C. Lambrot

A single‐substrate model to interpret intra‐annual stable isotope signals in tree‐ring cellulose

The carbon and oxygen stable isotope composition of wood cellulose (delta(13)C(cellulose) and delta(18)O(cellulose), respectively) reveal well-defined seasonal variations that contain valuable records of past climate, leaf gas exchange and carbon allocation dynamics within the trees. Here, we present a single-substrate model for wood growth to interpret seasonal isotopic signals collected in an even-aged maritime pine plantation growing in South-west France, where climate, soil and flux variables were also monitored. Observed seasonal patterns in delta(13)C(cellulose) and delta(18)O(cellulose) were different between years and individuals, and mostly captured by the model, suggesting that the single-substrate hypothesis is a good approximation for tree ring studies on Pinus pinaster, at least for the environmental conditions covered by this study. A sensitivity analysis revealed that the model was mostly affected by five isotopic discrimination factors and two leaf gas-exchange parameters. Modelled early wood signals were also very sensitive to the date when cell wall thickening begins (t(wt)). Our model could therefore be used to reconstruct t(wt) time series and improve our understanding of how climate influences this key parameter of xylogenesis.

Manipulating nutrient and water availability in a maritime pine plantation: effects on growth, production, and biomass allocation at canopy closure

Abstract• We present here the results of a water and nutrient manipulation experiment in a five-year-old plantation of maritime pine in south-western France.• Water and nutrient levels were manipulated in a factorial design with two levels of irrigation (control receiving only rainfall (C) and irrigated (I)) and three levels of fertilisation (control with no added nutrients (C), P-only (P) and annual addition of a complete nutrient mix (F)) in order to quantify growth limitations of plantation forest in this particular area.• The treatments applied during five years increased aboveground biomass annual increment by 4% (I) to 58% (IF) with respect to the control (C). The fertilised plots had a slightly non-significant lower root-to-shoot ratio. The effect of irrigation was maximal in 2002, resulting in 6%, 7% and 12% higher growth rate on the F, C and P plots, respectively. A windstorm disturbed the experiment in 1999 and has affected preferentially the fertilised plots, with IF plots displaying 60% damage.• The higher growth rate of fertilised and irrigated plots was attributed to both an increase (estimated at 5 to 15%) in the amount of light absorbed by the canopy, and an increase (estimated at 26% for IF plots) in the amount of above-ground biomass produced annually per unit leaf area.Résumé• Dans l’objectif de quantifier l’impact des facteurs limitant de la croissance du pin maritime dans le sud-ouest de la France, les apports d’eau et d’éléments minéraux sont manipulés selon un schéma expérimental factoriel à deux niveaux d’alimentation en eau (témoin recevant uniquement les pluies et irrigué) et à trois niveaux d’alimentation minérale (témoin, apport annuel de phosphore, apport annuel d’un mélange minéral complet).• Les traitements appliqués pendant cinq ans ont entrainé une augmentation de l’accroissement annuel en biomasse aérienne allant de +4 % (I) à + 58 % (IF). Les arbres fertilisés ont un rapport biomasse aérienne sur racinaire légèrement mais non significativement supérieur à celui des arbres témoins. L’effet de l’irrigation a été maximal en 2002, avec des accroissements en biomasse aérienne plus élevés de 6 %, 7 %, 12 % pour les arbres fertilisés, témoins et fertilisés en P. Une tempête a endommagé le dispositif en 1999, affectant préférentiellement les arbres fertilisés avec 60 % des arbres touchés, contre 13 % pour les témoins.• La plus forte croissance observée pour les placeaux fertilisés et irrigués a été attribuée à une augmentation d’une part de +5 à +15 % de la quantité de rayonnement absorbé par la canopée, et d’autre part de +26 % de la quantité de biomasse aérienne produite annuellement par unité d’indice foliaire.

Growth and uptake of mineral elements in response to sodium chloride of three provenances of maritime pine 1

Abstract Effect of sodium chloride (NaCl) on the growth, mineral concentration, and net accumulation of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) was established in one‐year‐old seedlings (Iberique, Landais, Tamjoute provenances) grown in a regulated greenhouse in nutrient solutions. Increasing concentration of NaCl induces a reduced rate of growth and the Iberique provenance was most affected. Accumulation of Na is significantly more intense in the Tamjoute provenance irrespective of the growth response. Macronutrient concentration are markedly modified, as a result of salinity, by increases in the N and K concentrations and decreases in P, Ca and Mg concentrations in the root. The nutrient concentrations in the tissues did not appear to become deficient or toxic under these saline conditions. Total accumulation of most ions was reduced as a consequence of relative growth and provide a good indication of geographic provenance response. The results presente...

