适度高温下亚热带阔叶树种叶片的光合速率和吸收光能的分配

 利用光合作用测定系统（Li-COR 6400和叶室荧光仪）,测定了亚热带阔叶树种的光合速率和荧光参数,分析了38 ℃适度高温对叶片光合作用 和吸收光能分配的影响。测试树种包括华南亚热带地区常见的阳生性树种木荷（Schima superba）、耐荫树种黄果厚壳桂（Cryptocarya concinna）和中生性树种红锥（Castanopsis hystrix）。适度高温处理均引起 所有树种的光合能力下降,而且木荷和红锥下降的程度比黄果 厚壳桂明显。与25 ℃的对照温度相比,适度高温处理的木荷叶片用于光化学反应所消耗的光能下降,红锥和黄果厚壳桂也有相似的反应,表明 适度高温限制叶片用于光化学反应的吸收光能。无论哪个树种,38 ℃适度高温处理的植物,叶片总吸收光能中额外多余的那部分和处于非活化 状态PSⅡ所吸收的那部分光能都增加,而且黄果厚壳桂比木荷和红锥显著,因此,亚热带阔叶森林的树种对适度高温的响应因种类而异。研究 结果意味着将来气候变化导致温度的上升对演替后期树种黄果厚壳桂的光合过程的限制比演替早期的树种木荷和中生性树种红锥会更严重。     

亚热带森林四种建群树种叶片叶肉导度对适度高温的响应

利用CO2气体交换和叶绿素荧光法,研究了适度高温(38℃)下亚热带森林4种建群树种叶片叶肉导度(gm).结果表明:阳生或早期演替树种荷木叶片gm较中后期演替的中生性或耐荫树种红椎、藜蒴和黄果厚壳桂高(P<0·05).生长在全日光下的叶片gm亦较遮荫的高(P<0·05).温度从25℃升至38℃,4个树种的平均叶肉导度Q10值为(1·59±0·27).gm对温度的响应依赖于植物种类和光环境.由于CO2在水中扩散的Q10值为1·25,gm除受温度影响外,还受到蛋白质的调控.适度高温可引起gm上升,导致叶绿体羧化部位的CO2浓度和羧化速率增高.无论是全日照还是遮荫处理,与荷木相比,适度增温可显著提高红椎、藜蒴和黄果厚壳桂叶绿体羧化速率,说明适度高温对演替中后期树种的演替进程有利.     

Effects of moderate high-temperature stress on photosynthesis in three saplings of the constructive tree species of subtropical forest

During the exposition to moderate high-temperature stress, photosynthetic rates and fluorescence of chlorophyll a were measured with a photosynthetic measurement system (Li-Cor 6400) and leaf chamber fluorometer (Li-Cor6400 LCF), respectively, in leaves of saplings, sun-adapted species (Schima superba), shade-adapted species (Cryptocarya concinna), and in mesophytic plant (Castanopsis hystrix) (42°C). The results showed that moderate high-temperature stress led to a decrease in F_v/F_>m, namely the primary photochemical quantum efficiency, indicating that moderate high-temperature stress causes a partial inhibition of PSII. It also showed that such an effect was more severe in the shade-adapted plant C. concinna than in the sun-adapted species S. superba. However, except for the sun-grown leaves of C. concinna, the moderate high-temperature stress increased the photosynthetic rate of leaves at high light intensity. Simultaneously, less photoinhibition was found to occur under high-light intensity, suggesting that the capacity of resistant-photoinhibition was stimulated by moderate high-temperature stress. The quantum yield of PSII (?_PSII) decreased in the sun-grown leaves of S. superba and C. hystrix but did not show any significant change in leaves of the shade plant C. concinna and shade-grown leaves of sun plant S. superba or the mesophytic plant C. hystrix because they already had a very low ?_PSII under this condition. Moderate high-temperature stress led to a decrease in ?_PSII/?_CO2 ratios, an estimate of the quantum requirement for CO2 assimilation, in the sun plant S. superba and the mesophytic plant C. hystrix because they were associated with the dissipation of a lower fraction of excitation energy. However, no significant changes were found in shade plant C. concinna and in shade-grown leaves of the other examined plants. The effect of moderate high-temperature (42°C) on photosynthesis depends on species and leaf type (sun and shade leaves) in the saplings of subtropical broad-leaved trees.     

