Interacting effects of temperature, soil moisture and plant biomass production on ecosystem respiration in a northern temperate grassland

Chamber measurements of total ecosystem respiration (TER) in a native Canadian grassland ecosystem were made during two study years with different precipitation. The growing season (April–September) precipitation during 2001 was less than one-half of the 30-year mean (1971–2000), while 2002 received almost double the normal growing season precipitation. As a consequence soil moisture remained higher in 2002 than 2001 during most of the growing season and peak aboveground biomass production (253.9 g m⁻²) in 2002 was 60% higher than in 2001. Maximum respiration rates were approximately 9 μmol m⁻² s⁻¹ in 2002 while only approximately 5 μmol m⁻² s⁻¹ in 2001. Large diurnal variation in TER, which occurred during times of peak biomass and adequate soil moisture, was primarily controlled by changes in temperature. The temperature sensitivity coefficient (Q₁₀) for ecosystem respiration was on average 1.83 ± 0.08, and it declined in association with reductions in soil moisture. Approximately 94% of the seasonal and interannual variation in R₁₀ (standardized rate of respiration at 10 °C) data was explained by the interaction of changes in soil moisture and aboveground biomass, which suggested that plant aboveground biomass was good proxy for accounting for variations in both autotrophic and heterotrophic capacity for respiration. Soil moisture was the dominant environmental factor that controlled seasonal and interannual variation in TER in this grassland, when variation in temperature was held constant. We compared respiration rates measured with chambers and that determined from nighttime eddy covariance (EC) measurements. Respiration rates measured by both techniques showed very similar seasonal patterns of variation in both years. When TER was integrated over the entire growing season period, the chamber method produced slightly higher values than the EC method by approximately 4.5% and 13.6% during 2001 and 2002, respectively, much less than the estimated uncertainty for both measurement techniques. The two methods for calculating respiration had only minor effects on the seasonal-integrated estimates of net ecosystem CO₂ exchange and ecosystem gross photosynthesis.     

水土保持措施对板栗林土壤呼吸的影响

为阐明板栗林土壤呼吸对水土保持措施的响应,采用IRGA法,对不同类型板栗林的土壤呼吸从2009年3月至2010年9月开展为期1年半的定位观测。结果表明:1)采取水土保持措施后,样地的土壤水分状况得到一定程度的改善,尤其随着采取水土保持措施年限的延长,其对土壤水分时空分布影响更为显著。2)4个板栗林样地的土壤呼吸速率均呈明显的单峰曲线变化,水土保持措施对土壤呼吸的季节动态无明显影响。3)样地Ⅰ和Ⅲ的参考呼吸R10分别为1.718和1.595μmol/(m2.s);而采取水土保持措施后,样地Ⅱ和Ⅳ的R10均表现为一定程度的降低,分别为1.092和1.324μmol/(m2.s)。样地Ⅰ和Ⅲ的土壤呼吸的温度敏感性指数Q10分别为1.927和1.899;采取水土保持措施后,样地Ⅱ和Ⅳ的Q10均表现为略微增加。采取水土保持措施后,土壤温度和土壤湿度对土壤呼吸速率的影响有一定程度的增强。研究结果可为把水土保持措施作为土壤严重侵蚀地区一种潜在的固碳减排模式提供基础数据。     

氮沉降增加和人类干扰对半干旱草地土壤呼吸的影响

土壤呼吸是全球碳循环的主要流通途径,但半干旱草地土壤呼吸对全球变化和人类干扰的响应机制尚不清楚。该研究以科尔沁沙质草地为研究对象,研究氮沉降增加、人类干扰（火烧、刈割）及其交互作用对沙质草地整个植物生长季（2017年5－9月）土壤呼吸的影响。结果表明,土壤呼吸呈明显的季节动态变化,在7月最高。氮沉降增加使根呼吸显著提高42%,土壤呼吸显著增加17%（P<0.001）,但对微生物呼吸无显著影响。火烧使根呼吸显著提高25%（P<0.01）,但使微生物呼吸降低13%（P<0.001）,从而导致土壤呼吸未显著增加（P>0.05）。刈割显著降低了土壤温度,诱导微生物呼吸和根呼吸分别降低13%（P<0.001）和20%（P<0.05）,从而显著抑制土壤呼吸（P<0.001）。氮沉降增强了火烧对土壤呼吸的促进作用,但未显著影响刈割对土壤呼吸的抑制作用。氮沉降、火烧和刈割对土壤呼吸的不同影响可对全球变化背景下沙质草地土壤碳循环的预测和天然草地的科学管理提供参考。     

