三源区分土壤呼吸组分研究

三源区分土壤呼吸组分是指将土壤呼吸区分为纯根呼吸、根际微生物呼吸和土壤有机质呼吸3个部分。土壤有机质呼吸、纯根呼吸和根际微生物呼吸是3种不同的生物学过程,这3种呼吸对环境变化具有不同的响应机制。区分土壤呼吸中由根系引起的自养和异养呼吸组分的研究对定量评价陆地生态系统碳平衡具有重要的意义。论述了三源区分土壤呼吸组分的意义、方法和应用,分析了不同条件下土壤呼吸组分区分的研究结果。实验室纯根和根际微生物呼吸占根源呼吸比重约为45%和55%;野外条件下约为60%和40%。最后对本研究未来的发展方向进行了展望。     

生态系统光合与呼吸拆分的同位素理论、方法和应用进展

生态系统光合和呼吸是构成净生态系统CO₂交换量(NEE)的重要组分。涡度相关技术可直接观测生态系统NEE,并通过建立温度回归或光响应曲线等函数将NEE统计拆分为生态系统光合和呼吸,但是存在自相关和高估白天呼吸等问题。稳定同位素红外光谱技术的进步使高时间分辨率大气CO₂及其稳定碳同位素组成(δ¹³C)的连续观测成为可能,与涡度相关技术观测的NEE数据相结合,可实现昼夜和季节尺度生态系统光合和呼吸拆分。本文系统阐述了生态系统光合与呼吸的同位素通量拆分方法的基本理论与假设,阐述了同位素通量观测技术的发展及其应用进展,综述了同位素通量拆分理论解析生态系统光合与呼吸过程的新机制认识,最后总结并展望了同位素通量拆分理论的不确定性以及开展多种拆分方法综合比较的必要性。     

土壤各组分呼吸区分方法研究进展

土壤呼吸分为自养型呼吸(根呼吸)和异养型呼吸(微生物和动物呼吸),区分各组分呼吸可了解在全球变化条件下土壤碳循环和碳平衡的动态。本文综述了3种主要区分自养呼吸和异养呼吸的方法:①组分法;②根去除术;③同位素法。其中同位素法对根和土壤的影响最小,是最可靠的一种方法;综合各方面考虑,根去除法是最切实可行的方法。     

土壤呼吸组分分离技术研究进展

分离土壤呼吸组分是理解陆地生态系统碳循环的重要步骤,研究农田生态系统土壤呼吸组分的呼吸过程和机理对促进农业温室气体减排和碳汇增加、气候变化适应、保障粮食安全以及推动农业可持续发展都具有积极意义。本文综述了近年来土壤呼吸组分分离的理论依据、主要技术及分类,系统比较了现有技术优势、劣势和应用领域,并总结了土壤呼吸组分分离技术在国内外农田生态系统中的应用情况。由于多数分离技术在森林生态系统的相关研究中发展而来,它们在农田生态系统的应用十分有限,目前应用以同位素法、根分离法和回归法为主。由于土壤呼吸理论划分和分离方法的差异,不同研究结果之间往往难以比较。分离技术的发展有赖于土壤呼吸源分离理论的进一步发展,未来土壤呼吸组分分离研究的主要方向在于：（1）利用现有观测技术促进组分集成分析法和根分离法在农田生态系统中的应用,强化土壤呼吸组分和环境因子的同步观测,准确评估农田碳收支;（2）利用定位观测数据开展大尺度模型研究,改进和重构现有全球碳模型的碳氮过程,并在其中考虑重要的土壤呼吸过程;（3）利用FACE试验评估气候变化对土壤呼吸组分的影响和土壤-植物碳循环的适应机制;（4）分析呼吸组分与植物-土壤-养分的交互作用,评估农田管理措施的综合影响。     

