Variation characteristics of soil respiration fluxes in four types of grassland communities under different precipitation intensity

In the global carbon cycle studies, terrestrial ecosys- tem has become one of the greatest uncertain ecosystems in the current carbon cycle studies owing to the complex- ity of its underlying surface and intense disturbance of anthropogenic activities[1], hence depth studies of it serveas a key in seeking for the “missing carbon sinks” of at-mosphere. In the terrestrial ecosystem, soil organic carbonreservoir is an important component of carbon reservoir inthe system, its carbon …     

Estimation of soil respiration in a paddy ecosystem in the subtropical resion of China

Water vapor, energy exchange, and CO2 flux were measured continuously from 2003 to 2005 using the eddy covariance technique in a paddy ecosystem in the subtropical region of China. The CO2 fluxes at nighttime during fallow periods （from middle October to late April） were used to analyze the dynamics of soil respiration and its relationship with soil temperature, and to simulate the annual dynamics of soil respiration in paddy ecosystems. The variation of soil respiration showed a clear seasonal pattern. The soil respiration rates at night during the fallow periods were 52--398 mg· m^-2· h^-1, and exponentially correlated （P〈0.001） with soil temperatures at different depths of soil （5, 10, and 20 cm）, particularly the temperature measured at a depth of 5 cm. Based on the simulated exponential equations developed, annual average soil respiration rates and total soil respiration of paddy soil in the subtropical region of China were estimated to be 178.5--259.9 mg· m^-2· h^-1 and 1.56--2.28 kg· m^-2· a^-1, respectively. The simulation equations can be applied to evaluating soil respiration in paddy ecosystems during the rice-growing season.     

The contribution of root respiration to soil CO2 efflux in Puccinellia tenuiflora dominated community in a semi-arid meadow steppe

Rising atmospheric CO2 and temperature are altering ecosystem carbon cycling. Grasslands play an important role in regional climate change and global carbon cycle. Below-ground processes play a key role in the grassland carbon cycle because they regulate …     

Fluxes of carbon dioxide and methane from swamp and impact factors in Sanjiang Plain,China

Incomplete decomposition of organic matter results in the accumulation of the carbon and other nutriments in wetlands. The wetland ecosystem gains a large amount of carbon from atmosphere CO2 by photosynthesis, and it loses much of which back into the atmosphere as CO2 and CH4 emission through the decomposition and respiration. Climate change, such as global warming and reduction of precipitation could drive the wetlands from carbon sink to source[1,2]. Wetland plays an important role in car…     

Evaluating the influences of measurement time and frequency on soil respiration in a semiarid temperate grassland

Soil respiration(Soil R)is one of the largest CO2fluxes from terrestrial ecosystems to the atmosphere.The largely seasonal and daily patterns of Soil R in semiarid grassland ecosystems indicate that measurement time and frequency would have significant influences on the assessment of seasonal soil carbon release.Based on a three-year continuous measurement of Soil R in a semiarid grassland,we found that the Soil R value measured at around 10:00 o’clock local time was the closest to its daily mean,while the value at 14:00 o’clock was found to be the highest daily rate.A measurement frequency higher than every 10 days was necessary for estimating the seasonal Soil R and its temperature sensitivity(Q10)reasonably.Our study would be useful as guidelines for manual Soil R measurements and model data selection in semiarid temperate grasslands.     

