植被类型变化对土壤微生物碳利用效率的影响研究进展

植被类型变化强烈影响着土壤碳循环。土壤微生物碳利用效率（CUE）是微生物将从环境中获取的碳分配给自身生长的比例,是土壤碳循环的综合指标。研究植被类型变化对CUE的影响有助于从微生物视角理解该过程中的土壤碳动态,可以为评估植被类型变化对土壤质量及生态系统碳循环的影响提供基础,具有重要的理论及实际价值。通过系统查阅相关文献,综述了植被类型变化导致的CUE变化情况,以及该过程中影响CUE的因子与机制。目前,相关研究主要涉及以林地、草地和农业用地为起点或终点的植被变化类型。天然林（原生林、次生林）变化为人工林、林地变化为草地后CUE普遍下降,随终点植被的发展CUE可能恢复至起点水平。植被成熟度越高,发生转变时CUE变化越剧烈。植被类型变化以农业用地为起点或终点时,CUE变化方向的不确定性及幅度的变异性均增加。植被类型变化导致的CUE变化主要受到植被、土壤、微生物因子及其交互作用的驱动,指示CUE的指标、采样季节和土层也会一定程度上影响CUE的变化。今后相关研究应采用直接的CUE测定方法,拓宽研究气候区及植被变化类型,关注植被变化过程中CUE变化的土层差异及动态监测,深入对植被类型变化导致的生态环境因子变化与CUE的关系及作用机制的研究。     

贡嘎山峨眉冷杉成熟林碳利用效率季节动态及其影响因子

碳利用效率(CUE)是植被生态系统的一个重要功能参数, 反映了植被生态系统的固碳能力, 适用于分析不同时间段内器官、个体和群落等不同层次的碳收支趋势, 因而有助于对陆地生态系统碳功能的确定与预测, 引起了广泛关注。该研究采用生物计量法, 测定和计算了川西贡嘎山东坡峨眉冷杉(Abies fabri)成熟林树木不同器官的呼吸与净生产力动态, 分析了乔木层及其各器官CUE动态及主要影响因子, 并估算了乔木层不同径级树木CUE。主要结果: (1)乔木层各器官月呼吸速率与温度呈正相关关系, 以细根月呼吸速率为最大; 不同径级树木年呼吸量无显著差异, 以小径级树木树干的年呼吸量为最小。(2)乔木层细根和树干月净初级生产力(NPP)均随温度增加而增加, 以细根月NPP为最大。小径级树木年NPP最大, 其针叶年NPP也显著高于中径级和大径级树木。(3)林分乔木层及其各器官CUE大多集中在0.30-0.60之间, 其中细根、树干CUE具有相似的月变化动态, 均随温度的升高而上升。不同径级树木CUE及树干和针叶CUE均随树木个体的增大而明显下降。(4)气温和土壤温度与乔木层树干和细根CUE呈正相关关系, 而降水量与针叶CUE呈负相关关系。细根CUE与树干CUE呈正相关关系,与针叶CUE呈负相关关系。峨眉冷杉成熟林乔木层CUE主要取决于树干和细根CUE。该研究证实了川西亚高山暗针叶成熟林仍具有较强的碳汇功能, 在区域碳储存和森林生态系统碳循环中发挥着极其重要的作用。     

氮添加土壤微生物群落结构影响微生物碳利用效率

尽管近年来中国氮(N)沉降水平逐渐趋于稳定,但中国东南地区N沉降相比于其他地区仍处于较高水平。N沉降对陆地生态系统碳循环过程的影响不容忽视。微生物碳利用效率(CUE)是指微生物将吸收的碳转化为生物量碳的效率,高微生物CUE意味着高土壤有机碳存储潜力。因此,探究N沉降背景下微生物CUE的变化将有助于进一步认识陆地生态系统土壤碳存储的变化。然而,目前关于N沉降下微生物群落结构的变化如何影响微生物CUE鲜有报道。在福建省泉州市戴云山国家级自然保护区的罗浮栲林通过N添加模拟N沉降。实验共包括三个N添加处理：对照(CT,+0 kg hm^-2 a^-1)、低氮(LN,+40 kg hm^-2 a^-1)和高氮(HN,+80 kg hm^-2 a^-1)。测定不同处理土壤基本理化性质、微生物生物量、酶活性和CUE,并使用高通量测序对微生物群落结构和多样性进行测定。结果表明,N添加显著影响微生物CUE,随着N添加水平的增加,CUE逐渐增加;相反,土壤pH、可提取有机碳(EOC)和微...     

