秸秆还田结合减氮调控旱地土壤硝化潜势维持作物产量的机理

  【目的】  氮肥过量使用所导致的氮素利用率低和环境污染等问题严重影响现代农业生产。研究秸秆还田改善旱地农田土壤性质、提升土壤肥力和氮素利用率的潜力和作用机理,为减少氮肥用量、提高作物氮素利用率和土壤肥力提供科学依据。  【方法】  本研究选取河南许昌潮土和云南曲靖红壤两种典型旱作农田,2016～2018年开展了田间玉米－大麦/小麦轮作定位试验,在两地同时设置以下4个处理:不施氮 (CK)、常规施氮 (N)、减氮20% (80%N)、减氮20%配合秸秆还田 (80%NS),研究不同处理对土壤养分、土壤硝化潜势和作物产量及氮肥利用率的影响。  【结果】  与N处理相比,80%NS处理可稳定保持麦季抽穗期和玉米季抽雄期两种旱地土壤可溶性有机碳氮养分含量,促进土壤中NH₄+-N的积累并降低了NO₃–-N含量;80%NS处理使潮土和红壤硝化潜势分别降低了5.5%～33.9%和7.8%～37.5%;3年连续减施20%氮肥配合秸秆还田能够稳定产量并表现出一定的增产效果 (11.2%～20.4%),提高氮肥利用率6.4%～10.3%;而80%N处理会使作物产量下降3.9%～13.4%,氮肥利用率降低1.8%～38.9%。  【结论】  连续3年减少常规氮施用量20%配合秸秆还田,不仅增加了土壤有机碳氮含量,还减缓了土壤的硝化作用,增加了土壤铵态氮积累,实现对作物所需养分的持续供应,因而在维持和提高作物产量的同时,提高了氮肥利用率。单纯降低氮肥用量则有降低作物产量的风险。     

太原城郊老菜区番茄氮肥利用率及氮去向研究

为了加强太原城郊老菜区蔬菜生产中氮素管理和降低蔬菜生产对环境的污染,在田间采用微区15N示踪法研究了番茄生产过程中农民习惯施氮(FAR)和推荐施氮(RAR)的氮肥利用效率和氮去向。结果表明:与习惯施氮比较,推荐施氮对番茄各部位干物质量、氮浓度和产量均无显著影响,且明显降低了番茄地上部吸收化学肥料氮的百分率,但对各部位氮肥利用效率和总氮肥利用效率无显著影响,氮肥利用效率仅为8%～9%,这可能与土壤原来氮库或所施有机肥矿化提供了大量氮素有关。两种施肥处理均导致65%左右的氮素损失,其中习惯施氮和推荐施氮分别导致30%和26%的氮素淋洗到40cm以下土层,为此有必要种植蔬菜后利用深根系粮食作物吸收土壤下层氮素来降低蔬菜生产对环境的影响。     

设施黄瓜产量、品质及养分利用对不同土壤调理措施的响应

针对设施菜地施肥量大、肥料利用率低、果实品质变差、土壤环境劣质等问题，采用田间试验法，研究了无机肥配施不同土壤调理措施对设施黄瓜产量、品质、养分利用及土壤改良的影响，为实现蔬菜安全生产和保护土壤环境质量提供科学依据。结果表明：与农民习惯施肥相比，推荐无机肥配施生物菌肥、中微量养分、沸石处理的氮磷钾无机肥用量均减少40%左右，黄瓜产量却提高6.3%~8.7%，纯收入增加18 663~19 958元/hm²，其中推荐无机肥配施生物菌肥的整株植物氮、钾积累量分别增加13.3%和22.7%，土壤细菌、放线菌数量和细菌/真菌比值分别增加3.2，1.7，7.7倍；推荐无机肥配施沸石的整株磷积累量增加31.7%，表层土壤NH₄⁺—N提升31.6%；配施生物菌肥和中微量养分处理的VC、可溶性蛋白和可溶性糖含量分别增加14.0%~18.6%，22.2%~34.6%，7.8%~10.0%，硝酸盐降低15.8%~21.7%。与推荐施肥比较，3种土壤调理措施氮磷钾肥生产效率提高6.2%~8.5%，氮磷钾肥农学效率增加26.1%~35.9%。说明3种土壤调理剂均促进黄瓜养分吸收，增加产量，改善其果实品质，降低土壤氮素残留，增加土壤有益微生物数量，其中以推荐无机肥配施生物菌肥既稳产提质，生物和土壤环境效益又较佳，值得在生产中推荐应用。     

