Effects of Gamma Irradiation on Wheat Gluten

The effects of γ-irradiation on wheat gluten were studied by means of gel filtration on Sephadex G-100, starch gel electrophoresis and analysis of amino acid composition. Analyses of gluten at a moisture content of 2% revealed no significant change in amino acid composition except for cystine which was decreased by about 8% with irradiation at 10 Mrad. Changes in the chromatogram from gel filtration were interpreted in terms of random depolymerization resulting from irradiation. The results of starch gel electrophoresis suggested that irradiation levels greater than 3 Mrad resulted in characteristic changes in the molecular configuration of gliadin components.     

Desiccation studies in relation to the storage of Araucaria seed

Relationships between seed moisture content (fresh weight basis) and germination were examined for nine Araucaria species by desiccation under mild environmental conditions. The lowest safe moisture content, below which germination percentage begins to decline, was estimated in each case. Seeds can be grouped into three moisture content categories: the first group (including A. araucana, A. angustifolia, A. hunsteinii and A. bidwillii) cannot be safely dried to below 25–40%; the second group (including A. columnaris, A. rulei, A. nemorosa and A. scopulorum) cannot be dried to below about 12% without damage; the third category contains A. cunninghamii, which can be dried to 2% without damage. Seeds in the first group should be stored at 0–5 °C with moisture contents above the lowest-safe value. Provided freezing damage does not exceed 10%, seeds in the second group should be kept at - 18°C or lower with about 7% moisture content for long-term storage and at 0–5 °C with about 12% moisture content in the short term. Seed of A. cunninghamii is best retained at near 5% moisture content and in -18°C or lower. The lowest-safe moisture content was found to be associated with seed size and weight, higher moisture content values coinciding with greater size and weight of seed. Food reserve materials also differed among the groups; seeds of the first group were mainly starchy, whilst those in the other categories possessed a high lipid content.     

半干旱黄土高原苜蓿草地撂荒过程土壤水分变化特征

土壤水分是黄土高原植被恢复和生态建设的主要限制因子,明确土壤水分随植被演替的变化规律是阐明黄土高原植被与水分相互作用机制的重要基础。以半干旱黄土高原小流域苜蓿草地撂荒过程为研究对象,通过对2016-2018年生长季苜蓿群落、苜蓿+赖草群落、赖草群落和长芒草群落四种草地群落0-1.8 m土壤水分进行动态监测以及0-5 m深度土壤水分测定,分析不同演替阶段苜蓿草地土壤水分的动态特征,探讨土壤水分对苜蓿草地撂荒过程的响应。结果表明：（1）在苜蓿草地撂荒演替过程中,土壤水分随群落恢复时间的延长呈先增加后降低的变化,降水的年际动态显著影响不同演替群落的土壤水分响应;（2）0-0.4 m土壤水分主要受降水影响,使得各草地群落在这一层次没有显著差异（P>0.05）,而1 m以下的土壤水分含量则主要受植被类型的影响,各草地群落之间存在显著差异（P<0.05）;（3）0-5 m深层土壤水分随群落的演替,1 m以下各土层土壤水分含量逐渐增加,表明撂荒过程中使土壤水分得到了一定程度的恢复。研究结果揭示了苜蓿草地撂荒过程土壤水分的变化规律,可为黄土高原生态恢复提供理论依据。     

黄土高寒区坡面土壤水分的时间稳定性

为揭示黄土高寒区人工林土壤水分的时空变化特征,基于2018年植被生长期一处典型人工植被恢复坡面0-200cm剖面土壤含水率连续动态数据,运用经典统计和时间稳定性分析,研究不同深度土壤含水率的时空变异性和时间稳定性。结果表明：在测定时段内,剖面各土层深度土壤含水率无显著差别,在空间上均表现为中等变异性,呈现随土层深度的增加而增大的趋势,在时间上表层表现为中等变异性,其余各层均表现为弱变异性,深层土壤水分的时间变异性小于浅层;随着测定时间变化,试验地0-200cm土壤含水率Spearman秩相关系数均达到0.8以上,且呈极显著相关,表现出一定的时间稳定性特征;土壤含水率的时间稳定性随土层深度的增加而增强,具有深度依赖性;基于相对差分分析可以选择代表性测点监测区域平均土壤含水率（决定系数R²为0.7138-0.8605）,以期为合理布设土壤水分监测点提供理论依据,对于植被恢复与生态重建模式的选择具有指导意义。     

