长白山阔叶红松林生态系统光能利用率的动态变化及其主控因子

生态系统光能利用率(LUE)反映了植被通过光合作用利用光能吸收和固定大气中CO₂的能力, 是表征生态系统生产力的重要指标。选取长白山温带阔叶红松(Pinus koraiensis)林生态系统为研究对象, 利用涡度相关通量观测数据, 采用直角双曲线方程获取了生态系统光合作用的表观量子效率(ε); 基于总生态系统初级生产力(GEP)与下垫面入射光合有效辐射(Q)的比值得到生态光能利用率(LUE_eco)。研究表明: 在季节尺度上, ε与LUE_eco均表现出显著的单峰变化特征, 并主要受到土壤温度和归一化植被指数(NDVI)的调控, 同时, ε和LUE_eco都受到GEP的显著影响, 而与Q的相关性较弱或无显著相关关系, 但散射辐射的增加在一定程度上有助于提高生态系统的LUE。ε与LUE_eco存在显著的线性正相关关系, 但ε明显高于LUE_eco。2003-2005年, ε与LUE_eco每年最大值的平均值分别为(0.087 ± 0.003)和(0.040 ± 0.002) μmol CO₂·μmol photon^-1, 年际间变异度分别为4.17%和4.25%, 而不同年份之间最大差异均达到8%或8%以上, 从而对模型模拟结果产生明显影响。因此, 在基于光能利用率模型的模拟研究中, 最大LUE的年际变异需要在参数反演和优化中给予重要考虑。     

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.     

蛋白核小球藻生长和无机碳利用对不同光照强度和CO2浓度的响应

为了探讨光照强度和CO₂浓度对蛋白核小球藻(Chlorella pyrenoidosa)生长、无机碳利用的复合效应, 丰富绿藻中无机碳浓缩机制的资料, 该文设置两种光照强度(40和120 µmol photons•m^-2•s^-1)和两种CO₂浓度(0.04%和0.16%)组合成4种条件, 比较了蛋白核小球藻生长、无机碳浓度、pH补偿点、光合放氧速率、碳酸酐酶(CA)活性和α-CA基因转录表达对这4种培养条件的响应。结果发现: 蛋白核小球藻在高光强高CO₂浓度组生长最快; 低光强高CO₂浓度组培养体系中总无机碳浓度为1163.3 µmol•L^-1, 显著高于其他3组; 高光强低CO₂浓度组藻的pH补偿点最高(9.8), 而低光强高CO₂浓度组藻的pH补偿点最低(8.6); 低光强高CO₂浓度组藻的最大光合速率(V_max)和最大光合速率一半时的无机碳浓度(K_0.5)最高, 分别是其他3组的1.28-1.91倍和1.61-2.00倍; 高光强低CO₂浓度组藻的胞外CA活性最高; 而低光强低CO₂浓度组藻的胞外α-CA基因表达量显著高于其他3组。以上结果表明低CO₂浓度可促进蛋白核小球藻的pH补偿点和无机碳亲和力的提高, 诱导胞外CA活性及α-CA基因的表达; 该藻主要以HCO₃^-为无机碳源, 其对无机碳的利用受光照的调节。     

A comparison of measured and calculated net community CO2 exchange: Scaling from leaves to communities

Leaf net photosynthesis is crucial for detecting the mechanism of photosynthesis, whereas community net photosynthesis is useful for understanding the photosynthetic capacity of communities and its relationship with environmental factors. In particular, we need to scale up eco-physiological models from leaf scale to canopy level to study carbon cycling at regional or global scale. We hypothesized that accumulated leaf net photosynthetic rate (P_c) at community scale, i.e., calculated based on leaf net photosynthetic rate (P_n) and leaf area index (LAI), equals to measured net community CO₂ exchange (NCE). The purpose of this study is to verify this hypothesis. Our field study was carried out in Duolun, Nei Mongol, China, where we constructed single-species communities by sowing Medicago sativa ‘Aohan’ seeds in three plots (3 m × 5 m) on May 30, 2012. On August 16, 2014, P_n of five healthy leaves of M. sativa ‘Aohan’ in each plot were measured with a LI-6400 portable photosynthesis system at 10:00, and net ecosystem CO₂ exchange (NEE) in each plot was measured simultaneously with a LI-8100 system connected with a assimilation chamber (0.5 m × 0.5 m × 0.5 m). P_c was calculated based on P_n, number of leaves (n), LAI percentage of healthy leaves (r) and percentage of received effective light by leaves (m). NCE was derived from NEE and ecosystem respiration rate (R_eco). P_c was 3.52 μmol CO₂·m^-2·s^-1, and very close to NCE (3.56 μmol CO₂·m^-2·s^-1), suggesting that leaf-scale photosynthesis may accurately predict community-scale photosynthesis. However, our method could not separate community respiration from soil respiration, and future studies, should be designed to counteract this effect. Scaling up from leaf photosynthesis to community photosynthesis should also consider vertical structure of communities and nonlinear responses of leaf photosynthesis to changes in light quantum.     

油蒿资源利用效率在生长季的相对变化及对环境因子的响应

为了探明西北半干旱区典型沙生植物油蒿(Artemisia ordosica)叶水平资源利用效率的相对变化及对环境因子的响应机制, 该研究于2018年5-10月, 使用LI-6400XT便携式光合仪测定了毛乌素沙地油蒿叶片的净光合速率(P_n)、蒸腾速率(E)、叶表面光合有效辐射(PAR_l)、叶表面温度(T_l)、叶表面相对湿度(RH_l), 在实验室计算叶片单位面积氮含量(N_area), 分析了叶片氮利用效率(NUE)、水分利用效率(WUE)、光利用效率(LUE)与环境因子之间的关系及NUE、WUE、LUE之间的相对变化。研究结果表明, 在充足且稳定光强下油蒿的P_n主要受温度的影响, NUE、WUE与VPD_l、T_l之间具有显著负相关关系, NUE、WUE与LUE间为正相关关系, NUE、WUE和LUE最大值分别发生在5、7和9月, 分别为9.43 μmol CO₂·g^-1·s^-1、3.86 mmol·mol^-1、0.04 mol·mol^-1, 资源利用效率的变化主要受P_n的影响。温度通过影响植物N分配来改变P_n, 进而影响着资源利用效率, WUE与LUE显著正相关, 对构建荒漠区生态系统能量交换过程模型有重要意义。     

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.     

光系统II实际光化学量子效率对光的响应模型的比较

为了比较光系统II实际光化学量子效率(Φ_PSII)对光的响应机理模型(简称机理模型)、负指数模型和指数模型的优缺点, 用LI-6400-40B光合作用测定仪控制CO₂浓度和温度, 测量了剑叶金鸡菊(Coreopsis lanceolata)、黄荆(Vitex negundo)和大狼杷草(Bidens frondosa)的电子传递速率(ETR)对光的响应曲线(ETR-I)和Φ_PSII对光的响应曲线(Φ_PSII-I), 然后用这3个模型分别拟合了这些数据。拟合结果表明: 3个模型都可以较好地拟合这3种植物的ETR-I的响应数据和Φ_PSII-I的响应数据, 但由指数模型拟合ETR-I和Φ_PSII-I的响应数据得到相应的饱和光强(PAR_sat)和光系统II最大光能利用效率(F_v/F_m)之间存在显著差异, 且估算的饱和光强远低于实测值。由机理模型可知, Φ_PSII不仅与光强的函数有关, 还与植物的内禀特性有关, 即与天线色素分子的本征光能吸收截面、激子的传递效率、能级的简并度、光化学反应常数、热耗散常数和处于最低激发态的平均寿命等参数有关。此外, 由机理模型还可知, Φ_PSII随光强的增加而下降的原因是捕光色素分子的有效光能吸收截面随光强增加而降低。     

Forest net primary productivity dynamics and driving forces in Jiangxi Province,China

Aims Subtropical forest ecosystem has great carbon sequestration capacity. Net primary productivity (NPP) plays a critical role in forest carbon cycle and is affected by a number of factors, including climate change, atmospheric composition, forest disturbance intensity and frequency, and forest age, etc. However, the contribution of these factors to the temporal-spatial dynamics of NPP is still not clear. Quantifying the main driving forces on the temporal-spatial dynamics of NPP for subtropical forest ecosystems is a critical foundation for understanding their carbon cycle.
Methods We utilized multi-sources dataset, including observed meteorological data, inversed annual maximum leaf area index (LAI), referenced NPP (simulated by Boreal Ecosystem Productivity Simulator (BEPS) model), forest age and forest types, land cover, digital elevation model (DEM), soil texture, CO₂ concentration and nitrogen deposition. We used the InTEC (integrated terrestrial ecosystem carbon-budget) model to simulate the NPP dynamics for forest ecosystems in Jiangxi Province during the period of 1901-2010. The effects of climate change, forest age, CO₂ concentration and nitrogen (N) deposition on forest NPP from 1970 to 2010 were discussed through designed scenarios.
Important findings (1) Validations by flux measurements and forest inventory data indicated that the InTEC model was able to capture the interannual and spatial variations of forest NPP. (2) The average forest NPP was 47.7 Tg C·a^-1 (± 4.2 Tg C·a^-1) during 1901-2010. The NPP in the 1970s, 1980s, 1990s and 2000s was 50.7, 48.8, 45.4, and 55.2 Tg C·a^-1, respectively. As forest regrows, NPP significantly increased for forests in Jiangxi Province in the 2000s, and exceed that in the 1970s for more than 60% of the forest area. (3) During 1970-2010, under the scenarios of disturbance and non-disturbance, the forest NPP were underestimated by 7.3 Tg C·a^-1 (14.5%) and overestimated by 3.6 Tg C·a^-1 (7.1%) compared to the scenarios of all disturbance and non-disturbance factors, respectively. Compared to the average NPP during 1970-2010, climate change decreased NPP by -2.0 Tg C·a^-1 (-4.7%), N deposition increased NPP by 4.5 Tg C·a^-1 (10.4%), CO₂ concentration change, and the integrated fertilization of CO₂ and N deposition increased NPP by 4.4 Tg C·a^-1 (10.3%) and 9.4 Tg C·a^-1 (21.8%), respectively.     

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。     

基于超声清洗的树木叶面颗粒物粒径分布与吸滞效率研究——以银杏和油松为例

明确在常规叶片清洗方法(泡洗或泡洗+刷洗)上增加超声清洗对叶面各径级颗粒物滞纳量定量评估的影响, 并在此基础上研究叶面颗粒物的粒径分布和吸滞效率, 可进一步提高城市树木大气颗粒物吸滞能力的定量评估精度。该文以城市森林建设常用阔叶树种银杏(Ginkgo biloba)和针叶树种油松(Pinus tabuliformis)为研究对象, 于雨后(降水量>15 mm) 4天(短滞尘时长)和14天(长滞尘时长)分别采集叶样, 并依次对其进行泡洗(WC)、刷洗(BC)、超声清洗(UC)等洗脱程序, 然后对每个清洗步骤下叶片洗脱液中颗粒物的质量和粒径分布进行测试, 并依此估算叶片各径级颗粒物的吸滞效率。结果表明, 以“泡洗+刷洗+超声清洗”清洗流程的测试结果为参照, 若只对叶片进行泡洗, 则银杏和油松对大气颗粒物(PM₁, 粒径d ≤1 µm)、PM_2.5 (d ≤ 2.5 µm)、PM₅ (d ≤ 5 µm)、PM₁₀ (d ≤ 10 µm)吸滞量会分别被低估约一半(54%、53%、53%和53%)和40% (42%、42%、42%和42%); 若只进行“泡洗+刷洗”, 则银杏和油松对相应径级颗粒物的吸滞量仍会分别被低估约15% (17%、16%、15%和15%)和20% (21%、20%、20%和20%)。油松叶面颗粒物粒径分布呈双峰曲线, 而银杏叶面颗粒物粒径则呈单峰分布, 且银杏叶面颗粒物平均粒径在短、长滞尘时长下均大于油松。油松叶片对PM₁、PM_2.5、PM₅、PM₁₀和总悬浮颗粒物的吸滞效率分别为8.96、23.92、23.96、23.96和23.96 mg·m^-2·d^-1, 分别比银杏叶片高112%、73%、34%、37%和42%。     

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.     

Dominant species and ecosystem gas exchange in temperate grassland under different land use patterns

在内蒙古温带草原围封、放牧和割草3种处理下的样地内, 对生态系统尺度和大针茅(Stipa grandis)、冷蒿(Artemisia frigida)、羊草(Leymus chinensis) 3种优势种植物叶片尺度上的气体交换和水分关系进行了测定, 对比研究了植物碳水对环境的响应。结果表明, 在优势种单株尺度和生态系统尺度上, 大气-植被CO₂交换因草地利用方式的不同而具有不同的表现。在生态系统层面, 放牧样地的群落净CO₂气体交换量和总初级生产力都与围封样地和割草样地有差异, 群落总初级生产力受生态系统呼吸的影响。在放牧处理下, 群落净CO₂气体交换量日变化表现为生态系统对碳的吸收, 而围封和割草则以碳释放为主。单叶光合速率出现负值并随时间推移而恢复的现象, 应是植物对干旱高温、高光照的特殊反应。生态系统水分利用效率没有明显不同, 但各样地的蒸散能力有趋势上的变化; 对于同种植物, 放牧样地植物单叶水分利用效率的日变化波动幅度最大, 围封样地最小。     

叶片和群落尺度净光合速率关系的探讨

叶片净光合速率(P_n)是研究光合作用机理的基本尺度; 而群落净光合速率(P_c)是研究群落光合能力及其与外部环境因子间关系的更好尺度, 特别是区域乃至全球尺度碳循环的研究, 需要将叶片尺度的生理生态模型扩展到冠层尺度。理论上, 群落内所有叶片的累积P_n与实测群落净气体交换速率(NCE)是相等的, 但在野外实际观测中, 两者之间的相互关系目前尚未见报道。该文选取敖汉苜蓿(Medicago sativa ‘Aohan’)人工草地, 采用美国LI-COR公司生产的便携式光合测定系统LI-6400测定P_n, 结合叶面积指数等参数推算P_c, 利用LI-8100连接同化箱测定生态系统净气体交换速率(NEE), 加上土壤呼吸速率, 得到NCE。结果表明: P_c为3.52 μmol CO₂·m^-2·s^-1, 与实测NCE (3.56 μmol CO₂·m^-2·s^-1)基本相等。这表明: 可利用P_n, 结合叶面积指数、群落叶片数目、健康叶片比例和群落可接收有效光照的平均比例等4个关键参数, 准确地换算P_c。然而, 利用同化箱式法测定群落呼吸速率时, 不可避免地会包含土壤呼吸, 所以在观测NCE时, 需要同时测定土壤呼吸。此外, 在冠层模型中, 群落垂直结构和光量子的非线性响应不可忽视。     

13C and 15N isotopic signatures of plant-soil continuum along a successional gradient in Dinghushan Biosphere Reserve

Aims The optimal patterns of plant community for water use and nutrient utilization, the responses of soil carbon and nitrogen turnover processes to forest succession, and the mechanisms of soil organic carbon accumulation, are three critical issues in forest ecosystem study. It is difficult to accurately detect these ecological processes with conventional methodologies in the short term, yet the application of ¹³C and ¹⁵N natural abundance technique may yield important information about these processes.Methods This study was conducted in Dinghushan Biosphere Reserve. We investigated the natural isotopic abundance of both ¹³C and ¹⁵N of plant-soil continuum along a successional gradient from Pinus massoniana forest (PF) to coniferous and broad-leaved mixed forest (MF), and monsoon evergreen broad-leaved forest (BF). We also analyzed the correlations of foliar stable carbon isotope ratio (δ¹³C) and stable nitrogen isotope ratio (δ¹⁵N) with foliar elemental contents and the variations of soil δ¹³C and δ¹⁵N along soil profiles at different successional stages.Important findings A significant positive correlation between foliar δ¹³C and foliar C:N was observed. In both litter and soil, the δ¹³C values tended to decrease along the forest succession, with the order as PF > MF > BF. Foliar δ¹⁵N was positively correlated with foliar N content. The δ¹⁵N values of litter and upper soil (0-10 cm) increased with successional status. Both soil δ¹³C and δ¹⁵N values increased with increasing soil depth at all three forests. Our results imply that 1) trade-off between water use efficiency and nitrogen use efficiency did not necessarily exist in subtropical forests of China; 2) the application of isotopic technique could assist understanding of the mechanisms of soil carbon accumulation in subtropical forests, especially in old-grow forests; 3) the ¹⁵N natural abundance of plant-soil continuum could be a potential indicator of soil nitrogen availability and ecosystem nitrogen saturation status.     

Carbon storage and its distribution of forest ecosystems in Zhejiang Province,China

Aims
The concentration of CO₂ and other greenhouse gases in the atmosphere has considerably increased over last century and is set to rise further. Forest ecosystems play a key role in reducing CO₂ concentration in the atmosphere and mitigating global climate change. Our objective is to understand carbon storage and its distribution in forest ecosystems in Zhejiang Province, China.
Methods
By using the 8th forest resource inventory data and 2011-2012 field investigation data, we estimated carbon storage, density and its distribution in forest ecosystems of Zhejiang Province.
Important findings
The carbon storage of forest ecosystems in Zhejiang Province was 602.73 Tg, of which 122.88 Tg in tree layer, 16.73 Tg in shrub-herb layer, 11.36 Tg in litter layer and 451.76 Tg in soil layer accounting for 20.39%, 2.78%, 1.88% and 74.95% of the total carbon storage, respectively. The carbon storage of mixed broadleaved forests was 138.03 Tg which ranked the largest (22.90%) among all forest types. The young and middle aged forests which accounted for 70.66% of the total carbon storage were the main body of carbon storage in Zhejiang Province. The carbon density of forest ecosystems in Zhejiang Province was 120.80 t·hm^-2 and that in tree layer, shrub-herb layer, litter layer and soil layer were 24.65 t·hm^-2, 3.36 t·hm^-2, 2.28 t·hm^-2 and 90.51 t·hm^-2, respectively. The significant relationship between soil organic carbon storage and forest ecosystem carbon storage indicated that soil carbon played an important role in shaping forest ecosystem carbon density. Carbon density of tree layer increased with age in natural forests, but decreased in the order over-mature > near-mature > mature > middle-aged > young forest in plantations. The proportions of young and middle aged forests were larger than any other age classes. Thereby, the carbon storage of forest ecosystems in Zhejiang Province could be increased through a proper forest management.     

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.     

CO2浓度倍增对红松幼苗根尖和叶解剖结构及生理功能的影响

大气CO₂浓度升高对植物的影响是目前植物生态学研究中普遍关注的问题。以往的研究主要关注植物地上部分叶解剖结构及生理功能的改变, 而对根解剖结构和生理功能变化以及根与叶变化之间潜在联系的研究较少。该文以三年生红松(Pinus koraiensis)幼苗为研究对象, 通过CO₂浓度倍增(从350 µmol·mol^-1增加到700 µmol·mol^-1)试验, 研究当年生针叶和根尖解剖结构及生理功能的变化。结果表明: (1) CO₂浓度倍增处理的红松幼苗, 气孔密度显著降低, 叶肉组织面积、木质部及韧皮部面积明显增加; (2) CO₂浓度倍增导致红松幼苗根尖直径增粗, 皮层厚度和层数显著增加, 管胞直径变小; (3)高CO₂浓度处理下, 叶气孔导度和蒸腾速率降低, 光合速率和水分利用效率提高, 同时根尖的导水率显著下降, 但管胞的抗栓塞能力显著提高。这些结果显示, 叶和根解剖结构及生理功能在CO₂浓度升高条件下具有一致的响应。未来研究中应该同时关注全球气候变化对植物地上和地下器官结构与功能的影响。     

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.     

潮汐作用下干湿交替对黄河三角洲盐沼湿地净生态系统CO2交换的影响

潮汐作用作为盐沼湿地独特的水文特征能在短时间内强烈影响盐沼湿地的碳平衡.利用涡度相关和微气象监测技术,对黄河三角洲盐沼湿地净生态系统CO₂交换(NEE)和环境因子进行监测,并同步监测潮汐变化,探究潮汐过程及潮汐作用下干湿交替对NEE的影响.结果表明: 潮汐过程促进了白天生态系统CO₂的吸收但未对夜晚CO₂的释放产生显著影响,潮汐淹水成为影响白天NEE的主要因子.干旱阶段和湿润阶段NEE的日平均动态均呈“U”型曲线,但干旱阶段NEE的变幅较小.干湿交替增强了白天生态系统CO₂的吸收,干旱阶段最大光合速率(A_max)、表观量子产量(α)和生态系统呼吸(R_eco)的均值均高于湿润阶段.此外,干湿交替减少了盐沼湿地夜晚NEE释放的同时增强了其温度敏感性.     

潮汐作用下干湿交替对黄河三角洲盐沼湿地净生态系统CO2交换的影响

潮汐作用作为盐沼湿地独特的水文特征能在短时间内强烈影响盐沼湿地的碳平衡.利用涡度相关和微气象监测技术,对黄河三角洲盐沼湿地净生态系统CO₂交换(NEE)和环境因子进行监测,并同步监测潮汐变化,探究潮汐过程及潮汐作用下干湿交替对NEE的影响.结果表明: 潮汐过程促进了白天生态系统CO₂的吸收但未对夜晚CO₂的释放产生显著影响,潮汐淹水成为影响白天NEE的主要因子.干旱阶段和湿润阶段NEE的日平均动态均呈“U”型曲线,但干旱阶段NEE的变幅较小.干湿交替增强了白天生态系统CO₂的吸收,干旱阶段最大光合速率(A_max)、表观量子产量(α)和生态系统呼吸(R_eco)的均值均高于湿润阶段.此外,干湿交替减少了盐沼湿地夜晚NEE释放的同时增强了其温度敏感性.