马尾松林土壤呼吸组分对不同营林措施的响应

针对不同营林措施(对照、除灌、采伐1(15%)、采伐2(70%)后的三峡库区马尾松飞播林,采用LI-8100对其土壤呼吸组分的呼吸速率和土壤温度、湿度进行为期1年的连续观测分析表明,不同营林措施对土壤呼吸组分的影响不同。1)观测期内,各营林措施下凋落物层呼吸速率差异并不显著,对照、除灌、采伐1、采伐2的根呼吸速率均值分别为:1.00、0.83、0.86、1.11μmolCO_2m~(-2)s~(-1);采伐处理下矿质土壤呼吸显著高于对照和除灌(P0.05);2)与对照相比,营林措施并未显著改变凋落物呼吸对于土壤总呼吸的贡献率(18.78%-23.70%),但降低了根呼吸的贡献率,其中以采伐1最为显著(P0.05);除灌的矿质土壤呼吸贡献率(37.00%)与对照(38.32%)相近,而采伐1(45.63%)和采伐2(43.07%)均显著增加了矿质土壤呼吸的贡献率,矿质土壤呼吸的变化是造成采伐措施下土壤呼吸变化的主要土壤呼吸组分;3)营林后仅采伐2措施下土壤温湿度显著高于对照,土壤温湿度双因子模型较单因子模型能更好的解释土壤呼吸组分变化,但仅能解释其部分变化(4.6%-59.3%),仍需对营林后其他相关因子进行深入的综合研究。     

柠檬酸,葡萄糖和有机质对植物磷素吸收和土壤磷素形态的影响

研究了柠檬酸、葡萄糖和有机质（栎树类凋落物和三叶草茎叶）对几种栽培和野生植物磷素吸收以及高度风化老成土中磷素形态的影响。在未加入无机磷的情况下,连续加入柠檬酸溶液增加了温室盆栽大豆（Ｇｌｙｃｉｎｅｍａｘ（Ｌ．）Ｍｅｒｒ．）和高粱（Ｓｏｒｐｈｕｍｂｉｃｏｌｏｒ）对磷素的吸收。这表明,柠檬酸可以溶解土壤中被铁、铝氧化物固定的磷。当无机磷和柠檬酸溶液同时加入后。由于有机配位体能够阻止土壤对磷素的吸附和固定,植物对磷的吸收总量明显高于仅仅加入无机磷的对照。不论是否加入无机磷,葡萄糖均没有增加植物对磷素的吸收,但却改变了土壤中磷素的形态。该试验的结果还表明,Ｈｅｄｌｄｙ等人提出的土壤磷素分级方法不适于有机质含量很低的酸性土壤。在另一种性质极为相似的酸性土壤中施入粉碎的栎树（Ｑｕｅｒｃｕｓｓｐｐ．）凋落物和三叶草（ＴｒｉｆｏｌｉｕｍＰｒａｔｅｎｓｅ）后,野生商陆（Ｐｈｙｔｏｌａｃｃａａｍｅｒｉｃａｎａ）吸收磷素的能力增强。通过进一步对土壤中的磷素进行化学分级,结果表明,这些有机物质可以改变土壤中磷素存在的形态。本文还就有机质分解过程中的中间产物对土壤磷素有效性的影响机理进行了探讨。     

基于多种同位素模型的侧柏林生态系统蒸散组分定量拆分

为了全面认识森林生态系统蒸散各组分及其对蒸散的贡献率在日尺度上的变化规律,本研究利用同位素稳态和非稳态假设理论结合水同位素分析仪系统,对生长季侧柏林生态系统蒸散各组分进行了定量拆分和比较.结果 表明:4个测定日(2016年8月5、8、10、11日)不同来源水体的18O都呈现表层土壤水氧同位素组成(δS)＞枝条水氧同位素...     

