地表臭氧浓度升高与干旱交互作用对杨树非结构性碳水化合物积累和叶根分配的短期影响

人类活动加剧和全球变化导致植物在生长季同时受到高浓度地表臭氧(O₃)和干旱的双重胁迫。为了探究两者对植物非结构性碳水化合物(TNC)积累和分配的影响, 该实验采用开顶式气室研究了2种O₃浓度(CF, 过滤空气; NF40, NF (未过滤空气) + 40 nmol·mol ^-1 O₃)和2个水分处理(对照, 充分灌溉; 干旱, 非充分灌溉)及其交互作用对杨树基因型‘546’ (Populus deltoides cv. ‘55/56’ × P. deltoides cv. ‘Imperial’)叶片和细根中TNC及其组分(葡萄糖、果糖、蔗糖、多糖、总可溶性糖和淀粉)含量的影响。结果表明: O₃浓度升高显著降低杨树叶片中淀粉和TNC的含量, 增加葡萄糖、果糖和总可溶性糖含量, 但对细根中淀粉和总可溶性糖含量的影响不显著。干旱胁迫显著增加细根中果糖和多糖含量, 降低蔗糖含量, 但对叶片中淀粉和总可溶性糖含量的影响不显著。充分灌溉下O₃浓度升高显著增加了杨树叶片多糖和总可溶性糖含量, 而干旱下O₃浓度升高显著增加了TNC含量的根叶比。该研究结果发现O₃主要影响叶片中TNC及各组分的含量, 而干旱主要影响细根中TNC及各组分的含量。从杨树叶片TNC的响应来看, 适度的水分限制有助于减缓O₃的负面伤害。     

南盘江流域云南松径向生长对气候暖干化的响应

全球气候变暖背景下, 西南地区气候呈现出明显的暖干化特征, 但区域优势树种云南松(Pinus yunnanensis)对气候暖干化的响应存在不确定性。该研究根据树木年代学方法选择研究区域87株云南松样本进行树芯采集, 构建云南松树轮年表, 结合1952-2016年的气温和降水等气象资料, 利用响应分析、多元回归分析以及滑动相关分析等方法研究了影响南盘江流域云南松径向生长的关键气候因子及其对气候暖干化的响应规律。研究结果表明: 1985年以来, 研究区域气候暖干化特征明显, 气温上升和降水量下降的速率是1984年前的5和6倍, 年平均气温、年平均最高气温、年平均最低气温的上升速率为0.044、0.041和0.050 ℃·a ^-1, 年降水量的下降速率为 6.02 mm·a ^-1。气候暖干化使云南松的生长对温度响应的敏感度降低, 对水分响应的敏感度增强, 气温的解释率由暖干化前的44.95%下降到21.97%, 水分的解释率由暖干化前的55.05%上升到78.03%。暖干化增强了当年气候因子对径向生长的影响, 减弱了上年气候因子的影响, 与径向生长显著相关的当年气候因子增加了3个, 当年气候因子对径向生长的解释率增加了16.05%。暖干化减弱了云南松生长的“滞后效应”, 气候变化对树木生长影响的时效性增强。在5-7月和9-11月, 气候变暖使径向生长与气温、水分的响应关系变得不稳定。该研究可为气候暖干化区域云南松林的经营、管理以及区域气候重建提供理论依据和基础数据。     

Sap flow characteristics and its responses to precipitation in Robinia pseudoacacia and Platycladus orientalis plantations

