模拟酸雨对毛竹叶片抗氧化酶活性及释放绿叶挥发物的影响

为了探讨酸雨胁迫与毛竹(Phyllostachys pubescens)绿叶挥发物(green leaf volatiles, GLVs)释放规律以及抗氧化酶活性的关系, 通过盆栽试验, 采用不同pH值(5.6、4.0、2.5)的模拟酸雨对毛竹三年生实生苗进行处理, 研究酸雨对毛竹叶片可溶性蛋白质含量、丙二醛(MDA)含量和抗氧化酶活性的影响, 并采用热脱附/气相色谱/质谱联用技术对毛竹释放的GLVs成分和含量进行分析。结果表明: 酸雨胁迫下毛竹叶片MDA含量明显增加, pH 2.5模拟酸雨胁迫处理45天毛竹叶片MDA含量与对照相比增加了43.0% (p < 0.01); pH 4.0处理MDA含量增加缓慢, 处理75天时MDA含量比对照增加了0.36倍(p < 0.01)。pH 4.0和pH 2.5模拟酸雨胁迫处理45天时, 毛竹叶片可溶性蛋白质含量极显著增加, 与对照相比分别增加了32.0%和65.0% (p < 0.01)。在酸雨胁迫下, 毛竹叶片超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)的响应时间存在一定差异, 表现为互相协调, pH 2.5模拟酸雨胁迫处理SOD活性和POD活性分别在45天和60天时达到最大值, 分别为对照的1.67倍和1.31倍(p < 0.01), 随后降低。pH 4.0和pH 2.5模拟酸雨胁迫处理, 毛竹叶片GLVs含量比对照分别增加26.4%和132.9% (p < 0.01), 新增GLVs为 (E)-2-辛烯醛、2-乙基己醛、(E)-2-己烯醛和(E)-2-壬烯醛。研究表明: 酸雨胁迫条件下, 毛竹可以通过调节保护酶活性、可溶性蛋白质含量和释放GLVs来提高适应环境的能力。     

迷迭香对干旱胁迫的生理响应及其诱导挥发性有机化合物的释放

为探讨干旱胁迫对迷迭香(Rosmarinus officinalis)生理生化特性及挥发性有机化合物(VOC)释放规律的影响, 该文采用盆栽称重控水法研究了轻度(LD)、中度(MD)和重度(SD)干旱胁迫对迷迭香二年生实生苗叶片细胞膜透性、可溶性糖、可溶性蛋白质和丙二醛(MDA)含量以及脂氧合酶和抗氧化保护酶活性的影响, 并采用热脱附/气相色谱/质谱联用技术对不同干旱胁迫下迷迭香释放的挥发性有机化合物成分进行了分析。结果表明: 干旱胁迫对迷迭香叶片可溶性糖和可溶性蛋白质含量有明显的影响, MD和SD处理12天时其含量极显著地增加(p < 0.01), 与对照相比可溶性糖分别增加了51.5%和87.4%, 可溶性蛋白质含量分别增加了0.82和1.40倍。在MD和SD胁迫下, 超氧化物歧化酶、过氧化物酶和过氧化氢酶对干旱胁迫的响应存在一定差异, 表现为相互协调的作用。随着干旱胁迫时间的延长, 迷迭香体内MDA含量极显著地增加(p < 0.01), 细胞膜损伤率显著增加。分析显示, 迷迭香释放的VOC主要是萜烯类化合物, 占总量的46.0%以上; 随着干旱胁迫增强, 迷迭香释放的VOCs总量减少, 种类增多; LD、MD和SD胁迫处理萜烯类化合物相对含量与对照相比分别增加了14.4%、17.0%和23.7%; 干旱胁迫还明显诱导绿叶挥发物(green leaf volatiles)和醛类化合物的释放, 诱导产生了2-己烯醛、叶醇、山梨醛和癸醛4种新组分。研究表明: 干旱胁迫条件下, 迷迭香能够通过调节保护酶活性、渗透调节物质含量和释放VOCs来提高抗旱性。     

