Tree differences in primary and secondary growth drive convergent scaling in leaf area to sapwood area across Europe

Abstract

Trees scale leaf (A ) and xylem (A ) areas to couple leaf transpiration and carbon gain with xylem water transport. Some species are known to acclimate in A : A balance in response to climate conditions, but whether trees of different species acclimate in A : A in similar ways over their entire (continental) distributions is unknown. We analyzed the species and climate effects on the scaling of A vs A in branches of conifers (Pinus sylvestris, Picea abies) and broadleaved (Betula pendula, Populus tremula) sampled across a continental wide transect in Europe. Along the branch axis, A and A change in equal proportion (isometric scaling: b ˜ 1) as for trees. Branches of similar length converged in the scaling of A vs A with an exponent of b = 0.58 across European climates irrespective of species. Branches of slow-growing trees from Northern and Southern regions preferentially allocated into new leaf rather than xylem area, with older xylem rings contributing to maintaining total xylem conductivity. In conclusion, trees in contrasting climates adjust their functional balance between water transport and leaf transpiration by maintaining biomass allocation to leaves, and adjusting their growth rate and xylem production to maintain xylem conductance.

Convergent xylem widening among organs across diverse woody seedlings

“…4). These findings are in agreement with previous studies focusing on adult plants (Waring et al, 1977;Coomes et al, 2008;Gleason et al, 2018;Petit et al, 2018). Natural selection endows plants with maximal transversal surface area per unit water volume (as in all exchange surfaces such as gills and blood capillaries); plants tend to maximize the number of the narrowest conduits in the terminus of the conductive system and ensure a constant conductance as the conductive stream grows longer, to retain their maximum photosynthetic productivity (West et al, 1999a,b;Sack et al, 2012).…”

Axial anatomy of the leaf midrib provides new insights into the hydraulic architecture and cavitation patterns of Acer pseudoplatanus leaves

“…The exponent of this relationship was significantly different from the one predicted by the WBE model (TCA∝ A leaf 1.13 ). Isometry between TCA and leaf area is a trait found in stems, branches, and leaves (Togashi et al , 2015; Fan et al , 2017; Petit et al , 2018), and the relationship between these two traits is used to understand the relationship between hydraulic capacity and photosynthesis (Petit et al , 2018).…”

Losing half the conductive area hardly impacts the water status of mature trees

“…In contrast to sporadic conduit failure by cavitation, cutting sapwood in half does reduce the potential conductive capacity across all conduit diameter classes, and thus, may represent a greater effective reduction of conductivity than under a drought-induced halving of conductivity (when flux is low and large vessels will quit first), because we also removed half of all smaller conduits that can be expected to remain intact under stress. Perhaps, branch xylem rather than trunk xylem represents a higher overall hydraulic constraint 16 , although this would be in conflict with the conservation of xylem cross-sectional area during branching (‘pipe model’ 25 ). A stem-cutting experiment in seedlings 26 revealed no effects on g and Ψ of transpiring leaves when branches were cut by up to 90%.…”