遮阴对三种木兰科幼苗生长和光合特性的影响

为探讨观光木、山白兰和灰木莲三种木兰科植物对不同光环境的光合适应机制,该文以其幼苗为材料,设置透光率分别为100% NS、72.3% NS、48.6% NS、24.9% NS的四种光照处理,测定其光合特性参数、生物量分配比例、叶绿素含量等,研究不同遮阴处理对其生长和光合作用的影响。结果表明:(1)过强或过弱的光照环境限制了幼苗株高及地径的生长,与全光照相比,72.3% NS有利于幼苗的形态生长。(2)随着遮阴程度的增加,观光木、山白兰和灰木莲幼苗的最大光合速率、光补偿点、光饱和点、暗呼吸速率、蒸腾速率逐渐降低,叶绿素含量增加,水分利用效率先升后降。(3)随着光强的减弱,观光木和山白兰地上部分的生物量积累增加,灰木莲的根生物量积累增加。(4)观光木的比叶面积随着遮阴程度的增加而先增后减; 灰木莲的比叶面积显著减小; 山白兰的比叶面积差异不显著; 观光木、山白兰和灰木莲对低光环境响应和适应的差异主要表现在生物量分配比例及叶的形态特征上。综上结果认为,72.3% NS最有利于幼苗的生长,观光木、山白兰和灰木莲在遮阴条件下可以通过降低P_max、LSP、LCP、R_d、T_r来增加叶绿素含量,适当调整生物量分配比例来增大光合能力,在中度遮阴时能增加水分利用效率、株高、地径来增大光合能力。     

淡水驯化对桐花树光合生理特性的影响

以实验地全光照条件下淡水和人工海水培养种植的桐花树（Aegiceras corniculatum）幼苗为材料,采用Li 6400光合测定仪对不同月份桐花树幼苗的光合生理生态特性日动态进行测定,研究了桐花树的光合生理生态特性。结果表明：在7、10月份桐花树的净光合速率日变化呈双峰型,均出现“光合午休”现象。在7月份人工海水组和淡水组的最大净光合速率（P_max）分别为9.97和11.95 μmol·m^-2·s^-1;而10月份的P_max分别为12.2和12.9 μmol·m^-2·s^-1。而且淡水驯化下,桐花树的净光合速率较人工海水组高。由光响应曲线可知,桐花树人工海水组的最大净光合速率（P_max）、光饱和点（LSP）、光补偿点（LCP）和表观量子效率（AQY）分别为7 μmol·m^-2·s^-1,1 477 μmol·m^-2·s^-1,30 μmol·m^-2·s^-1,0.031 3;而淡水组为8.69 μmol·m^-2·s^-1,980 μmol·m^-2·s^-1,40 μmol·m^-2·s^-1,0.011。在所测的生理生态因子中,光合有效辐射和气孔导度是影响桐花树光合作用最为强烈的因子,与桐花树的净光合速率和蒸腾速率均有极显著的相关关系（p<0.01）。试验说明淡水驯化的桐花树对光强的利用范围变窄,但有较高的净光合速率,表明桐花树对淡水环境具有较强的适应性。     

模拟氮沉降条件下木荷幼苗光合特性、生物量与C、N、P分配格局

设置模拟氮沉降的控制试验,以NH4NO3作为外加氮源,设计CK(0kg N hm-2·a-1)、LN(50 kg N hm-2·a-1)、MN(100 kg N hm-2·a-1)、HN(150 kg N hm-2· a-1)4个处理,历时9个月,测定木荷(Schima superba)幼苗的光合特性、生物量和C、N、P含量及其分配格局对氮沉降的响应.结果表明:(1)木荷幼苗的最大净光合速率和光饱和点随着氮处理水平增加呈先增加后减小的特点,在中氮处理下极显著增加(P＜0.01).氮处理降低了幼苗的光补偿点和暗呼吸速率,光补偿点在低氮处理下显著降低(P＜0.05),暗呼吸速率在低中氮处理下极显著降低(P＜0.01),高氮处理下显著降低(P＜0.05).未见氮处理对表观量子效率产生显著影响.(2)氮处理促进了木荷的全株生物量以及各部分生物量的增长.随着氮处理水平的增加,叶重比呈升高的趋势,而根重比和根冠比呈降低的趋势,在高氮处理下叶重比的增加和根重比、根冠比的降低都达到了显著水平(P＜0.05).(3)氮沉降促进各器官N含量的增加,在高氮处理下根和茎中N含量极显著增加(P＜0.01),叶中N含量显著增加(P＜0.05).而各器官C含量随着氮沉降程度的增加呈先增加后降低的趋势,在中氮处理下根和茎中C含量极显著增加(P＜0.01),叶中C含量显著增加(P＜0.05).但各器官P含量变化趋势各不相同,随着氮的增加,根中P含量是呈先增加后降低的趋势,而茎和叶中P含量是呈降低的趋势.氮沉降一定程度上降低了木荷各器官的C/N比值而增加了N/P比值.     

