Demographic characteristics of southern flounder,Paralichthys lethostigma,harvested by an estuarine gillnet fishery

Abstract The North Carolina (NC) southern flounder, Paralichthys lethostigma (Jordan and Gilbert), stock has experienced heavy exploitation during the past two decades. Recently, several management changes were initiated to lower harvest rates and restore stock biomass. Here, the age, growth and maturity of southern flounder harvested by a southeast NC estuarine gillnet fishery are characterised and compared with observations from previous studies and with statewide data on the stock to evaluate any regulatory effects and assess the potential for selective removal by the fishery. Despite regulatory changes, the estuarine gillnet fishery still harvested mainly age‐0 and age‐1 individuals that were mostly immature, meaning that the current fishing practices likely only allow a small portion of the harvestable stock the opportunity to reproduce. Relative to length‐at‐age patterns observed within the stock from statewide collections, fish captured by the gillnet fishery were above average length at each age; the legal size and the gear appeared to cause selective harvest of the fastest growers within each cohort. If the demographic characteristics of the catch observed in this study are broadly representative of gillnet fisheries in other estuarine nursery habitats throughout NC, the harvesting tactics in this sector of the fishery have the potential to cause population‐level effects and negatively affect long‐term fishery yield.     

Dormancy,a critical trait for weed success in crop production systems

Agricultural practices exert selective forces on weed populations. As these practices change over time, weed adaptive traits also evolve, allowing weeds to persist in the new environment. However, only weeds having individuals showing the trait with adaptive significance will be able to cope with these changes, thus allowing a sub‐population to be selected for persistence. In addition, changes in agricultural practices can select new weed species showing functional traits with characteristics adaptive to the modified system. Seed dormancy has long been recognized as a trait with enormous adaptive value to adjust weed biology to cropping systems. In this paper, we illustrate with examples of success and failure, the value of seed dormancy as a functional trait to cope with long‐term changes in crop production systems. We show that successful outcomes are mostly related to the existence of sufficient variability for the functioning of physiological mechanisms that control dormancy characteristics as influenced by the agricultural environment. Presented examples illustrate how knowledge about the relationship that exists between agricultural practices and their selective pressure on seed dormancy can be instrumental in predicting changes in weed biotype dormancy characteristics or foreseeing the appearance of new weed species in future agricultural scenarios. © 2019 Society of Chemical Industry     

Integrated agronomic practices management improved grain formation and regulated endogenous hormone balance in summer maize(Zea mays L.)

Compared with single agronomic practices management during grain formation, knowledge about integrated agronomic practices management on grain-filling characteristics and physiological function of endogenous hormones was limited. In order to clarify this issue, two field experiments, integrated agronomic practices management(IAPM), T1(local conventional cultivation practices), T2(an optimized combination of cropping systems and fertilizer treatment), T3(treatment based on high-yield studies), and T4(further optimized combination of cropping systems and fertilizer treatment), and nitrogen rate testing(NAT)(four nitrogen rates, 0, 129.0, 184.5, and 300.0 kg N ha–1) were performed with summer maize hybrid Zhengdan 958(ZD958). Results showed that with increased nitrogen rate, the endogenous hormone balance was promoted and the grain-filling characteristics were improved sufficiently to resulting in a significant increase in grain yield. However, the grain-filling characteristics deteriorated and yield was reduced with excessive nitrogen fertilization. However, IAPM could promote hormone balance and improve grain filling characteristic. The indole-3-acetic acid(IAA), zeatin riboside(ZR), and gibberellin(GA3) contents under T2 and T4 treatments were higher and the abscisic acid(ABA) content was lower, and the ZR and GA3 contents under T3 were higher than those under T1. Those resulted in the maximum grain-filling rate(Wmax) and the active grain-filling period(P) under T2, T3 and T4 were significantly increased than those under T1, and hence promoted kernel weight and grain yield. So IAPM promoted hormone balance by improving tillage model, optimizing fertilizer rate and fertilization period, appropriately increasing planting density and delaying harvest, which promoted grain filling rate and lengthened active grain-filling period, finally increased grain yield.     

综合农艺管理对夏玉米叶片生长发育及内源激素含量的影响

叶片可直接反映玉米植株的营养状况,是光合作用的主要场所,与干物质积累和产量形成密切相关。本研究以郑单958 (ZD958)为试验材料,以T1代表农民习惯处理; T2代表在T1的基础上,增加种植密度,推迟收获,降低施肥量,并优化施肥时期; T3代表在T2的基础上进一步增加种植密度和施肥量; T4代表在T3的基础上,降低种植密度和施肥量;N代表施氮量处理,设N0、N1、N2和N3分别为0、129.0、184.5和300.0kgNhm~(–2),研究综合农艺管理对夏玉米叶片生长及内源激素的调控作用。综合农艺管理措施包括优化耕作方式、种植密度、施肥量、施肥时期和收获时间等。结果表明,施氮量不足导致IAA、ZR和GA_3含量降低, ABA含量升高,叶片SPAD值、叶面积指数(LAI)及比叶重均显著降低;随施氮量的增加,叶片IAA、ZR和GA_3含量增加,ABA含量降低,LAI、SPAD和干物质积累量均显著增加。综合农艺管理处理可调节叶片内源激素含量,其中T4处理IAA、ZR和GA_3含量较T1处理分别高23.1%、9.8%和14.7%;ABA含量降低12.4%;叶片LAI适宜, SPAD值增加4.2%,最终单株干物质积累量增加12.6%。综合农艺管理在降低施氮量,配合最佳的农艺管理方式下,可调节内源激素含量,增加叶片SPAD和比叶重,有利于单株干物质积累,这可能是促进夏玉米产量增加的重要原因之一。     

