Clarifying soil nitrogen (N) acquisition by the same plant species with increasing age will further improve understanding of the importance of age in nutrient cycling in terrestrial ecosystems.
A series of monoculture rubber plantations were established to produce rubber latex driven by economic profit in Xishuangbanna in the past decades. This provides an opportunity to examine how age affects N uptake by rubber.
Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study to examine how root uptake rates and preferences for organic and inorganic N forms change with plantation age. They selected rubber plantations of 7, 16, 24, 32 and 49 years of age in the same region with similar topography.
To test the N uptake patterns of rubber trees of different age, a mixture of NH4+, glycine and NO3− was employed. The researchers investigated the uptake of NH4+, NO3− and glycine to evaluate differences in uptake rates by rubber trees of increasing age.
They found that the rubber trees used NH4+ as the dominant N source independent of age, in the order of NH4+ > glycine > NO3−. This indicates that rubber trees had a strong preference for NH4+, when roots were provided with equal concentrations of all three N forms.
They also observed significant shifts in the uptake rates of NH4+, NO3−or glycine with tree age. Young rubber trees had higher NH4+ and lower glycine preferences than adult trees. Older rubber trees utilized organic N in the form of glycine from soil solution as an important N source.
These findings indicate that N uptake patterns shift with age of rubber trees and might be influenced by their changes in N requirements, by N losses via rubber tapping or shifts in carbon allocation to mycorrhizal symbionts.