Molecular phylogeny of banana cultivars from Thailand based on HAT-RAPD markers

Musa acuminata Colla (AA genomes) and Musa balbisiana Colla (BB genomes) are the wild progenitors of the cultivated banana, they are highly variable in Thailand. The genetic system is relatively unknown and complicated due to interspecific hybridization, heterozygosity and polyploidy, which are common in most clones. These factors make identification of closely related banana cultivars difficult, especially when sterile. The high annealing temperature-random amplified polymorphic DNA (RAPD) technique was used to estimate the genetic relationship between 22 selected banana cultivars, utilizing 14 random primers. Phylogenetic relationship was determined by unweighted pair group method with arithmetical averages cluster analysis. The dendrogram constructed from the similarity data showed that all the 22 cultivars analysed were closely related with a narrow genetic base. There were sufficient RAPD polymorphisms that were collectively useful in distinguishing the cultivars. The dendrogram grouped all the AA, BB, AAA, AAB and ABB genomes into a major cluster. Several subgroups are recognized within the major clade. As expected, Ensete glauca Roxb. (Musaceae) and Strelitzia reginae Banks (Strelitziaceae) were clearly differentiated from the analysed edible bananas. Our study showed that RAPD markers are sufficiently abundant to classify and readily dissect genetic differences between the closely related Musa germplasm and provide a basis for the selection of parents for improvement of this germplasm.     

Effects of legume intercrops on soil-borne pests, biomass, nutrients and soil water in banana

Banana (Musa AAA) and plantain (Musa AAB) are important dietary staples for over 70 million people in sub-Saharan Africa. Banana weevil (Cosmopolites sordidus) and nematodes (Radopholus similis, Helicotylenchus multicinctus) are often the largest constraints to production. Leguminous crops in the genera Canavalia, Mucuna and Tephrosia have been reported as having repellent or insecticidal properties. We assessed: weevil and nematode populations and damage; banana growth and development; soil and foliar nutrient concentrations; and soil moisture status in banana intercropped with three legumes (Canavalia ensiformis, Mucuna pruriens and Tephrosia vogelii). The research took place at Kawanda, Uganda, on a field site infested with weevils and nematodes. The legume intercrops did not affect weevil populations or damage. The legumes also provided no benefit in terms of nematode control; in fact, banana root necrosis was higher in the T. vogelii intercrop than in the banana monoculture. Banana fruit yield was not adversely affected by the legume intercrops. The low yield noted across treatments was attributed to the high level of damage by the weevils and the nematodes. Significantly more NO₃-N accumulated from 0- to 0.3-m depth in the M. pruriens intercrop than in the other treatments. There was no treatment difference in soil moisture. In summary, there was no significant advantage in banana production associated with the legume intercrops. However, the lack of a significant difference in banana fruit production between the monoculture and the intercrops suggests that land use efficiency may be increased by incorporating food and or/fodder legumes into the banana cropping system.     

Development of key soil health indicators for the Australian banana industry

To improve the sustainability and environmental accountability of the banana industry there is a need to develop a set of soil health indicators that integrate physical, chemical and biological soil properties. These indicators would allow banana growers, extension and research workers to improve soil health management practices. To determine changes in soil properties due to the cultivation of bananas, a paired site survey was conducted comparing soil properties under conventional banana systems to less intensively managed vegetation systems, such as pastures and forest. Measurements were made on physical, chemical and biological soil properties at seven locations in tropical and sub-tropical banana producing areas. Soil nematode community composition was used as a bioindicator of the biological properties of the soil. Soils under conventional banana production tended to have a greater soil bulk density, with less soil organic carbon (C) (both total C and labile C), greater exchangeable cations, higher extractable P, greater numbers of plant-parasitic nematodes and less nematode diversity, relative to less intensively managed plant systems. The organic banana production systems at two locations had greater labile C, relative to conventional banana systems, but there was no significant change in nematode community composition. There were significant interactions between physical, chemical and nematode community measurements in the soil, particularly with soil C measurements, confirming the need for a holistic set of indicators to aid soil management. There was no single indicator of soil health for the Australian banana industry, but a set of soil health indicators, which would allow the measurement of soil improvements should include: bulk density, soil C, pH, EC, total N, extractable P, ECEC and soil nematode community structure.     

