中国毛竹林碳氮磷生态化学计量特征

碳(C)、氮(N)、磷(P)生态化学计量比是生态系统过程与功能的重要特征, 开展种群生态化学计量学研究可以细化植物种群化学计量学内容, 确定限制植物生长的元素类型, 同时为大尺度模型的发展提供数据基础。为阐明我国毛竹(Phyllostachys edulis)林C、N、P化学计量学特征, 通过对毛竹主要产区文献数据的搜集整理与分析, 探索我国毛竹林“植物-土壤-凋落物”系统C、N、P及C:N、C:P、N:P生态化学计量特征, 以及不同组分生态化学计量特征与经纬度之间的关系。结果表明: 1)我国毛竹林叶片C含量为478.30 mg·g^-1, N含量为22.20 mg·g^-1, P含量为1.90 mg·g^-1, C:N为26.80, C:P为299.60, N:P为14.40; 毛竹林0-20 cm土层C含量为21.53 mg·g^-1, N含量为1.66 mg·g^-1, P含量0.41 mg·g^-1, C:N为14.20, C:P为66.74, N:P为4.28; 毛竹凋落物C含量为438.49 mg·g^-1, N含量为13.39 mg·g^-1, P含量为0.86 mg·g^-1, C:N为22.53, C:P为665.67, N:P为22.55。2)毛竹林“植物-土壤-凋落物”系统中, C:N表现为: 叶片>凋落物>土壤, C:P和N:P均表现为: 凋落物>叶片>土壤, 叶片N、P再吸收率分别为39.68%和54.74%, 我国毛竹林生长发育总体上可能受到P限制或者N和P两种元素的双重限制。3)纬度梯度: 叶片N含量、N:P随纬度增加而增加, C:N随纬度增加而降低。经度梯度: 叶片N:P随经度增加而增加, P含量、C:N随经度增加而降低; 土壤C:N随经度增加而增加, N含量随经度增加而降低; 凋落物N含量随经度增加而降低。4)叶片N含量与年平均气温和年降水量均存在明显负相关关系, 但对温度的响应比降水更敏感, 叶片N含量与纬度呈正相关关系, 支持“温度-植物生理假说”, 反映了植物对自然环境的适应。     

C,N and P stoichiometry in different organs of Vitex rotundifolia in a Poyang Lake desertification hill

Aims The objectives were to clarify the responses of C, N and P stoichiometry of Vitex rotundifolia to desertification, and determine the C, N and P stoichiometric relationships among the organs.
Methods In this study, different organs (e.g. flowers, leaves, twigs, creeping stems, fine roots) of V. rotundifolia were sampled along a desertification gradient in a typical Poyang Lak sandy hill. Subsequently, C, N and P contents of various organs were measured.
Important findings The results showed nutrient contents in different organs ranged from 386.28 to 449.47 mg·g^-1 for carbon, 11.40 to 25.37 mg·g^-1 for nitrogen and 0.89 to 1.54 mg·g^-1 for phosphorus, respectively. C, N and P contents differed significantly among the five organs. The maximum N and P content were found in flowers, whereas the minimums were observed in twigs and creping stems. Moreover, desertification intensity only significantly affected C, N and C:P. C:N and N:P ratios maintained relatively stable. Except N:P, the other nutrient elements and associated stoichiometry significantly differed among the organs. Hence, organs, rather than desertification intensity mainly controlled the C, N and P content and their stoichiometry variability. Although there was a positive correlation between mass-based N content (N_mass) and P content (P_mass) across the three desertification zones, the N_mass-P_mass relationship in V. rotundifolia did not shift. Irrespective desertification intensity and organs, N:P stoichiometry of V. rotundifolia was well constrained. In addition, significant correlations of C, N and P contents among organs were mainly found in the above-ground parts, especially between twigs and creeping stems.     

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.     

