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首页> 外文期刊>Agricultural and Forest Meteorology >Competition for light in heterogeneous canopies: application of MAESTRA to a coffee (Coffea arabica L.) agroforestry system.
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Competition for light in heterogeneous canopies: application of MAESTRA to a coffee (Coffea arabica L.) agroforestry system.

机译：异类树冠中的光竞争：MAESTRA在咖啡（阿拉伯咖啡）农林业系统中的应用。

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In agroforestry systems (AFS), quantifying the competition for light is a prerequisite toward understanding the impact of shade trees on the productivity of the under-crop. Models for homogeneous canopies and shade/full-sun approaches do not address the intra-plot heterogeneity, typical of AFS. For the first time, MAESTRA, a 3D light absorption model, was fully parameterized in a heterogeneous 2-canopy layers AFS. We quantified competition for photosynthetic photon flux density (Q) between shade trees (Erythrina poepiggiana) and coffee (Coffea arabica), with a spatial resolution from the plant to the plot (2.7 ha) and a temporal resolution from half-hour to one full year. The predicted transmittance through the 2-canopy layers was verified against field measurements. The goodness of fit (R2 >0.75, RRMSE <26%) was comparable to the predictions from 10 other studies using 3D light models and mostly verified in one-layered systems (mean R2=0.89 and mean RRMSE=17%). Maps of absorbed Q showed that despite their low density in the plot (5.2 trees ha-1), the tall Erythrina trees reduced Q available for the coffee layer by 14% annually. Annual pruning of the oldest unproductive coffee resprouts maintained a large horizontal heterogeneity in coffee LAI, with direct impact on the Q absorption map. This management practice had a strong impact on seasonal variations of absorbed Q by the coffee canopy. We proposed also a simple approach to estimate Q absorbed yearly by the coffee plants in AFS of variable tree density, requiring only few measurements in the field. An extrapolation indicated that the amount of Q absorbed by the coffee canopy would display a negative exponential relationship (k=-0.34) when increasing shade tree density (from nil to 29 trees ha-1). The estimated k was similar to the shade tree extinction coefficient of diffuse radiation measured with a plant canopy analyzer. We showed that the presence of shade trees tends to reverse the diurnal time course of the fraction of Qa when compared to a plantation in the open. Overall, MAESTRA proved to successfully unlock the question of intra-plot heterogeneity for light absorption and to provide defensible light budgets as a continuous and mapped covariable, a crucial step for many field experimentations.
机译：在农林业系统（AFS）中，对光的竞争进行量化是了解树荫对下层作物生产力的影响的前提。均质冠层和阴影/全日照方法的模型无法解决AFS典型的图内异质性问题。首次将3D光吸收模型MAESTRA在异质2冠层AFS中完全参数化。我们量化了遮荫树（Erythrina poepiggiana）和咖啡（阿拉伯咖啡）之间的光合光子通量密度（Q）竞争，从植物到样地的空间分辨率（2.7公顷），从半小时到一个完整的时间分辨率年。相对于野外测量验证了通过2冠层的预测透射率。拟合优度（R 2 = 0.89，平均RRMSE = 17％）。吸收的Q值图显示，尽管该地块的密度较低（5.2棵ha -1 ），高刺桐树每年仍可将咖啡层的Q值降低14％。最老的非生产性咖啡新芽的年度修剪在咖啡LAI中保持了较大的水平异质性，直接影响了Q吸收图。这种管理实践对咖啡棚吸收的Q的季节性变化有很大影响。我们还提出了一种简单的方法来估算树木密度可变的AFS中咖啡植物每年吸收的Q值，仅需现场进行少量测量即可。外推表明，当增加遮荫树密度（从零到29棵树ha -1 ）时，咖啡冠层吸收的Q量将显示负指数关系（k = -0.34）。估计的k类似于用植物冠层分析仪测得的散射辐射的遮荫树消光系数。我们发现，与露天林相比，遮荫树的存在往往会改变Q a 的昼夜时间过程。总体而言，MAESTRA被证明可以成功地解开用于光吸收的图内异质性问题，并提供可辩护的光预算作为连续和映射的协变量，这是许多现场实验的关键步骤。

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