The sink-limitation hypothesis postulates that suppression of meristematic activity can limit growth at low temperatures (direct-cold-limitation) in situations where photosynthesis is not restricted. In accordance with this hypothesis, high concentrations of non-structural carbohydrates (NSC) have been found, in several studies, in plants at high altitudes or latitudes. However, high concentrations of NSC could also be due to nutrient deficiency. This study aimed to differentiate between nutrient- and direct-cold-limitation by comparing the growth and NSC concentrations of Abies veitchii saplings at two altitudes (high/low) and with two fertilization treatments (N-rich/N-poor).

N-rich saplings grew better at the low than the high site, but N-poor saplings were suppressed to similar degrees at both altitudes. Among N-rich saplings, the leaf nitrogen concentration was lower at the high site than the low site. Leaf NSC concentrations were higher in N-poor than N-rich saplings. However, NSC concentrations were higher at the high site than the low site in leaves with the same nitrogen concentrations. These results indicate that direct-cold and nutrient-limitation may occur simultaneously at high altitude, causing restricted growth and NSC accumulation. Therefore, NSC concentration should be interpreted in terms of both direct-cold and nutrient-limitation.