库布齐沙漠两个不同土地利用类型生态系统呼吸比较研究

陆地生态系统的呼吸作用是全球碳循环的一个主要通量和响应全球变化的一个潜在的重要正反馈机制。研究陆地生态系统的呼吸作用特征及其对生物环境因子的响应具有重要意义。本实验利用涡度相关技术对内蒙古库布齐沙漠两个不同土地利用类型的生态系统（人工种植杨树林和天然的油蒿灌丛）2006年生长季（4-10月）的生态系统呼吸特征进行比较研究，并分析了控制生态系统呼吸（Re）的生物与环境因子。结果表明：在这两种生态系统中Re存在着显著的日变化和季节变化，两个生态系统之间Re也存在着显著差异。Re日平均最大值分别2.0 mol CO2 m-2 s-1和1.7 mol CO2 m-2 s-1，都显著低于其他类似生态系统。杨树林和油蒿灌丛的生态系统Re与空气温度都表现出明显的指数相关关系，温度敏感指数Q10分别为1.11和1.12。两个生态系统的Re都与土壤水分含量呈显著的线性正相关关系，表明库布齐沙漠的生态系统的Re受到了土壤水分条件的限制。杨树林和油蒿灌丛生态系统呼吸Re都与叶面积指数的有线性回归关系，说明叶面积指数对生态系统呼吸有很好的指示作用。 本文还选择了两个生态系统内四种常见的土壤覆盖类型（分别是：杨树林生态系统的沙地SL和低洼地BL;油蒿灌丛生态系统的灌丛间BS和灌丛内WS），利用动态密闭气室测定了5-9月土壤呼吸的季节动态以及植株尺度的小尺度空间异质性。结果表明：1）不同土壤覆盖类型的土壤呼吸存在着很大的差异，其中低洼地BL和沙地SL分别有着最大和最小值，灌丛内WS的土壤呼吸要明显高于灌丛外BS。根生物量是导致它们之间差异的主要原因。2）土壤呼吸与土壤含水量之间的线性关系表明，土壤水分是两个生态系统土壤呼吸的限制因子。3）两个生态系统土壤呼吸存在着明显的小尺度差异，在靠近植株（0.5m内）地方的土壤呼吸的值明显高于距植株0.5m外的值，而0.5m外的土壤呼吸没有显著差异。小尺度土壤呼吸与根生物量之间明显的线性关系，说明根生物量是导致小尺度土壤呼吸差异的原因。本实验对沙漠生态系统的土壤呼吸和生态系统呼吸特征及其影响因子的研究，对准确的估计这一地区的碳收支有很大的帮助，为深入的理解干旱半干旱地区的生态系统碳循环提供了有价值的信息。

长白山典型森林生态系统土壤碳通量研究

森林生态系统是陆地最大的碳储存库，森林土壤呼吸是陆地生态系统土壤呼吸的重要组成部分，其动态变化将刘全球碳平衡产生深远的影响。精确测定土壤呼吸及其各组分的贡献，是目前全球变化研究中最基础和最迫切需要解决的问题。本文对长白山典型森林生态系统土壤碳通量及其过程机理进行了研究，结果表明：（1）阔叶红松林、红松云冷衫林、岳桦云冷杉林和岳桦林有不同的凋落节律；随海拔高度的上升，年凋落物量逐渐减少，分别为4.90、4.51、3.08和2.65thm-2；凋落物分解残留率与时间均呈指数关系，不同类型森林凋落物年分解常数的变化范围是25-47％之间。（2）阔叶红松林土壤总呼吸和断根土壤呼吸速率都存在明显的昼夜变化，为单峰型曲线，与土壤温度的昼夜变化趋势一致；不同森林类型土壤总呼吸和断根土壤呼吸的季节变化都比较明显，阔叶红松林、红松云冷杉林和岳桦云冷杉林变化趋势基本相似，都呈双峰型，岳桦林呈单峰型；土壤呼吸与土壤温度、大气温度之间都呈极显著（P＜0.01）指数相关关系，且与土壤温度的相关性要好于与大气温度的相关性；长白山四种类型森林土壤和根系呼吸的Q10值变化范围是1.8-2.9，根系呼吸的Q10值均大于土壤总呼吸和断根土壤呼吸的Q10值；土壤含水量对呼吸速率影响较为复杂，与土壤呼吸之间没有明显的相关关系；根系对土壤总呼吸贡献的季节变化与根系呼吸的季节变化相似，生长季内测定的阔叶红松林、红松云冷杉林、岳桦云冷杉林和岳桦杉林根系呼吸对土壤总呼吸贡献平均值分别为43.6％、44.1％、45.5％和44.4％。（3）长白山典型森林生态系统土壤碳的年释放量有随海拔高度上升而减小的趋势，且阔价卜林大于针叶林。阔叶红松林、红松云冷杉林、岳桦云冷杉林和岳桦林土壤碳的年释放量分别为7392.43、7181.83、6507.29和6841.09kghm-2a-1；根系的年碳释放量分别为3332.93、2965.68、2708.84和3015.48kghm-2a-1。