Carbon stable isotope ratio of phloem sugars in mature pine trees throughout the growing season: comparison of two extraction methods

The study presents a comparison of two phloem sugar extraction methods. The amount of phloem sugar extracted and the carbon isotope composition (delta(13)C) of the total extracts and of the main phloem compounds separated by high-performance liquid chromatography (sucrose, glucose, fructose and pinitol) are compared. These two phloem sap extraction methods are exudation in distilled water and a new method using centrifugation, which avoids the addition of any solvent. We applied both extraction methods on phloem discs sampled from 38-year-old Pinus pinaster trees in south-western France throughout the period from June 2007 to December 2008 on different time-scales: hourly, daily and monthly. We found that the centrifugation method systematically extracted ca. 50% less compounds from the phloem discs than the exudation method. In addition, the two extraction methods provided similar delta(13)C values of the total extracts, but the values obtained by the exudation method were 0.6 per thousand more negative than those calculated from the mass balance using the individual constituents. Over the growing season, both extraction methods exhibited lower total sugar content and more (13)C-enriched phloem sap in summer compared with winter values. These findings suggest that both extraction methods can be applied to study the carbon isotope composition of phloem sap, and the centrifugation method has the advantage that no solvent has to be added. The exudation method, however, is more appropriate for the quantification of the amounts of phloem sugars.

Micronutrient composition of xylem sap and needles as a result of P-fertilization in maritime pine

Xylem sap and foliar compositions (P, Cu, Zn, Mn) were examined over 4 months in control and P-fertilized maritime pine in a 7-year-old plantation. The absorption of copper, zinc, and boron appears to be reduced by phosphate fertilization. Manganese concentrations are positively related to P-supply increase. Foliar analysis and sap provides the same type of information in terms of antagonism or synergism between elements but the response to treatment is more often significant with sap throughout the seasons and is completely non-existent on a single classical autumn diagnosis with foliar concentration (i.e. Zn and Cu). In consequence foliar analysis is not sensitive enough for copper or zinc deficiency diagnoses in young plantations where nutritional growth disorders appear in a short period of spring, and xylem chemistry appears to be a convenient tool in monitoring micronutrient disorders in pine plantations.

Using a dune forest as a filtering ecosystem for water produced by a treatment plant – One decade of environmental assessment

A dune forest in SW France composed of maritime pines was irrigated with treated wastewater for a decade in an experiment (including irrigated plots versus control plots) to evaluate the environmental impact of applying wastewater on the water table, soil properties, and plants. The amount of treated wastewater (1921 mm yr-1) applied was twice the annual precipitation. Nutrient inputs were also very high, particularly nitrogen (N: 539 kg-N ha-1 yr-1), phosphorus (P: 102 kg-P ha-1 yr-1), and calcium (Ca: 577 kg-Ca ha-1 yr-1). Irrigation caused a rise in the water table, and increased its sodium (Na), NO3-, potassium (K), and calcium concentrations. Soil properties were affected by irrigation at least down to a depth of 1.2 m. After eight years of irrigation, soil pH had increased by 1.4 units, and soil available P content (POlsen) increased nearly 8-fold. In the short-term (i.e. 1-3 years), irrigation with treated wastewater improved growth, standing biomass, and the nutritional status of the vegetation. But tree dieback started in the fourth year of irrigation and worsened until the end of the monitoring period when almost all the irrigated trees were dead or moribund. The understory composition was drastically modified by irrigation, with an increase in α-biodiversity and in the biomass of herbaceous species, and a reduction in woody species abundance. The factor that best explained tree dieback was manganese nutrition (Mn): (i) the Mn content of the tree foliage was negatively affected by irrigation and below the deficiency values reported for pine species, and (ii) soil available Mn (CaCl2 extraction) decreased by half in the topsoil layer. Manganese deficiency was probably the consequence of the increase in soil pH, which in turn reduced soil Mn availability. Tree dieback was not related to either to a macronutrient deficiency or to toxicity caused by a trace element.