刈割、围封、放牧三种利用方式下草原生态系统的多功能性与植物物种多样性之间的关系

随着全球变化对生物多样性的影响不断加剧, 生物多样性与生态系统功能之间相互关系(BEF)的研究显得极为重要。过去的20多年, BEF的研究大多集中在对物种多样性与单一或少数生态系统功能之间关系的探讨, 但生态系统最为重要的价值是同时维持多种服务和功能的能力, 基于此, 该文首次在国内引入近年来不断完善的生态系统多功能性(multifunctionality)的概念, 并对目前主流的评价方法进行了改进, 从而对内蒙古三种利用方式(刈割、围封、放牧)下的草地群落进行了多功能性评价, 并探讨了多功能性与物种多样性之间的关系。结果显示本研究改进的方法和目前主流方法评价得出的多功能性指数在样方和样地尺度上都有很高的相关性(R² = 0.6956, p < 0.0001; R² = 0.9231, p < 0.0001), 表明该文作者改进后的方法是可靠的。重度放牧的草地群落物种多样性水平最低, 绝大多数土壤功能指标较差, 表现出退化特征; 7年的围封和刈割群落均有较高的物种多样性水平和改善的土壤功能指标; 三者的多功能性指数为刈割(0.2178) >围封(0.0704) >放牧(-0.8031)。植被样方主要沿水肥梯度分布; 多样性指数中, 均匀度指数(Pielou index)和丰富度指数(Margelf index)对多功能性的影响作用最大, 均为样方尺度(R² = 0.1871, p < 0.0001; R² = 0.1601, p < 0.0001)小于样地尺度(R² = 0.5921, p = 0.0093; R² = 0.7499, p = 0.0007), 有尺度依赖性; 多功能性在样方和样地尺度上均与物种均匀度呈线性正相关关系, 而与物种丰富度呈单峰曲线关系。该文研究结果表明, 相对于重度放牧和围封, 刈割更有利于维持该地区生态系统的多功能性; 物种丰富度适中且物种分布均匀的生态系统可能有更好的多功能性。     

Effects of grazing intensity and grazing exclusion on litter decomposition in the temperate steppe of Nei Mongol,China

Aims Grazing intensity and grazing exclusion affect ecosystem carbon cycling by changing the plant community and soil micro-environment in grassland ecosystems. The aims of this study were: 1) to determine the effects of grazing intensity and grazing exclusion on litter decomposition in the temperate grasslands of Nei Mongol; 2) to compare the difference between above-ground and below-ground litter decomposition; 3) to identify the effects of precipitation on litter production and decomposition. Methods We measured litter production, quality, decomposition rates and soil nutrient contents during the growing season in 2011 and 2012 in four plots, i.e. light grazing, heavy grazing, light grazing exclusion and heavy grazing exclusion. Quadrate surveys and litter bags were used to measure litter production and decomposition rates. All data were analyzed with ANOVA and Pearson’s correlation procedures in SPSS. Important findings Litter production and decomposition rates differed greatly among four plots. During the two years of our study, above-ground litter production and decomposition in heavy-grazing plots were faster than those in light-grazing plots. In the dry year, below-ground litter production and decomposition in light-grazing plots were faster than those in heavy-grazing plots, which is opposite to the findings in the wet year. Short-term grazing exclusion could promote litter production, and the exclusion of light-grazing could increase litter decomposition and nutrient cycling. In contrast, heavy-grazing exclusion decreased litter decomposition. Thus, grazing exclusion is beneficial to the restoration of the light-grazing grasslands, and more human management measures are needed during the restoration of heavy-grazing grasslands. Precipitation increased litter production and decomposition, and below-ground litter was more vulnerable to the inter-annual change of precipitation than above-ground litter. Compared to the light-grazing grasslands, heavy-grazing grasslands had higher sensitivity to precipitation. The above-ground litter decomposition was strongly positively correlated with the litter N content (R² = 0.489, p < 0.01) and strongly negatively correlated with the soil total N content (R² = 0.450, p < 0.01), but it was not significantly correlated with C:N and lignin:N. Below-ground litter decomposition was negatively correlated with the litter C (R² = 0.263, p < 0.01), C:N (R² = 0.349, p < 0.01) and cellulose content (R² = 0.460, p < 0.01). Our results will provide a theoretical basis for ecosystem restoration and the research of carbon cycling.     

