title: Developmental changes in mesophyll diffusion conductance and photosynthetic capacity under different light and water availabilities in Populus tremula: how structure constrains function.
abstract: Finite mesophyll diffusion conductance (g(m) ) significantly constrains net assimilation rate (A(n) ), but g(m)  variations and variation sources in response to environmental stresses during leaf development are imperfectly known. The combined effects of light and water limitations on g(m)  and diffusion limitations of photosynthesis were studied in saplings of Populus tremula L. An one-dimensional diffusion model was used to gain insight into the importance of key anatomical traits in determining g(m) . Leaf development was associated with increases in dry mass per unit area, thickness, density, exposed mesophyll (S(mes) /S) and chloroplast (S(c) /S) to leaf area ratio, internal air space (f(ias) ), cell wall thickness and chloroplast dimensions. Development of S(mes) /S and S(c) /S was delayed under low light. Reduction in light availability was associated with lower S(c) /S, but with larger f(ias)  and chloroplast thickness. Water stress reduced S(c) /S and increased cell wall thickness under high light. In all treatments, g(m)  and A(n)  increased and CO(2)  drawdown because of g(m) , C(i) -C(c) , decreased with increasing leaf age. Low light and drought resulted in reduced g(m)  and A(n)  and increased C(i) -C(c) . These results emphasize the importance of g(m)  and its components in determining A(n)  variations during leaf development and in response to stress.
authors: Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi 1, Tartu 51014, Estonia, Spain. tiina.tosens@emu.ee
authors: Tiina
authors: T
authors: Tosens
authors: Ulo
authors: U
authors: Niinemets
authors: Vivian
authors: V
authors: Vislap
authors: Hillar
authors: H
authors: Eichelmann
authors: Pilar
authors: P
authors: Castro Díez
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D003681:Dehydration; D004058:Diffusion; D008027:Light; D058503:Mesophyll Cells / Q000378:metabolism; D008954:Models, Biological; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects / Q000648:ultrastructure; D054046:Plant Stomata / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology*; D032107:Populus / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects / Q000648:ultrastructure; D013312:Stress, Physiological / Q000502:physiology*; D013997:Time Factors; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water; D002245:Carbon Dioxide