Temporal variation in plant-soil feedback controls succession

Soil abiotic and biotic factors play key roles in plant community dynamics. However, little is known about how soil biota influence vegetation changes over time. Here, we show that the effects of soil organisms may depend on both the successional development of ecosystems and on the successional position of the plants involved. In model systems of plants and soils from different successional stages, we observed negative plant–soil feedback for early-successional plant species, neutral feedback for mid-successional species, and positive feedback for late-successional species. The negative feedback of early-successional plants was independent of soil origin, while late-successional plants performed best in late- and worst in early-successional soil. Increased performance of the subordinate, late-successional plants resulted in enhanced plant community diversity. Observed feedback effects were more related to soil biota than to abiotic conditions. Our results show that temporal variations in plant–soil interactions profoundly contribute to plant community assemblage and ecosystem development.     

光强对四种亚热带树苗生长特征影响的比较

鼎湖山亚热带森林优势树种藜蒴、荷木、黄果厚壳桂和马尾松2－3年生树苗,盆栽于16％、40％和100％的自然光下生长16个月．3种阔叶树无论在全自然光还是在弱光下均能较好地存活,遮光下的马尾松则出现不同程度的死亡．全光下的马尾松、黄果厚壳桂树苗的基径和树高生长大于遮光下的树苗．4个树种的侧枝数均随光照的减弱而下降．在不考虑新老叶更新的情况下,全光下的藜蒴、黄果厚壳桂单株叶片数大于弱光下的树苗,而荷木则相反．如果以全光下单株树苗干物质量为100％,那么在相对光照为40％和16％下生长的马尾松、黄果厚壳桂、荷木和藜蒴单株树苗的干物质量分别为57．4％和32．7％、73．8％和62．1％、78．0％和78．6％、93．9％和76．2％．不同光强下的藜蒴、荷木地上部分干物质量的变化不大,地下部分则随光照的减弱而下降,马尾松、黄果厚壳桂无论地上还是地下部分干物质量均随光强的减弱而明显减少．遮光下生长的3个阔叶树种树苗的冠根比（CRR）、叶重比（LWR）、叶面积比（LAR）和比叶面积（SLA）均高于全光下的树苗．马尾松为喜光树种,对阴生环境的适应能力极为有限;黄果厚壳桂为耐阴树种,在全光下仍然比遮光条件下生长较快．     

Response of the photosynthetic apparatus of cotton (Gossypium hirsutum) to the onset of drought stress under field conditions studied by gas-exchange analysis and chlorophyll fluorescence imaging.

The functioning of the photosynthetic apparatus of cotton (Gossypium hirsutum) grown during the onset of water limitation was studied by gas-exchange and chlorophyll fluorescence to better understand the adaptation mechanisms of the photosynthetic apparatus to drought conditions. For this, cotton was grown in the field in Central Asia under well-irrigated and moderately drought-stressed conditions. The light and CO(2) responses of photosynthesis (A(G)), stomatal conductance (g(s)) and various chlorophyll fluorescence parameters were determined simultaneously. Furthermore, chlorophyll fluorescence images were taken from leaves to study the spatial pattern of photosystem II (PSII) efficiency and non-photochemical quenching parameters. Under low and moderate light intensity, the onset of drought stress caused an increase in the operating quantum efficiency of PSII photochemistry (varphi(PSII)) which indicated increased photorespiration since photosynthesis was hardly affected by water limitation. The increase in varphi(PSII) was caused by an increase of the efficiency of open PSII reaction centers (F(v)'/F(m)') and by a decrease of the basal non-photochemical quenching (varphi(NO)). Using a chlorophyll fluorescence imaging system a low spatial heterogeneity of varphi(PSII) was revealed under both irrigation treatments. The increased rate of photorespiration in plants during the onset of drought stress can be seen as an acclimation process to avoid an over-excitation of PSII under more severe drought conditions.     