Aim In the loess hilly region, drought stress frequently occurs during the late spring and early summer as a result of insufficient water supply and asynchronous changes between temperature and precipitation. Our objective was to quantify the characteristics of water-consumption through transpirations and their responses to precipitation in the dominant plantations in this region. Methods Thermal dissipation probe (TDP) was used to measure the sap flow density (F_d) of Robinia pseudoacacia and Platycladus orientalis from April through October in 2009 in Ansai National Ecological Experimental Station. Environmental variables, including meteorological factors and soil water content, were simultaneously measured. Important findings The diurnal variation of F_d exhibited a single-peak curve during the growing season of R. pseudoacacia and P. orientalis. The maximum F_d was three times greater in R. pseudoacacia (0.12068 m³·m^-2·h^-1) than that in P. orientalis (0.03737 m³·m^-2·h^-1). Except in the rapid-growth season (July to August), the F_d of these two species during the post-precipitation period were significantly higher than that during the pre-precipitation period. The F_d of P. orientalis and R. pseudoacacia was well fitted with transpiration (VT), an integrated index calculated from both vapor pressure deficit (VPD) and solar radiation (R_s), using an exponential saturation function. Generally, F_d increased in response to rising VT, while these values tended to be stable when VT reached about 50 kPa (W·m^-2)^1/2. Furthermore, R. pseudoacacia showed more sensitive to precipitation (p < 0.001) than P. orientalis, according to different hydraulic conductance model coefficients (fitting parameter b) between pre- and post-precipitation periods. Therefore, R. pseudoacacia could be considered as a precipitation-sensitive species, while P. orientalisasa precipitation-insensitive species. Through analyzing the different responses of plantation species to precipitation in the loess hilly region, this study provides a scientific basis for the local plantation management from the aspect of tree water use during ecological restoration.     

Simulation on the light-response curves of electron transport rate of Quercus variabilis and Robinia pseudoacacia leaves in the Xiaolangdi area,China

为了比较直角双曲线模型、非直角双曲线模型与叶子飘模型的优缺点, 研究阴生叶和阳生叶电子传递速率的差异, 探讨环境/生物因素对电子传递速率等参数的影响, 该文采用LI-6400XT荧光测定系统对黄河小浪底栓皮栎(Quercus variabilis)、刺槐(Robinia pseudoacacia)叶片电子传递速率-光响应(J-I)曲线进行了测定, 利用直角双曲线模型、非直角双曲线模型和叶子飘模型对J-I曲线进行了拟合。结果表明, 3种模型对叶片J-I曲线拟合的决定系数(R ²)在0.96以上, 叶子飘模型的R ²最高(> 0.99)。直角双曲线模型和非直角双曲线模型无法模拟植物叶片光系统II动力学下调现象, 且不能得出饱和光强(I_sat); 直角双曲线模型对最大电子传递速率(J_max)的模拟明显大于实测值; 叶子飘模型能很好地模拟光系统II动力学下调现象, 得出的J_max和I_sat均最接近实测值。对阴生叶和阳生叶J-I曲线研究发现, 栓皮栎、刺槐阴生叶的J_max分别低于阳生叶25.0%和18.0%, 阳生叶的I_sat分别高于阴生叶26.0%和10.1%。栓皮栎和刺槐J_max与气温显著正相关; 刺槐I_sat与气温、土壤水分含量和净光合速率具有显著的正相关关系; 栓皮栎和刺槐J-I曲线初始斜率α均与净光合速率呈显著负相关关系。     

镉胁迫对绢毛委陵菜-丛枝菌根真菌共生体根系结构和生理的影响

为从生理水平上揭示绢毛委陵菜（Potentilla sericea L.）-丛枝菌根真菌共生体对镉胁迫的应答机制,以绢毛委陵菜多年生植株为试验材料,分别接种根内根生囊霉（Rhizophagus intraradices）和摩西球囊霉（Funneliformis mosseae）,80 d后以不同浓度的镉胁迫处理并测定菌根侵染率,研究侵染率较高菌种的共生体植株的生理指标变化和结构变化。结果表明：摩西球囊霉较根内根生囊霉对绢毛委陵菜菌根侵染率高,达100%,而根内根生囊霉侵染率为89.33%;接种摩西球囊霉真菌的植物,当镉质量浓度达10 mg?L^-1时,细胞壁小范围破裂、液泡出现变小的趋势,高浓度镉（20 mg?L^-1）处理时,根系细胞壁破裂,细胞无法维持原有形态;镉胁迫下,Cd（5 mg?L^-1）~ Cd（10 mg?L^-1）MDA含量显著上升（P<0.05）,Cd（0 mg?L^-1）~Cd（5 mg?L^-1）SOD活性和脯氨酸含量变化显著（P<0.05）,可溶性蛋白含量和叶绿素含量显著减少（P<0.05）,Cd（10 mg?L^-1）~Cd（15 mg?L^-1）可溶性蛋白含量和叶绿素含量变化不显著（P>0.05）,植物可以抵抗一定浓度范围的镉胁迫。综合来看,接种摩西球囊菌可以增强绢毛委陵菜耐镉胁迫能力,为利用绢毛委陵菜修复镉污染土壤提供了理论依据。     

