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长期施肥下红壤旱地解钾菌变化及其驱动因子 总被引:5,自引:1,他引:4
在南方红壤区,研究长期施肥下土壤解钾菌的变化规律及其驱动因素,可为该地区土壤钾素资源管理和钾肥合理施用提供理论依据。基于红壤旱地长期定位施肥试验(始于1986年),选取不施肥(CK)、施氮磷肥(NP)、氮磷钾肥(NPK)和氮磷钾肥配施有机肥(NPKM)处理,分析玉米开花期根际土壤的解钾菌类型和解钾能力及其有机酸和激素含量,并结合玉米根系特性和根际土壤理化性质探讨影响红壤旱地解钾菌变化的关键因子。结果表明:与NPK处理相比,NPKM处理的根长、根表面积、根直径和根体积分别增加了112.3%、174.4%、32.43%和291.5%,根际土壤pH提高了0.67个单位,有机质、非交换性钾和交换性钾分别增加了29.50%、19.34%和53.89%。各施肥处理根际土壤中均存在解钾菌,CK和NP处理的解钾菌均为类芽孢杆菌属,NPK和NPKM处理则均为纤维菌属。与CK处理相比,NP、NPK和NPKM处理下根际土壤解钾菌的解钾效率分别增加了162.4%、139.0%和105.6%,其中NP处理解钾菌的解钾效率最高。偏最小二乘路径模型的结果显示,根系和施肥可同时调控解钾菌的解钾效率。冗余分析(RDA)进一步表明,根系长度和表面积与土壤解钾菌特性呈显著正相关关系(P0.05)。因此,红壤旱地长期不同施肥措施不仅直接影响玉米根系发育特征和根际土壤理化性质,还能显著改变土壤解钾菌群落及其解钾能力,其中根系长度和表面积是调控玉米根际土壤中解钾菌的关键因子。 相似文献
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为了研究聚乙烯类微塑料对玉米根际土壤微生物群落结构的影响,以玉米为试材,以平均分子量为2000、5000、10万的聚乙烯粉末模拟土壤中的微塑料污染,设置5个处理:不添加聚乙烯(CK)、添加分子量为2000(T1)、5000(T2)、10万以上(T3)的聚乙烯且种植玉米、未添加聚乙烯未种植玉米(CK0),分析玉米抽穗期各部位矿质元素代谢和根际土壤微生物群落结构差异。结果显示,矿质元素含量在玉米各部位存在差异,Fe、Cu主要集中在玉米根部, Ca、Mn、Mg在叶中分布最多, K主要集中在茎中;添加不同分子量聚乙烯微塑料后,不同部位的矿质元素较CK增加,且T1处理下增加最多。微生物多样性分析显示,不同分子量聚乙烯微塑料对玉米根际微生物群落组成影响不同。T1处理下除变形杆菌纲、伯克氏菌科细菌丰度增加外,其他细菌丰度较CK均减少;T3处理下,细菌和真菌的丰度较CK都有较大幅度的增加。总体来看,添加聚乙烯后,玉米不同部位矿质元素含量较CK显著增加, 2000分子量聚乙烯能够显著降低土壤中细菌和真菌的丰度, 10万以上分子量聚乙烯使得土壤中细菌和真菌丰度增加,各处理中与环境污染物降解相关的微生物增多。 相似文献
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【目的】探究生物有机肥施用对烟草根际土壤细菌、真菌群落结构和青枯雷尔氏菌丰度的影响机理。【方法】选用长沙市某公司生产的生物有机肥和常规烟草专用肥,在湘西花垣县长期定位试验点连续5年开展大田试验,研究施肥对土壤理化性质和微生物群落的影响。试验设置两种施肥处理:常规烟草专用肥(CF)和生物有机肥(BOF)。【结果】与CF相比,施用生物有机肥处理的土壤烟草青枯病发病率降低了89.8%,同时青枯雷尔氏菌相对丰度也显著降低,降幅达40.1%;土壤pH、碱解氮和有效磷显著增加,分别增加了1.2%、12.1%和60.2%;施用生物有机肥后根际土壤微生物如Roseiflexaceae,Gemmatimonadaceae,Nitrospira,Ramophialophora,Preussia等显著富集,且这些潜在有益菌与青枯雷尔氏菌相对丰度呈显著负相关关系。通过ABT预测模型分析发现潜在有益菌是影响青枯雷尔氏菌相对丰度的最主要生物因子。【结论】连续5年的试验结果表明,施用生物有机肥不仅改善了作物生长的土壤环境,显著提高了土壤pH和土壤速效养分含量,还促使潜在有益菌在根际土壤中富集,抑制了青枯雷尔氏菌的生... 相似文献