Soil respiration as affected by vegetation types in a semiarid region of China

There are variations in soil respiration across vegetation types; however, it is unclear which factors are mainly responsible for the variations. A field experiment was conducted in 2008 and 2009 in a semiarid region of China to investigate the daytime and monthly variation of soil respiration across vegetation types and to determine the factors controlling the variation. An automated portable soil carbon dioxide (CO₂) flux measurement system was used to measure the soil respiration in shrubland, grassland, fallow land, and cropland during the growing periods. The results showed that the relative daytime variation amplitude of soil respiration in the fallow land and cropland was as small as that of shrubland and grassland during July, but greater than that of shrubland and grassland during August and October. A hysteresis effect for the relationship between the daytime soil respiration and daytime soil temperature was observed for all four vegetation types. There was also a hysteresis effect for the relationship between the daytime soil respiration and daytime air temperature for the grassland. Over the study period, the monthly soil respiration rates of the fallow land and cropland were statistically comparable and significantly lower than those of the shrubland and grassland, with the exception of August, during which the monthly soil respiration of the cropland was as great as that of shrubland and grassland. The factors responsible for the monthly soil respiration variation across the vegetation types differed from month to month. In general, the soil temperature and soil water content were mainly responsible in August and September; however, the root biomass predominated in July and October. The results are valuable for accurately estimating regional carbon fluxes by considering the temporal variability of the soil respiration variation across vegetation types in the Loess Plateau of China.     

陆地生态系统土壤呼吸的影响因素研究综述

土壤呼吸是陆地生态系统碳循环中的一个重要过程,也是陆地生态系统最大的二氧化碳释放源,对全球气候和环境变化产生重要影响。对国内外关于陆地生态系统土壤呼吸影响因素的研究进行综述,分析了温度、水分、土壤性质等非生物因素,植被、土壤微生物、土壤动物等生物因素以及人类活动等对土壤呼吸产生的影响。最后分析了目前有关土壤呼吸研究中存在的问题,并提出了今后努力的方向:改进和创新土壤呼吸的测量方法,拓宽土壤呼吸的研究范围,加强土壤呼吸组分的区分研究,重视人类活动对土壤呼吸影响的研究。     

Effects of simulated nitrogen deposition on soil respiration components and their temperature sensitivities in a semiarid grassland

Nitrogen (N) deposition to semiarid ecosystems is increasing globally, yet few studies have investigated the ecological consequences of N enrichment in these ecosystems. Furthermore, soil CO₂ flux – including plant root and microbial respiration – is a key feedback to ecosystem carbon (C) cycling that links ecosystem processes to climate, yet few studies have investigated the effects of N enrichment on belowground processes in water-limited ecosystems. In this study, we conducted two-level N addition experiments to investigate the effects of N enrichment on microbial and root respiration in a grassland ecosystem on the Loess Plateau in northwestern China. Two years of high N additions (9.2 g N m⁻² y⁻¹) significantly increased soil CO₂ flux, including both microbial and root respiration, particularly during the warm growing season. Low N additions (2.3 g N m⁻² y⁻¹) increased microbial respiration during the growing season only, but had no significant effects on root respiration. The annual temperature coefficients (Q₁₀) of soil respiration and microbial respiration ranged from 1.86 to 3.00 and 1.86 to 2.72 respectively, and there was a significant decrease in Q₁₀ between the control and the N treatments during the non-growing season but no difference was found during the growing season. Following nitrogen additions, elevated rates of root respiration were significantly and positively related to root N concentrations and biomass, while elevated rates of microbial respiration were related to soil microbial biomass C (SMBC). The microbial respiration tended to respond more sensitively to N addition, while the root respiration did not have similar response. The different mechanisms of N addition impacts on soil respiration and its components and their sensitivity to temperature identified in this study may facilitate the simulation and prediction of C cycling and storage in semiarid grasslands under future scenarios of global change.     

