子叶期钵苗补苗末端执行器设计与试验

针对穴盘育苗由于受种子质量和育苗环境因素等影响导致空穴多的问题,为消除穴盘苗空穴,该文研制了蔬菜子叶期钵体苗补苗末端执行器。以72孔标准穴盘培育的子叶期番茄钵体苗为移取对象,以育苗基质配比与含水率、苗龄为因素,以子叶期钵体苗补苗末端执行器从穴孔取出基质的取净率为指标,进行了正交试验,结果表明:幼苗苗龄、基质配比对基质取净率影响显著,基质含水率对基质取净率影响不显著,对常见的基质配比、适宜基质含水率、苗龄16-26 d的穴盘苗基本均能完整、无损地取出,基质取净率最大的较优组合苗龄为26 d、基质配比2∶2∶1、基质含水率74.1%;对苗龄26 d、基质配比2∶2∶1、基质平均含水率75.5%的番茄钵体苗进行取苗、补苗试验,取出无苗基质和钵体苗的成功率均为100%,补苗成功率为100%,为子叶期蔬菜钵体苗补苗提供了性能优良的末端执行器。     

蔬菜穴盘苗插入顶出式取苗装置研制

针对蔬菜穴盘苗自动取苗装置结构复杂、取苗性能差等问题，该研究综合顶出式取苗与插入夹持式取苗的优缺点，设计了一种插入顶出式取苗装置。首先对钵苗顶出过程进行受力分析，对抛出后的钵苗进行运动过程分析，得出造成顶出式取苗的钵苗翻滚的影响因素，提出插入顶出式取苗结构的优化目标，然后对送盘机构、插入顶出式取苗机构进行受力分析和参数优化。以辣椒钵苗为试验对象，选取苗龄、钵体含水率和取苗频率为影响因素，以取苗合格率、基质损失率和伤苗率为指标进行正交试验。试验结果表明：苗龄30 d、基质含水率60%、取苗频率120 株/min时，取苗成功率为97.22%，基质损失率为18.06%，伤苗率为1.39%，取苗效果最佳。以苗龄25 d的甘蓝和花椰菜苗进行不同蔬菜作物取苗验证试验，取苗合格率分别为93.75%和95.14%，基质损失率分别为17.21%和16.67%，伤苗率分别为4.17%和3.47%，满足蔬菜穴盘苗全自动移栽机取苗作业要求。研究结果可为蔬菜穴盘苗全自动移栽机的设计和作业参数优化提供参考。     

顶钵-夹茎组合式取苗装置设计与试验

针对现有钵苗自动移栽技术中,夹钵式取苗方式受钵体强度及盘根性差异影响易导致钵体破损,降低取苗成功率,夹茎式取苗方式受茎秆强度及钵体与穴盘之间黏附力影响易造成伤苗、钵体不能取出等问题,该研究提出了一种顶钵-夹茎组合取苗方式,并进行了结构设计、装置试制与试验优化。对辣椒穴盘苗茎秆和钵体力学特性进行了测试,得到茎秆拉伸和径向压缩力学特性,及钵体拉拔与压缩力学特性,并建立了顶钵-夹茎组合式取苗装置在顶与夹过程中钵体和茎秆的受力模型,对取苗装置关键参数进行了设计。搭建试验台架,以“中农绿亨线椒363”穴盘苗为对象,以钵体含水率、取苗频率和顶钵高度为影响因素开展正交试验,结果表明经顶钵-夹茎取苗后的穴盘苗生长状态良好,确定最优水平为含水率45%,取苗频率60株/min,顶钵高度10 mm,该条件下钵体破损率为1.98%,取苗成功率为98%。田间试验表明平均取苗成功率为93.05%,株距合格率为88.17%。研究可为辣椒、番茄等旱地作物穴盘苗移栽技术改进优化提供参考。     

