基于低场核磁共振的热风干燥猕猴桃切片含水率预测模型

为研究猕猴桃切片热风干燥过程中水分迁移规律,该试验通过对猕猴桃切片进行热风干燥,考察不同干燥温度(70、80、90℃)、切片厚度(3、4、5 mm)下的干燥特性。试验采用直接干燥法测定含水率,运用低场核磁共振技术(Low-Field Nuclear Magnetic Resonance,LF-NMR)分析热风干燥过程中猕猴桃切片内部水分分布状态与变化规律,建立动力学模型,验证并预测。结果表明:猕猴桃切片热风干燥开始为外部控制,随后属于内部扩散控制,水分有效扩散系数范围为1.58×10-7～4.18×10-7 m2/s,扩散效率随温度升高而增大。升高温度能显著提高猕猴桃干燥速率,可加快结合水、不易流动水以及自由水的迁移。自由水和结合水先于不易流动水发生变化,自由水含量在干燥前期逐渐下降,此过程中不易流动水和结合水含量均表现为先升高后降低的趋势。当自由水被脱除后,不易流动水和结合水含量依次达到最大值;此后,随着干燥的进行,不易流动水逐渐被脱除,此时结合水含量开始下降直至干燥结束。整个干燥过程中,猕猴桃切片部分自由水先转化为不易流动水和结合水,结合水与不易流动水相互转化,循环往复伴随整个干燥过程。以干燥过程中的自由水、结合水、不易流动水的核磁峰值总和、切片厚度和干燥温度为自变量,猕猴桃切片含水率为因变量,进行多元线性回归分析,建立含水率预测模型,模型的拟合优度为0.982。结果表明,低场核磁共振技术结合数学模型可用于描述猕猴桃切片热风干燥过程,可实现对猕猴桃切片干燥过程中含水率的快速、无损检测,研究结果可为猕猴桃热风干燥工艺和过程设计提供理论依据。     

不同施肥条件下农田硝态氮迁移的试验研究

NO^-₃-N的淋失是旱地农田氮素损失的重要途径之一，也是引起地下水污染的一个主要原因。在黄土高原地区，夏玉米生长正逢雨季，是NO^-₃-N淋失的主要时期。该研究基于阻水层理论和黄土高原地区传统的垄作习惯，在手工模拟机具成垄压实施肥的基础上研究了该施肥法与传统的平地施肥、垄沟施肥(成垄不压实)条件下土壤NO^-₃-N的迁移动态，结果表明，在供水量相同条件下，由于平地和垄沟条件下水分分布的差异，导致平地土壤中的NO^-₃-N较垄沟耕作易于迁移。在生育前期，由于作物根系对NO^-₃-N的吸收和拦截，成垄压实与成垄不压实施肥对阻止NO^-₃-N随水下移差异不大；生育后期，当作物需肥量减小时，成垄压实施肥能够阻止NO^-₃-N向深层土壤迁移累积。玉米收获后，3种施肥方式下土壤NO^-₃-N迁移深度为平地(>60 cm)>垄沟施肥(>45 cm)>成垄压实施肥(＜35 cm)。     

山药片红外联合热风干燥热质传递收缩模拟与品质

为了准确揭示山药片红外联合热风干燥传热传质机理,在考虑山药片收缩变形特性的基础上,通过有限元软件COMSOL6.1建立了“温度场-湿度场”多场耦合的山药片红外联合热风干燥传热传质模型。模拟研究基于山药片在不同温度（50、60、70 ℃）下收缩变形的传热传质,并通过试验进行验证。分析不同温度对山药片品质（色差、复水比、多糖和尿囊素含量）的影响。结果表明：1）山药片体积比随干燥温度的升高而增加,在干燥温度分别为50、60、70 ℃时,其值分别为34.55%、37.23%、39.04%。2）在干燥温度为50、60、70 ℃时,红外联合热风干燥收缩模型可准确预测山药片干燥过程中干燥温度和含水率,其决定系数R²分别为0.973、0.976、0.981和0.983、0.984、0.974。3）山药片外部温度升高,表面水分开始蒸发,形成水分梯度。随着干燥的继续,红外热量在山药片内部不断积累,导致内部温度升高,水分向外扩散,进而减小了内外水分梯度。随着干燥温度的升高,增加了山药片温度和湿度梯度,促进了热量和质量的传递,提高了水分迁移的速率。4）在60 ℃时,干燥品质最优,其色差为7.49、复水比为2.65 kg/kg、多糖含量为24.17 mg/g、尿囊素含量为2.66 μg/g。该模型为其他物料在红外联合热风干燥技术的模拟研究提供有益借鉴。     

