Controls on soil respiration in semiarid soils

Soil respiration in semiarid ecosystems responds positively to temperature, but temperature is just one of many factors controlling soil respiration. Soil moisture can have an overriding influence, particularly during the dry/warm portions of the year. The purpose of this project was to evaluate the influence of soil moisture on the relationship between temperature and soil respiration. Soil samples collected from a range of sites arrayed across a climatic gradient were incubated under varying temperature and moisture conditions. Additionally, we evaluated the impact of substrate quality on short-term soil respiration responses by carrying out substrate-induced respiration assessments for each soil at nine different temperatures. Within all soil moisture regimes, respiration rates always increased with increase in temperature. For a given temperature, soil respiration increased by half (on average) across moisture regimes; Q₁₀ values declined with soil moisture from 3.2 (at −0.03 MPa) to 2.1 (−1.5 MPa). In summary, soil respiration was generally directly related to temperature, but responses were ameliorated with decrease in soil moisture.     

色季拉山4种林型土壤呼吸及其影响因子

土壤碳是森林生态系统最大的碳库,是其森林生态系统碳循环的极其重要组分。森林土壤呼吸时陆地生态系统土壤呼吸的重要组成部分,其动态变化对全球碳平衡有着重要的影响,然而目前对藏东南地区森林土壤呼吸的研究还比较薄弱。为探讨不同林型土壤呼吸差异及其影响因子,采用Li-8100便携式土壤呼吸测定仪,研究了藏东南色季拉山4种原始森林生态系统(高山灌丛AS、方枝柏SS、杜鹃RF、急尖长苞冷杉AGSF)的土壤碳动态。结果表明:(1)藏东南色季拉山寒温带森林土壤呼吸具有明显的日变化和季节变化。在日变化方面,CO2的排放通量存在明显的日变化规律,排放通量在白天16:00左右最高,最低值出现在凌晨6:00左右,一天内土壤呼吸作用均呈单峰型曲线变化。季节变化方面,CO2排放的通量的季节变化趋势表现为6月份随着天气转暖和植被生长土壤呼吸作用逐渐增大,7月份气温最高时土壤呼吸作用也达到最大值随后,9月份气温逐渐下降,土壤呼吸作用也逐渐降低。(2)4种森林类型的土壤呼吸速率在植物生长季内与土壤表层(10 cm)土壤温度均呈不同程度的正相关,而与土壤含水量的相关性较弱。土壤温度是决定藏东南色季拉山土壤呼季节变化的主要因子。该研究为明确森林生态系统土壤呼吸变化规律及其影响因素的控制提供参考,同时对估算地区碳平衡、评估区域碳源汇具有重要意义。     

Modeling soil respiration based on carbon, nitrogen, and root mass across diverse Great Lake forests

The variability in the net ecosystem exchange of carbon (NEE) is a major source of uncertainty in quantifying global carbon budget and atmospheric CO₂. Soil respiration, which is a large component of NEE, could be strongly influential to NEE variability. Vegetation type, landscape position, and site history can influence soil properties and therefore drive the microbial and root production of soil CO₂. This study measured soil respiration and soil chemical, biological and physical properties on various types of temperate forest stands in Northern Wisconsin (USA), which included ash elm, aspen, northern hardwood, red pine forest types, clear-cuts, and wetland edges. Soil respiration at each of the 19 locations was measured six times during 1 year from early June to mid-November. These data were combined with two additional data sets from the same landscape that represent two smaller spatial scales. Large spatial variation of soil respiration occurred within and among each forest type, which appeared to be from differences in soil moisture, root mass and the ratio of soil carbon to soil nitrogen (C:N). A soil climate driven model was developed that contained quadratic functions for root mass and the ratio of soil carbon to soil nitrogen. The data from the large range of forest types and site conditions indicated that the range of root mass and C:N on the landscape was also large, and that trends between C:N, root mass, and soil respiration were not linear as previously reported, but rather curvilinear. It should be noted this function appeared to level off and decline at C:N larger than 25, approximately the value where microbial nitrogen immobilization limits free soil nitrogen. Weak but significant relationships between soil water and soil C:N, and between soil C:N and root mass were observed indicating an interrelatedness of (1) topographically induced hydrologic patterns and soil chemistry, and (2) soil chemistry and root production. Future models of soil respiration should address multiple spatial and temporal factors as well as their co-dependence.     