Low temperature enhances photosynthetic down-regulation in French bean (Phaseolus vulgaris L.) plants

The mechanisms of photosynthetic adaptation to different combinations of temperature and irradiance during growth, and especially the consequences of exposure to high light (2000 micro mol m(-2) s(-1) PPFD) for 5 min, simulating natural sunflecks, was studied in bean plants (Phaseolus vulgaris L.). A protocol using only short (3 min) dark pre-treatment was introduced to maximize the amount of replication possible in studies of chlorophyll fluorescence. High light at low temperature (10 degrees C) significantly down-regulated photosynthetic electron transport capacity [as measured by the efficiency of photosystem II (PSII)], with the protective acclimation allowing the simulated sunflecks to be used more effectively for photosynthesis by plants grown in low light. The greater energy dissipation by thermal processes (lower F(v)'/F(m)' ratio) at low temperature was related to increased xanthophyll de-epoxidation and to the fact that photosynthetic carbon fixation was more limiting at low than at high temperatures. A key objective was to investigate the role of photorespiration in acclimation to irradiance and temperature by comparing the effect of normal (21 kPa) and low (1.5 kPa) O(2) concentrations. Low [O(2)] decreased F(v)/F(m) and the efficiency of PSII (Phi(PSII)), related to greater PSII down-regulation in cold pre-treated plants, but minimized further inhibition by the mild 'sunfleck' treatment used. Results support the hypothesis that photorespiration provides a 'safety-valve' for excess energy.     

Regulation of Light Energy Utilization and Distribution of Photosynthesis in Five Subtropical Woody Plants

The adaptations and responses of photosynthesis to long- and short-term growth light gradient treatments were investigated in five subtropical forest plants, namely Pinus massoniana Lamb., Schima superba Gardn. et Champ., Castanopsis flssa （Champ. ex Benth.） Rehd. et Wils., Acmena acuminatissima （BI.） Merr et Perry, and Cryptocarya concinna Hance. With diurnal changes in sunlight and air temperature, the de-epoxidation state and lutein content in the five woody plants under three light Intensities first increased and then decreased during the day. However, maximal photochemical efficiency （FvFm; where Fm is the maximum fluorescence yield and Fv Is variable fluorescence） and the photochemical quantum yields of photosystem （PS）Ⅱ （φPSⅡ） of the species examined changed in the opposite manner, with those in plants grown under 100% natural light changing the most. After long-term treatment （21 months）, anti-oxidant capacity （1,1-diphenyl-2-picrylhydrazyl radical （DPPH.）-scavenging capacity） and utilization of excitation energy showed differences in modulation by different light intensities. It was shown that A. acuminatissima and C. concinna, as dominant species in the late succession stage of a subtropical forest in Dinghu mountain, South China, were better able to adapt to different light environments. However, P. massonlana, the pioneer species of this forest, exhibited less adaptation to low light intensity and was definitely eliminated by the forest succession process.     

Changes in leaf nutrient traits and photosynthesis of four tree species: effects of elevated [CO2], N fertilization and canopy positions

