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

Abstract

Limitations to diffusion and biochemical factors affecting leaf carbon uptake were analyzed in young beech seedlings (Fagus sylvtica L.) growing in natural gaps of a beech-wood at the southern limit of the species. Half of the seedlings received periodic watering in addition to natural rainfall to reduce the severity of the summer drought. Plant water status was evaluated by measuring predawn water potential. Basic biochemical parameters were inferred from chlorophyll fluorescence and photosynthesis-CO 2 curves (A-C c ) under saturating light. The curves were established on three dates during the summer months. The main variables studied included: stomatal and mesophyll conductance to CO 2 (g s and g m respectively), maximum velocity of carboxylation (V cmax ) and maximum electron transport capacity (J max ). The g m was estimated by two methodologies: the curve-fitting and J constant methosds.Seedlings withstood moderate water stress, as the leaf predawn water potential (Ψ pd ) measured during the study was within the range -0.2 to -0.5 MPa. Mild drought caused g s and g m to decrease only slightly in response to Ψ pd . However both diffusional parameters explained most of the limitations to CO 2 uptake. In addition, it should be highlighted that biochemical limitations, prompted by V cmax and J max , were related mainly to ontogenic factors, without any clear relationship with drought under the moderate water stress experienced by beech seedlings through the study.The results may help to further understanding of the functional mechanisms influencing the carbon fixation capacity of beech seedlings under natural conditions. Key words: diffusion limitations; stomatal conductance; mesophyll conductance; photosynthesis; drought; regeneration. Resumen Limitaciones estomáticas y no-estomáticas en la asimilación foliar de carbono en brinzales de haya (Fagus sylvatica L.) bajo condiciones naturalesLas limitaciones a la difusión de CO 2 y los factores bioquímicos que afectan la captura foliar de carbono fueron analizadas en jóvenes brinzales de haya (Fagus sylvtica L.) que crecían en un claro de un hayedo en el límite Sur de la distribución de la especie. La mitad de los brinzales recibieron periódicamente un riego adicional a la lluvia caída durante el verano con el objeto de minimizar la sequía estival. El grado de estrés hídrico soportado por las plantas fue evaluado a través de la medida del potencial hídrico al pre-alba (Ψ pd ). Los parámetros funcionales básicos que condicionan la fijación de carbono fueron inferidos a través de curvas de respuesta bajo luz saturante en las que se relaciona la tasa neta de fotosíntesis (A), y la concentración de CO 2 en el interior de los cloroplastos (C c ), en conjunción con medidas de fluorescencia de la clorofila. Dichas curvas se elaboraron en tres momentos a lo largo de los meses de verano, infiriéndose de las mismas: las conductancias estomáticas y del mesófilo al CO 2 (g s y g m respectivamente), la velocidad máxima de carboxilación (V cmax ) y la tasa máxima de tr...

Resilient Leaf Physiological Response of European Beech (Fagus sylvatica L.) to Summer Drought and Drought Release

“…Leaf physiological responses were observed first for stomatal conductance ( g S ), intercellular CO 2 concentration ( c i ) and net-photosynthesis ( A N ), which started to decrease when ψ pd dropped below -0.6 MPa. Previous studies on beech showed similar responses of g S and A N to decreasing ψ pd , suggesting that a ψ pd of around -0.6 MPa represents a general threshold for drought effects on beech leaf gas exchange ( Aranda et al, 2012 ; Cocozza et al, 2016 ).…”

Seedlings from marginal and core populations of European beech (Fagus sylvatica L.) respond differently to imposed drought and shade

“…• The degree of stress tolerance might also reflect likelihood to migrate to higher elevations under climate change; a scenario sometimes predicted for beech populations (Sabaté et al 2002). Low photosynthetic rates and stomatal conductances under stressful summer conditions, of high evaporative demand and low soil moisture, have previously been reported for northern range-edge provenances compared to the other beech populations (Aranda et al 2012;Robson et al 2012;Sánchez-Gómez et al 2013). Hence, we expected the provenance from the northern range margin to have the lowest capacity to cope with drought stress during this experiment, reflected in lower photosynthetic rates in the sun and poorest control of water loss in general (Hypothesis 3).…”

Effects of drought on mesophyll conductance and photosynthetic limitations at different tree canopy layers

“…; Aranda et al . ). Sessile oaks had higher (less negative) Ψ pd than beech trees, suggesting sessile oak trees were able to extract water from deeper soil layers and hence were less affected by summer shortage of rainfall (Leuschner et al .…”

“…Nevertheless, the biochemistry related with carbon fixation, that is estimated through V Cmax , was unaffected by water stress, as recently shown in beech seedlings (Aranda et al . ).…”