巨桉和天竺桂幼树对不同浓度SO2的光合生理响应

二氧化硫是大气主要污染物之一,可对植物的关键生理过程光合作用产生重要影响。利用密闭环境控制室熏气处理,研究不同浓度(自然状态下浓度、0.5mg·L-1、1.5mg·L-1、3.0mg·L-1)SO2对盆栽巨桉和天竺桂幼树叶绿素含量、光响应曲线、光合特征参数、光合日变化及硫含量的影响。结果表明:(1)SO2胁迫显著减少了巨桉叶绿素a、b含量,且叶绿素a/b值显著降低,而天竺桂在SO2胁迫下叶绿素a、b含量显著增加,叶绿素a/b值无显著影响。(2)SO2胁迫显著抑制了两树种的净光合速率(Pn);在SO2胁迫下巨桉气孔导度(Gs)、胞间CO2浓度(Ci)和蒸腾速率(Tr)显著上升,而天竺桂的Gs和Tr显著被SO2抑制,Ci随SO2浓度的增加先升高后降低。(3)巨桉表观量子效率(AQY)、暗呼吸速率(Rd)、光补偿点(LCP)和光饱和点(LSP)及天竺桂Rd和LCP均随着SO2浓度的增加而先升高后降低,而天竺桂的AQY和LSP逐渐降低。(4)一天中,SO2胁迫显著提高了巨桉Pn、Gs和Tr,而对天竺桂Pn无显著影响,较低浓度SO2胁迫显著促进了天竺桂Gs和Tr,高浓度SO2胁迫则显著抑制其Gs和Tr;SO2胁迫显著抑制了两种植物的Ci。(5)SO2胁迫下,巨桉和天竺桂幼树叶片硫含量均显著增加。研究认为,巨桉对较低浓度的SO2胁迫有一定的适应能力,但对高浓度SO2胁迫的抗性不如天竺桂强,这可能与二者不同的叶片形态及生理特性有关。     

Effect of gibberellic acid on stomatal diffusive resistance and photosynthesis in waterlogged peanut plants

Plants of peanut (Arachis hypogaea L.) were subjected to 7-d and 14-d waterlogging and sprayed with 10 and 100 mg 1^-1 of gibberellic acid (GA₃). Waterlogging decreased the leaf area (A), net photosynthetic rate (P_n), chlorophyll content (Chi) and temporarily the leaf water potential (Ψ_w) and increased stomatal diffusive resistance (r_s) of both leaf surfaces. Application of GA₃ increased A and P_n and significantly decreased the r_s of both leaf surfaces but did not affect Ψ_w or Chl. Thus GA₃ partially alleviated the effects of waterlogging on A, r_s and P_n.     