土壤有机质含量对黔南喀斯特天然次生林土壤理化指标与植物多样性的影响

为探讨自然恢复过程中喀斯特森林土壤有机质含量(SOM)与土壤理化指标及植物多样性指数的相关性,对贵州省茂兰国家级自然保护区中不同森林类型的SOM、土壤理化性质和植物多样性进行了研究。根据乔木层物种的重要值,将保护区的41个调查样地划分为香叶树-枫香林、檵木-马尾松林、槭树-朴树林、小叶栾树-化香林、灯台-小花梾木林和四照花-青冈栎林类型。结果表明,部分森林类型土壤A层或B层的SOM差异显著,且部分森林类型的植物种数、直径、高度和密度,以及Margalef指数、Simpson指数、Shannon-Wiener指数和Pielou指数也差异显著。土壤孔隙度、蓄水量和主要肥力与养分指标随SOM增加而增大。乔木层的植物多样性指数与SOM呈正相关,与土壤A层SOM相关显著、Simpson指数和Pielou指数与土壤B层SOM相关显著。灌木层、草本层的植物多样性指数与SOM相关不显著。多元分析结果表明,植物多样性指数对土壤A层SOM的总贡献率呈灌木层乔木层草本层、对土壤B层SOM的总贡献率呈草本层乔木层灌木层的趋势,表明喀斯特地区SOM管理的植物多样性措施适宜以乔木树种为主、辅以灌木与草本层植物的复合经营方式。同时,土壤SOM不仅受乔木层植物多样性指数的影响、也受林分所处演替阶段与结构指标的影响,植物多样性指数的二次多项式拐点可成为喀斯特石漠化治理工程中物种量化管理的参考依据之一。     

北亚热带-南暖温带过渡区典型森林生态系统土壤呼吸及其组分分离

为阐明北亚热带．南暖温带过渡区典型森林生态系统土壤呼吸与其组分的碳排放速率及其对土壤水热变化的响应规律,本研究用壕沟断根法布设了土壤呼吸组分分离试验,并对土壤温湿度与呼吸速率进行了一年的观测。统计分析结果表明：土壤呼吸及其组分的呼吸速率在夏秋季较高、春冬季较低;土壤温度低于15℃时,呼吸速率的季节性变化主要受控于土壤温度;土壤温度高于15℃,而含水量低于0．20kg·kg^-1时,含水量对呼吸速率有明显的抑制作用;当土壤温湿度分别高于15℃与0．20kg·kg^-1,呼吸速率同时受到土壤温湿度的影响;土壤温湿度分别能解释呼吸速率季节性变化的80．36％～94．94％与7．20％～48．45％,温度的影响高于含水量;5种类型中土壤呼吸、自养与异养呼吸的Q10值变化范围分别为2．30～2．44、2．49～2．82与2．09～2．35,每个类型中自养呼吸的温度敏感性均为最高,其次为土壤呼吸,异养呼吸最低;锐齿栎幼林、锐齿栎老林、华山松与短柄袍针阔混交林、千金榆与短柄袍阔叶混交林及栓皮栎林自养呼吸日贡献率的变化范围分别为35．19％～57．73％、28．73％～49．24％、28．67％～49．82％、24．24％～41．70％与30．07％～46．22％,土壤呼吸的年排放量分别为1105．15gC·m^-2·a^-1、779．12gC·m^-2·a^-1、821．23gC·m^-2·a^-1、912．19gC·m^-2·a^-1与899．50gC·m^-2·a^-1,其中自养呼吸的年贡献率分别为52．89％、39．77％、44．17％、38．15％与43．26％,若考虑断根样方内细根分解的影响,则自养呼吸的年贡献率分别为65．56％、47．95％、53．80％、46．83％与53．86％;5个林分间的土壤呼吸速率、异养呼吸速率没有显著差异（P〉0．05）,而自养呼吸速率存在显著差异（P〈0．05）,类型间活细根生物量的差异解释了自养呼吸速率差异的94．71％。     