Leaf nitrogen and phosphorus concentration and the empirical regulations in dominant woody plants of shrublands across southern China

Aims Understanding the changes in N and P concentration in plant organs along the environmental gradients can provide meaningful information to reveal the underline mechanisms for the geochemical cycles and adaptation strategies of plants to the changing environment. In this paper, we aimed to answer: (1) How did the N and P concentration in leaves of evergreen and deciduous woody plants change along the environmental gradients? (2) What were the main factors regulating the N and P concentration in leaves of woody plants in the shrublands across southern China?
Methods Using a stratified random sampling method, we sampled 193 dominant woody plants in 462 sites of 12 provinces in southern China. Leaf samples of dominant woody plants, including 91 evergreen and 102 deciduous shrubs, and soil samples at each site were collected. N and P concentration of the leaves and soils were measured after lapping and sieving. Kruskal-Wallis and Nemenyi tests were applied to quantify the difference among the organs and life-forms. For each life-form, the binary linear regression was used to estimate the relationships between leaf log [N] and log [P] concentration and mean annual air temperature (MAT), mean annual precipitation (MAP) and log soil total [N], [P]. The effects of climate, soil and plant life-form on leaf chemical traits were modeled through the general linear models (GLMs) and F-tests.
Important findings 1) The geometric means of leaf N and P concentrations of the dominant woody plants were 16.57 mg·g^-1 and 1.02 mg·g^-1, respectively. The N and P concentration in leaves (17.91 mg·g^-1, 1.14 mg·g^-1) of deciduous woody plants was higher than those of evergreen woody plants (15.19 mg·g^-1, 0.89 mg·g^-1). The dependent of leaf P concentration on environmental (climate and soil) appeared more variable than N concentration. 2) Leaf N and P in evergreen woody plants decreased with MAT and but increased with MAP, whereas those in deciduous woody plants showed opposite trends. With increase in MAP, leaf P concentration decreased for both evergreen and deciduous woody plants. 3) Soil N concentration had no significant effect on both evergreen and deciduous woody plants. However, leaf P concentration of the tow increased significantly with soil P concentration. (4) GLMs showed that plant growth form explained 7.6% and 14.4% of variation in leaf N and P, respectively. MAP and soil P concentration contributed 0.8% and 16.4% of the variation in leaf P, respectively. These results suggested that leaf N was mainly influenced by plant growth form, while leaf P concentration was driven by soil, plant life-form, and climate at our study sites.     

陕西省森林各生态系统组分氮磷化学计量特征

研究森林植被、枯落物和土壤的氮(N)磷(P)化学计量关系对于理解生态系统各组分的相互作用和养分循环具有重要意义。该研究对陕西省不同类型森林生态系统植被、枯落物和土壤的N和P含量及其化学计量关系进行了研究分析。结果表明: 1)森林生态系统各组分的N、P化学计量特征存在显著差异(p < 0.05), N、P含量均以林下灌草层植物和枯落物层较高, 乔木层植物和土壤层较低; N:P值则稍有不同, 以枯落物层最高, 土壤层最低, 其他各层差异不显著; 各组分N、P含量和N:P值分别为0.72-11.99 mg·g^-1、0.47-1.07 mg·g^-1和1.86-14.84。0-1 m土层内N含量、N:P值均随土层加深而降低(p < 0.05), P含量则不随土层发生明显变化。2)各组分N、P含量和N:P值多表现为阔叶林高于针叶林, 但其差异不显著。3)生态系统同一组分内, N、P含量间极显著正相关, N、P含量与N:P值分别呈极显著正相关、负相关关系, 但是土壤层内N、P含量无显著相关关系。各组分间, 枯落物层与乔木层、草本层和土壤层的N、P含量和N:P值也均极显著正相关, 而枯落物层与灌木层植物无显著相关关系。4)生态系统各组分N、P含量和N:P值随空间变化表现不尽一致, 总体上呈稳态。该文通过对N、P化学计量特征的研究, 揭示了森林生态系统植被、枯落物和土壤组分间所存在的养分循环联系, 这些联系中也表现出分异特征, 而分异可能由各自所执行的不同生态功能所致。     

Stoichiometric characteristics of carbon,nitrogen and phosphorus of Sibiraea angustata shrub on the eastern Qinghai-Xizang Plateau

