Stand age-related effects on soil respiration in a first rotation Sitka spruce chronosequence in central Ireland

The effect of stand age on soil respiration and its components was studied in a first rotation Sitka spruce chronosequence composed of 10‐, 15‐, 31‐, and 47‐year‐old stands established on wet mineral gley in central Ireland. For each stand age, three forest stands with similar characteristics of soil type and site preparation were used. There were no significant differences in total soil respiration among sites of the same age, except for the case of a 15‐year‐old stand that had lower soil respiration rates due to its higher productivity. Soil respiration initially decreased with stand age, but levelled out in the older stands. The youngest stands had significantly higher respiration rates than more mature sites. Annual soil respiration rates were modelled by means of temperature‐derived functions. The average Q ₁₀ value obtained treating all the stands together was 3.8. Annual soil respiration rates were 991, 686, 556, and 564 g C m^?2 for the 10‐, 15‐, 31‐, and 47‐year‐old stands, respectively. We used the trenching approach to separate soil respiration components. Heterotrophic respiration paralleled soil organic carbon dynamics over the chronosequence, decreasing with stand age to slightly increase in the oldest stand as a result of accumulated aboveground litter and root inputs. Root respiration showed a decreasing trend with stand age, which was explained by a decrease in fine root biomass over the chronosequence, but not by nitrogen concentration of fine roots. The decrease in the relative contribution of autotrophic respiration to total soil CO₂ efflux from 59.3% in the youngest stand to 49.7% in the oldest stand was explained by the higher activity of the root system in younger stands. Our results show that stand age should be considered if simple temperature‐based models to predict annual soil respiration in afforestation sites are to be used.     

Soil respiration in a Mediterranean oak forest at different developmental stages after coppicing

To assess the variation of soil respiration at different forest stages we measured it in a coppiced oak (Quercus cerris L.) chronosequence in central Italy during two campaigns, spanning 2 successive years, in four stands at different stages of the rotation: 1 year (S1), 5 years (S5), 10 years (S10) and 17 years (S17) after coppicing. The contribution of the different components of soil respiration flux (aboveground litter, belowground decomposition soil organic matter and root respiration) was estimated by a paired comparison of manipulative experiments between the recently coppiced stand (S1) and mature stand (S17). Ninety percent of soil respiration values were between 1.7 and 7.8 μmol m^?2 s^?1, with an overall mean (±SD) of 4.0±2.7 μmol m^?2 s^?1. Spatial variation of soil respiration was high (CV=44.9%), with a mean range (i.e. patch size) of 4.8±2.7 m, as estimated from a semivariance analysis. In the absence of limitation by soil moisture, soil respiration was related to soil temperature with the exponential Q₁₀ model (average Q₁₀=2.25). During summer, soil moisture constrained soil respiration and masked its dependence on soil temperature. Soil respiration declined over the years after coppicing. Assuming a linear decline with stand age, we estimated a reduction of 24% over a 20‐year‐rotation cycle. The response of soil respiration to temperature also changed with age of the stands: the Q₁₀ was estimated to decrease from 2.90 in S1 to 2.42 in S17, suggesting that different components or processes may be involved at different developmental stages. The contribution of heterotrophic respiration to total soil respiration flux was relatively larger in the young S1 stand than in the mature S17 stand.     

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.     

Seasonal changes in the contribution of root respiration to total soil respiration in a cool-temperate deciduous forest