去除和添加凋落物对马尾松×红锥混交林土壤呼吸的影响

为探讨凋落物输入量改变对马尾松×红锥混交林碳排放的影响,以马尾松×红锥异龄混交林为研究对象,通过添加和去除凋落物人为地改变碳输入,研究凋落物处理方式对土壤呼吸的影响。结果表明:(1)去除凋落物可降低土壤湿度、提高土壤温度,而添加凋落物则提高土壤湿度、降低土壤温度。去除凋落物使土壤年均呼吸速率显著降低27.88%,而添加凋落物则使土壤年均呼吸速率显著增加34.02%。(2)去除凋落物能降低四季的土壤呼吸累积排放量,而添加凋落物则提高四季的土壤呼吸累积排放量。对照、去除和添加凋落物的土壤呼吸的年累积排放量(以C计)分别为(9.51±0.12) t·hm~(-2)、(6.88±0.21) t·hm~(-2)和(12.70±0.53) t·hm~(-2),可见去除凋落物使土壤呼吸年累积排放量降低27.66%,而添加凋落物使土壤呼吸年累积排放量提高33.54%。(3)不同凋落物处理方式下土壤呼吸速率与土壤温度均呈显著相关,土壤温度解释了土壤呼吸速率变异程度的74.26%～94.28%。去除凋落物增加了土壤呼吸温度敏感性系数Q10值,而添加凋落物则降低Q10值。凋落物处理方式对马尾松×红锥异龄混交林土壤呼吸产生了显著影响,证明凋落物对于改变森林生态系统土壤呼吸和碳循环具有重要作用。     

Distribution characteristics of ^137Cs in wind-eroded soil profile and its use in estimating wind erosion modulus

~~Distribution characteristics of ~(137)Cs in wind-eroded soil profile and its use in estimating wind erosion modulus1.Tamura, T, Jacobs, D. G, Structural implications in cesium sorp-tion, Health Physics, 1960, 6(2): 391-398. 2.Rogowshi, A. S., Tamura, T, Movement of 137Cs by runoff, erosion and infiltration on the alluvial captina silt loam, Health Physics, 1965, 11(12): 1333-3340. 3.Owens, P. N., Walling, D. E., He, Q. P., The behaviour of bomb-derived caesium-137 fallout in …     

Food-Chain Model of Grassland Degradation and Its Restoration Process in Northern Tibet Plateau：A Case Study in Nierong County

Based on the model of grassland climate ecological productivity, the process of grassland degradation and its restoration mechanism in northern Tibetan Plateau were discussed by the model of food-chain in which the environmental and human factors were corrected. The results of case study in Nierong County showed that： ① the climate trend of becoming warmer, more droughts and gales were conflicted with the restoration of grassland degradation, even under level of perfect management the climate ecological productivity was declined from 89. 3 kg/m^2 of 1983 to 71.8 kg/m^2 of 2003; ② from 1983 to 2003, the population increased fast, while the variation of livestock on hand was little, and the cost of its maintaining is rapid grassland degradation; ③ on the present condition of overgrazing, the livestock on hand can be maintained on the level of theoretical carrying capacity in 2033 by applying the mechanism of food-chain in grassland ecological system controlled with expected coefficients, so that to realize the policy of determining the quantity of livestock according to grass growth.     

不同生态系统呼吸模型在半干旱草原生长季碳循环研究中的比较及应用

利用锡林浩特国家气候观象台涡度协方差通量观测系统记录的湍流数据和土壤温度、湿度数据, 分析2010-2012年锡林郭勒半干旱区针茅草原生态系统的呼吸过程及主要气候影响因子, 探讨以土壤温度和土壤体积比含水量(VWC)为计算参数的3种连乘形式的呼吸模型和Q₁₀呼吸模型在该生态系统的适用性, 在此基础上讨论该生态系统生长季净碳交换速率(NEE)、呼吸速率(R_eco)以及总初级生产力(GPP)的年际变化特征。该草原生态系统的呼吸作用受土壤温度和土壤含水量的共同影响, 其中土壤含水量是重要的限制因子。2010和2011年, 生长季降水量偏少, 该生态系统受到一定程度的干旱胁迫, 当土壤含水量处于12%~20%区间时, 呼吸速率随其升高而显著增加, 而当土壤含水量<12%或>20%时, 呼吸速率对其变化不敏感; 2012年降水充沛, 呼吸速率与土壤温度的变化趋势相关性更显著。4种呼吸模型的拟合结果表明, Q₁₀模型的表现(R²=0.64)优于其他3 种连乘模型。使用Q₁₀模型模拟的2010, 2011和2012年生长季呼吸作用的累积碳交换量分别为157.32, 138.75和 246.32 gC/m²。该草原生态系统在这3年生长季中均表现出较显著的碳汇功能, 净碳交换累积总量分别为−110.28, −68.79和−310.05 gC/m², 总初级生产力累积总量分别为267.52, 207.57和555.85 gC/m²。干旱胁迫对光合作用的影响大于呼吸作用, 与总初级生产力和呼吸作用相比, 净碳交换量的年际差异更明显。     