萘对川西亚高山森林土壤呼吸、可溶性有机质和微生物生物量的影响

通过原位控制试验,研究了萘对川西亚高山森林土壤动物抑制效率、土壤呼吸、可溶性有机质和微生物生物量的影响.结果表明:萘施用显著抑制了大型和中小型土壤节肢动物的个体密度和类群数量,个体密度分别下降76.3%~78.5%和83.3%~84.8%,类群数量分别降低48.3%~56.1%和45.8%~58.3%.萘处理与对照的土壤呼吸速率季节动态呈单峰曲线,分别以2月和8月为最低值和最高值,而且未受萘施用的显著影响.与对照相比,萘处理显著降低了8月和10月土壤可溶性碳和可溶性氮含量,以及4月和8月微生物生物量碳,增加了4月的微生物生物量碳氮比.萘处理和采样时间的交互作用显著影响了微生物生物量碳和微生物生物量氮,但对土壤动物个体密度和类群数量以及可溶性碳含量影响不显著.总体上,萘作为抑制剂,在川西亚高山森林土壤能够有效地抑制土壤动物节肢动物,且并未显著影响土壤呼吸,但对土壤碳氮组分造成了不同程度的影响.     

Indirect partitioning of soil respiration in a series of evergreen forest ecosystems

A simple estimation of heterotrophic respiration can be obtained analytically as the y-intercept of the linear regression between soil-surface CO₂ efflux and root biomass. In the present study, a development of this indirect methodology is presented by taking into consideration both the temporal variation and the spatial heterogeneity of heterotrophic respiration. For this purpose, soil CO₂ efflux, soil carbon content and main stand characteristics were estimated in seven evergreen forest ecosystems along an elevation gradient ranging from 250 to 1740 m. For each site and for each sampling date the measured soil CO₂ efflux (R _S) was predicted with the model R _S = a × S _C + b × R _D ± ε, where S _C is soil carbon content per unit area to a depth of 30 cm and R _D is the root density of the 2–5 mm root class. Regressions with statistically significant a and b coefficients allowed the indirect separation of the two components of soil CO₂ efflux. Considering that the different sampling dates were characterized by different soil temperature, it was possible to investigate the temporal and thermal dependency of autotrophic and heterotrophic respiration. It was estimated that annual autotrophic respiration accounts for 16–58% of total soil CO₂ efflux in the seven different evergreen ecosystems. In addition, our observations show a decrease of annual autotrophic respiration at increasing availability of soil nitrogen. Section Editor: A. Hodge     

Partitioning the components of soil respiration: a research challenge

Little is known about the respiratory components of CO₂ emitted from soils and attaining a reliable quantification of the contribution of root respiration remains one of the major challenges facing ecosystem research. Resolving this would provide major advances in our ability to predict ecosystem responses to climate change. The merits and technical and theoretical difficulties associated with different approaches adopted for partitioning respiration components are discussed here. The way forward is suggested to be the development of non-invasive regression analysis validated by stable isotope approaches to increase the sensitivity of model functions to include components of rhizosphere microbial activity, changing root biomass and the dynamics of a wide range of soil C pools. Section Editor: A. Hodge     

Separating root and soil microbial contributions to soil respiration: A review of methods and observations

Forest soil respiration is the sum of heterotrophic (microbes, soil fauna) and autotrophic (root) respiration. The contribution of each group needs to be understood to evaluate implications of environmental change on soil carbon cycling and sequestration. Three primary methods have been used to distinguish hetero- versus autotrophic soil respiration including: integration of components contributing to in situ forest soil CO₂ efflux (i.e., litter, roots, soil), comparison of soils with and without root exclusion, and application of stable or radioactive isotope methods. Each approach has advantages and disadvantages, but isotope based methods provide quantitative answers with the least amount of disturbance to the soil and roots. Published data from all methods indicate that root/rhizosphere respiration can account for as little as 10 percent to greater than 90 percent of total in situ soil respiration depending on vegetation type and season of the year. Studies which have integrated percent root contribution to total soil respiration throughout an entire year or growing season show mean values of 45.8 and 60.4 percent for forest and nonforest vegetation, respectively. Such average annual values must be extrapolated with caution, however, because the root contribution to total soil respiration is commonly higher during the growing season and lower during the dormant periods of the year.     