Aims Little is known about the stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) in plateau shrubs across China. Sibiraea angustata is a typical and representative shrub species on the eastern Qinghai- Xizang Plateau, and exploring its C, N and P distribution patterns and stoichiometric properties in different organs (including root, shoot, leaf, twig and fruit) would help us better understand the mechanisms of C, N and P cycling and balance in the S. angustata dominated shrub ecosystem.
Methods Sixteen sampling sites were selected on the eastern Qinghai-Xizang Plateau by the stratified sampling method. The height and coverage of the dominant shrubs, latitude, longitude and altitude of the sites were recorded. Three 5 m × 5 m plots were selected at each site. At least 128 biological samples of plant organs of S. angustata were collected and measured, respectively. The C and N concentrations of plant samples were analyzed using an elemental analyzer (2400 II CHNS). The P concentration was analyzed using the molydate/ascorbic acid method after H₂SO₄-H₂O₂ digestion.
Important findings The C, N and P concentrations of different organs followed the order of: shoot (495.07 g·kg^-1) > twig (483.37 g·kg^-1) > fruit (480.35 g·kg^-1) > root (468.47 g·kg^-1) > leaf (466.33 g·kg^-1); leaf (22.27 g·kg^-1) > fruit (19.74 g·kg^-1) > twig (7.98 g·kg^-1) > shoot (4.54 g·kg^-1) > root (4.00 g·kg^-1) and fruit (2.85 g·kg^-1) > leaf (1.92 g·kg^-1) > twig (0.96 g·kg^-1) > root (0.52 g·kg^-1) > shoot (0.45 g·kg^-1), respectively. The ranges of the coefficient of variation (CV) for C, N and P concentrations were 1.71%-4.44%, 14.49%-25.50% and 11.46%-46.15%, respectively. Specifically, the C concentration was relatively high and stable, and the maximum CV values for N and P were found in roots. The N:P value of different organs varied from 7.12-12.41 and the minimum CV for N:P was found in twig, which indicated that N:P in twig had higher internal stability. In addition, correlation analysis indicated that the C concentration was significantly negatively correlated with N and P concentrations and correlation coefficients were -0.407 and -0.342, respectively. However, N concentration had dramatically positive correlation with P concentration and the correlation coefficient was 0.814. These results also could indicate that the C, N and P stoichiometric characteristics in the S. angustata shrub accorded with the homeostatic mechanism and growth rate hypothesis to some extent, the distributions of C, N and P concentrations were closely related to the function of the organs and it should be prudent to use ecological stoichiometric ratios to judge the condition of nutrient limitation at the species level.     

桂西北喀斯特森林植物-凋落物-土壤生态化学计量特征

探明我国西南喀斯特生态脆弱区植被恢复重建背景下, 森林植物、凋落物与土壤碳(C)、氮(N)、磷(P)化学计量特征有助于深入地认识喀斯特森林生态系统养分循环规律和系统稳定机制。该文选取桂西北典型喀斯特地区域3个原生林群落和3个自然恢复28年的次生林群落, 研究其“植物-凋落物-土壤”连续体的C、N、P化学计量学特征及其内在关联。结果表明: 1)圆果化香树(Platycarya longipes)、伞花木(Eurycorymbus cavaleriei)和青檀(Pteroceltis tatarinowii)以及圆叶乌桕(Sapium rotundifolium)、八角枫(Alangium chinense)和黄荆(Vitex negundo) 6种植物的C、N、P平均含量分别为427.5、21.2、1.2 mg·g^-1; 凋落物C、N、P平均含量分别为396.2、12.7、0.9 mg·g^-1, 而表层土壤(0-10 cm) C、N、P平均含量分别为92.0、6.35和1.5 mg·g^-1。2)原生林N再吸收率(平均值为42.7%)高于次生林(平均值为36.5%), P再吸收率(20.4%)显著低于次生林(32.3%) (p < 0.05); 6个森林群落N的再吸收率均大于P的再吸收率。3)不同群落凋落物的C:N值差异不显著, 原生林植物的C:N值小于次生林、土壤C:N显著大于次生林; 原生林土壤C:P与次生林无显著差异, 植物与凋落物C:P小于次生林; 原生林凋落物与土壤N:P值小于次生林, 植物N:P比平均值均为17.4。4)研究区典型森林群落植物中N和P含量呈显著的正相关关系, 植物C:N与N:P、C:P与N:P比值均无明显相关关系; 经过对数变换后的土壤C:N与N:P呈显著负相关关系, 凋落物的C:P与N:P值呈极显著正相关关系。研究结果可为我国西南典型喀斯特脆弱生态区的生态功能恢复与植被重建提供科学依据。     

