北亚热带地带性森林土壤温室气体通量对土地利用方式改变和降水减少的响应

弄清土地利用和降水变化对林地土壤主要温室气体(CO₂、CH₄和N₂O)排放通量变化的影响, 是准确评估森林土壤温室气体排放能力的重要基础。该研究以常绿落叶阔叶混交林原始林、桦木(Betula luminifera)次生林和马尾松(Pinus massoniana)人工林为对象, 采用静态箱-气相色谱法研究了3种土地利用方式(常绿落叶阔叶混交林原始林、桦木次生林和马尾松人工林)和降水减少处理状况下森林土壤CO₂、CH₄和N₂O通量排放特征, 并探讨了其环境驱动机制。研究结果表明: 原始林土壤CH₄吸收通量显著高于次生林和人工林, 次生林CH₄吸收通量显著高于人工林土壤。人工林土壤CO₂排放通量显著高于原始林和次生林土壤。次生林土壤N₂O排放通量高于原始林和人工林, 但三者间差异不显著。降水减半显著抑制了3种不同土地利用方式下林地土壤CH₄吸收通量; 降水减半处理对原始林和次生林土壤CO₂排放通量均具有显著的促进作用, 而对人工林土壤CO₂排放通量具有显著的抑制作用; 降水减半处理促进了原始林和人工林林地土壤N₂O排放而抑制了次生林林地土壤N₂O排放。原始林和次生林林地土壤CH₄吸收通量随土壤温度升高显著增加, CH₄吸收通量与土壤温度均呈显著相关关系; 原始林、次生林和人工林土壤CO₂和N₂O排放通量与土壤温度均呈显著正相关关系; 土壤湿度抑制了次生林和人工林土壤CH₄吸收通量, 其CH₄吸收通量随土壤湿度增加显著减少; 原始林土壤CO₂排放通量与土壤湿度呈显著正相关关系。自然状态下, 原始林土壤N₂O排放通量与土壤湿度呈显著正相关关系, 原始林和次生林土壤N₂O排放通量与硝态氮含量呈显著相关关系。研究结果表明全球气候变化(如降水变化)和土地利用方式的转变将对北亚热带森林林地土壤温室气体排放通量产生显著的影响。     

Effluxes of nitrous oxide,methane and carbon dioxide and their responses to increasing nitrogen deposition in the Gurbantünggüt Desert of Xinjiang,China

Aims Desert soils play an important role in the exchange of major greenhouse gas (GHG) between atmosphere and soil. However, many uncertainties existed in understanding of desert soil role, especially in efflux evaluation under a changing environment. Methods We conducted plot-based field study in center of the Gurbantünggüt Desert, Xinjiang, and applied six rates of simulated nitrogen (N) deposition on the plots, i.e. 0 (N0), 0.5 (N0.5), 1.0 (N1), 3.0 (N3), 6.0 (N6) and 24.0 (N24) g·m^-2·a^-1. The exchange rates of N₂O, CH₄ and CO₂ during two growing seasons were measured for two years after N applications. Important findings The average efflux of two growing seasons from control plots (N0) were 4.8 μg·m^-2·h^-1, -30.5 μg·m^-2·h^-1 and 46.7 mg·m^-2·h^-1 for N₂O, CH₄ and CO_2, respectively. The effluxes varied significantly among seasons. N0, N0.5 and N1 showed similar exchange of N₂O in spring and summer, which was relatively higher than in autumn, while the rates of N₂O in N6 and N24 were controled by time points of N applications. The uptake of CH₄ was relatively higher in both spring and summer, and lower in autumn. Emission of CO₂ changed minor from spring to summer, and greatly decreased in autumn in the first measured year. In the second year, the emission patterns were changed by rates of N added. N additions generally stimulated the emission of N₂O, while the effects varied in different seasons and years. In addition, no obvious trends were found in the emission factor of N₂O. The uptake of CH₄ was not significantly affected by N additions. N additions did not change CO₂ emissions in the first year, while high N significantly reduced the CO₂ emissions in spring and summer of the second year, without affected in autumn. Structure equation model analysis on the factors suggested that N₂O, CH₄ and CO₂ were dominantly affected by the N application rates, soil temperature or moisture and plant density, respectively. Over the growing seasons, both the net efflux and the global warming potential caused by N additions were small.     