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为了研究不同磷肥水平下酸性红壤上玉米不同部位丛枝菌根真菌(Arbuscular mycorrhizal fungi, AMF)群落多样性和组成结构,明确玉米不同部位AMF群落的分布特征及对磷肥的响应差别,为提高酸性红壤磷素利用提供理论依据。本实验设置三个磷肥水平:不施磷、低磷(25 mg P /kg)和高磷(100 mg P /kg),玉米培养4周后,测定玉米生物量和土壤理化性质,利用高通量测序技术检测玉米根部、根际和非根际土壤AMF群落结构和多样性。结果显示,随着磷肥水平增加,玉米生物量显著提高,高磷处理下玉米地上部磷含量显著高于不施磷和低磷处理。取样部位(根部、根际和非根际)显著影响了AMF群落优势属球囊霉属(Glomus)、巨孢囊霉属(Paraglomus)和近明球囊霉属(Claroideoglomus)相对丰度,但是磷肥影响不显著。类似的,取样部位而不是磷肥显著影响了AMF群落香农指数和物种丰富度。非度量多维标度(NMDS)结果显示,根部样品与非根际和根际土壤样品群落距离更远,而相同取样部位中不同磷肥水平间群落组成更为相似;置换多元方差分析(PERMANOVA)进一步表明,取样部位而不是磷肥显著影响了AMF群落组成结构,主要表现在根部样品与根际和非根际土壤不同。因此,酸性红壤上玉米不同部位对AMF群落的影响明显高于磷肥作用,表明AMF应用于酸性红壤时应重点考虑作物部位的特性。 相似文献
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试验选择中国东部3个气候带上的主要农田土壤:寒温带黑龙江海伦的黏化湿润均腐土(黑土)、暖温带河南封丘的淡色潮润雏形土(潮土)和中亚热带江西鹰潭的黏化湿润富铁土(红壤),在海伦、封丘和鹰潭3个生态试验站建立土壤置换试验,研究玉米不同生育期水热条件和土壤类型对好氧性纤维素分解菌数量的影响。结果表明,暖温带气候条件下土壤好氧性纤维素分解菌数量高于中温带和中亚热带气候条件;土壤类型显著影响了土壤好氧性纤维素分解菌数量,变化顺序为黑土>潮土>红壤;在玉米不同生育期土壤纤维素分解菌数量的顺序均为抽雄期>收获后>种植前;施用化肥提高了土壤中好氧性纤维素分解菌的数量。相关分析显示土壤好氧性纤维素分解菌数量与土壤有机质、全氮、全磷、全钾、含水量和pH值呈显著正相关,土壤温度和含水量是影响土壤好氧性纤维素分解菌数量的重要环境因子。通径分析结果表明,土壤养分是决定土壤好氧性纤维素分解菌数量的主要因子,水热条件对其直接作用并不明显,但水热、施肥、土壤类型对纤维素分解菌数量有显著的交互作用。 相似文献
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较低的土壤磷素有效性限制了酸性红壤生产潜力提升。作为磷素活化的主要执行者,解磷微生物对施肥和根际作用的综合响应尚不清楚。以玉米为试验材料,设置磷肥水平(施磷和不施磷)与不同氮形态(铵态氮肥和硝态氮肥)的交互试验,使用编码酸性磷酸酶和碱性磷酸酶的微生物phoC和phoD基因作为分子标记物,研究了施肥和根际作用对酸性红壤磷酸酶活性和相关功能微生物群落的影响。结果显示,根际作用显著提高了土壤磷酸酶活性,且作用强度大于氮形态和磷肥水平。氮形态、磷肥水平和根际作用均显著影响phoD细菌操作分类单元(OTU)数目和香农指数,然而仅有氮形态和根际作用影响phoC细菌OTU数目。根际作用对phoC和phoD细菌群落组成结构的影响程度显著高于氮形态和磷肥水平,而且对phoD细菌群落的作用更明显。根际磷酸酶活性提高与土壤有机质增加密切相关。phoC细菌群落组成和结构的变化主要与根际养分变化有关,而phoD细菌群落结构的变化可能是根系分泌物和养分变化共同作用的结果。总体而言,玉米根际作用对酸性红壤磷酸酶活性和相关功能细菌群落的影响大于氮形态和磷肥水平,但是其作用强度一定程度上依赖于上述施肥措施。 相似文献
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为探究生物质炭负载解钾菌对土壤微生物特性的影响,基于5个处理即空白(CK)、施用化学钾肥(KCl)、接种解钾菌(KSB)、施用生物质炭(BC)、施用生物质炭负载解钾菌(BC-KSB)的黑麦草盆栽耗竭试验,分析不同处理下土壤酶和微生物群落结构的响应特征。结果表明,BC-KSB相比其余施肥处理更有利于提高土壤脲酶、蔗糖酶、酸性磷酸酶和过氧化氢酶的活性,同时也提高了土壤细菌的物种多样性与菌群丰富度,并提高了土壤有益菌群(绿弯菌门、放线菌门、芽孢杆菌属和慢生根瘤菌属)的丰度,抑制了土壤致病菌群(变形菌门和罗河杆菌属)的繁殖。各施肥处理相比CK均显著提升了黑麦草干物质量,且以BC-KSB处理对黑麦草干物质量的提升最为显著。与CK和KCl相比,BC-KSB能显著提高土壤微生物生物量碳、微生物生物量氮、有机质、全氮和速效钾的含量(P <0.05)。冗余分析表明,土壤有机质、速效钾、酸性磷酸酶、脲酶和微生物生物量氮是影响细菌群落结构的主要因子,黑麦草的生长主要受伯克氏菌属和罗河杆菌属的影响较大。可见,BC-KSB对黑麦草产量、土壤养分、土壤酶活性和细菌群落结构均产生了积极的影响,对于改良土壤生态... 相似文献