A trenching method was used to determine the contribution of root respiration to soil respiration. Soil respiration rates in a trenched plot (R _trench) and in a control plot (R _control) were measured from May 2000 to September 2001 by using an open-flow gas exchange system with an infrared gas analyser. The decomposition rate of dead roots (R _D) was estimated by using a root-bag method to correct the soil respiration measured from the trenched plots for the additional decaying root biomass. The soil respiration rates in the control plot increased from May (240–320 mg CO₂ m^–2 h^–1) to August (840–1150 mg CO₂ m^–2 h^–1) and then decreased during autumn (200–650 mg CO₂ m^–2 h^–1). The soil respiration rates in the trenched plot showed a similar pattern of seasonal change, but the rates were lower than in the control plot except during the 2 months following the trenching. Root respiration rate (R _r) and heterotrophic respiration rate (R _h) were estimated from R _control, R _trench, and R _D. We estimated that the contribution of R _r to total soil respiration in the growing season ranged from 27 to 71%. There was a significant relationship between R _h and soil temperature, whereas R _r had no significant correlation with soil temperature. The results suggest that the factors controlling the seasonal change of respiration differ between the two components of soil respiration, R _r and R _h.     

荒漠草原4种典型植物枯落物分解过程中土壤呼吸对短期氮、水变化的响应

土壤呼吸作为陆地生态系统碳循环的重要组成部分,对研究干旱半干旱区荒漠草原碳平衡具有重要意义。选取荒漠草原4种典型植物枯落物进行裂区实验,设置氮、水添加实验处理,探讨不同的枯落物地表,短期氮、水处理对荒漠草原土壤呼吸的影响。结果表明,土壤呼吸日动态呈单峰曲线,最大值出现在10:00—12:00。相同处理间不同枯落物地表和相同枯落物地表不同处理间土壤呼吸在白天和夜间均有差异(P<0.05)。枯落物对土壤呼吸贡献表明,短期不做任何处理的枯落物对土壤呼吸的贡献最大,贡献率高达68%—89%。多因素方差分析显示,氮及氮和水交互作用对土壤呼吸的影响显著。呼吸在降水处理间存在显著差异(P<0.05),表现为减雨(P3)>增雨(P2)>正常(P1);呼吸在氮素处理间存在极显著差异(P<0.001),表现为添氮(N1)>不添氮(N0)。土壤呼吸与土壤温度、土壤湿度拟合发现,短期的氮、水处理下土壤温度与土壤呼吸显著相关(P<0.05),可解释呼吸变化的50.3%—69.9%;土壤湿度对呼吸影响不显著(P>0.05),温度、湿度的交互作用对土壤呼吸的影响显著(...     

Main determinants of forest soil respiration along an elevation/temperature gradient in the Italian Alps

The main determinants of soil respiration were investigated in 11 forest types distributed along an altitudinal and thermal gradient in the southern Italian Alps (altitudinal range 1520 m, range in mean annual temperature 7.8°C). Soil respiration, soil carbon content and principal stand characteristics were measured with standardized methods. Soil CO₂ fluxes were measured at each site every 15–20 days with a closed dynamic system (LI‐COR 6400) using soil collars from spring 2000 to spring 2002. At the same time, soil temperature at a depth of 10 cm and soil water content (m³ m^?3) were measured at each collar. Soil samples were collected to a depth of 30 cm and stones, root content and bulk density were determined in order to obtain reliable estimates of carbon content per unit area (kg C m^?2). Soil respiration and temperature data were fitted with a simple logistic model separately for each site, so that base respiration rates and mean annual soil respiration were estimated. Then the same regression model was applied to all sites simultaneously, with each model parameter being expressed as a linear function of site variables. The general model explained about 86% of the intersite variability of soil respiration. In particular, soil mean annual temperature explained the most of the variance of the model (0.41), followed by soil temperature interquartlile range (0.24), soil carbon content (0.16) and soil water content (0.05).     

