Antagonistic effects of species on C respiration and net N mineralization in soils from mixed coniferous plantations

Mixtures of litter from different plant species often show non-additive effects on decomposition and net N release (i.e., observed effects in mixtures differ from predictions based on litter of the component species), with positive non-additive (i.e., synergistic effects) being most common. Although large amounts of C and N reside in soil organic matter that contribute significantly to the overall C and N cycle, only a few studies have compared species monoculture vs. mixture effects on soil C and N dynamics. We studied the interactive effects of black spruce (Picea mariana), tamarack (Larix laricina), and white pine (Pinus strobus) on soil C respiration and net N mineralization in a plantation in northern Minnesota, USA. The trees were planted in monoculture and in all three possible two-species combinations (mixtures). After 10 years, we measured aboveground plant biomass and soil C respiration and net N mineralization rates in long-term (266 days) and short-term (13 days) laboratory incubations, respectively. Soil C respiration and net N mineralization were significantly lower in mixtures with tamarack than would be predicted from the monocultures of the two component species. Possibly, mixing of lignin rich litter from black spruce or white pine with N rich litter from tamarack suppressed the formation of lignolytic enzymes or formed complexes highly resistant to microbial degradation. However, these antagonistic effects on soil C respiration and net N mineralization in mixtures with tamarack did not result in reduced aboveground biomass in these plots after 10 years of growth. It remains to be seen if these antagonistic effects will affect long-term forest productivity and dynamics in boreal forests.     

烤烟纯作和套种对烟田土壤温度的影响

研究了纯作和套种对烟田土壤温度变化的影响,结果表明:8:00-19:00,各层土壤温度都随时间推移先升高后下降。5cm处,纯作土壤温度始终高于套种,10cm,15cm和20cm土温,分别在12:00,13:00和14:00之前表现为纯作高于套种,之后,套种高于纯作,两处理土壤温度继续升高,分别在16:00,17:00和18:00升至最高,然后开始下降,套种土壤温度升高和下降幅度均大于纯作,并且套种土壤温度日较差显著大于纯作。总体来说,8:00-19:00,5～20cm土层,套种土壤温度平均值和土壤积温均低于纯作。     

不同单养和混养海水实验围隔初级生产力的研究

１９９５年和１９９６年夏秋季进行的围隔实验表明投饵养殖时浮游植物毛初级生产力较低,水呼吸相对较高,多数围隔中毛初级生产力／水呼吸〈１,其中混养中国对虾和台湾红罗非鱼的围隔中毛初级生产力较高,而混养中国对虾,台湾红罗非鱼和菲律宾蛤仔的围隔中毛初级生产力最低;在投饵基础上酌情施肥后围隔毛初级生产力同于投饵养殖时,毛初级生产力／水呼吸〉１,但单养中国对虾,对虾与罗非鱼混养和对虾与海湾扇贝或缢蛏混养的围隔     

Effect of successive cauliflower plantings and Rhizoctonia solani AG 2-1 inoculations on disease suppressiveness of a suppressive and a conducive soil

Disease suppressiveness against Rhizoctonia solani AG 2-1 in cauliflower was studied in two marine clay soils with a sandy loam texture. The soils had a different cropping history. One soil had a long-term (40 years) cauliflower history and was suppressive, the other soil was conducive and came from a pear orchard not having a cauliflower crop for at least 40 years. These two soils were subjected to five successive cropping cycles with cauliflower or remaining fallow in a greenhouse experiment. Soils were inoculated with R. solani AG 2-1 only once or before every crop. Disease decline occurred in all treatments cropped with cauliflower, either because of a decreased pathogen population or increased suppressiveness of the soil. Disease suppressiveness tests indicated that the conducive soil became suppressive after five subsequent cauliflower crops inoculated each cycle with R. solani AG 2-1. Suppressiveness of all treatments was measured in a seed germination test (pre-emergence damping-off) as well as by measuring the spread of R. solani symptoms in young plants (post-emergence damping-off). Results showed that suppressiveness was significantly stimulated by the successive R. solani inoculations; presence of the cauliflower crop had less effect. Suppressiveness was of biological origin, since it disappeared after sterilization of the soil. Moreover, suppressiveness could be translocated by adding 10% suppressive soil into sterilized soil. The suppressive soil contained higher numbers of culturable filamentous actinomycetes than the conducive soil, but treatments enhancing suppressiveness did not show an increased actinomycetes population. The suppressiveness of the soil samples did also not correlate with the number of pseudomonads. Moreover, no correlation was found with the presence of different mycoparasitic fungi, i.e. Volutella spp., Gliocladium roseum, Verticillium biguttatum and Trichoderma spp. The suppressive soil contained a high percentage of bacteria with a strong in vitro inhibition of R. solani. These bacteria were identified as Lysobacter (56%), Streptomyces (23%) and Pseudomonas (21%) spp. A potential role of Lysobacter in soil suppressiveness was confirmed by quantitative PCR detection (TaqMan), since a larger Lysobacter population was present in suppressive cauliflower soil than in conducive pear orchard soil. Our experiments showed that successive cauliflower plantings can cause a decline of the damage caused by R. solani AG 2-1, and that natural disease suppressiveness was most pronounced after subsequent inoculations with the pathogen. The mode of action of the decline is not yet understood, but antagonistic Lysobacter spp. are potential key organisms.     