免耕与翻耕条件下农田土壤呼吸的比较

采用开路式土壤碳通量测量系统于2010年3-10月在冬小麦-大豆轮作期对免耕与翻耕田土壤呼吸速率、5cm深土壤温度和湿度进行测定,以研究耕作措施对农田土壤呼吸的影响。结果表明,在冬小麦、大豆生长时段,免耕与翻耕田土壤呼吸速率的季节变化趋势基本一致。冬小麦生长时段免耕与翻耕田土壤呼吸速率的平均值分别为2.50±0.14和2.40±0.29μmol.m-2.s-1,大豆生长时段分别为2.82±0.28和3.50±0.52μmol.m-2.s-1。冬小麦生长时段免耕与翻耕田土壤呼吸无显著差异,但大豆生长时段二者存在显著差异(P<0.05),差异最明显的阶段在大豆开花期(7月下旬-8月中旬)。利用温度影响函数(指数函数)和湿度影响函数(二次函数)耦合的模拟模型进行土壤呼吸与土壤温度和湿度的回归分析,得出免耕条件下土壤温度和湿度可以共同解释25.3%的土壤呼吸变异(R2=0.253,P<0.05),翻耕条件下二者可以共同解释44.0%的土壤呼吸变异(R2=0.440,P<0.01)。可见,一方面,耕作措施对土壤呼吸的影响因种植作物而异,与翻耕相比,免耕显著降低了大豆田土壤呼吸,但对冬小麦田无显著影响;另一方面,免耕下土壤温度和湿度对土壤呼吸的影响比翻耕要小。     

保护性耕作下大豆农田土壤呼吸及影响因素分析

为了探讨保护性耕作对旱作农田土壤呼吸的影响,采用LI6400-09仪器(LI6400便携式光合作用系统连接6400-09呼吸室)在重庆北碚西南大学试验农场对平作(T)、垄作(R)、平作+覆盖(TS)、垄作+覆盖(RS)、平作+覆盖+秸秆速腐剂(TSD)、垄作+覆盖+秸秆速腐剂(RSD)6种处理下的西南紫色土丘陵区小麦/玉米/大豆套作体系中大豆生长季节的土壤呼吸及其水、热、生物因子进行测定和分析,探讨西南丘陵区保护性耕作下大豆农田土壤呼吸及其影响因素。结果表明,大豆整个生育期内土壤呼吸先缓慢增强,到开花期开始增长迅速,成熟期明显下降。不同处理土壤呼吸速率存在差异,表现为TTSD>TS、R>RSD>RS,土壤呼吸的土温敏感指标Q10值排序为TS>TSD>RS=R>T>RSD。秸秆覆盖处理的土壤呼吸对于土壤温度敏感性较高,垄作则降低了土壤温度敏感性。5 cm土层的土壤含水量高低排序为TSD>RSD>TS>RS>T>R。本研究中土壤呼吸与土壤水分呈抛物线函数关系,垄作处理下土壤呼吸与土壤水分正相关,达到显著水平;其他处理均表现负相关,其中TS达到极显著水平。在大豆农田生态系统中优势类群有弹尾目、螨目和双翅目,干漏斗法、陷阱法捕获的土壤动物与土壤呼吸均没有显著的相关关系,两种方法所得土壤动物数量加总与土壤呼吸进行相关分析,发现处理T相关系数达到显著水平,r=0.901,P=0.037。     

长期定量施肥对黑土呼吸的影响

通过盆栽模拟试验,用静态箱法采样,气相色谱测定样品CO2浓度,研究大豆出苗到开花期长期定量施肥土壤CO2排放速率的变化规律。结果表明,长期定量施肥大豆生长对土壤呼吸影响有明显的规律性,NPK+OM>NPK>NP>NK>CK;长期定量施肥对裸土呼吸速率影响较小,NPK+OM呼吸速率较大为53.8mgCm-2h-1,NP次之为50.7mgCm-2h-1,其它施肥影响不大,气温对裸土呼吸影响较大,而对种植大豆的土壤呼吸前期(出苗后9天)影响较大,生长后期(出苗9天以后)影响较小。裸土呼吸速率变化与气温变化趋势相似,种植大豆促进土壤呼吸增大。如果忽略大豆生长对土壤有机质分解的激发效应,大豆根际呼吸占总土壤呼吸的23%～56%。     