Caragana korshinskii seedlings maintain positive photosynthesis during short-term,severe drought stress

Seedling performance may determine plant distribution, especially in water-limited environments. Plants of Caragana korshinskii commonly grow in arid and semiarid areas in northwestern China, and endure water shortage in various ways, but little is known about their performance when water shortage occurs at early growth stages. The water relations, photosynthetic activity, chlorophyll (Chl) content and proline accumulation were determined in 1-year-old seedlings growing in a 1:1 mixture of Loess soil and Perlite and subjected to (1) a water deficit for 20 days and (2) kept adequately watered throughout. The water deficit induced low (−6.1 MPa) predawn leaf water potentials (LWP), but did not induce any leaf abscission. Stomatal conductance (g _s), leaf transpiration rate (E), and net photosynthetic rate (P _N) decreased immediately following the imposition of the water deficit, while the maximal photochemical efficiency of photosystem II (PSII) (F_v/F_m) and the effective quantum yield of PSII (Φ_PSII) decreased 15 days later. An early and rapid decrease in g _s, reduced E, increased Chl (a+b) loss, increased the apparent rate of photochemical transport of electrons through PSII (ETR)/P _N, as well as a gradual increase in non-photochemical quenching of fluorescence (NPQ) and proline may have contributed to preventing Φ_PSII from photodamage. C. korshinskii seedlings used a stress-tolerance strategy, with leaf maintenance providing a clear selective advantage, considering the occasional rainfall events during the growing season.     

The responses of photosynthetic rate and stomatal conductance of Fraxinus rhynchophylla to differences in CO2 concentration and soil moisture

The photosynthetic parameters in leaves of three-year-old seedlings of Fraxinus rhynchophylla L. were studied under different soil water conditions and CO₂ concentrations ([CO₂]) with a LI-COR 6400 portable photosynthesis system. The objective was to investigate the response of photosynthesis and stomatal conductance (g _s) to various [CO₂] and soil water conditions, and to understand the adaptability of F. rhynchophylla to such conditions. The results showed that the soil water content (RWC) required to maintain high photosynthetic productivity in F. rhynchophylla was 49.5–84.3%; in this range, net photosynthetic rate (P _N) rose with [CO₂] increasing from 500 to 1,400 μmol mol^?1. Outside this RWC range, P _N decreased significantly. The apparent maximum photosynthetic rate (P _max,c) and carboxylation velocity (V _c) increased with increasing RWC and remained relatively high, when RWC was between 49.5 and 96.2%. CO₂ compensation points and photorespiration rate exhibited a trend opposite to that of P _max,c and V _c, indicating that moderate water stress was beneficial for increasing plant assimilation, decreasing photorespiration, and increasing production of photosynthates. g _s declined significantly with increasing [CO₂] under different water supplies, but the RWC range maintaining high g _s increased. g _s reached its maximum, when RWC was approximately 73% and then decreased with declining RWC. The maximal g _s was found with increasing RWC. Thus, based on photosynthetic characteristics in artificial, vegetation construction in semiarid loess hill and gully area, F. rhynchophylla could be planted in habitats of low soil water content.     

Verification of a threshold concept of ecologically effective precipitation pulse: From plant individuals to ecosystem

In water-limited ecosystems, an ecologically significant rainfall pulse was defined as a rainfall event that altered both soil water status and plant physiological activity. We developed a new threshold concept of an ecologically effective precipitation pulse (EEPP) applicable to both plant individual and ecosystem scales. The concept was tested in a typical steppe on Inner Mongolia plateau. Two EEPPs, single 3-mm rainfall and 5-mm rainfall, were applied to investigate their effects on soil and plant water status, CO₂ assimilation of five species (four C₃ plants and one C₄ plant), whole-plot soil respiration (R_s), and net ecosystem CO₂ exchange (NEE) on 1 June and 28 July 2009, respectively. Both EEPPs increased leaf water potential (Ψ_l) of all the species, which peaked 1–3 days after rainfall pulses. Soil water content (SWC) in two depths (5 cm and 20 cm) significantly increased after the two EEPPs for 1–3 days. Soil water potential (Ψ_s) within 20‐cm soil layer in EEPP treatments significantly differed (p < 0.05) from control. Net assimilation rates (A_net) of all C₃ plants had a slight increase at the next day after two EEPPs, in contrast to the C₄ species. R_s elevated and peaked 1–3 days later after water supply. Ecosystem net CO₂ absorption rate rose to maximum value 3 days after the 5-mm pulse on 28 July, higher than the response to 3-mm pulse on June 1. The grassland turned to net emission of CO₂ after 3-mm pulse on 28 July. The results supported that there was an ecosystem level threshold for EEPP, and the threshold was temporally variable. It also highlighted the necessity of considering the response threshold of EEPP in rainfall manipulative experiment. In addition, effective rainfall amount was more approriate than total rainfall amount in modeling ecosystem carbon balance.     

