Interactive effects of irradiance and water availability on the photosynthetic performance of Picea sitchensis seedlings: implications for seedling establishment under different management practices

Abstract

-The impact of water availability on the photosynthetic performance of three year old, commercially obtained, Sitka spruce (Picea sitchensis) seedlings under exposed and shaded conditions was evaluated to provide a physiological understanding of the factors controlling seedling performance under conventional and continuous cover forestry (CCF) management scenarios. Decreases in photosynthesis in response to water deficits, under exposed and shaded conditions, were associated with reductions in both stomatal (G s ) and mesophyll conductance (G m ), and an increase in the proportion of electrons consumed in non-photosynthetic pathways. After re-watering, photosynthesis of plants subjected to higher irradiances was inhibited for up to 6 days due to high photorespiratory activity and damage to photosystem II. Waterlogged seedlings grown under both exposed and shaded conditions showed smaller decreases in photosynthesis that were also associated with an altered G s and G m , but no changes in chlorophyll fluorescence related parameters were observed. We conclude that the performance of seedlings will be more susceptible to management-related or environmentally-induced water deficits in exposed sites typical of temperate latitudes and may, therefore, be improved in CCF systems.continuous cover forestry / irradiance / water availability / photosynthesis Résumé -Interactions entre intensité lumineuse et disponibilité en eau sur la performance photosynthétique de plants de Picea sitchensis : implications sur le développement des plants selon leur différentes pratiques culturales. L'impact de la disponibilité en eau sur la performance photosynthétique de jeunes plants de Picea sitchensis, âgés de 3 ans d'origine commerciale sous conditions ensoleillées et ombragées fut évalué pour comprendre physiologiquement les facteurs contrôlant la performance des plants dans les conditions conventionnelles et de couvert forestier continu (continuous cover forestry, CCF). Les diminutions de la photosynthèse en réponse aux déficits hydriques sous conditions de plein ensoleillement et d'ombre étaient accompagnées de réductions des conductivités stomatique (G s ) et mésophyllienne (G m ) et d'une augmentation de la proportion d'électrons consommés par les activités non-photosynthétiques. Après réhydratation, la photosynthèse chez les plants soumis aux hautes intensités lumineuses restait limitée jusqu'à 6 jours à cause de l'importante activité photorespiratoire et des dommages subits par le PSII. En conditions inondées, les plantules cultivées sous ensoleillement et à l'ombre présentèrent de moindres réductions de leur photosynthèse qui étaient associées à des modifications de G s et G m , mais sans changement des paramètres de la fluorescence chlorophyllienne. Nous en concluons que la performance des plants est plus sensible aux déficits hydriques liés à la pratique culturale ou aux conditions environnementales dans les sites ensoleillés typiques des latitudes tempérées et peut donc être amélioré par l'emploi de systèmes CCF. c...

Extremely thick cell walls and low mesophyll conductance: welcome to the world of ancient living!

“…Flexas et al (2012) set an average g m slightly above 100 mmol m –2 s –1 for conifers, and studies have shown a wide variation from as low as 18 up to 110 mmol m –2 s –1 in evergreen gymnosperms (Warren et al , 2003; De Lucia et al , 2003; Manter and Kerrigan, 2004; Black et al , 2005; Mullin et al , 2009; Peguero-Pina et al , 2012, 2016). Accordingly, g m varied from 10 to 124 mmol m –2 s –1 in this study.…”

Implementing Continuous Cover Forestry in Planted Forests: Experience with Sitka Spruce (Picea Sitchensis) in the British Isles

“…These findings are in line with modelling predictions [53] which indicated that a minimum of 20% transmittance would be necessary for seedling survival under a canopy. The various trials also suggest that optimal conditions for early survival and growth of Sitka spruce seedlings are likely to be found in conditions of about 50-60% RLI, since under full light seedlings may suffer from frost damage [46] or from moisture stress due to higher evaporative demand [47]. The few comparisons of growth and survival of Sitka spruce and other species under a range of light conditions [46,49] tended to confirm the categorisation of Sitka spruce as having only intermediate shade tolerance.…”

“…Several studies have examined the survival and growth of Sitka spruce seedlings in relation to light climate [46][47][48][49][50][51][52]. These used a mixture of greenhouse and nursery studies or field trials of varying duration (Table 1) to try to determine the most favourable understorey environment for regenerating or under-planted seedlings.…”

Photosynthesis and photosynthetic efficiencies along the terrestrial plant’s phylogeny: lessons for improving crop photosynthesis

“…Concerning g m in particular, values had been reported for a single moss species (Hanson et al ., ), six liverwort species (Meyer et al ., ), a single pteridophyte species (Volkova et al ., ) and no single lycophyte species. Even for gymnosperms, the number of species for which g m had been determined was lower than 15 species (DeLucia et al ., ; Manter and Kerrigan, ; Black et al ., ; Peguero‐Pina et al ., ). Moreover, the mechanisms behind the observed g m had not been studied in any of these species, with the exception of two gymnosperms of the genus Abies , for which anatomical constraints to g m were reported (Peguero‐Pina et al ., ).…”