Annual variation in soil respiration and its components in a coppice oak forest in Central Italy

In order to investigate the annual variation of soil respiration and its components in relation to seasonal changes in soil temperature and soil moisture in a Mediterranean mixed oak forest ecosystem, we set up a series of experimental treatments in May 1999 where litter (no litter), roots (no roots, by trenching) or both were excluded from plots of 4 m². Subsequently, we measured soil respiration, soil temperature and soil moisture in each plot over a year after the forest was coppiced. The treatments did not significantly affect soil temperature or soil moisture measured over 0–10 cm depth. Soil respiration varied markedly during the year with high rates in spring and autumn and low rates in summer, coinciding with summer drought, and in winter, with the lowest temperatures. Very high respiration rates, however, were observed during the summer immediately after rainfall events. The mean annual rate of soil respiration was 2.9 µ mol m^?2 s^?1, ranging from 1.35 to 7.03 µmol m^?2 s^?1. Soil respiration was highly correlated with temperature during winter and during spring and autumn whenever volumetric soil water content was above 20%. Below this threshold value, there was no correlation between soil respiration and soil temperature, but soil moisture was a good predictor of soil respiration. A simple empirical model that predicted soil respiration during the year, using both soil temperature and soil moisture accounted for more than 91% of the observed annual variation in soil respiration. All the components of soil respiration followed a similar seasonal trend and were affected by summer drought. The Q₁₀ value for soil respiration was 2.32, which is in agreement with other studies in forest ecosystems. However, we found a Q₁₀ value for root respiration of 2.20, which is lower than recent values reported for forest sites. The fact that the seasonal variation in root growth with temperature in Mediterranean ecosystems differs from that in temperate regions may explain this difference. In temperate regions, increases in size of root populations during the growing season, coinciding with high temperatures, may yield higher apparent Q₁₀ values than in Mediterranean regions where root growth is suppressed by summer drought. The decomposition of organic matter and belowground litter were the major components of soil respiration, accounting for almost 55% of the total soil respiration flux. This proportion is higher than has been reported for mature boreal and temperate forest and is probably the result of a short‐term C loss following recent logging at the site. The relationship proposed for soil respiration with soil temperature and soil moisture is useful for understanding and predicting potential changes in Mediterranean forest ecosystems in response to forest management and climate change.     

模拟氮沉降对长江滩地杨树林土壤呼吸温度敏感性的影响

研究氮沉降量增加对土壤呼吸温度敏感性的影响,对于研究土壤呼吸在气候变化中的作用有重要意义。以长江中下游滩地杨树人工林为对象,通过定位模拟氮沉降实验的方法,研究了滩地杨树人工林生态系统土壤呼吸的变化特征和土壤呼吸各组分的温度敏感性对几种氮沉降量浓度的短期响应。结果表明:(1)各处理土壤总呼吸、土壤微生物呼吸、根系呼吸与各层次土壤温度均呈显著正相关关系,和5cm层土壤温度相关性最大。5cm层土壤温度可以解释土壤总呼吸、土壤微生物呼吸和根系呼吸季节变化的比例分别为50.5%—71.0%、51.5%—73.9%、35.7%—63.2%;(2)对照组(CK,0g N m-2a-1)土壤总呼吸、土壤微生物呼吸与根呼吸的Q10值分别为2.54、2.72和1.94;(3)在各氮添加水平中,中氮水平(MN,10g N m-2a-1)促进了土壤总呼吸、土壤微生物呼吸和植物根呼吸的温度敏感性。高氮水平(HN,20g N m-2a-1)都降低了土壤总呼吸、土壤微生物呼吸和植物根呼吸的温度敏感性,低氮水平(LN,5g N m-2a-1)降低了土壤总呼吸和土壤微生物呼吸的温度敏感性,促进了根呼吸的敏感性。     

Site and temporal variation of soil respiration in European beech, Norway spruce, and Scots pine forests

