青藏高原东缘亚高山针叶林人工恢复过程中的土壤呼吸特征

采用动态密闭气室红外CO₂分析法,对青藏高原东缘云杉人工林的土壤呼吸进行连续定位测定,并用挖壕沟法区分土壤自养呼吸和异养呼吸.结果表明:4种云杉林的土壤呼吸速率与土壤5 cm层温度有显著的正指数关系,与土壤含水量的相关性不显著.4种云杉林土壤呼吸年通量在792.08～1070.20 g C·m^-2·a^-1,大小依次为：天然云杉林＞22年生云杉人工林＞65年生云杉人工林＞35年生云杉人工林,随着人工林的恢复呈先降低后升高的趋势.在森林恢复过程中,人工云杉土壤自养和异养呼吸年通量均先减少后增加, 在253.36～357.05 g C·m^-2·a^-1和538.69～703.82 g C·m^-2·a^-1范围变化.22年生、35年生、65年生云杉人工林和天然云杉林非生长季 （2007-11-2008-03）和生长季（2008-04-2008-10）的Q₁₀值分别为：4.59、6.54、4.77、3.18和4.17、4.66、3.11、2.74.除22年生云杉人工林,Q₁₀值随云杉林的恢复更新而逐渐降低, 且非生长季节Q₁₀值均明显高于生长季节.     

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。     

小兴安岭4种原始红松林群落类型生长季土壤呼吸特征

为阐明小兴安岭地带性植被原始红松林土壤呼吸各组分的碳排放速率及其对土壤水热变化的响应规律,采用挖壕法和红外气体分析法测定土壤表面CO2通量(Rs),确定4种原始红松林群落类型生长季的土壤总呼吸(Rt)中土壤微生物呼吸(Rh),根系呼吸(Rr)和凋落物呼吸(Rl)的贡献量动态变化及其影响因子。结果表明:生长季内,4种原始红松林群落类型的Rt、Rh、Rr具有明显的季节性变化,7-9月份较高,6月份和10月份较低。Rh对Rt的贡献量最高,平均在58.8%;Rr对Rt的贡献量次之,平均为26.5%;Rl对Rt的贡献量相对较小,平均为12.5%。生长季土壤呼吸速率与5cm深土壤温度相关性极显著(P0.01)。Rr和Rh的Q10值分别为2.88和2.23。表明根呼吸对土壤温度的敏感性高于微生物呼吸。生长季平均土壤呼吸速率的依次为:椴树红松林(6.38μmol·m-·2s-1)云冷杉红松林(6.32μmol·m-·2s-1)枫桦红松林(5.95μmol·m-·2s-1)蒙古栎红松林(2.86μmol·m-·2s-1)。4种原始叶红松林群落类型间的Rh和Rr也存在一定差异。     

中国森林土壤呼吸模式

通过收集国内62个森林样地的土壤呼吸及相关因子数据,分析中国森林土壤呼吸模式.结果表明,中国森林土壤呼吸年通量与年均气温、年均降水量、年凋落物量和年地上净生产力均呈显著的线性正相关,土壤呼吸的Q10则与年均气温和年均降水量均呈显著的负相关.根系呼吸、枯枝落叶层呼吸与土壤呼吸间均呈显著线性正相关;土壤异养呼吸和枯枝落叶层呼吸与年凋落物量呈显著正相关;土壤异养呼吸与自养呼吸间呈显著的线性正相关.根系呼吸、枯枝落叶层呼吸、矿质土壤呼吸占土壤呼吸的比例均值分别为34.7%、20.2%和50.2%.矿质土壤呼吸所占比例与气温和降水量呈显著负相关,而异养呼吸所占比例则与降水量呈显著负相关.根系呼吸所占比例与根系呼吸之间呈渐近线关系(渐近值为45.9%).     

土壤-玉米系统中土壤呼吸强度及各组分贡献

用特殊设计的气体采集箱法对玉米生长期间潮土呼吸强度进行了测定。结果表明,施用150kgNhm^-2的裸地土壤CO2累积排放量是294g C m^-2,约为种植玉米土壤的一半。用根去除法测得的玉米对土壤呼吸的贡献率,苗期小于20％,拔节到收获期波动在30％-70％之间,全生长期平均为46％。玉米生长期间因土壤有机碳分解而释放出的CO2总量为2．94MgChm^-2,大约是0—40cm土层中土壤有机碳总储存量的8％,因此需要输入7．35Mghm^-2的碳含量40％的作物残留物才能平衡土壤中有机碳的损失,约为玉米收获时残留于土壤中根量的一倍,但与残留根量及玉米生长期间根系分泌到土壤的有机物量的总和相当,因此土壤中有机碳总体处于平衡状态。在玉米生长期间,施用氮肥可使土壤CO2排放量降低10％。土壤排放CO2主要受土壤温度的影响,温度效应Q10为1．90-2．88。     

