Atmospheric carbon dioxide and fertilizer nitrogen effects on radiation interception by rice 1

In order to predict the potential impacts of global change, it is important to understand the impact of increasing global atmospheric [CO₂] on the growth and yield of crop plants. The objectives of this study were to determine the interaction of N fertilization rates and atmospheric [CO₂] on radiation interception and radiation-use efficiency of rice (Oryza sativa L. cv. IR72) grown under tropical field conditions. Rice plants were grown inside open top chambers in a lowland rice field at the International Rice Research Institute in the Philippines at ambient (about 350 μmol mol^-1) or elevated (about 600 μmol mol^-1 during the 1993 wet season and 700 μmol mol^-1 during the 1994 dry season) in combination with three levels of applied N (0, 50 or 100 kg N ha^-1 in the wet season; 0, 90 or 200 kg N ha-1 in the dry season). Light interception was not directly affected by [CO₂], but elevated [CO₂] indirectly increased light interception through increasing total absorbed N. Plant N requirement for radiation interception was similar for rice grown under ambient [CO₂] or elevated [CO₂] treatments. The conversion efficiency of intercepted radiation to dry matter, radiation-use efficiency (RUE), was about 35% greater at elevated [CO₂] than at ambient [CO₂]. The relationship between leaf N and RUE was curvilinear. At ambient [CO₂], RUE was fairly stable across levels of leaf N, but leaf N less than about 2.5% resulted in lower RUE for plants grown with elevated [CO₂] than for plant grown at ambient [CO₂]. Decreased leaf N with increased [CO₂], therefore decreased RUE of rice plants grown at elevated [CO₂]. When predicting responses of rice to elevated [CO₂], RUE should be adjusted with a decrease in leaf N. This revised version was published online in June 2006 with corrections to the Cover Date.     

紫椴幼苗的叶片运动与光截获*

从水平、垂直方向和叶片的旋转运动等角度对紫椴（Tilia amurensis)幼苗的叶片运动特征进行了描述,并就枝条、叶片空间取向及叶片运动对叶片截获光合有效辐射的影响进行了讨论。结果表明：紫椴幼苗通过叶片运动有效地调节了对光合有效辐射的截获,提高了早、晚叶片光合作用旺盛时间段内的光合有效辐射截获量,在一定程度上减缓了中午强光、高温对叶片生理活动的危害。由于活跃的叶片运动、适度遮荫环境中幼苗的西部叶片所截获的光合有效幅射接近于全光环境中个体各向叶平均截获量,这为该环境中紫椴幼苗叶片在全天保持较旺盛的光合作用提供了能量保障。枝条和叶片的空间取向决定了紫椴幼苗叶片的空间分布;适度遮荫环境中个体的东西向叶片所占比例最高,全光环境中个体次之,强度遮荫个体枝条与叶片的空间分布趋于随机化。这意味着强度遮荫环境中的紫椴幼苗叶片对太阳辐射截获的调节能力较差,这可能是该环境中紫椴个体生产力较低的重要原因之一。     

Influence of sampling effort on saproxylic beetle diversity assessment: implications for insect monitoring studies in European temperate forests

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Assessing the effects of architectural variations on light partitioning within virtual wheat–pea mixtures

Background and Aims

Predicting light partitioning in crop mixtures is a critical step in improving the productivity of such complex systems, and light interception has been shown to be closely linked to plant architecture. The aim of the present work was to analyse the relationships between plant architecture and light partitioning within wheat–pea (Triticum aestivum–Pisum sativum) mixtures. An existing model for wheat was utilized and a new model for pea morphogenesis was developed. Both models were then used to assess the effects of architectural variations in light partitioning.

Methods

First, a deterministic model (L-Pea) was developed in order to obtain dynamic reconstructions of pea architecture. The L-Pea model is based on L-systems formalism and consists of modules for ‘vegetative development’ and ‘organ extension’. A tripartite simulator was then built up from pea and wheat models interfaced with a radiative transfer model. Architectural parameters from both plant models, selected on the basis of their contribution to leaf area index (LAI), height and leaf geometry, were then modified in order to generate contrasting architectures of wheat and pea.

Key results

By scaling down the analysis to the organ level, it could be shown that the number of branches/tillers and length of internodes significantly determined the partitioning of light within mixtures. Temporal relationships between light partitioning and the LAI and height of the different species showed that light capture was mainly related to the architectural traits involved in plant LAI during the early stages of development, and in plant height during the onset of interspecific competition.

Conclusions

In silico experiments enabled the study of the intrinsic effects of architectural parameters on the partitioning of light in crop mixtures of wheat and pea. The findings show that plant architecture is an important criterion for the identification/breeding of plant ideotypes, particularly with respect to light partitioning.     

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Measuring leaf area index in rubber plantations − a challenge

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