太行山前平原冬小麦综合节水技术效应分析

在河北省鹿泉市南铜冶村试区实施了工程、农艺等综合节水技术,冬小麦全生育期浇2次水,使小麦产量达7500kg／hm²,水分利用效率达18kg／hm².mm。若种植节水品种、实施秸秆覆盖节水措施,冬小麦水分利用效率可达24．3kg／hm²·mm,为太行山前平原实施节水农业提供了科学依据。     

沃特和PAM保水剂对土壤水分及马铃薯生长的影响研究

在陕北黄土丘陵沟壑区以不施为对照，开展了浸种、穴施保水剂沃特和PAM对土壤水分和马铃薯生长影响研究。结果表明：沃特、PAM不同处理10～20 cm、30～40 cm土层土壤含水率在盛花前略高于对照，茎叶衰老后略低于对照。不同处理0～100 cm土层土壤水含量苗期略高于对照；花期沃特、PAM穴施用量15和30 kg/hm²处理极显著高于对照，沃特、PAM穴施用量60 kg/hm²和1.0%浸种处理显著低于对照；收获期不同处理均低于对照。不同处理花期、收获期均表现为沃特、PAM施用量越大，生物量、块茎产量越高，块茎个数越少，最大块茎越大。从播种到花期沃特、PAM穴施用量15和30 kg/hm²处理的耗水量显著低于对照，从播种到收获期不同处理的耗水量与对照无显著差异，但花期、收获期不同处理的水分利用率和水分产出率均极显著高于对照。沃特和PAM在马铃薯生产应用中，穴施应以30 kg/hm²到45 kg/hm²为宜。用1.0%的浓度浸种，可成为沃特和PAM在马铃薯生产中利用的主要方式。     

宁夏引黄灌区稻田氮素浓度变化与迁移特征

过量施氮与不合理灌水是农田面源污染加剧的主要原因。为了寻求较优的水氮管理模式以促进农业生产和减少农田退水对黄河水体的污染, 在宁夏引黄灌区典型稻田中开展了不同水氮条件下稻田氮素迁移转化规律研究。结果表明: 不同水氮条件下稻田田面水NH₄⁺-N 与NO₃^--N 浓度伴随施肥出现明显峰值, NO₃^--N 峰值出现时间较NH₄⁺-N 晚, 且变化较平缓。3 次追肥时期和整个生育期田面水NH₄⁺-N 平均浓度与施氮量和灌水量都呈显著相关, 田面水NO₃^--N 平均浓度与施氮量呈显著正相关, 与灌水量相关性不显著。稻田30 cm与60 cm 深度的直渗水NH₄⁺-N 浓度受施肥影响较大, 与田面水NH₄⁺-N 浓度变化规律相似, 90 cm 处直渗水NH₄⁺-N 浓度峰值出现较为滞后, 且浓度较上层土体低, 120 cm 处直渗水NH₄⁺-N 浓度大体呈现持续上升趋势,整个生育期直渗水NH₄⁺-N 平均浓度与施氮量呈显著相关, 仅30 cm 处NH₄⁺-N 平均浓度与灌水量呈负相关, 其他土层深度不显著。30 cm 与60 cm 直渗水NO₃^--N 浓度在首次灌水后急剧下降, 在施肥后有较小幅度上升, 90 cm 与120 cm 直渗水NO₃^--N 浓度下降缓慢, 仅30 cm 处NO₃^--N 平均浓度与施肥量显著正相关。总的结果表明减少施肥或灌水均可达到减少农田氮素淋失的目的。     

不同钠吸附比的咸水结冰融水入渗后滨海盐土的水盐分布

在室内利用相同矿化度(10 g·L^-1)、不同钠吸附比(5、10 和30)的咸水进行咸水结冰融水模拟试验、结冰融水入渗和咸水直接入渗的土柱试验, 以淡水处理为对照, 分析不同钠吸附比咸水结冰融水入渗下滨海盐土水盐分布特征。结果表明: 咸水冰融化过程中, 融出水的矿化度和钠吸附比均呈由高到低的变化趋势。咸水结冰融水入渗速度和入渗深度均快于和深于淡水。咸水钠吸附比越小, 结冰融水入渗速率越快、深度越深。水盐分布也表现为低钠吸附比咸水结冰处理的表层土壤含水量较低, 水分向深层迁移, 这种水分分布也使盐分向深层运移, 表现为表层土壤含盐量低, 深层土壤含盐量大。土层含水量低钠吸附比咸水处理高于高钠吸附比处理, 10~45 cm 土层则表现出相反的趋势; 表层土含盐量低钠吸附比处理高于高钠吸附比处理, 且咸水处理下土壤脱盐的深度大于淡水处理。钠吸附比5 的咸水结冰处理, 0~10 cm 土壤平均含水量和含盐量分别为30.3%和1.1 g·kg^-1, 显著低于其他处理。为比较咸水结冰灌溉和咸水直接灌溉的效果, 室内利用含盐量为10 g·L^-1、钠吸附比10 的咸水进行直接入渗的土柱(土壤含盐量为21.3 g·kg^-1)模拟试验, 结果表明: 与咸水直接入渗处理相比, 咸水结冰融水处理盐分淋洗效果更好, 该处理0~25 cm土层平均土壤含盐量为2.9 g·kg^-1, 显著低于咸水直接入渗的10.6 g·kg^-1。     