Aims Leaf traits of trees exposed to elevated [CO₂] in association with other environmental factors are poorly understood in tropical and subtropical regions. Our goal was to investigate the impacts of elevated [CO₂] and N fertilization on leaf traits in southern China.Methods Four tree species, Schima superba Gardn. et Champ. (S. superba), Ormosia pinnata (Lour.) Merr (O. pinnata), Castanopsis hystrix AC. DC. (C. hystrix) and Acmena acuminatissima (Blume) Merr. et Perry (A. acuminatissima) were studied in a factorial combination of atmospheric [CO₂] (ambient at ~390 μmol mol ? 1 and elevated [CO₂] at ~700 μmol mol^-1) and N fertilization (ambient and ambient + 100 kg N ha^-1 yr^-1) in open-top chambers in southern China for 5 years. Leaf mass per unit leaf area (LMA), leaf nutrient concentration and photosynthesis (A sat) were measured.Important findings Results indicated that leaf traits and photosynthesis were affected differently by elevated [CO₂] and N fertilization among species. Elevated [CO₂] decreased LMA in all species, while N fertilization did not affect LMA. Leaf mass-based N concentration (N M) was significantly greater in O. pinnata and C. hystrix grown in elevated [CO₂] but was lower in S. superba. Leaf mass-based P concentration (P M) was significantly greater in C. hystrix and A. acuminatissima exposed to elevated [CO₂] but was lower in S. superba. N fertilization significantly increased P M in O. pinnata but decreased P M in S. superba. Photosynthetic stimulation in O. pinnata, C. hystrix and A. acuminatissima was sustained after 5 years of CO₂ fumigation. N fertilization did not modify the effects of elevated [CO₂] on photosynthesis. Leaf traits (N M, N A, P M, P A) and light-saturated photosynthesis were decreased from the upper to lower canopy. Canopy position did not alter the responses of leaf traits and photosynthesis to elevated [CO₂]. Results suggest that photosynthetic stimulation by elevated [CO₂] in native species in subtropical regions may be sustained in the long term.     

Landslide-facilitated species diversity in a beech-dominant forest

To evaluate the extent to which landslides affect community dynamics and consequent species diversity in a beech-dominated forest, differences in the composition and size structure of tree species were compared between landslide and adjacent stable (control) stands. Demography and changes in size were compared between the two stands over a 5-year period about 60 years after a landslide. In the control stand, replacement occurred even amongst late-successional species, with beech (Fagus crenata)—the most dominant species—increasing in relative abundance. In the landslide stand, very few large individuals of late-successional species occurred, whereas large individuals of early-successional species occurred only in the landslide stand. The traits indicate that the landslide strongly facilitated species diversity, not only by reducing the dominance of late-successional species, but also by promoting recruitment of early-successional species. However, new recruitment of early-successional species was inhibited in the landslide stand, although we observed succeeding regeneration and subsequent population growth of late-successional species there. As a result, the relative dominance of late-successional species increased with succession after the landslide, thus decreasing future species diversity. In beech-dominant forest landscapes in Japan that include communities with different developmental stages, the mosaic of serial stages may facilitate species diversity after a landslide.     

Photosynthesis, photoprotection, and growth of shade-tolerant tropical tree seedlings under full sunlight

High solar radiation in the tropics is known to cause transient reduction in photosystem II (PSII) efficiency and CO(2) assimilation in sun-exposed leaves, but little is known how these responses affect the actual growth performance of tropical plants. The present study addresses this question. Seedlings of five woody neotropical forest species were cultivated under full sunlight and shaded conditions. In full sunlight, strong photoinhibition of PSII at midday was documented for the late-successional tree species Ormosia macrocalyx and Tetragastris panamensis and the understory/forest gap species, Piper reticulatum. In leaves of O. macrocalyx, PSII inhibition was accompanied by substantial midday depression of net CO(2) assimilation. Leaves of all species had increased pools of violaxanthin-cycle pigments. Other features of photoacclimation, such as increased Chl a/b ratio and contents of lutein, β-carotene and tocopherol varied. High light caused strong increase of tocopherol in leaves of T. panamensis and another late-successional species, Virola surinamensis. O. macrocalyx had low contents of tocopherol and UV-absorbing substances. Under full sunlight, biomass accumulation was not reduced in seedlings of T. panamensis, P. reticulatum, and V. surinamensis, but O. macrocalyx exhibited substantial growth inhibition. In the highly shade-tolerant understory species Psychotria marginata, full sunlight caused strongly reduced growth of most individuals. However, some plants showed relatively high growth rates under full sun approaching those of seedlings at 40?% ambient irradiance. It is concluded that shade-tolerant tropical tree seedlings can achieve efficient photoacclimation and high growth rates in full sunlight.     

