温度对克氏针茅草原生态系统生长季碳通量的影响

草地生态系统碳通量的驱动机制研究是碳循环研究的重要方面。利用涡度相关技术观测了克氏针茅草原生态系统的净生态系统碳交换（NEE）、生态系统初级生产力（GEP）、生态系统呼吸（Reco）的变化,探讨了2010年生长季内温度对该系统NEE、GEP和Reco的影响。结果表明,2010年生长季内,克氏针茅草原日尺度上NEE和GEP只出现了1个明显的吸收峰,Reco则呈现倒＂U＂型变化规律。克氏针茅草原空气温度与NEE、GEP和Reco呈极显著相关关系,气温日较差对该系统碳通量的影响程度较小;土壤温度与NEE、GEP和Reco之间也呈极显著相关关系,土壤温度的增加会同时提高克氏针茅草原生态系统的固碳能力、初级生产力及呼吸作用。空气温度和土壤温度都是影响克氏针茅草原生态系统碳收支的重要驱动因子。     

土壤温度和水分对克氏针茅草原生态系统碳通量的影响初探

草地和大气间碳通量的观测有助于理解草原生态系统的碳循环及其控制机理。利用涡度相关技术观测了克氏针茅草原生态系统与大气之间的净生态系统碳交换（NEE）、生态系统初级生产力（GEP）、生态系统呼吸（Rec）o的变化,探讨了2008年生长季内土壤温度和水分对克氏针茅草原生态系统NEE、GEP和Reco的影响。结果表明,2008年生长季内,克氏针茅草原日尺度上NEE和GEP都出现了3个峰,二者之间有极显著的相关性,Reco则呈现倒＂U＂型变化规律。克氏针茅草原土壤温度与NEE、GEP呈二次曲线的关系,而与Reco呈指数关系,土壤水分的增加会提高克氏针茅草原生态系统的固碳能力、初级生产力及呼吸作用。土壤温度和水分是影响克氏针茅草原生态系统碳收支的重要因子。     

黑河中游植被生长季土壤呼吸和净生态系统碳交换量的季节变化

基于涡度相关法和静态箱―气相色谱法的净生态系统碳交换量(net ecosystem exchange,NEE)与土壤呼吸(soil respiration,Rs)速率观测数据,探讨了黑河中游不同土地利用方式下净生态系统碳交换量和土壤呼吸的季节变化,以及土壤呼吸对净生态系统碳交换量的贡献率。结果表明,净生态系统碳交换量和土壤呼吸速率在时间尺度上呈现多峰变化趋势,7月底至8月初达到峰值;在空间尺度上受植被覆盖度的影响,植被稀疏的荒漠、戈壁和沙漠呈现较为一致的变化趋势,土壤呼吸对净生态系统碳交换量的贡献率达20%~68%;而植被密集的玉米地、果园和湿地则呈现较高的季节变异性,土壤呼吸对净生态系统碳交换量的贡献率为10%~21%。土壤呼吸的微小变动可能引起净生态系统碳交换量明显变化。     

不同放牧制度下短花针茅荒漠草原碳平衡研究

采用围栏封育、划区轮牧、禁牧休牧等措施进行退化草原修复和保护,是关系能否有效合理保护和利用草原、应对气候变化的一个重要命题.本研究以内蒙古短花针茅荒漠草原为对象,测定连续10年(1999～2009年)进行围栏禁牧、划区轮牧和自由放牧等不同放牧作用下的长久样区的草原碳输入、输出及平衡特征,旨在从碳平衡的角度为确定荒漠草原合理的放牧管理方式提供依据.采用野外调查法测定生物量季节动态,密闭气室法测定土壤呼吸动态.结果表明:(1)相较于自由放牧,划区轮牧能保持较高的凋落物量、家畜采食量以及地下生物量,在恢复地上植被方面无明显差别,禁牧保持较高的地上生物量、凋落物量及地下生物量;(2)土壤呼吸随着放牧的进行和季节水热条件的变化,呈现不同的变化趋势,自由放牧在干旱季节产生较小的土壤呼吸;(3)生长季内划区轮牧、自由放牧和围栏禁牧下的荒漠草原净生态系统生产力分别为413.78、401.45、416.80 g/(m2·a)C.短花针茅荒漠草原生态系统碳收支表现为碳汇,不同放牧制度对碳收支影响较小,相对而言,划区轮牧较自由放牧有微弱的碳积累优势.     