Relationship between photochemical reflectance index with multi-angle hyper-spectrum and light use efficiency in urban green-land ecosystems

Aims Light-use efficiency (LUE) is one of critical parameters in the terrestrial ecosystem production studies. Accurate determination of LUE is very important for LUE models to simulate gross primary productivity (GPP) at regional and global scales. We used eddy covariance technique measurement and tower-based, multi-angular spectro-radiometer observations in autumn 2012 to explore the relationship between bidirectional reflectance distribution function (BRDF) corrected photochemical reflectance index (PRI) and LUE in different phenology and environment conditions in urban green-land ecosystems. Methods Using the eddy covariance technique, we estimated the temporal changes in GPP during the autumn 2012 over Beijing Olympic Forest Park. LUE was calculated as the ratio of GPP to the difference between incoming photosynthetically active radiation (PAR) and PAR reflected from the canopy. Daily PRI values were averaged from the BRDF using semi-empirical kernel driven models. The absolute greenness index (2G_RB) was made by webcam at a constant view zenith and view azimuth angle at solar noon. The logistic function was used to fit the time series of the greenness index. The onset of phonological stages was defined as the point when the curvature reached its maximum value. Important findings Webcamera-observed greenness index (2G_RB) showed a decreasing trend. There was a highly significant relationship between 2G_RB and air temperature (R² = 0.60, p < 0.001). This demonstrates that air temperature is the main driving factor to determine the phenology. PRI estimated from multi-angle hyper-spectrum can estimate LUE in urban green-land ecosystems in vigorous photosynthetic period. The correlation was the strongest (R² = 0.70, p < 0.001) in the peak photosynthetic period. PRI relates better to LUE under high temperature (>15 °C) with high vapour pressure deficit (VPD) (>700 Pa) and high PAR (>300 μmol·m^-2·s^-1). The LUE was up-scaled to landscape/regional scales based on these relationships and phenology. It can also be used for the estimation of GPP of urban green-land with high accuracy.     

内蒙古温带草原不同放牧强度和围栏封育对凋落物分解的影响

放牧和围封通过影响植物群落结构和土壤微环境来调控草地生态系统的碳循环。该研究在内蒙古温带草原设置轻度放牧后围封、轻度放牧、重度放牧后围封、重度放牧4种样地, 通过测定干旱年(2011年)和湿润年(2012年)地上、地下凋落物产量、质量及其分解速率和土壤养分含量, 分析不同放牧强度对凋落物形成和分解的影响, 以及围栏封育对生态系统恢复的作用。结果表明: 重度放牧地上凋落物产量和分解速率均高于轻度放牧。干旱年轻度放牧样地地下凋落物产量和分解速率高于重度放牧, 湿润年相反。短期围封显著提高了凋落物产量, 轻度放牧样地围封后地上凋落物分解速率和养分循环加快, 而重度放牧样地围封后地上凋落物分解减慢。因此, 与重度放牧相比, 轻度放牧草地的恢复更适合采用围栏封育措施; 而重度放牧草地的恢复可能还需辅以必要的人工措施。降水显著促进地上、地下凋落物形成和分解。地下凋落物的生产和分解受降水年际波动影响较大, 重度放牧草地对降水变化的敏感度比轻度放牧草地高。地上凋落物分解速率与凋落物N含量显著正相关, 与土壤全N显著负相关, 与地上凋落物C:N和木质素:N相关性不大; 地下凋落物分解速率与凋落物C、C:N和纤维素含量显著负相关。该研究结果将为不同放牧强度的草地生态系统恢复和碳循环研究提供理论依据。     

Plant nutrient dynamics and stoichiometric homeostasis of invasive species Spartina alterniflora and native Cyperus malaccensis var. brevifolius in the Minjiang River estuarine wetlands

Aims Stoichiometric homeostasis is an important mechanism in maintaining ecosystem structure, function, and stability. The invasion of exotic species, Spartina alterniflora, has largely threatened the structure and function of native ecosystems in the Minjiang River estuarine wetland. However, how S. alterniflora invasion affect plant stoichiometric homeostasis is largely unknown. This could enhance our understanding on wetland ecosystem stability and expand the applications of ecological stoichiometry theory.
Methods Nitrogen (N) and phosphorus (P) contents of plant organs and soils in the S. alterniflora, Cyperus malaccensis var. brevifolius, and S. alterniflora-C. malaccensis var. brevifolius mixture were measured, and the homeostatic index (H) was calculated according to the stoichiometric homeostasis theory.
Important findings Our results showed that the invasion of S. alterniflora significantly increased soil N:P ratio (p < 0.05), but did not affect soil N or P contents. The N and P contents of leaf and stem were the highest for S. alterniflora, and those of the stem were the highest for C. malaccensis var. brevifolius. At the ecosystem level, the average of homeostatic index (H) of N (H_N, 25.31) was larger than those of P (H_P, 10.33) and N:P (H_N:P, 2.50). At the organ level, root H_N was significantly larger than stem H_N (p < 0.05) and sheath H_N:P was greater than root H_N:P (p < 0.05), while there was no significant difference for H_P among root, stem, leaf, and sheath (p > 0.05). As for species, root H_N of S. alterniflora was significantly larger than that of C. malaccensis var. brevifolius in the mixture community (p < 0.05). In the monoculture, stem H_N:P of S. alterniflora was significantly higher than that of C. malaccensis var. brevifolius (p < 0.05). Furthermore, root H_N, leaf H_N and sheath H_N of S. alterniflora in the mixed community was significantly larger than that of S. alterniflora in the monoculture (p < 0.05), suggesting that S. alterniflora invasions increased their stoichiometric homeostasis. Meanwhile, the stoichiometric homeostasis of invasive and native plants were influenced by multiple factors, such as nutrients, organs, vegetation, and invasion. However, larger homeostasis was found in S. alterniflora than in C. malaccensis var. brevifolius in some particular organs either in mixture or monoculture communities. Therefore, the successful invasion of S. alterniflora may result from higher homeostatic index than the native species, C. malaccensis var. brevifolius.     

