浙中三个桔园土壤的水分性质及结构改良剂的应用效果

在实验室条件下研究了浙中金衢盆地三个桔园土壤的持水特性、饱和导水率、蒸发强度及三种土壤结构改良剂对土壤团聚作用和蒸发强度的影响.结果表明,持水量与<0.01mm物理性粘粒含量呈正相关(r=0.933^*);饱和导水率与团聚体平均重量直径呈正相关(r=0.956^**),而与结构破坏率呈负相关(r=-0.996^**).当土壤吸力在50-100kPa时,桔园就需灌溉.加入三种土壤结构改良剂后能明显改善土壤水稳性团聚体,其效果为聚乙烯醇>聚丙烯酰胺>水解聚丙烯腈;使土壤的日平均蒸发强度减少,其减少的顺序为黄筋泥>紫砂土>红砂土.土壤饱和导水率K₁₀值紫砂土>黄筋泥>红砂土,主要取决于土壤水稳性团聚体的平均重量直径,二者呈正相关(r=0.956^**).     

北京山区典型植被枯落物和土壤层水文功能

[目的]研究枯落物和土壤层水文功能,从而明晰北京山区不同植被的水源涵养能力,可为当地植被建设提供借鉴。[方法]使用室内浸泡法、环刀法、定水头法等对北京山区不同植被的枯落物与土壤层水文功能进行了定量分析,并通过相关性分析明确了有机碳与土壤层水文功能之间的关系。[结果](1)枯落物最大持水率、最大拦蓄率、有效拦蓄率为侧柏(Platycladus orientalis)×灌木混交林>五角枫(Acer elegantulum)纯林>五角枫×侧柏混交林>侧柏纯林。最大持水量、最大拦蓄量、有效拦蓄量均为五角枫纯林>侧柏×灌木混交林>五角枫×侧柏混交林>侧柏纯林,且均为半分解层大于未分解层。(2)土壤饱和持水量和毛管持水量排序为侧柏纯林>五角枫纯林>侧柏×灌木混交林>五角枫×侧柏混交林。土壤非毛管持水量大小排序为五角枫×侧柏混交林>五角枫纯林>侧柏×灌木混交林>侧柏纯林。土壤饱和导水率沿剖面向下逐渐减小,平均饱和导水率最大的植被类型为侧柏×灌木混交林。(3)土壤有机碳含量表现为沿剖面向下逐渐减小,且土壤有机碳含量与容重、总孔隙度...     

不同根系构型草本与灌木复合对土壤饱和导水率的影响因素分析及模拟

[目的] 探究不同根系构型草本与灌木复合时的根土性质的差异对土壤饱和导水率的影响,并综合考虑根系和土壤性质建立估算土壤饱和导水率的经验方程,为黄土高原植被恢复后的水文模型建立提供理论参考。[方法] 选取不同根系构型草本与灌木的混合样地,分别为柠条锦鸡儿加冰草(须根系)和柠条锦鸡儿加铁杆蒿(直根系)。采用双环刀法测定不同样地土壤饱和导水率。[结果] 样地类型和土层深度对土壤饱和导水率的影响达到显著水平,两者对土壤饱和导水率影响的因子贡献率分别为26%和52%。直根系铁杆蒿与柠条锦鸡儿混合样地的土壤饱和导水率高于须根系冰草与柠条锦鸡儿混合样地,并且不同样地的土壤饱和导水率随土层深度的增加均表现出降低的趋势。根长密度、团聚体以及土壤容重能够较好地模拟土壤饱和导水率,其拟合精度R²可以达到0.86。[结论] 直根系草本与灌木复合时较须根系草本与灌木复合相比具有更高的饱和导水率。在不同样地中,根长密度、团聚体以及土壤容重是影响饱和导水率的主要因素。     

微波遥感裸露土壤和植被覆盖土壤含水量的研究

用X波段微波散射计研究了裸露土壤,有植被(红薯、大豆和花生)覆盖的土壤含水量与微波后向散射系数之间的关系,对X波段与C波段的结果做了分析对比。结果表明:在微波遥感裸露土壤含水量方面,入射角θ=6°时灵敏度S_v最大;在θ=45°时,S_v=0;在θ>45°时,土壤含水量增大,而后向散射系数反而变小。在小入射角时,两个波段的精度相差不大。微波遥感在有植被覆盖的土壤含水量方面,X波段比C波段的灵敏度和精度要低,但是只要工作参数选择适当,就能达到一定的灵敏度和精度。应用本文提出的估算模型,X波段土壤含水量的估算误差大约为±25%左右。     