宁夏陆地生态系统水分利用效率特征及其影响因子

生态系统水分利用效率(Water Use Efficiency, WUE)是表征生态系统碳水耦合程度的重要指标,能反映生态系统碳水循环规律及其相互作用关系。基于MODIS数据以及宁夏生态系统类型数据,分析2000—2017年宁夏不同生态系统WUE的变化特征,探讨了NPP和ET两种因子对WUE年际与年内变化的影响。结果表明:(1)全区陆地生态系统的年均WUE为1.03 g·C/kg·H_2O,值域在0.55—2.98 g·C/kg·H_2O之间,总体上呈现南北高、中部低的特征。(2)不同生态系统的WUE差异较大,由高到低为水体及湿地、森林、农田、草地、聚落、荒漠和其他生态系统,在同类生态系统中,植被生物量和盖度越高的亚类生态系统,其WUE也越高。(3)宁夏陆地生态系统WUE存在着每年0.0141 g·C/kg·H_2O的下降趋势,年内WUE呈典型的单峰形态,变化范围在0.02—2.16 g·C/kg·H_2O之间。(4)年际尺度上,宁夏陆地生态系统WUE与年蒸散(Evapotranspiration,ET)有极显著负相关性(P0.01),而与净初级生产力(Net Primary Production,NPP)没有相关性;年内尺度上,WUE变化与ET呈显著正相关(P0.05),与NPP呈极显著正相关(P0.01),这与植被的年内季节性生长过程有关。(5)根据ET强弱和WUE高低,可将宁夏陆地生态系统水分利用效率特征划分为4类,即低ET低WUE区、低ET高WUE区、高ET低WUE区和高ET高WUE区。宁夏的生态恢复工程在增强植被生产力的同时,也增强了区域水分消耗,致使陆地生态系统整体水分利用效率下降,这为宁夏未来水资源调控和生态重建提供了科学依据。     

生物质炭配施氮肥对雷竹林土壤微生物碳氮利用效率的影响

为进一步促进雷竹林固碳培肥,于2019年通过野外试验研究生物质炭配施氮肥对土壤养分含量、碳氮转化酶活性和微生物碳氮利用效率的影响。试验设置3个生物质炭梯度B0、B1、B2,分别为0、10、30 t/hm²,3个氮肥梯度N0、N1、N2,分别为0、0.5、1 t/hm²,共计9种处理(B0N0、B0N1、B0N2、B1N0、B1N1、B1N2、B2N0、B2N1、B2N2)。结果表明:生物质炭和氮肥配施明显提升土壤有机碳、总氮、铵态氮含量,除土壤速效磷外,总体上B2N1和B1N1处理下土壤有机碳和土壤养分含量最高。微生物生物量碳、氮含量和β-葡糖苷酶活性在B2N1处理达到最高,较B0N0处理显著增加65.1%、293.1%和59.6%。微生物生物量磷含量、N-乙酰氨基葡糖苷酶和亮氨酸氨基肽酶活性在B2N2处理最高,较B0N0处理显著增加193.3%、119.6%和64.0%。土壤微生物碳利用效率(CUE)和土壤总氮、有机碳、硝态氮、铵态氮、速效磷及微生物生物量碳氮显著正相关(P < 0.01),其中土壤有机碳、微生物生物量碳、硝态氮对CUE的解释率最高。土壤微生物氮利用效率(NUE)和土壤微生物生物量氮显著负相关(P < 0.01),其中土壤微生物生物量氮、有机碳和铵态氮对NUE的解释率最高。总体上,生物质炭配施氮肥下CUE增加、NUE降低,说明雷竹林土壤微生物对碳的固存增加,对氮的矿化增强。因此,配施生物质炭可作为固碳培肥和地力提升的潜在措施,但生物质炭与氮肥配施对土壤微生物群落的长期影响尚不明确,仍需进一步研究。     