Responses of soil respiration with biocrust cover to water and temperature in the southeastern edge of Tengger Desert,Northwest China

Aims Soil respiration of the lands covered by biocrusts is an important component in the carbon cycle of arid, semi-arid and dry-subhumid ecosystems (drylands hereafter), and one of the key processes in the carbon cycle of drylands. However, the responses of the rate of soil respiration with biocrusts to water and temperature are uncertain in the investigations of the effects of experimental warming and precipitation patterns on CO₂ fluxes in biocrust dominated ecosystems. The objectives of this study were to investigate the relationships of carbon release from the biocrust-soil systems with water and temperature in drylands. Methods Intact soil columns with two types of biocrusts, including moss and algae-lichen crusts, were collected in a natural vegetation area in the southeastern fringe of the Tengger Desert. Open top chambers were used to simulate climate warming, and the soil respiration rate was measured under warming and non-warming treatments using an automated soil respiration system (LI-8150). Important findings Over the whole observational period (from April 2016 to July 2016), soil respiration rates varied from -0.16 to 4.69 μmol·m^-2·s^-1 for the moss crust-covered soils and from -0.21 to 5.72 μmol·m^-2·s^-1 for the algae-lichen crust-covered soils, respectively, under different rainfall events (the precipitations between 0.3-30.0 mm). The mean soil respiration rate of the moss crust-covered soils is 1.09 μmol·m^-2·s^-1, which is higher than that of the algae-lichen crust-covered soils of 0.94 μmol·m^-2·s^-1. The soil respiration rate of the two types of biocrust-covered soils showed different dynamics and spatial heterogeneities with rainfall events, and were positively correlated with precipitation. The mean soil respiration rate of the biocrust-covered soils without warming was 1.24 μmol·m^-2·s^-1, significantly higher than that with warming treatments of 0.79 μmol·m^-2·s^-1 (p < 0.05). By increasing the evaporation of soil moisture, the simulated warming impeded soil respiration. In most cases, soil temperature and soil respiration rate displayed a similar single-peak curve during the diel cycle. Our results show an approximately two hours’ lag between soil temperature at 5 cm depth and the soil respiration rate of the biocrust-covered soils during the diel cycle.     

库布齐沙漠东部不同生物结皮发育阶段土壤温室气体通量

以流动沙地为对照,采用时空替代法分析库布齐沙漠东部固定沙地上不同发育阶段生物结皮藻类结皮和地衣结皮土壤温室气体通量特征及其与环境因子之间的关系,研究生物结皮发育对荒漠土壤温室气体通量的影响.结果表明: 荒漠土壤CO₂排放通量大小为地衣结皮(128.5 mg·m^-2·h^-1)>藻结皮(70.2 mg·m^-2·h^-1)>流动沙地(48.2 mg·m^-2·h^-1),CH₄吸收通量大小为地衣结皮(30.4 μg·m^-2·h^-1)>藻结皮(21.2 μg·m^-2·h^-1)>流动沙地(18.2 μg·m^-2·h^-1),N₂O排放通量大小为地衣结皮(6.6 μg·m^-2·h^-1)>藻结皮(5.4 μg·m^-2·h^-1)>流动沙地(2.5 μg·m^-2·h^-1).CO₂排放具有明显的季节变化,生长季显著大于非生长季;CH₄和N₂O季节变化差异不显著,前者生长季吸收大于非生长季,后者非生长季排放大于生长季.土壤有机碳和全氮含量、土壤微生物数量均是影响温室气体通量的重要因素,环境水热因子是影响土壤CO₂排放的关键因子,但CH₄和N₂O通量对水热因子的变化不敏感.随着植被恢复和生物结皮发育,荒漠土壤温室气体累积通量的不断增大导致其百年尺度的全球增温潜势亦显著提高,依次为地衣结皮(1135.7 g CO₂-e·m^-2·a^-1)>藻结皮(626.5 g CO₂-e·m^-2·a^-1) >流动沙地(422.7 g CO₂-e·m^-2·a^-1).     

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.     

长白山北坡不同土壤N2O和CH4排放的初步研究

用箱法技术原位测定了长白山北坡不同土壤(苔原土、生草森林土、棕色针叶林土和暗棕色森林土)6-8月间的N₂O和CH₄排放。结果表明,这些土壤既是N₂O的源,又同时是CH₄的汇。N₂O通量变化于6.17-12.33μg·m^-2·h^-3之间(平均9.37μg·m^-2·h^-1),CH₄通量为-85.63—7.58μg·m^-2·h^-1(平均-41.45μg·m^-3·h^-1),并观察到在N₂O排放和CH₄吸收之间有着相互消长关系。实验室培养实验表明,最大反硝化作用活性存在于土壤上层(0-6cm);不同土壤的反硝化作用活性明显不同。山地暗棕色森林土的CH₄吸收作用也主要发生在土壤的上层(0-12cm).     