Grazing and plant-canopy effects on semiarid soil microbial biomass and respiration

The major objectives of this study were to determine the influence of grazing on the soil microbial biomass and activity in semiarid grassland and shrubland areas and to quantify the canopy effect (the differences in soil microbial biomass and activities between soils under plant canopies and soils in the open between plants). We also quantified changes in microbial biomass and activity during seasonal transition from dry to moist conditions. Chronosequences of sites withdrawn from grazing for 0, 11, and 16 years were sampled in a grassland (Bouteloua spp.) area and a shrubland (Atriplex canescens) area on and near the Sevilleta National Wildlife Reguge in central New Mexico, USA. Samples were obtained from beneath the canopies of plants (Yucca glauca in the grassland and A. canescens in the shrubland) and from open soils; they were collected three times during the spring and summer of a single growing season. Organic C, soil microbial biomass C, and basal respiration rates (collectively called the soil C triangle) were measured. We also calculated the microbial: organic C ratio and the metabolic quotient (ratio of respiration to microbial C) as measures of soil organic C stability and turnover. Although we had hypothesized that individual values of the soil C triangle would increase and that the ratios would decrease with time since grazing, differences in microbial parameters between sites located along the chronosequences were generally not significant. Grazing did not have a consistion effect on organic C, microbial C, and basal respiration in our chronosequences. The microbial: organic C ratio and the metabolic quotient generally increased with time since grazing on the shrubland chronosequence. The microbial: organic C ratio decreased with time since grazing and the metabolic quotient increased with time since grazing on the grassland chronosequence. The canopy effect was observed at all sites in nearly all parameters including organic C, microbial C, basal respiration, the microbial: organic C ratio, and the metabolic quotient which were predominantly higher in soils under the canopies of plants than in the open at all sites. Microbial biomass and activity did not increase during the experiment, even though the availability of moisture increased dramatically. The canopy effects were approximately equal on the shrubland and grassland sites. The microbial: organic C ratios and the metabolic quotients were generally higher in the shrubland soils than in the grassland soils.     

Contributions of root respiration to total soil respiration before and after frost in Populus euphratica forests

Temporal changes in soil CO₂‐efflux rate was measured by a canopy‐gap method in a Populus euphratica forest located at the both sides of Tarim River banks (W China). Soil CO₂‐efflux rates in situ were correlated with key soil biotic (e.g., fungal, bacterial, and actinomycetes populations) and abiotic (e.g., soil moisture, temperature, pH, organic C) variables. Two kinds of measurement plots were selected: one under the crown of a living Populus euphratica tree and the other under a dead standing Populus euphratica tree. Diurnal variations in soil respiration in these plots were measured both before and after the occurrence of the first frost. Soil respiration of the dead standing Populus euphratica (Rd) was assumed to be a measure of heterotrophic respiration rate (Rh), and root respiration rate (Rr) was estimated as the difference between soil respiration under living (Rl) minus soil respiration under dead standing Populus euphratica. Daily variation of Rr contribution to the total soil respiration in Populus euphratica forests were analyzed before and after the frost. The contribution of root respiration to total soil respiration before and after frost varied from 22% to 45% (mean 30%) and from 38% to 50% (mean 45%), respectively. In addition, Rh was significantly correlated with soil temperature both before and after frost. In contrast, Rr was not significantly correlated with soil temperature. Change in Q₁₀ of Rr was different from that of Rh from before the frost to after the frost. Variation of Q₁₀ of Rr from before the frost to after the frost was larger than that of Q₁₀ of Rh. Thus, the results indicate that different soil respiration models are needed for Rr and Rh because different factors control the two components of soil respiration.     

Associations between soil texture,soil water characteristics and earthworm populations in grassland

Abstract

The aim of the present study was to investigate the relationships between soil physical characteristics and earthworms in a regional-scale field study in Denmark. The earthworm populations along within-field gradients in soil texture were quantified at five field sites, representing dominant soil types of Denmark. Eleven earthworm species were found, but populations were mainly dominated by Aporrectodea tuberculata and A. longa. Despite considerable variation in soil parameters across the five study sites the results suggest that the biomass of anecic worms (or A. longa as a species) was not causally associated with the soil parameters studied. This indicates that there must be other causal factors associated with the abundance (and composition) of anecic worms that are not among the soil texture and structure parameters studied. On the other hand, soil texture (Coarse sand) was associated with the abundance of the dominant endogeic species, A. tuberculata, but not endogeic worms in general. It was hypothesized that anecic and endogeic earthworms might respond to local soil water characteristics rather than soil texture, but this hypothesis could not be confirmed with the present data.     

