Background and Aims Pollen limitation is most prevalent among bee-pollinated plants, self-incompatible plants and tropical plants. However, we have very little understanding of the extent to which pollen limitation affects fruit set in mass-flowering trees despite tree crops accounting for at least 600 million tons of the 9200 million tons of annual global food production. Methods We determined the extent of pollen limitation in a bee-pollinated, partially self-incompatible, subtropical tree by hand cross-pollinating the majority of flowers on mass-flowering macadamia (Macadamia integrifolia) trees that produce about 200 000–400 000 flowers. We measured tree yield and kernel quality and estimated final fruit set. We genotyped individual kernels by MassARRAY to determine levels of outcrossing in orchards and assess paternity effects on nut quality. Key Results Macadamia trees were pollen-limited. Supplementary cross-pollination increased nut-in-shell yield, kernel yield and fruit set by as much as 97, 109 and 92 %, respectively. The extent of pollen limitation depended upon the proximity of experimental trees to trees of another cultivar because macadamia trees were highly outcrossing. Between 84 and 100 % of fruit arose from cross-pollination, even at 200 m (25 rows) from orchard blocks of another cultivar. Large variations in nut-in-shell mass, kernel mass, kernel recovery and kernel oil concentration were related to differences in fruit paternity, including between self-pollinated and cross-pollinated fruit, thus demonstrating pollen-parent effects on fruit quality (i.e. xenia). Conclusions This study is the first to demonstrate pollen limitation in a mass-flowering tree. Improved pollination led to increased kernel yield of 0.31–0.59 tons ha–1, which equates currently to higher farm-gate income of approximately $US3720–$US7080 ha–1. The heavy reliance of macadamia flowers on cross-pollination and the strong xenia effects on kernel mass demonstrate the high value that pollination services can provide to food production.

中文翻译：

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栽培的大量开花树澳洲坚果（Proteaceae）中的花粉限制和 xenia 效应

背景和目的花粉限制在蜜蜂授粉植物、自交不亲和植物和热带植物中最为普遍。然而，尽管在全球每年 92 亿吨粮食产量中，树木作物至少占 6 亿吨，但我们对花粉限制对大量开花树木结果的影响程度知之甚少。方法 我们通过人工对产生约 200 000-400 000 朵花的大量开花澳洲坚果 (Macadamia integrifolia) 树上的大部分花进行异花授粉，确定了一棵蜜蜂授粉、部分自交不亲和的亚热带树的花粉限制程度。我们测量了树木产量和籽粒质量并估计了最终结果。我们通过 MassARRAY 对单个籽粒进行基因分型，以确定果园的异交水平并评估亲子关系对坚果质量的影响。主要结果 澳洲坚果树的花粉有限。补充异花授粉使带壳坚果产量、仁产量和坐果率分别提高了 97%、109% 和 92%。花粉限制的程度取决于实验树与另一个品种的树的接近程度，因为澳洲坚果树高度异交。84% 到 100% 的果实来自异花授粉，即使在距离另一个品种的果园 200 m（25 行）处也是如此。坚果壳质量、仁质量、仁回收率和仁油浓度的巨大变化与果实亲子关系的差异有关，包括自花授粉和异花授粉果实之间的差异，从而证明花粉亲本对果实质量的影响（即 xenia ）。结论 本研究首次证明了大规模开花树的花粉限制。改进授粉导致籽粒产量增加 0.31-0.59 吨 ha-1，这相当于目前农场门口收入增加约 3720 美元至 7080 美元 ha-1 美元。澳洲坚果花对异花授粉的严重依赖以及对籽粒质量的强烈 xenia 影响表明授粉服务可以为粮食生产提供高价值。