Biotic and abiotic factors controlling the spatial and temporal variation of soil respiration in an agricultural ecosystem

Based on the continuous observation of soil respiration and environmental factors in a maize ecosystem from late April to late September in 2005, the spatial and temporal variation of soil respiration and their controlling factors were analyzed. There was a significant spatial pattern for soil respiration at the plant scale and higher soil respiration rates tended to occur near the maize plant during the growing season. On one measurement moment, root biomass (B) in soil collars exerted significant influence on the spatial pattern of soil respiration under the relatively homogeneous environmental conditions. A linear relationship existed between soil respiration rate and root biomass

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皆伐对杉木人工林土壤呼吸的影响

应用密闭室碱吸收法对杉木人工林皆伐后的土壤呼吸及各分室呼吸进行为期1年定位研究,结果表明,杉木林皆伐后前4个月土壤呼吸显著高于对照(未伐地)的,皆伐6个月后则显著低于对照的,但伐后1年内的平均土壤呼吸则与对照的无显著差异。皆伐地枯枝落叶层呼吸和矿质土壤呼吸分别在伐后的5个月和6个月内显著高于对照的,但此后则与对照的无显著差异。皆伐地根系呼吸除在伐后当月显著高于对照的外,第3个月迅速降低至消失。皆伐地土壤呼吸、枯枝落叶层呼吸和矿质土壤呼吸最大值出现时间均较对照的有所提前。伐后1年内皆伐地枯枝落叶层呼吸、矿质土壤呼吸和根系呼吸占土壤呼吸的比例分别为34·5%、63·9%和1·6%,而对照的则分别为23·4%、50·1%和26·5%。双因素关系模型拟合结果表明,土壤温度和土壤湿度共同解释皆伐和对照土壤呼吸速率变化的54%和90%。皆伐地土壤呼吸及各分室呼吸对土壤温度的敏感性低于对照的,但对土壤湿度的敏感性则高于对照的。皆伐地土壤呼吸、矿质土壤呼吸和枯枝落叶层呼吸的Q10分别为1·42、1·53和1·34,而对照的土壤呼吸、矿质土壤呼吸、枯枝落叶层呼吸和根系呼吸的Q10则分别为2·42、1·81、2·40和4·41。     

碘甲磺隆钠盐对土壤中过氧化氢酶活性及呼吸作用的影响

通过模拟实验研究了除草剂碘甲磺隆钠盐对土壤中过氧化氢酶活性和土壤呼吸作用的影响。结果表明,在施用量超过田间推荐用量7倍的浓度范围内,碘甲磺隆钠盐对土壤中过氧化氢酶活性的影响不明显;当其浓度为1mg/kg时,在不同培养时间下,碘甲磺隆钠盐施用后对土壤过氧化氢酶活性的影响呈现出轻微的抑制-激活-恢复的过程;在不同土壤类型中,碘甲磺隆钠盐对土壤过氧化氢酶的抑制性随土壤有机质的增加、pH值的降低而加强;碘甲磺隆钠盐对土壤呼吸作用有一定的影响,浓度愈大,土壤呼吸强度初期抑制愈强,随着时间的推移,逐步由抑制转为一定程度的刺激作用,到12天后施药土壤与对照组土壤的呼吸强度基本上趋于一致。实验结果表明,碘甲磺隆钠盐对土壤微生物影响较小,属于低毒或无实际危害的农药。     

