影响松毛虫种群动态的因素

综述了影响松毛虫种群动态的因素。气候、天敌、食料、林业技术措施等都不同程度地影响着松毛虫种群的变动。当气候条件适宜 ,天敌数量减少 ,食料丰富 ,林业技术措施缺乏时 ,松毛虫种群就会出现暴发的趋势。反之 ,当气候条件恶劣、天敌数量较多 ,食料植物缺乏或营养恶化 ,林业技术措施得当时 ,松毛虫种群就会得到遏制。尽管松毛虫的种群变动受到多种因素影响 ,但是对松毛虫自身调节能力的研究尚缺乏。     

萧氏松茎象危害与松树松脂量关系研究初报

萧氏松茎象HylobitelusxiaoiZhang是近年来暴发性松树害虫 ,主要危害 3种松树 :湿地松 (PinuselliottiiEngelm)、火炬松 (P .taeda)、马尾松 (P .massoniaanaLamb) ,其中以湿地松受害最为严重。为明确萧氏松茎象的危害与松脂流量的关系 ,作者对萧氏松茎象危害前后 3种松树 (湿地松、马尾松、火炬松 )松脂流量变化进行了研究。结果显示 ,在松树受害植株和未受害植株间松脂总流量间存在一定差异 ,其中以马尾松松脂流量变化最大 ,对受害株和未受害株松脂流量t-测验 ,差异达到显著水平 ;而湿地松和火炬松松脂总流量在受害植株和未受害植株间没有显著差异。对上述 3种松树松脂流量随时序动态变化的分析显示 ,松脂流量在 1年中以 5月到 6月之间为松脂流量高峰期 ,此后逐渐下降 ,到 3月中旬以后松脂流量又开始上升。就松脂流量时序动态而言 ,萧氏松茎象为害对马尾松松脂流量影响最大 ,对其它2个松树影响不明显。另外 ,不同松树树种在松脂流量及其时序动态上也存在一定差异 ,其中以马尾松脂流量较高。     

Genetic parameters for litter size in sheep: natural versus hormone-induced oestrus

The litter size in Suffolk and Texel-sheep was analysed using REML and Bayesian methods. Litters born after hormonal induced oestrus and after natural oestrus were treated as different traits in order to estimate the genetic correlation between the traits. Explanatory variables were the age of the ewe at lambing, period of lambing, a year*flock-effect, a permanent environmental effect associated with the ewe, and the additive genetic effect. The heritability estimates for litter size ranged from 0.06 to 0.13 using REML in bi-variate linear models. Transformation of the estimates to the underlying scale resulted in heritability estimates from 0.12 to 0.17. Posterior means of the heritability of litter size in the Bayesian approach with bi-variate threshold models varied from 0.05 to 0.18. REML estimates of the genetic correlations between the two types of litter size ranged from 0.57 to 0.64 in the Suffolk and from 0.75 to 0.81 in the Texel. The posterior means of the genetic correlation (Bayesian analysis) were 0.40 and 0.44 for the Suffolk and 0.56 and 0.75 for the Texel in the sire and animal model respectively. A bivariate threshold model seems appropriate for the genetic evaluation of prolificacy in the breeds concerned.     

水分胁迫对长白山阔红松林主要树种生长及生物量分配的影响

以长白山阔叶红松林主要树种红松、水曲柳、胡桃楸和椴树为研究对象 ,设置 3个水分处理 ,土壤含水量分别为田间持水量的 85 %～ 10 0 % (对照 )、6 5 %～ 85 % (MW )、4 5 %～ 6 5 %(LW )。对不同树种在不同处理下的生长进行测定 ,结果表明 :土壤水分含量对供试树种的单叶面积、单叶干重、叶片数量、茎干重、根长等生长指标均有显著影响。但各个树种对土壤水分胁迫的响应存在明显差异。在中度水分胁迫下 ,红松和水曲柳在总生物量降低的同时增加了地下生物量的比例 ,地下生物量 /地上生物量值比对照组分别提高了 79 31%和 2 3 91%。而胡桃楸和椴树的地下生物量 /地上生物量分别比对照组降低了 4 2 32 %和 7 92 %。在重度水分胁迫条件下 ,供试树种中只有红松的的地下生物量 /地上生物量比对照组提高了 2 7 5 % ,水曲柳、胡桃楸和椴树均呈下降趋势。由此可见 ,在供试树种中 ,红松对土壤水分胁迫的适应性最强 ,水曲柳仅对中度水分胁迫具有一定的适应性 ,而胡桃楸和椴树均不适宜在干旱的环境中生长。     

农田土壤枯枝落叶分解代谢的灰色分析

研究了农田土壤枯枝落叶分解代谢过程的影响因素。结果表明 ,农田土壤枯枝落叶分解速率有明显的季节变化 ;分解速率的高峰值主要是在 7,8月份。通过灰色关联分析表明 ,影响土壤枯枝落叶分解速率的主要因素是弹尾类动物、线虫类动物、无机磷转化作用和土壤含水量。建立了灰色数学模型     

西藏色季拉山暗针叶林凋落物层化学性质研究

The storage and chemical properties of the forest litter in dark coniferous forest of Sejila Mountain were studied. The results showed that the existing storage was 5. 863t·hm^-2 and the annual litter fall was 0. 3205 t·hm^-2 It implied that the forest litter decomposed slowly and accumulated quickly, and the turnover of nutrient circles was slow. The contents of N, Ca, Na, and Mn nutrient elements in litter layer were in the order of un-decomposed layer (U layer) > semi-decomposed layer (S layer) > decomposed layer (D layer), those of K, Fe, and Mg were in the order of D layer > S layer > U layer, and P element content was in the order of U layer > D layer> S layer. The pool of elements was 78. 483 kg·hm^-2 N, 3. 843 kg·hm^-2P, 48. 205 kg·hm^-2 K, 23.115 kg·hm^-2 Ca, 13. 157 kg·hm^-2 Na, 30.554 kg·hm^-2 Fe, 2. 113 kg·hm^-2 Mn and 27. 513 kg·hm^-2 Mg. The turnover of forest litter was the total of nutrient release accumulation. K, Fe, and Mg were enriched, and N,Ca, Na, Mn, and P were released with the turnover rate in the order of N > Ca > Na > Mn >P.     

