不同农艺措施对巢湖沿岸坡耕地不同形态磷径流输出的控制效果

为明确巢湖沿岸坡耕地不同农艺措施对生态保护和水环境治理的影响,以农业面源污染长期定位观测基地为平台,于2014—2015年连续2 a对常规耕作(CK)、植物篱(黄花菜,PH)、植物篱+秸秆覆盖(PHS)和等高垄作(CR)4种农艺措施下的水土及随地表径流迁移的各种形态磷进行了监测。结果表明,与常规耕作相比,PH、PHS和CR能有效地减少径流量和产沙量(P0.05),降低效果依次为:PHSPHCR。与CK相比,PH、PHS和CR可分别减少23.5%、36.5%和19.7%的径流流失和29.5%、45.2%和26.3%的土壤流失,表现出显著的水土保持作用。CK条件下的径流液总磷(TP)浓度是0.612~1.220 mg·L~(-1),其中颗粒态磷(PP)占总磷的71.5%~81.7%,颗粒态磷是磷随地表径流迁移的主要形态。在溶解态总磷(DTP)中,溶解态正磷酸盐(D-Ortho-P)所占比例较大,为87.4%~90.7%;溶解态有机磷(DOP)所占比例较小,仅占9.3%~12.6%。与CK相比,PHS、PH和CR显著降低了径流液PP和TP的浓度(P0.05),但却不同程度地提高了DTP和D-Ortho-P的浓度,而对DOP的浓度无显著影响(P0.05)。CK条件下,磷的年流失负荷平均为0.706 kg·hm~(-2),占当年作物施磷量0.98%。与CK处理相比,PH、PHS和CR处理磷的年流失负荷分别降低38.4%、53.8%和33.4%(P0.05),其对磷素输出的控制效应主要通过减少径流量和降低径流液PP的浓度来实现的。综上可知,植物篱(黄花菜)、植物篱+秸秆还田和等高垄作是控制巢湖沿岸坡耕地水土及磷径流输出的有效措施,其中植物篱配合秸秆覆盖还田效果最佳。该研究可为巢湖流域坡耕地水土流失和面源污染防治提供科学依据。     

土地利用方式对红壤坡地地表径流氮素流失的影响

为探明长期(1995年开始)不同土地利用方式对红壤坡地径流氮素流失的影响,通过2011年10月-2012年9月连续12个月23次径流水质动态分析,研究自然林、草地、农作、油茶林和湿地松5种坡地利用类型下径流水中氮素迁移特性及其泥沙和植物残体氮的年流失总量。结果表明:(1)径流水中氮素流失量随土地利用方式的不同表现出明显差异,径流水中氮素流失负荷为85.1~655.5g/hm2,大小顺序为农作油茶林湿地松草地自然林。(2)径流中氮素以无机态氮(DIN)为主,其中硝态氮是DIN的主要形态,占全氮的31.5%~54.8%,是铵态氮(NH+4-N)的1.8~5.8倍,可溶性有机氮(DON)含量较低,仅占径流TN的10.1%~17.1%,远小于颗粒态氮(PN)所占全氮比值(21.4%~37.2%)。(3)泥沙和植物残体氮素年流失量分别为37.0~154.2g/hm2和28.1~249.6g/hm2,占各利用方式下氮流失总量的17.0%~77.1%,其中自然恢复林地所占比例最高(77.1%),而其他利用方式泥沙和植物残体氮素年流失量(17.0%~30.3%)远低于通过径流水流失的氮量(69.7%~83.0%)。总体来看,径流量是导致土地利用方式间氮迁移通量产生差异的主要驱动因素。     

三峡库区小流域旱坡地氮磷流失特征研究

为探讨三峡库区小流域旱坡地氮磷流失特征,采用标准径流小区对重庆市涪陵区珍溪镇王家沟小流域常规耕作方式(顺坡耕作)以及水土保持耕作方式(常规顺坡耕作+PAM土壤调节剂、免耕+顺坡种植+稻草覆盖、常规顺坡耕作+植物篱、免耕+横坡垄作、常规横坡耕作)下土壤氮素和磷素的流失量及形态特征进行分析。结果表明:(1)就旱坡地土壤氮素的流失特征而言,径流中氮素的流失量相对较小,最大值仅为53.63mg/m2;而泥沙中所携带的氮素流失量相对较大,其最大值达131.25mg/m2;整个观测期内,氮素的流失主要以颗粒态为主,颗粒态氮的流失量占总氮流失量的53.0%～62.0%。(2)就旱坡地土壤磷素的流失特征而言,各处理径流中磷素的总体规律基本表现为:常规顺坡耕作>常规横坡耕作>免耕+顺坡种植+稻草覆盖>常规顺坡耕作+PAM土壤调节剂>免耕+横坡垄作>常规顺坡耕作+植物篱;泥沙中所携带的磷素流失量相对于径流中的磷素流失量而言较大,最大值为58.14mg/m2;整个观测期内,颗粒态总磷流失量为水溶态总磷流失量的1.75～2.15倍,流失方式同样以颗粒态为主。总体而言,水土保持耕作方式下的氮磷流失量均小于常规耕作处理,能有效减少径流及泥沙中各形态氮磷的流失。     

