in order to evaluate the effects of xanthium strumarium or amaranthus retroflexus competition under unsprayed and sprayed (half the recommended rate of imazethapyr) on canopy architecture of weed and soybean, field experiment was conducted at the research farm of university of tehran, during the growing season of 2007 and 2008. the experimental design was factorial based on randomized complete ...

Gap characteristics and effects of gaps on plasticity of Fargesia qinlingensis and tree regeneration were studied under canopy, and in small, medium, and large gaps in a mixed hardwood-conifer forest in the Qinling Mountains, China. Gap formation was mainly tree snapping (40%). Gapmakers were dominated by Betula albosinensis and Abies fargesii (85%). Gap area ranged from 23.8 to 594.2 m and ave...

Vegetation indices (VIs) are among the oldest tools in remote sensing studies. Although many variations exist, most of them ratio the reflection of light in the red and NIR sections of the spectrum to separate the landscape into water, soil, and vegetation. Theoretical analyses and field studies have shown that VIs are near-linearly related to photosynthetically active radiation absorbed by a p...

The study of plant under environmental conditions leads to an appreciation of their physical and chemical requirements for growth and reproduction. It contributes to increase the knowledge of where the plants grow. This study was conducted to determine the main autecological characteristics of Salvia hydrangea L. which is an endemic plant distributed in Mazanadarn province, Iran. The habitats o...

The within-plant distribution of soybean aphid, Aphis glycines Matsumura has been attributed to various causes, yet it is unclear which factor or combination of factors most influence aphid within-plant distribution. Understanding soybean aphid distribution within the soybean canopy is important both in developing sampling programs and in evaluating injury. Because natural enemies have the pote...

Shoot N concentration in plants decreases as they get bigger, due to the fact that N accumulates less rapidly than dry matter in plants during the plant growth process, leading to an allometric relationship between shoot N content (N(sh)) and shoot mass (W(sh)): N(sh)=a(W(sh))b. The results obtained on lucerne plants growing either under controlled low density conditions or in dense stands unde...

Mountain environments are currently among the ecosystems least invaded by non-native species; however, mountains are increasingly under threat of non-native plant invasion. The slow pace of exotic plant invasions in mountain ecosystems is likely due to a combination of low anthropogenic disturbances, low propagule supply, and extreme/steep environmental gradients. The importance of any one of t...

Whole-plant photosynthetic rate of rose (cv. Kardinal) was measured with an open system consisting of a computer-controlled data acquisition system and an infrared gas analyzer (IRGA). The system was used to monitor diurnal patterns of whole-plant gas exchange in response to environmental variables and a model to simulate this was constructed. A model for leaf photosynthesis was calibrated and ...

BACKGROUND AND AIMS Globally, conifer dominance is restricted to nutient-poor habitats in colder, drier or waterlogged environments, probably due to competition with angiosperms. Analysis of canopy structure is important for understanding the mechanism of plant coexistence in relation to competition for light. Most conifers are shade intolerant, and often have narrow, deep, conical crowns. In t...