Response of different decomposer communities to the manipulation of moisture availability: potential effects of changing precipitation patterns

The potential impacts of changes in precipitation patterns associated with global climate change on the relationship between soil community diversity and litter decomposition were investigated. For a period of ca. 5 months, two decomposer communities in litterbags (1000 and 45 μm mesh size) containing spruce litter were subjected to two irrigation treatments: constant and fluctuating (drying/rewetting) moisture conditions. The latter were expected to induce moisture stress on the decomposer communities. The two mesh sizes were used to exclude different faunal components from the decomposer communities. The 1000 μm mesh excluded only the macrofauna, whereas the 45 μm mesh excluded both the macro- and mesofauna. In the short-term perspective of the present study, mesofauna abundance showed no response to imposed fluctuating moisture conditions. Irrespective of the presence of mesofauna, mass loss, microbial biomass and the control mechanisms, regulating carbon mineralization appeared unaffected by fluctuating moisture conditions. The reduction in the functional/structural diversity of the decomposer communities in the 45 μm litterbags resulted in strongly increased Nematoda abundance but it did not alter the response of Nematoda to fluctuating moisture conditions. Processes in the nitrogen (N)-cycle and mass loss were sensitive indicators of changes in the structural and functional complexity of decomposer communities. However, a negative effect of fluctuating moisture conditions on extractable N was coupled to the presence of mesofauna. Extremes in rainfall patterns, generated by climate change, may have a negative impact on the availability of nutrients, particularly N, for plants. This effect could be amplified by an additional impoverishment in the structural and functional complexity of the respective decomposer communities.     

Slash Pile Burning Effects on Soil Biotic and Chemical Properties and Plant Establishment: Recommendations for Amelioration

Ponderosa pine forest restoration consists of thinning trees and reintroducing prescribed fire to reduce unnaturally high tree densities and fuel loads to restore ecosystem structure and function. A current issue in ponderosa pine restoration is what to do with the large quantity of slash that is created from thinning dense forest stands. Slash piling burning is currently the preferred method of slash removal because it allows land managers to burn large quantities of slash in a more controlled environment in comparison with broadcast burning slash. However burning slash piles is known to have adverse effects such as soil sterilization and exotic species establishment. This study investigated the effects of slash pile burning on soil biotic and chemical variables and early herbaceous succession on burned slash pile areas. Slash piles were created following tree thinning in two adjacent approximately 20‐ha ponderosa pine (Pinus ponderosa) restoration treatments in the Coconino National Forest near Flagstaff, Arizona. We selected 30 burned slash pile areas and sampled across a gradient of the burned piles for arbuscular mycorrhizal (AM) propagule densities, the soil seed bank, and soil chemical properties. In addition, we established five 1‐m² plots in each burned pile to quantify the effect of living soil (AM inoculum) and seeding amendments on early herbaceous succession in burned slash pile areas. The five treatments consisted of a control (no treatment), living soil (AM inoculum) amendment, sterilized soil (no AM inoculum) amendment, seed amendment, and a seed/soil (AM inoculum) amendment. Slash pile burning nearly eliminated populations of viable seeds and AM propagules and altered soil chemical properties. Amending scars with native seeds increased the cover of native forbs and grasses. Furthermore adding both seed and living soil more than doubled total native plant cover and decreased ruderal and exotic plant cover. These results indicate that seed/soil amendments that increase native forbs and grasses may enhance the rate of succession in burned slash pile areas by allowing these species to outcompete exotic and ruderal species also establishing at the site through natural regeneration.     

Seed Bank Viability in Disturbed Longleaf Pine Sites

Some of the most species‐rich areas and highest concentrations of threatened and endangered species in the southeastern United States are found in wet savanna and flatwood longleaf pine (Pinus palustris Mill.) communities. Where intensive forestry practices have eliminated much of the natural understory of the longleaf ecosystem, the potential for reestablishment through a seed bank may present a valuable restoration opportunity. Longleaf pine sites converted to loblolly pine plantations and non‐disturbed longleaf sites on the Coastal Plain of North Carolina were examined for seed bank presence and diversity. Conducting vegetation surveys and examining the seed bank using the seedling emergence technique allowed for verification of the seed bank presence, as well as evaluation of the quality of the seed bank on disturbed longleaf pine sites. Forty‐three species and over 1,000 individuals germinated, and the seed banks of both the disturbed and non‐disturbed stand types contained species not noted in the vegetation survey. Although many of these species were considered weedy and typical of disturbance, numerous taxa were indicative of stable longleaf pine communities. This study confirms both the presence and quality of seed banks in highly disturbed former longleaf pine sites, suggesting that the seed bank may be an important tool in restoration efforts.     

Protein Biosynthesis in the Embryo and Endosperm during Embryogenesis in Pinus sylvestris L.

Protein biosynthesis in the embryo and endosperm during embryogenesis in the Scots pine was studied using electrophoretic and immunochemical methods. Proteins of the albumin-globulin fraction were visualized already at the early embryonic stages. The major polypeptide components (48–60, 37–39, and 20–22 kDa) were gradually accumulated in the course of maturation. A high synchrony was noted between the stages of embryogenesis and molecular events related to protein biosynthesis and accumulation in the developing seed.