Background and aims

Masting is a widespread reproductive strategy in perennial plants. Its mechanism remains largely uncertain, although it is generally accepted that internal nutrient dynamics play a role. We aimed to examine whether soil nitrogen (N) supply influences plant N acquisition and drives masting.

Methods

We measured spatio-temporal variations in soil N mineralization rate and plant N uptake by roots using plant root simulator probes on the periphery of six fruiting and four non-fruiting trees in a mature Fagus crenata Blume forest. In parallel, N concentrations and biomass growth in leaves, current-year branches, cupules, nuts and winter buds were analysed for the same trees.

Results

Soil N mineralization rates exhibited significant seasonal variations in both nitrate- and ammonium-N, and varied spatially up to 38-fold between spots sampled on the same date and 39-fold for the same tree in a growing season. Fruiting did not enhance N uptake by roots, and a dramatic decrease in soil N mineralization rate was observed in autumn during nut ripening. Translocation from cupules supplemented this N shortfall in mature nuts. Consequently, the amount of N amount per whole shoot, but not in ripe nuts per shoot, was correlated with the cumulative soil inorganic N.

Conclusion

Masting is influenced ultimately by internal resource dynamics, which are decoupled from soil N dynamics. This may be a result of evolutionary selection to insulate trees from the high variation in local soil nutrients to ensure reproductive success.

中文翻译：

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水青冈树的结果物候与季节性土壤氮供应无关

 背景和目标

桅杆是多年生植物中广泛使用的繁殖策略。尽管人们普遍认为内部营养动态发挥了作用，但其机制在很大程度上仍不确定。我们的目的是研究土壤氮 (N) 供应是否影响植物氮获取并驱动肥大。

 方法

我们使用植物根模拟探针测量了成熟水青冈森林中六棵果树和四棵非果树周围土壤氮矿化率和植物根吸收氮的时空变化。同时，对同一棵树的叶子、当年枝条、壳斗、坚果和冬芽的氮浓度和生物量生长进行了分析。

 结果

土壤氮矿化率在硝酸盐和铵态氮方面均表现出显着的季节性变化，同一日期采样点之间的空间变化高达 38 倍，同一树木在生长季节的空间变化高达 39 倍。结果并没有增强根系对氮的吸收，并且在秋季坚果成熟期间观察到土壤氮矿化率急剧下降。来自壳斗的移位补充了成熟坚果中氮的短缺。因此，每个枝条的氮含量与土壤无机氮累积量相关，但每个枝条的成熟坚果中的氮含量不相关。

 结论

桅杆最终受到内部资源动态的影响，而内部资源动态与土壤氮动态脱钩。这可能是进化选择的结果，目的是使树木免受当地土壤养分的剧烈变化的影响，以确保繁殖成功。