We investigated whether tree species growing in mixtures and under different water supply would segregate their fine roots vertically, produce more fine roots overall, or only in specific soil layers. We examined the biomass, morphology, and distribution of fine roots down to 90 cm (forest floor, 0–5, 5–15, 15–30, 30–60, 60–90 cm) in pure and mixed stands of 10-year-old birch and pine trees, planted on a sandy podzol with discontinuous hardpan and seasonal high water table, following a randomized block design with four blocks receiving irrigation and four blocks left unirrigated during summer. Our results did not show any vertical root segregation between birch and pine in mixed plots. None of the species overyielded belowground throughout, but pine developed more roots in the top soil layer under irrigation. Both species had shallower fine root distributions in wet conditions, especially birch that was more plastic than pine in response to irrigation. Both species followed similar ecological strategies, occupying and competing for the same layers of the soil profile, under both control and irrigated conditions. However, the greater allocation of pine roots at the top soil horizons under irrigated conditions suggests locally favourable niches can lead to depth-specific asymmetric competition. This sheds new light on vertical niche partitioning of young tree mixtures under varying environmental conditions.

中文翻译：

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树木混合物和可用水量对种植在沙质灰化土上的桦木和松树细根地下互补性的影响

我们调查了在混合和不同供水条件下生长的树种是否会垂直分离其细根，总体上会产生更多的细根，还是仅在特定的土壤层中。我们检查了 10 年纯林和混交林中 90 厘米（林地，0-5、5-15、15-30、30-60、60-90 厘米）的细根的生物量、形态和分布。 - 老桦树和松树，种植在具有不连续硬土和季节性高地下水位的沙质灰化土上，遵循随机块设计，其中四个块接受灌溉，四个块在夏季未灌溉。我们的结果没有显示混合地块中桦树和松树之​​间的任何垂直根系分离。在整个过程中，没有一个物种在地下过度生长，但松树在灌溉下的表层土壤中长出了更多的根。这两个物种在潮湿条件下的细根分布较浅，尤其是桦树，在灌溉时比松树更具塑性。这两个物种遵循相似的生态策略，在控制和灌溉条件下占据和竞争相同的土壤剖面层。然而，在灌溉条件下，松树根在表层土层的更多分配表明当地有利的生态位会导致特定于深度的不对称竞争。这为不同环境条件下幼树混合物的垂直生态位划分提供了新的思路。在控制和灌溉条件下。然而，在灌溉条件下，松树根在表层土层的更多分配表明当地有利的生态位会导致特定于深度的不对称竞争。这为不同环境条件下幼树混合物的垂直生态位划分提供了新的思路。在控制和灌溉条件下。然而，在灌溉条件下，松树根在表层土层的更多分配表明当地有利的生态位会导致特定于深度的不对称竞争。这为不同环境条件下幼树混合物的垂直生态位划分提供了新的思路。