Ant-induced soil modification and its effect on plant below-ground biomass

Lasius flavus is a dominant mound-building ant species of temperate grasslands that significantly modifies soil parameters. These modifications are usually the result of workers’ activities such as food accumulation and nest construction. An alternative hypothesis that could explain changes in soil is colony founding in areas of higher soil fertility.In our study we investigated several soil parameters sampled in 10 ant nests and adjacent (control) plots in mountain grassland in Slovakia. The alternative hypothesis was tested by comparing occupied and abandoned mounds. While we found increased concentrations of available P and K in the nests, concentrations of total C, total N, Ca²⁺ and Mg²⁺ were lower there. We propose that differences found between the soil of nests and control plots are entirely a product of ant activity during mound occupancy and not due to initial soil differences during nest establishment. This was confirmed by the comparison of occupied and abandoned nests in which the soil fertility of abandoned nests was similar to conditions in the surrounding soil.Along with the modification of soil chemistry, we recorded changes in soil physical properties and the vertical distribution of nutrients. Ant nests were characterized by the dominance of 0.02–0.1 mm particles and lower bulk density. In the same habitat, nutrient concentrations did not change along the vertical gradient in contrast to control plots where soil nutrients decreased and bulk density increased with depth. Root biomass followed the vertical pattern observed with nutrients: in control plots, most roots were concentrated in the uppermost layer (0–3 cm), whereas they were evenly distributed along the vertical gradient in the nests. We also found that rhizome internodes of Agrostis capillaris were thinner and longer in plants from the mounds. Changes in soil physical properties, vertical distribution of nutrients and root biomass in the nests are most probably a consequence of mounding and soil mixing (bioturbation), which has been less reported on in ant-soil studies.     

转 AtPAP15基因大豆种植对根际土壤养分及酶活性的影响

以转入AtPAP15基因的两个磷养分高效转基因大豆株系AP15-1、AP15-3及其各自受体YC03-3、YC04-5为材料,在大田连续种植两季,通过在苗期、盛花期和成熟期采集根际土,对其进行pH和全磷、速效磷、有机磷、全氮、碱解氮、全钾、速效钾、及钼等八种微量元素含量的测定,并分析了盛花期AP15-1与其受体YC03-3根际土中酸性磷酸酶、过氧化氢酶、蔗糖酶和脲酶的活性变化,从而了解上述磷高效转基因大豆的种植是否会对根际土中主要养分和酶活性产生影响.研究结果显示:秋春两季根际土中除全钾和微量元素含量外,其他养分含量在个别时期,转基因大豆AP15-1或AP15-3与其受体之间,均存在显著性的差异,但这些显著性差异大部分出现在苗期,成熟期仅有机磷含量在AP15-1与其受体YC03-3、速效钾含量在AP15-3与其受体YC04-5之间呈显著差异,并且这些差异在两季中均未重复出现.根际土中四种土壤酶活性测定结果显示:同季转基因大豆与其受体之间差异不显著.总体结果表明,上述转AtPAP15基因磷高效大豆种植对根际土中磷、氮、钾等养分和四种土壤酶活性均未产生显著的影响.     

Poultry manure and banana waste are effective biofertilizer carriers for promoting plant growth and soil sustainability in banana crops

The aims of our study were to compare the effectiveness of poultry manure (PM) and banana waste (BW), with regard to their use as inoculant carriers of a bacterial consortium constituted by strains of Azospirillum, Azotobacter and P-solubiliser bacteria and to establish the most efficient dose of biofertilizer for a soil cultivated with banana (Musa paradisiaca AAA Simmonds), with respect to improving plant performance and soil physical and microbiological properties. Six months after planting, plant growth had increased with increase in dose of the biofertilizers applied. The biofertilizer prepared on BW enhanced the density of P-solubiliser bacteria, the concentrations of available P and foliar P to a greater extent than with the biofertilizer prepared on PM. The increases produced by the biofertilizer prepared on PM for the soil aggregate stability, enzymatic activities and the labile carbon fractions were highly correlated to the dose applied. Both biofertilizers can be considered potentially useful as inoculant carriers of PGPR but the usefulness of BW appears to be restricted to moderate doses of application (≤3%).     