巢湖流域不同耕作和施肥方式下农田养分径流流失特征

采用野外定位观测试验,研究巢湖流域不同耕作和施肥方式下农田养分径流流失特征,探索降低养分流失、提高湖区水质的有效耕作和施肥措施。2009-2010年结果表明,冬季麦田径流液总氮(TN)的浓度范围是2.12～4.34mg/L,溶解态氮(DN)约占TN的72%～92%,DN中又以硝态氮(NO3--N)为主,溶解态有机氮(DON)次之,铵态氮(NH4+-N)所占比例极小。径流液总磷(TP)浓度范围是0.095～0.360mg/L,颗粒态磷(PP)约占TP的51%～69%。DN和PP是农田氮磷径流流失的主要形态。长期的保护性耕作可提高径流液TN、DN、NO3--N、DON和DP的浓度,降低PN和PP的浓度,但对NH4+-N和TP浓度无明显影响;氮肥后移一定程度上易增加追肥后短期内降雨径流液各形态N的浓度,但可降低小麦整个生育期内径流液各形态P的浓度。在当地常规耕作条件下(处理CT),麦田TN和TP径流流失量分别为1.065,0.079kg/hm2,占当季施N量的0.71%,施P量的0.24%。与处理CT相比,处理CTS(常规+覆盖)、NFP(氮肥后移)和NTS+NFP(少免耕覆盖+氮肥后移)TN流失量分别减少了14%、21%和24%,TP流失量分别减少了20%、21%和24%。因此,保护性耕作和氮肥后移在保证小麦产量的前提下,可作为巢湖流域源头控制农田养分流失的主要措施。     

施肥条件下坡面菜地径流携氮流失模拟降雨试验

借助室内人工模拟降雨试验研究手段,以强降雨过程中红壤丘陵区坡菜地随径流、泥沙迁移的氮流失状况和规律为研究目的,分别在不同坡长(2 m,4 m)、不同植被覆盖度(0,30%,60%)和不同施肥处理(空白(CK),无机复合肥(CF))条件下进行有效模拟降雨试验共计12场次,每场次降雨试验的产流历时设计为30min,固定雨强为120mm/h。试验结果表明:(1)径流中全氮(TN)流失以硝态氮(NO3--N)和铵态氮(NH4+-N)为主要形式,两者(NO3--N、NH4+-N)之和占TN流失量及流失浓度的54.16%~91.41%,其中又以NO3--N流失为主要流失形态。坡长对径流中NO3--N和NH4+-N流失量的影响大于植被覆盖度。(2)通过比较CK和CF两施肥处理条件下全氮(TN)流失量,CF为CK的2.29~2.32倍,说明施肥可明显增加坡面径流和泥沙中各形式氮的流失量,其中径流中坡长的增加可降低氮流失强度。(3)侵蚀泥沙中氮流失主要受到植被覆盖度的影响,土壤侵蚀模数(Ms)与全氮在泥沙富集值(ERTN)可建立对数方程。(4)坡面TN流失主要以径流携带为主,径流是坡面TN流失的主要途径。     

红壤坡地氮的径流输出通量及形态组成

为研究自然降雨条件下红壤坡地氮素输出特征,于2015年5月—2016年5月采用野外大型土壤水分渗漏试验装置,对赣北第四纪红壤坡地植草覆盖、干草覆盖和裸露对照3种处理的地表径流和壤中流中不同形态氮素的输出开展了试验观测。结果表明:(1)在侵蚀不明显的第四纪红壤坡地,TN(总氮)、DIN(溶解态无机氮)、DON(溶解态有机氮)和PN(悬涂泥沙颗粒态氮)主要随105cm壤中流输出,占径流输出总通量的71%,而随地表径流和30cm、60cm壤中流输出通量分别为23%和6%;(2)氮素随壤中流输出主要以溶解态(DTN(溶解态总氮)占TN比例为54.8%~86.9%)为主,DTN又以无机态(DIN占DTN比例为57.8%~97.1%)尤其是NO3--N(硝态氮)为主。氮素随地表径流输出的主要形态则随处理措施的不同而不同;(3)保留草被覆盖可以较好地削减氮素径流流失,而采取干草覆盖有增大氮素径流流失尤其是深层损失的风险。     

自然降雨条件下香根草生物篱对菜地土壤地表径流和氮流失的影响

通过修建径流小区,开展了自然降雨条件下香根草生物篱对种植辣椒土壤地表径流的发生及其引起的水土流失和氮素流失影响的研究.试验结果表明,在菜地土壤种植香根草生物篱能有效地降低地表径流以及减少因地表径流引起的土壤氮素流失.在辣椒种植期间,香根草生物篱种植小区的总产流量比传统辣椒种植小区的降低了41.9%.与传统辣椒种植小区相比,香根草生物篱种植小区的地表径流中NH+4-N和NO-3-N流失量平均分别降低57.9%和59.7%,土壤侵蚀量平均降低64.5%,侵蚀土壤的氮流失量平均降低64.8%,试验结果还显示,降雨强度与地表径流量、地表径流NH+4-N、地表径流NO-3-N、地表径流全N流失量、土壤侵蚀量和侵蚀土壤N流失量之间的相关性均达到极显著水平,这一结果说明降雨强度影响水土流失和土壤氮素流失的主要因素.     

