Decline in photosynthetic nitrogen use efficiency with leaf age and nitrogen resorption as determinants of leaf life span

Abstract

Summary 1Cost-benefit models predict that leaf life span depends on its initial photosynthetic rate and construction cost and on the rate of decline in photosynthesis with age. Leaf gas exchange rates and N contents were measured in nine woody evergreen Mediterranean species with different leaf life spans to determine the effects of leaf ageing on photosynthetic N use efficiency (PNUE). N costs of leaf construction were assumed to be in part dependent on N resorption from senescing leaves. 2 Leaf ageing had significant negative effects on photosynthetic rates per unit leaf area. As N content per unit leaf area did not decline until the end of leaf life, PNUE also decreased with age. PNUE generally declined faster in species with a shorter leaf life span. There were no significant interspecific differences in maximum CO 2 assimilation rates per unit leaf area and in N resorption that could be related to differences in leaf life span. 3 As PNUE decreases with leaf age, shedding of the older leaves and retranslocation of N to the current year's leaf biomass would result in an increase in the mean instantaneous efficiency of use of the N retranslocated. However, total CO 2 assimilation can be improved by such shedding only when the increase in the efficiency of use of the remobilized N compensates for the remaining N lost in the shed leaves. 4 The photosynthesis of the old leaf cohorts exceeded the increase in photosynthesis that would be obtained from the N retranslocated to the younger leaves, given the observed efficiencies of N resorption. The retention of old leaves thus resulted in a higher whole-canopy CO 2 assimilation, despite their low PNUE.

Age-related nutrient content and carbon isotope composition in the leaves and branches of Quercus aquifolioides along an altitudinal gradient

“…2. Although it has been suggested that NUE declines with the age of tissue (Escudero and Mediavilla 2003), we observed a slight increase in NUE with aging. This ensemble of age effects is consistent with the hypothesis that tissue aging not only represents deterioration, but also resource redistribution (Field and Mooney 1983).…”

Nitrogen resorption and photosynthetic activity over leaf life span in an evergreen shrub, Rhododendron ferrugineum, in a subalpine environment

“…Total N and 15 N compartment analysis revealed that more than two-thirds of N remobilization in attached leaves of young R. ferrugineum occurred during the first 12 months of their life and that the remobilized N was mainly directed towards new shoots. That resorption is not a mechanism principally linked to leaf shedding but mainly occurs in healthy leaves agrees with the findings of Chabot & Hicks (1982) and Nambiar & Fife (1991) but is opposed to those of Escudero & Mediavilla (2003) and Wright & Westoby (2003). Our results show, for the first time to our knowledge, that: (i) N resorption is higher in shed than in attached leaves only in the second year of their life span; and (ii) N resorption increased with ageing in leaves older than 1 yr.…”

“…For instance, leaf photosynthetic capacity remains relatively high in 1-and 2-yr-old leaves (75% of the maximum) despite a decrease of c. 33% of leaf N. This suggests that PNUE remained high in old R. ferrugineum leaves, which disagrees with other findings (Garnier & Aronson, 1998) and (Kitajima et al, 1997;Escudero & Mediavilla, 2003).…”

Interactions between leaf nitrogen status and longevity in relation to N cycling in three contrasting European forest canopies

“…70 %), whereas the Douglas fir stand had a re-translocation efficiency of only 37 %, meaning that it relocated only 53 % as efficiently as the two other species (Table 2). Inclusion of data on the N re-translocation efficiency from previously published studies (Staaf, 1982;Son and Gover, 1991;Näsholm et al, 1994;Reich et al, 1995;Escudero and Mediavilla, 2003) revealed that the longer the needles stayed green, the lower the N retranslocation efficiency (η r ) was (Fig. 5).…”

“…In deciduous canopies, leaves can develop according to the local conditions which may vary little over the course of a Näsholm (1994) was assumed to be the same as that for P .s. in Escudero and Mediavilla (2003). year. In conifer canopies, leaves live longer and thus their relative position in the crown can change due to growth of new branches in the top.…”