Competition of Barnyardgrass with Rice Varieties

A field study was conducted to examine the competition of barnyardgrass with various rice varieties and its effect on propanil effectiveness. Six rice varieties, Ispaniki A', Strymonas and Roxani (Japonica type) and Rea, Skybonnet and Blue belle (Indica type), were grown in a silty loam soil, in 1994 and 1995. The varieties had different 1000 seed weights, which varied from 24 to 40 g. The herbicide propanil was applied at the four-leaf stage of barnyardgrass on half the plot area. Japonica type varieties emerged earlier and had lower numbers of barnyardgrass plants compared to Indica varieties. The time of seedling emergence was significantly and negatively correlated with the seed weight and positively with the number of barnyardgrass plants. The delayed establishment of Indica type varieties favoured rapid barnyardgrass growth at the early stages and resulted in lower effectiveness of propanil, compared to Japonica type varieties. Thus, in controlling barnyardgrass in rice fields it is necessary to take into account the variety grown in order to reduce production costs and the pollution risk to the environment.     

Influence of a vesicular-arbuscular mycorrhizal fungus on the competitive ability of Bradyrhizobium spp. for nodulation of cowpea Vigna unguiculata (L.) Walp in non-sterilized soil

Summary We examined the influence of a vesicular-arbuscular (VAM) fungus (Glomus pallidum Hall) on the competitive ability of introduced and native Bradyrhizobium strains to nodulate cowpeas [Vigna unguiculata (L) Walp]. Our experiments in non-sterilized soil revealed that in the presence of VAM fungus, introduced Bradyrhizobium spp. strains become more competitive than native rhizobia. For example, strain JRC29 occupied 59.2% of the total nodules when inoculated alone, but this figure increased to 71.2% when JRC29 was used in dual inoculations with VAM fungus. A similar pattern of enhanced competitiveness for nodule formation was observed with the two other strains in the presence of the VAM fungus. Our results suggest that the competitiveness of rhizobia can be enhanced by co-inoculating with a selected strain of a VAM fungus.     

我国生态农业历史中利用植物辅助效应的实践

我国有着悠久的生态农业历史,农、林生态系统中的植物种间关系被关注最多。种间关系主要有3种,即竞争、辅助和中性。过去,竞争关系是被研究最多的一种。近20年来,辅助关系逐渐受到重视并被引入主流生态学理论中。本文分析了这些经验记载的生态学机理,其中描述最多的是植物幼苗的遮阴以及土壤养分的改良(豆科植物固氮作用)。此外,在缓冲极端温度(夏季高温以及冬季低温)、减少杂草竞争、防止动物捕食、减少水分胁迫等方面也有少量记录。我国古代不仅有利用两种植物种间辅助效应的丰富记载,还有利用多种植物综合和复合的种间辅助关系,以及植物与动物之间的复杂关系构建生态系统的记载。特别是华南地区具有利用多种植物与动物间关系来构建基塘生态系统、复合果园生态系统、茶园生态系统等方面传统经验的记载。深入挖掘我国传统植物间辅助效应的记载,并对其进行科学研究,是生态学中非常有价值的课题。因此,本文从社会-生态记忆的角度,对古代文献中关于植物间辅助效应的记载进行梳理与分析,希望引起学界同仁对这些传统经验的重视,并在此基础上通过现代生态学的实验方法验证这些记载的真实性与适用性,为生态恢复、生态农业、现代林业及生态系统管理等提供有益的借鉴。     

Experimental evidence for nest-site competition between invasive ring-necked parakeets (Psittacula krameri) and native nuthatches (Sitta europaea)

Ring-necked parakeets (Psittacula krameri) originate from Africa and Asia, but have been widely introduced and are thought to compete for nest-sites with native hole-nesting birds, raising concerns for the loss of native avifauna. In this study, we adopt a replicated before-after-control experimental design to test for competition between parakeets and native cavity-nesters. In experimental plots in Brussels, Belgium we blocked parakeet nesting cavities and conducted surveys to evaluate availability and use of cavities by parakeets and native hole-nesters. Numbers of breeding pairs, as well as cavity quality index - based on cavity occupancy rates - were evaluated before and after blocking. After blocking, numbers of native nuthatches (Sitta europaea) declined significantly, largely due to nest take-overs by parakeets. Nuthatches and parakeets strongly overlap in preferred nest-sites and this overlap explains the competition that leads to a reduction in nuthatch numbers when suitable cavities become scarce. Average quality of parakeet nests was lower after blocking, indicating that parakeets will utilize alternative cavities when preferred sites are not available, bringing them into greater conflict with other cavity nesters. Although some nuthatches remain in areas dominated by ring-necked parakeets, our results raise conservation concerns for the vulnerability of native cavity-nesting birds to the expansion of invasive parakeet populations.     