Global warming and changes in rainfall amount and distribution may affect soil respiration as a major carbon flux between the biosphere and the atmosphere. The objectives of this study were to investigate the site to site and interannual variation in soil respiration of six temperate forest sites. Soil respiration was measured using closed chambers over 2 years under mature beech, spruce and pine stands at both Solling and Unterlüß, Germany, which have distinct climates and soils. Cumulative annual CO₂ fluxes varied from 4.9 to 5.4 Mg C ha^?1 yr^?1 at Solling with silty soils and from 4.0 to 5.9 Mg C ha^?1 yr^?1 at Unterlüß with sandy soils. With one exception soil respiration rates were not significantly different among the six forest sites (site to site variation) and between the years within the same forest site (interannual variation). Only the respiration rate in the spruce stand at Unterlüß was significant lower than the beech stand at Unterlüß in both years. Soil respiration rates of the sandy sites at Unterlüß were limited by soil moisture during the rather dry and warm summer 1999 while soil respiration at the silty Solling site tended to increase. We found a threshold of ?80 kPa at 10 cm depth below which soil respiration decreased with increasing drought. Subsequent wetting of sandy soils revealed high CO₂ effluxes in the stands at Unterlüß. However, dry periods were infrequent, and our results suggest that temporal variation in soil moisture generally had little effect on annual soil respiration rates. Soil temperature at 5 cm and 10 cm depth explained 83% of the temporal variation in soil respiration using the Arrhenius function. The correlations were weaker using temperature at 0 cm (r² = 0.63) and 2.5 cm depth (r² = 0.81). Mean Q₁₀ values for the range from 5 to 15 °C increased asymptotically with soil depth from 1.87 at 0 cm to 3.46 at 10 cm depth, indicating a large uncertainty in the prediction of the temperature dependency of soil respiration. Comparing the fitted Arrhenius curves for same tree species from Solling and Unterlüß revealed higher soil respiration rates for the stands at Solling than in the respective stands at Unterlüß at the same temperature. A significant positive correlation across all sites between predicted soil respiration rates at 10 °C and total phosphorus content and C‐to‐N ratio of the upper mineral soil indicate a possible effect of nutrients on soil respiration.     

武夷山不同林龄甜槠林土壤呼吸特征及影响因素

为揭示中亚热带常绿阔叶林群落优势种一甜槠天然林不同林龄林下土壤呼吸(Soil respiration,RS)差异及影响因素,采用LI-8100开路式土壤碳通量系统对武夷山自然保护区不同林龄(18、36、54、72 a)天然甜槠林进行了1年的野外原位测定。结果表明:(1)不同林龄甜槠林RS季节动态呈现明显的单峰趋势,林龄对冬季RS影响并不显著(P>0.05),秋季18 a甜槠林RS与其他3种林龄差异显著(P<0.05),林龄对土壤含水率的季节变化没有显著影响(P>0.05);(2)不同林龄甜槠林5 cm深土壤温度与RS拟合R2明显高于土壤含水率与RS拟合R2,随着林龄增大,RS温度敏感性指数Q10值呈上升趋势,依次为1.551、1.589、1.640、1.664,且54、72 a甜槠林RS温度敏感性指数Q10值显著高于18、36 a(P<0.05);(3)土壤含水率与5 cm深土壤温度共同解释了RS变异的86%—90.3%;0—60 cm土层根系生物量与5 cm深土壤温度共同解释了RS变异的88.3%—91.8%,由此可见,生物因子与非生物因子双因素拟合可以更好地解释不同林龄RS差异。在对未来森林植被土壤呼吸及碳汇功能进行研究时,应在考虑林龄及季节差异的基础上,加强对生物因子的测定。     

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     

增加降水对干旱河谷区云南松人工林土壤呼吸的影响

2013年5月至2014年6月,对干旱河谷区云南松(Pinus yunnanensis)人工林进行增加降水试验,试验设置对照(CK,0 mm m~(-2)a~(-1))、增水10%(A1,80 mm m~(-2)a~(-1))、增水20%(A2,160 mm m~(-2)a~(-1))和增水30%(A3,240 mm m~(-2)a~(-1))4个处理水平。采用LI-8100开路式土壤碳通量测量系统测定每月土壤呼吸速率。结果表明,4个处理云南松人工林土壤呼吸速率均呈明显的季节变化,7月最高,2月最低。与CK相比,A1年均土壤呼吸速率无显著性差异(P0.05),A2显著增加了12.88%(P0.05),而A3明显减少了17.71%(P0.05)。3个增水处理均提高了土壤呼吸的温度敏感性,减弱了土壤呼吸与土壤湿度的关系。与土壤温度相比,土壤湿度对土壤呼吸的影响相对较小。增水增加了湿季土壤微生物碳、氮含量,干季对微生物碳含量无影响,但明显降低了微生物氮含量。这说明,降水增加对干旱河谷区云南松人工林土壤呼吸的影响是不尽相同的,适当的增水会促进土壤呼吸,而过量的增水会抑制土壤呼吸。     