Effect of moisture evaporation from diatomaceous earth pellets on storage stability of Steinernema glaseri

Induction of anhydrobiosis and storage stability of entomopathogenic nematodes are influenced by moisture availability. Decreasing moisture content in diatomaceous earth (DE) pellets containing the Steinernema glaseri NJ-43 strain and its effect on survival time and infectivity of the nematode were determined. Pelletisation was performed in a vortex mixer, using DE Celite® 209 as the desiccant material. Pellets were stored at room temperature (23?±?2°C) and high relative humidity (96–100%). Nematode survival and infectivity against last instar greater wax moth, Galleria mellonella, were tested daily. Initial average and average equilibrium moisture content in pellets were 66.7% and 13.6%, respectively, and the infective juveniles mean survival time was 8.8 days. A moisture transfer model based on diffusion and evaporation was evaluated to predict moisture fluctuations within the pellets. We concluded that 84% of variation in S. glaseri infectivity on G. mellonella larvae was explained by the survival of the nematode, whereas 52% of variation in S. glaseri survival was explained by the loss of moisture from the pellets. The moisture transfer model achieved 78% reliability in predicting moisture content and fluctuations. Therefore, the mechanisms of moisture diffusion and evaporation from the surface to the surrounding atmosphere contribute significantly to moisture loss from the pellets.     

荒漠绿洲过渡带不同年限雨养梭梭(Haloxylon ammodendron)对土壤水分变化的响应

通过调查分析河西走廊荒漠绿洲过渡带不同种植年限（5、10、20、30和40a）人工梭梭生理生化变化（叶片渗透调节物质、丙二醛和叶绿素含量,根系活力）和个体形态特征（叶片、枝条和茎干生物量、枯枝落叶比、株高、冠幅等）以揭示不同种植年限雨养梭梭对土壤水分变化的响应机制。研究结果表明：随着梭梭种植年限增加,人工梭梭林内深层100-120cm和180-200cm土壤水分变化明显,在5-20a保持在3%-4%,而在种植后期（30-40a）土壤水分下降到1%-2%左右。在5-20a,梭梭主要通过显著提高叶片渗透调节物质可溶性糖和可溶性蛋白含量,维持叶片较低的丙二醛含量和较高的叶绿素含量,保持新叶光合能力;同时,显著提高0-20cm根系的活力,增强对表层土壤水分的吸收能力;但在30-40a,梭梭叶片渗透调节物质明显减少,梭梭叶片丙二醛含量增加,叶绿素含量下降,同时叶绿素a,b比例失调,渗透调节作用失效,梭梭叶片老化,老叶比例明显增加,光合作用能力下降,枝条和茎干退化严重,个体生物量进一步减少,在40a梭梭叶片、枝条和茎干生物量下降到最低值。研究表明在年降水100mm左右的荒漠绿洲过渡带,在种植梭梭5-20a土壤水分为3%-4%,梭梭可以通过生理调节适应土壤干燥,但是从30a土壤水分下降到1%-2%时,梭梭主要通过枯枝落叶降低个体蒸腾耗水量,在40a梭梭进入休眠（假死）状态,这暗示土壤水分下降到1%-2%,可能是梭梭的临界吸收土壤水分。     

贵州特有植物美丽红山茶水分胁迫的生理响应

采用水分抗逆性指标主成分分析法,选择4年实生苗,测定和评价了连续30 d水涝和干旱胁迫的生理响应.结果表明：(1)水涝处理的叶片生长旺盛,光泽度和观赏性无明显变化,叶片相对含水量、MDA含量、SOD活性、POD活性、CAT活性的变化差异在5％以内,土壤含水量增加3．47％,细胞膜透性减少1．59％,短期水涝对美丽红山茶伤害不明显;(2)随着干旱时间延长,新叶卷缩、老叶脱落,土壤含水量、叶片相对含水量随时间呈负相关缓慢减少,细胞膜透性呈正相关缓慢增长,但复水10 d 后可恢复正常生长,无明显生理变化响应;(3)SOD活性和MDA含量分别增加了0．66％和5．31％,POD活性随干旱时间上下波动而增加6．47％, CAT活性随干旱时间延长而增加,20 d增加33．33％达最大值20．8 U??g-1??min-1.在抗性生理中,维持膜稳定性的叶片含水量、POD和CAT的变化对抗旱能力大小起主要作用.     