Soil moisture and water use by pastures and silvopastures in a sub-humid temperate climate in New Zealand

Soil moisture content from 0 to 2 m depth was monitored under 2–6 year old radiata pine (Pinus radiata) with three understoreys of bare ground, lucerne (Medicago sativa) and ryegrass/clover (Lolium perenne/Trifolium spp.) and under adjacent open-grown lucerne and ryegrass/clover pastures. By the fifth year soil moisture depletion/recharge pattern under the trees alone was similar to that under open pasture and under trees with pasture understoreys. Maximum plant available moisture storage was 207–223 mm in the top meter of this Templeton silt loam soil but only 69–104 mm at 1–2 m depth where coarse textures often predominated. Lucerne reduced soil moisture content (SMC) to lower levels during drier summers and extracted more water from 1 to 2 m depth than ryegrass/clover. Evapotranspiration (ET) during early summer when soil moisture was high was close to the Penman potential evapotranspiration (E _p ), but the difference increased when SMC in the top meter dropped below 200 mm. The silvopasture treatments had higher ET in winter than pasture alone but this was still less than E _p . Soil moisture deficits (SMD) at the end of each summer were sufficiently large to require slightly higher than normal winter rainfall and ET < E _p to recharge the soil to field capacity before the next summer. The soil moisture results, taken together with root and growth data, suggest that trees and understorey pastures are complementary in the first three or four growing seasons but this balance subsequently declines in favor of the pine trees. Management options, to extend the period that understorey pastures are productive, include reducing tree stockings, more vigorous pruning, using competitive understoreys and changing from pines to deciduous trees. Research on new silvopastoral combinations is suggested.     

Determinants for successful reforestation of abandoned pastures in the Andes: Soil conditions and vegetation cover

The Andes of Ecuador are known for their outstanding biodiversity but also as the region with the highest deforestation rate in South America. This process is accompanied by accelerating degradation and loss of environmental services. Despite an extraordinary richness in native tree diversity, more than 90% of all forest plantations established in Ecuador consist of exotic species, primarily Eucalyptus spp. and Pinus spp. This is mainly due to the lack of information about the autecological and synecological requirements of the native species.     

2种种植方式下不同化感杂交稻组合和新品系对稗草的抑制作用

以美国强化感稻‘PI312777’为对照,比较不同化感杂交稻组合和新品系抑制稗草能力的田间表现,探索利用水稻化感作用的有效方法。采用移栽和直播2种水稻种植方式,对水稻封行前抑草率、竞争抑草率、灌浆期抑草率、伴生稗草平均株高和稗草单株干物重进行调查分析。化感稻移栽条件下对于稗草株高和干物重的抑制效果优于直播条件;直播条件下化感稻的化感抑草率大于移栽条件下,且变异系数较小,可见直播方式更利于化感稻种植;环境条件是化感稻抑草作用发挥的重要影响因子,其中竞争抑草率受环境的影响较大,化感作用表现相对稳定;相关分析表明化感稻的抑草作用并未对存活稗草的地上部分生长量有明显影响,增强化感稻的化感作用,能有效抑制田间稗草的萌发。实验结果显示了化感稻是更适于直播种植的材料,在生产上具有良好的应用前景。     

Response of climate-growth relationships and water use efficiency to thinning in a Pinus nigra afforestation

Thinning is the main forestry measure to increase tree growth by reducing stand tree density and competition for resources. A thinning experiment was established in 1993 on a 32-year-old Pinus nigra Arn. stand in central Spain. The response of growth, climate-growth relationships and intrinsic water use efficiency (WUEi) to a stand density reduction were compared between moderate thinned plots and a control plot by a combined analysis of basal area increments (BAI), and C and O stable isotope ratios (δ¹³C_c and δ¹⁸O_c). BAI in the control plot showed a decreasing trend that was avoided by thinning in the thinned plot. Thinning also partially buffered tree-ring response to climate and trees were less sensitive to precipitation although more sensitive to temperature. Δ¹³C_c in the thinned plot was not modified indicating that stomatal conductance (g) and photosynthetic capacity (A) did not change or change in the same direction. However, δ¹⁸O_c decreased in the control plot (unrelated to δ¹⁸O of precipitation) but not in the thinned plot, suggesting a relative increase of temperature and irradiance and/or a decrease of air humidity after reducing the density consistent with an increase in A, g and BAI. As WUEi did not increase in the thinned plot, faster growth in this plot was caused by higher abundance of resources per tree. The trend of WUEi in both plots indicated low-moderate CO₂-induced improvements. Thinning might be a useful adaptation measure against climate change in these plantations reducing their vulnerability to droughts. However, because WUEi was not affected, the positive growth response might be limited if droughts and warming continue and certain thresholds are exceeded.     

西部城市竞争力与西部城市化进程

西部地区城市化进程缓慢,一个重要的原因就是西部城市竞争力偏弱,因此培育西部城市竞争力,充分发挥中心城市的带动和辐射作用就成为推动西部城市化的一个重要手段。培育西部城市竞争力应注意从树立符合发展需要的新观念,加强对重点城市竞争力的培育,提高城市产业、企业的竞争力,加强人力资源的开发与管理,抓住机遇勇于创新、筑巢引凤招商引资,治理城市区域生态环境、建设生态城市等几个方面着手。     

林分密度的新指标--冠积指数

利用17块油松、31块落叶松人工林调查资料，根据林分密度与竞争理论，构建了一个包含冠幅和冠长的林木竞争指标——冠积指数。研究结果表明，冠积指数与直径、树高之间的相关关系存在着基本一致的规律，即在直径、树高较小或较矮阶段，冠积指数随着直径或树高的增大而增大；当直径、树高达到一定值时，冠积指数达到最大；之后随着直径、树高的增加，冠积指数逐渐变小。冠积指数与年龄、立地质量相关性不大。