克氏针茅草原生态系统生长季碳通量变化特征

植被和大气之间CO2通量的观测有助于理解陆地生态系统的碳循环及其控制机理。以中国北方典型草原克氏针茅草原为研究对象,以涡度相关法为主要技术手段,探讨了2008年生长季内克氏针茅草原净生态系统碳交换（NEE）的变化特征。结果表明,克氏针茅草原生态系统CO2通量的日变化进程可以依据高峰出现的时间分为两种,一种具有一个吸收高峰,出现在11：00左右,另一种则具有两个吸收高峰,在正午前后出现碳释放现象。2008年克氏针茅草原生态系统最大的CO2吸收速率为-0．4mg·m^-2·s^-1。克氏针茅草原在4月和10月的NEE昼夜变化比较平缓,在5—9月日间CO2吸收量和夜间CO2排放量都开始增大,出现了明显的CO2日吸收峰值,但各月的日动态格局差异较大。2008年生长季中7—9月白天碳吸收活动最强,6—9月夜间CO2释放量较大。克氏针茅草原碳通量日累积量在2008年出现了3个明显的碳吸收峰;NEE的日最大累积吸收量和最大累积释放量分别为-2．38和1．47gC·m^-2·d^-1,并且出现在植被生长最旺盛的7、8月份。研究表明,温度和水分是影响克氏针茅草原生态系统碳通量变化的重要因子。     

不同封育条件下荒漠草原生态系统健康评价

为定量评价围封对草原生态系统健康的影响,以宁夏盐池柳杨堡封育区为研究区域,采用生态系统健康指数对该区不同封育条件下荒漠草原进行评价分析.结果表明：1）从封育时间上看,封育时间越长,生态系统健康水平并非越好.2）从放牧压力上看,早期封育期间,放牧不利于草原生态系统健康恢复;封育达到一定年限后,适度放牧有利于草原生态系统健康恢复.因此,在荒漠草原植被恢复研究中,有必要调整封育年限、适度放牧,不仅能获得一定的经济效益,还能促进荒漠草原生态系统健康恢复.     

放牧对荒漠草原植物生物量及土壤养分的影响

以宁夏荒漠草原为研究对象,探讨放牧对荒漠草原植物多样性、 生物量及土壤养分特征的影响。结果表明, 放牧对荒漠草原植物群落多样性、 均匀度和丰富度影响显著。植物群落多样性和均匀度随着放牧强度的增加均呈先增加后降低的趋势,在轻度放牧达到最大值。同围封禁牧相比,重度、 中度和轻度放牧草地的植物地上和地下部生物量显著降低,分别降低了43.8%、 42.0%、 15.4% 和 27.7%、16.2%、11.9%。土壤有机碳随着放牧强度的增加而降低,而土壤全氮含量随着放牧强度的增加呈先增加后降低的趋势。围封禁牧草地土壤有机碳比重度放牧增加了18.1%,而土壤全磷、 速效磷和全钾含量分别降低了 21.1%、 51.9% 和 11.0%。土壤有机碳含量对植物群落地上和地下部生物量的影响大于土壤全氮、 全磷、 全钾、 速效磷和速效钾。放牧干扰下荒漠草原土壤环境及其养分含量,能在一定程度上反映植物群落多样性和生物量的变化。     