白刺叶片气孔特征对人工模拟降雨的响应

以荒漠生态系统典型植物白刺(Nitraria tangutorum Bobr)叶片为研究对象,利用数码图像显微镜处理系统,研究了不同人工模拟增雨处理下的白刺叶片气孔密度及形态特征的变化情况。结果表明,荒漠植物固有特征决定了白刺叶片下表皮气孔密度大于上表皮,上表皮、下表皮气孔密度对增雨响应差异不显著(P0.05)。增雨处理上表皮、下表皮气孔密度与对照差异显著(P0.05)。相同增雨季节,50%处理下叶片气孔密度高于100%处理;不同增雨季节,气孔密度对生长季后期增雨响应更明显。白刺叶表皮气孔分布遵循"一细胞间隔(one cell spacing rule)"法则。增雨后叶片上表皮和下表皮气孔长度、宽度均有不同程度的增加,气孔形态特征对100%处理的响应较50%处理更为明显,且生长季后期增雨对叶片气孔形态特征的影响更大。     

干旱胁迫下藜的光合特性研究

通过人工控制水分模拟干旱来研究生长期的藜对干旱胁迫的生理生化反应,以期望为干旱农业的高效生产提供理论依据。以盆栽的藜为材料,用称重控制浇水的方法,研究了干旱胁迫对藜叶片的光合特性。结果表明：干旱胁迫下藜的光合日变化呈双峰型,有“午休”现象（13:00）且受气孔限制;最大净光合速率出现在上午8:00。与正常条件下生长的藜相比,干旱胁迫下藜的光饱和点(LSP)、最大净光合速率(Pn)、表观量子效率(AQY)、二氧化碳饱和点(CSP)和羧化效率(CE)均降低,分别为1 200 μmolphoton·m^-2·s^-1、8.01 μmol CO₂·m^-2·s^-1、0.016 1 μmol CO₂·mol^-1 photons、1 200 μmol CO₂·mol^-1、0.017 6 μmol CO₂·m^-2·s^-1;光补偿点(LCP)、二氧化碳补偿点(CCP)升高,分别达到44.88 μmol photon·m^-2·s^-1、和46 μmol CO₂·mol^-1,干旱使藜的光合能力下降。干旱胁迫下藜的光合能力虽有所下降,但与其它C3植物相比仍具有较强的CO₂同化能力。藜是一种耐旱力较强的植物。     

Do fruit sunburn control measures affect leaf photosynthetic rate and stomatal conductance in ‘Royal Gala’ apple?

A field study was conducted on a 5-year-old orchard of ‘Royal Gala’ apple (Malus domestica Borkh.) in Stellenbosch, South Africa, to investigate whether the measures employed to control sunburn in fruit, viz., evaporative cooling, Surround WP and 20% black shade net affect leaf photosynthetic gas exchange attributes in comparison to untreated control during the 2003/2004 season. Shade net significantly reduced midday leaf net photosynthetic rate (A) compared to evaporative cooling. Furthermore, shade net and Surround WP significantly reduced midday leaf stomatal conductance (g_s) compared to evaporative cooling and control. Evaporative cooling increased light saturated photosynthetic rate by 27 and 24% compared to shade net and Surround WP, respectively. Light compensation point and dark respiration of shaded leaves were about a third of the other treatments and about 50% less than the control leaves, respectively. Shade net down-regulated photosynthetic capacity of the leaves as evidenced by lower maximum rate of carboxylation and light saturated rate of electron transport compared to control leaves. Sunburn control treatments reduced day respiration by 60–70% compared to the control. Response of A and g_s to increasing temperature showed only slight increase in both A and g_s with increasing temperature from 20 to 30 °C. A declined at 35 °C in Surround WP and shade net leaves while it declined at 40 °C in evaporatively cooled and control leaves. Evaporative cooling and control had higher g_s than shade net and Surround WP at all leaf temperatures. In conclusion, shade net down-regulated photosynthetic reactions and Surround WP and shade net reduced leaf g_s and increased the vulnerability of leaf A and g_s to high temperature compared to evaporative cooling and control.     