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.     

科尔沁沙丘-草甸梯级生态系统土壤温室气体通量特征及其影响因素

采用静态箱-气相色谱法,对科尔沁半干旱地区典型的沙丘-草甸梯级生态系统中半流动沙丘和草甸湿地的温室气体(CO₂、CH₄、N₂O)通量进行了观测,分析了生长季温室气体的动态变化及其与环境影响因子的关系.结果表明: 生长季半流动沙丘和草甸湿地CH₄通量均整体表现为吸收,平均值分别为-52.7和-34.7 μg·m^-2·h^-1,介于-176.1～49.8 μg·m^-2·h^-1之间变化,8月22日半流动沙丘CH₄吸收值达到生长季最大值;8、9月降雨集中时段内草甸湿地CH₄通量表现为持续排放,与半流动沙丘呈明显差异.N₂O通量在7月21日达到生长季最大值,半流动沙丘N₂O通量的月均值表现为7月>8月>9月>6月>5月.土壤温湿度是影响CO₂和CH₄通量的关键因子,N₂O通量主要受土壤温度的影响.样地土壤温度敏感性(Q₁₀)表现为半流动沙丘(1.009)<草甸湿地(1.474),半流动沙丘土壤受到水分胁迫,导致其温室气体通量对土壤温度变化的敏感性明显低于草甸湿地.     

Short-term responses of winter soil respiration to snow removal in a Picea asperata forest of western Sichuan

Aims Seasonal snow cover is one of the most important factors that control winter soil respiration in the cold biomes. The warming-induced decreases in snowpack could affect winter soil respiration of subalpine forests. The aim of this study was to explore the effects of snow removal on winter soil respiration in a Picea asperata forest.Methods A snow removal experiment was conducted in a P. asperata forest stand in western Sichuan during the winter of 2015/2016. The snow removal treatment was implemented using wooden roof method. Soil temperatures, snow depth and soil respiration rate were simultaneously measured in plots of snow removal and controls during the experimental period.Important findings Compared to the control, snow removal increased the fluctuations of soil temperatures. The average daily temperature of the soil surface and that at 5 cm depth were 1.12 °C and 0.34 °C lower, respectively, and the numbers of freeze-thaw cycles of the soil surface and that at 5 cm depth were increased by 39 and 12, respectively, in plots of snow removal than in the controls. The average rate of winter soil respiration and CO₂ efflux were 0.52 μmol·m^-2·s^-1 and 88.44 g·m^-2, respectively. On average, snow removal reduced soil respiration rate by 21.02% and CO₂ efflux by 25.99%, respectively. More importantly, the snow effect mainly occurred in the early winter. The winter soil respiration rate had a significant exponential relationship with soil temperature. However, snow removal significantly reduced temperature sensitivity of the winter soil respiration. Our results suggest that seasonal snow reduction associated with climate change could inhibit winter soil respiration in the subalpine forests of western Sichuan, with significant implications for the carbon dynamics of the subalpine forests.     

若尔盖高原湿地不同微地貌区甲烷排放通量特征

若尔盖高原是我国泥炭沼泽湿地的主要分布区、青藏高原的主要甲烷(CH₄)排放中心。为了研究湿地微地貌环境对高原湿地CH₄排放通量的影响, 2014年5-10月, 采用静态箱和快速温室气体分析仪原位测量若尔盖高原湖滨湿地3种泥炭沼泽5种微地貌环境下的CH₄排放通量特征。结果表明: (1)常年性淹水泥炭湿地洼地(P-hollow)和草丘(P-hummock)生长季平均CH₄排放通量为68.48和40.32 mg·m^-2·h^-1, 季节性淹水的泥炭湿地洼地(S-hollow)和草丘(S-hummock)平均CH₄排放通量为2.38和0.63 mg·m^-2·h^-1, 而无淹水平坦地(Lawn)平均CH₄排放通量为3.68 mg·m^-2·h^-1; (2)湿地5种微地貌区CH₄排放通量为(23.10 ± 30.28) mg·m^-2·h^-1 (平均值±标准偏差)), 变异系数为131%。分析显示这5种微地貌区CH₄排放通量的平均值与其水位深度平均值存在显著的线性正相关关系(R² = 0.919, p < 0.01), 表明水位深度是控制湿地微地貌区CH₄排放通量空间变化的主要因子; (3) P-hummock、P-hollow和S-hummock的CH₄排放通量存在显著的季节变化, Lawn和S-hollow无明显的季节性变化, 但5种微地貌区在夏季或秋季均观测到CH₄排放通量峰值, 其影响因子可能与水位深度、土壤温度和凋落物输入密切相关; (4) P-hollow可能时常发生冒泡式CH₄排放, 这可能导致过去低估了若尔盖高原湿地的CH₄排放量。     