The Use of Rice Varietal Diversity for Rice Blast Control

Field experiments of mixed- (intercropping) and pure-planting (monoculture) of four rice vari-eties, representing improved hybrid varieties (Shanyou63 and Shanyou22) and high-quality traditional varie-ties (Huangkenuo and Zigu) from Yunnan Province, were conducted based on their differences in genetic back-ground and agro-economical characteristics. The results demonstrated that the mixed-planting of the hybridrice and high-quality traditional rice varieties had a significantly greater effect on controlling rice blast diseasethan the monocuiture of these varieties, particularly the traditional ones. It is evident for the highly suscepti-ble traditional varieties in mixed-planting to achieve disease control, with significant decreases in blast inci-dences and severity indexes. The blast control efficiency reached up to 83 - 98 % under such planting model.This suggests that an appropriate mixed-planting of rice varieties with diverse genetic background and agro-e-conomical characteristics is an effective approach for rice blast control. In addition, resistance of the tradi-tional rice varieties to lodging was considerably increased in the plots with mixed-planting, compared with theplots with monoculture. The average rate of grain-yield increase ranged from 6.5 to 9.7 % in the plots withmixed-planting.     

紫色土小流域种植模式对土壤氮素流失的影响初探

种植模式变化是农业非点源污染流域治理最佳管理措施的主要内容之一,以紫色土区徐家湾和桑树土典型农业小流域为例,初步探讨了套种和单作模式下自然降雨侵蚀过程次降雨土壤氮素的流失特征。结果表明,土壤硝态氮流失表现为套种与单作模式下的差异不显著,而铵态氮的流失受流域种植模式变化的影响强烈,套种模式下的平均流失浓度(0.453mg/L)明显大于单种模式下的(0.169mg/L)。套种模式应与流域土壤-作物系统的科学管理有机结合才能在提高土地生产力的同时有效地减控流域土壤氮素的非点源流失。     

<Emphasis Type="Italic">Eucalyptus</Emphasis> agroforestry system for small farms: 2-year experiment with rice and beans in Minas Gerais,Brazil

In Minas Gerais, Brazil, Eucalyptus plantation agroforestry techniques for small farms appear to be an adequate alternative to small-scale plantations, and by integrating timber and food production, they can meet local demands for aliment and wood. Intercropping of Eucalyptus camaldulensis with rice and beans was studied to compare yields of intercropping and monocultures over 2 years. In the first year, no differences were found in the productivity between the intercropped and monoculture systems of E. camaldulensis, rice and beans in both seasons. In the second year, E. camaldulensis in monoculture showed the lowest productivity. If compared with E. camaldulensis intercropped with agricultural crops, during the rainy season, beans intercropped with E. camaldulensis showed similar productivity when compared to monoculture. In the dry season, the productivity of beans in monoculture was higher than intercropping. In the second year, rice productivity was very low for both systems due to the lack of precipitation during the fructification phase. The equivalence area index (EAI) confirmed the advantages of the intercropping system over the monoculture system for E. camaldulensis and beans and rice, at least in the first 2 years.     

