亚洲中部干旱区3个典型生态系统生长季水碳通量特征

亚洲中部干旱区地处欧亚大陆腹地, 干旱少雨, 生态环境十分脆弱, 研究该地区大气与地表之间的能量和物质交换对干旱区水资源利用和生态环境保护具有重要意义。该文分析了亚洲中部干旱区荒漠与草地生态系统能量、水汽和CO₂通量的日变化及季节变化特征, 探究了水汽和CO₂通量对主要环境因子的响应。通过分析亚洲中部干旱区3个站点的涡度相关资料发现: 亚洲中部干旱区荒漠和草地生态系统在生长季(4-10月)能量、水汽通量、净CO₂通量和总初级生产力的日变化呈“单峰型”, 而荒漠生态系统呼吸日变化相对稳定; 草地生态系统白天的潜热通量占净辐射通量的比例明显高于荒漠生态系统; 草地生态系统在5-8月呈现较强的碳汇, 而荒漠生态系统表现为弱碳汇。亚洲中部干旱区草地和荒漠生态系统水汽通量和总初级生产力对降水、净辐射通量或光合有效辐射、饱和水汽压差、气温均表现出明显的敏感性。     

Precipitation Pattern Determines the Inter-annual Variation of Herbaceous Layer and Carbon Fluxes in a Phreatophyte-Dominated Desert Ecosystem

Arid and semi-arid ecosystems dominated by shrubby species are an important component in the global carbon cycle but are largely under-represented in studies of the effect of climate change on carbon flux. This study synthesizes data from long-term eddy covariance measurements and experiments to assess how changes in ecosystem composition, driven by precipitation patterns, affect inter-annual variability of carbon flux and their components in a halophyte desert community dominated by deep-rooted shrubs (phreatophytes, which depend on groundwater as their primary water source). Our results demonstrated that the carbon balance of this community responded strongly to precipitation variations. Both pre-growing season precipitation and growing season precipitation frequency significantly affected inter-annual variations in ecosystem carbon flux. Heavy pre-growing season precipitation (November–April, mostly as snow) increased annual net ecosystem carbon exchange, by facilitating the growth and carbon assimilation of shallow-rooted annual plants, which used spring and summer precipitation to increase community productivity. Sufficient pre-growing season precipitation led to more germination and growth of shallow-rooted annual plants. When followed by high-frequency growing season precipitation, community productivity of this desert ecosystem was lifted to the level of grassland or forest ecosystems. The long-term observations and experimental results confirmed that precipitation patterns and the herbaceous component were dominant drivers of the carbon dynamics in this phreatophyte-dominated desert ecosystem. This study illustrates the importance of inter-annual variations in climate and ecosystem composition for the carbon flux in arid and semi-arid ecosystems. It also highlights the important effect of changing frequency and seasonal pattern of precipitation on the regional and global carbon cycle in the coming decades.     

小叶锦鸡儿灌丛化对典型草原群落结构与生态系统功能的影响

草原灌丛化是全球干旱半干旱地区面临的重要生态问题。灌丛化对草原生态系统结构与功能的影响较为复杂, 有待于在更广泛的区域开展研究。该研究在内蒙古锡林郭勒典型草原选择轻度、中度和重度灌丛化草地, 通过群落调查, 结合植物功能性状和土壤理化性质观测, 研究了小叶锦鸡儿(Caragana microphylla)灌丛化对草原群落结构(物种多样性、功能多样性和功能群组成)和生态系统功能(初级生产力、植被和土壤养分库)的影响。结果表明: 1)不同程度灌丛化草地的物种丰富度、功能性状多样性和群落加权性状平均值差异显著, 其中, 中度灌丛化草地的物种多样性和功能多样性较高, 表明一定程度的灌丛化有利于生物多样性维持。2)重度灌丛化草地的地上净初级生产力(ANPP)显著高于轻度和中度灌丛化草地, 其原因主要是随着灌丛化程度加剧, 群落内一/二年生草本植物显著增加, 而多年生禾草和多年生杂类草显著减少。三个灌丛化草地的植被叶片和土壤碳、氮库差异均不显著。3)灌丛化对草原生态系统功能包括ANPP、植被和土壤养分库均没有直接的影响, 而是通过影响功能群组成、土壤理化性质和功能多样性, 间接地影响生态系统功能; 灌丛化导致功能群发生替代和土壤旱碱化是最重要的生物和非生物因素。     