模拟酸雨胁迫对青冈幼苗光合特性和叶绿素荧光参数的影响

选择亚热带常绿阔叶林优势树种青冈幼苗为研究对象,设置3个酸雨处理：pH 2.5、pH 4.0、pH 5.6(CK),研究不同强度的模拟酸雨对青冈幼苗光合特性、叶绿素荧光参数和叶绿素含量的影响.结果表明：经过2年酸雨处理,青冈的净光合速率随着酸雨强度的增加而显著上升.pH 2.5、pH 4.0处理的酸雨增大了青冈的气孔导度和蒸腾速率,且对pH 2.5处理的影响更为显著.胞间CO₂浓度的大小顺序是pH 2.5>pH 5.6>pH 4.0.pH 2.5、pH 4.0处理青冈的最大净光合速率、光补偿点、光饱和点、暗呼吸速率显著高于对照,表观量子效率对酸雨胁迫不敏感.pH 2.5、pH 4.0处理青冈的PSⅡ原初光能转化效率和PSⅡ的潜在活性显著高于对照.青冈的叶绿素相对含量大小顺序是pH 2.5>pH 5.6>pH 4.0,且pH 2.5与pH 4.0之间有显著差异.说明青冈幼苗的光合参数、叶绿素荧光参数指标在pH 2.5和pH 4.0的酸雨处理下有所增加,且在pH 2.5强度下增加更为明显.     

酸雨胁迫对苦槠幼苗气体交换与叶绿素荧光的影响

常绿阔叶树苦槠(Castanopsis sclerophylla)是亚热带地带性顶极群落的建群种之一, 在区域森林资源保护和可持续利用方面具有重要的地位。在该区域日益严重的酸雨胁迫下, 研究其对于胁迫的生理生态响应具有重要的理论价值和实践意义。该文以苦槠幼苗为研究材料, 研究了酸雨胁迫对苦槠幼苗光合生理的影响。结果表明: (1)短时间内, pH 2.5处理下的幼苗叶绿素相对含量最低, 且与pH 5.6处理下的存在显著性差异(p < 0.05); 经过一段时间处理后, pH 4.0处理下的叶绿素相对含量最高, 表明低浓度的酸雨会促进叶绿素相对含量的增加。(2) 2007年4月, 光合速率(P_n)、PSⅡ最大光化学效率(F_v/F_m)和PSⅡ的潜在活性(F_v/F₀)在不同酸雨浓度处理下基本无变化。随着酸雨处理时间的延长, pH 2.5处理下的P_n、光饱和点、光补偿点和暗呼吸速率有显著降低, 且与pH 5.6处理下的存在显著性差异(p < 0.05)。pH 2.5处理组与pH 5.6处理组之间的F_v/F_m和F_v/F₀差异性逐渐减小。表观量子效率和气孔导度变化规律不明显。综合来说, 酸雨处理前期, 高浓度的酸雨胁迫对苦槠幼苗叶绿素相对含量、光合生理参数有显著影响, 但随着酸雨处理时间的增加, 酸雨胁迫对苦槠幼苗的影响逐渐减小, 表明其对外界不良环境具有一定的抵御能力和适应能力。     

不同起源时期的3种被子植物对酸雨胁迫响应的光合生理生态特征

为了验证起源时间较长的植物具有较强适应性的假设, 人工模拟酸雨胁迫, 研究了在不同酸雨处理下不同起源时期的3种被子植物乐东拟单性木兰(Parakmeria lotungensi)、石栎(Lithocarpus glaber)和山核桃(Carya cathayensis)的光合生理适应特性。实验设置了酸雨对照处理(pH 5.6)、中度酸雨胁迫处理(pH 4.0)和重度酸雨胁迫处理(pH 2.5), 并测定了这3种植物的光合特性。研究结果显示: 1)在不同强度的酸雨处理下, 乐东拟单性木兰的光合能力大小趋势为pH 2.5 > pH 4.0 > pH 5.6, 石栎则为pH 5.6 > pH 4.0 > pH 2.5, 但山核桃在酸雨处理之间差异不显著; 2)在酸雨对照处理(pH 5.6)中, 石栎的光合能力相对较高, 其次是乐东拟单性木兰, 山核桃最小。但在重度和中度酸雨胁迫下(pH ≤ 4.0), 3种植物光合能力的大小趋势为乐东拟单性木兰 > 石栎 > 山核桃, 且酸雨胁迫越严重, 上述趋势越明显。研究结果表明: 在重度酸雨胁迫下, 起源时间较早的乐东拟单性木兰表现出较高的光合与适应能力。从应用的角度出发, 建议考虑将乐东拟单性木兰作为酸雨灾害严重地区植被构建的物种之一。     