罗浮栲林土壤微生物碳利用效率对短期氮添加的响应

作为调节土壤碳矿化过程的重要参数,微生物碳利用效率(CUE)对理解陆地生态系统中的碳循环至关重要。本研究在戴云山罗浮栲林设置对照(0 kg N·hm^-2·a^-1)、低氮(40 kg N·hm^-2·a^-1)和高氮(80 kg N·hm^-2·a^-1) 3个氮添加水平以模拟氮沉降,测定了表层(0～10 cm)土壤基本理化性质、有机碳组分、微生物生物量和酶活性;并利用¹⁸O标记水方法测定土壤微生物CUE,以更好地理解氮沉降加剧对微生物CUE的影响及其影响因素。结果表明: 短期氮添加显著降低了土壤微生物的呼吸速率、碳和氮获取酶活性,但显著增加了土壤微生物CUE。β-N-乙酰氨基酸葡糖苷酶(NAG)/微生物生物量碳(MBC)、微生物呼吸速率、β-葡萄糖苷酶(BG)/MBC、纤维素水解酶(CBH)/MBC和土壤有机碳含量是影响CUE的主要因素,且CUE与NAG/MBC、微生物呼吸速率、BG/MBC和CBH/MBC呈显著负相关,与土壤有机碳呈显著正相关。综上,短期氮添加导致土壤微生物获取碳和氮的成本降低,减少微生物呼吸,从而提高了土壤微生物CUE,这将有助于提高罗浮栲林土壤碳固存潜力。     

植物源和微生物源土壤有机碳转化与稳定研究进展

土壤有机碳库是陆地生态系统碳汇的重要组成部分,探明土壤有机碳的转化与稳定机制是深入理解陆地生态系统碳汇功能及应对气候变化的关键。近年提出的“土壤微生物碳泵”理论,即：植物残体是土壤有机碳的初始来源,微生物同化产物也是土壤稳定有机碳库的重要贡献者,对土壤有机碳的固存机制提出了新的见解。由于植物残体分解过程的复杂性、多变性以及参与分解过程的微生物种群的高异质性,植物残体和微生物残体向土壤有机碳的转化和稳定机理尚不十分明确。本文阐述了植物残体和微生物残体定量的表征方法以及它们在土壤中的稳定机制,探讨了植物和微生物源残体碳对土壤有机碳的贡献及其在土壤有机碳积累过程中的主要影响因素,最后对该研究领域未来的发展方向和研究重点进行展望,以期为陆地生态系统土壤固碳研究提供科学支撑。     

马尾松根际碳氮利用效率对土壤微生物群落结构的影响

微生物元素利用效率在调节土壤碳(C)和氮(N)矿化过程中有重要作用,然而土壤微生物转化的有机碳(SOC)、N比例研究尚不充分。以千岛湖5年生、9年生、19年生、29年生、35年生马尾松林为研究对象,测定根际SOC、土壤总氮(TN)、土壤微生物量碳氮(MBC、MBN)、土壤C、N获得酶活性和土壤微生物群落结构,阐明土壤微生物C、N利用效率(CUE、NUE)和元素阈值比(TER)与微生物群落结构关系。结果表明：5年生马尾松根际SOC、TN均明显高于其它林分(P<0.05),其土壤微生物量C/N比则显著(除9年生)低于其它林分(P<0.05),证实了微生物CUE对底物养分状态敏感性较低。35年生马尾松根际微生物NUE均显著高于其它林龄(除19年生),说明土壤中大部分N转化为MBN,与35年生马尾松土壤微生物生物量显著高于其它林分一致。马尾松根际NUE和TER与土壤微生物总生物量及其组分生物量均呈显著正相关关系(P<0.05),说明土壤微生物生长繁殖受NUE影响。所有林龄马尾松TER均大于土壤C/N比,表示研究区域生态系统处于C或者能源限制,而非N限制;证实了土壤C/N比减少到TER以下时,土壤有机物获得C的成本高于获得N的成本。5年生马尾松微生物CUE和TER均最低,二者没有明显的相关关系,可能低龄马尾松林CUE和NUE有补偿性关系。研究强调了土壤根际微生物元素利用效率和微生物群落对土壤C和N循环过程的重要性,为亚热带森林生态系统土壤经营管理提供了依据。     

排水对我国两种典型湿地土壤有机碳微生物转化过程的影响

湿地储存了全球三分之一的土壤有机碳（SOC）,并受到人为排水的强烈影响。然而,排水引起的水位下降对不同湿地碳循环（特别是微生物转化）过程的影响尚不明确。为此,本研究以我国两种典型湿地（贫营养型的大九湖湿地和富营养型的红原湿地）土壤为研究对象,通过添加¹³C标记葡萄糖的室内培养试验,分析了短期和长期排水对SOC降解、胞外酶活性、微生物碳利用效率（CUE）和微生物碳积累效率（CAE）的影响。结果表明：长期和短期排水显著提高了两种湿地SOC降解速率(从淹水处理的1.47μg C·g^-1·h^-1升高到排水处理的2.47μg C·g^-1·h^-1)、葡萄糖来源的微生物生物量碳(从0.21 mg C·g^-1升高到1.00 mg C·g^-1)和CAE（从0.29升高到0.73）,但未改变CUE（变化范围为0.34～0.86）。长期排水提高了大九湖湿地α-葡萄糖苷酶活性,但降低了红原湿地β-葡萄糖苷酶和酚氧化酶活性。综上,排水主要通过增强微生物胞内代谢过程（包括呼吸）提高湿地土壤“微生物碳泵”作用和效率,同时加速了SOC降解。     