Changes in the redox potential of primary and secondary electron-accepting quinones in photosystem II confer increased resistance to photoinhibition in low-temperature-acclimated Arabidopsis

Exposure of control (non-hardened) Arabidopsis leaves for 2 h at high irradiance at 5 degrees C resulted in a 55% decrease in photosystem II (PSII) photochemical efficiency as indicated by F(v)/F(m). In contrast, cold-acclimated leaves exposed to the same conditions showed only a 22% decrease in F(v)/F(m). Thermoluminescence was used to assess the possible role(s) of PSII recombination events in this differential resistance to photoinhibition. Thermoluminescence measurements of PSII revealed that S(2)Q(A)(-) recombination was shifted to higher temperatures, whereas the characteristic temperature of the S(2)Q(B)(-) recombination was shifted to lower temperatures in cold-acclimated plants. These shifts in recombination temperatures indicate higher activation energy for the S(2)Q(A)(-) redox pair and lower activation energy for the S(2)Q(B)(-) redox pair. This results in an increase in the free-energy gap between P680(+)Q(A)(-) and P680(+)Pheo(-) and a narrowing of the free energy gap between primary and secondary electron-accepting quinones in PSII electron acceptors. We propose that these effects result in an increased population of reduced primary electron-accepting quinone in PSII, facilitating non-radiative P680(+)Q(A)(-) radical pair recombination. Enhanced reaction center quenching was confirmed using in vivo chlorophyll fluorescence-quenching analysis. The enhanced dissipation of excess light energy within the reaction center of PSII, in part, accounts for the observed increase in resistance to high-light stress in cold-acclimated Arabidopsis plants.     

Salinity treatment shows no effects on photosystem II photochemistry,but increases the resistance of photosystem II to heat stress in halophyte Suaeda salsa

Photosynthetic gas exchange, modulated chlorophyll fluorescence, rapid fluorescence induction kinetics, and the polyphasic fluorescence transients were used to evaluate PSII photochemistry in the halophyte Suaeda salsa exposed to a combination of high salinity (100-400 mM NaCl) and heat stress (35-47.5 degrees C, air temperature). CO(2) assimilation rate increased slightly with increasing salt concentration up to 300 mM NaCl and showed no decrease even at 400 mM NaCl. Salinity treatment showed neither effects on the maximal efficiency of PSII photochemistry (F(v)/F(m)), the rapid fluorescence induction kinetics, and the polyphasic fluorescence transients in dark-adapted leaves, nor effects on the efficiency of excitation energy capture by open PSII reaction centres (F(v)'/F(m)') and the actual PSII effciency (Phi(PSII)), photochemical quenching (q(P)), and non-photochemical quenching (q(N)) in light-adapted leaves. The results indicate that high salinity had no effects on PSII photochemistry either in a dark-adapted state or in a light-adapted state. With increasing temperature, CO(2) assimilation rate decreased significantly and no net CO(2) assimilation was observed at 47.5 degrees C. Salinity treatment had no effect on the response of CO(2) assimilation to high temperature when temperature was below 40 degrees C. At 45 degrees C, CO(2) assimilation rate in control plants decreased to zero, but the salt-adapted plants still maintained some CO(2) assimilation capacity. On the other hand, the responses of PSII photochemistry to heat stress was modified by salinity treatment. When temperature was above 35 degrees C, the declines in F(v)/F(m), Phi(PSII), F(v)'/F(m)', and q(P) were smaller in salt-adapted leaves compared to control leaves. This increased thermostability was independent of the degree of salinity, since no significant changes in the above-described fluorescence parameters were observed among the plants treated with different concentrations of NaCl. During heat stress, a very clear K step as a specific indicator of damage to the O(2)-evolving complex in the polyphasic fluorescence transients appeared in control plants, but did not get pronounced in salt-adapted plants. In addition, a greater increase in the ratio (F(i)-F(o))/(F(p)-F(o)) which is an expression of the proportion of the Q(B)-non-reducing PSII centres was observed in control plants rather than in salt-adapted plants. The results suggest that the increased thermostability of PSII seems to be associated with the increased resistance of the O(2)-evolving complex and the reaction centres of PSII to high temperature.     