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。     

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。     

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％。     

东北东部森林生态系统土壤呼吸组分的分离量化

对森林生态系统的土壤呼吸组分进行分离和量化,确定不同组分CO2释放速率的控制因子,是估测局域和区域森林生态系统碳平衡研究中必不可少的内容。采用挖壕法和红外气体分析法测定无根和有根样地的土壤表面CO2通量(RS),确定东北东部6种典型森林生态系统RS中异养呼吸(RH)和根系自养呼吸(RA)的贡献量及其影响因子。具体研究目标包括:(1)量化各种生态系统的RH及其与主要环境影响因子的关系;(2)量化各种生态系统RS中根系呼吸贡献率(RC)的季节动态;(3)比较6种森林生态系统RH和RA的年通量。土壤温度、土壤含水量及其交互作用显著地影响森林生态系统的RH(R2=0.465~0.788),但其影响程度因森林生态系统类型而异。硬阔叶林和落叶松人工林的RH主要受土壤温度控制,其他生态系统RH受土壤温度和含水量的联合影响。各个森林生态系统类型的RC变化范围依次为:硬阔叶林32.40%~51.44%;杨桦林39.72%~46.65%;杂木林17.94%~47.74%;蒙古栎林34.31%~37.36%;红松人工林33.78%~37.02%;落叶松人工林14.39%~35.75%。每个生态系统类型RH年通量都显著高于RA年通量,其变化范围分别为337~540 gC.m-2.a-1和88~331 gC.m-2.a-1。不同生态系统间的RH和RA也存在着显著性差异。     

亚热带毛竹人工林土壤呼吸组分动态变化及其影响因素

利用Li-8100土壤碳通量测量系统,研究了2013年4月—2014年3月浙江临安市毛竹人工林土壤呼吸、异养呼吸和自养呼吸速率的动态变化规律.结果表明：毛竹人工林土壤总呼吸速率、异养呼吸速率和自养呼吸速率均呈现出明显的季节变化特征,最高值出现在7月,最低值出现在1月,年平均值分别为2.93、1.92和1.01 μmol CO₂·m^-2·s^-1.毛竹林土壤总呼吸、异养呼吸和自养呼吸年累积CO₂排放量分别为37.25、24.61和12.64 t CO₂·hm^-2·a^-1.土壤呼吸各组分均与土壤5 cm温度呈显著指数相关,土壤总呼吸、异养呼吸和自养呼吸的温度敏感系数Q₁₀值分别为2.05、1.95和2.34.土壤总呼吸速率、异养呼吸速率与土壤水溶性有机碳(WSOC)含量均呈显著相关,而自养呼吸与WSOC无显著相关性;土壤呼吸各组分与土壤含水〖JP2〗量以及微生物生物量碳均无显著相关性.土壤温度是影响毛竹人工林土壤呼吸及其组分季节变化的主要驱动因子,土壤WSOC含量是影响土壤总呼吸和异养呼吸的重要环境因子.     

Soil and total ecosystem respiration in agricultural fields: effect of soil and crop type

A study was made of the effect of soil and crop type on the soil and total ecosystem respiration rates in agricultural soils in southern Finland. The main interest was to compare the soil respiration rates in peat and two different mineral soils growing barley, grass and potato. Respiration measurements were conducted during the growing season with (1) a closed-dynamic ecosystem respiration chamber, in which combined plant and soil respiration was measured and (2) a closed-dynamic soil respiration chamber which measured only the soil and root-derived respiration. A semi-empirical model including separate functions for the soil and plant respiration components was used for the total ecosystem respiration (TER), and the resulting soil respiration parameters for different soil and crop types were compared. Both methods showed that the soil respiration in the peat soil was 2–3 times as high as that in the mineral soils, varying from 0.11 to 0.36 mg (CO₂) m^–2 s^–1 in the peat soil and from 0.02 to 0.17 mg (CO₂) m^–2 s^–1 in the mineral soils. The difference between the soil types was mainly attributed to the soil organic C content, which in the uppermost 20 cm of the peat soil was 24 kg m^–2, being about 4 times as high as that in the mineral soils. Depending on the measurement method, the soil respiration in the sandy soil was slightly higher than or similar to that in the clay soil. In each soil type, the soil respiration was highest on the grass plots. Higher soil respiration parameter values (R_s0, describing the soil respiration at a soil temperature of 10°C, and obtained by modelling) were found on the barley than on the potato plots. The difference was explained by the different cultivation history of the plots, as the potato plots had lain fallow during the preceding summer. The total ecosystem respiration followed the seasonal evolution in the leaf area and measured photosynthetic flux rates. The 2–3-fold peat soil respiration term as compared to mineral soil indicates that the cultivated peat soil ecosystem is a strong net CO₂ source.     