太白山不同海拔森林根际土壤微生物碳利用效率差异性及其影响因素

探索森林根际土壤微生物碳利用效率(CUE)是权衡森林生态系统微生物合成代谢和分解代谢强弱的关键过程。然而不同海拔森林根际土壤微生物CUE的变化规律与影响因子尚不清楚。该研究选取秦岭太白山6个不同海拔的森林根际土壤为研究对象,测定其理化性质、胞外酶活性、微生物群落与植被特征等指标,利用酶化学计量比计算微生物CUE,分析根际土壤微生物CUE沿海拔梯度的变化规律,定量研究其影响因子。结果表明:根际土壤微生物CUE随海拔升高总体呈上升趋势。CUE从最低海拔的0.505至最高海拔的0.527升高了4.36%,但在海拔1 603和2 405m处出现了下降。海拔梯度内根际土壤微生物CUE变化受多种环境因子综合影响,土壤基质的影响(如可溶性有机碳和铵态氮含量)占主导地位,植被因子次之,二者分别解释了CUE变化的17.0%和5.7%,且二者相互作用解释了CUE变化的31.9%。研究结果可为秦岭森林土壤微生物碳同化能力和固碳潜力,以及全球变化背景下森林土壤碳循环提供科学依据。     

CO2 balance of boreal, temperate, and tropical forests derived from a global database

Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this carbon over both short and long timescales. Relevant data to address these uncertainties are being collected at many sites around the world, but syntheses of these data are still sparse. To facilitate future synthesis activities, we have assembled a comprehensive global database for forest ecosystems, which includes carbon budget variables (fluxes and stocks), ecosystem traits (e.g. leaf area index, age), as well as ancillary site information such as management regime, climate, and soil characteristics. This publicly available database can be used to quantify global, regional or biome‐specific carbon budgets; to re‐examine established relationships; to test emerging hypotheses about ecosystem functioning [e.g. a constant net ecosystem production (NEP) to gross primary production (GPP) ratio]; and as benchmarks for model evaluations. In this paper, we present the first analysis of this database. We discuss the climatic influences on GPP, net primary production (NPP) and NEP and present the CO₂ balances for boreal, temperate, and tropical forest biomes based on micrometeorological, ecophysiological, and biometric flux and inventory estimates. Globally, GPP of forests benefited from higher temperatures and precipitation whereas NPP saturated above either a threshold of 1500 mm precipitation or a mean annual temperature of 10 °C. The global pattern in NEP was insensitive to climate and is hypothesized to be mainly determined by nonclimatic conditions such as successional stage, management, site history, and site disturbance. In all biomes, closing the CO₂ balance required the introduction of substantial biome‐specific closure terms. Nonclosure was taken as an indication that respiratory processes, advection, and non‐CO₂ carbon fluxes are not presently being adequately accounted for.     

Simulated chronic nitrogen deposition increases carbon storage in Northern Temperate forests

High levels of atmospheric nitrogen (N) deposition in Europe and North America were maintained throughout the 1990s, and global N deposition is expected to increase by a factor of 2.5 over the next century. Available soil N limits primary production in many terrestrial ecosystems, and some computer simulation models have predicted that increasing atmospheric N deposition may result in greater terrestrial carbon (C) storage in woody biomass. However, empirical evidence demonstrating widespread increases in woody biomass C storage due to atmospheric N deposition is uncommon. Increased C storage in soil organic matter due to chronic N inputs has rarely been reported and is often not considered in computer simulation models of N deposition effects. Since 1994, we have experimentally simulated chronic N deposition by adding 3 g N m⁻² yr⁻¹ to four different northern hardwood forests, which span a 500 km geographic gradient in Michigan. Each year we measured tree growth. In 2004, we also examined soil C content to a depth of 70 cm. When we compared the control treatment with the NO₃⁻ deposition treatment after a decade of experimentation, ecosystem C storage had significantly increased in both woody biomass (500 g C m⁻²) and surface soil (0–10 cm) organic matter (690 g C m⁻²). The increase in surface soil C storage was apparently driven by altered rates of organic matter decomposition, rather than an increase in detrital inputs to soil. Our results, for study locations stretching across hundreds of kilometers, support the hypothesis that chronic N deposition may increase C storage in northern forests, potentially contributing to a sink for anthropogenic CO₂ in the northern Hemisphere.     

