Baldissera Tiago Celso, Frak Ela, Carvalho Paulo Cesar de Faccio, Louarn Gaëtan
INRA UR4 URP3F, BP6, F86600 Lusignan, France.
Ann Bot. 2014 Jan;113(1):145-57. doi: 10.1093/aob/mct251. Epub 2013 Nov 7.
The growth of crops in a mixture is more variable and difficult to predict than that in pure stands. Light partitioning and crop leaf area expansion play prominent roles in explaining this variability. However, in many crops commonly grown in mixtures, including the forage species alfalfa, the sensitivity and relative importance of the physiological responses involved in the light modulation of leaf area expansion are still to be established. This study was designed to assess the relative sensitivity of primary shoot development, branching and individual leaf expansion in alfalfa in response to light availability.
Two experiments were carried out. The first studied isolated plants to assess the potential development of different shoot types and growth periods. The second consisted of manipulating the intensity of competition for light using a range of canopies in pure and mixed stands at two densities so as to evaluate the relative effects on shoot development, leaf growth, and plant and shoot demography.
Shoot development in the absence of light competition was deterministic (constant phyllochrons of 32·5 °Cd and 48·2 °Cd for primary axes and branches, branching probability of 1, constant delay of 1·75 phyllochron before axillary bud burst) and identical irrespective of shoot type and growth/regrowth periods. During light competition experiments, changes in plant development explained most of the plant leaf area variations, with average leaf size contributing to a lesser extent. Branch development and the number of shoots per plant were the leaf area components most affected by light availability. Primary axis development and plant demography were only affected in situations of severe light competition.
Plant leaf area components differed with regard to their sensitivity to light competition. The potential shoot development model presented in this study could serve as a framework to integrate light responses in alfalfa crop models.
作物混播时的生长比单播时更具变化性且难以预测。光照分配和作物叶面积扩展在解释这种变化性方面起着重要作用。然而，在许多常见的混播作物中，包括饲用作物苜蓿，叶面积扩展的光调节所涉及的生理反应的敏感性和相对重要性仍有待确定。本研究旨在评估苜蓿初级枝条发育、分枝和单叶扩展对光照可利用性的相对敏感性。
进行了两项实验。第一项实验研究单株植物，以评估不同枝条类型和生长时期的潜在发育情况。第二项实验包括在两种密度下，通过在纯播和混播种植中使用一系列冠层来控制光照竞争强度，从而评估对枝条发育、叶片生长以及植株和枝条数量特征的相对影响。
在没有光照竞争的情况下，枝条发育是确定性的（主枝和侧枝的叶龄期常数分别为32.5℃日和48.2℃日，分枝概率为1，腋芽萌发前叶龄期常数延迟1.75），且与枝条类型和生长/再生时期无关。在光照竞争实验中，植株发育的变化解释了大部分植株叶面积的变化，平均叶片大小的贡献较小。枝条发育和单株枝条数量是受光照可利用性影响最大的叶面积组成部分。主枝发育和植株数量特征仅在严重光照竞争情况下受到影响。
植株叶面积组成部分对光照竞争的敏感性不同。本研究提出的潜在枝条发育模型可作为一个框架，用于整合苜蓿作物模型中的光反应。