Environmental controls on photosynthetic production and ecosystem respiration in semi-arid grasslands of Mongolia

The Mongolian steppe zone comprises a major part of East Asian grasslands. The objective of this study was to separately evaluate the quantitative dependencies of gross primary production (GPP) and ecosystem respiration (R_eco) on the environmental variables of temperature, moisture, radiation, and plant biomass in a semi-arid grassland ecosystem. We determined GPP and R_eco using transparent and opaque closed chambers in a grassland dominated by Poaceae species in central Mongolia during five periods: July 2004, May 2005, July 2005, September 2005, and June 2006. Values of GPP were linearly related to live aboveground biomass (AGB) enclosed by the chamber. The amount of GPP per unit ground area differed among the study periods, whereas GPP normalized by the amount of AGB did not differ significantly among the periods, suggesting that plant production per unit green biomass did not depend on the phenological stage. GPP/AGB fit well a rectangular hyperbolic light–response curve for all the study periods. When the air and soil were dry, considerable reduction in GPP was observed. The GPP/AGB ratio was also expressed as individual functions of air temperature, vapor pressure deficit, and volumetric soil water content. R_eco was exponentially related to the soil temperature and the relationship was modified by soil moisture. The amount of R_eco and its temperature sensitivity (Q₁₀) declined with decreasing soil moisture. Sharp increases of R_eco after rainfall events were observed. The values of R_eco, even including the rain-induced pulses, were expressed well as a bivariate function of soil temperature and soil moisture near the soil surface.     

沙漠化对科尔沁沙质草地土壤呼吸速率及碳平衡的影响

在科尔沁沙地测定了不同类型沙漠化草地土壤呼吸速率的日进程和季节变化,以及植物碳储量和土壤有机碳储量,分析了沙漠化对沙质草地土壤呼吸速率及草地碳平衡的影响。结果表明:(1)沙漠化可导致草地土壤呼吸速率日变化幅度变小,日均土壤呼吸速率明显降低;与非沙漠化草地相比,在生长季轻度、中度、重度和严重沙漠化草地日均土壤呼吸速率依次下降6.4%、12.8%、33.0%和39.4%;(2)受沙漠化的影响草地碳储量明显下降,与非沙漠化草地相比,4种类型沙漠化草地碳储量依次下降50.3%、74.0%、86.4%和90.2%;其中,凋落物碳储量的下降幅度最大,土壤有机碳储量下降幅度次之,植物碳储量下降幅度最小;(3)沙漠化可使草地碳平衡受到严重破坏,草地一旦沙漠化,土壤呼吸消耗碳量将超过植物固定碳量,这时土壤有机碳库将作为后备碳源来弥补土壤呼吸过程中植物固碳量的不足。为了促进沙漠化草地碳库的恢复,应加强沙漠化草地的治理,促进草地植被的恢复重建。     

沙质草地生境中植物群落对土壤质地演进的响应

利用空间代替时间,选取6个沙地生境类型(硬质灰钙土H_1,沙质灰钙土H_2,固定沙地H_3,半固定沙地H_4,半流动沙地H_5和流动沙地H_6),通过对其土壤颗粒组成、草地植物群落结构及数量特征的分析,研究沙质草地植物群落演替对土壤沙化过程的响应。结果表明:(1)从硬质灰钙土到流动沙地,物种丰富度分别为9,12,9,9,9,5种;演替初期(H_1-H_2)多年生草本植物种占绝对优势,演替中期(H_3-H_4)一年生植物优势度明显,演替后期(H_5-H_6)则以半灌木占主导地位;各演替阶段禾本科植物均有很高的优势度,在半流动沙地阶段成为最大优势物种,在沙质灰钙土后藜科植物优势度保持相对稳定,菊科和豆科植物分别在固定沙地和半固定沙地阶段逐渐消失。(2)物种多样性在沙质灰钙土最高,到固定沙地持续递减,而到流动沙地时又增大,生态优势度与物种多样性变化趋势正好相反,均匀度表现出先减小后增大的趋势,相邻的两个群落间具有较高的相似度。(3)从硬质灰钙土到流动沙地,0—10cm土层土壤黏粉粒含量极显著减少(p0.01),而粗砂粒极显著增加(p0.01),土壤颗粒分形维数由2.52下降到1.73。(4)一年生草本植物优势度与土壤黏粉粒含量、土壤颗粒分形维数呈显著负相关(p0.05);豆科植物优势度与土壤粉粒组分、土壤颗粒分形维数间呈显著正相关(p0.05);物种多样性与粉粒组分含量呈极显著正相关(p0.01),与细砂粒组分含量、土壤颗粒分形维数间呈显著正相关(p0.05)。     