吉林老白山鱼鳞云杉树轮蓝光强度和轮宽指数与气候响应关系随海拔变化的对比

树轮数据是晚全新世古气候研究中最重要的代用指标。树轮参数各具优缺点, 蓝光强度(BI)是一种获取成本低廉的最大晚材密度(MXD)的光学替代参数, 其蓝色光反射率或强度最小值(256-BI)与相应的MXD值高度相关, 被很多的学者认为是树轮气候学研究中一个具有重要潜能的新兴参数。该研究以吉林老白山3个海拔(900、1 200和1 500 m)的鱼鳞云杉(Picea jezoensis)为例, 分析鱼鳞云杉的BI及轮宽指数(RWI)与气候因子的响应差异, 以期为BI参数在树轮气候学的进一步应用提供参考。结果表明: 不同海拔鱼鳞云杉BI或RWI对气候的响应趋势基本一致。BI与温度主要呈正相关关系, 而RWI与温度主要呈负相关关系, 其中BI与当年夏季及生长季最高温度显著正相关, 而RWI (低、中海拔)与全年平均气温、当年生长季和全年最低温度显著负相关。BI与当年夏季标准化降水蒸散指数(SPEI)显著负相关, RWI与夏季SPEI负相关关系较弱或为正相关; BI和RWI几乎相反的生长-气候关系可能是早、晚材权衡关系的体现。研究区域鱼鳞云杉的BI参数可能与年轮宽度记录不同的气候信号, 在空间尺度上对于当年夏季降水、最高温度以及SPEI的响应好于传统宽度指标。BI与主要气候因子相关关系的时间稳定性好于RWI, 因此, BI在树轮气候学的研究中具有一定的应用潜能。     

毛乌素沙地油蒿叶建成成本及相关叶性状沿降水梯度的变化

干旱区植物在如何提高水分利用效率与降低叶建成成本之间可能存在一种权衡。我们假设: 与湿润区植物相比, 干旱区植物能通过调节叶功能性状之间的关系(如通过提高单位面积叶氮含量(N_area)), 实现在相同的叶建成成本下具有更高的水分利用效率。为了验证这一假设, 该研究以毛乌素沙地的广布物种油蒿(Artemisia ordosica)为研究对象, 分析了油蒿叶建成成本沿降水梯度的变化规律及其与比叶面积(SLA)、单位质量叶氮含量(N_mass)、N_area和叶碳稳定同位素比率(δ ¹³C)的关系。结果表明: 油蒿单位质量叶建成成本(CC_m)在不同降水条件下差异不显著, 而单位面积叶建成成本(CC_a)在不同降水条件下虽有显著差异, 但并未随降水减少而明显增加。油蒿CC_m与SLA无显著相关性, 与叶δ ¹³C值呈显著正相关关系。油蒿叶建成成本与N_area呈显著正相关关系, 但这种关系格局在低降水量(264 mm)区与高降水量(310-370 mm)区之间存在策略位移现象——即在相同叶建成成本下, 低降水量区植物比高降水量区植物具有更高的N_area。以上结果表明, 尽管高水分利用效率与高叶建成成本相关, 但与高降水量区植物相比, 低降水量区植物具有较高的N_area并没有导致其叶建成成本增加。     

Correlation between vein density and water use efficiency of Salix matsudana in Zhangye Wetland,China