An integrated diagnostic approach to understand drought tolerance in mulberry (Morus indica L.)

Four popular mulberry cultivars (Morus indica L. cvs.V-1, MR-2, S-36 and K-2) were assessed for drought tolerance with an integration of selective approaches. The potted plants were subjected to two watering treatments for 75 days: control pots were watered up to 100% field capacity (FC) and stressed pots were maintained at 25–30% FC. Net photosynthetic rate (P_n), stomatal conductance (g_s), transpiration rate (E) and instantaneous water use efficiency (WUE_i) were the key parameters to assess photosynthetic gas exchange performance. Drought caused marked down-regulation in leaf gas exchange in all cultivars (cvs) except V-1 which maintained better P_n, g_s, E and higher WUE_i under severe water deficit. All the four cvs also showed differential antioxidative responses under water stress. Higher concentrations of carotenoids, ascorbic acid, glutathione, α-tocopherol and proline were observed in the leaf extracts of V-1, while minimum accumulation of those metabolites was recorded with K-2 and S-36. An endogenous loss of α-tocopherol and higher lipid peroxidation were encountered in K-2, S-36 and MR-2, whereas V-1 showed minimum lipid peroxidation under water deficit regimes. Comparative morpho-anatomical analysis revealed a well-developed root system and a better anatomical architecture in V-1 which could further contribute tolerance during drought stress.     

Growth and gas exchange response to water shortage of a maize crop on different soil types

The effect of water shortage on growth and gas exchange of maize grown on sandy soil (SS) and clay soil was studied. The lower soil water content in the SS during vegetative growth stages did not affect plant height, above-ground biomass, and leaf area index (LAI). LAI reduction was observed on the SS during the reproductive stage due to early leaf senescence. Canopy and leaf gas exchanges, measured by eddy correlation technique and by a portable photosynthetic system, respectively, were affected by water stress and a greater reduction in net photosynthetic rate (A _N) and stomatal conductance (g _s) was observed on SS. Chlorophyll and carotenoids content was not affected by water shortage in either condition. Results support two main conclusions: (1) leaf photosynthetic capacity was unaffected by water stress, and (2) maize effectively endured water shortage during the vegetative growth stage.     

Over-expression of PaSOD in transgenic potato enhances photosynthetic performance under drought

Drought stress enhances the production of superoxide radical (O₂ ^._) and superoxide dismutase catalyses dismutation of it to H₂O₂ and O₂, and hence provides a first line of defense against oxidative stress. Over-expression of a cytosolic copper-zinc superoxide dismutase, cloned from Potentilla atrosanguinea (PaSOD), in potato (Solanum tuberosum ssp. tuberosum L. cv. Kufri Sutlej) resulted in enhanced net photosynthetic rates (P_N) and stomatal conductance (g_s) compared to that in the wild type (WT) plants under control (irrigated) as well as drought stress conditions. Drought stress declined leaf water potential, P_N, g_s, photosystem II activity, and chlorophyll content, but increased proline and O₂ ^._ content more in WT than transgenic potato plants (SS5). The significantly higher SOD activity in SS5 coincided well with lower O₂ ^._ content suggesting its role in maintaining higher g_s and P_N in transgenic potato plants.     