氮添加和凋落物去除对黔中喀斯特地区柳杉人工林土壤呼吸的影响

凋落物是土壤呼吸的主要碳源,日益增加的大气氮沉降通过改变森林凋落物的输入与分解影响土壤呼吸。为揭示氮沉降及凋落物管理对森林土壤呼吸及其组分的影响,以贵州省国有扎佐林场15年生柳杉人工林为研究对象,设置4个氮添加处理:对照(CK,0 gN m^-2 a^-1)、低氮(LN,15 gN m^-2 a^-1)、中氮(MN,30 gN m^-2 a^-1)和高氮(HN,60 gN m^-2 a^-1),并在每种氮添加处理下设置去除凋落物和保留凋落物两种处理,于2021年3月-2022年2月利用LI-8100测定土壤呼吸速率,并分析氮添加及凋落物处理对土壤呼吸速率影响,确定影响土壤呼吸速率变化的主要因子。结果表明:氮添加和去除凋落物处理没有改变土壤呼吸速率的时间变化,土壤呼吸速率月均最大值出现在7月,月均最小值出现在2月。氮添加对土壤呼吸速率无显著影响(P > 0.05),除CK外,去除凋落物处理会显著降低土壤呼吸速率(P < 0.05)。凋落物对土壤总呼吸速率的贡献率为8.6%-28.5%,且LN处理下凋落物对土壤呼吸速率的贡献率最大。土壤呼吸速率与5 m土壤温度呈显著指数相关(P < 0.01),与5 cm土壤湿度呈显著负线性相关(P < 0.01)。土壤温度解释了土壤呼吸速率变异的58.5%-79.5%,土壤湿度解释了土壤呼吸速率变异的26.4%-39.5%,以土壤温度和湿度构建的双变量模型拟合效果均好于单因子模型,土壤温湿度共同解释土壤呼吸速率变异的59.1%-85.8%。结论表明在大气氮沉降增加的背景下,温度是影响土壤呼吸的主要因素,凋落物管理是调控土壤呼吸的关键过程。     

Contribution of Root Respiration to Total Soil Respiration in a Leymus chinensis （Trin.） Tzvel, Grassland of Northeast China

The loss of carbon through root respiration Is an Important component of grassland carbon budgets. However, few data are available concerning the contribution of root respiration to total soil respiration in grasslands in China. We Investigated seasonal variations of soil respiration rate, root blomaaa, microbial blomaaa C and organic C content of the soil In a semi-arid Leymus chinensis （Trin.） Tzvel. grassland of northeast China during the 2002 growing season （from May to September）. The linear regression relationship between soil respiration rate and root blomaaa was used to determine the contribution of root respiration to total soil respiration. Soil respiration rate ranged from 2.5 to 11.9 g C/m^2 per d with the maximum in late June and minimum In September. The microbial blomaaa C and organic C content of the soil ranged from 0.3 to 1.5 g C/m^2 and from 29 to 34 g C/kg respectively. Root blomaaa had two peaks, In early June （1.80 kg/m^2） and mid-August （1.73 kg/m^2）. Root respiration rate peaked In mid-August （6.26 g C/m^2 per d）, whereas microbial respiration rate peaked In late June （7.43 g C/m^2 per d）. We estimated that the contribution of root respiration to total soil respiration during the growing season ranged from 38% to 76%.     