Forest species diversity mapping based on clustering algorithm

该研究基于机载激光雷达(LiDAR)和高光谱数据, 从森林物种叶片的生理化学源头探寻生化特征与光谱特征的内在关联, 探讨生化多样性、光谱多样性与物种多样性之间的响应机制, 选择最优植被指数并结合最优结构参数, 通过聚类方法构建森林物种多样性遥感估算模型, 在古田山自然保护区开展森林乔木物种多样性监测。研究结果表明: (1)从16种叶片生化组分中, 筛选出叶绿素a、叶绿素b、类胡萝卜素、叶片含水量、比叶面积、纤维素、木质素、氮、磷和碳可通过偏最小二乘法用叶片光谱有效模拟(R² = 0.60-0.79, p < 0.01), 并选择有效的植被指数: 转换型吸收反射指数/优化型土壤调整指数(TCARI/OSAVI)、类胡萝卜素反射指数(CRI)、水波段指数(WBI)、比值植被指数(RVI)、生理反射指数(PRI)和冠层叶绿素浓度指数(CCCI)表征相应的最优生化组分; (2)基于机载LiDAR数据利用结合形态学冠层控制的分水岭算法获得高精度单木分离结果(R ² = 0.77, RMSE = 16.48), 同时采用逐步回归方法从常用的森林结构参数中选取树高和偏度作为最优结构参数(R ² = 0.32, p < 0.01); (3)基于6个最优植被指数和2个最优结构参数, 以20 m × 20 m为窗口通过自适应模糊C均值方法进行聚类, 实现了研究区森林乔木物种丰富度(Richness, R ²= 0.56, RMSE = 1.81)和多样性指数Shannon-Wiener (R ² = 0.83, RMSE = 0.22)与Simpson (R ² = 0.85, RMSE = 0.09)的成图。该研究在冠层尺度上获取了与物种多样性相关的生化、光谱和结构参数, 将单木个体作为最小单元, 利用聚类算法直接估算物种类别差异, 无需判定具体的树种属性, 是利用遥感数据进行区域尺度森林物种多样性监测与成图的实践, 可为亚热带地区常绿阔叶林的物种多样性监测提供借鉴。     

城市绿地生态系统多角度高光谱光化学反射植被指数与光能利用率的关系

光能利用率(LUE)是陆地生态系统总初级生产力(GPP)估算的一个重要参数。LUE的准确估算对于在区域甚至全球尺度上使用LUE模型估算GPP是非常重要的。一个基于通量塔的观测视场与通量观测足迹在时空上相匹配的自动多角度遥感平台为LUE在站点尺度上的准确估算提供了一个好方法。该文基于通量塔涡度相关(EC)和自动多角度高光谱连续观测获取的连续30 min的数据, 在站点空间尺度和0.5 h与日时间尺度上, 探讨了城市绿地生态系统秋季光化学反射植被指数(PRI)与LUE之间的关系。研究发现, 反映植被叶面积和色素变化的植被绿度指数在秋季呈现逐渐下降的趋势, 表征了植被冠层的状态与结构变化, 叶片从绿色逐渐变黄凋落, 植被冠层叶片的叶绿素逐渐减少, 裸露的枝干增多; 用空气温度和代表物候过程的绝对绿度指数(2G_RB)做线性回归分析, 得到回归系数(R²)为0.60 (p < 0.001)。说明在城市绿地生态系统中, 空气温度是决定植被物候过程的主要驱动因素, 随着植被物候变化, 叶片的凋落导致的裸露土壤的增多以及随时间变化的色素含量和其比例的变化将影响PRI和LUE的关系; 采用植被生长模型(logistic曲线), 拟合时间与2G_RB, 得到曲率变化最快的点, 确定为秋季植被落叶期的初日, 即第290天。在0.5 h和日时间尺度上, PRI都可以捕捉LUE的变化。但是日尺度上不同物候期, PRI和LUE的关系发生了急剧的变化。在秋季植被正常生长期, PRI和LUE之间的关系最密切(R² = 0.70, p < 0.001)。当土壤温度大于15 ℃、光合有效辐射(PAR)大于300 μmol·m^-2·s^-1以及饱和水汽压差(VPD)大于700 Pa的情况下, PRI能够更好地预测LUE。基于通 量塔尺度上时空尺度相匹配, 利用半经验的核驱动二向反射分布函数模型得到的高光谱PRI和通量观测得到的LUE在不同环境条件下的关系以及考虑到在植被的不同物候期对PRI和LUE的关系的优化, 将会更加准确地估算城市绿地生态系统的LUE。     

