Leaf internal diffusion conductance limits photosynthesis more strongly in older leaves of Mediterranean evergreen broad‐leaved species

Abstract

Leaf age-dependent changes in structure, nitrogen content, internal mesophyll diffusion conductance ( g m ), the capacity for photosynthetic electron transport ( J max ) and the maximum carboxylase activity of Rubisco ( V cmax ) were investigated in mature non-senescent leaves of Laurus nobilis L., Olea europea L. and Quercus ilex L. to test the hypothesis that the relative significance of biochemical and diffusion limitations of photosynthesis changes with leaf age. The leaf life-span was up to 3 years in L. nobilis and O. europea and 6 years in Q. ilex . Increases in leaf age resulted in enhanced leaf dry mass per unit area ( M A ), larger leaf dry to fresh mass ratio, and lower nitrogen contents per dry mass ( N M ) in all species, and lower nitrogen contents per area ( N A ) in L. nobilis and Q. ilex . Older leaves had lower g m , J max and V cmax . Due to the age-dependent increase in M A , mass-based g m , J max and V cmax declined more strongly (7-to 10-fold) with age than area-based (5-to 7-fold) characteristics. Diffusion conductance was positively associated with foliage photosynthetic potentials. However, this correlation was curvilinear, leading to lower ratio of chloroplastic to internal CO 2 concentration ( C c / C i ) and larger drawdown of CO 2 from leaf internal air space to chloroplasts ( D D D D C ) in older leaves with lower g m . Overall the agedependent decreases in photosynthetic potentials were associated with decreases in N M and in the fraction of N in photosynthetic proteins, whereas decreases in g m were associated with increases in M A and the fraction of cell walls. These age-dependent modifications altered the functional scaling of foliage photosynthetic potentials with M A , N M , and N A . The species primarily differed in the rate of agedependent modifications in foliage structural and functional characteristics, but also in the degree of agedependent changes in various variables. Stomatal openness was weakly associated with leaf age, but due to species differences in stomatal openness, the distribution of total diffusion limitation between stomata and mesophyll varied among species. These data collectively demonstrate that in Mediterranean evergreens, structural limitations of photosynthesis strongly interact with biochemical limitations. Age-dependent changes in g m and photosynthetic capacities do not occur in a co-ordinated manner in these species such that mesophyll diffusion constraints curb photosynthesis more in older than in younger leaves.

Needle age dependence of photosynthesis along a light gradient within an Abies alba crown

“…Increasing needle tissue density has lowered CO 2 concentration in intercellular spaces and probably increases mesophyll resistance to CO 2 that leads to a reduction of PNUE with A. alba needle age (Niinemets et al 2005(Niinemets et al , 2006. The other authors showed that mesophyll (internal) conductance to CO 2 (g i ) was correlated with the surface area of chloroplasts exposed to intercellular air space and g i decreased with leaf age which might also be expected in our study tree (Hanba et al 2001;Miyazawa and Terashima 2001).…”

Two tropical conifers show strong growth and water-use efficiency responses to altered CO2concentration

“…While limited stomatal conductance is widely recognized to limit photosynthetic rate, Niinemets et al (2011) reviewed the effects of mesophyll conductance in plants and highlighted the limited internal diffusion conductance of sclerophyllous plants, including conifers, as providing a constraint to photosynthetic rate that can be as large as that due to stomatal conductance. Reduced mesophyll conductance in sclerophyllous plants is in turn attributable to greater investment in support tissue, particularly thicker cell walls, associated with greater leaf longevity (Niinemets et al, 2005). Low mesophyll conductance has been observed in the New Zealand podocarp Dacrydium cupressinum, to the extent that the diffusive constraint on photosynthesis imposed by mesophyll exceeded that imposed by stomata (DeLucia et al, 2003).…”

Stomatal and non-stomatal limitations on leaf carbon assimilation in beech (Fagus sylvatica L.) seedlings under natural conditions

“…Technical advances in the measurement of gas exchange and fluorescence, and isotopic techniques, have provided more-accurate means to assess successive resistances across the entire CO 2 diffusion pathway through the leaf, prompting their importance for carbon uptake to be reconsidered Ennahli and Earl, 2005;Warren, 2006). In this context, it is important to elucidate the changes in biochemical factors and diffusion resistances during photosynthesis when plants are submitted to naturally stressful conditions, such as drought (Niinemets et al, 2005;Galmés et al, 2007;Flexas et al, 2009). This dual limitation influences the potential of seedlings to maintain a positive leaf carbon balance, and should be accounted for when assessing the ultimate consequences of water stress on ecological succession and niche partitioning under sub-Mediterranean environments (Kunstler et al, 2005;Robson et al, 2009).…”