旱地农田两种土壤呼吸测定方法的比较

在旱地农田少耕(RT)、传统耕作(CT)和免耕(NT)3种耕作土壤上,采用动态密闭气室法(IRGA)与碱液吸收法(AA)同时测定土壤呼吸速率,并对测定结果进行比较.结果表明:(1)在RT、CT和NT3种耕作土壤上,IRGA与AA两种方法测定结果均呈显著相关,前者测定值分别约为后者的4.48、3.74和4.07倍.(2)...     

放牧强度对中国内蒙古草原土壤水分状况与通量的影响

In the past few decades,the increase in grazing intensity has led to soil degradation and desertification in Inner Mongolia grassland,China,due to population growth and shift in the socio-economic system.Two sites with different grazing intensities,continuous grazing site(CG) with 1.2 sheep ha 1 year 1 and heavy grazing site(HG) with 2.0 sheep ha 1 year 1,were investigated at the Inner Mongolia Grassland Ecosystem Research Station(43 37 50 N,116 42 18 E) situated in the northern China to i) characterize the temporal distribution of soil water content along soil profile;and ii) quantify the water fluxes as affected by grazing intensity.Soil water content was monitored by time domain reflectometry(TDR) probes.Soil water retention curves were determined by pressure membrane extractor,furthermore processed by RETC(RETention Curve) software.Soil matric potential,plant available water and water flux were calculated using these data.Both sites showed an identical seasonal soil water dynamics within four defined hydraulic periods:1) wetting transition coincided with a dramatic water increase due to snow and frozen soil thawing from March to April;2) wet summer,rainfall in accordance with plant growth from May to September;3) drying transition,a decrease of soil water from October to November due to rainfall limit;and 4) dry winter,freezing from December to next February.Heavy grazing largely reduced soil water content by 43%-48% and plant available water by 46%-61% as compared to the CG site.During growing season net water flux was nearly similar between HG(242 mm) and CG(223 mm) sites between 5 and 20 cm depths.However,between 20 and 40 cm depths,the upward flux was more pronounced at HG site than at CG site,indicating that water was depleted by root uptake at HG site but stored at CG site.In semi-arid grassland ecosystem,grazing intensity can affect soil water regime and flux,particularly in the growing season.     

内蒙古典型草原区退耕方式对植物群落特征与土壤特性的影响

退耕后不恰当的植被建设会严重影响植物群落演替及土壤性质.本文以内蒙古太仆寺旗境内典型草原为研究区,以天然草地为对照,研究退耕后自然恢复与人工种草2种退耕方式对植物群落特征及土壤性状的影响,揭示不同退耕方式的生态恢复效应.通过样方法调查不同退耕方式草地的盖度、生物量和多样性特征,并对土壤密度、机械组成及养分含量等进行了室内测定分析.结果表明:1)植物群落多样性、盖度、地上及地下生物量均表现为人工种草＜自然恢复＜天然草地,且相比于人工种草,自然恢复草地的物种组成与天然草地更为相似;2)不同退耕方式影响下土壤性质的差异主要集中在表层0～10 cm;3)在表层0～ 10 cm,土壤密度及砂粒含量表现为人工种草＞自然恢复＞天然草地,而土壤黏粒、有机质(SOM)及全氮(TN)含量则表现为人工种草＜自然恢复＜天然草地.以上结果说明,在内蒙太仆寺旗退耕后采用自然恢复方式比人工种草更有助于改善土壤理化性质、建立稳定的植被系统.经过12年的恢复,退耕草地(人工种草与自然恢复草地)仍未恢复到天然草地的水平.     