Effects of nitrogen addition on soil respiration of Rhododendron simsii shrubland in the subtropical mountainous areas of China

Aims As the second largest C flux between the atmosphere and terrestrial ecosystems, soil respiration plays a vital role in regulating atmosphere CO₂ concentration. Therefore, understanding the response of soil respiration to the increasing nitrogen deposition is urgently needed for prediction of future climate change. However, it is still unclear how nitrogen deposition influences soil respiration of shrubland in subtropical China. Our objectives were to explore the effects of different levels of nitrogen fertilization on soil respiration, root biomass increment, and litter biomass, and to analyze the relationships between soil respiration and soil temperature and moisture.
Methods From January 2013 to September 2014, we conducted a short-term simulated nitrogen deposition experiment in the Rhododendron simsii shrubland of Dawei Mountain, located in Hunan Province, southern China. Four levels of nitrogen addition treatments (each level with three replicates) were established: control (CK, no nitrogen addition), low nitrogen addition (LN, 2 g·m^-2·a^-1), medium nitrogen addition (MN, 5 g·m^-2·a^-1) and high nitrogen addition (HN, 10 g·m^-2·a^-1). Soil respiration was measured by LI-8100 soil CO₂ efflux system. At the same time, we measured root biomass increment and litter biomass in each plot.
Important findings Soil respiration exhibited a strong seasonal pattern, with the highest rates found in summer and the lowest rates in winter. Annual accumulative soil respiration rate in the CK, LN, MN and HN was (2.37 ± 0.39), (2.79 ± 0.42), (2.26 ± 0.38) and (2.30 ± 0.36) kg CO₂·m^-2, respectively. Annual mean soil respiration rate in the CK, LN, MN and HN was (1.71 ± 0.28), (2.01 ± 0.30), (1.63 ± 0.27) and (1.66 ± 0.26) μmol CO₂·m^-2·s^-1, respectively, and it was 17.25% higher in the LN treatment compared with CK (p = 0.06). The root biomass increment was increased by LN, MN, and HN treatments by 18.36%, 36.49% and 61.63%, respectively, compared to CK. The litter biomass was increased by LN, MN, and HN treatments by 35.87%, 22.17% and 15.35%, respectively, compared with CK. Soil respiration exhibited a significant exponential relationship with soil temperature (p < 0.01, R² is 0.77 to 0.82) and a significant linear relationship with soil moisture at the depth of 5 cm (p < 0.05, R² is 0.10 to 0.15). The temperature sensitivity (Q₁₀) value of CK, LN, MN and HN plots was 3.96, 3.60, 3.71 and 3.51, respectively. These results suggested that nitrogen addition promoted plant growth and decreased the temperature sensitivity of soil respiration. The increase of root biomass under N addition may be an important reason for the change of soil respiration in the study area.     

Effects of grazing intensity on windblown sediment mass flux and particle size distribution in the desert steppe of Nei Mongol,China

Aims Grazing activities degrade soil aggregates, reduce vegetation coverage and affect the amount of deposited material, and make the land more vulnerable to wind erosion. Although livestock increase was considered as the main issue leading to the degradation, only very few studies have quantitatively investigated the relationship between grazing and soil erosion. The relationship between different stocking rates and sediment flux, and sediment soil particle was studied to reveal the mechanism of different grazing intensities on soil erosion process, to provide basic parameters for grazing optimization in the Stipa breviflora desert steppe. Methods In the Stipa breviflora desert steppe research area, BSNE collecting sand boxes were set in the randomly distributed paddock experiment sites for 11 year with different grazing intensities (0.15、0.30、0.45、0 sheep·hm^-2·month^-1, corresponding to light grazing LG, moderate grazing MG, heavy grazing HG and control CK, respectively). The quantitative relationship between grazing intensity and sediment flux, and the characteristics of sediment soil particle were conducted in four sampling periods through 2 years (April 2013 to April 2015).Important findings (1) Grazing intensity had a significant effect on the sediment flux (p< 0.05), and the sediment flux increased with the increase of grazing intensity. The response of sediment flux to grazing intensity was variable with season. The daily average sediment flux (13.12 g·m^-1·d^-1) during the period of April to October was smaller than that from October to April (18.74 g·m^-1·d^-1). The sediment flux difference of different grazing intensities was greater from April to October, with the 5 times daily average sand flux in the heavy grazing paddock that in the control. The average sediment flux difference of different grazing intensities was small from October to April. (2) The relationship between the natural logarithm of sediment flux at different height and the vertical height had a better binomial fitting from April to October, and there was no obvious regular pattern about flux vertical distribution from October to April, and the vertical flux difference of grazing intensities was mainly expressed in 0-50 cm layer. (3) Sand sediment particle ≤250 μm accounted for more than 85% of the total sediment, the sand sediment particle of ≤50 μm) size was significantly enriched, and the enrichment ratio increased with the increase of vertical height. The enrichment ratio of 125-250 μm particle and 50-125 μm particle decreased with the increase of vertical height, and the enrichment ratio of 125-250 μm particle was smaller than that of 50-125 μm particle (p< 0.05). Therefore grazing intensity had different influence on the sand flux in Stipa breviflora desert steppe, the greater the grazing intensity, the heavier the wind erosion was, and the effect of grazing intensity on grassland was enhanced by wind erosion.     