不同诱导子对怀牛膝细胞生长及多糖含量的影响

为提高怀牛膝(Achyranthes bidentata)悬浮培养细胞中牛膝多糖的含量,以酵母提取物、榆黄蘑(Pleurotus citrinopileatus)及水杨酸作为诱导子,分别在同一时期以不同浓度或在不同时期以相同浓度添加至细胞培养物中,收获时测定细胞生长量和牛膝多糖含量。结果显示,在培养12天时添加2.5%(v/v)酵母诱导子,细胞干重最大,可达46.75 g·L–1,多糖含量为5.76 mg·g~(–1);在培养9天时添加5 mg GE·L–1榆黄蘑诱导子,收获时细胞中多糖含量可达6.56 mg·g~(–1),细胞干重达28.3g·L–1;1 mg·g~(–1)水杨酸对牛膝多糖的诱导效果不如以上2种诱导子明显。     

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

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

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.     

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.     

Carbon storage,spatial distribution and the influence factors in Tianshan forests

Aims
Accurate estimation of carbon density and storage is among the key challenges in evaluating ecosystem carbon sink potentials for reducing atmospheric CO₂ concentration. It is also important for developing future conservation strategies and sustainable practices. Our objectives were to estimate the ecosystem carbon density and storage of Picea schrenkiana forests in Tianshan region of Xinjiang, and to analyze the spatial distribution and influencing factors.
Methods
Based on field measurements, the forest resource inventories, and laboratory analyses, we studied the carbon storage, its spatial distribution, and the potential influencing factors in Picea schrenkiana forest of Tianshan. Field surveys of 70 sites, with 800 m² (28.3 m × 28.3 m) for plot size, was conducted in 2011 for quantifying arbor biomass (leaf, branch, trunk and root), grass and litterfall biomass, soil bulk density, and other laboratory analyses of vegetation carbon content, soil organic carbon content, etc.
Important findings
The carbon content of the leaf, branch, trunk and root of Picea schrenkiana is varied from 46.56% to 52.22%. The vegetation carbon content of arbor and the herbatious/litterfall layer was 49% and 42%, respectively. The forest biomass of Picea schrenkiana was 187.98 Mg·hm^-2, with 98.93% found in the arbor layer. The biomass in all layers was in the order of trunk (109.81 Mg·hm^-2) > root (39.79 Mg·hm^-2) > branch (23.62 Mg·hm^-2) > leaf (12.76 Mg·hm^-2). From the age-group point of view, the highest and the lowest biomass was found at the mature forest (228.74 Mg·hm^-2) and young forest (146.77 Mg·hm^-2), respectively. The carbon density and storage were 544.57 Mg·hm^-2 and 290.84 Tg C, with vegetation portion of 92.57 Mg·hm^-2 and 53.14 Tg C, and soil portion of 452.00 Mg·hm^-2 and 237.70 Tg C, respectively. The spatial distribution of carbon density and storage appeared higher in the western areas than those in the eastern regions. In the western Tianshan Mountains (e.g., Ili district), carbon density was the highest, whereas the central Tianshan Mountains (e.g., Manas County, Fukang City, Qitai County) also had high carbon density. In the eastern Tianshan Mountains (e.g., Hami City), it was low. This distribution seemed consistent with the changes in environmental conditions. The primary causes of carbon density difference might be a combined effects of multiple environmental factors such as terrain, precipitation, temperature, and soil.     

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

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

Storage of carbon,nitrogen and phosphorus in temperate shrubland ecosystems across Northern China