半干旱黄土区苜蓿退化对坡面草本植物分布及多样性的影响

半干旱黄土丘陵区土壤水分亏缺引起人工苜蓿草地退化会显著影响其他草本植物的分布及多样性,然而地形驱动下的苜蓿草地退化及植被群落多样性响应还尚不清楚。以典型半干旱黄土丘陵区龙滩小流域为研究区,对不同地形条件下退化苜蓿草地地上生物量、草本多样性及生长季内0—200 cm土壤水分进行了定位监测,利用方差分析、相关分析和典范对应分析(CCA)明确坡面地形、苜蓿生长状况和土壤水分与其他草本植物分布及多样性之间的关系。结果表明:(1)地形显著影响植被群落特征,西坡、东坡和北坡样带苜蓿地上生物量明显不同,西坡和东坡样带中、下坡位苜蓿地上生物量明显高于上坡位,而其他草本的生物量、物种丰富度和多样性指数的变化趋势则与苜蓿相反;(2)苜蓿地上生物量与80—200 cm土壤水分显著正相关,而与0—20 cm和20—80 cm土壤水分的相关性较小;(3)地形特征、不同深度土壤水分和苜蓿地上生物量解释了退化苜蓿草地其他草本群落变异的87.8%,其中坡向、苜蓿地上生物量、0—20 cm和20—80 cm土壤水分4个因子解释了79.3%的群落变异。研究认为,半干旱黄土丘陵区不同地形条件引起坡面土壤水分变化,进而影响退化苜蓿草地地上生物量,使得苜蓿退化程度不同,而苜蓿退化程度和0—80 cm土壤水分决定了不同部位草本分布及多样性。     

The lethal effects of gamma irradiation on larvae of the Huhu beetle, Prionoplus reticularis: a potential quarantine treatment for New Zealand export pine trees

Gamma irradiation was investigated as a possible method for disinfestation of huhu beetle larvae, Prionoplus reticularis White, in Pinus radiataD. Don. Larvae of four representative size classes were irradiated at six doses, and the lethal dose (LD₉₉) calculated from mortality data 3 days and 10 days post treatment. All larval size classes showed a similar sensitivity to gamma irradiation and required 3677 Gray (Gy) and 2476 Gy for a LD₉₉ 3 and 10 days post-treatment, respectively. The penetration of gamma irradiation into pine wood was found to be lowest in freshly cut logs, and decreased linearly at a rate of 0.698 Gy mm^–1 of wood. The penetration was greatest in wood that had been stored for 2 years, and decreased 0.512 Gy mm^–1 of wood. These results are likely to be correlated with wood moisture content. Gamma irradiation appears to be a potential alternative method to fumigation for quarantine treatment of P. reticularis.     

荒漠人工固沙植被区土壤水分的时空变异性

表层土壤水分具有高度的时间和空间变异性.研究的目的:(1)揭示沙坡头人工固沙植被区浅层土壤水分的时空变异性特征;(2)确定驱动土壤水分变异的主要环境因子.在人工固沙植被区内一个4500m2的网格样地上每隔10m设置取样点,在连续7个月的时间内 (2005年4～10月),每隔15d用时域反射仪测量各样点表层以下15cm和30cm深度的土壤容积含水量.结果表明,该区网格尺度上浅层土壤水分的分布具有明显的空间变异性,其变异性随着土壤水分含量的降低而减小;相对海拔是驱动土壤水分空间变异的主要环境因子,其作用在降雨后尤为显著,且其对土壤下层的影响比上层更明显;植被和土壤水分含量的相关性时间序列与相对海拔一致--降雨使其相关性增加;土壤质地(土壤粒径分布)和土壤水分含量的相关性时间序列特征与植被和相对海拔相反,且其对土壤上层的影响比下层更明显.因此,在沙坡头荒漠人工固沙植被区,降雨后的短暂湿润期,地形和植被是驱动浅层土壤水分变异的主要影响因子,而随着降雨之后土壤逐渐变干,土壤质地的影响变得更加明显.     