中国典型陆地生态系统波文比特征及影响因素

波文比(β)是陆面过程中的重要参数, 影响着地表和大气间的能量交换, 明确β的空间变异规律和影响因素有助于对地表能量平衡和气候间反馈关系的预测。该研究收集了在中国不同生态系统类型开展的用涡度相关法(EC)测量地表能量平衡的公开发表文献, 构建了β和气象环境因子数据库, 分析了β在生态系统之间的差异、空间变异特征及影响因素。主要结果: (1)所有生态系统β平均值为0.95 ± 0.64, 变异系数67%, 偏度1.58, 峰度3.07, 整体服从对数正态分布, β平均值最高为灌木生态系统(1.26), 最低为湿地生态系统(0.49)。(2) β在生态系统类型间差异显著: 森林和湿地生态系统β无显著差异, 灌木生态系统β >草地生态系统 β >森林和湿地生态系统 β, 农田生态系统β介于草地生态系统与森林和湿地生态系统之间。(3) β随着纬度的增加而增加, 不随经度和海拔变化。纬度每增加1°,β增加0.038。(4) β随着年降水量(MAP)、年平均气温(MAT)、净辐射(R_n)、当年降水量(PPT)、当年平均气温(T_a)和叶面积指数(LAI)的增加而降低。(5)不同生态系统中β对生物和非生物因素的响应存在显著差异: 草地、森林和灌木生态系统的β对生物和非生物因素变化较为敏感, 而农田和湿地生态系统的β与所有生物和非生物因素均无显著相关关系。(6) MAP和R_n是β变化的直接影响因素, LAI通过影响R_n间接影响β。结果表明了植被类型与气候因素之间具有交互作用, 能量分配最主要的影响因素是降水, 叶面积对能量分配的调节作用并不显著。     

物种多样性和功能群多样性与生态系统生产力的关系——以内蒙古短花针茅草原为例

生物多样性与生态系统生产力之间的关系是当前生态学领域的热点问题。短花针茅(Stipa breviflora)草原是内蒙古荒漠草原的主要类型, 生态系统脆弱, 气候波动剧烈, 研究内蒙古短花针茅草原生物多样性与生产力的关系具有十分重要的意义。该研究在内蒙古短花针茅草原区设置了202个样地进行群落调查, 在干旱区及半干旱区两种资源供给下, 分析了物种丰富度、功能群丰富度与生产力的关系, 旨在解决两个科学问题: 1)物种多样性和功能群多样性中, 哪一种与生产力关系更为密切?2)资源供给对多样性和生产力关系的影响。结果表明: 1)物种丰富度、群落生产力与年降水量呈正相关关系, 而功能群丰富度与年降水量之间不存在显著相关性; 2)群落生产力随物种丰富度的增加而增加, 且两者间呈正线性关系, 功能群丰富度与生产力之间不存在显著相关关系; 3)资源供给会影响多样性与生产力之间的关系, 资源供给低时, 多样性对生产力贡献较低, 资源供给高时, 多样性对生产力的贡献较高。该研究丰富了多样性与生产力关系的研究, 同时, 考虑到植物功能性状的研究在近几年受到生态学家的重视, 且多数研究集中于小尺度的人工控制实验, 因此, 在大尺度自然生态系统中开展功能性状多样性与生态系统功能关系的研究将十分必要。     

Alpine grassland water use efficiency based on annual precipitation,growing season precipitation and growing season evapotranspiration