Rhizospheric and heterotrophic components of soil respiration in six Chinese temperate forests

Partitioning soil respiration (R_S) into heterotrophic (R_H) and rhizospheric (R_R) components is an important step for understanding and modeling carbon cycling in forest ecosystems, but few studies on R_R and R_H exist in Chinese temperate forests. In this study, we used a trenching plot approach to partition R_S in six temperate forests in northeastern China. Our specific objectives were to (1) examine seasonal patterns of soil surface CO₂ fluxes from trenched (R_T) and untrenched plots (R_UT) of these forests; (2) quantify annual fluxes of R_S components and their relative contributions in the forest ecosystems; and (3) examine effects of plot trenching on measurements of R_S and related environmental factors. The R_T maximized in early growing season, but the difference between R_UT and R_T peaked in later summer. The annual fluxes of R_H and R_R varied with forest types. The estimated values of R_H for the Korean pine (Pinus koraiensis Sieb. et Zucc.), Dahurian larch (Larix gmelinii Rupr.), aspen‐birch (Populous davidiana Dode and Betula platyphylla Suk.), hardwood (Fraxinus mandshurica Rupr., Juglans mandshurica Maxim. and Phellodendron amurense Rupr.), Mongolian oak (Quercus mongolica Fisch.) and mixed deciduous (no dominant tree species) forests averaged 89, 196, 187, 245, 261 and 301 g C m⁻² yr⁻¹, respectively; those of R_R averaged 424, 209, 628, 538, 524 and 483 g C m⁻² yr⁻¹, correspondingly; calculated contribution of R_R to R_S (RC) varied from 52% in the larch forest to 83% in the pine forest. The annual flux of R_R was strongly correlated to biomass of roots <0.5 cm in diameter, while that of R_H was weakly correlated to soil organic carbon concentration at A horizon. We concluded that vegetation type and associated carbon metabolisms of temperate forests should be considered in assessing and modeling R_S components. The significant impacts of changed soil physical environments and substrate availability by plot trenching should be appropriately tackled in analyzing and interpreting measurements of R_S components.     

西双版纳地区稻田CO2排放通量

采用静态暗箱-气相色谱法对云南西双版纳地区单季稻田CO2排放及氮肥、水热因子对CO2排放的影响进行田间原位观测研究.试验设3个氮肥水平处理:N0(0 kg N hm-2)、N150(150 kg N hm-2)和N300(300 kg N hm-2).结果表明,受一天温度变化的影响,西双版纳地区稻田生态系统呼吸日变化为单峰型,其最大值出现在11:00～13:00之间,最小值出现在凌晨.稻田土壤呼吸呈明显的季节变化趋势,土壤呼吸平均速率为水稻收获后休闲季节>种植前休闲季节>水稻生长季节,差异达到1%显著水平.不同季节影响土壤呼吸的环境因子不同.土壤水分含量低于34%时,土壤呼吸速率与土壤含水量呈正相关,达5%显著水平;地面淹水时,土壤呼吸速率与淹水深度呈1%极显著负相关;水分含量高于38%时,土壤呼吸速率与温度呈极显著指数相关.长期考虑(整个生长季节),氮肥的施用对稻田土壤呼吸和生态系统呼吸无影响;N300处理抑制植株呼吸作用,单位生物量呼吸速率下降.氮肥的施用对土壤呼吸有短期影响,氮肥用量增加,土壤呼吸速率增加.计算得出N0、N150和N300处理年土壤呼吸量分别为6.27、6.31 t C hm-2 a-1和5.89 t C hm-2 a-1;年净固定大气中CO2-C分别为1.41、2.22 t C hm-2 a-1和1 11 t C hm-2 a-1,表明西双版纳稻田生态系统是碳汇.     