模拟秋季酸雨对三角枫叶片光合生理特性的影响

以三角枫幼苗为材料,采用盆栽方法,研究了pH 5.6、pH 4.0、pH 3.0和pH 2.0酸度模拟酸雨胁迫对三角枫叶片光合生理特性的影响,以探讨酸雨胁迫下三角枫的光合生理响应机制。结果显示:(1)随着酸雨浓度的增加和胁迫时间的延长,三角枫叶片相对叶绿素含量下降幅度逐步增大;叶片丙二醛含量呈逐渐上升的趋势,且各处理均显著高于对照;叶片质膜透性和脯氨酸含量均呈先升高后降低的趋势,且pH 2.0处理的叶片质膜透性在试验20d时迅速增大,升高幅度最大(146.3%)。(2)叶片净光合速率、蒸腾速率、水分利用效率、表观光能利用效率以及表观CO2利用效率在胁迫下也均呈显著下降趋势,且以pH 3.0和pH 2.0处理降幅最大。研究表明,pH 4.0的模拟酸雨对三角枫叶片的光合生理指标无显著影响,而pH≤3.0的强酸雨胁迫使三角枫叶片叶绿素含量显著下降、膜保护系统受损、光合作用效率显著下降;三角枫能适应弱酸雨(pH≥4.0)环境,可作为酸雨地区的园林绿化树种。     

Responses of phenolic acid and defensive enzyme activities to mechanical damage in Artemisia frigida

Aims The study aims at understanding the effects of feed intake and trample damage on the phenolic acid formation and antioxidant enzyme activities in Artemisia frigida, and elucidating the adaptive mechanisms in A. frigida to grazing in secondary metabolites and their related enzyme activities.
Methods We analyzed the phenolic acid content and the activities of polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL) and protective enzymes in leaves and roots in A. frigida under three levels (light, moderate, and heavy) of manipulative grazing condition. The measurements of the 9 phenolic acid contents started after 6 h of the mechanical damage of the plants by using the high performance liquid chromatography (HPLC), and the enzyme activities in leaves and roots were measured by a spectrophotometry method.
Important findings The light damage treatment induced productions of PPO, PAL and significantly (p < 0.05) increased antioxidant enzyme activities in the leaves and roots of A. frigida. The contents of PPO, PAL and antioxidant enzymes increased with increasing intensity of mechanical damage. Compared to the control, the content of free caffeic, syringic, ferulic and cinnamic acid in the leaves A. frigida were significantly elevated (p < 0.05) by 150.4%, 93.5%, 154.4% and 121.7%, respectively. They were significantly (p < 0.05) positively correlated with PAL activity in the moderate damage treatment. The content of free chlorogenic acid and catechol decreased by 91.1%, and 69.3%, respectively, compared with the control they had a negative correlation with PPO activity in the heavy damage treatment. The contents of gallic and protocatechuic acids increased (p < 0.05) by 280.6% and 215.7%, respectively, in the heavy damage treatment. With increasing intensity of mechanical damage, the content of 9 free phenolic acids significantly increased in roots but the increasing range was less than the one in leaves. Mechanical damage induced an increasing trend in the total amount of free and bounded phenolic acids in the leaves but a decreasing trend in the total amount of bounded phenolic acids in the roots of A. frigida. The results indicated that mechanical damage could firstly induce an increase of antioxidant enzymes and key enzymes in phenolic metabolism in A. frigida, leading to the accumulation of antioxidant substances of phenolic acids, further regulate the biosynthesis of lignins, quinones and tannins, and then enhance the resistance to mechanical damage and improved the tolerance of A. frigida to grazing.     