Aims The correlation between vein density and water use efficiency (WUE) affects the balance between water supply and demand of plant leaves, which is significant for comprehending the ecological adaptation strategies of plants. The objective of this study was to study how Salix matsudana modulated vein density and WUE along a soil moisture gradient in Zhangye Wetland, China. Methods The study was conducted in floodplain wetland near Heihe River in Zhangye City, Gansu Province, China. Three sample plots, at a spatial interval of 70 m, were set up along a soil moisture gradient ordinally from the area near the water body to the wetland edge, plot I (69.23%), spot II (48.38%) and spot III (35.27%). Community traits were investigated by using diagonal method, and all individuals of S. matsudana were used for measurements of height and canopy. At each plot, 5 individuals of S. matsudana at 4 vertices and diagonal intersection were selected for measurements of vein density, WUE, net photosynthetic rate (P_n), transpiration rate (T_r), photosynthetically active radiation (PAR), saturated vapor pressure differences (VPD), specific leaf area, stomatal conductance (G_s) and intercellular CO₂ concentration (C_i). We used mathematical methods of correlation analysis and standardized major axis to investigate relationships between vein density and WUE. Important findings With decreasing soil moisture, the height, canopy, specific leaf area, G_s and C_i of S. matsudana decreased gradually, while the vein density, WUE, P_n, T_r, PAR and VPD increased gradually. The correlation between vein density and WUE was positive in all the three plots, but the relationship varied along the soil moisture plots gradient. There was a highly significant positive correlation (p < 0.01) between the vein density and WUE at plot I and III, whereas the correlation only reached a significant level (p < 0.05) at plot II; The correlation coefficient between vein density and WUE is significantly smaller than 1 at plot I (p < 0.05), while the correlation coefficient is significant greater than 1 at plot II and III (p < 0.05). We can conclude that varied relationships between vein density and WUE of S. matsudana along a soil moisture gradient could reflect plant acclimation.     

Edge effects of forest gap in Pinus massoniana plantations on the ecological stoichiometry of Cinnamomum longepaniculatum

Aims Pinus massoniana is one of the major plantation tree species in the low hilly lands along the upper reaches of the Yangtze River Valley in China’s “Grain for Green” project. The objective of this study was to explore the edge effects of forest gap on the ecological stoichiometry of dominant tree species in a P. massoniana plantation forest.Methods We collected Cinnamomum longepaniculatum leaves in a 39-year-old P. massoniana plantation forest with seven forest gap sizes (G1: 100 m²; G2: 225 m²; G3: 400 m²; G4: 625 m²; G5: 900 m²; G6: 1 225 m²; G7: 1 600 m², and the control: closed canopy) located in Gao County, south Sichuan Province during different seasons. The contents of C, N and P in leaves were measured, and the effects of edges, seasons and their interaction on leaf C, N and P contents and C:N:P stoichiometry were evaluated.Important findings The leaf C content, C:N and C:P of C. longepaniculatum at the edge of forest gaps in different seasons were all significantly higher than those of understory plants in P. massoniana plantation. With increasing size of forest gaps, leaf C content and C:N ratio, C:P and N:P of C. longepaniculatum increased initially and then decreased with the maximum at medium size (400-900 m²). From spring to winter, leaf N and P contents of C. longepaniculatum increased after an obvious decrease; and the C:N and C:P increased first but then decreased. However, the inflection point all appeared in the summer. The nutrient utilization of C. longepaniculatum at the edge of forest gaps was more efficient in summer and autumn than in spring and winter, indicating significant edge effects. The results of principal component analysis (PCA) suggested that gap size, relative light intensity and monthly average air temperature were the main environmental factors affecting the stoichiometry of C. longepaniculatum at the different edge of forest gaps in the P. massoniana plantation. These results indicated that forest gap with size 625 m² had the highest organic matter storage and nutrient utilization efficiency in the edge areas in all seasons, and therefore had the most significant edge effect on leaf element stoichiometry.     