施肥对油茶园土壤呼吸和异养呼吸及其温度敏感性的影响

油茶是中国南方重要的木本食用油料树种,研究施肥对油茶园土壤呼吸及其温度敏感性的影响,对于估算中国南方典型种植园林温室气体排放及其对气候变化的响应具有重要意义。设置对照(CK)、施肥(OF)、断根(CK-T)和断根施肥(OF-T)4个处理,采用静态箱-气相色谱法,通过多年观测,分析探讨施肥对油茶园土壤呼吸和异养呼吸及其温度敏感性的影响。结果表明:(1)施肥对油茶园土壤呼吸和异养呼吸无显著影响。研究期间,各处理(OF、CK、OF-T、CK-T)土壤CO_2通量依次为(77.91±2.59)、(73.71±0.97)、(66.82±1.02)mg C m~(-2)h~(-1)和(66.84±3.94)mg C m~(-2)h~(-1);(2)各处理土壤呼吸温度敏感性(Q_(10))表现为OF-T(1.96±0.01)CK-T(1.79±0.03)OF(1.77±0.01)CK(1.75±0.03),其中,OF-T处理下Q_(10)显著高于其他3个处理,即施肥显著增加了断根处理土壤呼吸Q_(10);(3)施肥显著增加了土壤表层NH_4~+-N和NO_3~--N含量,Q_(10)与土壤表层NH_4~+-N和NO_3~--N含量表现出显著的正相关关系。     

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。     

Roles of dominant understory Sasa bamboo in carbon and nitrogen dynamics following canopy tree removal in a cool‐temperate forest in northern Japan

To clarify the role of dense understory vegetation in the stand structure, and in carbon (C) and nitrogen (N) dynamics of forest ecosystems with various conditions of overstory trees, we: (i) quantified the above‐ and below‐ground biomasses of understory dwarf bamboo (Sasa senanensis) at the old canopy‐gap area and the closed‐canopy area and compared the stand‐level biomasses of S. senanensis with that of overstory trees; (ii) determined the N leaching, soil respiration rates, fine‐root dynamics, plant area index (PAI) of S. senanensis, and soil temperature and moisture at the tree‐cut patches (cut) and the intact closed‐canopy patches (control). The biomass of S. senanensis in the canopy‐gap area was twice that at the closed‐canopy area. It equated to 12% of total biomass above ground but 41% below ground in the stand. The concentrations of NO₃^? and NH₄⁺ in the soil solution and soil respiration rates did not significantly change between cut and control plots, indicating that gap creation did not affect the C or N dynamics in the soil. Root‐length density and PAI of S. senanensis were significantly greater at the cut plots, suggesting the promotion of S. senanensis growth following tree cutting. The levels of soil temperature and soil moisture were not changed following tree cutting. These results show that S. senanensis is a key component species in this cool‐temperate forest ecosystem and plays significant roles in mitigating the loss of N and C from the soil following tree cutting by increasing its leaf and root biomass and stabilizing the soil environment.     