模拟酸雨对白筋叶片抗氧化酶活性及叶绿素荧光参数的影响

采用棚内盆栽方法, 设置pH值5.6 （对照）、4.0、3.0和2.0的模拟酸雨胁迫试验, 探讨其对白簕幼苗叶片MDA含量、保护酶活性、叶绿素含量、气体交换参数和叶绿素荧光参数的影响。结果表明, 随着模拟酸雨pH值的降低, MDA含量呈先降低后升高的趋势; SOD活性逐渐降低, POD活性逐渐升高, APX活性呈先升高后降低的变化。叶绿素a、叶绿素b、总叶绿素含量均比对照高, 在pH 4.0时达最大值。气孔限制值（Ls）、PSII实际光化学量子产量（ΦPSII）、光化学淬灭系数（qP）均随pH值的降低而下降, 净光速率（Pn）、气孔导度（Gs）、蒸腾速率（Tr）、水分利用效率（WUE）、PSII最大光化学效率（Fv/Fm）、PSII的潜在活性（Fv/Fo）、非光化学淬灭系数（qN）呈先升高后降低趋势, 且也都在pH 4.0时达最大值。由此推测, pH 4.0的酸雨处理有利于白簕幼苗的生长, 表明白簕幼苗可能喜欢生活在微酸环境中, 但是随着酸度加强, 反而起到抑制作用。     

酸雨胁迫对秃瓣杜英幼苗叶片叶绿素荧光特性和生长的影响

采用盆栽试验和模拟酸雨喷淋的试验方法,研究了重度酸雨(pH 2.5)、中度酸雨(pH 4.0)和对照(pH 5.6)处理下,不同季节秃瓣杜英幼苗叶片的叶绿素荧光特性及其生长差异.结果表明：不同季节相同处理下,秃瓣杜英幼苗叶片的相对叶绿素含量(SPAD)、PSⅡ的最大光化学效率(F_v/F_m)、PSⅡ实际光化学量子产量(Φ_PSⅡ)、株高和地径均为10月＞7月＞4月＞1月;同一季节不同处理中,SPAD、F_v/F_m、Φ_PSⅡ、株高和地径为重度酸雨＞中度酸雨＞对照;不同pH酸雨梯度处理和季节的交互作用对秃瓣杜英的SPAD、F_v/F_m、株高和地径的影响显著,而对Φ_PSⅡ、光化学淬灭系数和非光化学淬灭系数的影响不显著.     

荒漠区不同微生境下齿肋赤藓对一次降雪的生理生化响应

耐旱苔藓广泛分布于干旱半干旱荒漠地区, 对荒漠生态系统稳定性与功能多样性具有重要作用。齿肋赤藓(Syntrichia caninervis)是古尔班通古特沙漠苔藓结皮层的优势物种, 生于不同的微环境中。古尔班通古特沙漠冬、春季降雪频繁, 并能形成稳定的积雪层。目前关于降雪与微生境对齿肋赤藓生理生化特征影响的研究极为缺乏。该研究探讨了初冬一次降雪前后活灌丛、死灌丛和裸露地3种微生境下齿肋赤藓相关生理生化特征。结果表明, 与降雪前相比, 降雪后各微生境下齿肋赤藓植株的含水量、荧光活性、可溶性糖含量、超氧化物歧化酶(SOD)和过氧化物酶(POD)活性均有明显提高, 但脯氨酸、可溶性蛋白和丙二醛(MDA)含量有不同程度的降低。微生境对齿肋赤藓的生理指标有不同程度的影响, 而且与降雪具有显著的交互作用(脯氨酸除外)。降雪前后, 活灌丛下的齿肋赤藓具有较高的含水量和光合活性, 以及较低的保护酶(POD和SOD) 活性, 裸露地则表现出完全相反的特点。表明前者面临的胁迫最小, 生理活性最大, 但抗性较弱; 而后者具有更大的抗胁迫能力, 但生理活性低。降雪后, 脯氨酸、MDA、POD及SOD均与植株含水量呈显著负相关, 而荧光活性、可溶性糖及可溶性蛋白含量与植株含水量为显著正相关, 表明降雪降低了齿肋赤藓的水分胁迫程度, 改善并促进了生理活性与光合作用, 而且初冬的低温也起到了促进作用。     

