Water and nitrogen (N) are essential factors affecting the tomato plant-fruit system. However, little is known about to what extent water and N could regulate the water and carbon fluxes between the source-sink system, thus influencing fruit growth. In this study, the source-sink ratio (Rss) was proposed and then related to water and N supply by a WN-Jensen function, according to the experimental observations from tomatoes grown under various water and N conditions. A process-based model was applied to investigate the effects of water and N supply on fruit growth through modifying one of the major model inputs, the sucrose concentration in phloem solution (Cp), which was assumed to be proportional to Rss. The model was then assessed with the data sets from tomatoes grown under different water and N conditions. The results showed that, N deficit and water stress at fruit early /whole growth stage had significant limitation on plant and fruit growth, together with low stem water potential and water consumption. The dynamics of fruit growth were better simulated by the model when the effects of water and N on source-sink regulation were taken into consideration through modifying Cp. Compared to the original model simulation, MAE and RRMSE of fruit growth prediction decreased by up to 82.0 % and 79.9 %. The simulation efficiency of fruit fresh and dry weights was in the range of 77.4 %-96.4 % and 72.9 %-92.9 % by the modified model, respectively. Model-assisted analysis showed that water supply could be reduced by 11.9 %, 27.0 % and 41.1 % at fruit early, middle and late stage together with a reduction of 27.5 % N application (saving investment of 131 $/ha), while ensuring the same fruit growth by considering water and nitrogen regulation on source-sink relation.

中文翻译：

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番茄果实生长对水氮调控源汇比响应的模型辅助分析


水和氮 （N） 是影响番茄植物-水果系统的重要因素。然而，关于水和氮在多大程度上可以调节源汇系统之间的水和碳通量，从而影响果实生长，人们知之甚少。在这项研究中，提出了源汇比 （Rss），然后根据在各种水和氮条件下生长的西红柿的实验观察，通过 WN-Jensen 函数与水和氮的供应相关联。应用基于过程的模型，通过修改主要模型输入之一，即韧皮部溶液 （Cp） 中的蔗糖浓度，研究水和氮供应对果实生长的影响，假设其与 Rss 成正比。然后使用在不同水和 N 条件下生长的西红柿的数据集对模型进行评估。结果表明，果实早期/全生育期氮素缺乏和水分胁迫对植物和果实的生长有显著限制，同时茎水势和耗水量低。当通过修改 Cp 考虑水和 N 对源汇调节的影响时，模型更好地模拟了果实生长动力学。与原始模型模拟相比，水果生长预测的 MAE 和 RRMSE 分别下降了 82.0 % 和 79.9 %。修正模型对水果鲜重和干重的模拟效率分别在 77.4 %-96.4 % 和 72.9 %-92.9 % 之间。模型辅助分析表明，在果实早期、中期和晚期，供水量可以减少 11.9 %、27.0 % 和 41.1%，氮肥施用量减少 27.5%（节省投资 131 美元/公顷），同时通过考虑水氮对源-汇关系的调节来确保相同的果实生长。