The variation of soil microbial respiration with depth in relation to soil carbon composition

The vertical variation in soil microbial respiratory activity and its relationship to organic carbon pools is critical for modeling soil C stock and predicting impacts of climate change, but is not well understood. Mineral soil samples, taken from four Scottish soils at different depths (0–8, 8–16, 16–24, 24–32 cm), were analyzed and incubated in the laboratory under constant temperature and environmental conditions. The vegetation type/plant species showed significant effects on the absolute concentration of C components and microbial activity, but the relative distribution of C and respiration rate with soil depth are similar across sites. Soil C pools and microbial respiratory activity declined rapidly with soil depth, with about 30% of total organic carbon (TOC) and dissolved organic carbon (DOC), and about half microbial carbon (C_mic) and respired CO₂ observed in the top 8 cm. The ratio of CO₂:TOC generally decreased with soil depth, but CO₂:DOC was significantly higher in the top 8 cm of soil than in the subsoil (8–32 cm). No general pattern between qCO₂ (CO₂:C_mic) and soil depth was found. The vertical distributions of soil C pools and microbial respiratory activity were best fitted with a single exponential equation. Compared with TOC and DOC, C_mic appears to be an adequate predictor for the variation in microbial respiration rate with soil depth, with 95% of variation in normalized respiration rate accounted for by a linear relationship.     

Effect of elevated atmospheric CO2 concentration on soil and root respiration in winter wheat by using a respiration partitioning chamber

Soil respiration in a cropland is the sum of heterotrophic (mainly microorganisms) and autotrophic (root) respiration. The contribution of both these types to soil respiration needs to be understood to evaluate the effects of environmental change on soil carbon cycling and sequestration. In this paper, the effects of free-air CO₂ enrichment (FACE) on hetero- and autotrophic respiration in a wheat field were differentiated and evaluated by a novel split-root growth and gas collection system. Elevated atmospheric pCO₂ of approximately 200 μmol mol⁻¹ above the ambient pCO₂ significantly increased soil respiration by 15.1 and 14.8% at high nitrogen (HN) and low nitrogen (LN) application rates, respectively. The effect of elevated atmospheric pCO₂ on root respiration was not consistent across the wheat growth stages. Elevated pCO₂ significantly increased and decreased root respiration at the booting-heading stage (middle stage) and the late-filling stage (late stage), respectively, in HN and LN treatments; however, no significant effect was found at the jointing stage (early stage). Thus, the effect of increased pCO₂ on cumulative root respiration for the entire wheat growing season was not significant. Cumulative root respiration accounted for approximately 25–30% of cumulative soil respiration in the entire wheat growing season. Consequently, cumulative microbial respiration (soil respiration minus root respiration) increased by 22.5 and 21.1% due to elevated pCO₂ in HN and LN, respectively. High nitrogen application significantly increased root respiration at the late stage under both elevated pCO₂ and ambient pCO₂; however, no significant effects were found on cumulative soil respiration, root respiration, and microbial respiration. These findings suggest that heterotrophic respiration, which is influenced by increased substrate supplies from the plant to the soil, is the key process to determine C emission from agro-ecosystems with regard to future scenarios of enriched pCO₂.     