Variations and interrelationships of foliar hydraulic and photosynthetic traits for Larix gmelinii

Aims Variations and potential trade-offs of leaf hydraulic and photosynthetic traits are essential for assessing and predicting the effect of climate change on tree survival, growth and distribution. Our aims were to examine variations and interrelationships of leaf hydraulic and photosynthetic traits in response to changes in site conditions for Dahurian larch (Larix gmelinii)—a dominant tree species in Chinese boreal forests.Methods This study was conducted at the Maoershan Forest Ecosystem Research Station. A transect of 27 year-old Dahurian larch plantation was established that consisted of five plots extending from the valley to the ridge of a slope. The predawn leaf water potential (Ψ_pre), area- and mass-based leaf hydraulic conductance (K_area and K_mass, respectively), resistance to embolism capacity (P₅₀), leaf mass per area (LMA), net photosynthetic rate (A), and leaf nitrogen content (N) were measured in August 2016.Important findings The Ψ_pre, K_area, K_mass, P₅₀, A, LMA, and N all varied significantly among the plots (p < 0.05), indicating significant intra-specific variations in these traits in response to the changes in site conditions. The P₅₀ was significantly (p < 0.05) correlated with Ψ_pre, K_area or K_mass, suggesting that a trade-off between hydraulic efficiency and safety exist within the species to some degree. There were significant (p < 0.05) pairwise correlations between A, LMA, and N. Nevertheless, there was no significant (p < 0.05) correlation between the measured photosynthetic traits and hydraulic traits. We concluded that the intra-specific variations and multiple interrelationships of the leaf hydraulic and photosynthetic traits for the larch reflect the plasticity of its leaf traits and strategies of its survival and growth as a result of its acclimation to diverse site conditions.     

Differential uptakes of different forms of soil nitrogen among major tree species in subalpine coniferous forests of western Sichuan,China

Aims Although acquisition of soil organic nitrogen (N)(mainly amino acids) by plants is a widespread ecological phenomenon in many terrestrial ecosystems, the rate of organic N uptake and their contributions to plant nutrient supply are poorly understood. Our objective was to determine the relative contributions of inorganic N (NO₃^–-N and NH₄⁺-N) and organic N (amino acids) to plant N uptake in a high-frigid forest ecosystem.Methods The differences in the uptake rate of three different forms of N (NO₃^–-N, NH₄⁺-N and glycine) were quantified by exposing seedlings of two dominant tree species (Picea asperata and Betula albo-sinensis) in subalpine coniferous forests of western Sichuan, China, to trace quantities of K¹⁵NO₃,¹⁵NH₄Cl and (U-¹³C₂/¹⁵N) glycine.Important findings Both ¹³C and ¹⁵N were significantly enriched in fine roots 2 h after tracer application, indicating the occurrence of glycine uptake in P. asperata and B. albo-sinensis seedlings. The seedlings of two tree species had a significant preference for NO₃^–-N compared with glycine and NH₄⁺-N, and the uptake rate of NO₃^–-N was 5 to 10 times greater than that of glycine and NH₄⁺-N. The roots of seedlings in the two species took up glycine more rapidly than NH₄⁺-N, implying that soil organic N (i.e., amino acids) could be an important N source for the two species in subalpine coniferous forests. The results of this study are of great theoretical significance for understanding N utilization strategies and nutrient regulation processes in plants of the high-frigid forest ecosystems.     

丛枝菌根真菌对不同性别组合模式下青杨雌雄植株根系生长的影响

丛枝菌根真菌(AMF)对雌雄异株植物根系生长, 尤其是对邻近生长的不同雌雄个体的影响还鲜有研究。该研究以泥土:河沙:蛭石体积比为1:1:1的混合物为培养基质, 分别在雄-雄、雌-雌和雄-雌3种组合栽培模式下对青杨(Populus cathayana)雌雄幼苗进行接种和不接种摩西球囊霉(Funneliformis mosseae)处理, 通过比较接种AMF与否雌雄植株根系在侵染率、生物量、形态、碳、氮含量等方面的差异来分析AMF对青杨雌雄幼苗根系生长发育的影响。结果发现: 与对照组相比, 接种AMF对3种栽培模式下青杨雌雄植株的侵染率、根干质量、根系形态(除分枝强度、比表面积)和碳、氮含量影响显著。此外, 不同性别组合模式对青杨雌雄植株的根干质量、根系形态和碳、氮含量影响显著。接种AMF后, 与雌-雌合栽模式下的雌株相比, 雄-雌合栽模式下雌株的根干质量、氮含量都有不同程度的提高, 根系形态发生改变; 而与雄-雄合栽模式下的雄株相比, 雄-雌合栽模式下雄株的相应指标出现降低或轻微增加。该研究表明AMF对不同性别组合模式下青杨植株根系生长具有显著促进作用, 尤其是雄-雌合栽模式下AMF接种最有利于雌株根系的生长发育。     