氮肥优化减施对土壤-莴苣系统氮磷平衡及产量效益的影响

采用田间小区试验, 研究了氮肥减施20%(80%N)与施肥优化[施缓释尿素并减氮20%(80%N+CRU)、氮肥减施20%并添加脲酶抑制剂/硝化抑制剂(80%N+QD)、氮肥减施20%并添加土壤调理剂(80%N+SC)]对土壤-莴苣系统氮磷平衡以及产量效益的影响。结果表明: 3 种优化减氮处理均在一定程度上降低了菜地土壤NO₃^--N(硝态氮)、Olsen-P(有效磷)含量及硝化率水平, 从而降低了氮磷流失进入环境的风险; 同时减氮处理还提高了土壤氮素的利用效率, 增加了蔬菜鲜样产量及菜农实际收入, 效益明显。其中, 80%N+CRU 处理降低土壤NO₃^--N 和Olsen-P 含量最为明显, 但该处理植株可食部分容易累积硝酸盐, 收获时莴苣茎硝酸盐含量显著高于常规施肥处理(CF)和《农产品安全质量无公害蔬菜安全要求》(GB18406.1—2001)(P<0.05); 80%N+QD 处理对各时期土壤Olsen-P 及蔬菜可食部分硝酸盐含量影响较小, 却显著降低了菜地土壤的硝化率水平(P<0.05),从而提高了养分利用效率, 同时与CF 处理相比, 该处理较大幅度增加了莴苣鲜样产量(茎21.7%, 叶7.6%)、总收入(13.0%)、实际收入(14.0%)和产投比(14.2%), 是最佳减氮优化处理。试验地80%N+SC 处理效果不稳定,与常规施肥差异不显著。兼顾经济、食用风险、生态环境等效益, 建议在高肥力菜地土壤中, 氮肥减量与脲酶抑制剂、硝化抑制剂配合施用。     

氮肥对黄土高原大棚蔬菜及土壤硝酸盐累积的影响

通过对黄土高原大棚蔬菜不同施肥水平及采收期试验,研究了氮肥施用量对蔬菜产量、品质以及土壤硝酸盐积累的影响.结果表明:在土壤氮素水平较低情况下,随氮肥施用量的增加蔬菜产量随之提高,当黄瓜施用量达300kg·hm-2、芹菜施用量达400kg·hm-2时,其产量分别较对照提高16.7%和37.5%,而菜体中硝态氮含量与对照差异不大;但当施用量超过500kg·hm-2及600kg·hm-2时,会使黄瓜、芹菜产量逐渐下降同时导致蔬菜及土壤中硝态氮含量迅速增高,使蔬菜达到高污染水平.施肥后随时间的推移,蔬菜中的硝酸盐含量逐渐降低,在中等施肥条件下30d后可达到食用水平.黄土高原土壤氮素淋溶强烈,在氮肥施用后15d,50cm左右土层中硝态氮累积量最多形成峰值,且随时间的推移其峰值有逐渐向下移动的趋势.本实验证实:适量氮肥有利于蔬菜生长,还可有效减少氮素污染,在黄土高原大棚蔬菜生产中氮肥最佳用量为400～500kg·hm-2,同时应严格控制采收时间,在蔬菜采食前30d内不能施用氮肥.     