放牧干扰对荒漠草原土壤和植被的影响

放牧是草原生态系统最主要的干扰因子之一,影响着草地生态系统植被和土壤的生态进程。以宁夏盐池县荒漠草原区为研究对象,根据地表植被以及地表羊粪的积累量设置6个放牧干扰梯度,分别为CK、T1、T2、T3、T4、T5,运用方差分析、回归分析研究了植被和土壤对不同放牧干扰的响应。结果表明：地上生物量、枯落物、植被覆盖度随着放牧干扰强度的加大呈现先增加后减小的趋势,支持了＂中度干扰理论＂;随着放牧干扰强度的增大,土壤水分随之增加,土壤容重则无显著变化;土壤有机碳与全氮随放牧干扰的变化趋势大致相同,二者有很强的曲线线性关系,C/N的变化趋势与有机碳的变化规律稍有不同,C/N和地上生物量都与地表羊粪量有显著的曲线线性关系,表明地表羊粪量对土壤碳氮分布及草地生产力有着很强的影响,体现了有机碳与全氮含量变化的复杂性及各因子之间的互作效应。     

淮河流域典型农田生态系统碳通量变化特征

为了准确评价农田生态系统在全球碳平衡中的作用,利用涡度相关技术对安徽省寿县冬小麦／水稻生态系统进行了碳通量的监测,并在数据校正、剔除和插补的基础上,研究生长季农田净生态系统碳交换（NEE）的变化特征。结果显示,2008年寿县农田生态系统CO2通量的日变化进程为单峰型,冬小麦和水稻最大的CO2吸收速率分别为2．45和2．48mg·m^-2·s^-1。从物候期的角度来看,冬小麦在抽穗期碳通量值最小,乳熟期最大;水稻拔节时期碳通量值最小,即固碳能力最强。冬小麦,水稻生态系统不同月份碳通量月均日变化也呈U型曲线,作物生命活动越旺盛,NEE峰值越高,夜间CO2排放则在8月份达到最高值。2008年冬小麦和水稻月平均最大日CO2吸收峰分别出现在4月和8月,分别为1．30和1．07mg·m^-2．s^-1。冬小麦生态系统NEE的日最大累积吸收量出现在4月16日．可达11．76gC·m^-2·d^-1,水稻生态系统的出现在8月3日,为10．40gC·m^-2·d^-1。冬小麦从拔节到成熟时间段内的固碳能力为326．87gC·m^-1,水稻从返青到成熟时间段内的固碳能力也达到了300．05gC·m^-2。     

生草免耕桃园生态系统的碳交换动态变化特征

植物固碳是减缓全球气候变暖的有效途径。然而,农田尺度果园固碳能力目前还不清楚。该文采用涡度相关技术,研究粗砂土立地条件下12a生树龄生草免耕桃园生态系统碳交换和能量平衡各分量的动态变化。结果表明,在盛花期存在明显的固碳能力,日峰值为-0.33mg/(m2·s)(以CO2计)。在旺盛生长期波文比值在0.3以下,日净固碳值最高为-25.1g/(m2·d)(以CO2计)。落叶期存在明显的高CO2排放,日峰值为0.60mg/(m2·s)(以CO2计)。监测期内桃园生态系统日平均波文比值和净固碳量分别为(1.22±1.56)和(-2.90±6.63)g/(m2·d)(以CO2计),年净生态系统碳交换量(net ecosystem exchange,NEE)为-1052g/(m2·a)(以CO2计)。以上结果揭示粗砂土12a生树龄生草免耕桃园生态系统有较强的固碳能力。该文为评价果园碳汇功能提供基础数据。     

Increasing net CO2 uptake by a Danish beech forest during the period from 1996 to 2009