Variation of δ13C in karst soil in Yaji Karst Experiment Site, Guilin

This study deals with δ₁₃ C variation in karst soil system of Yaji Karst Experiment Site, Guilin, a typical region of humid subtropical karst formations. Samples of near ground air, plant tissue, soil and water (soil solution and karst spring) were respectively collected on site in different seasons during 1996–1999. Considerable variation of δ₁₃ C values are not only found with different carbon pools of soil organic carbon, soil air CO₂ and soil water HCO₃⁻, but also with the soil depths and with different seasons during a year. The °₁₃ C values of CO₂ both of near ground air and soil air are lower in July than those in April by 1‰–4‰ PDB. Our results indicate that the δ₁₃ C values of carbon in the water and air are essentially dependent on interface carbon interaction of air-plant—soil-rock—water governed by soil organic carbon and soil CO₂ in the system.     

Coastal acidification in summer bottom oxygen-depleted waters in northwestern-northern Bohai Sea from June to August in 2011

Dissolved oxygen(DO) and pH in the central part of the Bohai Sea were surveyed in late June and late August,2011.During the June cruise,the bottom DO was in the range of 215-290 μmol-O2 kg-1(i.e.85%-115% of the saturation level),and the bottom pH was in the range of 7.82-8.04 on the total-hydrogen-ion scale.In August,however,both the bottom DO and the pH had significantly declined in the northwestern-northern near-shore areas,where the water depth was no more than 35 m.The lowest bottom DO was 100-110 μmol-O2 kg-1(only 44%-47% of the June DO values) in the northern near-shore area,where the bottom pH was 7.64-7.68 on the total-hydrogen-ion scale(0.16-0.20 units lower than the June pH value).The largest decreases in DO and in pH were observed in the northwestern near-shore bottom waters,corresponding to declines of 170 μmol-O2 kg-1(as high as 59% of the June DO value) and 0.29 pH units,respectively.The greatest pH decline of 0.29 pH units meant that the total-hydrogen-ion concentration doubled in the bottom waters from June to August.Based on field measurements of bottom DO/pH combined with a simplified model simulation,we suggest that respiration/remineralization-derived CO2 increased the acidity in the bottom oxygen-depleted waters of northwestern-northern near-shore areas in the Bohai Sea as a result of coastal red tides and/or marine aquaculture.This aquatic chemistry is suggested to be partially responsible for scallop-breeding failures in the northwestern Bohai Sea in summer 2011.     

Preliminary study of microscale zircon oxygen isotopes for Dabie-Sulu metamorphic rocks： Ion probe in situ analyses

151 in situ analyses of oxygen isotopes were carried out by ion micro-probe for zircons from 8 localities of HP-UHP metamorphic rocks including eclogites in the Dabie-Sulu terrane. The results show significant heterogeneity in δ^18O values, with variation in different rocks from -8.5‰ to 9.7‰ and within one sample from 2‰ to 12‰. No measurable difference in δ^18O was observed between protolith magmatic (detrital) zircons and metamorphic recrystallized zircons within analytical uncertainties from the ion micro-probe measurements. This indicates that the metamorphic zircons have inherited the oxygen isotopic compositions of protolith zircons despite the HP to UHP metamorphism. According to their protolith ages from zircon U-Pb in situ dating by the same ion micro-probe, two groups of oxygen isotope composition are recognized, with one having δ^18O values of 6‰-7‰ for old protolith of 1.9-2.5 Ga ages and the other 0‰-2‰ for young protolith of 0.7-0.8 Ga ages. The latter anomalously low δ^18O values of zircons indicate that the magma has had the obvious involvement of meteoric water when forming the young protolith of high-grade metamorphic rocks. This may be correlated with the snowball Earth event occurring in South China and the world elsewhere during the Neoproterozoic.     