Enhanced biodegradation of nematicides after repetitive applications and its effect on root and yield parameters in commercial banana plantations

The effects of five consecutive applications, every 4 months, of Counter, Furadan, Mocap, Nemacur, Rugby, and Vydate on functional root percentage, production parameters, and on enhanced biodegradation were compared in a commercial banana plantation in Costa Rica. To quantify nematode numbers and estimate functional root percentage, root samples were taken monthly from the field experiment. The enhanced biodegradation test was carried out in the laboratory. Samples taken from the field after five consecutive applications of each nematicide were treated in the following way: (1) not sterilized and no nematicide applied; (2) not sterilized but nematicide applied; and (3) nematicide applied after sterilization. The number of Radopholus similis which had penetrated the maize plantlets was used as a parameter to determine the degradation of the applied nematicide. Degradation was measured 0, 2, 4, 6 and 8 weeks after inoculation of pregerminated maize plantlets with 500 nematodes in soil under laboratory conditions. At harvest, 20 months after starting the field experiment, the lowest percentage of functional roots ( P =0.024) and bunch weight ( P =0.0001) were found in the non-treated control, followed by the Furadan treatment. On average, nematicides increased the bunch weight by 38%. In general, higher bunch weights coincided with higher percentages of functional roots. Furadan showed a high level of enhanced biodegradation while for Counter and Rugby this phenomenon was not detected. In the case of Mocap and Nemacur, a relatively high level of enhanced biodegradation in the soil biotest coincided with a high number of nematodes per 100 g roots in the field experiment. A high correlation between mean nematode numbers per 100 g roots and mean percentage of functional roots was observed ( R ²=0.81, P =0.006) for all treatments together. Data show that a rotation of different nematicidal molecules is the best option for long-term nematode management in commercial banana plantations.     

氨基酸菌肥施用量对茶树生长及土壤肥力的影响

为探究不同氨基酸菌肥施用量对茶树生长和土壤肥力含量的影响,以鸿雁12号茶树为研究对象,采用田间微区试验的方法,设置了不施用氨基酸菌肥作对照组(CK)和氨基酸菌肥施用量分别为75 kg·hm^-2(T1)、150 kg·hm^-2(T2)、225 kg·hm^-2(T3)和300 kg·hm^-2(T4)的处理,研究不同氨基酸菌肥施用量对茶树生长、茶叶品质及土壤肥力的影响。结果表明：氨基酸菌肥施用后能显著增加茶叶芽头密度及茶叶产量,提高茶叶中氨基酸含量和土壤中碱解氮含量。试验6个月后与CK相比,T4组的芽头密度显著增加了63.4%,茶叶产量显著增加了71.5%;T1～T4处理茶叶中氨基酸含量分别增加了9.73%、6.41%、7.57%和13.2%,土壤中碱解氮含量分别增加了25.0%、36.0%、46.0%和37.6%。综上,氨基酸菌肥的施用能提高茶叶产量及品质,改善茶园土壤环境质量,为茶园生产的合理施肥及优质高效生产提供数据参考。     

Plant nutrients in a degraded soil treated with water treatment sludge and cultivated with grasses and leguminous plants

The objective of this work was to evaluate rates for applications of water treatment sludge (WTS) as a nutrient source for grasses and leguminous plants cropped in a soil degraded by tin mining in the Amazon Region (Natural Forest of Jamari, Rondonia State, Brazil). The treatments consisted of three rates of nitrogen supplied by WTS (100, 150 and 200 mg kg⁻¹ soil), five combinations of plants, two controls (absolute control, without fertilization; and chemical control, soil+lime+chemical fertilizers). WTS modified the contents of macro and micronutrients in the degraded soil, but it was not, as used in the present study, sufficient for the rehabilitation of the degraded area.     

