CONTEXT

Tree-based intercropping (TBI) systems show promise in reducing the vulnerability of field crops to increasing water stress. TBI can generate several above- and belowground interactions between trees and crops. These interactions remain poorly documented, especially in the context of moisture limitation.

OBJECTIVE

The objective of this study was to determine the performance of soybean within a TBI system under moisture limitation. We hypothesized that TBI generates both positive (near the alleyway centre) and negative (near the trees) effects on soybean performance and that these effects are accentuated when moisture availability decreases.

METHODS

A partial rainfall interception treatment (50% of the soil surface) in a soybean crop (stages R1 to R7) was installed for two years (2018 and 2019) in a TBI (50 trees/ha planted in 2012) in southern Quebec. TBI was composed of hybrid poplars (Populus deltoides × P. nigra) and different high-value hardwood species that were planted alternately within rows. A tree root-pruning treatment was also applied to understand belowground effects of tree roots on soybean growth under moisture limitation. Various microclimatic (light availability, wind speed and soil moisture) and soybean performance variables (leaf traits, 100-grain weight and yield) were measured at four distances from the tree row (4, 12 and 20 m, and control).

RESULTS AND CONCLUSIONS

Rainfall exclusion decreased soil moisture and had a negative effect on soybean yield (−14%). The effect of the rain exclusion treatment on soybean performance was similar across all tree row distances and in both root-pruning treatments, which is contrary to our prediction. In 2018, an abnormally dry and warm season, yield near the alley centres was higher than near the tree row and tended to outperform the control. In 2019, a season with normal rainfall and temperature, soybean yield within the alleys was consistent among the different measured distances and did not differ from that in the control. Moderate shading at 4 m (−26% of PAR) was not associated with a change in soybean yield or leaf traits compared to other distances where shading was negligible or absent. Root pruning negatively affected soybean yield in 2018 (−14%) and 2019 (−22%), which is contrary to our prediction.

SIGNIFICANCE

This case study adds to our knowledge regarding interactions between crops and trees in widely spaced TBI systems. TBI effects on spatial patterns of crop yield may vary substantially depending upon inter-annual variation in climatic conditions. This study suggests that more facilitative effects would prevail in dryer and warmer years, in contrast to near neutral effects in normal years.

中文翻译：

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温带树种间作系统水分限制条件下大豆性能

语境

基于树的间作 (TBI) 系统在减少大田作物对日益增加的水分胁迫的脆弱性方面显示出希望。TBI 可以在树木和作物之间产生几种地上和地下的相互作用。这些相互作用仍然很少记录，特别是在水分限制的情况下。

客观的

本研究的目的是确定大豆在 TBI 系统中在水分限制下的性能。我们假设 TBI 对大豆性能产生正面（靠近小巷中心）和负面（靠近树木）影响，并且当水分可用性降低时，这些影响会加剧。

方法

在魁北克南部的 TBI（2012 年种植 50 棵树/公顷）中安装了为期两年（2018 年和 2019 年）的大豆作物（R1 至 R7 阶段）的部分降雨拦截处理（50% 的土壤表面）。TBI 由杂交杨树（Populus deltoides × P. nigra）和不同的高价值硬木树种组成，它们在行内交替种植。还应用树根修剪处理来了解树根对水分限制下大豆生长的地下影响。在距树行的四个距离（4、12 和 20 m，以及对照）处测量了各种小气候（光照、风速和土壤水分）和大豆性能变量（叶性状、100 粒重和产量）。

结果和结论

降雨排除会降低土壤水分并对大豆产量产生负面影响（-14%）。雨水排除处理对大豆性能的影响在所有树行距离和两种根修剪处理中都是相似的，这与我们的预测相反。2018年是异常干燥温暖的季节，胡同中心附近的产量高于树行附近的产量，并且往往优于对照。2019年是雨量、气温正常的季节，巷内大豆产量在不同测距间基本一致，与对照无差异。与阴影可忽略或不存在的其他距离相比，4 m 处的中等阴影（PAR 的 -26%）与大豆产量或叶片性状的变化无关。根部修剪对 2018 年（-14%）和 2019 年（-22%）的大豆产量产生负面影响，

意义

本案例研究增加了我们对大间距 TBI 系统中作物和树木之间相互作用的了解。TBI 对作物产量空间格局的影响可能因气候条件的年际变化而有很大差异。这项研究表明，与正常年份接近中性的影响相比，在干燥和温暖的年份会出现更多的促进效应。