玉米生长中的土壤呼吸及其受氮肥施用的影响

运用盆栽试验研究了玉米生长和施氮水平(N 150 mg kg-1和300 mg kg-1)对土壤呼吸的影响。结果表明种植玉米的土壤呼吸速率(C)的变化范围为19. 6 ~ 762. 1 mg m-2h-1,而裸土为4. 3 ~ 36mg m-2h-1。在玉米生长的条件下,苗期土壤呼吸最低,73%的土壤呼吸分配在拔节孕穗期和成熟期。玉米生长中各阶段根际呼吸对土壤呼吸的贡献在58%~98%,苗期最小。施氮对裸土呼吸速率无显著影响;在玉米生长的条件下,施用高氮的土壤呼吸比施用低氮高28%,且两种施氮水平下土壤呼吸的差异主要发生在生长中后期。玉米生长的条件下土壤呼吸与温度的相关性不显著,而裸土下土壤呼吸速率与气温、表土温度、5 cm土壤温度均呈极显著的相关性;裸土施用高氮下的土壤呼吸与温度的相关性大于低氮。总之,玉米生长和土壤施氮不仅影响土壤呼吸速率和呼吸量,也影响土壤呼吸在各生长阶段的分配,还影响到土壤呼吸与温度的关系。     

长期施肥对冬小麦/夏玉米轮作下土壤呼吸及其组分的影响

为阐明施肥对农田土壤呼吸的影响,于2002年6月至2003年6月在河南封丘潮土上进行的长期试验地上测定了玉米/冬小麦轮作系统下的土壤呼吸,分析了土壤呼吸与土壤水分和温度的关系,并利用统计分析方法研究了土壤呼吸各组分的贡献。土壤呼吸变化与作物生长发育规律一致,施肥通过影响作物的生长发育而对土壤呼吸产生影响。不同作物生长期,根际呼吸、土壤原有机质以及前作根茬和有机肥中碳对土壤呼吸的贡献不同。玉米期土壤有机质、根际呼吸、前作根茬和有机肥中的碳对土壤呼吸的平均贡献率分别为70.19%、19.43%和10.37%;而小麦生长期则分别为23.75%、62.26%和14.11%。由于不同施肥处理的作物生长量、土壤有机质含量以及前作根茬和有机肥施入而进入的有机碳量不同,造成土壤呼吸个体上存在着较大差异。土壤有机质的消耗主要发生在玉米生长阶段。     

喀纳斯自然保护区林地和草地土壤呼吸速率差异及影响因素

为了研究新疆喀纳斯国家自然保护区森林生态和草地生态系统与大气的相互作用,分析土壤呼吸速率的时空变异特征及与影响因子的关系,2012年及2013年5月上旬至9月上旬利用土壤碳通量测量系统LI-8150对林地和草地两种植被类型土壤的呼吸速率日动态进行了全天连续自动监测,研究了两类土壤呼吸速率在生长季各月日的变化规律。结果表明:林地和草地生态系统土壤呼吸速率在植被生长季内均呈现较明显的单峰曲线型日变化,其月最大值均出现在7月,林地土壤呼吸速率的最大值(2.43μmol/(m~2·s))显著高于草地土壤呼吸速率最大值(1.55μmol/(m~2·s)),且各月林地生态系统的土壤呼吸速率均明显高于草地,波峰出现在北京时间17:00—18:00,波谷出现在北京时间9:00—10:00,草地最小值出现在6月(0.35μmol/(m~2·s)),而林地最小值出现在5月,其呼吸速率仅0.71μmol/(m~2·s),且整个生长季白天大于晚上,全天以呼出CO_2为主。植被生长季内林地和草地土壤呼吸速率与土壤温度的变化趋势相似,具有显著的正相关性,但与土壤含水量的变化没有这样的趋势。     