Greenhouse gas fluxes of typical northern subtropical forest soils: Impacts of land use change and reduced precipitation

Aims It is important to study the effects of land use change and reduced precipitation on greenhouse gas fluxes (CO₂, CH₄ and N₂O) of forest soils. Methods The fluxes of CO₂, CH₄ and N₂O and their responses to environmental factors of primary forest soil, secondary forest soil and artificial forest soil under a reduced precipitation regime were explored using the static chamber and gas chromatography methods during the period from January to December in 2014. Important findings Results indicate that CH₄ uptake of primary forest soil ((-44.43 ± 8.73) μg C·m^-2·h^-1) was significantly higher than that of the secondary forest soil ((-21.64 ± 4.86) μg C·m^-2·h^-1) and the artificial forest soil ((-10.52 ± 2.11) μg C·m^-2·h^-1). CH₄ uptake of the secondary forest soil ((-21.64 ± 4.86) μg C·m^-2·h^-1) was significantly higher than that of the artificial forest ((-10.52 ± 2.11) μg C·m^-2·h^-1). CO₂ emissions of the artificial forest soil ((106.53 ± 19.33) μg C·m^-2·h^-1) were significantly higher than that of the primary forest soil ((49.50 ± 8.16) μg C·m^-2·h^-1) and the secondary forest soil ((63.50 ± 5.35) μg C·m^-2·h^-1) (p < 0.01). N₂O emissions of the secondary forest soil ((1.91 ± 1.22) μg N·m^-2·h^-1) were higher than that of the primary forest soil ((1.40 ± 0.28) μg N·m^-2·h^-1) and the artificial forest soil ((1.01 ± 0.86) μg N·m^-2·h^-1). Reduced precipitation (-50%) had a significant inhibitory effect on CH₄ uptake of the artificial forest soil, while it enhanced CO₂ emissions of the primary forest soil and the secondary forest soil. Reduced precipitation had a significant inhibitory effect on CO₂ emissions of the artificial forest soil and N₂O emissions of the secondary forest (p < 0.01). Reduced precipitation promotes N₂O emissions of the primary forest soil and the artificial forest soil. CH₄ uptake of the primary forest and the secondary forest soil increased significantly with the increase of soil temperature under natural and reduced precipitation. CO₂ and N₂O emission fluxes of the primary forest soil, secondary forest soil and artificial forest soil were positively correlated with soil temperature (p < 0.05). Soil moisture inhibited CH₄ uptake of the secondary forest soil and the artificial forest soil (p < 0.05). CO₂ emissions of the primary forest soil were significantly positively correlated with soil moisture (p < 0.05). N₂O emissions of primary forest soil and secondary forest soil were significantly correlated with the nitrate nitrogen content (p < 0.05). It was implied that reduced precipitation and land use change would have significant effects on greenhouse gas emissions of subtropical forest soils.     

Characteristics of nitrogen and phosphorus stoichiometry across components of forest ecosystem in Shaanxi Province

Aims Nitrogen (N) and phosphorus (P) stoichiometry between vegetation, litter, and soil were important for understanding biogeochemical cycles in terrestrial ecosystems, but remain poorly understood. Here, our aims were to study characteristics of N and P stoichiometry for the plant, litter, and soil and the interactions between its components across forest ecosystems in Shaanxi Province.Methods A total of 121 sampling sites, covering the most main forest types in Shaanxi, were established across the whole province in 2012. And N and P concentration of vegetation (tree and understory), litter and soil layers were measured for each site.Important findings 1) There were significant differences in the N and P stoichiometry among the forest ecosystem components (p < 0.05). N and P contents were higher in understory and litter layer, and lower in tree and soil. Whereas the N:P was slightly different, highest in litter and lowest in the soil layer, with little differences among remaining components. The contents of N, P and N:P ranged from 0.72 to11.99 mg·g^-1, 0.47 to 1.07 mg·g^-1, and 1.86 to 14.84, respectively. Within top 1 m soil layer N content and N:P decreased with soil depth (p < 0.05), however the P content did not exhibit significant changes. 2) N and P contents, and N:P of each component were higher in broadleaf forest than in coniferous forest, although the difference is not significant. 3) N was positively correlated with P content except for soil and N:P was negatively correlated with P content, but positively correlated with N content within each component. In addition, there was a significant positive correlation for N and P stoichiometric characteristics between litter layer and tree, herb, soil layer. 4) Although spatial pattern of N and P contents, and N:P differed in relation to longitude, latitude, and elevation for forest ecosystem components, a stable distribution was exhibited in general.     