夏玉米叶片气体交换参数对干旱过程的响应

目前已经开展了大量的干旱对作物叶片气体交换参数影响的研究,但关于作物叶片气体交换参数对干旱过程的响应及其关键阈值的研究仍较少。基于夏玉米七叶期开始的5个初始水分梯度的长时间持续干旱模拟实验资料,分析了不同强度持续干旱过程中夏玉米叶片气体交换参数(净光合速率Pn,气孔导度Gs,蒸腾速率Tr,胞间CO_2浓度Ci和气孔限制值Ls)的变化规律及其关键阈值。结果表明,玉米的净光合速率(Pn),蒸腾速率(Tr)和气孔导度(Gs)在干旱发生初期呈大幅度下降,但随着干旱持续会出现一定的适应性。利用统计容忍限方法确定了夏玉米拔节期Pn,Tr和Gs响应干旱的临界土壤相对湿度(0—30cm)分别为53%,51%和48%,对应的临界叶含水率分别为81.8%,81.3%和81.2%。夏玉米光合作用由气孔限制向非气孔限制转换的0—30cm土壤相对湿度均为44%±2%,对应的叶含水率均为77.6%±0.3%。研究结果可为夏玉米干旱发生发展过程的监测预警提供依据。     

Storage behavior of Zygophyllum xanthoxylon (Bge.) Maxim seeds at low moisture contents

This research aimed to determine whether low moisture content storage improves the longevity and storability of Zygophyllum xanthoxylon (Bge.) Maxim seeds. The seeds of Z. xanthoxylon were dried from 11.43 to 4.81%, 3.81 and 2.41% moisture content in a desiccating container with silica gel. After storage for 24 months their level of vigor was measured. After the ageing process, some physiology indices, including the relative electrical conductivity, SOD, PER, CAT, volatile aldehydes and malondialdehyde were tested. The results indicated that SOD, PER and CAT activities of the low moisture content seeds were higher than the control seeds while volatile aldehydes and malondialdehyde were lower than the control group. The electrical conductivity showed that there was obvious statistical difference between low moisture content seeds with the control group. All the results showed that low moisture content storage is beneficial for maintaining the vigor of Z. xanthoxylon seeds. Thus Z. xanthoxylon seeds can be stored with low moisture content at ambient temperature condition for a long time.     

Experimental short time production of aflatoxins by Aspergillus parasiticus in mixed feeds as related to various moisture contents

Experimental short time production of aflatoxins in mixed feeds at 22, 28 and 37 °C as related to various moisture contents was studied. Growth of Aspergillus parasiticus was not observed in the meals with a moisture content ranging around 15% (22, 28 and 37 °C); the lowest quantifiable total aflatoxins at the fourth day was detected at 22 °C with 19.4% of moisture content; the higher total quantity of aflatoxins (113 mg/kg) was produced at 28 °C with 29.3% of moisture content. The ratio aflatoxin B₁/aflatoxin G₁ increased as the temperature raised.     

Effects of post-application irrigation and substrate moisture on the efficacy of entomopathogenic nematodes against western flower thrips, Frankliniella occidentalis

The efficacy of entomomatogenic nematodes (Steinernema bicornutum Tallosi, Peters and Ehlers and/or Heterorhabditis indica LN2 Poinar, Karunakar and David) against the soil‐dwelling life stages of western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) was assessed under different moisture conditions in a commercial plant‐growing substrate in laboratory experiments. In the first experiment, both nematode species were tested at substrate moisture ranges of 67, 78, 88, or 95% relative moisture content, that were maintained before applying the nematodes at 100 or 400 infective juveniles (IJs) cm^?2. In the second experiment, 10, 25, 50, 100, or 120 ml irrigation water, resulting in relative moisture contents of 72, 81, 90, 99%, or more than the saturation level of the substrate, respectively, was applied to the substrate. Heterorhabditis indica LN2 was applied either in 3 ml water and followed by irrigation, or by suspending the infective juveniles in the water amounts indicated above to apply the nematodes in higher volume. Results indicated that at the higher application rate, initial moisture content did not significantly affect the efficacy of H. indica LN2. On the other hand, increasing moisture content resulted in an improved efficacy of H. indica LN2 and S. bicornutum at lower and higher application rates, respectively. Similar thrips control levels of 44 and 60% at the lower and higher application rate of H. indica LN2, respectively, were obtained at 88% relative moisture content. In the second experiment, higher and statistically similar thrips mortality of 40 and 50% at lower and higher application rates of H. indica LN2, respectively, were obtained when the infective juveniles were applied in a high volume suspension of 100 ml, or when followed by irrigation with 25 ml water, resulting in both cases in 81% relative moisture content. Generally, efficacies of the nematodes for thrips control can be improved by using an appropriate moisture content and/or post‐application irrigation. Thus, the high nematode application rates required for successful F. occidentalis control can be partly attributed to substrate moisture content and/or post‐application irrigation.     