Biocrusts modulate warming and rainfall exclusion effects on soil respiration in a semi-arid grassland

Soil surface communities composed of cyanobacteria, algae, mosses, liverworts, fungi, bacteria and lichens (biocrusts) largely affect soil respiration in dryland ecosystems. Climate change is expected to have large effects on biocrusts and associated ecosystem processes. However, few studies so far have experimentally assessed how expected changes in temperature and rainfall will affect soil respiration in biocrust-dominated ecosystems. We evaluated the impacts of biocrust development, increased air temperature and decreased precipitation on soil respiration dynamics during dry (2009) and wet (2010) years, and investigated the relative importance of soil temperature and moisture as environmental drivers of soil respiration, in a semiarid grassland from central Spain. Soil respiration rates were significantly lower in the dry than in the wet year, regardless of biocrust cover. Warming increased soil respiration rates, but this response was only significant in biocrust-dominated areas (>50% biocrust cover). Warming also increased the temperature sensitivity (Q₁₀ values) of soil respiration in biocrust-dominated areas, particularly during the wet year. The combination of warming and rainfall exclusion had similar effects in low biocrust cover areas. Our results highlight the importance of biocrusts as a modulator of soil respiration responses to both warming and rainfall exclusion, and indicate that they must be explicitly considered when evaluating soil respiration responses to climate change in drylands.     

黄土丘陵区油松、沙棘人工林土壤呼吸动态及其对土壤温度和水分的响应

作为陆地生态系统碳通量的重要组成部分,土壤呼吸在维持全球碳循环及碳平衡中具有重要作用.以黄土丘陵区油松、沙棘人工林为研究对象,于2015年6月至2016年5月,采用LI-8100土壤碳通量测量系统,分别观测二者的土壤呼吸(Rs)、5 cm土壤温度(T)和水分(W),分析2种人工林Rs的动态特征及其对T和W的响应.结果表明:1)季节尺度油松、沙棘人工林Rs夏季(6-8月)最高(2.31和2.89 μmolCO2/m2·s),冬季(12-2月)最低(0.60和0.65μmolCO2/m2·s),年均值分别为1.51和1.92 μmolCO2/m2·s,年呼吸总量分别为18.90和22.81tCO2/hm2·a,冬季呼吸量占年呼吸总量比例分别为14.67％和12.65％;日尺度最高值出现在10:00-16:00,最低值均出现在6:00.2)季节尺度2种林分Rs与T均呈显著指数关系(P＜0.01),与W则呈显著线性负相关(P＜0.01),且沙棘林全年尺度土壤呼吸Q10值(1.40)显著高于油松林(1.34,P＜0.01).3)日尺度上,油松、沙棘人工林W分别大于13％和12％时,T对Rs的解释量(R2)均有所提高.因此,在充分考虑温度和水分对土壤呼吸影响的同时,加强冬季土壤呼吸的观测,对未来气候变化条件下,区域碳循环估算模型的完善具有重要意义.     

玉米农田生态系统土壤呼吸作用季节动态与碳收支初步估算

从2005年4月底到9月底对玉米农田生态系统的土壤呼吸作用进行了连续观测.结果表明: 2005年玉米生长季土壤呼吸速率均值为3.16 μmol (CO2)·m-2·s-1, 最大值为4.77 μmol (CO2)·m-2·s-1, 出现在7月28日, 最小值为1.31 μmol (CO2)·m-2·s-1, 出现在5月4日.通过建立土壤呼吸速率与玉米根系生物量的回归方程, 对土壤异养呼吸作用占土壤呼吸作用的比例进行间接估算.玉米生长季中, 土壤异养呼吸作用占土壤呼吸作用的比例在36.4%～56.9%之间波动, 均值为45.5%.假定玉米果实和秸秆中的碳在收获期间未从农田中转移走, 2005年整个生长季中玉米农田生态系统的碳收支为-1 127.0 g (C)·m-2, 碳交换速率在0.52～ -18.05 g (C)·m-2·d-1之间波动.玉米生长初期, 玉米农田生态系统表现为碳的弱源; 玉米播种后36 d一直到收获, 玉米农田生态系统表现为碳汇.