香蕉茎秆及其生物炭对珠江三角洲土壤团聚体特征的影响

为了探究施用香蕉茎秆(蕉秆)及其制备的生物炭对珠江三角洲农田土壤肥力的影响,本文通过土壤培养和盆栽试验,研究了施用0.5%、1.0%和2.0%蕉秆和水稻秸秆(稻秆)及其生物炭后,土壤中不同粒级水稳性团聚体的组成,并采用团聚体平均重量直径(MWD)、几何平均直径(GMD)、分形维数(D)和平均重量比表面积(MWSSA)等评价团聚体的稳定性。结果表明:1)珠江三角洲农田土壤水稳定性团聚体以0.25 mm微团聚体为主,占团聚体比例29.80%～52.52%;1～0.5mm团聚体次之,占18.19%～20.08%。2)施用1.0%、2.0%蕉秆和2.0%稻秆显著增加0.25 mm土壤团聚体总量,并显著提高土壤团聚体水稳定性;与不施用有机物料对照相比,团聚体MWD分别增加45.60%、62.37%和65.50%,GMD分别增加43.45%、55.34%和60.66%,D分别降低2.23%、2.32%和2.78%, MWSSA分别降低18.14%、20.09%和23.01%。3)MWD、GMD与 5mm、5～2 mm和2～1 mm团聚体所占比例呈极显著或显著正相关,与0.25 mm微团聚体所占比例呈极显著负相关; D、MWSSA与0.25 mm微团聚体所占比例呈极显著正相关,与5 mm、5～2 mm和2～1 mm团聚体所占比例呈极显著或显著负相关。4)综合主成分和差异显著性分析结果表明,施用2.0%和1.0%蕉秆提高土壤团聚体稳定性效果佳,均与施用2.0%稻秆没有显著差异,而施用蕉秆生物炭和稻秆生物炭短期内不能提高土壤团聚体稳定性。研究结果可为蕉秆废弃物资源化利用、提高土壤肥力提供参考依据。     

Effects of biomass and size of Millsonia anomala (Oligochaeta: Acanthodrilidae) on particle aggregation in a tropical soil in the presence of Panicum maximum (Gramineae)

Summary The present study assessed the effect of the tropical geophagous earthworm, Millsonia anomala, on the aggregate-size distribution of a sieved (2 mm), tropical ferruginous soil in the presence and absence of the perennial tropical grass Panicum maximum. The effect of two size groupings and graded biomass densities of M. anomala on soil aggregation was analysed in time and with depth in the containers within which the plants were grown. In the absence of earthworms, aggregation was rapid although limited (13.5% of soil as aggregates >2.0 mm), and probably arose from a combination of microbial activity and physical processes (interparticle bonding due to clays and other colloids). The roots of the test species contributed little to aggregation. In contrast, the effect of earthworm activity on soil aggregation was rapid and important. The effects of both biomass and, to a lesser extent, size were significant. After 79 days, aggregation reached a maximum with 3 g per container of small earthworms (ca. 59% of soil as aggregates >2.0 mm) and a minimum with 1 g per container of large earthworms (ca. 35% of aggregates >2.0 mm). Aggregation was considered to occur through three different mechanisms: (1) A rapid aggregation due to the interactions of colloids; (2) an intermediate aggregation due to a combination of unquantified processes related to earthworm activity (mucus secretion, development of fungus hyphae); (3) egestion of soil as earthworm casts which are stable macroaggregates.     

Changes in active microbial biomass by earthworms and grass amendments in agricultural soil

The influence of the earthworm Aporrectodea caliginosa on the biomass and the proportion of active and dormant soil microorganisms after the addition of cut perennial ryegrass (Lolium perenne) to upper soil from agricultural field was studied in a microcosm experiment. During a 2-month period, soil samples were taken 1, 8, 22, 36, 50, and 64 days after cut grass addition. A substrate-induced respiration (SIR) method was used to analyse the samples for total microbial biomass and the distribution of active and dormant microbial biomass. It was found that the addition of grass increased the microbial biomass (SIR) because of an increase in the active microbial biomass. After the initially high values, the active microbial biomass decreased slowly, and at day 64, it was still higher in the grass-amended soils than in the control treatment without grass addition. After 1 day, the active microbial biomass was higher in the soil with A. caliginosa than without the earthworm. At the subsequent samplings, there were no differences in microbial biomass or the proportion of dormant vs active microorganisms between the grass-amended soils. The average from all sampling occasions of SIR was higher in earthworm-treated soil.     

