Letting Leaves Live Longer

Leaf longevity is an important plant trait associated with diverse aspects of plant function and life history, contributing to characteristic patterns of material cycling and energy flow in ecosystems. A large number of studies have shown that leaf longevity is intimately associated with leaf nitrogen (N) concentration, and that soil N addition often leads to shortened leaf longevities. Leaf longevity is thought to decrease with increased N availability because nitrogen promote photosynthesis. Despite this, we know little about the biochemical mechanisms underlying N-dependent leaf longevity. And increasing N availability does not always result in reduced leaf longevity.

Ethylene has long been recognized as a key plant hormone involved in leaf senescence and defoliation. Ethylene production from plants responds to various abiotic and biotic stresses. Nitrogen-induced ethylene production may be behind N-dependent changes in leaf longevity.

As the dominant vegetation type in the semiarid regions of Eurasia, the temperate steppe of Inner Mongolia in northern China is reported to be sensitive to environmental change. As N is one of the key limiting factors for plant growth in this area, projected increases in N deposition will presumably impact plant physiological process. A recent paper in Annals of Botany explores the role of ethylene in the mechanisms underlying how N addition decreases leaf longevity. Three main results emerged: (1) N addition enhanced leaf ethylene production; (2) increased leaf ethylene production was associated with decreased leaf longevity; and (3) N addition reduced leaf longevity mainly through altering leaf ethylene production. This study has produced the first experimental evidence that ethylene modulates the N-induced decrease in leaf longevity, providing a novel yet intuitive explanation for a widely observed ecological phenomenon.

Ren, H., Xu, Z., Zhang, W., Jiang, L., Huang, J., Chen, S., Wang, L. & Han, X. (2013. Linking ethylene to nitrogen-dependent leaf longevity of grass species in a temperate steppe. Annals of Botany, 112(9), 1879-1885.
Leaf longevity is an important plant functional trait that often varies with soil nitrogen supply. Ethylene is a classical plant hormone involved in the control of senescence and abscission, but its role in nitrogen-dependent leaf longevity is largely unknown. Pot and field experiments were performed to examine the effects of nitrogen addition on leaf longevity and ethylene production in two dominant plant species, Agropyron cristatum and Stipa krylovii, in a temperate steppe in northern China. Nitrogen addition increased leaf ethylene production and nitrogen concentration but shortened leaf longevity; the addition of cobalt chloride, an ethylene biosynthesis inhibitor, reduced leaf nitrogen concentration and increased leaf longevity. Path analysis indicated that nitrogen addition reduced leaf longevity mainly through altering leaf ethylene production. These findings provide the first experimental evidence in support of the involvement of ethylene in nitrogen-induced decrease in leaf longevity.