UV-B辐射胁迫对杨桐幼苗生长及光合生理的影响

通过对UV-B辐射胁迫下亚热带典型木本杨桐幼苗的生长及光合生理的研究,探讨植物对于UV-B辐射胁迫的生理响应及适应性机理,进而揭示UV-B辐射变化对亚热带森林树种的影响.实验设置UV-B辐射滤光组、自然光对照组以及辐射增强组,选择亚热带典型树种杨桐(Cleyera japonica Thunb.)幼苗为实验材料.研究结果表明:(1)增强UV-B辐射会降低杨桐幼苗的叶绿素含量,而降低辐射则会显著促进叶绿素的增加,且这种胁迫在时间上具有积累性.(2)增强或降低辐射强度都会抑制杨桐地径的生长,增强辐射会产生更显著的抑制;降低辐射强度会对杨桐幼苗的株高生长产生促进作用,反之,则会抑制其生长.3个测定期数据综合分析显示随着处理时间的加长,这种胁迫作用有减小的趋势.(3)对光响应曲线的分析表明相对于自然光条件下的UV-B辐射,降低其强度对杨桐幼苗光合作用有显著的促进作用,反之则会抑制,不过抑制作用并不显著;对于光合特征参数的分析表明增强或降低UV-B辐射会显著降低杨桐幼苗的光饱和点(LSP)和光补偿点(LcP),而对最大净光合速率(Amax)、表观光合量子效率(AQY)、暗呼吸速率(Rd)影响均不显著,表明辐射胁迫对杨桐幼苗利用光能的效率影响不大,从而也并未对杨桐的光合作用产生显著性的伤害,但是由于森林树种的多年生特性,这种影响将是积累性的或延迟的,UV-B所造成的光合作用或光能利用率的微小变化都可能会积累成长期影响.因此,对森林树种进行长期研究是必要的.     

Photosynthetic response to precipitation/rainfall in predominant tree (<Emphasis Type="Italic">Ulmus pumila</Emphasis>) seedlings in Hunshandak Sandland,China

The responses of gas exchange and chlorophyll fluorescence of field-growing Ulmus pumila seedlings to changes in simulated precipitation were studied in Hunshandak Sandland, China. Leaf water potential (Ψ_wp), net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were significantly increased with enhancement of precipitation from 0 to 20 mm (p<0.01), indicating stomatal limitation of U. pumila seedlings that could be avoided when soil water was abundant. However, P _N changed slightly when precipitation exceeded 20 mm (p>0.05), indicating more precipitation than 20 mm had no significant effects on photosynthesis. Maximum photochemical efficiency of photosystem 2, PS 2 (F_v/F_m) increased from 0.53 to 0.78 when rainfall increased from 0 to 10 mm, and F_v/F_m maintained a steady state level when rainfall was more than 10 mm. Water use efficiency (WUE) decreased significantly (from 78–95 to 23–27 μmol mol⁻¹) with enhancement of rainfalls. P _N showed significant linear correlations with both g _s and Ψ_wp (p<0.0001), which implied that leaf water status influenced gas exchange of U. pumila seedlings. The 20-mm precipitation (soil water content at about 15 %, v/v) might be enough for the growth of elm seedlings. When soil water content (SWC) reached 10 %, down regulation of PS2 photochemical efficiency could be avoided, but stomatal limitation to photosynthesis remained. When SWC exceeded 15 %, stomatal limitation to photosynthesis could be avoided, indicating elm seedlings might tolerate moderate drought.     

A morphophysiological analysis of the effects of drought and shade on <Emphasis Type="Italic">Catalpa bungei</Emphasis> plantlets

The interactive effects of shade and drought on the morphological and physiological traits of Catalpa bungei plantlets were assessed. Seedling growth, biomass, biomass allocation, leaf morphology, chlorophyll (Chl) content and gas-exchange parameters were measured in plants raised for 3 months under three light levels [80% (HI), 50% (MI), 30% (LI)] and two water levels [moisture (M) and drought (D)]. The results showed that shade greatly decreased growth, biomass, leaf area (LA) and Chl a/b; increased specific leaf area (SLA) and Chl content; and reduced photosynthetic rate (P _n). Drought reduced the growth, biomass, LA, SLA, Chl a/b, P _n, stomatal conductance (G _s), transpiration rate (T _r) and intercellular carbon dioxide concentration (C _i) and increased the Chl content. Stomatal closure was an early physiological response to water stress. Light, water and their interaction significantly affected plant traits and their bivariate relationships. The phenotypic plasticity index of light (0.47) was much higher than that of water (0.21), indicating that light was the main driver of the variations observed. Under drought stress, growth, biomass, leaf and stem biomass allocation significantly decreased in the HI and MI environments, whereas no significant difference was observed in growth or biomass parameters under the LI condition. Furthermore, no significant difference was observed in P _n, G _s, or T _r under the LI condition under water stress. Our results showed that shade did not alter the negative effects caused by drought stress in MI but did alleviate the negative effects of the LI condition. In summary, the effect of drought on C. bungei plantlets depends on the irradiance conditions.     