不同恢复方式下盐渍化弃耕地土壤生物学活性的变化

以干旱区新疆玛纳斯河流域冲积扇缘定点定位试验地为研究对象, 研究灌溉处理、人工草地处理和补植处理对盐渍化弃耕地土壤微生物量、酶活性及土壤呼吸速率的影响。结果表明, 不同恢复方式均明显增加了土壤微生物数量和土壤微生物量碳、氮及土壤酶活性。不同处理土壤微生物量碳、氮分别比原始弃耕地高17.80%、26.38%、5.33%和7.89%、12.75%、21.93%; 不同处理土壤微生物数量分别是原始弃耕地的4.72倍、6.04倍和4.56倍; 不同处理土壤蔗糖酶活性分别比原始弃耕地高3.4倍、3.2倍和7.7倍, 多酚氧化酶活性比原始弃耕地高1.7倍、1.2倍和1.5倍, 脲酶活性比原始弃耕地高11.1%、52.3%和37.1%; 灌溉处理土壤过氧化氢酶活性最高, 是原始弃耕地的1.53倍, 土壤呼吸速率变化表现为人工草地处理>灌溉处理>补植处理>原始弃耕地, 其中, 人工草地处理土壤呼吸速率比弃耕地高52.25%。相关分析表明, 微生物量碳与微生物C/N和微生物数量之间均呈显著正相关关系(P<0.05); 土壤呼吸速率与土壤脲酶、微生物数量和微生物量碳的相关性达到显著水平(P<0.05), 与土壤微生物量氮呈负相关关系, 但相关性不显著; 土壤蔗糖酶与其他3种酶以及微生物量氮呈显著正相关关系, 土壤脲酶与微生物数量呈显著正相关关系, 多酚氧化酶与过氧化氢酶相关性达到显著水平(P<0.05)。本研究表明干旱区盐渍化弃耕地采用灌溉与人工草地处理有利于土壤养分积累, 可在一定程度上改善土壤质量。     

Relationships between soil respiration and soil moisture

The interaction of soil microbes with their physical environment affects their abilities to respire, grow and divide. One of these environmental factors is the amount of moisture in the soil. The work we published almost 25 years ago showed that microbial respiration was linearly related to soil-water content and log-linearly related to water potential. The paper arose out of collaboration between two young researchers from different areas of soil science, physics and microbiology. The project was driven by not only our curiosity but also the freedom to operate without the constraints common to the current system of science management. The citation history shows three peaks, 1989, 1999 and from 2002 to the present day. Interestingly, the annual citation rate is as high as it has ever been. The initial peak is due to the application of the work to studies on microbial processes. The second peak is associated with the rise of simulation modelling and the third with the relevance of the findings to climate change research. In this article, our paper is re-evaluated in the light of subsequent studies that allow the principle of separation of variables to be tested. This re-evaluation lends further credence to the linear relationship proposed between soil respiration and water content. A scaled relationship for respiration and water content is presented. Lastly, further research is suggested and more recent work on the physics of gas transport discussed briefly.     

重庆缙云山3种林型土壤呼吸及其影响因子

2011年1～12月,采用LI-Cor 8100开路式土壤碳通量测量系统对重庆缙云山保护区3种主要林分类型(针阔混交林、常绿阔叶林和毛竹林)的土壤呼吸速率和林内气温、土壤温度和湿度进行了野外观测。结果表明:针阔混交林、常绿阔叶林和毛竹林的土壤呼吸碳通量分别为654.70、1008.37和910.64 g C m-2a-1;3种林型土壤呼吸速率均呈现显著的季节性变化,且夏季>秋季>春季>冬季,最大值出现在7月,最小值出现在1月;3种林型土壤呼吸速率全年平均值分别为1.73、2.66和2.40μmol m-2s-1;3种林型土壤呼吸速率均与林内气温存在显著正相关关系(P<0.05),且与5 cm土壤温度均存在极显著的指数正相关(P<0.05);与5 cm土壤含水量的相关性不显著(P>0.05),但土壤含水量较低而温度较高时,较低的土壤含水量对呼吸速率具有一定抑制作用;3种林型的土壤呼吸对温度的敏感系数(Q10值)存在差异,全年表现为毛竹林(2.44)>针阔混交林(1.76)>常绿阔叶林(1.72),同时均表现显著的季节差异。     

酸雨对土壤呼吸的影响机制研究进展与展望

土壤呼吸是陆地生态系统与大气之间进行碳交换的主要途径,其动态变化直接影响着全球碳平衡。由于人类活动的影响,酸雨成为人类当前面临的最严重的生态环境问题之一,但其对土壤呼吸的影响及其机理尚无定论。本文综述了不同生态系统土壤呼吸对酸雨的响应特征,多数文献表明,高强度的酸雨抑制土壤呼吸,而在低强度的酸雨作用下土壤呼吸的响应存在差异。从影响土壤呼吸的4个关键生物因子,即光合作用、微生物、凋落物和根系生物量,重点讨论了酸雨对土壤呼吸的影响机制。在此基础上,提出了以下研究展望:①开展土壤呼吸对不同组成类型酸雨的响应研究;②开展与土壤碳排放相关的功能微生物对酸雨的响应研究;③开展不同物候期土壤呼吸对酸雨的响应研究;④开展土壤呼吸各过程对酸雨的响应研究;⑤建立全球酸雨地区土壤碳排放监测研究网络。     