苯并[α]芘对不同修复潜力羊茅属植物的根系分泌物中几种低分子量有机物的影响

根系分泌物是植物与土壤间进行物质交换和信息传递的重要载体, 是植物响应外界胁迫的重要途径, 也是构成根际微生态特征的关键因素。根系分泌物与有机污染物的植物修复密切相关, 研究胁迫条件下不同修复潜力植物间根系分泌物的释放特征有助于揭示植物修复的内在机制。该文借助根际袋土培试验研究了苯并[α]芘(BaP)胁迫下5种羊茅属(Festuca)植物根系不同生长期(30-70天)几种低分子量有机物的分泌特征。结果表明: 1) BaP浓度在10.25-161.74 mg·kg^-1范围内时, 待试植物能有效地促进土壤中BaP的去除, 其修复潜力依次为苇状羊茅(F. arundinacea) > 草原羊茅(F. chelungkiangnica) ≥ 毛稃羊茅(F. rubra subsp. arctica) ≥ 贫芒羊茅(F. sinomutica) > 细芒羊茅(F. stapfii)。2) BaP胁迫增强了植物根系对可溶性糖的分泌: 随着胁迫强度的增大、胁迫期的延长, 其分泌量变化呈“先升后降”趋势。3) BaP胁迫促进了植物根系低分子量有机酸的释放, 植物的修复潜力越大, 有机酸高峰值出现时的胁迫浓度越高; 组成成分较稳定, 草酸、乙酸、乳酸和苹果酸为主要组分(>97.34%), 在修复潜力较强植物的根系分泌物中检测出微量的反丁烯二酸。4) BaP胁迫对氨基酸种类影响不大, 但对分泌量影响较大。其中, 苏氨酸、丝氨酸、甘氨酸、丙氨酸的分泌量随BaP胁迫强度的增强而剧增; 脯氨酸、羟脯氨酸和天冬氨酸近乎以加和效应甚至协同效应的形式参与植物对BaP胁迫的应激反应: 参与应激组分的分泌量随胁迫强度的增强而剧增, 植物的修复潜力越强, 参与的组分越多。可见BaP胁迫下, 5种羊茅属植物根系分泌物中几种低分子量有机物的释放特征与植物自身的修复潜力有关: 修复潜力越强, 释放量越多且成分也越复杂, 并呈现出较强的环境适应性及生理可塑性。     

模拟酸雨胁迫对杨梅幼苗水分生理特性的影响

选择浙江省典型亚热带经济植物杨梅为对象,通过盆栽试验研究了重度酸雨(pH2.5)、中度酸雨(pH4.0)和对照(pH5.6)处理对杨梅幼苗水分生理特性的影响.结果表明:季节、年份和酸雨对杨梅幼苗的光合速率均有显著影响,各处理中,夏季的差异大于春、秋季,pH4.0处理对光合速率有促进作用;季节、年份、酸雨,季节-年份交互作用以及三者交互作用对气孔导度均有显著影响,各处理在夏季的差异大于春、秋季,酸雨对气孔导度有抑制作用;季节、年份、酸雨及季节-年份和季节-酸雨两两交互作用对蒸腾速率有显著影响,各处理夏季的差异大于春秋季,且pH2.5处理对蒸腾速率的抑制作用最强;酸雨、季节-年份和季节-酸雨交互作用对水分利用率有显著影响,且pH2.5处理对水分利用率有一定的促进作用.     

Leaf hydraulic traits and their trade-offs for nine Chinese temperate tree species with different wood properties

