三阶时滞泛函微分方程解的渐近性

本文讨论一类三阶时滞泛函微分方程解的渐近性质,给出了若干解的有界性及解趋于零的判定准则.     

浅圆仓膜下氮气气调膜上控温储粮试验

通过改造浅圆仓测温电缆,实现了浅圆仓膜下充氮气调和膜上中央空调控温,提高了卸粮口、大门口、通风口等死角的害虫致死率。将浅圆仓氮气气调杀虫与控温储粮相结合,实现了储粮安全度夏。     

Flowering phenology of a herbaceous species (Poa annua) is regulated by soil Collembola

The role of soil organisms as possible driver of flowering has never been investigated. We hypothesized that Collembola (microarthropods) will change plant allocation to reproductive modes by changing soil nutrient availability. Individual seedlings of Poa annua were planted in microcosms, in the presence or absence of Collembola. Collembola affected biotic (fungal biomass) and abiotic ($\text{N}-{{\text{NO}}_3}^{-}$, P₂O₅) soil properties and some morphological (number of leaves, root biomass) and chemical (C:N, K, Mg, N) traits of P. annua. As a result, flowering of P. annua was promoted by the presence of Collembola. This provides experimental evidence that soil microarthropods can affect the reproduction strategy and phenology of a plant.     

Designing the ideal habitat for entomopathogen use in nursery production

BACKGROUND: Greenhouse and nursery producers use entomopathogens (nematodes and fungi) to control soil pests. Although it is known that the physical and chemical properties of mineral soil significantly impact upon soil pathogens, the influence of soilless media used for plant production on entomopathogen performance is poorly understood. RESULTS: Survival and foraging distance were differently affected by sand:peat, bark and sawdust media for entomopathogenic nematodes, but not for the immobile fungus Metarhizium anisopliae. Redwood sawdust medium consistently had a negative impact upon entomopathogenic nematodes. Dividing media into individual components supported the hypothesis that redwood sawdust reduced foraging and infection abilities of S. riobrave and H. bacteriophora. Physically altering the components by adding sand significantly improved foraging and infection success for S. riobrave in media not optimum for foraging. CONCLUSION: This study is the first to highlight the importance of selecting the appropriate soilless media and pathogen species combinations to increase efficacy of biological control. H. bacteriophora was able to find hosts in a wider diversity of medium components than S. riobrave, although both nematode species performed well in peat moss and recycled plant material. These results suggest that peat moss, recycled plant material and hardwood bark are components amenable to EPN biological control programs. Copyright © 2012 Society of Chemical Industry     

Seasonal variations in species diversity, dry matter and net primary productivity of herb layer of Quercus leucotrichophora-Pinus roxburghii mixed forest in Kumaun Himalaya, India

Plant biomass, species diversity and net primary productivity are presented for herb layer of banj oak (Quercus leucotrichophora A. Camus)-chir pine (Pinus roxburghii Sarg.) mixed forest in Kumaun, central Himalaya, India. The species diversity declined from a maximum (3.56) in September to a minimum (2.11) in December. The monthly live shoots biomass exhibited a single peak growth pattern with highest live shoot biomass of 185 g·m-2 in August. The seasonal pattern showed that the maximum above-ground production (131 g·m-2) occurred during the rainy season and the minimum (1 g·m-2) during winter season. The below-ground production was maximum during winter season (84 g·m-2) and minimum during summer season (34 g·m-2). The annual net shoot production was 171 g·m-2 and total below-ground production was 165 g·m-2. Of the total input 61% was channeled to above-ground parts and 39% to below-ground parts. Transfer of live shoots to dead shoots compartments and that of dead shoots to litter compartments was 61% and 66%, respectively. The total dry matter disappearance was 61% of the total input within annual cycle. The herb layer showed a net accumulation of organic matter, indicating the seral nature of the community.     

Forest management and carbon sequestration in wood products

Wood products are considered to contribute to the mitigation of carbon dioxide emissions. A critical gap in the life cycle of wood products is to transfer the raw timber from the forest to the processing wood industry and, thus, the primary wood products. Therefore, often rough estimates are used for this step to obtain total forestry carbon balances. The objectives of this study were (1) to examine the fate of timber harvested in Thuringian state forests (central Germany), representing a large, intensively managed forested region, and (2) to quantify carbon stocks and the lifetime of primary wood products made from this timber. The analyses were based on the amount and assortments of actually sold timber, and production parameters of the companies that bought and processed this timber. In addition, for coniferous stands of a selected Thuringian forest district, we calculated potential effects of management, as expressed by different thinning regimes on wood products and their lifetimes. Total annual timber sale of soft- and hardwoods from Thuringian state forests (195,000 ha) increased from about 136,893 t C (~0.7 t C ha⁻¹ year⁻¹) in 1996 to 280,194 t C (~1.4 t C ha⁻¹ year⁻¹) in 2005. About 47% of annual total timber harvest went into short-lived wood products with a mean residence time (MRT) < 25 years. Thirty-one per cent of the total harvest went into wood products with an MRT of 25–43 years, and only 22% was used as construction wood and glued wood, products with the longest MRT (50 years). The average MRT of carbon in harvested wood products was 20 years. Thinning from above throughout the rotation of spruce forests would lead to an average MRT in harvested wood products of about 23 years, thinning from below of about 18 years. A comparison of our calculations with estimates that resulted from the products module of the CO2FIX model (Nabuurs et al. 2001) demonstrates the influence of regional differences in forest management and wood processing industry on the lifetime of harvested wood products. To our knowledge, the present study provides for the first time real carbon inputs of a defined forest management unit to the wood product sector by linking data on raw timber production, timber sales and wood processing. With this new approach and using this data, it should be possible to substantially improve the net-carbon balance of the entire forestry sector.     