Water use efficiency (WUE) is an important parameter to understand the coupling between the water, and carbon cycles of terrestrial ecosystems. Previous studies on the grassland ecosystem WUE on the Qinghai-Xizang Plateau mainly based on annual precipitation (AP). However, vegetation water use mainly occurs in growing season. Therefore, we aimed to explore the differences of ecosystem WUE between alpine meadow and alpine steppe, and the relationships between ecosystem WUE and environmental factors from 2000 to 2010, using annual precipitation use efficiency (PUE_a), growing season precipitation use efficiency (PUE_gs), growing season water use efficiency (WUE_gs) based on AP, growing season precipitation (GSP) and growing season evapotranspiration (ET_gs ) respectively. Combining satellite-derived above-ground net primary productivity (ANPP), satellite-derived evapotranspiration and meteorological data from 2000 to 2010, we calculated PUE_a (ANPP / AP), PUE_gs (ANPP / GSP) and WUE_gs (ANPP / ET_gs) to find the differences of PUE_a, PUE_gs and WUE_gs between alpine meadow and alpine steppe. Moreover, we explored the relationships between PUE_a, PUE_gs or WUE_gs and precipitation (or evapotranspiration) or air temperature. We found that (1) the PUE_a and PUE_gs of alpine meadow were higher than that of alpine steppe, but there were no significant difference between WUE_gs of the two grassland types, indicating that there may be similar intrinsic water use efficiencies of the two grassland types. (2) The inter-annual variation of PUE_a and PUE_gs were similar while WUE_gs showed a larger fluctuation, implying that ET-based WUE_gs was more sensitive than precipitation-based PUE_a and PUE_gs, therefore WUE_gs is a better indicator of ecosystem water use efficiency than PUE_a or PUE_gs. (3) The PUE_a, PUE_gs and WUE_gs were negatively correlated with AP, GSP and ET_gs respectively, reflecting a consistency of the three water use efficiency measurements. In the alpine steppe, only WUE_gs was observed positively correlated with air temperature among the three measurements, but in the alpine meadow, no significant relationships between water use efficiency and air temperature was detected, suggesting that the WUE_gs of alpine steppe was more sensitive to air temperature than that of alpine meadow.     

Elevated CO2 does not stimulate carbon sink in a semi‐arid grassland

Elevated CO₂ is widely accepted to enhance terrestrial carbon sink, especially in arid and semi‐arid regions. However, great uncertainties exist for the CO₂ fertilisation effects, particularly when its interactions with other global change factors are considered. A four‐factor (CO₂, temperature, precipitation and nitrogen) experiment revealed that elevated CO₂ did not affect either gross ecosystem productivity or ecosystem respiration, and consequently resulted in no changes of net ecosystem productivity in a semi‐arid grassland despite whether temperature, precipitation and nitrogen were elevated or not. The observations could be primarily attributable to the offset of ecosystem carbon uptake by enhanced soil carbon release under CO₂ enrichment. Our findings indicate that arid and semi‐arid ecosystems may not be sensitive to CO₂ enrichment as previously expected and highlight the urgent need to incorporate this mechanism into most IPCC carbon‐cycle models for convincing projection of terrestrial carbon sink and its feedback to climate change.     

Spatial patterns and drivers of root turnover in grassland ecosystems in China

根系周转是陆地生态系统物质循环的关键指标, 也是陆地生态系统净初级生产力及碳固持潜力估算的核心参数。然而, 由于地下净初级生产力数据获取困难, 区域和全球尺度上的相关研究十分有限, 尤其是分布广泛的中国草地, 区域尺度上的整合研究几乎为空白。基于样地实测数据、已发表文献和在线数据库数据, 对中国草地5种植被类型、共计154个草地生态系统根系周转的空间格局进行整合分析, 并结合气象和土壤数据, 揭示了草地生态系统根系周转的关键驱动因子。研究发现: (1)根系周转速率随纬度升高而降低, 低纬度温暖地区根系周转更快; (2)气候因子(年平均气温、年降水量)和土壤理化性质(砾石含量、容重、pH值)共同影响根系周转, 对周转变异性的解释度为44%, 其中气候因子的相对贡献率为57%, 土壤理化性质的相对贡献率为43%; (3)中国草地根系周转的格局和驱动因子与全球尺度的研究结果不尽相同。该研究对根系周转的驱动因子提出了新的观点和证据, 为全球尺度上的整合研究提供了关键数据。     

Testing parameter sensitivities and uncertainty analysis of Biome-BGC model in simulating carbon and water fluxes in broadleaved-Korean pine forests