膜下滴灌灌溉频率对马铃薯生长、产量及水分利用率的影响

膜下滴灌作为当今重要的节水灌溉技术之一, 在内蒙古马铃薯种植上的应用存在过量灌水或灌水不及时等问题, 使其优势没有得到充分发挥。为了探讨适合内蒙古呼和浩特市武川地区膜下滴灌马铃薯生产的最佳灌溉频率, 以"克新一号"马铃薯的脱毒原种为材料, 采用田间小区试验, 研究了总灌水量为120 mm条件下, 3种不同灌溉周期(灌溉周期分别为4 d、8 d、12 d )对马铃薯生长、产量和水分利用效率的影响。结果表明, 灌溉周期为8 d的土壤湿润深度0~40 cm, 与马铃薯根系集中层吻合, 有利于马铃薯生长, 平均株高、干物质积累量、淀粉含量和水分利用效率分别为40.8 cm、8 683.0 kg·hm^-2、13.9%、11.2 kg·mm^-1, 分别比4 d和12 d灌溉周期的增加3.1%和4.1%、8.9%和10.1%、37.2%和9.3%、26.3%和33.3%; 而4 d灌溉周期的产量较高, 为35 398.5 kg·hm^-2, 比8 d和12 d灌溉周期的分别增加12.1%和15.4%, 与8 d灌溉周期之间差异不显著。综合分析膜下滴灌灌溉频率对内蒙古武川地区马铃薯生长、产量和水分利用效率的影响, 得出8 d灌溉周期较为适宜。     

甘肃河西走廊水资源供需分析及耕作节水研究

根据河西走廊有62.42×10⁸ m³地表水资源、4.94×10⁸ m³地下水资源和每年耗水70.44×10⁸ m³的矛盾，分析了水对这一地区的影响，指出了河西走廊只能靠减少水分蒸发、农业节约用水、提高水的利用率和灌水生产效率来实现水资源的平衡。在试验的基础上 ，提出了灌水生产率比传统耕作高60.78％和节水41.29%的保护性耕作方法。     

基于灌溉的北方冬小麦水分供需风险研究

依据风险原理，利用北方冬麦区近40年冬小麦水分供需的相关资料，基于灌水定额为675 m³/hm²，估算了冬小麦全生育期无灌溉、灌1～5水条件下不同水分供需率等级出现的风险概率。结果表明：北方冬麦区不同水分供需率等级出现的风险概率，呈由北向南逐渐减少的趋势；其中中南部地区呈由中部向沿海、由中部向西部逐渐减少的趋势。以冬小麦全生育期水分供需率≥70%的风险概率≥90%、水分供需率≥80%的风险概率≥75%为主导指标，确定了基于风险的不同地区的冬小麦全生育期适宜补充灌溉次数。北方冬麦区在补充灌溉1～4水后，即可基本满足冬小麦稳产增产的水分需求；在适宜补充灌溉3～4水的地区，传统方式灌5～6水，过量灌溉严重，目前可至少减少灌溉1～2次，节水675～1350 m³/hm²。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.     

Electron donor and pH relationships for biologically enhanced dissolution of chlorinated solvent DNAPL in groundwater

Biologically enhanced dissolution offers a method to speed removal of chlorinated solvent dense non-aqueous-phase liquid (DNAPL) sources such as tetrachloroethene (PCE) and trichoroethene (TCE) from aquifers. Bioremediation is accomplished by adding an electron donor to the source zone where fermentation to intermediates leading to acetic acid and hydrogen results. The hydrogen and possibly acetic acid are used by dehalogenating bacteria to convert PCE and TCE to ethene and hydrochloric acid. Reductive dehalogenation is thus an acid forming process, and sufficient alkalinity must be present to maintain a near neutral pH. The bicarbonate alkalinity required to maintain pH above 6.5 is a function of the electron donor: 800 mg/L of bicarbonate alkalinity is sufficient to achieve about 1.2 mM TCE dechlorination with glucose, 1.7 mM with lactate, and a much higher 3.3 mM with formate. Laboratory studies indicate that in mixed culture, formate can be used as an electron donor for complete conversion to ethene, contrary to pure cultures studies indicating it cannot. Various strategies can be used to add electron donor to an aquifer for DNAPL dehalogenation while minimizing pH problems and excessive electron donor usage, including use of injection-extraction wells, dual recirculation wells, and nested injection-extraction wells.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.