Aims Studying storage of carbon (C), nitrogen (N) and phosphorus (P) in ecosystems is of significance in understanding carbon and nutrient cycling. Previous researches in ecosystem C, N and P storage have biased towards forests and grasslands. Shrubland ecosystems encompass a wide gradient in precipitation and soil conditions, providing a unique opportunity to explore the patterns of ecosystem C, N and P storage in relation to climate and soil properties.
Methods We estimated densities and storage of organic C, N and P of shrubland ecosystems in Northern China based on data from 433 shrubland sites.
Important findings The main results are summarized as follows: the average organic C, N and P densities in temperate shrubland ecosystems across Northern China were 69.8 Mg·hm^-2, 7.3 Mg·hm^-2 and 4.2 Mg·hm^-2, respectively. The average plant C, N and P densities were 5.1 Mg·hm^-2, 11.5 × 10^-2 Mg·hm^-2 and 8.6 × 10^-3 Mg·hm^-2, respectively, and were significantly correlated with precipitation and soil nutrient concentrations. The average litter C, N and P densities were 1.4 Mg·hm^-2, 3.8 ×10^-2 Mg·hm^-2, 2.5 ×10^-3 Mg·hm^-2 and were significantly correlated with temperature and precipitation. The average soil organic C, N and P densities in the top 1 m were 64.0 Mg·hm^-2, 7.1 Mg·hm^-2 and 4.2 Mg·hm^-2, respectively and the former two were significantly correlated with temperature and precipitation. The total organic C, N and P storage of shrublands in Northern China were 1.7 Pg, 164.9 Tg and 124.8 Tg, respectively. The plant C, N and P storage were 128.4 Tg, 3.1 Tg and 0.2 Tg, respectively. The litter C, N and P storage were 8.4 Tg, 0.45 Tg, 0.027 Tg, respectively. Soil is the largest C, N and P pool in the studied area. The soil organic C, N and P storage in the top 1 meter were 1.6 Pg, 161.3 Tg and 124.6 Tg, respectively.     

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).     

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.     

Carbon,nitrogen and phosphorus stoichiometry in leaves and fine roots of dominant plants in Horqin Sandy Land

Aims The stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) in plant organism is vital to understand plant adaptation to environment. In particular, the correlations of elemental stoichiometric characteristics between leaf and fine root could provide insights into the interaction and balance among the plant elements, nutrient use strategies and plant response to global change.Methods We measured C, N, P contents and C:N, C:P, N:P in leaves and fine roots of 60 dominant plants in Horqin sandy land. The 60 plant species were classified into five life forms and two categories such as perennial forb, annual forb, perennial grass, annual grass, shrub, legume, and non-legume. We statistically analyzed the differences and correlations of C, N and P stoichiometry either between fine root and leaf or among five life forms.Important findings The average C, N and P concentrations in leaves of 60 plant species in Horqin sandy land are 424.20 mg·g^-1, 25.60 mg·g^-1 and 2.10 mg·g^-1, respectively. In fine roots, the corresponding element concentrations are 434.03 mg·g^-1, 13.54 mg·g^-1, 1.13 mg·g^-1. N and P concentrations in leaf are approximately twice as high as averages in fine root. Furthermore, similar N:P between leaf and fine root indicates conservative characteristic of elemental stoichiometry in plant organism, suggesting that nutrients distribution is proportional between aboveground and underground of plants. There are significant difference of C, N, P, C:N, C:P and N:P in leaf and root among five life forms. N and P in forb and C:N and C:P in grass are averagely higher than those in other life forms. N:P in annual forb and grass, however, are lower than those in other life forms. C, N in legume are higher than those in non-legume, while C:N in legume is lower than in non-legume. These results imply that nutrient use strategies are significantly different among plant life forms. Correlations analysis showed that N and P in leaf or fine root positively correlated, but C and N, C and P in fine root negatively correlated, suggesting coupling relationship among C, N and P in leaf and fine root. Subsequently, we detected positively significant correlations in C, N, P and their ratios between leaf and fine root, suggesting proportional distribution of photosynthate and nutrient between aboveground and underground during plant growth. Generally, these results supplied fundamental data to understand mass turnover and nutrients cycling of leaves and roots in sand land.     

Responses of growth and litterfall production to nitrogen addition treatments from common shrublands in Mt. Dongling,Beijing, China