生态过程模型的发展为研究者在长时间序列和区域尺度的研究提供了便利, 但模型模拟的准确性受到模型自身结构、模型参数估计合理性的影响。敏感性分析能够定量或定性筛选出对模型模拟结果影响较大的敏感参数, 是模型参数校准过程中的重要工具, 也是建模和应用的先决条件。该文以阔叶红松林为研究对象, 采用全局敏感性分析方法——傅里叶幅度灵敏度检验扩展法(EFAST)对Biome-BGC模型的生理生态参数进行了敏感性分析, 分别分析了红松(Pinus koraiensis)和阔叶树的净初级生产力(NPP)、蒸散(ET)对参数变化的敏感性。结果表明: (1)模拟红松NPP的不确定性高于阔叶树, 但二者的模拟ET的不确定性均较小。阔叶树的NPP和ET对生理生态参数的敏感性总体上都小于红松。(2)无论是红松、阔叶或其他植被类型, 模拟NPP均表现出对叶片碳氮比、细根碳氮比、比叶面积(SLA)和冠层截留系数的敏感性, 这4个参数的高敏感性主要是由模型自身结构所决定的, 与植被类型和研究地区的关系较小。对模拟ET而言, 细根与叶片碳分配比、新茎与新叶碳分配比和SLA均是影响红松和阔叶树ET的敏感参数, 但红松ET主要受参数与参数间的二阶或多阶交互作用的间接影响, 而阔叶树ET则主要是受到敏感参数直接效应的影响。(3)除了上述影响红松和阔叶树碳水通量的共性参数外, 诸如核酮糖-1,5-二磷酸羧化酶中叶氮含量、叶片与细根周转率、所有叶面积与投影叶面积之比等也是对模拟结果有影响的重要参数, 但是其敏感程度随物种不同和研究区不同而不同, 所以这类参数可以根据具体情况进行参数本地化, 对于其他不敏感参数则可以采用模型缺省值。     

Advances in the carbon use efficiency of forest

植物碳利用效率(CUE)指净初级生产力与总初级生产力的比率, 它不仅反映了植被生态系统将大气中CO₂转化为生物量的能力和固碳潜力, 而且可确定呼吸对植被生产力的影响。CUE是比较不同生态系统碳循环差异的重要参数, 了解生态系统CUE有助于分析陆地生态系统是碳源还是碳汇, 对于预测全球变化和人类干扰对森林碳收支的影响具有重要意义。我国在森林CUE研究方面还十分欠缺。该文在介绍森林CUE计算方法和测定技术的基础上, 综述了植被、气象、森林经营等因子对森林CUE的影响, 得出主要结论: (1)关于不同森林植被类型CUE变化有两种截然相反的观点, 即: 恒定CUE和变量CUE。越来越多的研究支持第二种观点, 不同生态系统、不同森林类型、不同物种和植物发育阶段的CUE存在较大差异, 森林CUE较灌丛和草地低, 落叶林比混交林和常绿林具有较高的CUE, 热带森林CUE通常低于温带森林, CUE与植被演替和林龄相关, 森林地上、地下部分和不同组织的CUE不同, 以树干为最高; (2)植被的CUE与气温相关, 全球尺度上, 森林植被年平均CUE与年平均气温呈抛物线关系, 温带、寒带、干旱地区植物呼吸的温度适应驱动其较高的CUE; CUE随着降水量的增加而减少, 在水分充足或过剩的地区保持不变; 光照减弱降低维持呼吸系数, 增加生长呼吸系数, 导致植物CUE降低, 生长在高光照下的植物CUE高于低光照下的植物; (3) CO₂浓度升高引起植物CUE的升高或降低, 也有人认为CO₂浓度升高对森林CUE没有影响, CO₂浓度升高对CUE的影响可能取决于树木年龄或基因型; (4)生长在土壤瘠薄、低温、干旱等胁迫环境下的植物CUE通常比生长在适宜环境下的植物具有较大的可塑性, 施肥、灌溉和择伐等管理措施影响森林CUE; (5)植物CUE具有明显的季节变化, 温带森林以春季CUE为最高。建议今后森林CUE研究应着重围绕以下3个关键问题: (1)从不同空间尺度和生态系统层次, 探讨森林CUE的变异特征及其驱动机制; (2)从不同时间尺度, 探讨森林CUE动态过程与机制; (3)森林CUE对气候变化的响应与适应。     