Effects of nitrogen addition on soil respiration in shrublands in Mt. Dongling,Beijing, China

Aims Soil respiration from terrestrial ecosystems is an important component of terrestrial carbon budgets. Compared to forests, natural or semi-natural shrublands are mostly distributed in nutrient-poor sites, and usually considered to be relatively vulnerable to environmental changes. Increased nitrogen (N) input to ecosystems may remarkably influence soil respiration in shrublands. So far the effects of N deposition on shrubland soil respiration are poorly understood. The aim of this study is to investigate the soil respiration of Vitex negundo var. heterophylla and Spiraea salicifolia shrublands and their response to N deposition. Methods We carried out a N enrichment experiment in V. negundo var. heterophylla and S. salicifolia shrublands in Mt. Dongling, Beijing, with four N addition levels (N₀, control, 0; N₁, low N, 20 kg N·hm^-2·a^-1; N₂, medium N, 50 kg N·hm^-2·a^-1 and N₃, high N, 100 kg N·hm^-2·a^-1). Respiration was measured from 2012-2013 within all treatments.Important findings Under natural conditions, annual total and heterotrophic respiration were 5.91 and 4.23, 5.76 and 3.53 t C·hm^-2·a^-1 for the V. negundo var. heterophylla and S. salicifolia shrublands, respectively and both were not affected by short-term N addition. In both shrubland types, soil respiration rate exhibited significant exponential relationships with soil temperature. Temperature sensitivity (Q₁₀) of total soil respiration in V. negundo var. heterophylla and S. salicifolia shrublands ranged from 1.44 to 1.58 and 1.43 to 1.98, and Q₁₀ of heterotrophic soil respiration ranged from 1.38 to 2.11 and 1.49 to 1.88, respectively. Short-term N addition decreased only autotrophic respiration rate during the growing season, but had no significant effects on total and heterotrophic soil respiration in V. negundo var. heterophylla shrubland. In contrast, N addition enhanced the heterotrophic soil respiration rate and did not influence autotrophic and total soil respiration in S. salicifolia shrubland.     

Soil water use strategy of dominant species in typical natural and planted shrubs in loess hilly region

Aims Artemisia gmelinii is a dominant specie naturally established after abandonment of cultivated lands in the Loess Plateau, and Caragana korshinskii is one of the main planted shrub species to control soil erosion. Improved understanding of water use strategies of these two species is of great significance to evaluate the sustainable development of the Loess Plateau under the trend of climate warming and increasing drought events.
Methods Stable oxygen-18 isotope was used to determine seasonal variations in the water sources of native A. gmelinii communities established after abandonment of cultivated lands for 7 and 30 years and planted C. korshinskii after 30 years. The contributions of soil water from different depths to water uptake were estimated by the MixSIR Bayesian mixing model. The geometric mean regression method was used to fit the line of precipitation to get the local meteoric water line (LWML).
Important findings The stable hydrogen isotope rate (δD) and stable oxygen isotope rate (δ¹⁸O) of soil water and xylem water plotted to the right side of the LWML, indicating that the isotopic compositions of soil water were enriched due to evaporation. The native A. gmelinii communities established after abandonment of cultivated lands for 7 years and planted C. korshinskii after 30 years showed plasticity in switching water sources from different soil layers, extracting water from shallow soil (0-40 cm) when soil water was available, but deeper soil (40-80 cm) when shallow soil water was dry. In contrast, A. gmelinii growing in site after cultivation abandonment for 30 years mainly relied on water from the surface soil (0-10 cm) throughout the growing season. Our results suggest that the ability of A. gmelinii to compete for soil water reduces with aging of the community while the planted C. korshinskii will have competitive advantage under the condition of increasing frequency of drought events in the future.     