Aims The shrublands of northern China have poor soil and nitrogen (N) deposition has greatly increased the local soil available N for decades. Shrub growth is one of important components of C sequestration in shrublands and litterfall acts as a vital link between plants and soil. Both are key factors in nutrient and energy cycling of terrestrial ecosystems, which greatly affected by nitrogen (N) addition (adding N fertilizer to the surface soil directly). However, the effects and significance of N addition on C sequestration and litterfall in shrublands remain unclear. Thus, a study was designed to investigate how N deposition and related treatments affected shrublands growth related to C sequestration and litterfall production of Vitex negundo var. heterophylla and Spiraea salicifolia in Mt. Dongling region of China.
Methods A N enrichment experiment has been conducted for V. negundo var. heterophylla and S. salicifolia shrublands in Mt. Dongling, Beijing, including four N addition treatment levels (control (N₀, 0 kg N·hm^-2·a^-1), low N (N₁, 20 kg N·hm^-2·a^-1), medium N (N₂, 50 kg N·hm^-2·a^-1) and high N (N₃, 100 kg N·hm^-2·a^-1)). Basal diameter and plant height of shrub were measured from 2012-2013 within all treatments, and allometric models for different species of shrub’s live branch, leaf and root biomass were developed based on independent variables of basal diameter and plant height, which will be used to calculate biomass increment of shrub layer. Litterfall (litterfall sometimes is named litter, referring to the collective name for all organic matter produced by the aboveground part of plants and returned to the surface, and mainly includes leaves, bark, dead twigs, flowers and fruits.) also was investigated from 2012-2013 within all treatments.
Important findings The results showed 1) mean basal diameter of shrubs in the V. negundo var. heterophylla and S. salicifolia shrublands were increased by 1.69%, 2.78%, 2.51%, 1.80% and 1.38%, 1.37%, 1.59%, 2.05% every year; 2) The height growth rate (the shrub height relative growth rate is defined with the percentage increase of plant height) of shrubs in the V. negundo var. heterophylla and S. salicifolia shrublands were 8.36%, 8.48%, 9.49%, 9.83% and 2.12%, 2.86%, 2.36%, 2.52% every year, respectively. Thee results indicated that N deposition stimulated growth of shrub layer both in V. negundo var. heterophylla and S. salicifolia shrublands, but did not reach statistical significance among all nitrogen treatments. The above-ground biomass increment of shrub layer in the V. negundo var. heterophylla and S. salicifolia shrublands were 0.19, 0.23, 0.14, 0.15 and 0.027, 0.025, 0.032, 0.041 t C·hm^-2·a^-1 respectively, which demonstrated that short-term N addition had no significant effects on the accumulation of C storage of the two shrublands. The litter production of the V. negundo var. heterophylla and S. salicifolia communities in 2013 were 135.7 and 129.6 g·m^-2 under natural conditions, respectively. Nitrogen addition promoted annual production of total litterfall and different components of litterfall to a certain extent, but did not reach statistical significance among all nitrogen treatments. Above results indicated that short-term fertilization, together with extremely low soil moisture content and other related factors, lead to inefficient use of soil available nitrogen and slow response of shrublands to N addition treatments.     

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 environmental factors on gross caloric values of three life-forms aquatic plants on the Qinghai-Xizang Plateau,China

Aims Gross caloric value (GCV) reflected plants’ capability of converting solar energy. It provided a reliable indicator of plants’ adaptations to environments in perspective of energy conversion and fixation. The aims of this study were (1) to illustrate the characteristics of GCV of aquatic plants on the Qinghai-Xizang Plateau, (2) to explore the geographical and environmental patterns and (3) to discuss the underlying mechanisms in forming the patterns.
Methods In July and August 2015, we collected 533 samples of aquatic plants’ leaves in 143 field sites on the Qinghai-Xizang Plateau, and measured their GCV using SDACM-4000 oxygen bomb calorimeter. Together with mean annual temperature (MAT) of climatic factor and properties of water body, this study compared the differences of GCV among submerged, emergent and floating-leaved plants by analysis of variance (ANOVA) and Tukey’s HSD. We further regressed GCV of submerged and emergent plants against geographical and climatic factors and properties of water body by simple regression to explore the relative effects of environmental factors on GCV.
Important findings On the Qinghai-Xizang Plateau, the mean GCV was (15.95 ± 3.90) kJ·g^-1. Among the three life forms, the rank of GCV was the emergent plants (18.10 kJ·g^-1) > the floating-leaved plants (16.77 kJ·g^-1) > the submerged plants (14.31 kJ·g^-1). With an increasing latitude, the GCV of emergent and submerged plants increased. Only GCV of emergent plants decreased with increasing altitude and temperature. The GCV of emergent and submerged plants increased with increased water salinity. Dissolved oxygen had significant negative effects on emergent plants, while pH value had no significant effects.