盆栽荷木、肖蒲桃和黄果厚壳桂幼苗对土壤温室气体排放影响的培育实验研究

通过对土壤65d的室内培养,比较研究了种上荷木、肖蒲桃和黄果厚壳桂幼苗并受模拟酸雨淋洗42月的盆栽土壤温室气体CO2、CH4、N2O排放的差异。结果发现,种植肖蒲桃的土壤CO2排放显著大于种植荷木和黄果厚壳桂的土壤,种植肖蒲桃和黄果厚壳桂的土壤CH4吸收显著大于种植荷木的土壤,而树种对土壤N2O的排放影响不明显。分析表明,土壤CO2的排放和对CH4的吸收的树种间差异并不完全由树种导致的土壤碳氮性质差异引起的,而导致树种对N2O的排放无差异的原因则很复杂。     

鼎湖山森林群落不同演替阶段优势种叶生态解剖特征研究

对南亚热带鼎湖山森林群落不同演替阶段8种优势树种进行了叶生态解剖学研究。观察的叶片解剖特征有：叶腹角质膜厚度、栅栏组织厚度、海绵组织厚度、叶背角质膜厚度及叶总厚度等。马尾松（Pinus massoniana)在针叶林群落和针阔叶混交林群落生境中,针阔叶混交林中叶片厚度变小,主脉管胞、树脂道平均直径变小。从针阔叶混交林演替阶段到季风常绿阔叶林演替阶段,锥栗（Castanopsis chinensis)叶片厚度、海绵组织厚度增加,栅栏组织厚度、P／S值（栅栏组织与海绵组织厚度比）减少;荷木（Schima superba)和黄果厚桂（Cryptocarya concinna)叶片厚度、栅栏组织厚度、叶腹及叶背角质膜厚度差异显著;从针阔叶混交林演替阶段到季风常绿阔叶林演替阶段,锥栗、荷木、黄果厚寺叶片厚度和栅栏组织厚度等差异均显著。不同生境下林内气温、相对湿度、光合有效辐射等小气候特征是叶片结构特征差异的主要影响因子,叶片结构差异反映了叶片结构在一定程度上对生境的适应。     

全日光强下5种植物叶片的UV-B防护

通过测定马尾松(Pinus massoniana)和荷木(Schima superba),及黄果厚壳桂(Cryptocarw concinna)、藜蒴(Castanopsis fissa)和锥树(Castartopsis chinensis)叶片中甲醇提取物和细胞壁碱性酚类提取物中UV-B吸收物质的含量,以及叶片叶绿素含量和比叶面积,研究全日光强下植物对UV-B的防护策略。结果表明,在全日光强下植物叶片甲醇提取物的UV-B吸收能力较遮阴下的高,如藜蒴和锥树分别高出42．6％和32．6％,而马尾松仅高出4．2％。全日光强下的黄果厚壳桂和荷木叶片细胞壁碱性酚类提取物的UV-B吸收能力亦分别比遮阴下的高3596和11．7％,而马尾松、锥树和藜蒴则较遮阴下的低,可能这些树种在全日光下细胞壁UV-B吸收物质有部分转移到细胞质,以增强栅栏组织细胞的保护。全目光强下这几种植物叶片的叶绿素含量较遮阴下的低,但有较高的比叶面积,这可能有利于减少对光的吸收和对深层组织细胞器的保护。可见不同植物是采取不同的策略来适应增高的UV-B辐射。     

Effects of canopy gaps on the growth of tree seedlings from subtropical broad-leaved evergreen forests of southern China

Seedling performance, morphology, and leaf characteristics of evergreen tree species from different successional stages of Chinese broadleaved evergreen forests were studied in four simulated gap environments: in 100, 55, 33, and 18% of full sunlight. The first two represent the light regimes of clearings (gaps secondarily become more open due to human activity and natural erosion). The hypothesis was tested that early-successional species achieve their greatest seedling size in clearings and contrast in this respect with late-successional species. Late-successional species were expected to show a stronger morphological response (leaf/root ratio) to clearings than early-successional ones. The results provided some evidence in support of these hypotheses with one exception, namely that late-successional Castanopsis fargesii appeared to be a highly sun-tolerant species. It is suggested that Castanopsis seedlings are competitive in large gaps and clearings.     

