Berendse Frank
Department of Landscape Ecology and Nature Management, University of Utrecht, Opaalweg 20, Utrecht, The Netherlands.
Oecologia. 1981 Mar;48(3):334-341. doi: 10.1007/BF00346491.
In a previous paper in this series a model was proposed lor the competition between plant populations with different rooting depths. This model predicts that in mixtures of plant populations with different rooting depths the Relative Yield Total will exceed unity. Secondly it predicts that in these mixtures the relative crowding coefficient of the deep rooting population with respect to the shallow rooting one will decrease with increasing plant frequency. Two competition experiments in deep pots are carried out to test these predictions. In the first experiment a comparison is made between a series in which nutrients limited plant growth severely and a series in which nutrients were applied in a quantity that allowed high productivity. In the nutrient poor series the Relative Yield Total exceeded unity by about twenty per cent, while in the nutrient rich series only a small deviation from one was observed. The second experiment was divided into a series of deep pots in which different rooting depths were possible and a series of shallow pots in which the two species were forced to share the same space. In the series of shallow pots the relative crowding coefficient of the two species was found to be independent of plant frequency. In the series of deep pots the relative corowding coefficient of the two species with respect to each other did decrease significantly with increasing frequency.The observed frequency-dependence for the shallow rooting species could be explained by an extension of the theory presented previously. In the spacing series used in the same experiment a decrease of the shoot to root ratio with increasing plant density was observed. Furthermore, in the replacement series the shoot to root ratio in mixture was found to be lower than in monoculture. The consequences of these phenomena for the estimation of the relative crowding coefficient and the Relative Yield Total on the basis of shoot weights are discussed. However, it is argued that the fact that shoot to root ratios change with plant frequency does not provide an alternative explanation for the frequency-dependence observed.
在本系列的上一篇论文中，提出了一个关于不同生根深度植物种群间竞争的模型。该模型预测，在不同生根深度植物种群的混合体中，相对产量总和将超过1。其次，它预测在这些混合体中，深根种群相对于浅根种群的相对拥挤系数将随着植物频率的增加而降低。进行了两项在深花盆中的竞争实验来检验这些预测。在第一个实验中，对营养严重限制植物生长的系列和施加了允许高生产力数量营养的系列进行了比较。在营养贫瘠的系列中，相对产量总和超过1约20%，而在营养丰富的系列中，仅观察到与1有很小的偏差。第二个实验分为一系列可以有不同生根深度的深花盆和一系列两个物种被迫共享相同空间的浅花盆。在浅花盆系列中，发现两个物种的相对拥挤系数与植物频率无关。在深花盆系列中，两个物种相互之间的相对拥挤系数确实随着频率的增加而显著降低。对于浅根物种观察到的频率依赖性可以用先前提出的理论的扩展来解释。在同一实验中使用的间距系列中，观察到随着植物密度的增加，茎根比下降。此外，在替代系列中，发现混合体中的茎根比低于单作。讨论了这些现象对基于地上部重量估计相对拥挤系数和相对产量总和的影响。然而，有人认为茎根比随植物频率变化这一事实并不能为观察到的频率依赖性提供另一种解释。