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.     

Spatial variations of ginsenosides in Panax ginseng and their impact factors

Aims This study aimed to reveal how ginsenosides content in Panax ginseng varied spatially and the regulating roles of environmental factors.Methods Twenty eight P. ginseng samples were collected from Heilongjiang, Jilin and Liaoning provinces, and nine kinds of ginsenosides content in P. ginseng were measured. The one-way ANOVA was used to evaluate their spatial variations. The method of UPLC was employed to determine the content of nine kinds of ginsenosides in P. ginseng. The principal component analysis (PCA), correlation analysis (CA) and redundancy analysis (RDA) were used to analyze the relationship between ginsenosides content and ecological factors (including climate and soil factors).Important findings The results showed that the content of ginsenosides in P. ginseng from Jilin and Liaoning was similar, and higher than that in Heilongjiang. Precipitation was the most important climate factor affecting the contents of ginsenosides. High temperature and strong sunshine limited the content of ginsenosides. The analysis on ginsenosides and soil factors indicated that soil nitrogen content, Fe, K, organic matter, pH value, Mn, P, Zn all had significant influences on the content of ginsenosides.     

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.     

Effects of biochar addition on dynamics of soil respiration and temperature sensitivity in a Phyllostachys edulis forest

Aims Recent studies have shown that artificial addition of biochar is an effective way to mitigate atmospheric carbon dioxide concentrations. However, it is still unclear how biochar addition influences soil respiration in Phyllostachys edulis forests of subtropical China. Our objectives were to examine the effects of biochar addition on the dynamics of soil respiration, soil temperature, soil moisture, and the cumulative soil carbon emission, and to determine the relationships of soil respiration with soil temperature and moisture.Methods We conducted a two-year biochar addition experiment in a subtropical P. edulis forest from 2014.05 to 2016.04. The study site is located in the Miaoshanwu Nature Reserve in Fuyang district of Hangzhou, Zhejiang Province, in southern China. The biochar addition treatments included: control (CK, no biochar addition), low rate of biochar addition (LB, 5 t·hm^-2), medium rate of biochar addition (MB, 10 t·hm^-2), and high rate of biochar addition (HB, 20 t·hm^-2). Soil respiration was measured by using a LI-8100 soil CO₂ efflux system.Important findings Soil respiration was significantly reduced by biochar addition, and exhibited an apparent seasonal pattern, with the maximum occurring in June or July (except LB in one of the replicated stand) and the minimum in January or February. There were significant differences in soil respiration between the CK and the treatments. Annual mean soil respiration rate in the CK, LB, MB and HB were 3.32, 2.66, 3.04 and 3.24 μmol·m^-2·s^-1, respectively. Compared with CK, soil respiration rate was 2.33%-54.72% lower in the LB, 1.28%-44.21% lower in the MB, and 0.09%-39.22% lower in the HB. The soil moisture content was increased by 0.97%-75.58% in LB, 0.87%-48.18% in MB, and 0.68%-74.73% in HB, respectively, compared with CK. Soil respiration exhibited a significant exponential relationship with soil temperature and a significant linear relationship with combination of soil temperature and moisture at the depth of 5 cm; no significant relationship was found between soil respiration and soil moisture alone. The temperature sensitivity (Q₁₀) value was reduced in LB and HB. Annual accumulative soil carbon emission in the LB, MB and HB was reduced by 7.98%-35.09%, 1.48%-20.63%, and -4.71%-7.68%, respectively. Biochar addition significantly reduced soil carbon emission and soil temperature sensitivity, highlighting its role in mitigating climate change.     