Application of static and dynamic enclosures for determining dimethyl sulfide and carbonyl sulfide exchange in Sphagnum peatlands: Implications for the magnitude and direction of flux

A static enclosure method was applied to determine the exchange of dimethyl sulfide (DMS) and carbonyl sulfide (OCS) between the surface of Sphagnum peatlands and the atmosphere. Measurements were performed concurrently with dynamic (flow through) enclosure measurements with sulfur-free air used as sweep gas. This latter technique has been used to acquire the majority of available data on the exchange of S gases between the atmosphere and the continental surfaces and has been criticized because it is thought to overestimate the true flux of gases by disrupting natural S gas gradients. DMS emission rates determined by both methods were not statistically different between 4 and >400 nmol m−2 h−1, indicating that previous data on emissions of at least DMS are probably valid. However, the increase in DMS in static enclosures was not linear, indicating the potential for a negative feedback of enclosure DMS concentrations on efflux. The dynamic enclosure method measured positive OCS flux rates (emission) at all sites, while data using static enclosures indicated that OCS was consumed from the atmosphere at these same sites at rates of 3.7 to 55 nmol m−2 h−1. Measurements using both enclosure techniques at a site devoid of vegetation showed that peat was a source of both DMS and OCS. However, the rate of OCS efflux from decomposing peat was more than counterbalanced by OCS consumption by vegetation, including Sphagnum mosses, and net OCS uptake occurred at all sites. We propose that all wetlands are net sinks for OCS.

Effects of temperature, glucose and inorganic nitrogen inputs on carbon mineralization in a Tibetan alpine meadow soil

High levels of available nitrogen (N) and carbon (C) have the potential to increase soil N and C mineralization We hypothesized that with an external labile C or N supply alpine meadow soil will have a significantly higher C mineralization potential and that temperature sensitivity of C mineralization will increase To test the hypotheses an incubation experiment was conducted with two doses of N or C supply at temperature of 5 15 and 25 C Results showed external N supply had no significant effect on CO2 emission However external C supply increased CO2 emission Temperature coefficient (Q(10)) ranged from 113 to 1 29 Significantly higher values were measured with C than with N addition and control treatment Temperature dependence of C mineralization was well-represented by exponential functions Under the control CO2 efflux rate was 425 g CO2-Cm-2 year(-1) comparable to the in situ measurement of 422 g CO2-Cm-2 year(-1) We demonstrated if N is disregarded microbial decomposition is primarily limited by lack of labile C It is predicted that labile C supply would further increase CO2 efflux from the alpine meadow soil (C) 2010 Elsevier Masson SAS All rights reserved

Effects of nitrogen fertilization on soil respiration in temperate grassland in Inner Mongolia, China