穴盘苗自动移栽钵体力学特性试验

穴盘苗钵体的力学特性,是穴盘苗自动移栽机取苗机构设计的重要依据。以黄瓜为育苗对象,选用镇江培蕾育苗有机土,使用128孔正方形锥体穴盘,在Venlo型玻璃温室培育穴盘苗。试验时,穴盘苗苗龄28d,长出两片子叶和第一片心叶,钵体含水率范围为54.21%～60.47%。对穴盘苗钵体进行了平板压缩、加卸载循环和蠕变试验,试验仪器为TA-XT2i型质地分析仪,测前、测试、测后速度均为1mm/s。钵体压缩试验测试10mm压缩量下的抗压特性,试验重复20次,钵体加卸载循环试验测试2、4、6、8mm压缩量下的加卸载特性,每个压缩量重复10次,钵体蠕变试验试验测试2、4、6、8N不同加载力下的蠕变特性,保持时间为120s,每个测试力重复10次。试验表明穴盘苗钵体的抗压力与变形呈非线性变化,抗压力随着变形的增大先缓慢增大再显著增大。在平板压缩过程中,钵体无明显的屈服破坏点。穴盘苗钵体的压缩破坏是从钵体盘根较少的区域开始,逐渐扩大破碎度。在弹塑性方面,随着压缩量的增大,滞后损失、抗压峰值力均增大,弹性度减小,并且穴盘苗钵体压缩变形越大,其塑变能力越强,具有一定的可塑性,可以从两侧或四周夹紧钵体而不破坏其整体性。利用Burgers模型能有效表征穴盘苗钵体的压缩蠕变特性,获得了对应的黏弹性参数。通过钵体不同压力下的蠕变试验,得到随着加载力的增大,瞬时弹性系数、延迟时间均减小,在1s内,加载力为2、4、6、8N时,钵体平均蠕变量分别为0.0244、0.0308、0.0446、0.0549mm,表明其蠕变量比较小,这对快速夹取穴盘钵体的夹紧松弛特性影响不大,即钵体一旦夹紧不会松弛掉落。     

蔬菜移栽机曲柄摆杆式夹苗机构的设计与试验

通过对穴盘苗进行抗压特性试验、试验平台的夹取试验,研究分析了适于夹取式自动取苗机构工作的相关参数组合以及最佳的钵苗含水率状况,为机构设计提供参考依据。该文基于辣椒穴盘苗抗压特性设计了全自动蔬菜移栽机曲柄摆杆式穴盘苗夹苗机构,该机构可与顶出机构配合完成全自动蔬菜移栽取苗和投苗工作。该文完成了曲柄摆杆式夹苗机构主要结构的设计,并对曲柄摆杆式夹苗机构的工作过程进行了力学、运动学分析和仿真,确定了结构和工作参数,即曲柄、连杆、摆杆长度分别为80、236.22、172.5 mm,夹苗爪具有较好的运动特性。曲柄摆杆式夹苗机构性能试验结果表明,夹取爪为金属材质,弹簧劲度系数为90 N/m,钵苗脱落率为0,钵苗破碎率为4.2%,综合取苗成功率可达95.8%,性能指标符合设计要求,夹苗爪"V"形结构设计有效防止穴盘苗在夹取过程中脱落,保证了取苗成功率。试验表明钵苗含水率为60.8%时,钵苗在不同的弹簧劲度系数及夹取爪材质下均有良好的适应性,在该含水率下钵苗的取苗平均成功率为94.4%。该机构从取苗到投苗采用圆弧形工作轨迹,夹苗爪采用八字形轨道与复位弹簧控制其开合,结构简单、性能可靠,无需调整即可适应多种不同尺寸穴盘苗的取苗工作,对不同含水率穴盘苗适应性强,对穴盘苗损伤小,机构成套使用可达到较高工作效率。     

用于机械化栽植的西兰花钵苗力学特性试验

为了降低西兰花钵苗机械化栽植过程中的破损率,避免栽植嘴已经运行到栽植位置而钵苗还未滑到栽植嘴的底部而造成移栽失败,该文采用正交试验的方法,以土钵体积(表示穴盘规格)、苗龄和含水率为试验因素,针对栽植过程农艺要求,进行了不同方案下土钵的抗压强度试验和钵苗沿栽植嘴壁面下滑的运动阻力系数测试。通过建立西兰花土钵与栽植嘴壁面碰撞过程接触力学模型,分析得到为避免土钵破损钵苗和栽植嘴碰撞时不同组合允许的最大相对速度。以栽植作业中避免钵苗破损,同时运动阻力不能过大为目标,采用综合评分法,得到适宜机械化栽植的4个土钵体积、苗龄和含水率组合,进而对这4个组合进行模拟田间栽植试验,得到最优的组合:土钵体积为中(穴盘规格为128),苗龄为2~3片真叶,含水率约为63%。该研究为栽植机构的设计提供依据。     