The exchange of CO₂ between the atmosphere and a beech forest near Sorø, Denmark, was measured continuously over 14 years (1996-2009). The simultaneous measurement of many parameters that influence CO₂ uptake makes it possible to relate the CO₂ exchange to recent changes in e.g. temperature and atmospheric CO₂ concentration. The net CO₂ exchange (NEE) was measured by the eddy covariance method. Ecosystem respiration (RE) was estimated from nighttime values and gross ecosystem exchange (GEE) was calculated as the sum of RE and NEE. Over the years the beech forest acted as a sink of on average of 157 g C m⁻² yr⁻¹. In one of the years only, the forest acted as a small source. During 1996-2009 a significant increase in annual NEE was observed. A significant increase in GEE and a smaller and not significant increase in RE was also found. Thus the increased NEE was mainly attributed to an increase in GEE. The overall trend in NEE was significant with an average increase in uptake of 23 g C m⁻² yr⁻². The carbon uptake period (i.e. the period with daily net CO₂ gain) increased by 1.9 days per year, whereas there was a non significant tendency of increase of the leafed period. This means that the leaves stayed active longer. The analysis of CO₂ uptake by the forest by use of light response curves, revealed that the maximum rate of photosynthetic assimilation increased by 15% during the 14-year period. We conclude that the increase in the overall CO₂ uptake of the forest is due to a combination of increased growing season length and increased uptake capacity. We also conclude that long time series of flux measurements are necessary to reveal trends in the data because of the substantial inter-annual variation in the flux.     

Response of the carbon cycle in sub-arctic black spruce forests to climate change: Reduction of a carbon sink related to the sensitivity of heterotrophic respiration

Assessment of the response of the carbon cycle to climate change is important for predicting future climate, especially in northern high latitudes, where the warming may be highly pronounced. In this paper, three years of data measured by the eddy covariance method were used to verify the carbon dynamics of a black spruce forest in interior Alaska with the BIOME-BGC model. The model was modified and calibrated to the cold regions. The calibrated model simulation satisfactorily performed reproduction of the observed net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (RE). The daily output of the model also correlated with field-based estimates of NEE (42%), GPP (89%), and RE (89%). The model simulation showed that the heterotrophic respiration occupied a substantial portion of total carbon exchange, and that inter-annual variation of the heterotrophic respiration determined the sink/source strength of carbon. According to our simulation, the black spruce forest in interior Alaska was a net carbon sink between 1949 and 2005, and the trend of the projected sink strength was not obvious in the recent climate warming. The model analysis suggested that the change in the seasonal weather pattern strongly affected the carbon balance. A potentially increased carbon sink due to future warming climate and elevated CO₂ will be at least partly offset by a concurrent increase of VPD, since the response of the stomatal conductance to increased VPD could increase the soil moisture, and thus stimulate heterotrophic respiration, rather than net primary productivity. The results of this study should be useful to forecast the response of the carbon cycle to warming in black spruce forests of interior Alaska.     

在纤毛狼尾草为主的草原上植物叶片以及生态系统的气体交换对夏季降水的响应特征

Sporadic rain events that occur during summer play an important role in the initiation of biological activity of semi-arid grasslands.To understand how ecosystem processes of a buffel grass(Cenchrus ciliaris L.)-dominated grassland respond to summer rain events,an LI 6 400 gas exchange system was used to measure the leaf gas exchange and plant canopy chambers were used to measure net ecosystem CO2exchange(NEE) and ecosystem respiration(Reco), which were made sequentially during periods before rain(dry) and after rain(wet). Gross ecosystem photosynthesis(GEP) was estimated from NEE and Reco fluxes, and light use efficiency parameters were estimated using a rectangular hyperbola model. Prior to the monsoon rain, grassland biomass was non-green and dry exhibiting positive NEE(carbon source) and low GEP values during which the soil water became increasingly scarce. An initial rain pulse(60 mm) increased the NEE from pre-monsoon levels to negative NEE(carbon gain) with markedly higher GEP and increased green biomass. The leaf photosynthesis and leaf stomatal conductance were also improved substantially. The maximum net CO2uptake(i.e.,negative NEE) was sustained in the subsequent period due to multiple rain events. As a result, the grassland acted as a net carbon sink for 20 d after first rain. With cessation of rain(drying cycle), net CO2 uptake was reduced to lower values. High sensitivity of this grassland to rain suggests that any decrease in precipitation in summer may likely affect the carbon sequestration of the semiarid ecosystem.     