Nitrogen addition to soil can play a vital role in influencing the losses of soil carbon by respiration in N-deficient terrestrial ecosystems. The aim of this study was to clarify the effects of different levels of nitrogen fertilization (HN, 200 kg N ha(-1) year(-1); MN, 100 kg N ha(-1) year(-1); LN, 50 kg N ha(-1) year(-1)) on soil respiration compared with non-fertilization (CK, 0 kg N ha(-1) year(-1)), from July 2007 to September 2008, in temperate grassland in Inner Mongolia, China. Results showed that N fertilization did not change the seasonal patterns of soil respiration, which were mainly controlled by soil heat-water conditions. However, N fertilization could change the relationships between soil respiration and soil temperature, and water regimes. Soil respiration dependence on soil moisture was increased by N fertilization, and the soil temperature sensitivity was similar in the treatments of HN, LN, and CK treatments (Q (10) varied within 1.70-1.74) but was slightly reduced in MN treatment (Q (10) = 1.63). N fertilization increased soil CO2 emission in the order MN > HN > LN compared with the CK treatment. The positive effects reached a significant level for HN and MN (P < 0.05) and reached a marginally significant level for LN (P = 0.059 < 0.1) based on the cumulative soil respiration during the 2007 growing season after fertilization (July-September 2007). Furthermore, the differences between the three fertilization treatments and CK reached the very significant level of 0.01 on the basis of the data during the first entire year after fertilization (July 2007-June 2008). The annual total soil respiration was 53, 57, and 24% higher than in the CK plots (465 g m(-2) year(-1)). However, the positive effects did not reach the significant level for any treatment in the 2008 growing season after the second year fertilization (July-September 2008, P > 0.05). The pairwise differences between the three N-level treatments were not significant in either year (P > 0.05).

Nitrogen isotopic fractionation during a simulated diatom spring bloom: importance of N-starvation in controlling fractionation

N isotope fractionation (epsilon) was first determined during ambient NO3- depletion in a simulated diatom spring bloom. After 48 h of N-starvation, NH4+ was resupplied to the diatoms in small pulses to simulate grazer-produced N and then epsilon was determined. Large variations in epsilon values were observed: from 2.0-3.6 to 14-0 parts per thousand during NO3- and NH4+ uptake, respectively. This is the first study reporting an epsilon value as low as 0 to 2 parts per thousand for NH4+ uptake and we suggest that greater N demand after N-starvation may have drastically reduced NH3 efflux out of the cells. Thus the N status of the phytoplankton and not the ambient NH4+ concentration may be the important factor controlling epsilon, because, when N-starvation increased, epsilon values for NH4+ uptake decreased within 30 h. This study may thus have important implications for interpreting the delta(15)N of particulate N in nutrient-depleted regimes in temperate coastal oceans.

Soil organic carbon storage and soil CO2 flux in the alpine meadow ecosystem

High-resolution sampling, measurements of organic carbon contents and C-14 signatures of selected four soil profiles in the Haibei Station situated on the northeast Tibetan Plateau, and application of C-14 tracing technology were conducted in an attempt to investigate the turnover times of soil organic carbon and the soil-CO2 flux in the alpine meadow ecosystem. The results show that the organic carbon stored in the soils varies from 22.12x10(4) kg C hm(-2) to 30.75x10(4) kg C hm(-2) in the alpine meadow ecosystems, with an average of 26.86x10(4) kg C hm(-2). Turnover times of organic carbon pools increase with depth from 45 a to 73 a in the surface soil horizon to hundreds of years or millennia or even longer at the deep soil horizons in the alpine meadow ecosystems. The soil-CO2 flux ranges from 103.24 g C m(-2) a(-1) to 254.93 gC m(-2) a(-1), with an average of 191.23 g C m(-2) a(-1). The CO2 efflux produced from microbial decomposition of organic matter varies from 73.3 g C m(-2) a(-1) to 181 g C m(-2) a(-1). More than 30% of total soil organic carbon resides in the active carbon pool and 72.8%. 81.23% of total CO2 emitted from organic matter decomposition results from the topsoil horizon (from 0 cm to 10 cm) for the Kobresia meadow. Responding to global warming, the storage, volume of flow and fate of the soil organic carbon in the alpine meadow ecosystem of the Tibetan Plateau will be changed, which needs further research.

