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 nitrogen 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 nitrogen 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 nitrogen 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 nitrogen 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 nitrogen 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 nitrogen in the form of glycine from soil solution as an important nitrogen source. 

These findings indicate that nitrogen uptake patterns shift with age of rubber trees and might be influenced by their changes in nitrogen requirements, by nitrogen losses via rubber tapping or shifts in carbon allocation to mycorrhizal symbionts. 

The study entitled "Age alters uptake pattern of organic and inorganic nitrogen by rubber trees" has been published online in Tree Physiology.