Effects of glyphosate on interspecific competition between Solidago canadensis and Imperata cylindrica

Aims The extensive use of herbicide to control invasive plants would change the relationship between alien and neighboring plants. In order to provide data for rational use of herbicide and a theoretical reference for further studies on the ecological effects of glyphosate, we explored the variation of the relationship between an invasive plant Solidago canadensis and a native plant Imperata cylindrica when they were sprayed glyphosate.
Methods A replacement series experiment was conducted from June to August 2016 in Wetland Ecosystem Research Station of Hangzhou Bay, State Forestry Administration, to examine the effects of glyphosate at seven concentration levels (0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8 mL·L^-1) on the growth and interspecific competition of S. canadensis and I. cylindrica.
Important findings (1) Glyphosate treatment significantly inhibited the growth of S. canadensis and I. cylindrica (p < 0.05). During the test, cumulative growth of height and leaf number of S. canadensis were apparently reduced with the increase of glyphosate concentration, but the leaf number of S. canadensis treated with 0.3- 1.5 mL·L^-1 glyphosate was re-growing with time, while the one treated with 1.8 mL·L^-1 was mostly dead. The withering rate of tiller and green leaf of I. cylindrica also significantly increased with the increase of glyphosate concentration, and the growth indices of this plant treated with 0.3-0.6 mL·L^-1 were also re-growing with time. (2) Glyphosate treatment significantly affected interspecific competition (p < 0.05), which diminished as the glyphosate concentration increased. (3) Interspecific competition has significant influence on the biomass allocation of S. canadensis (p < 0.05). When facing competition, S. canadensis would allocate more organic matter to root and thus increase the ratio of root to shoot. Competition only inhibited the tiller number and total biomass of I. cylindrica, but insignificantly affected its ratio of root to shoot. (4) The interaction between glyphosate treatment and S. canadensis-I. cylindrica interspecific relationship also significantly influenced the biomass of S. canadensis and I. cylindrica (p < 0.05), but insignificantly affected the root/shoot ratio of two plants. Different plants have different tolerance to glyphosate stress. Compared with native plant I. cylindrica, S. canadensis has stronger tolerance to glyphosate. Low-concentration glyphosate could decrease the competitive intensity between S. canadensis and I. cylindrica, which may disturb the structure and dynamics of plant communities.     

Canopy structure and radiation interception of Salix matsudana: Stand density dependent relationships

Aims Plants can enhance their photosynthetic efficiency and competitiveness by adjusting canopy structure and radiation interception. The objective of this paper was to quantify the relationship between canopy structure (crown depth and crown area) and light interception (LI) in a Salix matsudana stand under three different stand densities in a flood plain of Zhangye.Methods Our study site is located at the Heihe flood plain of Xichengyi in Ganzhou district, Zhangye City, Gansu Province in the middle Heihe River, where S. matsudana is the dominant species. Based on stand density (10 m × 10 m), the S. matsudana community is divided into three types: low density (I, 25-36 Ind.·plot^-1), medium density (II, 37-48 Ind.·plot^-1), and high density (III, 49-60 Ind.·plot^-1). Community characteristics, soil physical and chemical properties of each type were measured. At each plot, we measured photosynthetically active radiation (PAR), LI, net photosynthetic rate (P_n), transpiration rate (T_r), crown depth, crown area, leaf area index (LAI), twig numbers, twig length, and bifurcation angle. The standardized major axis (SMA) estimation method was used to determine the relationships between LI and canopy structure.Important findings With increasing in stand density, we found that soil moisture increased, and soil electric conductivity decreased, while twig length and crown depth increased, and PAR, twig numbers, bifurcation angle and crown area decreased. LAI and LI, P_n and T_r reached their maximum at the stand of medium density. There was a significant, positive correlation and negative correlation (p < 0.01), respectively, between the LI, crown depth and crown area at low density (I), whereas low significant (p < 0.05) at high density (III), and high significantly positive correlation (p < 0.01) at the medium density (II). S. matsudana has more horizontal branches that reduce LI. Canopy thickness and increased crown area at low density. More vertical distribution of branches at high density, and a more balanced spacial distribution were found at medium density.     