半干旱黄土地区幼龄侧柏叶蒸腾的数学模型

 通过人工控制水分,形成单株幼龄侧柏的不同土壤水分梯度环境。在自然环境下对侧柏叶片定时、定位进行蒸腾速率及林冠层的光照、空气温度、空气湿度、叶水势和土壤水分等因子的同步观测。蒸腾速率与各个因子的相关分析表明:黄土半干旱地区侧柏蒸腾速率η_t/(μg·cm^-2·s^-1)与光照强度E/(μmol·m^-2·s^-1)、空气饱和差p_v/kPa、叶水势Ψ/kPa、气温t/℃的关系可以分别表示为:η_t=>αE_b,η_t=αp_vb,η_t=αψ^b,η_t=αt²+bt+c;侧柏的蒸腾速率η_t与气孔阻力R_s/(s·cm^-1)和土壤含水量W/％有密切关系,可以分别表示为:η_t=α+bW+cW₂+dW₃,R_s=α+bW+cW₂+dW₃。用气温、空气饱和差、叶水势3个因素建立了半干旱黄土地区幼龄单株侧柏蒸腾速率的非线性指数预测模型:η_t=0.6950_exp（0.03158t-14.2492/p_v+0.7606/Ψ）,经检验获得了满意的数值模拟结果。     

黄土高原典型退耕草地植被特征对土壤入渗过程的影响

植被恢复过程可显著影响土壤入渗性能。通过选取黄土高原典型草地白羊草和铁杆蒿草地,设置不同种植密度（5,10,15,20,25,30株/m²）和采用人工模拟降雨试验（60 mm/h,60 min）,系统研究了草地植被特征对土壤入渗过程的影响。结果表明：（1）种植密度增加可显著延缓产流,不同种植密度下白羊草草地和铁杆蒿草地初始产流时间分别为0.76~5.74,0.87~2.08 s,且随盖度、根系生物量和有机质的增加呈幂函数增加（R²≥0.18,p<0.05）。（2）不同种植密度下白羊草草地的平均入渗速率、稳定入渗速率、入渗总量分别为0.47~0.82,0.46~0.82 mm/min和7.12~11.84 mm,铁杆蒿草地分别为0.38~0.67,0.35~0.60 mm/min和5.70~10.07 mm。当种植密度为20株/m²时,土壤入渗各参数均最大;平均入渗速率、稳定入渗速率、入渗量总量、入渗系数（K）随土壤有机质的提高呈幂函数增大（R²≥0.26,p<0.01）,衰减系数（α）随生物结皮盖度呈降低趋势（p>0.05）。（3）白羊草草地具有较高的根系生物量、生物结皮盖度和有机质含量,其初始产流时间、平均入渗速率、稳定入渗速率、入渗量总量及入渗系数（K）均不同程度高于铁杆蒿草地,衰减系数（α）低于铁杆蒿草地,土壤入渗性能较强。总体而言,对于典型退耕草地,土壤入渗总量（A）可表征为根系生物量密度（RMD）和土壤有机质（SOC）的拟合函数（A=2.77×RMD^0.149 SOC^0.614,R²=0.663,NSE=0.653）。研究结果可为黄土高原退耕草地生态水文过程和植被建设提供数据来源和理论依据。     

区域性土壤流失预测方程的初步研究

应用我国南方花岗岩侵蚀红壤区的径流小区观测资料,采用数值分析方法推导出适合花岗岩侵蚀红壤区,计算各次降雨吋土壤流失量和年土壤流失量方程:A₁=4·y_s·K·LS;并利用野外调查量测资料,推导出适合长江三峡低中山区的土壤流失方程:A₂=(152.5D-1016)·R·LS·C^-2.3利用上述方程可以预测特定区域的土壤流失量。     