Strong temperature dependence and no moss photosynthesis in winter CO2 flux for a Kobresia meadow on the Qinghai-Tibetan plateau

We examined the CO2 exchange of a Kobresia meadow ecosystem on the Qinghai-Tibetan plateau using a chamber system. CO2 efflux from the ecosystem was strongly dependence on soil surface temperature. The COZ efflux-temperature relationship was identical under both light and dark conditions, indicating that no photosynthesis could be detected under light conditions during the measurement period. The temperature sensitivity (Q(10)) of the COZ efflux showed a marked transition around -1.0 degrees C; Q(10) was 2.14 at soil surface temperatures above and equal to -1.0 degrees C but was 15.3 at temperatures below -1.0 degrees C. Our findings suggest that soil surface temperature was the major factor controlling winter COZ flux for the alpine meadow ecosystem and that freeze-thaw cycles at the soil surface layer play an important role in the temperature dependence of winter CO2 flux. (c) 2005 Elsevier Ltd. All rights reserved.

Characterizing CO2 fluxes for growing and non-growing seasons in a shrub ecosystem on the Qinghai-Tibet Plateau

To assess carbon budget for shrub ecosystems on the Qinghai-Tibet Plateau, CO2 flux was measured with an open-path eddy covariance system for an alpine shrub ecosystem during growing and non-growing seasons. CO2 flux dynamics was distinct between the two seasons. During the growing season from May to September, the ecosystem exhibited net CO2 uptake from 08:00 to 19:00 (Beijing Standard Time), but net CO2 emission from 19:00 to 08:00. Maximum CO2 uptake appeared around 12:00 with values of 0.71, 1,19, 1.46 and 0.67 g CO2 m(-2) h(-1) for June, July, August and September, respectively. Diurnal fluctuation Of CO2 flux showed higher correlation with photosynthetic photon flux density than temperature. The maximum net CO2 influx occurred in August with a value of 247 g CO2 m(-2). The total CO2 uptake by the ecosystem was up to 583 g CO2 m(-2) for the growing season. During the non-growing season from January to April and from October to December, CO2 flux showed small fluctuation with the largest net CO2 efflux of 0.30 g CO2 m(-2) h(-1) in April. The diurnal CO2 flux was close to zero during most time of the day, but showed a small net CO2 eff lux from 11:00 to 18:00. Diurnal CO2 flux, is significantly correlated to diurnal temperature in the non-growing season. The maximum monthly net CO2 eff lux appeared in April, with a value of 105 g CO2 m(-2). The total net CO2 eff lux for the whole non-growing season was 356 g CO2 m(-2).

Grazing intensity alters soil respiration in an alpine meadow on the Tibetan plateau

Grazing intensity may alter the soil respiration rate in grassland ecosystems. The objectives of our study were to (1) determine the influence of grazing intensity on temporal variations in soil respiration of an alpine meadow on the northeastern Tibetan Plateau; and (2) characterise, the temperature response of soil respiration under different grazing intensities. Diurnal and seasonal soil respiration rates were measured for two alpine meadow sites with different grazing intensities. The light grazing (LG) meadow site had a grazing intensity of 2.55 sheep ha(-1), while the grazing intensity of the heavy grazing (HG) meadow site, 5.35 sheep ha(-1), was approximately twice that of the LG site. Soil respiration measurements - showed that CO2 efflux was almost twice as great at the LG site as at the HG site during the growing season, but the diurnal and seasonal patterns of soil respiration rate were similar for the two sites. Both exhibited the highest annual soil respiration rate in mid-August and the lowest in January. Soil respiration rate was highly dependent on soil temperature. The Q(10) value for annual soil respiration was lower for the HG site (2.75) than for the LG site (3.22). Estimates of net ecosystem CO2 exchange from monthly measurements of biomass and soil respiration revealed that during the period from May 1998 to April 1999, the LG site released 2040 g CO2 m(-2) y(-1) to the atmosphere, which was about one third more than the 1530g CO2 m(-2) y(-1) released at the HG site. The results suggest that (1) grazing intensity alters not only soil respiration rate, but also the temperature dependence of soil CO2 efflux; and (2) soil temperature is the major environmental factor controlling the temporal variation of soil respiration rate in the alpine meadow ecosystem. (C) 2003 Elsevier Ltd. All fights reserved.