Endogenous sink–source interactions and soil nitrogen regulate leaf life‐span in an evergreen shrub

Abstract

Summary• How the balance between exogenous and endogenous nitrogen for shoot growth varies with soil nitrogen availability, and its consequences on leaf life-span, have rarely been studied within a single species in the field.• In this study, we investigated two Rhododendron ferrugineum populations with contrasting leaf life-span. Soil nitrogen availability and nitrogen resorption of different leaf age classes were assessed, as were the interactions between plant compartments, using 15 N labelling and sink organ suppression.• The population growing on poorer soil had a shorter leaf life-span (17.9 vs 21.5 months) and a higher net contribution of leaf reserves to shoot growth (32% vs 15%), achieved by faster nitrogen resorption and greater shedding of young nitrogen-rich leaves. For both populations, wood contributed to over 40% of shoot nitrogen demand. Both the negative relationship between current-year shoot mass and the percentage of 1-yr-old attached leaves and the delay of leaf shedding after bud removal suggest that shoot development has a strong effect on leaf life-span.• Our results suggest that, contrary to the evolutionary response, plastic response to low soil nitrogen could reduce leaf life-span in evergreen plants. In addition, leaf life-span seems to be strongly influenced by the discrepancy between shoot nitrogen demand and soil nitrogen uptake rather than nitrogen demand alone.Abbreviations: ALx, attached/green leaves of the xth age cohort (0, 1, 2, 3 yr); DLx, dead/fallen leaves of the xth age cohort (0, 1, 2, 3 yr); LLS, leaf life-span (months); LMA, leaf mass area; MRT, mean residence time; N mass , nitrogen content [g (g DW −1 )]; NR, nitrogen resorption of ALx (g g −1 ); R EFF , nitrogen resorption efficiency (g g −1 ).

Mean residence time of leaf number, area, mass, and nitrogen in canopy photosynthesis

“…Shorter leaf longevities in plants growing under conditions of high N availability have been reported in many studies (Shaver 1983;Harper 1989;Lajtha and Whitford 1989;Cordell et al 2001;Kazakou et al 2007; but see Marty et al 2009;Pornon et al 2011). For example, Ackerly and Bazzaz showed in the study cited above that a high-N treatment decreased leaf longevity although it increased the number of leaves produced.…”

“…It is therefore even more interesting and important that the MRT of leaf N was much longer than leaf longevity. The reason for this was that a large fraction of leaf N was resorbed through the process of leaf senescence to be used for constructing new leaves (Small 1972;Aerts 1996;Killingbeck 1996;Eckstein et al 1999;Aerts and Chapin 2000;Marty et al 2009). Peak N concentration usually occurs when leaves reach full maturation, with a gradual decrease in N concentration thereafter (Thomas and Stoddart 1980;Ono et al 1996;Oikawa et al 2006;Marty et al 2009; but see Escudero and Mediavilla 2003).…”

Rubber Trees Demonstrate a Clear Retranslocation Under Seasonal Drought and Cold Stresses

“…It has been suggested that increased nutrient retranslocation can increase plant fitness, and as such, it is a major nutrient-conservation mechanism (Chapin, 1980; Chabot and Hicks, 1982; Aerts, 1990, 1996), especially in nutrient-poor environments (Berendse and Aerts, 1987; May and Killingbeck, 1992; Grime, 2001; Gloser, 2005; Marty et al, 2009). …”

Photosynthetic ecophysiology of evergreen leaves in the woody angiosperms – a review

“…Leaf life span may be shortened in plants growing on nitrogen-poor soils (e.g. by 3.5 months in Rhododendron ferrugineum; Marty et al 2009) as the onset of leaf abscission may be induced by the demand for nitrogen from growing parts (Ono et al 2001;Oleksyn et al 2003;Marty et al 2009). In intraspecific and biogeographic analyses, evergreen habit and extended life span are associated with poor nutrient availability (Monk 1966;Givnish 2002;Wright et al 2002) and low temperature van Ommen Kloeke et al 2012).…”