Preparation of semi-solid aluminum alloy slurry poured through a water-cooled serpentine channel

A water-cooled serpentine channel pouring process was invented to produce semi-solid A356 aluminum alloy slurry for rheocasting, and the effects of pouring temperature and circulating cooling water flux on the microstructure of the slurry were investigated. The results show that at the pouring temperature of 640-680℃ and the circulating cooling water flux of 0.9 m3/h, the semi-solid A356 aluminum alloy slurry with spherical primary α(Al) grains can be obtained, whose shape factors are between 0.78 and 0.86 and the grain diameter can reach 48-68 μm. When the pouring temperatures are at 660-680℃, only a very thin solidified shell remains inside the serpentine channel and can be removed easily. When the serpentine channel is cooled with circulating water, the microstructure of the semi-solid slurry can be improved, and the serpentine channel is quickly cooled to room temperature after the completion of one pouring. In terms of the productivity of the special equipment, the water-cooled serpentine channel is economical and efficient.     

High resolution stalagmite δ18O records over the past 1000 years from Dongge Cave in Guizhou

Based on MC-ICP-MS U-series dating andstable O-isotope analysis results, a 4-5 years resolution monsoon record over the past 1000 years has been established for two stalagmites from Dongge Cave, Guizhou. The high resolution oxygen isotope record serves as a proxy for variations in rainfall of Asian southwest monsoon over the Yunnan-Guizhou Plateau. A close relation of the δ18O record with the A^14C record from tree rings largely reflects impact of centennial-scale solar activity on the monsoon climate changes. The conspicuous decrease in the δ18O value at AD 1720 indicates an abrupt increase in monsoon rainfall, suggesting that an atmospheric-oceanic couple over the tropical Indian Ocean plays an important role in rapid increase of the Northern Hemisphere temperature over the last century.     

Estimation on the response of glaciers in China to the global warming in the 21st century

Glaciers in China can be categorized into 3 types, i.e. the maritime (temperate) type, sub-continental (sub-polar) type and extreme Continental (polar) type, which take 22%, 46% and 32% of the total existing glacier area (59 406 km2) respectively. Researches indicate that glaciers of the three types show different response patterns to the global warming. Since the Maxima of the Little Ice Age (the 17th century), air temperature has risen at a magnitude of 1.3℃on average and the glacier area decreased corresponds to 20% of the present total glacier area in western China. it is estimated that air temperature rise in the 2030s, 2070s and 2100s will be of the order of 0.4-1.2, 1.2-2.7 and 2.1-4.0 K in western China. With these scenarios, glaciers in China will suffer from further shrinkage by 12%, 28% and 45% by the 2030s, 2070s and 2100s. The uncertainties may account for 30%-67% in 2100 in China.     

Dynamic of Grassland Biomass in Different Degenerative Stages

The dynamics of plant community and above- and belowground biomass of the different degenerative stages was researched of Kobresia hurnlis meadows of Nakchu prefecture in Tibet Autonomous Region. The results indicated that the aggravation of the degree of deterioration of alpine meadow is, the lower the vegetation coverage, percentage of excellent forage, and biodiversity are. The total aboveground biomass is highest in the lightly degraded stages while it is lowest in the extremely degraded stages. With the aggravation of degradation, the aboveground biomass of forbs increases while that of Cyperaceae decreases. We found that the belowground biomass was mostly distributed in the 0-10 cm soil depth in the alpine meadow with a ＂T＂-shape distribution feature, and with the acceleration of deterioration, the numbers of roots becomes less and less. Meanwhile, the above- and belowground biomass of the different degraded communities was significantly correlated（r= 0. 963）. There is an obvious positive correlation with the above- and belowground biomass in different degenerative stages, and their ratio increased with the aggravation of degradation.     

