Leaf enzyme plays a more important role in leaf nitrogen resorption efficiency than soil properties along an elevation gradient

1. Nitrogen (N) resorption is a strategy for plant N conservation through
which plants withdraw N from senescing leaves prior to litterfall and its
underlying mechanisms are important for better understanding of N cycling.
However, most current studies focused on the impacts of soil and leaf
nutrients on leaf N resorption efficiency (NRE), and plant physiological
regulation that is species-dependent is still unclear. 2. Here, we
conducted a field experiment to investigate the variations of leaf NRE
along an altitudinal gradient in a temperate forest of Northeastern China.
3. Results showed that leaf NRE of Q. mongolica and F. mandshurica
increased with altitude, while leaf NRE of T. amurensis, A. mono and A.
pseudosieboldianum exhibited an opposite trend, although the relationships
were not significant for F. mandshurica and A. mono. The inconsistent
responses of leaf NRE of different species to increasing altitude were
primarily due to the effect of leaf Glutamate dehydrogenase (GDH), an
enzyme responsible for N translocation. Leaf GDH activity in senescing
leaves explained the variation of NRE more than soil and climate factors
did, suggesting that different plant species had different physiological
regulation strategies for their N conservation under similar environment.
4. Synthesis. Our study highlights the role of leaf enzyme as a pivotal
regulator of leaf NRE and helps us better understand and predict N cycling
under climate change in forest ecosystems.