A new approach for tracking seed dispersal of large plants: soaking seeds with 15N-urea
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Although various tracking methods have been used in many ecosystems to investigate seed dispersal and seedling recruitment, it is still difficult to measure seed dispersal patterns due to methodological challenges in tracking seed movement away from parent trees and in finding the locations of seedlings.
Here, we aimed to develop a new approach to track seed dispersal by animals in the field.
Our approach involves soaking seeds directly into 15N-urea solutions with different dosages to enrich them isotopically. This new method is expected to create a reliable differentiation between the enriched seeds and natural ones and consequently between the corresponding seedlings.
We showed that acorns of Quercus variabilis and Cyclobalanopsis glauca and seeds of Pinus koraiensis soaked in 15N-urea solutions were successfully enriched. We did not find that δ15N value of seeds was a linear function of 15N-urea soaking duration. However, with high urea dosage and extending soaking duration, the δ15N values in seedlings of Q. variabilis and P. koraiensis were higher than those of normal plants. As expected, 15N isotope was significantly diluted in the growing seedlings germinated from 15N-enriched seeds. Using the 15N-urea soaking method, we successfully located five seedlings of Q. variabilis germinated from the enriched acorns in the field.
The 15N-urea soaking technique is powerful in tracking seed dispersal and seedling recruitment. This new method solves some of the problems inherent in traditional methods for tracking secondary seed dispersal and could further improve the study of seed dispersal ecology.