穴盘苗吹叶补苗机构设计与试验

针对叶片遮挡穴盘苗空穴机械补苗作业时存在损伤待补空穴周围穴盘苗叶片的问题,该研究提出一种使用射流气管吹开遮挡叶片进行机械补苗的吹叶补苗方法。作业时,射流气管内通高压气流,由待补空穴底端渗水孔向上移动,吹开遮挡叶片,到达穴盘苗叶片顶部后,补苗机械手夹持待补苗使基质块底部靠近射流气管顶端,并与射流气管同步下移完成补苗作业。吹叶机构射流气管内径5 mm,顶端封闭,靠近顶端的水平截面均布开设8个直径1.2 mm的射流孔。搭建由吹叶机构与挂接于Denso机械手臂的补苗机械手组成的试验装置,对72穴穴盘培育的红掌、白掌、芥蓝、菜心、白菜和生菜6种不同叶片遮挡程度的穴盘苗进行单穴吹叶补苗性能试验。结果表明,吹叶机构与补苗机械手协同作业的补苗成功率与穴盘苗初始叶片遮挡率(穴盘待补空穴被相邻穴盘苗叶片遮挡的面积与穴孔面积的比值)、遮挡叶片倾角和射流气管压力有关。在射流气管射流孔数为8,射流孔直径1.2 mm条件下,射流气管压力为0.28 MPa时,初始叶片遮挡率59.4%的红掌穴盘苗的补苗成功率可达92%;射流气管压力为0.22 MPa时,初始叶片遮挡率56.2%的白掌穴盘苗的补苗成功率可达94%;射流气管压力为0.22～0.31 MPa时,初始叶片遮挡率35.4%的芥蓝穴盘苗的补苗成功率均可达90%;射流气管压力为0.16～0.31 MPa时,初始叶片遮挡率29.7%～35.8%的菜心、白菜和生菜穴盘苗的补苗成功率均可达90%。研究结果可为叶片遮挡穴盘苗空穴的机械补苗设备开发提供技术参考。     

基于苗钵力学特性的自动移栽机执行机构参数优化试验

为有效减少加工番茄机械化移栽过程钵苗基质的损伤,提高移栽机取苗、植苗成功率,该文构建了移栽过程中取苗、植苗阶段加工番茄钵体的力学模型,结合钵体的抗压力学特性试验,研究移栽过程中造成钵苗基质破损、影响取苗、植苗成功率的因素,通过试验分析适合机械化移栽的钵体和移栽机执行机构的相关参数。参数组合重复性验证试验表明：钵体基质配比（珍珠岩：砾石：泥炭）为1∶1∶2,钵体绝对含水率为72%,取苗夹片插入穴孔深度为35 mm,取苗夹片对钵体的夹持角度为14°,投苗点与接苗碰撞点高度为90 mm,鸭嘴锥度为38°时,移栽成功率满足加工番茄穴盘苗机械移栽要求。该研究为机械化移栽的加工番茄钵苗培育农艺及移栽机参数优化设计提供了参考。     

蔬菜穴盘苗弧形展开式自动取投苗装置设计与试验

针对穴盘苗取投苗装置机械结构较复杂、取投苗易失败等问题,该研究设计了一种蔬菜穴盘苗弧形展开式自动取投苗装置。通过对取投苗作业过程进行分析,提出整排取苗、弧形展开投苗的自动取投苗作业方式,对夹苗组件、导向槽、旋转接苗机构等进行设计,并确定各部件关键参数,搭建PLC自动控制系统,设计执行单元的气动回路方案,并提出匹配延时函数。以辣椒穴盘苗为试验对象,以平均取投苗频率、供气压力、基质平均含水率为试验因素,以取投苗成功率、损伤率为试验指标进行正交试验,并以较优参数组合进行重复验证试验。试验结果表明：平均取投苗频率为90株/min、供气压力为0.4 MPa、基质平均含水率为30%时,取投苗成功率为94.05%,损伤率为1.19%,该研究可为自动取投苗装置的研发提供参考。     