生物质炭对土壤N2O消耗的影响及其微生物影响机理

生物质炭在温室气体减排方面具有很大的发展前景,它不仅能实现固碳,对于在大气中停留时间长且增温潜势大的N₂O也能发挥积极作用。本研究采用室内厌氧培养试验,按照生物质炭与土壤质量比（0、1%和5%）加入一定量生物质炭,土壤重量含水率控制在20%。利用Robotized Incubation平台实时检测N₂O和N₂浓度变化,通过测定土壤中反硝化功能基因丰度（nirK、nirS、nosZ）分析生物质炭对N₂O消耗的影响及其微生物方面的影响机理。结果表明：经过20 h厌氧培养后,0生物质炭处理的反硝化功能基因丰度（基因拷贝数·g^-1）分别为6.80×10⁷（nirK）、5.59×10⁸（nirS）和1.22×10⁸（nosZ）。与0生物质炭处理相比,1%生物质炭处理的nirS基因丰度由最初的2.65×10⁸基因拷贝数·g^-1升至7.43×10⁸基因拷贝数·g^-1,nosZ基因丰度则提高了一个数量级,由4.82×10⁷基因拷贝数·g^-1升至1.50×10⁸基因拷贝数·g^-1,然而nirK基因丰度并无明显变化;5%生物质炭处理的反硝化功能基因丰度并未发生显著变化。试验结束时,添加生物质炭处理的N₂/（N₂O+N₂）比值也明显高于0生物质炭处理。相关性分析结果表明,nirS基因丰度和nosZ基因丰度均与N₂O浓度在0.01水平上显著相关。试验末期nirS基因丰度和nosZ基因丰度均随着N₂O浓度的降低而升高。因此在本试验中,添加1%生物质炭可显著提高nirS和nosZ基因型反硝化细菌的丰度,增大N₂/（N₂O+N₂）比值,促进N₂O彻底还原成N₂。生物质炭对于N₂O主要影响机理是增大了可以还原氧化亚氮的细菌活性,促进完全反硝化。     

生物结皮生长发育对黄绵土抗侵蚀性能的影响

[目的] 黄土高原退耕还林(草)工程驱动的生物结皮发育可显著抑制土壤侵蚀,为探明土壤抗侵蚀性能随生物结皮生长发育的变化特征及其响应机制。[方法] 设置藻结皮、藓结皮和自然演替结皮3个处理,培育176天,系统研究生物结皮不同发育阶段及其类型差异对黄绵土抗侵蚀性能的影响。[结果] (1)生物结皮盖度、厚度、生物量、叶绿素和粗糙度随生长时间均显著增加,培育初期藓结皮较高,培育末期自然演替结皮反而最高。(2)随生物结皮发育,土壤黏结力呈幂函数增强,较初期增加39.8%~60.3%;质量损失率呈指数函数减小,较初期降低45.6%~57.3%;饱和导水率变化趋势较为复杂,但培育末期均最低(0.08~0.12 mm/min)。(3)土壤黏结力随生物结皮盖度、厚度、叶绿素、生物量和表面粗糙度的增加呈幂函数增长,质量损失率随生物结皮盖度、厚度、叶绿素、生物量和表面粗糙度的增加呈指数函数下降。(4)土壤抗侵蚀综合指数(C_ser)可表示为盖度(Cov)、厚度(T)和生物量(B)的幂函数(C_ser=0.279 Cov^0.194 T^0.188 B^0.119, R²=0.73, p＜0.05)。[结论] 黄土高原生物结皮发育可显著提高黄绵土抗侵蚀性能,藓结皮效果最强。     

滨海盐渍土土壤物化性质与水动力学性质变异

为分析不同梯度盐渍土土壤的物理性质与水动力学性质变异状况,在江苏沿海连云港市徐圩新区开展了试验研究。对5种不同盐渍化级别土壤进行取样,测定其pH、EC_e、容重、总孔隙度、含水率和饱和导水率等,分析不同级别滨海盐渍土壤物化特性参数和水动力学性质变化规律。结果表明:(1)不同级别盐渍土0—50 cm剖面土壤EC_e先变小后增大,但40—50 cm剖面EC_e明显大于0—10 cm剖面。非盐渍土和极重度盐渍土0—50 cm剖面土壤EC_e变化较小,轻度盐渍土、中度盐渍土、重度盐渍土的0—50 cm剖面土壤EC_e值变化较大。(2)土壤EC_e和容重呈极显著负相关关系,与毛管孔隙度、非毛管孔隙度、总孔隙度、含水率、毛管持水量、田间持水量、最大持水量呈极显著正相关关系。土壤孔隙度和持水量呈极显著正相关关系。(3)极重度盐渍土饱和导水率明显小于其他级别的盐渍土,且0—20 cm剖面土壤饱和导水率大于20—50 cm剖面。研究结果可为滨海盐渍土水盐管理和生态环境建设提供理论参考依据。     

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.