Aims Trees with different wood properties display variations in xylem anatomy and leaf vein structure, which may influence tree water transport efficiency and water-use strategy, and consequently constrain tree survival, growth and distribution. However, the effects of wood properties on leaf hydraulic conductance and vulnerability and their potential trade-offs at leaf level are not well understood. Our aims were to examine variations in leaf hydraulic traits of trees with different wood properties and explore potential trade-offs between leaf hydraulic efficiency and safety.
Methods Nine tree species with different wood properties were selected for measuring the leaf hydraulic traits, including three diffuse-porous species (Populus davidiana, Tilia amurensis, Betula platyphylla), three ring-porous species (Quercus mongolica, Fraxinus mandshurica, Juglans mandshurica), and three non-porous species (Picea koraiensis, Pinus sylvestris var. mongolica, Pinus koraiensis). Four dominant and healthy trees per species were randomly selected. The hydraulic traits measured included leaf hydraulic conductance on leaf area (K_area) and dry mass (K_mass) basis, leaf hydraulic vulnerability (P₅₀), and leaf water potential at turgor loss point (TLP), while the leaf structural traits were leaf dry mass content (LDMC), leaf density (LD) and leaf mass per unit area (LMA).
Important findings The K_area, K_mass, and P₅₀ differed significantly among the tree species with different woody properties (p < 0.05). Both K_area and K_mass were the lowest for the non-porous trees, and did not differ significantly between the diffuse-porous and ring-porous trees. The ring-porous trees had the highest P₅₀ values, while the diffuse-porous and non-porous trees showed no significant differences in P₅₀. Both K_area and K_mass were negatively correlated with P₅₀ (p < 0.05) for all the trees, and the relationships for the diffuse-porous, ring-porous, and non-porous trees were fitted into linear, power, exponential functions, respectively. This indicates that significant trade-offs exist between leaf hydraulic efficiency and safety. The K_mass was correlated (p < 0.01) with TLP in a negative linear function for the diffuse- and ring-porous trees and in a negative exponential function for the non-porous trees. The P₅₀ increased with increasing TLP. These results suggest that apoplastic and symplastic drought resistance are strictly coordinated in order to protect living cells from approaching their critical water status under water stresses. The K_mass was negatively correlated (p < 0.01) with LDMC, LD, or LMA, while the P₅₀ was positively correlated with LDMC and LD; this suggests that variations in K_mass and P₅₀ are driven by similar changes in structural traits regardless of wood traits. We conclude that the tree tolerance to hydraulic dysfunction increases with increasing carbon investment in the leaf hydraulic system.     

不同演替阶段典型树种幼苗对酸胁迫响应的高光谱监测

通过在为期2a的可控酸雨试验下对处于不同演替阶段的典型树种幼苗的高光谱测定,得到不同梯度酸雨下各树种的叶片光谱反应曲线及相应叶片的生理生化参量.对测定的3种树种的叶片叶绿素含量及一阶导数光谱进行分析,发现随着酸雨浓度的增加,处于演替前期的先锋树种马尾松的幼苗叶绿素含量呈现增加趋势,而处于演替中、后期的木荷和青冈幼苗叶绿素含量则呈现减少趋势;随着试验时间的推移,马尾松的红边位置呈现"红移"趋势,其中pH2.5处理下的"红移"趋势较明显;而木荷和青冈的红边位置则呈现不同程度的"蓝移"趋势.较长时期高浓度酸胁迫对先锋树种马尾松的幼苗生长有一定促进作用,而对演替中期和后期树种木荷和青冈幼苗生长则主要表现为抑制作用.     

模拟酸雨对3种菊科入侵植物光合特性的影响

研究了模拟酸雨(pH值分别为2.5、4.5和5.6)对3种菊科入侵植物--三裂叶蟛蜞菊(Wedelia trilobata)、薇甘菊(Mikania micrantha)和飞机草(Chromolaena odoratum)光合生理生态特性的影响。结果表明, 重度酸雨(pH值2.5)对3种入侵植物叶片均造成可见伤害, 其中飞机草受害最严重, 薇甘菊次之, 三裂叶蟛蜞菊受害最轻。同时, 3种入侵植物对酸雨胁迫表现出不同的光合响应, 随着酸雨pH值的降低, 飞机草和薇甘菊叶片叶绿素含量均有所下降, 其净光合速率(P_n)受到抑制, 而三裂叶蟛蜞菊叶片叶绿素含量变化不大, 其P_n值呈上升趋势。酸雨处理下, 3种入侵植物的细胞膜透性、丙二醛含量(MDA)及超氧化物歧化酶(SOD)和过氧化物酶(POD)活性均有不同程度的增加, 表明它们受到酸雨的胁迫并具有一定的抵抗力。其中, 经pH值2.5酸雨处理后的三裂叶蟛蜞菊叶片SOD活性增幅最大, 其对酸雨胁迫的反应最为迅速。上述研究结果表明, 三裂叶蟛蜞菊对酸雨胁迫的耐受性和适应性均高于飞机草和薇甘菊。在酸雨污染日趋严重的今天, 应对其危害予以高度重视。     