Effects of cloudiness change on net ecosystem exchange, light use efficiency, and water use efficiency in typical ecosystems of China

As a weather element, clouds can affect CO₂ exchange between terrestrial ecosystems and the atmosphere by altering environmental conditions, such as solar radiation received on the ground surface, temperature, and moisture. Based on the flux data measured at five typical ecosystems of China during mid-growing season (June-August) from 2003 to 2006, we analyzed the responses of net ecosystem exchange of carbon dioxide (NEE), light use efficiency (LUE, defined as Gross ecosystem photosynthesis (GEP)/Photosynthetically active radiation (PAR)), and water use efficiency (WUE, defined as GEP/Evapotranspiration (ET)) to the changes in cloudiness. The five ecological sites included Changbaishan temperate mixed forest (CBS), Dinghushan subtropical evergreen broad-leaved forest (DHS), Xishuangbanna tropical rainforest (XSBN), Inner Mongolia semi-arid Leymus chinensis steppe (NMG), and Haibei alpine frigid Potentilla fruticosa shrub (HB). Our analyses show that cloudy sky conditions with cloud index (k_t) values between 0.4 and 0.6 increased NEE, LUE, and WUE of the ecosystems at CBS, DHS, NMG and HB from June to August. The LUE of tropical rainforest at XSBN was higher under cloudy than under clear sky conditions, but NEE and WUE did not decrease significantly under clear sky conditions from June to August. The increase in GEP with increasing diffuse radiation received by ecosystems under cloudy skies was the main reason that caused the increases in LUE and net carbon uptake in forest ecosystem at CBS, DHS, and alpine shrub ecosystem at HB, compared with clear skies. Moreover, for the ecosystem at CBS, DHS, and HB, when sky condition became from clear to cloudy, GEP increased and ET decreased with decreasing VPD, leading to the increase in WUE and NEE under cloudy sky conditions. The decrease in R_e with decreasing temperature and increase in GEP with decreasing VPD under cloudy skies led to the increase in LUE, WUE, and net carbon uptake of semi-arid steppe at NMG, compared to clear skies. These different responses among the five ecosystems are attributable to the differences in canopy characteristics and water conditions. From June to August, the peaks of the k_t frequency distribution in temperate ecosystems (e.g., CBS, NMG, and HB) were larger than 0.5, but they were smaller than 0.4 in subtropical/tropical forest ecosystems (e.g., DHS and XSBN). These results suggest that the pattern of cloudiness during the years from 2003 to 2006 in the five ecosystems was not the best condition for their net carbon uptake. This study highlights the importance of cloudiness factor in the prediction of net carbon absorption in the Asia monsoon region under climate change.     

Vegetation characteristics and soil properties in grazing exclusion areas of the Inner Mongolia desert steppe

In arid and semi-arid desert steppe areas, grazing exclusion with fencing is widely regarded as an effective strategy for restoring degraded vegetation and enhancing the quality of degraded soil. In this study, we hypothesized that grazing exclusion caused by fencing enhances both vegetation and soil properties, and that the longer an area is fenced, the more considerable the improvement. We conducted an observational study wherein random sampling was utilized to select 9 plots fenced for ten or more years, 25 plots fenced for four to nine years, 25 plots fenced for one to three years and 29 free-grazing plots within an area of approximately 63,000 km² of Inner Mongolia desert steppe. A one-way ANOVA revealed no significant differences in the characteristics of grassland vegetation or soil properties between grasslands fenced for one to three years and free-grazing grassland. After 4 years of fencing, noticeable increases in above-ground biomass, litter content, Simpson index, soil organic carbon, and available nitrogen were observed. Significant positive differences in vegetation coverage, height, species richness, soil available phosphorus, and available potassium were associated with plots with a minimum of 10 years of fencing. The soil layer with the greatest difference in the fenced-in areas for soil organic carbon was at 0–25 cm. For available nitrogen and available phosphorus, fencing produced the most significant differences in the 0–20 cm soil layer, while for available potassium, fencing produced the most significant differences in the 0–30 cm soil layer. However, the fencing did not indicate any statistically significant differences in terms of clay, silt, and sand content in any soil layer. The data support our hypothesis that grazing exclusion improves both vegetation and soil properties, and that longer periods of grazing exclusion result in greater degrees of improvement. This research offers technical guidance for the reasonable choice of fencing time across a vast area of the Inner Mongolian desert steppe.     