Heat inactivation of Salmonella spp. in fresh poultry compost by simulating early phase of composting process

Aims: The purpose of this study was to determine the effect of moisture on thermal inactivation of Salmonella spp. in poultry litter under optimal composting conditions. Methods and Results: Thermal inactivation of Salmonella was studied in fresh poultry compost by simulating early phase of composting process. A mixture of three Salmonella serotypes grown in Tryptic soy broth with rifampin (TSB‐R) was inoculated in fresh compost with 40 or 50% moisture at a final concentration of c. 7 log CFU g^?1. The inoculated compost was kept in an environmental chamber which was programmed to rise from room temperature to target composting temperatures in 2 days. In poultry compost with optimal moisture content (50%), Salmonella spp. survived for 96, 72 and 24 h at 50, 55 and 60°C, respectively, as compared with 264, 144 and 72 h at 50, 55 and 60°C, respectively, in compost with suboptimal moisture (40%). Pathogen decline was faster during the come‐up time owing to higher ammonia volatilization. Conclusions: Our results demonstrated that Salmonella spp. survived longer in fresh poultry compost with suboptimal moisture of 40% than in compost with optimal moisture of 50% during thermophilic composting. High nitrogen content of the poultry compost is an additional factor contributing to Salmonella inactivation through ammonia volatilization during thermal exposure. Significance and Impact of the Study: This research validated the effectiveness of the current composting guidelines on Salmonella inactivation in fresh poultry compost. Both initial moisture level and ammonia volatilization are important factors affecting microbiological safety and quality of compost product.     

Optimization of the spray drying of a Paenibacillus polymyxa-based biopesticide on pilot plant and production scales

Spore survival and moisture content are two important properties of biopesticides, and both are related to field biocontrol efficacy and storage shelf life. In this study, Paenibacillus polymyxa (HY96-2) was spray-dried on both pilot plant and production scales, and the effects of inlet and outlet temperatures on spore survival and moisture content were investigated. The results showed that inlet temperatures ranging from 170 to 230 °C (at an outlet temperature of 80 °C) had no obvious effect on the two properties during pilot scale processing, although an inlet temperature of 230 °C resulted in higher feed speed. When the outlet temperature on the pilot scale was reduced from 100 to 80 °C, no obvious variations in spore survival and moisture content were found, while a further reduction from 80 to 65 °C resulted in a decline in spore survival from 81.0 to 67.0% and an increase in moisture content from 2.3 to 31.7%. These results indicate that both outlet temperature and moisture content have an effect on spore survival. Optimum inlet and outlet temperatures for P. polymyxa processing were 230 °C and 85–90 °C on a production scale. Under these conditions, spore survival and moisture content were 83.5–86.6% and 2.73––4.12%, respectively.     

Prevalence and development of storage fungi in peanut Arachis hypogaea seed

Summary A batch of peanutArachis hypogaea seed were divided into 4 2-kilogram portions and stored 6 months at 22–28° C. One portion was stored with the moisture content slowly increasing from 4 to 28 %; the other portions were maintained at approximately 4.5, 8.9 and 11.5 %. After 1, 2, 3, 4, and 6 months storage, 100 seed of each treatment were cultured on malt-10 % NaCl agar and the fungi isolated identified. The storage fungi present after intervals of storage were compared with those initially present. In seed stored at 4.4 % moisture,Aspergillus species remained about the same andPenicillium decreased. At 8.9 % moistureA. flavus, A. repens andPenicillium were reduced, andA. amstelodami andA. ruber increased. At 11.5 % moisture, 100% of the seed yieldedA. ruber after 4 months storage and the other storage fungi decreased to 0–2 %. The moisture content of seed stored at 99 % R. H. increased slowly to 28 % and resulted in monthly changes in the dominant fungi. Under such a circumstance with competition between these storage fungi,A. ruber grew best at 12–15 %,A. repens at 18.5 %,A. flavus andPenicillium at 20 %, andA. amstelodami between 20–28 %.Fusarium increased very rapidly as moisture content increased above 18 %.This investigation was supported by Agricultural Research Service, U.S. Department of Agriculture, Contract No. 12-14-100-8179 (34), administered by the Crops Research Division, Beltsville, Maryland.Former Research Associate, North Carolina State University, Raleigh, N. C., currently Research Plant Pathologist, Market Quality Research Division, Agricultural Research Service, United States Department of Agriculture; and Professor, North Carolina State University, Raleigh, N.C.Paper number 2489 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh, North Carolina.     