模拟氮沉降对南亚热带两种乔木幼苗生物量及其分配的影响

探讨了南亚热带季风常绿阔叶林两种优势树种荷木(Schima superba)和黄果厚壳桂(Cryptocarya concinna)幼苗的生物量及其分配对氮沉降增加的响应。实验分为对照(CK)、T₅、T₁₀、T₁₅和T₃₀ 5个处理,每个处理设置3次重复。所施氮肥为NH₄NO₃,以溶液方式喷施,5个处理浓度分别为0、0.12、0.24、0.36、0.72 mol N·L^-1。每月喷施2次,5个样方1年喷施的总氮量分别相当于氮沉降率0、5、10、15、30 g N·m^-2·a^-1。经过11个月的施氮处理,两种幼苗对氮沉降的响应存在差异,其中黄果厚壳桂幼苗的基径、株高、全株生物量和相对生长速率除最高处理T₃₀外,均高于对照,但荷木幼苗的基径、全株生物量和相对生长速率除T₁₀外,均小于对照。氮处理也对生物量的分配产生了明显的影响,两种幼苗的叶重比以T₃₀最低,表明高氮处理不利于幼苗叶片的生长;枝重比均以T₃₀最高,反映了高氮处理的幼苗生物量分配到枝干的比例最高;根重比和根冠比均以对照样方幼苗的最高,表明氮处理抑制根的生长,分配到根部分的生物量下降。总的来看,经过11个月的处理,除最高处理T₃₀外,氮处理仍对黄果厚壳桂幼苗的生长有促进作用,而对荷木幼苗的生长则趋向于一定程度的抑制效应,表明黄果厚壳桂幼苗更能耐受高氮条件。     

Alleviation of photoinhibition in drought-stressed wheat (Triticum aestivum) by foliar-applied glycinebetaine

Effects of foliar application of 100 mmol/L glycinebetaine (GB) on PS II photochemistry in wheat (Triticum aestivum) flag leaves under drought stress combined with high irradiance were investigated. The results show that GB-treated plants maintained a higher net photosynthetic rate during drought stress than non-GB treated plants. Exogenous GB can preserve the photochemical activity of PSII, for GB-treated plants maintain higher maximal photochemistry efficiency of PSII (F(v)/F(m)) and recover more rapidly from photoinhibition. In addition, GB-treated plants can maintain higher anti-oxidative enzyme activities and suffer less oxidative stress. Our data suggest that GB may protect the PSII complex from damage through accelerating D1 protein turnover and maintaining anti-oxidative enzyme activities at higher level to alleviate photodamage. Diethyldithiocarbamate as well as streptomycin treatment can impair the protective effect of GB on PSII. In summary, GB can enhance the photoinhibition tolerance of PSII.     

Assessing the relationship between respiratory acclimation to the cold and photosystem II redox poise in Arabidopsis thaliana

We examined the effect of manipulating photosystem II (PSII) redox poise on respiratory flux in leaves of Arabidopsis thaliana. Measurements were made on wild-type (WT) plants and npq4 mutant plants deficient in non-photochemical quenching (NPQ). Two experiments were carried out. In the first experiment, WT and mutant warm-grown plants were exposed to three different irradiance regimes [75, 150 and 300 micromol photosynthetically active radiation (PAR)], and leaf dark respiration was measured in conjunction with PSII redox poise. In the second experiment, WT and mutant warm-grown plants were shifted to 5 degrees C and 75, 150 or 300 micromol PAR, and dark respiration was measured alongside PSII redox poise in cold-treated and cold-developed leaves. Despite significant differences in PSII redox poise between genotypes and irradiance treatments, neither genotype nor growth irradiance had any effect upon the rate of respiration in warm-grown, cold-treated or cold-developed leaves. We conclude that changes in PSII redox poise, at least within the range experienced here, have no direct impacts on rates of leaf dark respiration, and that the respiratory cold acclimation response is unrelated to changes in chloroplast redox poise.