大气CO2浓度升高对春玉米土壤呼吸的影响

为探讨春玉米不同生育期土壤呼吸速率对大气CO₂浓度升高的响应,以黄土高原旱作春玉米为研究对象,通过改进的开顶式气室（OTC）模拟大气CO₂浓度升高的环境,在田间条件下设置自然大气CO₂浓度（CK）、OTC对照（OTC,CO₂浓度同CK）与CO₂浓度升高（OTC+CO₂,OTC系统自动控制CO₂浓度700 μmol/mol）3种处理。研究了旱区覆膜高产栽培春玉米播前（V0）、六叶期（V6）、九叶期（V9）、吐丝期（R1）、乳熟期（R3）、蜡熟期（R5）及完熟期（R6）土壤呼吸速率对大气CO₂浓度升高的响应特征,以及大气CO₂浓度升高对土壤呼吸速率的温度与水分效应的影响。研究发现,OTC+CO₂处理土壤呼吸速率,与CK相比,在R3和R5期分别增加43%、104%（P<0.05）,与OTC相比,R3和R5期分别提升了63%、109%（P<0.05）;OTC处理与CK相比,在整个生育期对土壤呼吸影响不显著;3种处理条件下,土壤温度和水分随生育期变化趋势基本一致,土壤呼吸速率与土壤温度和水分分别呈指数相关和抛物线型相关;结果表明：大气CO₂浓度升高对土壤呼吸的影响因生育期而异,土壤温度和土壤水分是影响旱地农田土壤呼吸的重要因素,CO₂浓度升高会使土壤呼吸温度效应值（Q₁₀）降低,土壤呼吸对土壤水分响应的阈值提高。     

Examination of the method for measuring soil respiration in cultivated land: Effect of carbon dioxide concentration on soil respiration

An acceleration of soil respiration with decreasing CO₂ concentration was suggested in the field measurements. The result supporrs that obtained in laboratory experiments in our previous study. The CO₂ concentrations in a chamber of the alkali absorption method (the AA-method) were about 150–250 parts/10⁶ lower than that in the atmosphere (about 350 parts/10⁶), while those observed in the open-flow IRGA method (the OF-method) were nearly equal to the soil surface CO₂ levels. The AA-method at such low CO₂ levels in the chamber appears to overestimate the soil respiration. Our results showed that the rates obtained by the AA-method were about twice as large as those by the OF-method in field and laboratory measurements. This finding has important consequences with respect to the validity of the existing data obtained by the AA-method and the estimation of changes in the terrestrial carbon flow with elevated CO₂     

Estimating respiration of roots in soil: Interactions with soil CO2, soil temperature and soil water content

Little information is available on the variability of the dynamics of the actual and observed root respiration rate in relation to abiotic factors. In this study, we describe I) interactions between soil CO₂ concentration, temperature, soil water content and root respiration, and II) the effect of short-term fluctuations of these three environmental factors on the relation between actual and observed root respiration rates. We designed an automated, open, gas-exchange system that allows continuous measurements on 12 chambers with intact roots in soil. By using three distinct chamber designs with each a different path for the air flow, we were able to measure root respiration over a 50-fold range of soil CO₂ concentrations (400 to 25000 ppm) and to separate the effect of irrigation on observed vs. actual root respiration rate. All respiration measurements were made on one-year-old citrus seedlings in sterilized sandy soil with minimal organic material.Root respiration was strongly affected by diurnal fluctuations in temperature (Q₁₀ = 2), which agrees well with the literature. In contrast to earlier findings for Douglas-fir (Qi et al., 1994), root respiration rates of citrus were not affected by soil CO₂ concentrations (400 to 25000 ppm CO₂; pH around 6). Soil CO₂ was strongly affected by soil water content but not by respiration measurements, unless the air flow for root respiration measurements was directed through the soil. The latter method of measuring root respiration reduced soil CO₂ concentration to that of incoming air. Irrigation caused a temporary reduction in CO₂ diffusion, decreasing the observed respiration rates obtained by techniques that depended on diffusion. This apparent drop in respiration rate did not occur if the air flow was directed through the soil. Our dynamic data are used to indicate the optimal method of measuring root respiration in soil, in relation to the objectives and limitations of the experimental conditions.     

Evaluation of soil respiration and soil CO2 concentration in a lowland moist forest in Panama

Soil gas exchange was investigated in a lowland moist forest in Panama. Soil water table level and soil redox potentials indicate that the soils are not waterlogged. Substantial microspatial variation exists for soil respiration and soil CO₂ concentration. During the rainy season, soil CO₂ at 40 cm below the surface accumulates to 2.3%–4.6% and is correlated with rainfall during the previous two weeks. Temporal changes in soil CO₂ are rapid, large and share similar trends between sampling points. Possible effects of soil CO₂ changes on plant growth or phenology are discussed.