Effects of plant diversity on plant biomass production and soil macrofauna in Amazonian pastures

We examined the effect of plant diversity on plant production and soil macrofauna density and diversity. Four plants species (Arachis pintoi, an herbaceous legume; Brachiaria brizantha, a perennial grass; Leucaena leucocephala, a legume shrub; Solanum rugosum, a non-legume shrub) were used in a field experiment and communities of all combinations of one, two, three or four species were established. Plant diversity neither significantly affected density and diversity of soil macrofauna nor total plant biomass, however, the biomass of specific plants was negatively affected by plant diversity. Earthworm and ant densities were significantly higher in the presence of A. pintoi although this plant influenced neither the density of the other group nor fauna diversity. Earthworm and diplopod densities increased significantly with shoot biomass of A. pintoi. Fauna diversity increased significantly with shoot biomass (specific and total). Root biomass did not affect fauna density and diversity. Our results suggest that fauna density is affected by litter quality and that it is more affected by resource quantity than quality. Our results also confirm the importance of nitrogen fixers to ecosystem function.     

土壤质地对柱花草生长发育、生物量及土壤肥力变化的影响

采用大田试验的方法,在云南省元谋县小雷宰流域内壤土、砂壤土和重壤土3种质地土壤上,以热研5号柱花草为材料,研究土壤质地对柱花草生长发育、生物量及土壤有机质、有机碳、全氮和全磷的影响。试验结果表明:3种土壤质地上种植柱花草,柱花草地上部和地下部生长量和生物量表现幼苗期增加缓慢,而分枝期后增加快的趋势。壤土耕性好,兼有砂土和重壤土的优点,有利柱花草地上部分的生长发育,柱花草地上部生长量、生物量及改善土壤肥力方面显著高于重壤土。砂壤土有利于柱花草根系向深层土壤生长,柱花草地下部生长量、生物量及根瘤显著高于种植在重壤土。在3种土壤质地种植柱花草后,土壤有机质、有机碳、全氮和全磷均有上升趋势。综合而言,通气性和保肥保水能力居中的壤土更适合柱花草的生长发育及干物质的积累。     

Effects of plant species on microbial biomass phosphorus and phosphatase activity in a range of grassland soils

Soil P transformations are primarily mediated by plant root and soil microbial activity. A short-term (40 weeks) glasshouse experiment with 15 grassland soils collected from around New Zealand was conducted to examine the impacts of ryegrass (Lolium perenne) and radiata pine (Pinus radiata) on soil microbial properties and microbiological processes involved in P dynamics. Results showed that the effect of plant species on soil microbial parameters varied greatly with soil type. Concentrations of microbial biomass C and soil respiration were significantly greater in six out of 15 soils under radiata pine compared with ryegrass, while there were no significant effects of plant species on these parameters in the remaining soils. However, microbial biomass P (MBP) was significantly lower in six soils under radiata pine, while there were no significant effects of plant species on MBP in the remaining soils. The latter indicated that P was released from the microbial biomass in response to greater P demand by radiata pine. Levels of water soluble organic C were significantly greater in most soils under radiata pine, compared with ryegrass, which suggested that greater root exudation might have occurred under radiata pine. Activities of acid and alkaline phosphatase and phosphodiesterase were generally lower in most soils under radiata pine, compared with ryegrass. The findings of this study indicate that root exudation plays an important role in increased soil microbial activities, solubility of organic P and mineralization of organic P in soils under radiata pine.     