辣椒穴盘苗自动移栽机设计与试验

针对新疆广泛应用的半自动辣椒移栽机效率低、劳动强度大的问题,该研究设计了一种辣椒穴盘苗自动移栽机。整机主要由全自动取投苗系统与栽植机构组成,采用整排取苗再分苗投苗的方式,实现128(16列×8行)穴辣椒穴盘苗的自动取苗、投苗。在分析现有移栽机结构和工作原理的基础上,确定了辣椒穴盘苗自动移栽机的整体结构,完成了全自动取投苗系统的关键参数设计;制定了全自动取投苗系统的气动回路方案,并基于Fluid SIM软件进行仿真及优化。采用平均苗高166.7 mm的辣椒苗,以取投苗成功率,栽植频率,株距变异系数,倒伏率为评价指标进行田间试验。试验结果表明:在工作气压0.4 MPa及移栽机作业速度1.4～1.7 km/h时,平均取投苗成功率为97.07%,栽植频率为123株/min,倒伏率1.67%,株距变异系数为3.67%,各项性能指标均满足辣椒穴盘苗移栽的农艺要求。该研究可为自动化移栽机的研究提供参考。     

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.     

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.     

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.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Effect of some fungicide seed treatments on the survival of Bradyrhizobium japonicum and on the nodulation and yield of soybean [Glycine max. (L) Merr.]

Several commercial fungicide seed treatments were evaluated for their possible effect on the survival of Bradyrhizobium japonicum on seeds and on the nodulation and yield of soybeans in a greenhouse and a field experiment. quinolate Pro (carbendazim and oxine copper), Vitavax 200FF (carboxin and thiram), and Monceren (pencycuron) had a small effect or no effect on the survival of B. japonicum and on the nodulation and yield of soybeans. They can thus be considered compatible with soybean seed inoculation. Germipro UFB (carbendazim and iprodione), Apron 35J (metalaxyl), and Tachigaren (hymexazol) decreased B. japonicum survival and the nodulation and yield of soybeans and thus cannot be considered compatible with soybean seed inoculation.     

Einfluss der düngungsmethoden auf die entwicklung von zuckerrübenkrankheiten

Während neunjähriger (1994-2002) Untersuchungen in der Versuchsanstalt Ba?cyny (Fahlerde, Fall-Gleyboden, ausgebildet aus leichtem Lehmboden) wurde der Befall mit Krankheiten an der Zuckerrübe in Abhängigkeit von der Düngungsmethode bewertet. Folgende Methoden wurden angewendet: A - Mineraldünger, B - Stalldung und Mineraldünger, C - Stroh-, Gründung und Mineraldünger, D - Kompostdünger und Biopräparate (ökologische Düngung). Auf den Objekten A, B, C wurden bei konstanter Phosphor-Kalium-Düngung die Stickstoffgaben von 0 bis 180 kg.ha^?1 differenziert. Auf dem ökologischen Objekt D ohne Mineraldünger wurden statt Stickstoff die Biopräparate P₅₀₀ und P₅₀₁ verabreicht. Der geringste Befall von Krankheiten wurde an der Zuckerrübe auf jenem Objekt festgestellt, das mit Kompost und den Biopräparaten gedüngt worden war. Im Rahmen der konventionellen Düngungsmethoden wurde allgemein die höchste Intensität der Krankheiten an der mit Stroh, Gründung und Mineraldünger gedüngten Zuckerrübe beobachtet. Ausnahmen von dieser Regel bildete das Vorkommen von echtem Mehltau und Keimlingsfäule. Auf den Objekten A, B, C nahm die Intensität der Krankheiten mit der Steigerung der Stickstoffgabe zu. Auch die auf Objekt D verabreichten Biopräparate stimulierten die Entwicklung der Krankheiten. The effect of various fertilization methods on the diseases of sugar beet was estimated on the basis of nine-year studies (1994-2002) conducted in the Experimental Production Farm in Ba?cyny on loess-based, sedimentary-gley, light-clay soil. The following fertilization methods were applied: A - mineral fertilization, B - mineral and manure fertilization, C - straw, green manure and mineral fertilization, D - ecological compost and biodynamic preparations fertilization. In the objects A, B and C fertilized with phosphorus and potassium, various doses of nitrogen ranging from 0 to 180 kg/ha^?1 were used. In the ecological object D, where mineral fertilization was not used, biodynamic preparations P₅₀₀ and P₅₀₁ were applied instead of nitrogen. The lowest ratio of the diseases of sugar beet was observed in the object fertilized with the compost and biodynamic preparations. In view of the conventional fertilization methods, generally the highest incidence of diseases was noted in the sugar beet fertilized with straw, green manure and mineral fertilizers. The exception was the occurrence of powdery mildew and the black leg. In objects A, B and C the incidence of the diseases increased with the increase in nitrogen doses. The applied biodynamical preparations in the object D stimulated the development of diseases too.     

