Plant diversity and arthropod communities: Implications for temperate agroforestry

Polyculture in crop agroecosystems has been examined in numerous studies with the aim of reducing pest populations by increasing diversity among insect populations over those found in traditional monoculture. Resource concentration and enemies hypotheses predict decreased pest populations in more diverse plant communities. Although results have been mixed, insect diversity has been generally increased in polyculture over traditional monoculture. Maintaining natural insect diversity in managed forests to limit possible pest outbreaks has been the goal in forestry systems. Increased arthropod diversity with increased tree diversity has been observed, though fewer studies have been conducted in forestry compared to agriculture. Agroforestry holds promise for increasing insect diversity and reducing pest problems because the combination of trees and crops provides greater niche diversity and complexity in both time and space than does polyculture of annual crops. This revised version was published online in August 2006 with corrections to the Cover Date.     

Soil Enzymatic Activity in Eucalyptus Grandis Plantations of Different Ages

Eucalyptus plantations have become increasingly common in Latin America. However, because Eucalyptus is an exotic species, its presence has raised concerns about changes in the environment, especially to soil properties. The objective of this study was to investigate possible changes in selected soil enzyme activity after several years of Eucalyptus cultivation. Soil samples were collected from four locations: a native forest (Atlantic Forest) used as a reference for the original soil conditions and three E. grandis plantations aged 2, 3 and 5 years, established in 2008, 2007 and 2005, respectively. The native vegetation had been removed and the soil graded and ploughed to establish these plantations. We evaluated soil enzymatic activities (β‐glucosidase, acid phosphatase, dehydrogenase, urease and arylsulfatase) at each location. The activity of β‐glucosidase, phosphatase, dehydrogenase and urease was improved after 5 years, whereas arylsulphatase was impacted negatively. The multivariate analysis showed that the majority of enzyme activities reached the values observed in native forest after the third year of reforestation. The activity of β‐glucosidase was crucial in differentiating the area with 2 years of reforestation from the native forest. The removal of native vegetation in order to establish commercial plantations raises concerns about the real impacts of this practice on the soil. In the present study, plantations of Eucalyptus improved most of the selected enzyme activities after the third year of reforestation. Copyright © 2015 John Wiley & Sons, Ltd.     

Changes in microbial biomass and protease activities of soil associated with long-term sugar cane monoculture

 As part of a broader study, the aim of which is to identify soil factors that might be associated with yield decline of sugar cane, microbial biomass and protease activities were examined in soil samples collected from seven paired old and new land sites in three cane-growing districts of north Queensland. No consistent changes in soil protease activities were observed, although some sites exhibited specific effects, as a result of extensive periods of sugar cane monoculture. Soil microbial biomass, however, was significantly lower in those soils where sugar cane had been grown for extended periods. The implications of a lowering of soil microbial biomass on sugar cane yields and sustainability are discussed. Received: 24 June 1997     

春大豆长期连作对土壤线虫群落结构和食物网的影响

以土壤线虫为指示生物,研究了大豆不同耕作系统土壤线虫群落结构、生态指数和食物网指数的变化特征,以期明确大豆长期连作对土壤生物多样性和土壤食物网结构的影响。结果表明:大豆轮作土壤线虫属最丰富,大豆长期连作25年后土壤线虫属水平种类最少。大豆轮作和大豆短期连作3年土壤线虫群落组成Jaccard相似性最高(0.81),大豆轮作和大豆长期连作25年Jaccard相似性最低(0.66)。大豆短期连作3年土壤中植物寄生线虫的数量最高,显著高于大豆轮作和大豆长期连作25年。食真菌线虫在大豆长期连作25年土壤中较丰富,显著高于大豆轮作和大豆短期连作3年。大豆长期连作25年植物寄生线虫成熟度指数(PPI)高于大豆短期连作3年和大豆轮作。土壤线虫的通路指数(CI)在3个处理中均小于50,土壤腐蚀食物网的降解以细菌降解通路为主。大豆短期连作3年处理位于富集指数(EI)和结构指数(SI)食物网特征图的A象限,大豆轮作和长期连作25年位于食物网特征图的B象限。结果表明,大豆长期连作改变了土壤线虫的群落结构,降低了属的多样性,食物网结构向成熟稳定的方向恢复。     