Effect of plant growth-promoting bacteria and soil compaction on barley seedling growth, nutrient uptake, soil properties and rhizosphere microflora

Inoculants are of great importance in sustainable and/or organic agriculture. In the present study, plant growth of barley (Hordeum vulgare) has been studied in sterile soil inoculated with four plant growth-promoting bacteria and mineral fertilizers at three different soil bulk densities and in three harvests of plants. Three bacterial species were isolated from the rhizosphere of barley and wheat. These bacteria fixed N₂, dissolved P and significantly increased growth of barley seedlings. Available phosphate in soil was significantly increased by seed inoculation of Bacillus M-13 and Bacillus RC01. Total culturable bacteria, fungi and P-solubilizing bacteria count increased with time. Data suggest that seed inoculation of barley with Bacillus RC01, Bacillus RC02, Bacillus RC03 and Bacillus M-13 increased root weight by 16.7, 12.5, 8.9 and 12.5% as compared to the control (without bacteria inoculation and mineral fertilizers) and shoot weight by 34.7, 34.7, 28.6 and 32.7%, respectively. Bacterial inoculation gave increases of 20.3–25.7% over the control as compared with 18.9 and 35.1% total biomass weight increases by P and NP application. The concentration of N and P in soil was decreased by increasing soil compaction. In contrast to macronutrients, the concentration of Fe, Cu and Mn was lower in plants grown in the loosest soil. Soil compaction induced a limitation in root and shoot growth that was reflected by a decrease in the microbial population and activity. Our results show that bacterial population was stimulated by the decrease in soil bulk density. The results suggest that the N₂-fixing and P-solubilizing bacterial strains tested have a potential on plant growth activity of barley.     

深松深度对砂姜黑土耕层特性、作物产量和水分利用效率的影响

研究深松深度对砂姜黑土耕层特性、作物产量和水分利用效率的影响,可为构建砂姜黑土合理耕层的耕作深度指标提供依据。本研究基于多年定位大田试验,采用大区对比设计,设置4个深松深度(30 cm、40 cm、50 cm、60 cm)处理,以旋耕(RT,平均耕作深度为15 cm)作为对照,研究不同深松深度对土壤紧实度、土壤三相比(R)值、作物根系形态、作物产量和水分利用效率的影响。研究结果表明,深松深度增加能显著降低土壤紧实度,使土壤的三相比(R)更加合理,进而促进作物根系生长。不同深松深度中,深松60 cm处理的土壤紧实度和三相比(R)值与对照相比降幅最大,深松40 cm处理的冬小麦根系生物量最大,深松50 cm处理的夏玉米根系生物量最大。深松不仅增加作物产量,还提高作物水分利用效率。深松30 cm处理的周年作物产量最高,比对照增产12.2%,但与深松40 cm处理差异不显著。深松50 cm处理的周年水分利用效率最高,但与深松30 cm和深松40 cm处理差异不显著。深松30 cm、40 cm和50 cm的周年水分利用效率比对照分别增加9.1%、8.8%和12.7%。因此,砂姜黑土适宜的深松深度为30~40 cm。     

秸秆还田配施氮肥对冬春季稻虾田水质、土壤养分及酶活性的影响

为探究稻虾种养模式冬春季节合理的秸秆还田方式,本研究以秸秆还田配施氮肥调节C/N为切入点,在2017年12月—2018年5月通过田间试验,设秸秆不还田不施氮肥(对照, CK)、秸秆还田C/N为35(S)、秸秆还田配施氮肥C/N为25(SN1)、秸秆还田配施氮肥C/N为15(SN2)以及单施氮肥处理(N1)。探讨秸秆还田不同C/N对冬春季稻虾田养殖水体、土壤养分及酶活性的影响。结果表明:1)CK处理后期的水体总磷含量最低,各处理水体总氮含量在还田前期变化幅度不大;不同处理水体铵态氮含量低于克氏原螯虾安全耐受限度。2)秸秆还田后,SN2处理显著增加了土壤有机质含量,同时土壤硝态氮含量较还田前增加240%;秸秆还田降低了土壤容重,SN2处理组容重最低。3)N1和SN2处理提高了土壤多酚氧化酶活性,其中SN2处理组酶活性最高。在3种秸秆还田处理中, SN2处理土壤脲酶活性高于其他处理, N1处理前期表现出较高酶活性,后期开始降低。综上,秸秆还田配施氮肥调节C/N为15在稻虾田土壤养分含量、酶活性等方面优于其他处理。     