Variation of soil respiration at three spatial scales: Components within measurements, intra-site variation and patterns on the landscape

Soil respiration is an important component of terrestrial carbon cycling and can be influenced by many factors that vary spatially. This research aims to determine the extent and causes of spatial variation of soil respiration, and to quantify the importance of scale on measuring and modeling soil respiration within and among common forests of Northern Wisconsin. The potential sources of variation were examined at three scales: [1] variation among the litter, root, and bulk soil respiration components within individual 0.1 m measurement collars, [2] variation between individual soil respiration measurements within a site (<1 m to 10 m), and [3] variation on the landscape caused by topographic influence (100 m to 1000 m). Soil respiration was measured over a two-year period at 12 plots that included four forest types. Root exclusion collars were installed at a subset of the sites, and periodic removal of the litter layer allowed litter and bulk soil contributions to be estimated by subtraction. Soil respiration was also measured at fixed locations in six northern hardwood sites and two aspen sites to examine the stability of variation between individual measurements. These study sites were added to an existing data set where soil respiration was measured in a random, rotating, systematic clustering which allowed the examination of spatial variability from scales of <1 m to 100+ m. The combined data set for this area was also used to examine the influence of topography on soil respiration at scales of over 1000 m by using a temperature and moisture driven soil respiration model and a 4 km² digital elevation model (DEM) to model soil moisture. Results indicate that, although variation of soil respiration and soil moisture is greatest at scales of 100 m or more, variation from locations 1 m or less can be large (standard deviation during summer period of 1.58 and 1.28 μmol CO₂ m⁻² s⁻¹, respectively). At the smallest of scales, the individual contributions of the bulk soil, the roots, and the litter mat changed greatly throughout the season and between forest types, although the data were highly variable within any given site. For scales of 1-10 m, variation between individual measurements could be explained by positive relationships between forest floor mass, root mass, carbon and nitrogen pools, or root nitrogen concentration. Lastly, topography strongly influenced soil moisture and soil properties, and created spatial patterns of soil respiration which changed greatly during a drought event. Integrating soil fluxes over a 4 km² region using an elevation dependent soil respiration model resulted in a drought induced reduction of peak summer flux rates by 37.5%, versus a 31.3% when only plot level data was used. The trends at these important scales may help explain some inter-annual and spatial variability of the net ecosystem exchange of carbon.     

Interactions between microclimatic variables and the soil microbial biomass

Summary Soil moisture, temperature, microbial substrate-induced respiration and basal respiration were monitored in two plots in an agricultural field from April 30 to September 25, 1987, and in a further two plots from May 26 to August 27, 1988. An attempt to relate biological variables to microclimatic variables was made through the use of correlation analysis. The microbial substrate-induced and basal respiration were both strongly positively correlated with the soil moisture content, and to a lesser extent positively related to soil temperature, especially when partial correlation was used to control for variation in soil moisture. Short-term changes in substrate-induced and basal respiration were correlated with changes in soil moisture but were largely independent of soil temperature. The ratio of basal to substrate-induced respiration (indicating the respiration: biomass ratio and therefore ecosystem stability or persistence) was negatively associated with the soil moisture content and in some instances with soil temperature when partial correlation analysis (correcting for soil moisture variation) was used. This suggests that the climatic conditions which contributed to the lowest ecosystem stability were low temperature, low moisture conditions.     