Changes in carbon storage and fluxes in a chronosequence of ponderosa pine

Forest development following stand‐replacing disturbance influences a variety of ecosystem processes including carbon exchange with the atmosphere. On a series of ponderosa pine (Pinius ponderosa var. Laws.) stands ranging from 9 to> 300 years in central Oregon, USA, we used biological measurements to estimate carbon storage in vegetation and soil pools, net primary productivity (NPP) and net ecosystem productivity (NEP) to examine variation with stand age. Measurements were made on plots representing four age classes with three replications: initiation (I, 9–23 years), young (Y, 56–89 years), mature (M, 95–106 years), and old (O, 190–316 years) stands typical of the forest type in the region. Net ecosystem productivity was lowest in the I stands (?124 g C m^?2 yr^?1), moderate in Y stands (118 g C m^?2 yr^?1), highest in M stands (170 g C m^?2 yr^?1), and low in the O stands (35 g C m^?2 yr^?1). Net primary productivity followed similar trends, but did not decline as much in the O stands. The ratio of fine root to foliage carbon was highest in the I stands, which is likely necessary for establishment in the semiarid environment, where forests are subject to drought during the growing season (300–800 mm precipitation per year). Carbon storage in live mass was the highest in the O stands (mean 17.6 kg C m^?2). Total ecosystem carbon storage and the fraction of ecosystem carbon in aboveground wood mass increased rapidly until 150–200 years, and did not decline in older stands. Forest inventory data on 950 ponderosa pine plots in Oregon show that the greatest proportion of plots exist in stands ～ 100 years old, indicating that a majority of stands are approaching maximum carbon storage and net carbon uptake. Our data suggests that NEP averages ～ 70 g C m^?2 year^?1 for ponderosa pine forests in Oregon. About 85% of the total carbon storage in biomass on the survey plots exists in stands greater than 100 years, which has implications for managing forests for carbon sequestration. To investigate variation in carbon storage and fluxes with disturbance, simulation with process models requires a dynamic parameterization for biomass allocation that depends on stand age, and should include a representation of competition between multiple plant functional types for space, water, and nutrients.     

Changing Global Climate: Historical Carbon and Nitrogen Budgets and Projected Responses of Ohio’s Cropland Ecosystems

As the evidence of global climate change continues to mount, its consequences for cropland productivity assume particular significance. Against the backdrop of past agricultural practices, simulation models offer a glimpse into the future, showing the effect of temperature changes on crop production. In this study, we first quantified the carbon (C) and nitrogen (N) budgets of Ohios cropland ecosystems using inventory yield data of corn for grain, oat, and all wheat for the period 1866–1996 and soybean for the period 1924–96. Then we explored the responses of Ohios continuous soybean croplands to changes in temperature, carbon dioxide (CO₂) concentration, initial soil organic C and N (SOC-N) pools, soil texture, and management practices by developing a simple cropland ecosystem model (CEM) and performing a long-term sensitivity analysis. Finally, CEM simulations were evaluated against independent observations of SOC values (0–19 cm) averaged over 470 northwest Ohio sites between 1954 and 1987 under conventional tillage and rotations of corn–soybean–winter wheat by using the historical yield data (r ² = 0.8). The C contents per hectare of crop harvests increased by 178% for oats, 300% for corn for grain, and 652% for all wheat between 1866 and 1996 and by 305% for soybean between 1924 and 1996. Ohio croplands acted as C–N sources, releasing average net ecosystem emissions (NEE), including the removal of harvested C–N, of 4,598 kg CO₂ ha^–1 and 141 kg N ha^–1 in 1886 and 205 kg CO₂ ha^–1 (except for the corn-for-grain cropland) and 39 kg N ha^–1 in 1996. The continuous corn croplands continued to become a C sink, sequestering 255 kg C ha^–1 in 1996. Results of the sensitivity analysis for Ohios continuous soybean croplands revealed that the SOC pool increased by 6.9% and decreased by 7.5% in response to a doubled CO₂ concentration and a temperature increase of 2.8°C over 100 years, respectively. The sequestration potential of the SOC pool increased by 6.5% at a rate of 24.6 kg C ha^–1 y^–1 for the same period with finer soil texture (loam to silty clay loam). The shift from conventional to conservation residue practice led to an 11% increase in the steady-state SOC storage at a rate of 42 kg C ha^–1 y^–1 for 100 years.