Dynamics and regulations of ecosystem light use efficiency in a broad-leaved Korean pine mixed forest,Changbai Mountain

Aims Ecosystem light use efficiency (LUE) reflects the ability of CO₂ uptake and light utilization via photosynthesis, which is a key parameter in ecosystem models to evaluate ecosystem productivity. The objectives of this study were to: (1) compare the differences of LUE derived from different methods; (2) elucidate the seasonal dynamics of LUE and its regulatory factors; and (3) evaluate the maximum LUE (LUE_max) and its variability based on eddy-covariance (EC) flux.Methods Using the flux data from an EC tower during 2003-2005 at a broad-leaved Korean pine (Pinus koraiensis) mixed forest, Changbai Mountain, two types of LUE indicators were generated from: 1) the apparent quantum yield (ε) estimated with rectangular hyperbolic curve, and 2) the ecological light use efficiency (LUE_eco) calculated as the ratio between gross ecosystem productivity (GEP) and photosynthetically-active radiation (Q).Important findings The seasonal variation of ε and LUE_eco appeared a unimodal pattern within a year, with the variations significantly dominated by soil surface temperature and Normalized Difference Vegetation Index (NDVI). A positive correlation between GEP and LUE was found for both ε and LUE_eco, with the effect of Q on LUE relatively weak. The increase in diffusion radiation appeared favorable for enhanced LUE. Generally, there was a significant positive relationship between ε and LUE_eco, while ε was higher than LUE_eco, especially during the mid-season. The annual maximum value of ε and LUE_eco was (0.087 ± 0.003) and (0.040 ± 0.002) μmol CO₂·μmol photon^-1 over the three years, respectively. The interannual variability of LUE_max for ε and LUE_eco was 4.17% and 4.25%, respectively, with a maximum difference of >8%, likely resulted from considerable uncertainty in model simulations. Our results indicated that the inversion and optimization of maximum LUE should be taken seriously in the application of LUE models.     

Foliar stable carbon isotope ratios of Phragmites australis and the relevant environmental factors in marsh wetlands in Tianjin

Aims Phragmites australis marshes in Tianjin play an important role in ecosystem functioning. Wetlands of Tianjin municipality have been suffering from serious nitrogen loading, salinization and water shortage. The foliar stable carbon isotope ratio (δ¹³C) is a good parameter which records environmental change information associated with the plant growth process, and reflects physiological and ecological responses of plants to environment changes. The objective of this study is to investigate the effects of environment stress on the leaf δ¹³C of P. australis in marsh wetlands in Tianjin municipality.Methods This study was conducted in Qilihai, Beidagang, and Dahuangpu marsh wetlands. We investigated the foliar δ¹³C of P. australis and sediment properties, and evaluated the relationships between the foliar δ¹³C and sediment environmental factors. Important findings 1) Foliar δ¹³C ranged from -26.3‰ to -23.6‰, with an average value of -25.8‰. 2) Sediment water and nitrogen status were the important factors affecting reed foliar δ¹³C. Foliar δ¹³C was negatively correlated to sediment relative water content, and positively correlated to sediment total nitrogen and available nitrogen content. In contrast, foliar δ¹³C was not significantly correlated to sediment salinity and phosphorus content. 3) Leaf δ¹³C were significantly positively correlated with leaf nitrogen content, and negatively correlated with leaf carbon and nitrogen ratio across all site. However, these relationships were not detected due to the wetland drainage at Qilihai site in August. Wetland drainage changed the plant water and nitrogen balance, and further affected water and nitrogen utilization strategies of P. australis. Moreover, wetland drainage had stronger effects on these processes than nitrogen loading and salinization.     

阴天和晴天对黄河三角洲芦苇湿地净生态系统CO2交换的影响

云量以及大气气溶胶含量变化引起的阴天和晴天会对局地的微气候环境产生综合效应, 影响地面接收的太阳辐射强度, 同时引起环境因子的变化, 最终对净生态系统CO₂交换(NEE)产生影响。该文通过涡度相关系统以及微气象梯度观测系统, 对黄河三角洲芦苇(Phragmites australis)湿地NEE以及环境要素进行了观测。在自然条件下选择12对相邻阴天和晴天数据, 在生物要素(生物量、叶面积指数)、土壤水分以及养分特征保持不变的前提下, 揭示了阴天和晴天变化对湿地生态系统NEE的光响应和温度响应的影响。结果表明: 12对阴天和晴天生态系统NEE的日平均动态均呈“U”型曲线, 但阴天NEE的变幅较小。晴天条件下湿地生态系统NEE的日均值显著高于阴天(p < 0.01)。阴天和晴天湿地生态系统NEE与光合有效辐射(PAR)之间均呈直角双曲线关系, 但晴天条件下, 最大光合速率(A_max)显著大于阴天(p < 0.01), 同时白天生态系统呼吸(R_eco,daytime)也显著大于阴天(p < 0.01)。不论阴天还是晴天, R_eco,daytime与气温均呈显著的指数关系。晴天湿地生态系统呼吸的温度敏感系数Q₁₀ (5.5)远大于阴天(1.9)。阴天和晴天昼间PAR差值以及气温差值对NEE差值的协同影响达到63%。     