大兴安岭重度火烧迹地天然次生林土壤温室气体通量及其影响因子

为研究大兴安岭重度火烧迹地自然恢复后的林分土壤温室气体源汇强度及其影响因素,采用静态箱/气相色谱法,对生长季(6—9月)天然次生林土壤温室气体CO₂、CH₄、N₂O通量进行原位观测.结果表明: 1)生长季内天然次生林土壤为大气CO₂、N₂O的源,CH₄的汇,平均通量分别为575.81 mg·m^-2·h^-1、17.81 μg·m^-2·h^-1和-68.69 μg·m^-2·h^-1;CO₂与CH₄通量在生长季内表现出明显的双峰变化规律,N₂O通量则呈单峰变化,且均在8月达到观测期的最大值.2)土壤温度是影响该区天然次生林土壤温室气体通量的主控因子,土壤湿度和大气湿度在昼夜与季节尺度上与土壤温室气体通量的相关性不同.3)该区天然次生林9:00—12:00时段观测获得的土壤气体通量值经矫正后可代表当日气体通量.研究补充了大兴安岭火烧迹地森林生态系统温室气体通量数据,为该区土壤温室气体源汇的相关研究提供了依据.     

采伐对小兴安岭森林沼泽非生长季土壤温室气体排放的影响

中高纬度地区非生长季温室气体排放对生态系统碳、氮循环具有重要影响,但采伐干扰如何影响森林沼泽非生长季土壤温室气体排放尚不明确.本研究采用静态箱-气相色谱法,观测小兴安岭4种森林沼泽(毛赤杨沼泽、白桦沼泽、落叶松苔草沼泽、落叶松藓类沼泽)不同采伐方式下(对照、择伐45%、皆伐,试验处理已10年)非生长季土壤CO₂、CH₄、和N₂O通量及其相关环境因子(温度、湿度及碳氮含量等),分析采伐干扰对温带森林沼泽非生长季土壤温室气体排放的影响规律及主控因子.结果表明: 采伐干扰10年后,4种森林沼泽土壤CO₂、CH₄和N₂O非生长季平均通量分别在53.08～81.31 mg·m^-2·h^-1、0.09～3.07 mg·m^-2·h^-1和4.07～8.83 μg·m^-2·h^-1,其中,皆伐显著提高毛赤杨沼泽和落叶松藓类沼泽非生长季土壤CO₂、CH₄和N₂O排放量,择伐显著提高白桦沼泽、落叶松藓类沼泽及降低毛赤杨沼泽的CO₂排放量,且显著降低4种森林沼泽CH₄排放量及落叶松苔草沼泽的N₂O排放量;天然森林沼泽非生长季土壤CO₂排放受土壤温度、有机碳含量及C/N调控,CH₄受土壤温度、有机碳含量调控,N₂O受气温、土壤pH调控,采伐增加了CO₂排放与气温、土壤含水量及积雪深度的相关性,增加了CH₄排放与气温、土壤含水量、C/N的相关性,增加了N₂O排放与土壤全氮和C/N的相关性;温带天然森林沼泽非生长季土壤CO₂、CH₄和N₂O的年贡献率分别为33.2%～46.5%、6.3%～9.1%和61.5%～68.3%,皆伐提高了白桦沼泽和落叶松藓类沼泽CO₂年贡献率和除落叶松藓类沼泽外其他样地的N₂O年贡献率,择伐提高了落叶松苔草沼泽、落叶松藓类沼泽CO₂、CH₄和N₂O年贡献率,但降低了白桦沼泽3种气体年贡献率.温带天然森林沼泽非生长季土壤N₂O和CO₂的年贡献率相对较大,皆伐使两者年贡献率进一步提高,择伐却较大幅度提高了其CH₄的年贡献率.     