重新被“激活”的土壤无机碳研究

荒漠区植被稀疏、土壤有机碳含量低,在全球碳循环研究中,一直被忽略。但2006年前后,若干研究显示干旱荒漠区具有潜在的碳汇功能,一直被认为是死碳的土壤无机碳开始受到关注,长期被忽视的干旱荒漠区无机碳碳循环重新进入人们的视野。后续的研究显示,土壤中的溶解性无机碳并非来自土壤本身的碳酸盐,而是来自土壤空气或大气,是现代碳循环的一个重要环节。土壤温度的变化改变了CO2在土壤溶液中的溶解度,催生出一个日出夜进的"无机呼吸"过程。这个"无机呼吸"过程在广义干旱、盐碱土区普遍存在;在土壤生物过程微弱的荒漠区,可以主导地-气界面的碳交换。盐碱土改良过程中溶解性无机碳的淋洗,更可以直接形成储存于地下咸水层的无机碳汇。总之,在生命过程微弱的干旱荒漠区,无机碳过程可以主导地-气界面碳交换与碳汇的形成:尽管这里起关键作用的不是土壤碳酸盐,而是土壤中的溶解性无机碳。     

北方风沙区放牧和封育对水土保持植被效益的影响分析

为了从宏观层面科学认识北方风沙区放牧和封育对草地水土保持生态效益的影响,搜集并筛选了大量文献,从中采集相关数据,采用荟萃分析方法,研究了典型草原和荒漠草原放牧强度、放牧年限和封育年限对植被地上生物量和植被盖度的影响。结果表明:(1)无论是荒漠草原还是典型草原,随着放牧强度增加,植被相对地上生物量和植被盖度均明显下降;(2)放牧年限对植被地上生物量的影响极显著,长期的放牧会使草原植被地上生物量显著降低;(3)随着封育年限的增加,荒漠草原与典型草原的植被地上生物量和植被盖度都明显增加。综上,放牧和封育都是影响北方风沙区植被生态效益的重要因素,应重点关注其对植被水土保持效益的影响,以实现对该区域的水土保持生态效益进行综合分析,为该区做好水土保持工作提供技术支撑。     

Carbon stocks and carbon fluxes from a 10‐year prescribed burning chronosequence on a UK blanket peat

Prescribed burning is a common land management technique in many areas of the UK uplands. However, concern has been expressed at the impact of this management practice on carbon stocks and fluxes found in the carbon‐rich peat soils that underlie many of these areas. This study measured both carbon stocks and carbon fluxes from a chronosequence of prescribed burn sites in northern England. A range of carbon parameters were measured including above ground biomass and carbon stocks; net ecosystem exchange (NEE), net ecosystem respiration (R_eco) and photosynthesis (P_g) from closed chamber methods; and particulate organic carbon (POC). Analysis of the CO₂ data showed that burning was a significant factor in measured CO₂ readings but that other factors such as month of sampling explained a greater proportion of the variation in the data. Carbon budget results showed that whereas all the plots were net sources of carbon, the most recent burn scars were smaller sources of carbon compared with the older burn scars, suggesting that burning of Calluna‐dominated landscapes leads to an ‘avoided loss’ of carbon. However, this management intervention did not lead to a transition to a carbon sink and that for carbon purposes, active peat‐forming conditions are desirable.