Contaminant seeds in imported crop seed lots: a non‐negligible human‐mediated pathway for introduction of plant species to islands

Contaminant seeds in crop seed lots constitute a pathway for plant species introduction into new areas, and these non‐native weeds may be an environmental problem if they become invasive. Seed certification is a process that regulates and guarantees the quality of seed lots, including their purity. In this study, we assessed weed contamination in certified and non‐certified seed lots (n = 116) from 12 crop species commonly cultivated in the Balearic Islands. Contaminant seeds were separated using sieves, and then manually under a stereomicroscope, before they were germinated to confirm taxonomic identity. Weight, number and diversity of the contaminant seeds per kilogram of seed lot, number released per hectare according to sowing rate, and taxonomic identity and biogeographical origin of contaminant species were recorded. Although certification reduced the number of contaminant seeds in the seed lots, it did not entirely eliminate contaminants, because we found up to 2000 contaminant seeds kg^?1 of certified ryegrass and sulla. Overall, contaminant seeds represented 118 taxa; of which, 82 were identified to species level, 70% of species were native, 19% were cultivated, and 11% were non‐native. Two of the identified taxa were first records for the Balearic Islands. In conclusion, contaminant seeds in imported crop seed lots represent a non‐negligible pathway for plant species introduction.     

不同节水灌溉方式及栽培模式下粳稻生长特性研究

[目的]缓解农业水资源供需矛盾,保障粳稻种植可持续发展,开展不同灌溉栽培模式下粳稻生长特性、耗水规律研究,为粳稻节水栽培技术提供支撑.[方法]利用称重式蒸渗仪,设置了湿润灌溉(SR)、控制灌溉(KZ)、浅湿灌溉(QS)3种节水灌溉方式,水直播(SZB)、旱直播(HZB)2种栽培模式,分析了不同节水灌溉方式和栽培模式下粳...     

Modelling pasture management practices for soil organic carbon gain in livestock systems

Our ability to develop strategies to mitigate climate change includes an understanding of, and our capacity to predict soil organic carbon (SOC) dynamics in livestock systems. Here we assess the capability of the Sustainable Grazing System (SGS) Pasture Model for predicting pasture growth (elongated wheatgrass, Thinopyrum ponticum) and SOC accumulation in different environments and under a range of pasture management practices in hydrohalomorphic soils located in South-eastern Buenos Aires Province, Argentina. After Model calibration, aerial net primary productivity (ANPP) and TSOC content under two grazing intensities (7.5 and 11 cm post-grazing target heights) and two N fertilization levels (0 and 100 kg N ha⁻¹ yr⁻¹) were simulated over a 10 year-period. The SGS Pasture Model predicted 87% of the observed ANPP, with observed and predicted ANPPs averaging 1.46 and 1.42 Mg ha⁻¹ yr⁻¹, respectively. There were differences in simulated ANPP between fertilized and unfertilized treatments both at high and low grazing intensities for the last year of the period. Total SOC contents from the modelling showed differences between high (83.7 to 84.2 Mg ha⁻¹) and low (86.8 to 87.5 Mg ha⁻¹) grazing intensities, with treatments receiving N also showing higher carbon stocks. The positive effect of reduced grazing intensity on soil carbon was explained by an increased input of aerial and subterranean dry matter into the soil. Sensitivity analysis showed that SGS is a robust model, capable of performing effectively under a variety of conditions. Hence, it can be used for exploring management practices to mitigate the impact of livestock systems on emissions and SOC stocks.     

Impact of living mulch on soil C:N:P stoichiometry in orchards across China: A meta-analysis examining climatic, edaphic, and biotic dependency

The use of living mulch in orchards is a widely accepted management strategy for improving soil quality and enhancing tree productivity.Although the effects of living mulch on soil organic carbon(C)and nutrients have been previously investigated,changes in the stoichiometric ratios of C,soil total nitrogen(N),and soil total phosphorous(P)under different climatic,edaphic,and biotic conditions are currently unknown.These factors are important indicators of elemental balance associated with ecological interactions.In order to examine the effects of living mulch in orchards on soil C:N:P stoichiometry under different conditions,a meta-analysis was undertaken.The results showed that in general,living mulch significantly(P<0.05)increased C:P and N:P ratio,while the impact on C:N ratio was not significant,a result that was related to the coupled increase of C and N.Phosphorous limitation occurred shortly after the addition of living mulch;after four years this effect receded.In contrast,an increase in C occurred simultaneously with N increase at all stages.Specifically,the treatment effect was context-dependent.The living mulch did not change soil stoichiometry in orchards with old trees(>10 years),an occurrence which may be related to changes in the amount of fungi.Grass life history also had a significant influence on the treatment effect on soil stoichiometry,while N-fixing characteristics did not.The treatment effect was significant in areas with moderate mean annual temperature and mean annual precipitation,which might be related to the litter ratio of grass and trees.Effects on stoichiometric ratios were significant in the top soil layer(0–20 cm),in contrast to the deep soil layers.Therefore,grass species and management practices,such as fertilization,should be selected according to the specific soil and climatic conditions of the management area.     

中国菜用大豆研究现状、生产中的问题及展望

菜用大豆(毛豆),对调节人们膳食结构和改善营养状况具有重要作用,是当今公认的保健食品,它的开发利用是一个新兴的产业,已越来越被人们所重视.本文概述了中国蔬菜大豆的品种选育、栽培技术研究现状及生产中存在的问题,并提出了蔬菜大豆今后的发展策略.