荒漠草原与典型草原NPP、碳积累对不同降雨年份和利用方式的响应

不同草原利用方式正在影响着内蒙古的草原生态系统,而且在未来降水空间格局变化的背景下,它们共同决定了生态系统植被类型、净初级生产力(NPP)和生态系统碳积累。选取内蒙古中部两个重要的草地类型:荒漠草原和典型草原,研究不同草原利用方式(围栏禁牧、划区轮牧、割草、自由放牧)植物群落在降雨量不同的两个生长季节地上(ANPP)、地下净初级生产力(BNPP)的变化,同时也评估了植物群落的碳积累,研究结果表明:1)在降雨量亏缺年份,与围封相比,荒漠草原自由放牧区ANPP、BNPP及碳积累分别下降了57.1%、51.7%和56.0%,而典型草原自由放牧区分别下降了18.4%、25.1%和17.9%。2)在降雨量充足年份,与围封相比,荒漠草原划区轮牧区ANPP、BNPP以及碳积累分别增加了18.2%、9.8%和21.9%,而典型草原各处理下围封禁牧区ANPP仍是最高;3)两种草地类型下,降雨量对自由放牧的调控作用高于其它草地利用方式;4)荒漠草原ANPP在丰雨年是欠雨年的2倍,而典型草原仅增加了79.0%,降雨量对荒漠草原生产力的季节调控作用远高于典型草原。在未来全球气候变暖和降水格局变化的情况下,荒漠草原降雨量是影响荒漠植物群落NPP和碳积累的主导因子。     

极端降水和极端干旱事件对草原生态系统的影响

当前人类活动的加剧显著地影响着全球大气循环的格局。大气循环的多个模型均预测未来全球气候变化的显著特征是极端降水事件和极端干旱事件发生的频率会显著增加。水分是干旱、半干旱区草原植物生长发育的限制性资源, 而草原生态系统是陆地生态系统中对降水格局变化非常敏感的系统。但是, 关于极端降水事件和极端干旱事件对草原生态系统结构和功能的影响还是以分散的个案研究为主, 甚至关于极端气候事件的定义迄今也不尽相同。为此, 该文在分析极端气候事件定义及其研究方法的基础上, 总结了极端降水事件和极端干旱事件对草原生态系统土壤水分和养分状况、植物生长发育和生理特性、群落结构、生产力和碳循环过程的影响, 并提出了未来极端气候事件研究中应重点关注的5个重要方向, 以及控制试验研究的2个关键科学问题, 对开展全球变化背景下草原生态系统对极端气候事件响应机制的研究具有指导意义。     

Trade-offs between water yield and carbon sequestration for sub-alpine catchments in western Sichuan,China

Aims There is increasing concern on the trade-off between carbon sequestration and water yield of forest ecosystems. Our objective was to explore the effects of vegetation composition on water and carbon trade-off in the sub-alpine watersheds of western Sichuan during 1982-2006.Methods The WaSSI-C, which is an eco-hydrological model with coupled water and carbon cycles, was employed to calculate the key components in water balance and carbon sequestration for the 22 sub-catchments in the upper reaches of Zagunao River. Spearman’s Rho trend analysis was used to examine the trends in runoff and net ecosystem productivity. Important findings Compared with either subalpine meadow or mixed forest dominated catchments, the conifer-dominated catchments had much higher water loss due to high evapotranspiration, and the loss was not offset by its higher soil water infiltration during the growing season. The change in soil water storage for subalpine meadow, mixed forest and coniferous forest are -44 mm, -18 mm and -5 mm, respectively, which indicated significant decline in soil water storage and thus water yield particularly in alpine meadow catchments. Significant negative relationship was found between runoff and net ecosystem productivity, the alpine meadow as the dominant vegetation type showed high water yield and low carbon sequestration, and the conifer-dominant and mixed forest vegetation showed low water yield and high carbon sequestration, moreover, the higher the forest coverage, the lower the water yield. Upward trends in net ecosystem productivity were observed in the three vegetation types during the study period and the alpine meadow type was significant.     

