Differential response of leaf conductance, carbon isotope discrimination and water‐use efficiency to nitrogen deficiency in maritime pine and pedunculate oak plants

Abstract

SVMMARYGrowth, COj assimilation rate {A), leaf conductance {g), transpiration efficiency (W = ratio biomass production/plant water use) and carbon isotope discrimination (A) were assessed in maritime pine (Pinus pinaster Ait.) and pedunculate oak (Quercus robur L.) grown on a sand-peat mixture with three levels of fertilization : FlOO, optimal complete fertilization; F25, 25 "o of the optima! fertilizer supply; FO, no fertilization. Leaf phosphorus (P) and potassium (K) concentrations were affected little by the diminishing nutrient availability. Reduced fertilization decreased plant nitrogen (N) concentration in both species but leaf N concentration was less affected in oak than in pine. In pine W was markedly reduced in response to reduced leaf or whole plant N concentration, which was consistent with the sharp decrease also observed for plant intrinsic water-use efficiency (ratio A/g) both at the instantaneous (gas exchange data) and time-integrated (A/g derived from A measurements) levels. In this species, lowered W in the N deficient conditions was primarily associated with enhanced values of g. The existence of such a stomatal response pattern, confirmed by the increase in plant transpiration between FlOO and F25, has not been reported before. In oak, both A and g were decreased in F25 and FO as compared with FlOO. W was not affected -and instantaneous as well as time-integrated A/g values were oni}' slightly decreased -in relation to decreasing plant N concentration. For FlOO, no difference in W was noticed between pine and oak though the A values were 2-6°^ lower in oak. We speculate that this discrepancy was linked with higher plant-carbon losses through processes like respiration, fine-root mortality or root exudation in oak. The isotopic approach proved useful for assessing the effects of nutritional status on W^ but has to be used with caution w hen comparing different species.Key words: Pinuspinaster (maritime pine), Quercus robur [pedunculate o-dk), nitrogen deficiency, gas exchange and water-use efficiency, carbon isotope discrimination.

Effects of water supply on gas exchange in Pinus pinaster Ait. provenances during their first growing season

“…Moreover, it can be presumed that water use efficiency increases in response to leaf nitrogen content by the increase of mesophyl conductance, without stomatal conductance increase. This is the case sometimes [15,25], but not always [38]; even the response can depend on water availability conditions [17].…”

Phenotypic plasticity in Pinus pinaster δ13C: environment modulates genetic variation

“…Stomatal regulation plays a key role when water vapor pressure increases, but results in lower photosynthetic rates. Intrinsic water-use efficiency (WUE) or the ratio of total dry matter production to the total amount of transpiration during a certain carbon fixation period (Fischer and Turner, 1978), is a complex trait sometimes associated to the superior performance of genotypes in drought-prone environments (Sun et al, 1996), although there are evidences of the contrary (Guehl et al, 1995, Lauteri et al, 1997. WUE in maritime pine may vary with both, the environment (Nguyen-Queyrens * Corresponding author: lcorcuera@aragon.es et al, 1998) and the genetics of the species (Brendel et al, 2002).…”

The ?13C of Scots pine (Pinus sylvestris L.) needles: spatial and temporal variations

“…When photosynthesis is the main, direct source of carbon, stable carbon isotope composition (d 13 C) of conifer needles is a useful integrator of the long-term balance between photosynthetic capacity and stomatal conductance [13,26] and of intrinsic water use efficiency [16,37].…”