放牧对草地生态系统服务和功能权衡关系的影响

内蒙古草原是我国北方的重要生态屏障和绿色畜牧业基地, 放牧是草原生态系统的主要利用和管理方式, 在放牧管理中充分发挥生态系统某一项或几项服务和功能最大利用价值时, 往往会与其他服务(功能)发生冲突, 需要权衡多项生态系统服务和功能, 制定合理的放牧管理制度。该研究以内蒙古锡林郭勒典型草原为例, 通过设置不放牧、轻度放牧、中度放牧以及重度放牧的放牧梯度, 从多项生态系统服务和功能权衡的角度比较了最适放牧管理强度。结果显示, 在放牧管理的草地生态系统服务和功能的权衡中, 权衡、协同、不相关关系同时存在, 如土壤呼吸速率与植物群落净生长量、生物多样性与植物群落净光合速率表现为权衡关系, 植物群落净生长量分别与土壤含水量、植物群落净光合速率及草地蒸散速率存在协同关系, 土壤有机碳含量与其他服务或功能间呈不相关关系; 放牧能不同程度地削弱多项生态系统服务及功能间的权衡关系(冲突对立关系); 中度放牧条件下的多项生态系统服务及功能的协同性最佳。     

Trade-off between leaf size and vein density of Achnatherum splendens in Zhangye wetland

Aims Trade-offs between leaf size and vein density are the basis of the theory of leaf economics spectrum, and are to understand the relationship between the physical build and physiological metabolism of plant leaves under different degrees of competition for resources. Our objective was to study the changes in the relationship between leaf size and vein density (leaf dry biomass and leaf area) in Achnatherum splendens populations with four plant bundle densities located in the flood plain wetland of Zhangye. Methods The study site was located at floodplain wetlands of Zhangye, Gansu Province, China. Survey and sampling were carried out in the communities that A. splendens dominated. According to the plant bundle density, the A. splendens communities were divided into four density gradients with “bundle” for the sampling units, high density (I, > 12 bundle·m^-2), medium density (II, 8-12 bundle·m^-2), medium density (III, 4-8 bundle·m^-2) and Low density (IV, <4 bundle·m^-2). According to the density of each combination, we chose seven (5 m × 5 m) A. splendens samples, resulting in a total of 28 samples (4 × 7). The soil physical and chemical properties of four density gradients were investigated and six samples of A. splendens were used to measure the leaf area, leaf dry biomass and vein density in laboratory, and biomass of different organs was measured after being dried at 85 °C in an oven. 28 plots were categorized into three groups: high, medium and low density, and the standardized major axis (SMA) estimation method was used to examine the allometric relationships between leaf area, leaf dry biomass and vein density. Important findings The results showed that with the population density changed from high, medium, to low, the soil moisture decreased, and soil electric conductivityincreased. The leaf area, leaf biomass and height of A. splendens decreased, and the vein density, specific leaf area and photosynthetically active radiation (PAR) increased gradually. In addition, leaf net photosynthetic rate (P_n), transpiration rate (T_r) and twig number firstly increased then decreased. There was a highly significantly negative correlation (p < 0.01) between the leaf size and vein density on the high- and low-level densities (I, IV), whereas less significant (p < 0.05) on the level of medium density (II, III). The SMA slope of regression equation in the scaling relationships between leaf size and vein density was significantly smaller than -1 (p < 0.05).     

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.     

Carbon,nitrogen and phosphorus stoichiometry of Myrica nana in Yunnan,China

Aims Carbon (C), nitrogen (N) and phosphorus (P) play important roles in plant growth and physiological functions. We aimed at exploring the intrinsic relationships of C, N and P in Myrica nana—a common shrub in Yunnan Province—as well as their relationships with pant biomass and soil nutrients.
Methods We measured the concentration of C, N and P of M. nana from 29 sites for their magnitudes and correlations with soil nutrients.
Important findings 1) The arithmetic mean value of C, N and P concentration in the roots, stems and leaves of M. nana was 45.94%, 0.54%, 0.03%, and 46.32%, 0.58%, 0.03%, and 49.05%, 1.70%, 0.06%, respectively. C, N and P concentrations in the leaves were significantly higher than those in the roots and the stems. The C:N:P in roots, stems and leaves was 1531:18:1, 1544:19:1, and 818:10:1, respectively. 2) The C concentration and N:P in leaves of M. nana decreased with the increase of biomass of M. nana; the leaf C concentration was significantly correlated with biomass (p < 0.01), while the correlation between N:P and biomass was not significant (p > 0.05). The leaf N increased with the increase of plant biomass, the P was significantly correlated with biomass (p < 0.05), but the correlation between N concentration and biomass was not significant (p > 0.05). N:P in leaves was 34.2, suggesting that plant growth was limited by P. 3) C, N and P concentration in the roots were significantly correlated with soil P (p < 0.05), with N, P concentrations correlated with soil P positively (p < 0.01) and C negatively (p < 0.05). C concentration in the stems was significantly and negatively correlated with soil C, N, with significant correlation with C, N, and P concentration (p < 0.01). P concentration in the stems was significantly and positively correlated with soil P concentration (p < 0.01), while leaf P significantly and positively correlated with soil C, N and P (p < 0.01); leaf C concentration was significantly and negatively correlated with soil P (p < 0.01).