The interactive effects of nitrogen addition and increased precipitation on gross ecosystem productivity in an alpine meadow

氮水添加对高寒草甸生态系统生产力的影响 降水变化和大气氮沉降增加对草原生态系统碳交换具有重要的影响,进而影响草地生产力、群落组成和生态系统功能。然而,氮水添加对高寒草甸生态系统碳交换的影响目前尚不清楚。因此,本研究在青藏高原高寒草甸布设氮水添加试验,设置4种不同处理：对照、 加氮、加水和同时添加氮水,对生态系统碳交换过程进行了连续4年的原位观测。研究结果发现,氮添加可以增加总生态系统生产力(GEP)、植物地上生物量、群落盖度和群落加权平均高度(CWMh),而水分添加没有显著影响。生态系统碳交换对氮水添加的响应在干湿年存在显著差异。水分添加仅在干旱年对净生态系统碳交换(NEE)具有显著影响,原因是GEP的增加量大于生态系统呼吸(ER)。相反,氮添加仅在湿润年显著提高了生态系统碳交换,其中GEP的增加归因于NEE的增加量大于ER。结构方程结果表明,氮添加主要通过增加优势种的盖度从而提高NEE。本研究强调了降水和优势物种在调节高寒草甸生态系统响应环境变化中的重要作用。     

放牧和模拟增温对藏北高寒草地植物群落特征及生产力的影响

气候变化和放牧活动对草地植物物种多样性和生产力具有重要影响。为探索藏北高寒草地植物物种多样性和生产力对增温、放牧及其交互作用的响应, 于2011年在藏北高原开始建立增温实验平台, 2016年起增设放牧、增温+放牧实验, 连续2年(2016-2017年)观测了植物群落特征、群落组成、生产力和物种多样性。结果表明, 增温和放牧对高寒草地植物高度和净初级生产力具有显著交互作用。在放牧条件下, 增温对植物高度无显著影响; 但在不放牧条件下, 增温却显著增加了植物高度。在放牧条件下, 增温对净初级生产力的影响存在年际差异, 2016年增温对生产力无显著影响, 2017年增温显著降低了植物净初级生产力; 但在不放牧条件下, 增温对植物净初级生产力无显著影响。增温和放牧对高寒草地植物物种丰富度、盖度、重要值及多样性均无显著交互作用。植物盖度在增温和放牧条件下显著降低, 杂类草物种比例显著增加, 但物种多样性均无显著变化。研究表明, 增温和放牧显著改变高寒草地群落结构。未来气候变化条件下, 放牧活动加剧有可能导致高寒草地生产力降低。     

Water- and Plant-Mediated Responses of Ecosystem Carbon Fluxes to Warming and Nitrogen Addition on the Songnen Grassland in Northeast China

Background

Understanding how grasslands are affected by a long-term increase in temperature is crucial to predict the future impact of global climate change on terrestrial ecosystems. Additionally, it is not clear how the effects of global warming on grassland productivity are going to be altered by increased N deposition and N addition.

Methodology/Principal Findings

In-situ canopy CO₂ exchange rates were measured in a meadow steppe subjected to 4-year warming and nitrogen addition treatments. Warming treatment reduced net ecosystem CO₂ exchange (NEE) and increased ecosystem respiration (ER); but had no significant impacts on gross ecosystem productivity (GEP). N addition increased NEE, ER and GEP. However, there were no significant interactions between N addition and warming. The variation of NEE during the four experimental years was correlated with soil water content, particularly during early spring, suggesting that water availability is a primary driver of carbon fluxes in the studied semi-arid grassland.

Conclusion/Significance

Ecosystem carbon fluxes in grassland ecosystems are sensitive to warming and N addition. In the studied water-limited grassland, both warming and N addition influence ecosystem carbon fluxes by affecting water availability, which is the primary driver in many arid and semiarid ecosystems. It remains unknown to what extent the long-term N addition would affect the turn-over of soil organic matter and the C sink size of this grassland.     

