均使玉米产量降低,其中授粉前0～14d弱光处理的产量降幅最大,费玉3号对弱光胁迫的反应较泰玉2号敏感.弱光胁迫后籽粒灌浆高峰出现时间延迟、灌浆速率慢、积累量小;弱光胁迫开始的时间越早,籽粒达到最大灌浆速率的时间(Tmax)越晚.弱光胁迫期内,玉米Chl(a b)、Chla/b、光合速率(Pn)、光系统Ⅱ最大光化学效率(Fv/Fm)和光系统Ⅱ实际光化学效率(ФPSⅡ)显著下降,Chlb相对含量提高,胞间二氧化碳浓度(Ci)和非光化学淬灭系数(NPQ)则显著上升;胁迫结束后,玉米Chl(a b)、Chla/b、Pn、Fv/Fm、ФPSⅡ、Ci和NPQ逐渐恢复接近自然光照条件(CK)水平,而Chlb相对含量下降.表明非气孔因素是弱光胁迫下玉米光合速率降低的原因之一.     

Acclimation of photosynthetic characteristics of the moss Pleurozium schreberi to among‐habitat and within‐canopy light gradients

Light availability varies strongly among moss habitats and within the moss canopy, and vertical variation in light within the canopy further interacts with the age gradient. The interacting controls by habitat and canopy light gradient and senescence have not been studied extensively. We measured light profiles, chlorophyll (Chl), carotenoid (Car) and nitrogen (N) concentrations, and photosynthetic electron transport capacity (J_max) along habitat and canopy light gradients in the widespread, temperate moss Pleurozium schreberi to separate sources of variation in moss chemical and physiological traits. We hypothesised that this species, like typical feather mosses with both apical and lateral growth, exhibits greater plasticity in the canopy than between habitats due to deeper within‐canopy light gradients. For the among‐habitat light gradient, Chl, Chl/N and Chl/Car ratio increased with decreasing light availability, indicating enhanced light harvesting in lower light and higher capacity for photoprotection in higher light. N and J_max were independent of habitat light availability. Within the upper canopy, until 50–60% above‐canopy light, changes in moss chemistry and photosynthetic characteristics were analogous to patterns observed for the between‐habitat light gradient. In contrast, deeper canopy layers reflected senescence of moss shoots, with pigment and nitrogen concentrations and photosynthetic capacity decreasing with light availability. Thus, variation in chemical and physiological traits within the moss canopy is a balance between acclimation and senescence. This study demonstrates extensive light‐dependent variation in moss photosynthetic traits, but also that between‐habitat and within‐canopy light gradient affects moss physiology and chemistry differently.     

Effects of nitrogen addition on photosynthetic characteristics of Leymus chinensis in the temperate grassland of Nei Mongol,China

Aims The increased atmospheric nitrogen (N) deposition due to human activity and climate change greatly causes grassland ecosystems shifting from being naturally N-limited to N-eutrophic or N-saturated, and further affecting the growth of grass species. The aims of this study are: 1) to evaluate the effects of different N addition levels on morphology and photosynthetic characteristics of Leymus chinensis; 2) to determine the critical N level to facilitate L. chinensis growth.
Methods We conducted a different N addition levels experiment in dominant species in the temperate steppe of Nei Mongol. The aboveground biomass, morphological and leaf physiological traits, pigment contents, chlorophyll a fluorescence parameters and biochemical parameters of L. chinensis were investigated.
Important findings Our results showed that aboveground biomass first increased and then decreased with the increased N, having the highest values at the 10 g N·m^-2·a^?1 treatment, but the 25 g N·m^-2·a^?1 still significantly increased the aboveground biomass relative to 0 g N·m^-2·a^?1. Leymus chinensis accommodate low N situation through allocating less N to carboxylation system and decreasing leaf mass per area (LMA) in order to get more light energy. Moderate N addition captured more light energy through increasing total chlorophyll (Chl) contents and decreasing the ratio of Chl a/b. Moderate N addition increased LMA, carboxylation efficiency, maximum carboxylation rate (V_cmax), maximum electron transport rate (J_max) and decreased J_max/V_cmax, thus allocating more N to carboxylation system to enhance carboxylation capability. Moreover, the photochemical activity of PSII was increased through higher effective quantum yield of PSII photochemistry, electron transport rate and photochemical quenching coefficient. Excessive N addition had negative effects on physiological variables of L. chinensis due to lower carboxylation capability and photochemical activity of PSII, further leading to decreased net photosynthetic rate, whereas increased non-photochemical quenching coefficient and carotenoids played the role in the dissipation of excess excitation energy. Overall, moderate N addition facilitated the photosynthetic characteristics of dominant species, but excessive N addition inhibited photosynthetic characteristics. The most appropriate N addition for the growth of L. chinensis was 5-10 g N·m^-2·a^?1 in the temperate steppe of Nei Mongol, China.