Impact of varied frequency of nitrogen fertilization on the grow‐out performance of Labeo rohita (Hamilton)

A grow‐out monoculture experiment for rohu, Labeo rohita was conducted for 1 year in nine earthen ponds of 0.04 ha each to study the impact of varied frequency of nitrogen fertilization on fish growth. Ponds were stocked at 8000 fingerlings ha^?1 density. While ponds were applied with cattle manure and phosphate fertilizer at conventional dosages followed for grow‐out carp culture, nitrogen fertilization was carried out at 15‐, 10‐ and 7‐day intervals and were designated as treatments T‐1, T‐2 and T‐3 respectively. Although all the water parameters in the treatments were within the suitable range for grow‐out carp farming, annual average concentration of dissolved oxygen (DO), plankton as well as availability of nutrients such as total ammonia‐ and nitrate‐nitrogen in ponds were significantly higher in T‐3 compared with T‐1 and T‐2. Greater fluctuation of critical parameters like DO, plankton concentration and total ammonia nitrogen were observed in T‐1 and T‐3 while the same were more consistent in T‐2, revealing the prevalence of a better growing environment in the latter. Fish in T‐2 also showed better specific growth rate, higher body weight attainment and higher biomass yield compared with the other two treatments, revealing the desirability of nitrogen fertilization at 10‐day intervals in carp culture.     

Understory development in young Cordia alliodora plantations

The biomass and composition of theunderstory plant community associated with Cordiaalliodora planted at 2 m × 2 m spacing arecharacterized for the first (1992) and fifth (1996)years after stand establishment. The study plantationscomprise three replicates each of C. alliodoramonocultures and C. alliodora interplanted withperennial monocots (polycultures), part of anexperiment located at the La Selva Biological Stationin northern Costa Rica. In the first year, there wasno significant difference in the mean abovegroundunderstory biomass between the monocultures of C.alliodora (7975 kg/ha) and the polycultures of treesand monocots (5427 kg/ha). After 5 years, theunderstory biomass in the monocultures increased(16,918 kg/ha), while in the polycultures it decreased(116 kg/ha). In contrast to the first year, therefore, by the fifth year the understory biomass differed significantly between the two types of plantations (p = 0.005, R² = 0.78, LSD = 5200 kg).In the first year, 109 plant species were present inthe understory of the C. alliodora monoculturesand polycultures. The dominant species in both themonocultures and polycultures was the monocot Tripogandra serrulata; Panicum polygonatum wasranked second. After 5 years, 20 species representing15 families were present in the monocultures. Thedominant species was Paspalum conjugatum,followed by Tripogandra serrulata. Only two newspecies were recruited, and both were woody shrubs:Nectandra membranacea and Vernonia patens.     

不同单养和混养海水实验围隔浮游生物的研究

1995年6～10月和1996年6～8月对中国对虾单养及其与台湾红非鲫、菲律宾蛤仔、海湾扇贝或缢蛏的不同混养实验围隔浮游生物的研究结果表明:养殖管理措施和放养种类对围隔浮游生物种类和生物量都会产生一定影响,其中前者往往具主要作用。投饵养殖时围隔浮游植物以20μm以下的种类为主,生物量较低,其中混养台湾红非鲫的围隔叶绿素a(Chl-a)相对较高,混养菲律宾蛤仔的围隔Chl-a较低;在投饵的基础上施肥后甲藻等鞭毛藻类易大量发生成为优势种,浮游植物生物量较单纯投饵时有所升高,但单养和混养对围隔Chl-a的影响不明显。非鲫捕食往往导致大型桡足类在浮游动物生物量中的比例下降,贝类则通过食物竞争同时使桡足类生物量降低和种类小型化,由于非鲫与海产贝类的食物灶存在一定分化,二者混养至少对贝类有利,因此鱼虾贝混养应较鱼虾混养或虾贝混养效果更好。     