Dilatometric Measurement of the Partial Molar Volume of Water Sorbed to Durum Wheat Flour

Moisture sorption isotherms were measured at 25 °C for untreated, dry-heated and pre-gelatinized durum wheat flour samples. The isotherms could be expressed by the Guggenheim-Anderson-de Boer equation. The amount of water sorbed to the untreated flour was highest for low water activity, with water sorbed to the pre-gelatinized and dry-heated flour samples following. The dry-heated and pregelatinized flour samples exhibited the same dependence of the moisture content on the partial molar volume of water at 25 °C as the untreated flour. The partial molar volume of water was ca. 9 cm³/mol at a moisture content of 0.03 kg-H₂O/kg-d.m. The volume increased with increasing moisture content, and reached a constant value of ca. 17.5 cm³/mol at a moisture content of 0.2 kg-H₂O/kg-d.m. or higher.     

祁连山北坡青海云杉林下苔藓层对土壤水分空间差异的影响

苔藓层是青海云杉林(Picea crassifolia forest)下的一个重要层片,它通过截持降水和减少土壤蒸发,对土壤水分产生影响。以祁连山北坡排露沟小流域的一个阴坡(海拔2700 m,植被为青海云杉林)作为样坡,于2010—2012年生长季对青海云杉林下有、无苔藓层覆盖地点的土壤水分进行对比观测。结果表明在祁连山青海云杉林下,苔藓层覆盖能减少土壤水分的空间差异。主要表现为:(1)无苔藓覆盖各观测点土壤含水量极差达62.2 mm,空间变异系数(CV)为17.3%;有苔藓层覆盖观测点土壤含水量空间变异系数为2.3%,仅为无苔藓覆盖地点的1/7.5,空间差异极显著(sig.0.001)。(2)在持续无雨、小雨后和连阴雨天气下,有苔藓覆盖地点土壤含水量空间差异均显著小于无苔藓覆盖地点(sig.0.05)。在持续无雨的情况下,无苔藓层覆盖各观测点土壤含水量空间变异系数平均值为19.8%,有苔藓覆盖地点土壤含水量空间变异系数平均值为6.6%,仅为无苔藓覆盖地点的1/3。小雨后,无苔藓覆盖各观测点土壤含水量空间变异系数平均值为15.2%,有苔藓覆盖地点土壤水分空间变异系数平均为5.1%,为无苔藓覆盖地点的1/3。连阴雨后,无苔藓覆盖各观测点土壤含水量空间变异系数平均为15.4%,有苔藓覆盖地点土壤水分空间变异系数平均为4.6%,为无苔藓覆盖地点的1/3.3。(3)持续无雨的情况下,苔藓层减小土壤水分空间差异的作用主要反映在土壤表层0—15 cm,对深层的作用不显著。而小雨和连阴雨后,苔藓层对15—80 cm深层土壤影响显著,而表层0—15 cm没有明显规律。     

Response of soil CO2 efflux to water manipulation in a tallgrass prairie ecosystem

Although CO₂ efflux plays a critical role in carbon exchange between the biosphere and atmosphere, our understanding of its regulation by soil moisture is rather limited. This study was designed to examine the relationship between soil CO₂ efflux and soil moisture in a natural ecosystem by taking advantage of the historically long drought period from 29 July to 21 September 2000 in the southern Central Great Plain, USA. At the end of August when soil moisture content at the top 50 mm was reduced to less than 50 g kg^–1 gravimetrically, we applied 8 levels of water treatments (simulated to rainfall of 0, 10, 25, 50, 100, 150, 200, and 300 mm) with three replicates to 24 plots in a Tallgrass Prairie ecosystem in Central Oklahoma, USA. In order to quantify root-free soil CO₂ efflux, we applied the same 8 levels of water treatments to 24 500-mm soil columns using soil from field adjacent to the experimental plots. We characterized dynamic patterns of soil moisture and soil CO₂ efflux over the experimental period of 21 days. Both soil moisture content and CO₂ efflux showed dramatic increases immediately after the water addition, followed by a gradual decline. The time courses in response to water treatments are well described by Y=Y₀+ate^–bt, where Y is either soil moisture or CO₂ efflux, t is time, Y ₀, a, and b are coefficients. Among the 8 water treatments, the maximal soil CO₂ efflux rate occurred at the 50 mm water level in the field and 100 mm in the root-free soil 1 day after the treatment. The maximal soil CO₂ efflux gradually shifted to higher water levels as the experiment continued. We found the relationship between soil CO₂ efflux and soil moisture using the data from the 21-day experiment was highly scattered, suggesting complex mechanisms determining soil CO₂ efflux by soil moisture.