稻田CH4和N2O的排放及养萍和施肥的影响

用箱法对我国东北稻田CH₄和N₂O排放进行观测研究表明,东北稻田的CH₄排放通量比南方稻田小,平均日排放通量和生长季节排放总量分别为0.07和7.4g·m^-2.稻田淹水期几乎没有N₂O的净排放,但在非淹水期内却有大量N₂O排放(平均通量59μgN₂O·m^-2·h^-1).稻田养萍和施肥明显促进CH₄和N₂O排放。稻田CH₄和N₂O排放之间存在消长关系。制定稻田温室气体减排技术措施时应充分注意这一关系。     

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.     

广州地区晚稻田 CH4和N2O 的排放通量及其影响因素

用密闭箱法同时研究了广州地区晚稻田CH₄和N₂O的排放通量。结果表明,连续淹水、常规连作和水旱轮作等3种处理的CH₄平均排放通量分别为1.763、2.84和0.36mg·m^-2·h^-1,而N₂O的平均排放通量分别为6.74、11.69和55.07μgN₂O-N·m^-2·h^-1,表明稻田连续淹水显著增加CH₄的排放而降低N₂O的排放。水旱轮作降低CH₄排放而提高N₂O的排放,说明稻田CH₄和N₂O排放之间存在着消长关系。讨论了这2种温室气体排放的影响因素,并初步分析了它们对温室效应的相对贡献。     

喀斯特石漠化地区土壤温室气体的地气交换特征

利用密闭箱-气相色谱法于2006～2007年对黔中喀斯特地区土壤二氧化碳、氧化亚氮和甲烷的释放通量进行原位观测,研究我国南方喀斯特石漠化地区土壤温室气体地气交换特征.结果表明:喀斯特石漠化地区土壤是大气CO₂、N₂O的释放源,CH₄的吸收汇.土壤CO₂的释放通量介于450.8±50.8～1281.3±214.7 mg·m^-2·h^-1在之间,夏秋季节高于冬春季节;N₂O的释放通量介于-25.4±4.1～105.8±31.2μg·m^-2·h^-1之间,在夏季最高,在9月、11月和12月出现土壤对大气N₂O的吸收;全年CH₄交换通量介于-0.27±0.18～0.81±0.26 mg·m^-2·h^-1之间,随季节的变化不明显.气候条件对土壤CO₂和CH₄交换通量的影响较小,土壤水分对N₂O释放通量的影响效应在不同的季节不同.相关分析结果显示,土壤N₂O和CH₄地气交换通量受到土壤硝态氮含量的调控.     

Effects of nitrogen enrichment on root exudative carbon inputs in Sibiraea angustata shrubbery at the eastern fringe of Qinghai-Xizang Plateau

Aims Understanding the responses of root exudative carbon (C) to increasing nitrogen deposition is important for predicting carbon cycling in terrestrial ecosystems. However, fewer studies have investigated the dynamics of root exudation in shrubbery ecosystems compared to forests and grassland ecosystems. This objective of this study was to determine the effects of nitrogen fertilization on the rate and C flux of root exudates.Methods Three levels of nitrogen addition treatments were applied to a Sibiraea angustata shrubbery ecosystem situated at the eastern fringe of Qinghai-Xizang Plateau, including N₀ (without nitrogen application), N₅ (nitrogen addition rate of 5 g·m^-2·a^-1), and N₁₀ (nitrogen addition rate of 10 g·m^-2·a^-1), respectively, in 5 m ´ 5 m plots. Root exudates were collected in June, August and October of 2015, using a modified culture-based cuvette system. Root biomass in each plot was measured with root core method.Important findings The rates of root exudates on biomass, length, and surface area basis all displayed apparent seasonal variations during the experimental period, with the magnitude ranked in the order of: August > June > October, consistent with changes in soil temperature at 5 cm depth. With increases in the nitrogen addition rate, the rate of root exudates on biomass, length, and area basis all trended lower. Compared with the control (N₀), the N₅ and N₁₀ treatments significantly reduced fine root biomass in the Sibiraea angustata shrubbery, by 23.36% and 33.84%, respectively. The decreasing root exudation and fine root biomass in response to nitrogen addition significantly decreased C flux of root exudates. Our results provide additional evidences toward a robust theoretical foundation for better understanding soil C-nutrient cycling process mediated by root exudation inputs in Alpine shrubbery ecosystems under various environmental changes.     

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.     

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.     

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.