不同养殖模式对点篮子鱼的生长和摄食的影响

本试验研究了上海地区低盐度条件下池塘单养和混养对点篮子鱼（Siganus guttatus）幼鱼生长和摄食的影响.平均体重1.14±0.63g、平均体长3.57±0.88 cm的点篮子鱼,经90d的养殖后,单养点篮子鱼成活率82.86％,平均体重增加到55.08 ±14.21 g,平均体长增加到11.39±1.19 cm,最大规格体重达101.42 g;与拟穴青蟹（Scylla paramamosain）混养点篮子鱼成活率85.26％,平均体重增加到56.37 ±4.60 g、平均体长增加到11.60 ±0.42 cm,最大规格达118.71 g,拟穴青蟹平均体重从0.04g增长到209.88 g,最大规格达350.13 g.结果表明,在本试验条件下,混养模式中的点篮子鱼的存活率较单养模式高,生长摄食情况好,增重速度快,且摄食率低而饲料转化效率高.     

基于风险的农田镉污染综合管理实践与思考

如何在重金属镉 (Cd)超标的土壤中生产出质量达标米已成为亟需解决的问题。为探讨稻-鱼种养对大米Cd积累的减控效果,本研究建立了稻 (喜两优超占) -鱼 (合方鲫2号)种养系统,比较了稻-鱼共作系统和水稻单作系统中环境介质、米、鱼等Cd含量,以及米、鱼的生物学性状。结果显示,稻-鱼共作合方鲫2号平均体重为331.7 g,相比鱼种增重1.7倍。不同种养系统大米的营养品质无显著差异。稻田土壤总Cd平均含量为0.472 mg/kg (pH=5.5),略高于污染临界值0.40 mg/kg (5.5≤pH≤6.5),不同种养系统土壤总Cd含量与土壤pH无显著差异。合方鲫2号内脏虽有少量Cd积累[ (0.060±0.032)mg/kg],但肌肉Cd含量很低 (<0.003 mg/kg)。水稻单作大米Cd平均含量为0.311 mg/kg,达到国家粮食安全标准限定值的1.6倍。稻-鱼共作大米Cd平均含量仅0.034 mg/kg,较水稻单作大米Cd含量下降89.1%,水稻单作大米Cd含量与土壤总Cd含量呈极显著正相关 (r=0.802),而稻-鱼共作系统则无该显著相关性。研究表明,合方鲫2号是适合稻-鱼种养的好品种,以此为养殖品种可以建立完善的稻-鱼综合种养模式,该种模式能有效抑制土壤Cd的生物活性,对大米Cd积累有显著的减控效能,且经济效益显著。本研究为稻-鱼等生态种养综合生产模式的推广应用提供了重要数据支撑和参考。     

湖南会同不同林分类型杉木人工林凋落物水文效应

目的 以我国亚热带不同林分类型杉木人工林为研究对象,分析比较其凋落物层生态水文效应的差异,为杉木人工林林下生态管理和生态系统服务评估提供科学依据。 方法 采用野外调查和室内浸提试验相结合的方法,对湖南会同3种不同类型杉木人工林（杉木纯林、杉木-樟树混交林、杉木-桤木混交林）的各分解层凋落物储量、吸持水特性以及有效拦蓄能力进行测定分析。 结果 （1）不同林分类型杉木人工林凋落物现存量在7.94～8.88 t·hm−2,杉木-桤木混交林 > 杉木-樟树混交林 > 杉木纯林,半分解层现存量占总现存量的比例高于未分解层;（2）杉木人工林凋落物在浸水0～4 h内吸水速率增加较快,4～10 h内持水量增加速率减缓,并逐渐趋于饱和;最大持水率和最大持水量表现为半分解层大于未分解层,针阔混交林各分解层凋落物最大持水率和最大持水量高于杉木纯林;（3）3种类型杉木人工林最大拦蓄率变化范围为152.33%～229.55%,最大拦蓄量和有效拦蓄量分别在12.62～17.94 t·hm−2和10.26～14.75 t·hm−2,且均为杉木-樟树混交林和杉木-桤木混交林显著高于杉木纯林（P < 0.05）。 结论 湖南会同不同林分类型杉木人工林的水文效应存在一定差异,杉木-樟树混交林和杉木-桤木混交林的水文功能优于杉木纯林,建议今后该地区杉木人工林经营管理和植被恢复中优先考虑杉木与阔叶树种混交的模式。