连作年限对香蕉园土壤线虫群落结构及多样性的影响

为研究连作对蕉园土壤生态系统的影响,以海南香蕉种植区为例,采集不同连作年限(l a、3 a、5 a、7a、10 a和15 a)蕉园土壤,采用线虫形态学鉴定方法,分析了不同连作年限蕉园土壤线虫群落结构及多样性的变化规律。结果表明:整个生育期不同连作年限地块共发现土壤线虫属45个。苗期随连作年限增加线虫总数、食细菌线虫数量和食真菌线虫数量逐渐降低(15 a除外);营养生长期随连作年限增加线虫总数、食细菌线虫数量和食真菌线虫数量先增加后降低;抽蕾期随连作年限增加线虫总数和食细菌线虫数量先增加后降低,食真菌线虫数量逐渐降低。整个生长季,随着连作年限增加植物寄生线虫数量先增加后降低。苗期、营养生长期和成熟期,随着连作年限增加捕食/杂食线虫数量逐渐降低。苗期和抽蕾期的线虫总数显著高于营养生长期和成熟期。苗期的食真菌线虫数量和营养生长期的植物寄生线虫数量显著低于其他各生长时期。苗期和营养生长期的捕食/杂食线虫数量显著低于抽蕾期和成熟期。苗期随连作年限增加,优势度指数(λ)先增加后降低,香农多样性指数(H)和植物寄生线虫成熟度指数(PPI)逐渐增加,瓦斯乐斯卡指数(WI)和通路指数(NCR)逐渐降低;营养生长期随连作年限增加,λ先增加后降低,NCR和PPI逐渐增加,H、自由生活线虫成熟度指数(MI)和WI逐渐降低;抽蕾期随连作年限增加,λ先增加后降低,NCR和PPI逐渐增加,H和WI逐渐降低;成熟期随连作年限增加,H和MI逐渐降低,PPI逐渐增加。从整个生育期来看,随生长时间推移,H逐渐增加,λ逐渐降低,苗期和营养生长期的MI低于抽蕾期和成熟期,苗期和成熟期的WI低于营养生长期和抽蕾期。本研究显示,土壤线虫群落结构可有效反映连作蕉园土壤的健康状况,土壤线虫可作为土壤中重要的指示生物。     

Heterogeneity of soil nutrients and subsurface biota in a dryland ecosystem

Dryland ecosystems have long been considered to have a highly heterogeneous distribution of nutrients and soil biota, with greater concentrations of both in soils under plants relative to interspace soils. We examined the distribution of soil resources in two plant communities (dominated by either the shrub Coleogyne ramosissima or the grass Stipa hymenoides) at two locations. Interspace soils were covered either by early successional biological soil crusts (BSCs) or by later successional BSCs (dominated by nitrogen (N)-fixing cyanobacteria and lichens). For each of the 8 plant type×crust type×locations, we sampled the stem, dripline, and 3 interspace distances around each of 3 plants. Soil analyses revealed that only available potassium (K_av) and ammonium concentrations were consistently greater under plants (7 of 8 sites and 6 of 8 sites, respectively). Nitrate and iron (Fe) were greater under plants at 4 sites, while all other nutrients were greater under plants at less than 50% of the sites. In contrast, calcium, copper, clay, phosphorus (P), and zinc were often greater in the interspace than under the plants. Soil microbial biomass was always greater under the plant compared to the interspace. The community composition of N-fixing bacteria was highly variable, with no distinguishable patterns among microsites. Bacterivorous nematodes and rotifers were consistently more abundant under plants (8 and 7 sites, respectively), and fungivorous and omnivorous nematodes were greater under plants at 5 of the 8 sites. Abundance of other soil biota was greater under plants at less than 50% of the sites, but highly correlated with the availability of N, P, K_av, and Fe. Unlike other ecosystems, the soil biota was only infrequently correlated with organic matter. Lack of plant-driven heterogeneity in soils of this ecosystem is likely due to (1) interspace soils covered with BSCs, (2) little incorporation of above-ground plant litter into soils, and/or (3) root deployment patterns.