冬枣果实硬核期对15N尿素吸收、分配及再利用特性研究

以盆栽冬枣为试材,研究了冬枣果实硬核期土施¹⁵N尿素条件下N的吸收、分配和再利用特性.结果表明,果实膨大期,细根中的肥料氮比率（Ndff%）最高为10.64%,其次为新生营养器官.果实采收后,叶片和枣吊中的¹⁵N回撤;翌年萌芽前,粗根中的Ndff%最高（3.69%）;盛花期,新生营养器官（当年生枣头枝、枣吊、叶片和花）中的Ndff%最高.果实硬核期施肥后,当年根系吸收的¹⁵N尿素主要用于营养生长（叶片、枣吊、根系）,回撤¹⁵N优先贮藏于根系,休眠季节根系（54.01%）贮藏¹⁵N略高于地上部器官(45.99%),主要的¹⁵N贮藏器官为粗根(38.61%).地上部枝干中的贮藏¹⁵N从采果后到萌芽前含量变化剧烈,可作为贮藏¹⁵N营养诊断的“靶器官”,同期粗根中贮藏¹⁵N变幅较小,属长期 “库”.贮藏¹⁵N具有就近利用的特性,其分配随生长中心的转移而转移.     

Plant–Soil Feedbacks Contribute to the Persistence of Bromus inermis in Tallgrass Prairie

As invasive plants become a greater threat to native ecosystems, we need to improve our understanding of the factors underlying their success and persistence. Over the past 30 years, the C₃ nonnative plant Bromus inermis (smooth brome) has been spreading throughout the central grasslands in North America. Invasion by this grass has resulted in the local displacement of natives, including the tallgrass species Panicum virgatum (switchgrass). To determine if factors related to resource availability and plant–soil interactions were conferring a competitive advantage on smooth brome, field plots were set up under varying nitrogen (N) levels. Plots composed of a 1:1 ratio of smooth brome and switchgrass were located in a restored tallgrass prairie and were randomly assigned one of the following three N levels: (a) NH₄NO₃ added to increase available N, (b) sucrose added to reduce available N, and (c) no additions to serve as control. In addition, soil N status, soil respiration rates, plant growth, and litter decomposition rates were monitored. Results indicate that by the 2nd year, the addition of sucrose significantly reduced available soil N and additions of NH₄NO₃ increased it. Further, smooth brome had greater tiller density, mass, and canopy interception of light on N-enriched soils, whereas none of these characteristics were stimulated by added N in the case of switchgrass. This suggests that smooth brome may have a competitive advantage on higher-N soils. Smooth-brome plant tissue also had a lower carbon–nitrogen (C:N) ratio and a higher decomposition rate than switchgrass and thus may cycle N more rapidly in the plant–soil system. These differences suggest a possible mechanism for the persistence of smooth brome in the tallgrass prairie: Efficient recycling of nutrient-rich litter under patches of smooth brome may confer a competitive advantage that enables it to persist in remnant or restored prairies. Increased N deposition associated with human activity and changing land use may play a critical role in the persistence of smooth brome and other N-philic exotic species.     

麝,獐,麂和鹿间线粒体DNA的差异及其系统进化研究

用PCR技术和序列测定方法从线粒体DNA上得到367bp的细胞色素b基因片段序列。分析得出,麝与獐、麂和鹿的遗传差异在12．53％～14．44％之间,处在科间变化范围之内,在分子水平上进一步表明麝应作为一独立科;獐、麂和虎间序列的平均差异为10．28％,属于业科间的差异,与形态研究结果一致。麝、獐、麂和鹿的系统进化中,麝约在600万年前与鹿科分歧,而鹿科的三个亚科是在350～500万年开始分歧;麝、獐、麂和鹿共同组成一单系群．在600万年前具有一共同祖先。     

Predation of annual grass weed seeds in arable field margins

Seeds of three species of annual grass weeds (Alopecurus myosuroides, Avena fatua and Bromus sterilis) were placed in field margins around arable fields in a randomised block split-plot design experiment. The field margin vegetation was either sown or naturally regenerated and either cut or uncut. The seeds were either placed in cages designed to exclude small mammals and birds or were uncaged. The proportion of seeds removed was monitored on 10 occasions and mean seed loss was analysed. In general, a greater proportion of weed seeds was removed from uncaged trays in uncut swards, suggesting predation by small mammals, which inhabit tall grass. This effect was mainly due to removal of seeds of the two large-seeded species (A. fatua and B. sterilis), with A. fatua being especially favoured. It is therefore likely that small mammals play a role in the population dynamics of major crop weeds by feeding on their seeds in field margins, especially when these are dense and uncut.     

The unique interaction between the summer annual desert plant Salsola inermis Forssk and weevils residing on its roots: mutualism or parasitism?