Root respiration rate before and just after clear-felling in a mature,deciduous, broad-leaved forest

Soil respiration was measured throughout the year (June 1992 to May 1993) in a mature, deciduous, broad-leaved forest and an adjacent, clear-felled stand which was made in November 1991, in Hiroshima Prefecture, west Japan. The same soil temperature and soil moisture content as those in the forest stand were maintained in two frame boxes covered with sheets of white netting in the clear-felled stand to observe soil respiration. A herbicide was applied to the cut end of all stumps in one of the two frame boxes in order to kill the root system. There was no significant difference in the aboveground biomass and soil environmental conditions between the forest and the frame boxes in the clear-felled stands. The difference in soil respiration rate between the forest and the frame box, in which the root system was killed by the herbicide, was considered to be due largely to the contribution of root respiration. Taking into consideration CO₂ evolution due to the decomposition of roots killed and the change in A₀ layer respiration rate after clear-felling, the proportion of root respiration to the total soil respiration before clear-felling was estimated to be 51% annually, which coincides closely with those values estimated previously in mature forests by other methods. The difference in the soil respiration rate between the two frame boxes (one with killed roots and the other with undisturbed roots) suggested that the annual root respiration rate just after clear-felling dropped to about two-thirds (70%) of that before clear-felling.     

湖南会同林区毛竹林地的土壤呼吸

采用CID-301PS光合分析仪(配带土壤呼吸室),对湖南会同林区毛竹林地土壤呼吸进行测定,结果表明,毛竹林地土壤总呼吸速率、异养呼吸速率、自养呼吸速率及凋落物呼吸速率的年平均值分别为2.13、1.44、0.69μmolCO2·m-2·s-1和0.31μmolCO2·m-2·s-1,并呈现明显的季节变化规律和日变化规律,季节变化曲线呈单峰型,表现为1～7月份随着气温、地温的升高呈上升的趋势,在8月达年呼吸速率的最大值,分别达4.95、3.01、1.94μmolCO2·m-2·s-1和0.80 μmolCO2·m-2·s-1,此后随温度的降低而呈逐渐递减的趋势,直到翌年的1月份或2月份,分别为0.76、0.70、 0.06μmolCO2·m-2·s-1 和 0.05μmolCO2·m-2·s-1.日变化曲线图表现为单峰形态,一般也是随着温度的升高而加大,随着温度的降低而减小.6:00～14:00,随着土壤温度的升高而增加,一般在16:00～18:00出现最高峰,此后,一直递减,直到次日4:00～8:00.由此计算出毛竹林地土壤年释放CO2量为33.94 t·hm-2·a-1,其中,林地异养呼吸、自养呼吸和凋落物呼吸分别占总呼吸的59.5%、28.3%和12.2%.     

南方型杨树人工林土壤呼吸及其组分分析

采用开沟隔离法,利用LI-8100型土壤呼吸测定系统,对15年生的南方型杨树(Populus deltoides)人工林土壤呼吸进行了研究,并试图区分根系呼吸和土壤微生物呼吸。结果表明,开沟隔离处理后的10个月内,由于土壤中被截断根系具有自养呼吸和分解作用,土壤呼吸中的根系呼吸与微生物呼吸尚难以区分。尽管如此,研究表明15年生杨树人工林的土壤总呼吸通量为9.74 tC.hm-.2a-1,其中,枯枝落叶等土壤表层凋落物分解所释放的碳通量是2.63 tC.hm-.2a-1,占总量的27.0%;林木根系呼吸与土壤微生物呼吸通量的和为7.11 tC.hm-.2a-1,占总量的73.0%。土壤各组分呼吸速率与10 cm深处的土壤温度之间存在着显著的指数函数关系。不同直径的杨树根系被截断后的活力变化有所不同,根系越粗,存活时间越长。     

锐齿栎林年龄序列土壤呼吸组分特征研究

林龄作为影响土壤呼吸的因素已是碳循环关注的热点问题之一,且林龄在模拟演替及长期碳动态的监测过程中发挥重要作用。该研究采用Li-Co-r8100土壤呼吸仪,研究林龄对土壤呼吸通量及其组分的影响。结果表明：锐齿栎林年龄序列(40 a,80 a,>160 a)及不同组分的土壤呼吸速率都表现出明显的单峰型季节动态,且与5 cm土壤温度呈显著指数相关。这可能是由于温度变化影响土壤生物活性引起的,土壤温度与土壤呼吸关系的指数方程可以解释80％以上的土壤呼吸变化。土壤呼吸及其不同组分在林龄间均无明显差异,土壤呼吸对温度的敏感性在锐齿栎林年龄序列及各组分间也无显著差异,这可能与林龄间土壤特性、森林生产力、微环境条件等相差不大有关。加倍凋落物的累计土壤呼吸通量显著( P<0.05)高于对照、断根和去除凋落物处理的累积呼吸量,说明增加凋落物输入为土壤提供了更丰富的养分,改善了样地微环境,有利于激发土壤微生物活性。锐齿栎林累计土壤呼吸通量与土壤有机碳( SOC)、细根生物量( FR)和微生物呼吸( MR)也显著相关,表明该地区土壤特性以及地下新陈代谢能很好地解释锐齿栎林土壤呼吸格局。     

Does the different photosynthetic pathway of plants affect soil respiration in a subtropical wetland?

