Tiger Nut Nutrient Coordination Under Limited Rhizosphere Conditions: A Study on Root and Tuber Development

When stolons tillered without any fertilization, the nitrogen and phosphorus content of tiger nut roots were found to be restricted by the nutrient content of the rhizosphere soil, which showed a positive correlation between them (Fig. 12, 14). Interestingly, tiger nuts allocated more carbon to the root, resulting in a remarkably high C:N ratio of the root (Fig. 5, 11), indicating their high demand for nitrogen. However, the N:P ratio of the roots was significantly higher than other treatments (Fig. 11), implying that their root growth was limited by the available nutrients in the poor rhizosphere soil, resulting in relatively insufficient nitrogen and phosphorus acquisition in leaves and stolons (Fig. 4). Nonetheless, tiger nuts were able to take timely remedial measures by maintaining a high C:N ratio in the roots to facilitate nitrogen acquisition when tubers were produced (Fig. 10, 11). The results of the analysis of the correlation between total nitrogen and phosphorus in the rhizosphere soil and the content of root nitrogen and phosphorus showed that tiger nut roots might activate inorganic nutrients in the rhizosphere soil to ensure nutrient acquisition, which is a common function of plant roots (Badri and Vivabco, 2009) (Fig. 14). In contrast, the stolons and tubers maintained a high C:N ratio to ensure that the available nutrients obtained from the rhizosphere soil were transported into the tubers (Fig. 10). As the tubers moved towards maturity, a lower nitrogen content in the rhizosphere soil resulted in higher C:N ratios of the tubers and relatively low N:P ratios, suggesting that tiger nuts have the ability to optimize tuber quality to the fullest extent possible (Fig. 11, 14). It can be inferred that tiger nuts might use limited nitrogen to form relatively stable cell walls of tubers as soon as possible (Fig. 3, 4) (Tian et al., 2022) to stabilize the tuber structure and ensure the subsequent storage of nutrients such as phosphorus (Fig. 3, 9). Therefore, tiger nuts have employed a nutrient coordination pattern to channel energy towards their tubers in response to inadequate nutrient availability, thereby securing the reproduction of their progeny. This coordination pattern is constrained by nutrients in the rhizosphere soil in limited environments, making it difficult to achieve optimal results, but it can be optimized as much as possible.