1. Herbivores and parasites are likely to impose less damage on their host when their growth rate is slow and their dependency on the host is high. Accordingly, it was hypothesised that evolution would favour neutral or even beneficial interactions between a below-ground herbivore and a plant during the harsh season in a desert ecosystem. 2. This study characterised the relationship between the summer annual plant Salsola inermis Forssk (Chenopodiaceae) and weevils developing in a mud chamber attached to its roots in the Negev Desert of Israel. Plant seedlings were exposed to adult weevils (Conorhynchus palumbus Olivier or Menecleonus virgatus Schoenherr; Coleoptera: Curculionidae) in a controlled outside setting, to induce oviposition and larval establishment. The following were quantified: plant growth, above-ground biomass, fruit biomass, and fruit size, as well as relative C and N contents, and isotopic signatures (δ¹³C and δ¹⁵N) in plant tissues. 3. Exposure to weevils did not reduce plant survival but significantly and negatively affected plant growth and seed production. However, these effects were mainly due to above-ground herbivory by adults rather than root herbivory by larvae, and might have been overestimated. Interestingly, %N and δ¹⁵N were significantly higher, and the C:N ratio was significantly lower, in plants with larval establishment, suggesting that weevils affect the plant nitrogen budget. 4. The overall results do not support the notion of mutualistic interactions; yet, slow consumption, a low infestation level, and, possibly, N supplementation to the plant may enable the plant to tolerate herbivory under natural conditions.     

Introduced annual grass increases regional fire activity across the arid western USA (1980–2009)

Non‐native, invasive grasses have been linked to altered grass‐fire cycles worldwide. Although a few studies have quantified resulting changes in fire activity at local scales, and many have speculated about larger scales, regional alterations to fire regimes remain poorly documented. We assessed the influence of large‐scale Bromus tectorum (hereafter cheatgrass) invasion on fire size, duration, spread rate, and interannual variability in comparison to other prominent land cover classes across the Great Basin, USA. We compared regional land cover maps to burned area measured using the Moderate Resolution Imaging Spectroradiometer (MODIS) for 2000–2009 and to fire extents recorded by the USGS registry of fires from 1980 to 2009. Cheatgrass dominates at least 6% of the central Great Basin (650 000 km²). MODIS records show that 13% of these cheatgrass‐dominated lands burned, resulting in a fire return interval of 78 years for any given location within cheatgrass. This proportion was more than double the amount burned across all other vegetation types (range: 0.5–6% burned). During the 1990s, this difference was even more extreme, with cheatgrass burning nearly four times more frequently than any native vegetation type (16% of cheatgrass burned compared to 1–5% of native vegetation). Cheatgrass was also disproportionately represented in the largest fires, comprising 24% of the land area of the 50 largest fires recorded by MODIS during the 2000s. Furthermore, multi‐date fires that burned across multiple vegetation types were significantly more likely to have started in cheatgrass. Finally, cheatgrass fires showed a strong interannual response to wet years, a trend only weakly observed in native vegetation types. These results demonstrate that cheatgrass invasion has substantially altered the regional fire regime. Although this result has been suspected by managers for decades, this study is the first to document recent cheatgrass‐driven fire regimes at a regional scale.     

PHYSICOCHEMICAL CHARACTERISTICS AND ANTIOXIDANT EFFICACY OF CHITOSAN FROM THE INTERNAL SHELL OF SPINELESS CUTTLEFISH Sepiella inermis

Cuttlefish chitosan was extracted from the cuttlebone of Sepiella inermis by demineralization and deproteinization and produced by deacetylation, and its physical and chemical parameters were also compared with that of commercial chitosan. Ash, moisture, and mineral and metal content of the chitosan was estimated by adopting standard methodologies. The rate of deacetylation was calculated as 79.64% by potentiometric titration. Through viscometry and gel permeation chromatography, the molecular weight of chitosan was found to be significantly lower than that of the commercial chitosan. Optical activity was found to be levorotatory. The structure of the chitosan was elucidated with spectral techniques such as Fourier-transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. Cuttlefish chitosan showed a melting endothermic peak at 117.32°C. The x-ray diffraction (XRD) pattern of chitosan and standard chitosan exhibited the same crystalline peaks. Through scanning electron microscopy (SEM) the fine structure of chitosan was studied. The binding capacity (water and fat) of cuttlefish chitosan was found to be significantly higher than that of the commercial chitosan. The antioxidant efficacy of chitosan was determined through the conjugated diene method, scavenging ability on DPPH radicals, reducing power, and chelating ability on ferrous ions. This study has brought out the importance of shell as a potential source for obtaining another natural antioxidant.     

Generational differences in response to desiccation stress in the desert moss Tortula inermis

BACKGROUND AND AIMS: Active growth in post-embryonic sporophytes of desert mosses is restricted to the cooler, wetter months. However, most desert mosses have perennial gametophytes. It is hypothesized that these life history patterns are due, in part, to a reduced desiccation tolerance for sporophytes relative to gametophytes. METHODS: Gametophytes with attached post-embryonic sporophytes of Tortula inermis (early seta elongation phenophase) were exposed to two levels of desiccation stress, one rapid-dry cycle and two rapid-dry cycles, then moistened and allowed to recover, resume development, and/or regenerate for 35 d in a growth chamber. KEY RESULTS: Gametophytes tolerated the desiccation treatments well, with 93 % survival through regenerated shoot buds and/or protonemata. At the high stress treatment, a significantly higher frequency of burned leaves and browned shoots occurred. Sporophytes were far more sensitive to desiccation stress, with only 23 % surviving after the low desiccation stress treatment, and 3 % surviving after the high desiccation stress treatment. While the timing of protonemal production and sporophytic phenophases was relatively unaffected by desiccation stress, shoots exposed to one rapid-dry cycle produced shoots more rapidly than shoots exposed to two rapid-dry cycles. CONCLUSIONS: It is concluded that sporophytes of Tortula inermis are more sensitive to rapid drying than are maternal gametophytes, and that sporophyte abortion in response to desiccation results from either reduced desiccation tolerance of sporophytes relative to gametophytes, or from a termination of the sporophyte on the part of the gametophyte in response to stress.