Prospects for control of Pythium damping-off of lettuce with Trichoderma,Gliocladium and Enterobacter spp.

Summary Damping-off of lettuce (Lactuca sativa) caused by Pythium ultimum was studied in pots containing a non-sterile potting mix in the glasshouse. Fifty P. ultimum sporangia g^-1 compost reduced the plant stand to 15% and shoot dry weight to 18%, but this reduction was totally prevented by applying Trichoderma harzianum at 2×10⁵ viable propagules g^-1 potting mix. Gliocladium virens and Enterobacter cloacae also alleviated the damping-off. E. cloacae did not adversely affect the action of the fungal antagonists. The co-existence of the bacterial and fungal antagonists was revealed on the root surface and inner surface of the testa by scanning electron microscopy, indicating the compatibility of the biocontrol agents.     

细菌、真菌及植物氮营养信号研究进展

氮素吸收代谢是所有生物生命活动的核心部分,因此,各种生物对氮的吸收与同化过程都有精细的调节。这种调节依赖于生物对体内氮素状况信号及体外（生长介质中）氮素信号的感受。过去几十年中,在细菌、真菌中已经对氮素营养信号有了较好的研究,而植物中则相对缓慢,但也有了一定的认识。本文重点比较细菌、真菌及植物中氮信号系统的组成,以期为进一步认识植物中的氮信号接受与转导系统提供启示。     

Aircraft operations near concentrations of birds in Antarctica: The development of practical guidelines

Aircraft operations have the potential to disturb and to impact negatively on bird life. A gradient of increasing behavioural response is evident in birds when exposed to increasing aircraft stimulus. The most major disturbance is likely to lead to impacts on the health, breeding performance and survival of individual birds, and perhaps bird colonies. A process of revision to policies on aircraft operations contained in management plans for a number of specially protected areas in Antarctica by the United Kingdom, accompanied by consultations made within the scientific community through the Scientific Committee on Antarctic Research (SCAR) and with operational interests through the Council of Managers of National Antarctic Programmes (COMNAP) resulted in new guidelines being adopted by the Antarctic Treaty Consultative Parties in June 2004. The principal recommendations of the guidelines are that bird colonies should not be overflown below 2000 ft (∼610 m) above ground level and landings within 1/2 nautical mile (∼930 m) of bird colonies should be avoided wherever possible. These guidelines are less stringent and less specific than those that were recommended by the SCAR specialist group on birds, and represent a compromise to accommodate operational needs. While the adoption of clear and consistent guidelines for the operation of aircraft in Antarctica is welcome in that this provides practical advice that is likely to reduce incidences of close aircraft/bird encounters, there remains insufficient knowledge of the interactions between aircraft and birds in Antarctica, and the consequent impacts on individual birds and on bird populations. It is important, therefore, that the guidelines adopted are considered interim, and should be kept under scrutiny with revisions made as new and improved research results appear.     

The abundance of heterocystous blue-green algae in rice soils and inocula used for application in rice fields

Summary Algal populations were quantified (as colony-forming units [CFU] per square centimetre) in 102 samples of rice soils from the Philippines, India, Malaysia and Portugal, and in 22 samples of soil-based inocula from four countries. Heterocystous blue-green algae (BGA) were present in all samples. Nostoc was the dominant genus in most samples, followed by Anabaena and Calothrix. In soils, heterocystous BGA occurred at densities ranging from 1.0 × 10² to 8.0 × 10⁶ CFU/cm² (median 6.4 × 10⁴) and comprised, on average, 9% of the total CFU of algae. Their abundance was positively correlated with the pH and the available P content of the soils. In soil-based inocula, heterocystous BGA occurred at densities ranging from 4.6 × 10⁴ to 2.8 × 10⁷ CFU/g dw (dry weight), comprising only a moderate fraction (average 13%) of the total algae. In most soils, the density of indigenous N₂-fixing BGA was usually higher than that attained by applying recommended rates of soil-based inoculum. Whereas research on the practical utilization of BGA has been mostly directed towards inoculation with foreign strains, our results suggest that attention should also be given to agricultural practices that enhance the growth of indigenous strains already adapted to local environmental conditions.Maître de Recherches ORSTOM (France), Visiting Scientist at IRRI