太湖地区高产稻田氮肥施用与作物吸收利用的研究

本讨论长期高量偏施氮素化肥的高产稻田氮肥施用与作物产量、作物对养分吸收利用之间的关系。研究结果表明：化学氮肥施用量（养分量，下同）３００ｋｇ／ｈａ·ｙｒ．，作物增产显，每公斤氮增产１３．５ｋｇ粮食，氮素利用率达４０．３％，省肥、经济、合理；施用量达４５０ｋｇ／ｈａ·ｙｒ．，作物产量增长甚微；施用量达６００ｋｇ／ｈａ·ｙｒ．，每公斤氮只增产７．２９ｋｇ粮食，氮肥利用率降至１７．２％，水稻茎秆中含     

甜玉米填闲减缓菜田土壤硝酸盐淋溶的研究

为提高菜田氮肥的利用率，降低氮肥对环境的污染风险。在中德合作项目东北旺试验田（土壤类型为潮土），三年（1999～2001）9季蔬菜长期传统施氮灌水与推荐施氮灌水处理的地力基础上，于高温多雨的夏季选择甜玉米作为填闲作物，以休闲处理作对照，研究甜玉米在土壤硝态氮淋溶关键期对土壤残留硝态氮素分布及对后茬蔬菜产量的影响。研究结果表明甜玉米生长迅速、生物量大、吸收氮素能力强，吸氮量可达205.6～246.1 kg/hm²；与休闲处理相比，种植甜玉米能有效的吸收0～60 cm土壤中残留氮素，实现了土壤残留氮素的再利用。0～180 cm剖面中土壤硝态氮的残留量都有不同程度的降低，有效阻抑了氮素向土壤深层的淋洗。甜玉米也获得了较高的经济产量，穗净鲜重达9.2～10.2 t/hm²。后茬作物菠菜收获后未被利用的氮素大部分残留在土壤浅层；甜玉米处理与休闲处理相比未显著影响后季菠菜的生长，产量达18.4～20.7 t/hm²。该研究表明：甜玉米是较为理想的填闲作物。     

减氮配施有机物质对土壤氮素淋失的调控作用

采用室内土柱模拟试验方法,研究不同氮肥施用下1m土体中氮素的分布和移动特征,揭示土壤氮素动态变化规律。结果表明:FN(农民习惯施无机氮用量)、RN(根据土壤养分供应和作物需求确定的推荐无机氮用量)显著增加了土壤上层NH_4^+-N和NO_3^--N向下层淋失。RN+HA(与推荐无机氮纯养分相等的锌腐酸尿素)和RN40%+OMB(推荐无机氮肥减60%基础上配施自制有机调理物质)可延长上层土壤NH_4^+-N峰值出现时间,降低下层NH_4^+-N。淋溶结束后,等氮量下增施HA较RN降低60cm以下NH_4^+-N残留29.7%～54.2%;降低60—80cm NO_3^--N累积17.4%。RN40%+OMB处理无机氮肥用量最小,0—20cm的NH_4^+-N最高,40—100cm稳定在2.0mg/kg左右;0—20,20—40cm土层NO_3^--N较RN+HA增加12.3%和2.0%,显著降低40cm以下NO_3^--N残留。RN+HA和RN40%+OMB较RN的土壤总无机氮残留分别减少7.4%和20.2%,降低表观淋失率。因此,RN40%+OMB可较好地抑制氮素下移,降低氮素淋失风险,为减少氮素淋失、明确合理氮肥施用方式提供科学依据。     

辽西褐土施肥及养分循环再利用中长期试验：Ⅱ．土壤养分收支

持续10a的田间试验结果表明，在保持农业系统养分循环再利用的基础上，根据土壤养分供给力设计化肥施用量，可以在实现作物高产的同时，平衡土壤养分收支，从而避免土壤中肥料养分（主要是氮）过剩而进入环境。     

滴灌施肥时机对设施蔬菜产量品质与氮肥利用效率的影响

为了提高设施蔬菜滴灌水肥利用效率,在日光温室内开展了为期15个月不同滴灌施肥时机对设施蔬菜产量品质、土壤-蔬菜系统中氮素分布、氮素平衡和氮素利用效率的研究。结果表明:滴灌施肥时机对果实产量、全氮和硝酸盐含量有显著影响,灌水中前期施肥处理产量、全氮和硝酸盐含量均较高,随着施肥时段向后推移,蔬菜吸收氮素先增大后减小;灌水后期施肥处理在收获后各层土壤硝态氮含量最低且消耗量最高,灌水中期施肥处理土壤-蔬菜系统表观损失和氮盈余小,较其他处理低15.35%~59.13%;灌水中期施肥处理氮肥偏生产力和氮肥表观利用率高于前后期施肥处理,3茬平均氮肥表观利用率T2处理高于其他处理7.09%,7.41%,11.48%。施肥时机对土壤-蔬菜系统产量品质和氮素分布等综合影响明显,推荐滴灌施肥过程中尽量使施肥时机保持在灌水过程的中期。     

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.     