土壤呼吸日动态同温度的关系以及最适测定时间

一天一次的土壤呼吸测定方式可能会引起结果的偏差, 为了估计这种偏差以及确定土壤呼吸测定的最适宜时间, 2011年6?8月在河北省塞罕坝地区开展4种植被类型(森林、灌丛、草原和草甸)、13个群落类型土壤呼吸速率日动态以及土壤表层10 cm温度和气温的同步测定。结果表明: 在一天内不同时间进行测定, 可导致土壤呼吸速率偏离程度在-26%~68%; 森林在一天内不同时间进行测定, 对土壤呼吸速率的影响较小(距离日平均值的偏离<10%); 草原和草甸通常在早上7:30-10:30和下午17:00-19:00进行测定对土壤呼吸速率的影响较小(距离日平均值的偏离<10%)。土壤呼吸速率的日变化与土壤温度和气温的日变化密切相关。研究表明, 如果忽略土壤呼吸的日动态, 将会对土壤呼吸速率的估算带来显著影响。     

人工草地土壤水分动态规律的研究

根据１９８５～１９８８年四年的动态监测资料，研究分析了人工草地土壤水分的动态变化规律．结果表明：表层土壤的水分含量波动剧烈，对降水反应迅速，主要受大气降水的影响．０～４０ｃｍ土层的水分含量从生长季初期到７月下旬逐渐减少，随后开始回升，其波动情况除受大气降水的影响以外，还与植物的生长发育节律及根系吸水有密切关系．下层土壤水分含量波动幅度较小，有比较明显的滞后现象，在整个生长季中表现出“Ｕ”形曲线的变化特点．     

北方农牧交错带不同土地利用方式土壤呼吸速率探究

农牧交错带地区土地利用方式多变,人为的改变土地利用方式会影响土壤释放CO2的速率.分别对新开垦农田、多年耕种农田、退耕还草草地、多年生草地4种利用类型的土壤温度、土壤有机碳含量、土壤呼吸速率进行监测和研究,结果表明：4种土地利用类型土壤呼吸速率的日变化图像呈单峰性曲线,其中草地平均呼吸速率最大,为0.85g·m-2·d-1.4种土地利用类型土壤温度与土壤呼吸速率呈正相关关系,其中新开垦农田变化明显,K值最高,达到0.045.从整个生长季来看,4种土地利用类型平均呼吸速率表现为新开农田＞草地＞还草草地＞农田,分别为0.97g·m-2·d-1、0.85g·m-2·d-1、0.77g·m-2·d-1和0.56g·m-2·d-1.0-10cm和10-20cm土层土壤有机碳含量大小关系与土壤呼吸速率基本吻合.试验表明不论对草地进行开垦还是对农田进行退耕还草都会增加土壤CO2的释放.     

Responses of soil respiration in non-growing seasons to environmental factors in a maize agroecosystem,Northeast China

Based on continuous three-year measurements (from 2004 to 2007) of eddy covariance and related environmental factors, envi-ronmental controls on variation in soil respiration (R_s) during non-growing season were explored in a maize agroecosystem in Northeast China. Our results indicated that during non-growing seasons, daily Rs was 1.08–4.08 g CO2 m^–2 d^–1, and the lowest occurred in late November. The average R_s of non-growing season was 456.06 ± 20.01 g CO2 m^–2, accounting for 11% of the gross primary production (GPP) of the growing season. Additionally, at monthly scale, the lowest value of R_s appeared in January or February. From the beginning to the end of non-growing season, daily R_s tended to decrease first, and then increase to the highest. There was a significant quadratic curve relationship between Rs and soil temperature at 10 cm depth when soil temperature was more than 0°C (P<0.001), with the explaining ratio of 38%–70%. When soil water content was more than 0.1 m³ m^–3, soil moisture at 10 cm depth was significantly parabolically correlated with R_s (P<0.001), explaining the rate of 18%–60%. Based on all the data of soil temperature of more than 0°C, a better model for R_s was established by coupling soil temperature and moisture, which could explain the rate of up to 53%–79%. Meanwhile, the standard error of regression estimation between the values of prediction and observation for R_s could reach 2.7%–11.8%. R_s in non-growing season can account for 22.4% of R_s in growing season, indicating that it plays a critical role in assessing the carbon budget in maize agroecosystem, Northeast China.