Physiological responses of tagasaste to a progressive drought in its native environment on the Canary Islands

Diurnal courses of gas exchange, chlorophyll fluorescence, shoot water potential (Ψ) and leaf relative water content (RWC_leaf) were recorded in Chamaecytisus proliferus (L. fil.) Link ssp. proliferus var. palmensis (Christ) (tagasaste) growing in natural conditions in the North-West slope of Tenerife, Canary Islands. During the studied period (April–July 2000), the soil relative water content (RWC_soil) progressively decreased, while the air vapour pressure deficit increased. As a consequence a decrease in Ψ and RWC_leaf took place as well as a decrease in stomatal conductance (g_s) and CO₂ assimilation rate (A). These characteristics, typical of an anisohydric plant, allowed this species to endure a mild drought.Photochemical efficiency of PSII (φ_PSII) followed the inverse pattern to that observed for the photosynthetic photon flux density (PPFD), decreasing at midday and recovering during the late afternoon. This recovering at the end of each day, and the constant values of the maximum quantum yield of PSII photochemistry (F_v/F_m) during the studied period, indicate that there was no permanent damage to the photosynthetic apparatus due to mild water stress.     

不同模拟增雨下白刺比叶面积和叶干物质含量的比较

以荒漠生态系统典型植物白刺(Nitraria tangutorum)为研究对象,根据内蒙古磴口多年平均降水量和植物生长规律,设计两个增雨时段(生长季前期与生长季后期),每个增雨时段设置两个增雨梯度(72.5mm/a(50%)、145mm/a(100%)),对天然白刺灌丛进行增雨实验,研究了不同模拟增雨处理下2012年与2013年生长季白刺叶片的比叶面积(SLA)与叶干物质含量(LDMC)的变化。结果表明,增雨处理可以增加白刺叶片的SLA及LDMC,同时期增雨100%处理对SLA及LDMC的影响大于50%处理,但同时期增雨的两个处理之间无显著差异;白刺叶片SLA在生长季前期对水分响应明显,LDMC则在生长季后期对水分反应敏感;相同增雨处理,2012年白刺叶片SLA及LDMC的净增加值高于2013年;SLA与LDMC在2012年呈显著负相关,在2013年虽呈负相关,但相关性不显著。在未来降雨增加的背景下,荒漠植物白刺叶片SLA与LDMC对增雨具有较强的协调适应能力,在不同生长季节可以通过改变不同的叶片性状来适应环境变化。     

盐胁迫对二色补血草光合生理生态特性的影响

以黄河三角洲贝壳堤岛贝壳沙为基质,及该岛上生长的优势草本植物二色补血草幼苗为材料,用不同浓度的NaCl溶液(0,50,100,200,300mmol/L)模拟盐胁迫处理30d,探讨二色补血草光合生理生态特性对盐胁迫的响应特征。结果表明:二色补血草对盐胁迫和光合有效辐射(PAR)具有较强的适应能力,在盐浓度为50～100mmol/L条件下,其净光合速率(Pn)、瞬时水分利用效率(WUE)、表观光能利用效率(LUE)、羧化效率(CE)、光饱和点(LSP)、表观量子效率(AQY)均达到最高值,光补偿点(LCP)最低,表明其在此盐分范围内,利用光的能力较强,光照生态幅最宽。当盐分浓度为300mmol/L时,其Pn、WUE、LUE、CE、LSP和AQY显著下降,LCP升高,Pn、Tr、Gs、WUE、LUE、CE对PAR的响应曲线与对照差异较大,即高盐胁迫加重了二色补血草对光的敏感性;WUE、LUE、CE的最优PAR和盐分范围存在一定的差异,低PAR下有利于光能的利用,中PAR下有利于水分的利用,高PAR下有利于CO2的利用;WUE对盐分的适应范围最大,CE其次,LUE最小。