Rhizosphere isoflavones (daidzein and genistein) levels and their relation to the microbial community structure of mono-cropped soybean soil in field and controlled conditions

Despite an increase in the understanding of the soybean isoflavones involved in root-colonizing symbioses, relatively little is known about their levels in the rhizosphere and their interactions with the soil microbial community. Based on a 13-year experiment of continuous soybean monocultures, in the present study we quantified isoflavones in the soybean rhizosphere and analyzed the soil microbial community structure by examining its phospholipid fatty acid (PLFA) profile. Two isoflavones, daidzein (7, 4′-dihydroxyisoflavone) and genistein (5,7,4′- trihydroxyisoflavone), were detected in the rhizosphere soil of soybean plants, with the concentrations in the field varying with duration of mono-cropping. Genistein concentrations ranged from 0.4 to 1.2 μg g⁻¹ dry soil over different years, while daidzein concentrations rarely exceeded 0.6 μg g⁻¹ dry soil. PLFA profiling showed that the signature lipid biomarkers of bacteria and fungi varied throughout the years of the study, particularly in mono-cropping year 2, and mono-cropping years 6-8. Principal component analysis clearly identified differences in the composition of PLFA during different years under mono-cropping. There was a positive correlation between the daidzein concentrations and soil fungi, whereas the genistein concentration showed a correlation with the total PLFA, fungi, bacteria, Gram (+) bacteria and aerobic bacteria in the soil microbial community. Both isoflavones were easily degraded in soil, resulting in short half-lives. Concentrations as small as 1 μg g⁻¹ dry soil were sufficient to elicit changes in microbial community structure. A discriminant analysis of PLFA patterns showed that changes in microbial community structures were induced by both the addition of daidzein or genistein and incubation time. We conclude that daidzein and genistein released into the soybean rhizosphere may act as allelochemicals in the interactions between root and soil microbial community in a long-term mono-cropped soybean field.     

带状复合种植对玉米和大豆光合特性及籽粒产量的影响

为比较带状复合种植和清种种植模式下玉米和大豆光合特性以及产量的差异,2015年和2016年进行大田试验,研究了玉米和大豆2∶4带状复合种植模式及清种种植对玉米和大豆光合特性及籽粒产量的影响。结果表明:(1)与清种玉米相比,对于高秆品种(垦丰41),带状复合种植提高了玉米净光合速率、蒸腾速率、气孔导度、胞间CO2浓度和水分利用效率;对于矮秆品种(垦丰40),2015年带状复合种植净光合速率等指标略小于清种玉米,但水分利用效率和胞间CO2浓度均大于清种玉米,有利于玉米籽粒内含物质的积累,而2016年净光合速率和蒸腾速率等指标均大于清种玉米;(2)对于高秆品种(垦丰41),除叶绿素含量略小外,清种大豆的各光合生理指标均大于带状复合种植;对于矮秆品种(垦丰40),带状复合种植净光合速率、气孔导度和叶绿素均大于清种大豆,且净光合速率均达到极显著差异水平;(3)带状复合种植增加了玉米穗粒数、穗重、籽粒重,虽产量较清种略有降低,但总经济效益高于清种;(4)带状复合种植大豆较清种大豆单株荚数、单株粒数、单株粒重和百粒重均有所降低,且产量明显下降,但总体经济效益高于清种经济效益。综合分析认为:玉米大豆带状复合种植增加了玉米光合生理特性,且对于增加玉米和大豆总产量和总体经济效益具有重要意义。     

山东生态条件下纯作春棉的适宜密度研究

以常规抗虫棉鲁棉研28号为材料,在山东广饶、夏津和冠县三地大田条件下纯作种植,研究了不同密度（3.00～9.00株/m2）下的棉花产量及产量构成。结果表明,种植密度对纯作抗虫棉产量、产量构成以及熟相均有显著的影响,对经济产量的调控效应三个试验点大致相同,都随密度的增加呈现先升后降的趋势。即低密度（3.00株/m2）和高密度（9.00株/m2）处理的产量低,中高密度（4.50～7.50株/m2）的产量较高。三个点平均,6.00株/m2密度处理的籽棉和皮棉产量与4.50株/m2处理相当,但比3.00株/m2分别增产10.1%和12.0%,比9.00株/m2处理分别增产22.3%和22.8%。提高密度能提高单位面积的生物产量和单位面积铃数,但可显著降低棉柴比、铃重和早熟性。密度偏高和偏低都不能获得较高的经济产量和协调的产量结构,山东春棉纯作条件下适宜种植密度为4.50～6.00株/m2。