杂交中稻齐穗期下部叶片对结实率的影响与组合间库源结构的关系

以26个杂交中籼迟熟组合为材料,通过齐穗期剪叶及本田密肥、疏株处理,研究了杂交中稻齐穗期下部叶片对结实率的影响与组合间库源结构的关系.结果表明,杂交中稻齐穗期倒4以下叶片提高结实率的作用程度在杂交组合间存在较大差异,表现为倒4以下叶片提高结实率的作用与组合间着粒数呈极显著正相关关系,当杂交组合群体的着粒数≥185粒/穗时,倒4以下叶片对结实率才有显著作用.原因在于组合间着粒数与单位颖花的绿叶占有量呈极显著负相关关系,着粒数越多的大穗型组合,其"库"" 源"矛盾越大,则越需要充分利用倒4以下叶片的光合物质,才能保证籽粒的正常灌浆结实;反之,着粒数较少的中小穗型组合,其光合源相对较充分,顶部3片叶的光合产物基本能满足籽粒的正常灌浆结实,对下部叶片光合物质量的需求量相对较小.此外,倒4以下叶片提高结实率的作用还与本田移栽密度呈极显著负相关,植株基部光照强度的改善有利于倒4以下叶片提高结实率的作用.     

从地下的角度分析膜下滴灌棉花发生早衰的可能机制

在膜下滴灌条件下,棉花早衰问题严重。在对国内外关于棉花早衰研究成果及膜下滴灌条件特殊根区微环境深入分析的基础上,提出了膜下滴灌棉花早衰原因的合理假设,认为不合理的根系构型及其高蕾铃负荷是造成膜下滴灌棉花早衰的根本原因：膜下滴灌条件下棉花根系生长和构型分布发生的明显变化不利于棉花根系吸收土壤深层的水分和养分,抗逆性减弱,对环境的改变无法做出及时的反应,加之覆膜增温及优越的水肥供应,棉花地上部生长良好,蕾铃负担增加,一旦遇到逆境条件,在高蕾铃负荷前提下,即使对根系养分吸收功能最轻微的损害或者暂时的养分供应短缺均有可能造成对地上部养分供应的不足并发生早衰。因此,如何通过调控构建与地上部生长更为匹配的、构型分布更加合理的、抗逆性更强的棉花根系就成为解决膜下滴灌棉花早衰问题的关键。     

Measuring ecologically important quantities at relevant operational scales: An example using the dusky flycatcher in selectively logged forests in Idaho

Effective management of forest wildlife requires information about habitat features that can be altered by operations, if those habitat features promote reproductive success and survival, and if changes in organism density influence reproductive success and survival. Habitat selection studies often provide the first type of information, although relatively few studies examine how different selection decisions or densities of organisms influence fitness measures or measure habitat features at relevant operational scales. We examined patterns of habitat selection and estimated how habitat use, territory size, and conspecific density were associated with territory success (probability of a territory producing one or more fledglings) for the dusky flycatcher in 2002–2003 on eight study plots in managed grand fir (Abies concolor) forests in Idaho, USA. Flycatchers selected territories with greater cover of deciduous vegetation in two different height strata (1–2 and 3–4 m) and reduced cover of conifers less than 4 cm dbh compared to what was available. While flycatchers selected habitat characteristics at the territory scale, model selection results did not support any associations between vegetation features and territory success. Territory success had weak positive associations, for a given territory size, with conspecific density, although the relationship was highly variable. An interaction between territory size and density was not supported. These results are consistent with the view that avian breeding habitat selection occurs at multiple scales, and that the nest site scale may explain more of the variance in reproductive success than larger scales. Our results suggest that operational management of vegetation features, which often occurs at the stand scale, may not influence variation in critical demographic metrics. Increasing total shrub cover of commonly used plant species should benefit the dusky flycatcher, as well as other shrub-nesting forest birds, but stand-level habitat alterations alone cannot be relied upon to increase reproductive success, an important component of population change.