Seasonal and spatial variability of soil respiration in four Sitka spruce stands

We investigated the causes for the seasonal and spatial variation of soil respiration in a first rotation Sitka spruce chronosequence composed of four age classes (10, 15, 31, and 47 year old) in Central Ireland. The study aimed at identifying easily determinable environmental parameters that explained the variation in soil respiration rates. The variation in temperature and soil water content influenced the seasonal trend observed in the spatial variability of soil respiration. The highest coefficients of variation in soil respiration were observed during autumn drought, while lower coefficients were generally observed during periods with highest soil respiration rates. On average, the sampling strategy of 30 sampling points per stand was adequate to obtain an average rate of soil respiration within 20% of its actual value at the 95% confidence level. Significantly higher soil respiration rates were observed at locations with high accumulation of organic matter and in collars established in close vicinity to tree stems. The organic layer thickness was the only variable that yielded significant regressions for explaining spatial variation in soil respiration in all the stands. Correlation analyses between the studied variables and soil respiration suggested the relative importance of heterotrophic and autotrophic components differed in their annual contribution to total soil respiration at each forest stand. Multiple regression analyses were used to assess the relative importance of primary temporal and spatial controls over soil respiration. Soil temperature and organic layer thickness explained most of the variance of soil respiration for the different sampling periods, while soil water content had a weaker effect as well as a different influence on soil respiration depending on the time of the year. The strong linear correlation between forest floor carbon and soil carbon stock further confirmed organic layer thickness as an integrative factor encompassing the effect of soil carbon pools on soil respiration. Moreover, its inclusion in the multiple regression analyses overrode the influence of both distance and fine root biomass. Overall, a multiple linear regression model driven by easily determinable environmental variables such as soil temperature, organic thickness, soil water content, soil bulk density, and soil organic carbon concentration allowed us to explain 54% of total variance of soil respiration over the different stand ages for the entire year (P < 0.05). Our results show that the adoption of an adequate sampling strategy, and the determination of some key environmental variables may help to explain a large proportion of total variation of soil respiration over the entire rotation length of afforested ecosystems.     

黄土旱塬区免耕玉米田土壤呼吸对降雨的响应

在多年定位试验的基础上,采用LI-8150-16多通道土壤碳通量测量系统对传统耕作和免耕处理下玉米田的土壤呼吸进行了连续观测,以探讨不同耕作措施处理下土壤呼吸对降雨的响应。结果表明:降雨发生瞬间,土壤呼吸受应激反应影响迅速降低,传统耕作和免耕处理下分别较降雨前降低62.9%—92.9%和35.8%—56.9%;降雨后,传统耕作和免耕处理土壤呼吸的降幅范围分别为31.5%—89.2%和15.7%—59.9%;土壤体积含水量接近于18%时,传统耕作下土壤呼吸比免耕下高51.8%,当土壤体积含水量高于30%时,传统耕作下土壤呼吸比免耕处理下低43.0%,表明传统耕作土壤呼吸更易受土壤水分的影响,波动幅度大;传统耕作处理下土壤呼吸随土壤温度的升高而增大,免耕处理下土壤呼吸随土壤温度的升高变化不明显;土壤体积含水量较小(20%)时,不同耕作处理下土壤呼吸均随土壤含水量增加而增加,含水量较高(30%)时则均随土壤含水量的升高而减小,两种情况下均为免耕处理的变化速率更大;双因子线性模型可较好地描述玉米田土壤呼吸对温度和水分变化的响应。     

Root respiration in temperate mountain grasslands differing in land use

In grasslands the proportionally largest emission of CO₂ comes from the soil. This study aimed to assess how root respiration, a major flux component, is affected by land management and changes in land use. Respiration of roots, separated to classes of different diameter, was measured in 11 temperate mountain grasslands, including meadows, pastures and abandoned sites at three geographic locations. Specific root respiration was affected by nitrogen (N) concentration, root class and land use. The relationship between root N concentration and respiration differed between locations. With increasing root diameter there was a decrease in root respiration, N concentration, respiration per unit N and Q₁₀. In grasslands abandoned for several years specific root respiration was lower than in meadows, pastures and a recently abandoned site. This was due to lower root N concentrations and/or lower respiration rates per unit N within each root class. Since root biomass was higher on abandoned grasslands, total ecosystem root respiration did not differ consistently between sites. Ecosystem root respiration showed distinct seasonal changes due to changes in root biomass, which were less pronounced on abandoned grasslands. Fine roots generally made up the largest portion of ecosystem root respiration, their contribution varying between 35% and 96%. On meadows, clipping increased soil and root respiration by increasing soil temperature. When corrected for temperature effects soil respiration was reduced by 20–50%, whilst root respiration was little affected, suggesting that carbohydrate reserves sustained root metabolism for several days and that microbial respiration strongly responded to short‐term changes in assimilate supply.