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健康与罹患青枯病的番茄土壤细菌群落特征比较 总被引:1,自引:1,他引:1
应用实时荧光定量PCR及MiSeq高通量测序技术,全面地研究了连作番茄田块中健康与感染青枯病植株周围土体及根际土壤细菌群落结构和组成。结果表明:健康番茄土体土壤的pH及全碳含量显著高于感病番茄土体土壤;土体及根际土壤的细菌群落结构和组成明显不同于感病番茄土体及根际土壤细菌群落。与感病番茄根际相比,健康番茄根际细菌的数量显著升高而青枯菌数量显著降低;细菌群落的Shannon多样性指数显著增高;拟杆菌门及其所含的噬几丁质菌属、金杆菌属、动杆菌属、黄杆菌属及Taibaiella的相对丰度显著增高而变形菌门及其所含的青枯菌属的相对丰度显著降低。综上,抑制土传青枯病发生的番茄根际土壤细菌群落特征明显,其生物量及多样性高,土著有益菌群数量多而病原菌数量少,为番茄土传青枯病的生物防控提供了指导方向与理论依据。 相似文献
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Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage 总被引:1,自引:0,他引:1
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. 相似文献
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I.L. Boyd 《Biological conservation》2010,143(7):1664-1674
“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. 相似文献
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Yoav Bashan Bernardo Salazar Ma. Esther Puente Macario Bacilio Robert Linderman 《Biology and Fertility of Soils》2009,45(6):585-594
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. 相似文献
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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. 相似文献
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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. 相似文献
16.
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. 相似文献
17.
Prospects for control of Pythium damping-off of lettuce with Trichoderma,Gliocladium and Enterobacter spp. 总被引:1,自引:0,他引:1
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. 相似文献
18.
细菌、真菌及植物氮营养信号研究进展 总被引:1,自引:0,他引:1
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。 相似文献
19.
Colin M. Harris 《Biological conservation》2005,125(3):309-322
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. 相似文献
20.
P. A. Roger S. Santiago-Ardales P. M. Reddy I. Watanabe 《Biology and Fertility of Soils》1987,5(2):98-105
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 相似文献