新疆达坂城盐湖不同植物群落土壤呼吸研究

新疆盐湖分布地域广泛而不均匀。盐湖生态系统碳循环是干旱区生态系统碳循环的重要组分,其动态变化对干旱区碳平衡有着重要的影响,然而目前对干旱区盐湖土壤呼吸的研究相对薄弱。为探讨盐湖沿岸不同植物群落土壤呼吸及其影响因子,以新疆达坂城盐湖为典型研究区,选取沿岸小獐毛(Aeluropus pungens)、鸢尾(Iris tectorum)、芨芨草(Achnatherum splendens)、黑果枸杞(Lycium ruthenicum Murr)植物群落土壤为主要研究对象,以周边农田撂荒地为对照,利用LI-COR 8100对达坂城盐湖沿岸4种植物群落和撂荒地土壤呼吸进行了监测,结果表明:盐湖沿岸土壤呼吸具有明显的日变化。监测时段内土壤呼吸作用均为单峰曲线,排放通量在13:00左右最高,07:00左右出现最低值。不同群落土壤呼吸速率变化范围在0.89~4.34μmol/(m~2·s)之间,撂荒地为1.77~3.48μmol/(m~2·s),表现为黑果枸杞小獐毛芨芨草撂荒地鸢尾。不同植物群落地下生物量影响土壤CO_2排放,研究区土壤呼吸日平均累计CO_2排放通量为209.28 mg/(m~2·d)。土壤呼吸速率与土壤5 cm温度呈现显著正相关(P0.01),可以解释土壤呼吸日变化的69%~78%,是决定达坂城盐湖土壤呼吸变化的主要因子。利用土壤5 cm处温度得到小獐毛、鸢尾、芨芨草、黑果枸杞、撂荒地的Q_(10)值分别为2.30、1.24、1.20、1.57、1.28,小獐毛样地土壤呼吸对温度更敏感。除撂荒地外各群落土壤呼吸与土壤湿度呈显著负相关(R~2=0.38~0.51)。该研究对进一步明确干旱区盐湖生态系统土壤呼吸变化规律和影响因素,以及对估算区域碳平衡及"碳汇"功能具有重要意义。     

两种轮作模式下秸秆还田对土壤呼吸及其温度敏感性的影响

通过分析不同作物轮作模式下秸秆还田对土壤呼吸及其温度敏感性的影响,为深入探究关中地区农田生态系统碳循环提供理论依据。试验设置于陕西省杨凌地区,在2012年10月至2014年9月期间以冬小麦-夏玉米轮作模式和冬小麦-夏大豆轮作模式作为研究对象,分别设置秸秆还田(SM)和秸秆不还田(NS)两个处理,测定分析不同处理下土壤呼吸、土壤温度及土壤含水量的变化趋势和差异,并估算土壤呼吸的温度敏感性(Q_(10))。结果表明:土壤呼吸存在明显的季节变化,在作物生育期大部分时间内,SM处理的土壤呼吸速率均显著高于NS处理(P0.05),且SM处理的作物生育期土壤呼吸平均速率及土壤呼吸累计排放量也极显著高于NS处理(P0.01);不同作物生育期土壤呼吸平均速率依次为夏玉米夏大豆冬小麦,土壤呼吸总量表现为冬小麦夏玉米夏大豆、冬小麦-夏玉米轮作冬小麦-夏大豆轮作。冬小麦-夏玉米轮作与冬小麦-大豆轮作的土壤温度间存在差异;其中,在冬小麦生育前期,冬小麦-夏玉米轮作的土壤温度显著高于冬小麦-大豆轮作;第2季夏玉米生育期内5 cm深度的土壤温度显著低于同季的夏大豆;相比NS处理,SM处理能提高冬季土壤的温度,并降低春季和夏季的土壤温度;在高温少雨的时期内,SM处理能够提高0~30 cm土壤的平均含水量,不同的前茬作物引起两种轮作模式中冬小麦耕作层土壤含水量间明显的差异,夏玉米耕作层土壤含水量显著高于夏大豆。相关分析表明,土壤呼吸与5 cm和10 cm土壤温度均存在极显著的正相关性,且与5 cm土壤温度的相关性更好;但土壤呼吸与0~30 cm的土壤平均含水量无显著相关性。5 cm和10 cm土壤温度变化能够分别解释土壤呼吸变化的64.6%~67.3%和51.5%~59.6%。整个研究周期内,温度敏感性(Q_(10))为1.70~2.01,冬小麦-夏玉米轮作的温度敏感性显著高于冬小麦-大豆轮作,且同一轮作模式下SM处理的温度敏感性显著低于NS处理。因此,秸秆还田能够提高农田的土壤呼吸作用,降低土壤呼吸的温度敏感性,同时能够调节土壤的水热状况。