Pasture persistence is a key determinant of the economic and environmental performance of pastoral animal production systems. Large and deep root systems that help resist summer water stress have been proposed as a relevant trait for vegetative persistence of perennial temperate forage species growing in subtropical climates or under future climatically challenging scenarios. In a previous study [Jauregui et al., 2017. Persistence of tall fescue in a subtropical environment: Tiller survival over summer in response to flowering control and nitrogen supply. Grass and Forage Science 72, 454–466] we have shown that nitrogen fertilization and grazing management aimed at ‘control flowering’ increased the survival of tall fescue tillers during harsh summers in Uruguay (lat. 32°S). Here we assessed: (i) to what extent tiller survival is mediated by root system size in spring and (ii) what consequences tiller survival entails for root mass, depth and morphology the following autumn. In two field experiments, significant increases in tiller survival in response to nitrogen fertilization and grazing management (+60% and +80% in 2011/12 and 2012/13, respectively) were not related to concomitant effects on the size or depth of the root system in spring (p > .10). Even when six-fold within-treatment variation in root mass was observed, within-treatment variation in summer tiller survival was little affected (<15%, p = .08). In turn, differences in tiller survival over summer affected little root system characteristics the following autumn. Therefore, we found scant support for the hypothesis that large and deep root systems contribute to survival of tall fescue tillers in this subtropical humid climate. Except for soils with less than 30 mm of plant available water holding capacity, summer water deficits did not induce severe tiller mortality in tall fescue in this climate.

中文翻译：

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高羊茅分蘖在亚热带环境中夏季的生存：根系大小和深度的作用

牧场持续性是畜牧生产系统经济和环境绩效的关键决定因素。有助于抵抗夏季水分胁迫的大而深的根系已被认为是在亚热带气候或未来气候挑战条件下生长的多年生温带牧草物种的营养持久性的相关特征。在之前的一项研究中 [Jauregui et al., 2017. 高羊茅在亚热带环境中的持久性：分蘖在夏季的存活对开花控制和氮供应的反应。草和饲料科学 72 , 454–466] 我们已经证明，旨在“控制开花”的施氮肥和放牧管理提高了乌拉圭严酷夏季（南纬 32°）期间高羊茅分蘖的存活率。在这里，我们评估了：（i）春季根系大小在多大程度上介导分蘖存活；（ii）分蘖存活对接下来秋季的根质量、深度和形态产生什么影响。在两项田间试验中，氮肥和放牧管理对分蘖存活率的显着增加（2011/12 年和 2012/13 年分别增加 60% 和 +80%）与对耕地大小或深度的伴随影响无关。春季根系 ( p  > .10)。即使观察到根质量的处理内变异有六倍，夏季分蘖存活率的处理内变异也几乎没有受到影响（<15%，p  = .08）。反过来，夏季分蘖存活率的差异对第二年秋季的根系特征影响很小。因此，我们发现，大而深的根系有助于高羊茅分蘖在这种亚热带潮湿气候中的生存这一假设缺乏支持。除了植物有效持水量小于30毫米的土壤外，夏季缺水并没有导致这种气候下高羊茅严重的分蘖死亡。