Dominant species and ecosystem gas exchange in temperate grassland under different land use patterns

在内蒙古温带草原围封、放牧和割草3种处理下的样地内, 对生态系统尺度和大针茅(Stipa grandis)、冷蒿(Artemisia frigida)、羊草(Leymus chinensis) 3种优势种植物叶片尺度上的气体交换和水分关系进行了测定, 对比研究了植物碳水对环境的响应。结果表明, 在优势种单株尺度和生态系统尺度上, 大气-植被CO₂交换因草地利用方式的不同而具有不同的表现。在生态系统层面, 放牧样地的群落净CO₂气体交换量和总初级生产力都与围封样地和割草样地有差异, 群落总初级生产力受生态系统呼吸的影响。在放牧处理下, 群落净CO₂气体交换量日变化表现为生态系统对碳的吸收, 而围封和割草则以碳释放为主。单叶光合速率出现负值并随时间推移而恢复的现象, 应是植物对干旱高温、高光照的特殊反应。生态系统水分利用效率没有明显不同, 但各样地的蒸散能力有趋势上的变化; 对于同种植物, 放牧样地植物单叶水分利用效率的日变化波动幅度最大, 围封样地最小。     

放牧对草地生态系统服务和功能权衡关系的影响

内蒙古草原是我国北方的重要生态屏障和绿色畜牧业基地, 放牧是草原生态系统的主要利用和管理方式, 在放牧管理中充分发挥生态系统某一项或几项服务和功能最大利用价值时, 往往会与其他服务(功能)发生冲突, 需要权衡多项生态系统服务和功能, 制定合理的放牧管理制度。该研究以内蒙古锡林郭勒典型草原为例, 通过设置不放牧、轻度放牧、中度放牧以及重度放牧的放牧梯度, 从多项生态系统服务和功能权衡的角度比较了最适放牧管理强度。结果显示, 在放牧管理的草地生态系统服务和功能的权衡中, 权衡、协同、不相关关系同时存在, 如土壤呼吸速率与植物群落净生长量、生物多样性与植物群落净光合速率表现为权衡关系, 植物群落净生长量分别与土壤含水量、植物群落净光合速率及草地蒸散速率存在协同关系, 土壤有机碳含量与其他服务或功能间呈不相关关系; 放牧能不同程度地削弱多项生态系统服务及功能间的权衡关系(冲突对立关系); 中度放牧条件下的多项生态系统服务及功能的协同性最佳。     

Shifts in the dynamics of productivity signal ecosystem state transitions at the biome‐scale

Understanding ecosystem dynamics and predicting directional changes in ecosystem in response to global changes are ongoing challenges in ecology. Here we present a framework that links productivity dynamics and ecosystem state transitions based on a spatially continuous dataset of aboveground net primary productivity (ANPP) from the temperate grassland of China. Across a regional precipitation gradient, we quantified spatial patterns in ANPP dynamics (variability, asymmetry and sensitivity to rainfall) and related these to transitions from desert to semi‐arid to mesic steppe. We show that these three indices of ANPP dynamics displayed distinct spatial patterns, with peaks signalling transitions between grassland types. Thus, monitoring shifts in ANPP dynamics has the potential for predicting ecosystem state transitions in the future. Current ecosystem models fail to capture these dynamics, highlighting the need to incorporate more nuanced ecological controls of productivity in models to forecast future ecosystem shifts.     

Growing season net ecosystem CO2 exchange of two desert ecosystems with alkaline soils in Kazakhstan

Central Asia is covered by vast desert ecosystems, and the majority of these ecosystems have alkaline soils. Their contribution to global net ecosystem CO₂ exchange (NEE) is of significance simply because of their immense spatial extent. Some of the latest research reported considerable abiotic CO₂ absorption by alkaline soil, but the rate of CO₂ absorption has been questioned by peer communities. To investigate the issue of carbon cycle in Central Asian desert ecosystems with alkaline soils, we have measured the NEE using eddy covariance (EC) method at two alkaline sites during growing season in Kazakhstan. The diurnal course of mean monthly NEE followed a clear sinusoidal pattern during growing season at both sites. Both sites showed significant net carbon uptake during daytime on sunny days with high photosynthetically active radiation (PAR) but net carbon loss at nighttime and on cloudy and rainy days. NEE has strong dependency on PAR and the response of NEE to precipitation resulted in an initial and significant carbon release to the atmosphere, similar to other ecosystems. These findings indicate that biotic processes dominated the carbon processes, and the contribution of abiotic carbon process to net ecosystem CO₂ exchange may be trivial in alkaline soil desert ecosystems over Central Asia.