Dominique Gerant - Academia.edu (original) (raw)

Papers by Dominique Gerant

New Phytologist, 2011

• Phloem is the main pathway for transferring photosynthates belowground. In situ 13 C pulse labe... more • Phloem is the main pathway for transferring photosynthates belowground. In situ 13 C pulse labelling of trees 8-10 m tall was conducted in the field on 10 beech (Fagus sylvatica) trees, six sessile oak (Quercus petraea) trees and 10 maritime pine (Pinus pinaster) trees throughout the growing season. • Respired 13 CO 2 from trunks was tracked at different heights using tunable diode laser absorption spectrometry to determine time lags and the velocity of carbon transfer (V). The isotope composition of phloem extracts was measured on several occasions after labelling and used to estimate the rate constant of phloem sap outflux (k P). • Pulse labelling together with high-frequency measurement of the isotope composition of trunk CO 2 efflux is a promising tool for studying phloem transport in the field. Seasonal variability in V was predicted in pine and oak by bivariate linear regressions with air temperature and soil water content. V differed among the three species consistently with known differences in phloem anatomy between broadleaf and coniferous trees. • V increased with tree diameter in oak and beech, reflecting a nonlinear increase in volumetric flow with increasing bark cross-sectional area, which suggests changes in allocation pattern with tree diameter in broadleaf species. Discrepancies between V and k P indicate vertical changes in functional phloem properties.

Tree Physiology, 2015

Potassium (K) is an important limiting factor of tree growth, but little is known of the effects ... more Potassium (K) is an important limiting factor of tree growth, but little is known of the effects of K supply on the long-distance transport of photosynthetic carbon (C) in the phloem and of the interaction between K fertilization and drought. We pulse-labelled 2-year-old Eucalyptus grandis L. trees grown in a field trial combining K fertilization (+K and -K) and throughfall exclusion (+W and -W), and we estimated the velocity of C transfer by comparing time lags between the uptake of (13)CO2 and its recovery in trunk CO2 efflux recorded at different heights. We also analysed the dynamics of the labelled photosynthates recovered in the foliage and in the phloem sap (inner bark extract). The mean residence time of labelled C in the foliage was short (21-31 h). The time series of (13)C in excess in the foliage was affected by the level of fertilization, whereas the effect of throughfall exclusion was not significant. The velocity of C transfer in the trunk (0.20-0.82 m h(-1)) was twice as high in +K trees than in -K trees, with no significant effect of throughfall exclusion except for one +K -W tree labelled in the middle of the drought season that was exposed to a more pronounced water stress (midday leaf water potential of -2.2 MPa). Our results suggest that besides reductions in photosynthetic C supply and in C demand by sink organs, the lower velocity under K deficiency is due to a lower cross-sectional area of the sieve tubes, whereas an increase in phloem sap viscosity is more likely limiting phloem transport under drought. In all treatments, 10 times less (13)C was recovered in inner bark extracts at the bottom of the trunk when compared with the base of the crown, suggesting that a large part of the labelled assimilates has been exported out of the phloem and replaced by unlabelled C. This supports the &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;leakage-retrieval mechanism&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; that may play a role in maintaining the pressure gradient between source and sink organs required to sustain high velocity of phloem transport in tall trees.

Annales des Sciences Forestières, 1996

... Indeed, