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。     

Relationship between ecosystem multifuntionality and species diversity in grassland ecosystems under land-use types of clipping,enclosure and grazing

Aims Over the past twenty years, most biodiversity and ecosystem functioning (BEF) research has focused on the effects of species diversity on single or just a few ecosystem functions. However, ecosystems are primarily valued for their ability to maintain multiple functions and services simultaneously (i.e. multifunctionality here- after). This paper first introduced the constantly perfected concept of “multifunctionality”, and then tried to make some modifications to the current mainstream quantitative method in order to evaluate the multifunctionality of grassland communities with the management of clipping, enclosure and grazing in Inner Mongolia, investigating the relationship between the multifunctionality and species diversity. Methods In free grazing grassland, four sites were set and each site was divided into two parts to conduct enclosure and clipping management respectively. After seven years, 15 quadrats (1 m × 1 m) were established for each type of management in each site (total 60 quadrats for each type) using the regular arrangement method; as a control, we also established 20 quadrats (two sites) in grazing grassland. For each quadrat, we carried out plants census and collected soil mixture sample, measuring 16 soil variables, and then calculated the biodiversity indices and multifunctionality index (M-index) by means of factor analysis. Important findings The results showed that M-indexes by the two evaluation methods were strongly correlated at both quadrat and site scale, suggesting that our modified method was reliable. Over-grazed communities had the lowest biodiversity indices and their most soil indicators were also low, showing obvious degradation features. Enclosure and clipping communities (seven years) had higher biodiversity and better soil indicators. The rank of M-indexes was clipping community (0.2178) > enclosure community (0.0704) > grazing community (-0.8031). The vegetation was distributed mainly along the gradients of water and fertility. Among the biodiversity indices, evenness (Pielou) index and richness (Margelf) index were most strongly correlated with multifunctionality, and their explanatory power (R²) for M-index were higher at site scale (R² = 0.5921, p = 0.0093; R² = 0.7499, p = 0.0007) than at quadrat scale (R² = 0.1871, p < 0.0001; R² = 0.1601, p < 0.0001), indicating study scale played an important role in the determinants of multifunctionality. At both quadrat and site scales, M-indexes is a linear positive function with species evenness and a hump-shaped function of species richness. Therefore, in contrast to enclosure, clipping was more conducive to maintain the ecosystem multifunctionality in this region, and the ecosystem with moderate specie richness, where these species are evenly distributed might have better multifunctionality.     

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.     

Effect of altered litter input and nitrogen addition on ecosystem aboveground primary productivity and plant functional group composition in a semiarid grassland

不同的草原利用方式(围封、放牧和割草等)随着大气氮沉降的不断加剧, 改变了凋落物输入量。凋落物作为连接地上-地下碳循环过程的关键环节, 对草原生态系统生产力和碳循环过程影响显著。氮是草原生产力的主要限制因子, 凋落物输入量的变化对草原生态系统结构和功能的影响仍缺乏长期实验证据支持。该研究在内蒙古半干旱典型草原建立一个凋落物输入变化和氮添加控制实验平台, 通过连续6年对群落生产力和功能群组成的监测, 研究了凋落物添加与去除和氮添加对半干旱草原群落生产力和功能群组成的影响。研究发现: 1)凋落物输入量增加和氮添加均显著提高了群落生产力, 在对照和氮添加处理下, 凋落物去除处理导致生产力分别降低了8.4%和7.6%, 而凋落物添加处理使生产力分别提高了10.7%和6.3%; 2)不同植物功能群对凋落物输入变化和氮添加的响应存在差异, 导致群落功能群结构发生变化。随着凋落物输入量增加和氮添加, 群落优势功能群多年生禾草(包括多年生丛生禾草和多年生根茎禾草)的生物量显著提高, 对群落生产力的贡献增加, 在群落中的优势地位增强; 而另一优势功能群多年生杂类草生物量对凋落物和氮添加处理均无显著响应, 进而导致在氮添加处理下其对群落生物量的贡献比例显著降低; 3)凋落物输入主要改善土壤水分状况, 而氮添加则主要通过提高土壤养分含量, 促进群落生产力, 并通过影响主要功能群生物量, 导致群落结构发生变化。以上结果表明, 适当的草原管理方式如围封禁牧和降低放牧强度等都能通过增加凋落物的输入来提高草原生产力, 维持生态系统稳定性。而适量的氮等养分添加管理也有助于提高草原生产力, 促进其恢复。     

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 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.     

亚热带不同树种凋落叶分解对氮添加的响应

为探究不同质量凋落物对氮(N)沉降的响应, 该研究采用尼龙网袋分解法, 在亚热带福建三明格氏栲(Castanopsis kawakamii)自然保护区的米槠(Castanopsis carlesii)天然林, 选取4种本区常见的具有不同初始化学性质的树种凋落叶进行模拟N沉降(N添加)分解实验(施N水平为对照0和50 kg·hm ^-2·a ^-1)。研究结果表明: 在2年的分解期内, 对照处理的各树种凋落叶的分解速率依次为观光木(Michelia odora, 0.557 a ^-1)、米槠(0.440 a ^-1)、台湾相思(Acacia confusa, 0.357 a ^-1)、杉木(Cunninghamia lanceolata, 0.354 a ^-1); N添加处理凋落叶分解速率依次为观光木(0.447 a ^-1)、米槠(0.354 a ^-1)、杉木(0.291 a ^-1)、台湾相思(0.230 a ^-1), 除杉木凋落叶外, N添加显著降低了其他3种凋落叶分解速率。N添加不仅使4种树木凋落叶分解过程中的N释放减慢, 同时还抑制凋落叶化学组成中木质素和纤维素的降解; N添加在凋落叶分解过程中总体上提高β-葡萄糖苷酶(βG)和酸性磷酸酶活性, 对纤维素水解酶的活性影响不一致, 而降低β-N-乙酰氨基葡萄糖苷酶活性和酚氧化酶活性。凋落叶分解速率与凋落叶中的碳获取酶(βG)活性以及其化学组分中的可萃取物含量极显著正相关, 与初始碳浓度、纤维素和木质素含量极显著负相关, 与初始N含量没有显著相关性。凋落物类型和N添加的交互作用虽未影响干质量损失速率, 但对木质素和纤维素的降解具有显著效应。综上所述, 化学组分比初始N含量能更好地预测凋落叶分解速率, 而N添加主要通过抑制分解木质素的氧化酶(如PHO)来降低凋落叶分解速率。     

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.     

Predicting phenology shifts of herbaceous plants on the Qinghai-Xizang Plateau under climate warming with the space-for-time method

气候变暖背景下的植物物候变化广受关注, 然而常用的植物物候变化预测模型未充分考虑植物对环境的适应性, 给预测结果带来了较大的不确定性。该文基于2002-2011年青藏高原10个站点的地面物候观测资料以及年平均气温数据, 对空间换时间模型预测车前(Plantago asiatica)和蒲公英(Taraxacum mongolicum)各主要物候事件(展叶始期、开花始期和黄枯普遍期)变化的可行性及其在升温背景下的变化规律进行了分析。首先利用不同海拔高度的气温和物候事件分别与地理因子(经度、纬度和海拔)建立多元线性回归模型, 然后在此基础上剔除经度和纬度的影响, 单独考察海拔变化所引起的气温与植物物候变化, 最后以海拔高度作为桥梁来考察物候变化与温度变化的关系。结果表明, 采用各站点对应的海拔高度来模拟年平均气温空间差异的R²均大于0.89, 表明海拔梯度可以用来反映时间尺度下的年际温度变化; 车前和蒲公英各物候事件发生日期拟合值均与海拔高度变化关系显著, R²均大于0.70, 表明海拔变化是影响它们各物候事件变化的主要地理因子; 在物候事件发生日期拟合值和年平均气温拟合值的回归方程中, R²均大于0.93, 说明基于不同海拔高度模拟得到的年平均气温变化可以对时间尺度上车前和蒲公英的物候事件变化进行预测。空间换时间预测表明, 温度每升高1 ℃, 车前展叶始期和开花始期分别提前5.1和5.4 d, 而黄枯普遍期推迟4.8 d; 蒲公英展叶始期和开花始期分别提前6.5和7.8 d, 而黄枯普遍期推迟6.7 d。     

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).     

Leaf decomposition and nutrient release of dominant species in the forest and lake in the Jiuzhaigou National Nature Reserve,China

AimsLitter decomposition is an important ecological process in nutrient cycling and productivity of ecosystems. Our objective is to quantify the differences of litter decomposition and nutrient release (N and P) under the forest and in an alpine lake among the dominant tree species in the Jiuzhaigou National Nature Reserve.
Methods Fresh leaf litters of Abies ernestii, Pinus tabulaeformis, Betula albo-sinensis, and Salix cupularis were collected and placed in bags under the forest and in an alpine lake for a year.
Important findings The mass remaining ratio (MR) of the leaf litters was well predicted with Olson’s decay model (r > 0.93, p < 0.01). The time for 99% decomposition was the shortest for S. cupularis (6.80 a), followed by B. albo-sinensis (10.34 a), A. ernestii (18.88 a), and P. tabulaeformis (27.21 a). These values were 1.48-, 1.55-, 1.80-, and 1.65-folds of the corresponding values in the lake, respectively. Both MR and nitrogen remaining ratio (NR) had significantly negative correlations with the leaf initial N concentration, but significantly positive correlations with the initial C:N. The nutrient release was significantly different among the four species and between the two sites (i.e., forest and alpine lake). The N release of S. cupularis was consistent between forest and the lake (i.e. directly released in the beginning of decomposition), while other species had an obvious N enrichment process before it released. The release of P among was similar among the four species and between the two sites, with a release—enrichment—release pattern. Overall, the leaf litter decomposition appeared as an intricate process that was affected by the litter chemistry and and the environment. The fast litter decomposition in the lake may have a profound influence on the water quanlity in the Jiuzhaigou National Nature Reserve.     

Spatio-temporal characteristics of evapotranspiration and water use efficiency in grasslands of Xinjiang

Aims Xinjiang is located in the hinterland of the Eurasian arid areas, with grasslands widely distributed. Grasslands in Xinjiang provide significant economic and ecological benefits. However, research on evapotranspiration (ET) and water use efficiency (WUE) of the grasslands is still relatively weak. This study aimed to explore the spatio-temporal characteristics on ET and WUE in the grasslands of Xinjiang in the context of climate change.Methods The Biome-BGC model was used to determine the spatio-temporal characteristics of ET and WUE of the grasslands over the period 1979-2012 across different seasons, areas and grassland types in Xinjiang.Important findings The average annual ET in the grasslands of Xinjiang was estimated at 245.7 mm, with interannual variations generally consistent with that of precipitation. Overall, the value of ET was lower than that of precipitation. The higher values of ET mainly distributed in the Tianshan Mountains, Altai Mountains, Altun Mountains and the low mountain areas on the northern slope of Kunlun Mountains. The lower values of ET mainly distributed in the highland areas of Kunlun Mountains and the desert plains. Over the period 1979-2012, average annual ET was 183.2 mm in the grasslands of southern Xinjiang, 357.9 mm in the grasslands of the Tianshan Mountains, and 221.3 mm in grasslands of northern Xinjiang. In winter, ET in grasslands of northern Xinjiang was slightly higher than that of Tianshan Mountains. Average annual ET ranked among grassland types as: mid-mountain meadow > swamp meadow > typical grassland > desert grassland > alpine meadow > saline meadow. The highest ET value occurred in summer, and the lowest ET value occurred in winter, with ET in spring being slightly higher than that in autumn. The higher WUE values mainly distributed in the areas of Tianshan Mountains and Altai Mountains. The lower WUE values mainly distributed in the highland areas of Kunlun Mountains and part of the desert plains. The average annual WUE in the grasslands of Xinjiang was 0.56 g·kg^-1, with the seasonal values of 0.43 g·kg^-1 in spring, 0.60 g·kg^-1 in summer, and 0.48 g·kg^-1 in autumn, respectively. Over the period 1979-2012, the values of WUE displayed significant regional differences: the average values were 0.73 g·kg^-1 in northern Xinjiang, 0.26 g·kg^-1 in southern Xinjiang, and 0.69 g·kg^-1 in Tianshan Mountains. There were also significant differences in WUE among grassland types. The values of WUE ranked in the order of mid-mountain meadow > typical grassland > swamp meadow > saline meadow > alpine meadow > desert grassland.     

Effects of tree species on soil organic carbon density: A common garden experiment of five temperate tree species

Aims Forest trees alter litter inputs, turnover and rhizospheric activities, modify soil physical, chemical and biological properties, and consequently affect soil organic carbon (SOC) storage and carbon sink strength. That how to select appropriate tree species in afforestation, reforestation and management practices is critical to enhancing forest carbon sequestration. The objective of this study was to determine the effects of tree species on SOC density and vertical distributions.Methods A common garden experiment with the same climate, soil, and management history was established in Maoershan Forest Ecosystem Station, Northeast China, in 2004. The experimental design was a completely randomized arrangement with twenty 25 m × 25 m plots, consisting of monocultures of five tree species, including white birch (Betula platyphylla), Manchurian walnut (Juglans mandshurica), Manchurian ash (Fraxinus mandshurica), Dahurian larch (Larix gmelinii), and Mongolian pine (Pinus sylvestris var. mongolica), each with four replicated plots. A decade after the establishment (2013-2014), we measured carbon density and related factors (i.e., bulk density, total nitrogen concentration, microbial biomass carbon, microbial biomass nitrogen, pH value) in soils of the 0-40 cm depth for these monocultures. Important findings Results showed that tree species significantly influenced the SOC density in the 0-40 cm depth (p < 0.05). SOC density in the 0-10 cm depth varied from 2.79 to 3.08 kg·m^-2, in the order of walnut > ash> birch > larch > pine, in the 10-20 cm depth from 1.56 to 2.19 kg·m^-2, in the order of pine > walnut > ash > birch > larch, in the 20-30 cm depth from 1.17 to 2.10 kg·m^-2, and in the 20-40 cm depth from 0.84 to 1.43 kg·m^-2. The greatest SOC density occurred in the birch stands in the 20-40 cm depth. The vertical distributions of SOC density varied with tree species. The percentage of SOC in the 0-10 cm depth over the total SOC in the soil profile was significantly higher in the walnut and larch stands than in others, while the percentage of SOC in the 20-40 cm depth over the total SOC was highest in the birch stands. SOC concentration and soil bulk density differed significantly among the stands of different tree species, and were negatively correlated. SOC density was positively correlated with soil microbial biomass and soil pH in the walnut, ash, and larch stands, and with total nitrogen density in all the stands. We conclude that tree species modifies soil properties and microbial activity, thereby influencing SOC density, and that different patterns of vertical distributions of SOC density among monocultures of different tree species may be attributed to varying SOC controls at each soil depth.     

Effect of p53 genotype on gene expression profiles in murine liver

The tumor suppressor protein p53 is a key regulatory element in the cell and is regarded as the “guardian of the genome”. Much of the present knowledge of p53 function has come from studies of transgenic mice in which the p53 gene has undergone a targeted deletion. In order to provide additional insight into the impact on the cellular regulatory networks associated with the loss of this gene, microarray technology was utilized to assess gene expression in tissues from both the p53^−/− and p53^+/− mice. Six male mice from each genotype (p53^+/+, p53^+/−, and p53^−/−) were humanely killed and the tissues processed for microarray analysis. The initial studies have been performed in the liver for which the Dunnett test revealed 1406 genes to be differentially expressed between p53^+/+ and p53^+/− or between p53^+/+ and p53^−/− at the level of p ≤ 0.05. Both genes with increased expression and decreased expression were identified in p53^+/− and in p53^−/− mice. Most notable in the gene list derived from the p53^+/− mice was the significant reduction in p53 mRNA. In the p53^−/− mice, not only was there reduced expression of the p53 genes on the array, but genes associated with DNA repair, apoptosis, and cell proliferation were differentially expressed, as expected. However, altered expression was noted for many genes in the Cdc42-GTPase pathways that influence cell proliferation. This may indicate that alternate pathways are brought into play in the unperturbed liver when loss or reduction in p53 levels occurs.     

C:N:P stoichiometry in forest floor litter of evergreen broad-leaved forests at different successional stages in Tiantong,Zhejiang, eastern China

地表凋落物在森林物质循环中起着重要作用, 但是目前缺乏对其不同分解层次中碳(C)、氮(N)、磷(P)演替动态的研究。该文以浙江天童常绿阔叶林为研究对象, 用空间代替时间序列的方法, 通过测定5个演替阶段地表凋落物不同分解层次的凋落物量、有机碳库和氮磷养分库的储量及C:N:P化学计量特征, 探讨地表凋落物特征的演替动态。结果表明: 1)随着演替的进行, 地表凋落物量和有机碳储量呈现下降的趋势。2)在各演替阶段, 有机碳含量在各分解层表现出未分解层(L) > 半分解层(F) > 已分解层(Y)的趋势; 有机碳储量均表现为Y < F。3)演替前期群落氮含量和储量显著低于演替中后期群落; 不同分解层的氮含量在各演替阶段皆表现为: Y > F > L, 且各层氮含量随着演替的进行均趋于升高。4)磷含量在演替中期群落最低, 各演替阶段不同分解层的磷含量皆表现为Y > F > L。磷储量的演替趋势不明显。L层磷储量随着演替进行趋于降低。5)随着演替进行, 凋落物C:N、C:P和N:P皆趋于下降(p < 0.05)。在各分解层之间, C:N和C:P皆表现为Y < F < L, N:P差异不显著。总之, 随着演替进行, 天童常绿阔叶林地表凋落物量降低, 有机碳库及氮磷养分库的含量趋于升高, 储量趋向降低, C:N:P趋于下降, 体现了生态系统碳和养分循环随着演替进行在不断优化。     

Characteristics of methane emission fluxes in the Zoigê Plateau wetland on microtopography

AimsThe Zoigê Plateau, as a very important wetland distribution region of China, was the major methane (CH₄) emission center of the Qinghai-Xizang Plateau. The objective of this study is to study the effects of microtopographic changes on CH₄ emission fluxes from five plots across three marshes in the littoral zone of the Zoigê Plateau wetland.
Methods CH₄ emission fluxes were measured in five plots across three marshes in Zoigê Plateau wetland using the closed chamber method and Fast Greenhouse Gas Analyzer from May to October in 2014.
Important findings During the growing season, mean CH₄ emission fluxes from the permanently flooded hollow (P-hollow) and hummock (P-hummock) in the Zoigê Plateau wetland were 68.48 and 40.32 mg·m^-2·h^-1, while mean CH₄ emission fluxes from the seasonally flooded hollow (S-hollow) and hummock (S-hummock) were 2.38 and 0.63 mg·m^-2·h^-1. CH₄ emission fluxes from non-flooded lawn was 3.68 mg·m^-2·h^-1. Mean CH₄ emission fluxes from five plots across three sites was 23.10 mg·m^-2·h^-1, with a standard deviation of 30.28 mg·m^-2·h^-1 and the coefficient of variation was 131%. We also found that there was a significant and positive correlation between mean CH₄ emission fluxes and mean water table depth in the five plots across three sites (R² = 0.919, p < 0.01), indicating that water table depth was controlling the spatial variability of CH₄ emission fluxes from the Zoigê Plateau wetland on microtopography. CH₄ emission fluxes in the P-hollow, P-hummock, and S-hummock showed an obvious seasonal pattern, which was not observed in the lawn and S-hollow. However, CH₄ emission peaks were observed in all the plots during summer and/or autumn, which could be closely related to the water table depth, soil temperature, and the magnitude of litter mass. In addition, we found that the CH₄ emission flux in the P-hollow was much higher than the other four plots in the Zoigê Plateau wetland, suggesting that CH₄ in the P-hollow could be often transported to the surface by ebullition and CH₄ emission from the Zoigê Plateau wetland may be under estimated in the past.     

Effects of streams on lignin degradation during foliar litter decomposition in an alpine forest

AimsStreams are widely distributed in alpine forests, and litter decomposition in which is an important component of material cycling across the forest landscape. The leaching and fragmenting effects as well as the unique environmental factors in streams may have significant impacts on lignin degradation during litter decomposition, but studies on this are lacking.
Methods Using litterbag methods, we investigated the dynamics of lignin mass remaining and concentration (percent litter mass, %) during the decomposition of four foliar litters, which varied significantly in the initial litter chemical traits, from the dominant species of Salix paraplesia, Rhododendron lapponicum, Sabina saltuaria, and Larix mastersiana under different habitats (forest floor, stream, and riparian zone) in the upper reaches of the Minjiang River.
Important findings After two year’s incubation, litter lignin mass remaining for a specific litter species varied significantly (p < 0.05) among habitats, with an order of stream < riparian zone < forest floor. Lignin was degraded substantially in the early stage of litter decomposition process, and the lignin concentration first decreased and then increased with the proceeding of litter decomposition, but varied significantly (p < 0.05) among different litter species. Lignin mass showed a general trend of decrease across the 2-year decomposition course. In addition, habitat type, decomposition period and microenvironmental factors (e.g., temperature, pH value and nutrient availability) showed substantial influences on lignin degradation rate. These results suggest that the traditional view that lignin was relatively recalcitrant with an increase of concentration in the early stage of litter decomposition is challenged, but the loss of lignin in the early phrase is in line with recent findings about the fate of lignin during litter decomposition. Moreover, the significant differences of lignin degradation rates among different decomposition period and habitat types indicated that local-scale environmental factors can play a significant role in litter decomposition and lignin degradation processes.     

凋落物输入变化和氮添加对半干旱草原群落生产力及功能群组成的影响

不同的草原利用方式(围封、放牧和割草等)随着大气氮沉降的不断加剧, 改变了凋落物输入量。凋落物作为连接地上-地下碳循环过程的关键环节, 对草原生态系统生产力和碳循环过程影响显著。氮是草原生产力的主要限制因子, 凋落物输入量的变化对草原生态系统结构和功能的影响仍缺乏长期实验证据支持。该研究在内蒙古半干旱典型草原建立一个凋落物输入变化和氮添加控制实验平台, 通过连续6年对群落生产力和功能群组成的监测, 研究了凋落物添加与去除和氮添加对半干旱草原群落生产力和功能群组成的影响。研究发现: 1)凋落物输入量增加和氮添加均显著提高了群落生产力, 在对照和氮添加处理下, 凋落物去除处理导致生产力分别降低了8.4%和7.6%, 而凋落物添加处理使生产力分别提高了10.7%和6.3%; 2)不同植物功能群对凋落物输入变化和氮添加的响应存在差异, 导致群落功能群结构发生变化。随着凋落物输入量增加和氮添加, 群落优势功能群多年生禾草(包括多年生丛生禾草和多年生根茎禾草)的生物量显著提高, 对群落生产力的贡献增加, 在群落中的优势地位增强; 而另一优势功能群多年生杂类草生物量对凋落物和氮添加处理均无显著响应, 进而导致在氮添加处理下其对群落生物量的贡献比例显著降低; 3)凋落物输入主要改善土壤水分状况, 而氮添加则主要通过提高土壤养分含量, 促进群落生产力, 并通过影响主要功能群生物量, 导致群落结构发生变化。以上结果表明, 适当的草原管理方式如围封禁牧和降低放牧强度等都能通过增加凋落物的输入来提高草原生产力, 维持生态系统稳定性。而适量的氮等养分添加管理也有助于提高草原生产力, 促进其恢复。     

Responses of plant community biomass to nitrogen and phosphorus additions in natural and restored grasslands around Qinghai Lake Basin

Aims Plant biomass reflects the primary productivity of community vegetation, and is the main resource of carbon input in the terrestrial ecosystem. It is usually limited by nitrogen (N) and phosphorus (P) availability in the soil. Alpine grassland around Qinghai Lake Basin has experienced extensive land-use changes due to the cultivation of native grassland and vegetation recovery on cropped land. In this experiment, two grassland types were chosen, natural alpine grassland (NG) and its adjacent restored grassland (RG), to determine the responses of plant community biomass to N and P additions with different land-use. Methods NH₄NO₃ and Ca(H₂PO₄)₂·H₂O were added in a completely randomized block design, with medium levels of 10 g N·m^-2 and 5 g P·m^-2. Soil NO₃^--N and available P contents, and the plant community biomass were measured in the two grasslands. Two-way ANOVA was used to determine the effects of nutrient additions on all measured indicators, and regression analysis was used to analyze the correlations between plant biomass and soil NO₃^--N and available P contents.Important findings Results showed: (1) N and P additions both increased grass biomass in the NG, and significantly elevated the total aboveground biomass, with the promoting effect of N addition higher than that of P addition; N addition significantly increased both grass and forb biomass in the RG, and markedly promoted the total aboveground biomass, while P addition had no effects on the functional groups and total aboveground biomass (p > 0.05). (2) N and P additions both had no effects on the belowground and total biomass in the NG, whereas N addition significantly increased the total biomass by 34% in the RG, which suggested that the effect of N limitation on the vegetation primary productivity was stronger in the RG at present stage. (3) The aboveground biomass in the NG increased with soil NO₃^--N content (p < 0.05), and the above- and below-ground as well as the total biomass were all positively correlated with soil NO₃^--N content in the RG (p < 0.01). These results indicated that the plant growth in alpine grassland around Qinghai Lake Basin was prone to N limitation, and the effect of P limitation changed with land-use. Soil available N might be the key limiting factor for vegetation restoration and reconstruction in the RG. The “Grain for Green” project (the land-use policy) and atmospheric N deposition are benefiting both plant growth and C accumulation in the alpine grassland ecosystem around Qinghai Lake Basin.     

荒漠草原不同放牧强度背景下添加氮水对凋落物分解的影响

凋落物分解是连接生态系统地上、地下过程的重要环节,决定了生态系统养分循环速率,但到目前为止对凋落物分解在荒漠草地生态系统受放牧以及外源资源补给影响的研究较少。本研究通过对不同放牧强度(对照、轻牧、中牧和重牧)短花针茅草原群落进行添加氮素(10.0 g N m~(-2) a~(-1))和增水(108 mm/a)处理,探讨群落水平凋落物分解速率的变化。研究结果显示,过去不同强度放牧历史对群落凋落物分解影响极显著(P0.0001)。凋落物前期分解(135 d)过程中,凋落物初始C∶N比与凋落物分解速率常数呈显著负相关关系,表明凋落物可降解性在凋落物前期分解中起主要作用。轻度放牧影响下凋落物分解速度最快,这与该条件下凋落物C∶N比显著低于其他放牧强度下的有关,说明适度放牧不仅有利于群落维持,也在一定程度上有利于生态系统养分循环。当凋落物分解更长时间(870 d)后,对照区凋落物分解速率显著低于放牧处理样地,但凋落物初始C∶N比对凋落物分解速率没有显著影响。进一步分析显示,不同放牧强度背景下长期凋落物分解速率与分解环境的土壤微生物多样性成正相关关系,与群落盖度呈极显著(P0.001)负相关关系。添加氮素显著(P0.05)降低凋落物分解速度,但对凋落物氮含量无显著影响。生长季加水未影响凋落物质量及凋落物分解速度。研究结果表明,凋落物前期分解受凋落物质量影响,但较长时间凋落物分解则与分解过程中接受到的太阳辐射量有关。