Impacts of the removal of vascular plants on physiological and biochemical characteristics of Syntrichia caninervis during winter season in a temperate desert

Aims Patchily distributed biological soil crusts and shrubs is one of the main vegetation cover types in Gurbantünggüt desert. The existence of shrubs in desert areas serves not only as a shelter for small animals, but also a good living condition for cryptogams and some herbs. Syntrichia caninervis, a dominant moss species in Gurbantünggüt desert, is patchily distributed under shrub canopy and open spaces between vascular plants. To our knowledge, the impacts of the removal of shrub canopy on physiological and biochemical characteristics of S. caninervis during the winter is still unknown.
Methods We simulated grazing of animals on Ephedra distachya at various rates (shrubs left intact, 50% shrubs removed, and shrubs removed completely) by cutting different percent of above-ground shoots of E. distachya. The shoot water content, chlorophyll fluorescence, proline content, soluble sugar content, soluble protein content, malonyldialdehyde (MDA) content, peroxidase (POD) and superoxide dismutase (SOD) activity were compared.
Important findings The results show that, as for proline and soluble sugar contents of tested S. caninervis, there were no significant differences among three treatments of shrub canopy. However, the MDA content, and the activities of POD, SOD, CAT were significantly higher than nature shrubs in snow cover periods. During snow-melting periods, soil moisture and temperature did not served as limiting factors on the growth of S. caninervis. The soluble sugar content, and the activities of POD, CAT with shrub removal were significantly higher than shrubs left intact. This may indicate that the decline of the function of maintaining constant soil temperature due to shrub canopy increased the damage of temperature on moss plants. In addition, as for physiological and biochemical characteristics, there were no significant differences between two treatments of 50% shrub canopy and shrub canopy left intact. In snow covered periods and snow melting periods, the MDA content, the activities of POD, SOD and CAT of S. caninervis under shrub canopy removed completely were significantly higher than that of 50% shrub canopy and shrub canopy left intact, except for soluble protein content. The duration of chlorophyll fluorescence activity of S. caninervis growing in habitats with shrubs removed completely was significantly shorter than that of S. caninervis growing in habitats of 50% shrub canopy and shrub canopy left intact. This result indicated that the removal of shrubs may increase the UV-B radiation and weaken the “moisture island effects” developed by the existence of shrub canopy.     

铜和模拟酸雨复合胁迫对酸模铜富集、生长及抗氧化酶系统的影响

采用盆栽方法,研究了Cu(0～1500 mg·kg^-1)和酸雨(pH 2.5～5.6)复合胁迫对酸模Cu富集、生长和抗氧化酶系统的影响.结果表明：酸模根和地上部Cu的积累量随土壤Cu浓度增大而增加,且根>茎叶,酸雨能促进酸模对Cu的吸收;随着土壤中Cu浓度和酸雨强度的增加,酸模的生物量逐渐下降,根和叶中MDA含量增加,且与Cu处理浓度显著正相关,根和叶中SOD和POD活性则均呈先上升后下降的趋势.酸模对Cu和酸雨有很强的耐受能力,在酸雨地区Cu污染土壤修复中具有很好的应用潜力.     

Effects of dew on eco-physiological traits and leaf structures of Leymus chinensis and Agropyron cristatum grown under drought stress

Aims To investigate the effects of dew on plants, we conducted the experiment to determine the physiological characteristics and leaf structures of Leymus chinensis and Agropyron cristatum in response to increasing dew under drought stress.Methods Four treatments (no dew, three times dew and five times dew per week under drought stress, and well-watering) were designed to examine leaf relative water content, water potential, net photosynthetic rate, water use efficiency, biomass, and leaf structures of L. chinensis and A. cristatum. Important findings There was a significant increase in the relative water content and water potential by simulated dew increase for two plants species under drought stress (p < 0.05). For A. cristatum, simulated dew increase significantly enhanced the net photosynthetic rate, stomatal conductance, and transpiration rate of plants under drought stress (p < 0.05). On the other hand, there was no significant difference in the stomatal conductance and transpiration rate for L. chinensis among treatments. Simulated dew increase improved the aboveground biomass and root biomass of two species. The ratio of yellow leaves to the total leaves was decreased by simulated dew increase for two species. Dew increase also protected leaf structures against the drought stress, suggesting that the dew increase can slow down the death process of leaves resulted from drought stress. Therefore, the study demonstrated that dew increased the available water for the leaves of L. chinensis and A. cristatum grown in the drought stress and thus had positive effects on the photosynthesis, water physiology and plant development.     