Distribution pattern and influencing factors of soil salinity at Tamarix cones in the Taklimakan Desert

柽柳(Tamarix chinensis)沙包是塔克拉玛干沙漠特殊的生物地貌景观, 对维持区域生态环境的稳定具有极其重要的作用。该研究采用野外调查与室内分析相结合的方法, 选取且末、阿拉尔、策勒、塔中4个典型区域的柽柳沙包为研究对象, 对柽柳沙包0-500 cm土壤垂直剖面进行采样, 测定土壤pH值、枯落物含量、电导率及HCO₃ ^-、Cl ^-、SO₄ ^2-、Ca ²⁺、Mg ²⁺、K ⁺、Na ⁺含量, 分析柽柳沙包中土壤盐分的空间变化规律及其影响因素。结果表明: 1)从且末、阿拉尔、策勒到塔中, 土壤pH值总体呈升高趋势, 土壤电导率及Na ⁺、Ca ²⁺、Mg ²⁺、SO₄ ^2-含量总体呈降低趋势, K ⁺、Cl ^-、HCO₃ ^-含量没有明显的变化规律。2)盐分在4个样区的垂直分布主要表现为: 且末和策勒样区柽柳沙包的土壤盐分呈表层聚集现象; 阿拉尔和塔中样区柽柳沙包的土壤盐分呈深层聚集现象。随着土层深度的增加, 土壤pH值总体呈升高的趋势, 土壤枯落物含量总体呈降低趋势; 土壤电导率在且末和策勒样区总体呈降低趋势, 阿拉尔样区呈先降低后升高再降低的变化趋势, 而塔中样区呈先升高后降低再升高的变化趋势。3)根据相关性分析和主成分分析, 且末样区土壤枯落物含量、SO₄ ^2-、Na ⁺、K ⁺为影响土壤盐分含量的主要因子, 且土壤盐分以硫酸盐为主; 阿拉尔样区影响土壤盐分组成的主要因子为Cl ^-、Na ⁺; 策勒样区为Cl ^-、K ⁺、Na ⁺; 塔中样区为Cl ^-、Na ⁺、Ca ²⁺、SO₄ ^2-, 且土壤盐分均以氯化物为主。综合分析表明, 不同区域柽柳沙包中土壤盐分存在空间变异性, 柽柳沙包土壤盐分的变化与干旱沙漠地区强烈的蒸发作用、地表风蚀强度、地下水埋深、土壤中枯落物及柽柳的生物积盐效应等因素密切相关, 是影响不同区域土壤盐分分布的关键因子。     

Construction of CO2-response model of electron transport rate in C4 crop and its application

准确估算光合电子流对CO₂响应的变化趋势对深入了解光合过程具有重要意义。该研究在植物光合作用对CO₂响应新模型(模型I)的基础上构建了电子传递速率(J)对CO₂的响应模型(模型II), 并对用LI-6400-40便携式光合仪测量的玉米(Zea mays)和千穗谷(Amaranthus hypochondriacus)的数据进行了拟合。结果表明, 模型II可以很好地拟合玉米和千穗谷叶片J对CO₂浓度的响应曲线(J-C_a曲线), 得到玉米和千穗谷的最大电子传递速率分别为262.41和393.07 mmol·m ^-2·s ^-1, 与估算值相符合。在此基础上, 对光合电子流分配到其他路径进行了探讨。结果显示, 380 mmol·mol ^-1 CO₂浓度下玉米和千穗谷碳同化所需的电子流为247.92和285.16 mmol·m ^-2·s ^-1, 分配到其他途径的光合电子流为14.49和107.91 mmol·m ^-2·s ^-1(考虑植物CO₂的回收利用)。比较两种植物的其他途径光合电子流分配值发现, 两者相差6倍之多。分析认为这与千穗谷和玉米的催化脱羧反应酶种类以及脱羧反应发生的部位不同密切相关。该发现为人们研究C₄植物中烟酰胺腺嘌呤二核苷磷酸苹果酸酶型和烟酰胺腺嘌呤二核苷酸苹果酸酶型两种亚型之间的差异提供了一个新的视角。此外, 构建的电子传递速率对CO₂的响应模型为人们研究C₄植物的光合电子流的变化规律提供了一个可供选择的数学工具。