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.     

Biodiversity and ecogeography of wild Lactuca spp. in some European countries

Staff members of the Department of Botany of Palacký University in Olomouc and Gene Bank Department – Workplace Olomouc, Research Institute of Crop Production in Prague, Czech Republic, conducted an expedition in seven European countries (Austria, Czech Republic, France, Germany, Italy, the Netherlands, Switzerland) in August/September 1999 to collect wild Lactuca spp. germplasm and study its geographic distribution, ecology and biodiversity. During the mission, more than 600 locations were visited resulting in the collection of 602 seed samples (accessions) of wild Lactuca species and 13 seed samples of related genera (Chondrilla and Mycelis). Lactuca serriola f. serriola, L. serriola f. integrifolia, L. saligna and L. viminea subsp. chondrilliflora were prevalent in southern Europe (Italy, France), however, only L. serriola was common in central and western Europe (Austria, Czech Republic, Germany, Netherlands, Switzerland). The greatest diversity of Lactuca species was found in France, where also the most seed samples (165) were collected. The most characteristic habitats with a high density of Lactuca spp. populations were observed along roads and highways, grassy ditches, ruderal communities, and dust-heaps. Natural infections by powdery mildew (Erysiphe cichoracearum) and downy mildew (Bremia lactucae) on some wild Lactuca spp. were observed. Recent observations concerning the geographic distribution, population structure, habitats, and natural occurrence of diseases of Lactuca spp. are discussed. This assemblage of genetic resources of Lactuca spp. can serve as the basis of future studies of species diversification, spatial population structure, plant microevolution, domestication processes, and genetic variability of host-parasite interactions.     

Increase in auxiliary photoprotective photosynthetic pigments in wheat seedlings induced by Azospirillum brasilense

Inoculation of wheat seedlings with the plant growth-promoting bacterium Azospirillum brasilense Cd was immobilized in alginate microbeads and, without applying any stress, significantly increased the quantity of several photosynthetic pigments, such as chlorophyll a, chlorophyll b, and the auxiliary photoprotective pigments violaxanthin, zeaxanthin, antheroxanthin, lutein, neoxanthin, and β-carotene. This resulted in greener plants with no apparent visible stress. After monitoring the quantity of photosynthetic pigments for 4 weeks, we observed that inoculated plants had higher quantities of pigments in shoot and stem. The greatest difference in the quantity of all pigments between inoculated and noninoculated plants occurred in the first week of growth. Regardless of treatment, the quantity of pigments in stems was three to four times less than the quantity of these pigments in shoots. Application of Azospirillum, either as liquid inoculant or as alginate microbeads, did not alter the positive effect of the bacteria on pigment production or the positive response of the plants towards A. brasilense Cd inoculation.     

Responses of native legume desert trees used for reforestation in the Sonoran Desert to plant growth-promoting microorganisms in screen house

Three slow-growing legume trees used for desert reforestation and urban gardening in the Sonoran Desert of Northwestern Mexico and the Southwestern USA were evaluated whether their growth can be promoted by inoculation with plant growth-promoting bacteria (Azospirillum brasilense and Bacillus pumilus), unidentified arbuscular mycorrhizal (AM) fungi (mainly Glomus sp.), and supplementation with common compost under regular screenhouse cultivation common to these trees in nurseries. Mesquite amargo (Prosopis articulata) and yellow palo verde (Parkinsonia microphylla) had different positive responses to several of the parameters tested while blue palo verde (Parkinsonia florida) did not respond. Survival of all tree species was over 80% and survival of mesquite was almost 100% after 10 months of cultivation. Inoculation with growth-promoting microorganisms induced significant effects on the leaf gas exchange of these trees, measured as transpiration and diffusive resistance, when these trees were cultivated without water restrictions.