Eco-physiological responses of linseed (Linum usitatissimum) to salt and alkali stresses

AimsEffects of salt and alkali stresses (NaCl-Na₂SO₄ and NaHCO₃-Na₂CO₃) were compared on growth, photosynthesis characters, ionic balance and osmotic adjustment of linseed (Linum usitatissimum), to elucidate the mechanisms of salt and alkali stress (high pH value) damage to plants, and their physiological adaptive mechanisms to the stresses. MethodsThe experiment was carried out in an artificial greenhouse. Plants grew at approximately 700 mmol·m^-2·s^-1 photosynthetic photon flux density (PPFD) in greenhouse under photoperiod of 15 h in light and 9 h in dark. In each plastic pot (17 cm diameter) which contained 2.5 kg of washed sand, 20 linseed seeds were sown. The seedlings were exposed to stresses lasting 14 days after 2 months.Important findingsThe inhibitory effects of alkali stress on linseed growth were more remarkable than those of salt stress, indicating that alkali and salt represent two distinct forms of stress. The alkali stress increased the Na⁺ content in shoots, damaged the photosynthetic system, and highly reduced the net photosynthetic rate and C assimilation capacity. Under salinity stress, the Na⁺ content increased, the K⁺ content decreased with increasing stress. Greater changes were observed under alkali than under salt stress. Alkali stress caused the massive influx of Na⁺, which probably explained that the harmful of alkali stress on plants was stronger than that of salt stress. Under alkali stress, Ca²⁺ and Mg²⁺ decreased in roots, showing that high pH value around roots hindered the absorption of them. Fe²⁺ and Zn²⁺ had little effects on the osmotic adjustment, mainly because of they had a low ion content. Under salt stress, anion increased in order to balance the sharp increase of Na⁺. However, alkali stress made severe deficit of negative charge, broke the intracellular ionic balance and pH homeostasis, and caused a series of strain response. Our results showed that linseed enhanced the synthesis of soluble sugars to balance massive influx of Na⁺ under salt stress, but linseed enhanced the synthesis of organic acids to compensate for the shortage of inorganic anions, which might be a key pathway for the pH adjustment. In conclusion, the alkali stress (high pH value) clearly inhibited the growth, element absorption, ion homeostasis reconstruction of plants. Organic acid concentration is possibly a key adaptive factor for linseed to maintain intracellular ion balance and regulate high pH value under alkali stress.     

Silicon alleviates simulated acid rain stress of <Emphasis Type="BoldItalic">Oryza sativa</Emphasis> L. seedlings by adjusting physiology activity and mineral nutrients

Silicon (Si) has been a modulator in plants under abiotic stresses, such as acid rain. To understand how silicon made an effect on rice (Oryza sativa L.) exposed to simulated acid rain (SAR) stress, the growth, physiologic activity, and mineral nutrient content in leaves of rice were investigated. The results showed that combined treatments with Si (1.0, 2.0, or 4.0 mM) and SAR (pH 4.0, 3.0, or 2.0) obviously improved the rice growth compared with the single treatment with SAR. Incorporation of Si into SAR treatment decreased malondialdehyde (MDA) content; increased soluble protein and proline contents; promoted CAT, POD, SOD, and APX activity; and maintained the K, Ca, Mg, Fe, Zn, Cu content balance in leaves of rice seedlings under SAR stress. The moderate concentration of Si (2.0 mM) was better than the low and high concentration of Si (1.0 and 4.0 mM). Therefore, application of Si could be a better strategy for maintaining the crop productivity in acid rain regions.