控释尿素减施对双季稻田径流氮素变化、损失及产量的影响

为了探究双季稻田典型自然降雨径流过程中氮(N)的输出特点,采用田间径流池法,通过长期田间定位试验,比较普通尿素(U)和控释尿素(CRU)减施稻田径流水中总氮(TN)、铵态氮(NH_4~+-N)和硝态氮(NO_3~--N)的动态变化及N素径流流失量和流失率。结果表明:稻田施肥初期出现N素径流峰值,是防控N素径流损失的关键时期。早、晚稻季生育期间施N处理径流水中以NH_4~+-N为主要形态,分别占TN径流损失量的64.5%~66.3%,61.0%~68.6%。早、晚稻季U处理径流水TN流失量(率)分别为5.6(2.2%),5.0(1.7%)kg/hm~2;CRU处理较U处理径流水TN流失量分别降低17.4%~34.1%,17.3%~37.7%;且随着N肥用量的减少,TN流失量(率)逐渐降低。受降雨强度的影响,早稻季N素径流损失较晚稻季高,且晚稻季CRU处理N素径流损失减排效果优于早稻季。早、晚稻季及连作周期CRU处理TN径流累计损失量和籽粒产量与施N量呈显著线性关系,随着N用量的增加而增加。总之,U处理显著提高径流水中N素浓度以及NH_4~+-N占TN的比例。CRU处理有效减缓N素释放速度,降低施肥初期N素径流损失量,实现增产;而CRU减施有利于进一步防控稻田N素流失风险,促进农业面源污染减排,且以减N 10%效果较好。     

平衡减量施肥和行间配植对白茶园氮磷流失的影响

安吉白茶经济效益高,施肥量大,茶园氮磷流失已成为西苕溪流域农业面源污染的主要来源之一。通过2个生长周期的野外径流小区试验连续观测了减量施肥和行间配植乔木控制白茶园氮磷径流损失的效应。试验设置习惯施肥处理(CK)、减氮减磷处理(T1)、减磷+配植合欢处理(T2)和减氮减磷+配植合欢处理(T3)4个处理,各处理重复2次。结果表明:行间配植合欢处理(T2、T3)2个观测周期的径流水量、泥沙量显著小于无行间配植处理(CK、T1)(P0.05)。CK处理2个观测周期径流总氮及各形态氮的累积流失量均显著大于其他3个处理,泥沙氮素累积携出量显著大于T3处理(P0.05);CK处理2个观测周期径流总磷及无机磷的累积流失量均显著大于其他3个处理,泥沙磷素累积携出量显著大于T2和T3处理(P0.05)。白茶园氮素流失以径流水为主,磷素流失以径流泥沙为主。减施氮磷、行间配植和两者结合均能有效削减白茶园氮磷流失,减氮减磷与行间配植的组合措施效果更好,推荐的施肥和植被管理技术为N 270 kg/hm~2,P_2O_5 90 kg/hm~2,行间配植合欢密度200株/hm~2。     

水肥一体化结合植物篱对减缓果园土壤氮磷地表径流流失的效果

为了探究降低集约化果园氮、磷流失,减缓农业面源污染的技术措施。通过田间定位试验,比较分析了水肥一体化施肥方式结合田间植物篱对减少果园氮、磷地表径流流失影响,提升沟渠水质量的技术效果。结果表明:果园中构建植物篱提高了发生地表径流的最低日降雨量,减少了径流发生频次,地表径流水发生量比没有植物篱降低19.18%。与常规施肥相比,水肥一体化施肥全氮(TN)、全磷(TP)浓度分别降低31.23%和25.18%;植物篱处理TN、TP浓度分别降低16.74%和13.60%;水肥一体化+植物篱处理径流水中TN、TP浓度最低,分别比对照降低52.32%和43.89%。水肥一体化+植物篱处理TN、TP流失总量分别比对照降低45.38%和36.81%,该处理相对应的沟渠水中TN、TP浓度分别比对照降低23.98%和26.64%。在果园等集约化农田中推行水肥一体化灌溉施肥结合植物篱措施能够有效降低氮、磷径流流失,减缓农业面源污染物的排放,在实际应用中具有很大的推广应用价值。     

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