Plants with different photosynthetic pathways could produce different amounts and types of root exudates and debris which may affect soil respiration rates. Therefore, wetland vegetation succession between plants with different photosynthetic pathways may ultimately influence the wetland carbon budget. The middle and lower reaches of the Yangtze River has the largest floodplain wetland group in China. Tian'e Zhou wetland reserve (29°48'N, 112°33′E) is located in Shishou city, Hubei province and covers about 77.5 square kilometers. Hemathria altissima (C4) was found gradually being replaced by Carex argyi (C3) for several years in this place. An in situ experiment was conducted in Tian'e Zhou wetland to determine the change of soil respiration as the succession proceeds. Soil respiration, substrate‐induced respiration, and bacterial respiration of the C4 species was greater than those of the C3 species, but below‐ground biomass and fungal respiration of the C4 species was less than that of the C3 species. There were no significant differences in above‐ground biomass between the two species. Due to the higher photosynthesis capability, higher soil respiration and lower total plant biomass, we inferred that the C4 species, H. altissima, may transport more photosynthate below‐ground as a substrate for respiration. The photosynthetic pathway of plants might therefore play an important role in regulating soil respiration. As C. argyi replaces H. altissima, the larger plant biomass and lower soil respiration would indicate that the wetland in this area could fix more carbon in the soil than before.     

Effects of experimental drought on soil respiration and radiocarbon efflux from a temperate forest soil

Soil moisture affects microbial decay of SOM and rhizosphere respiration (RR) in temperate forest soils, but isolating the response of soil respiration (SR) to summer drought and subsequent wetting is difficult because moisture changes are often confounded with temperature variation. We distinguished between temperature and moisture effects by simulation of prolonged soil droughts in a mixed deciduous forest at the Harvard Forest, Massachusetts. Roofs constructed over triplicate 5 × 5 m² plots excluded throughfall water during the summers of 2001 (168 mm) and 2002 (344 mm), while adjacent control plots received ambient throughfall and the same natural temperature regime. In 2003, throughfall was not excluded to assess the response of SR under natural weather conditions after two prolonged summer droughts. Throughfall exclusion significantly decreased mean SR rate by 53 mg C m^?2 h^?1 over 84 days in 2001, and by 68 mg C m^?2 h^?1 over 126 days in 2002, representing 10–30% of annual SR in this forest and 35–75% of annual net ecosystem exchange (NEE) of C. The differences in SR were best explained by differences in gravimetric water content in the Oi horizon (r²=0.69) and the Oe/Oa horizon (r²=0.60). Volumetric water content of the A horizon was not significantly affected by throughfall exclusion. The radiocarbon signature of soil CO₂ efflux and of CO₂ respired during incubations of O horizon, A horizon and living roots allowed partitioning of SR into contributions from young C substrate (including RR) and from decomposition of older SOM. RR (root respiration and microbial respiration of young substrates in the rhizosphere) made up 43–71% of the total C respired in the control plots and 41–80% in the exclusion plots, and tended to increase with drought. An exception to this trend was an interesting increase in CO₂ efflux of radiocarbon‐rich substrates during a period of abundant growth of mushrooms. Our results suggest that prolonged summer droughts decrease primarily heterotrophic respiration in the O horizon, which could cause increases in the storage of soil organic carbon in this forest. However, the C stored during two summers of simulated drought was only partly released as increased respiration during the following summer of natural throughfall. We do not know if this soil C sink during drought is transient or long lasting. In any case, differential decomposition of the O horizon caused by interannual variation of precipitation probably contributes significantly to observed interannual variation of NEE in temperate forests.     

锡林河流域一个放牧草原群落中根系呼吸占土壤总呼吸比例的初步估计

 采取根系生物量梯度上土壤呼吸变化趋势线外推法对锡林河流域一个放牧羊草(Leymus chinensis)群落中根系呼吸占土壤总呼吸的比例进行了估计。结果表明：在测定年度整个生长季的不同月份,该群落中根系呼吸量占土壤呼吸总量的比例在15%～37%之间,平均为24%;根系呼吸所占比例较高的月份与根系生长的高峰期基本一致,均出现在6月中旬和8月上旬;上述结果与国外同类研究结果相比,具有很好的一致性。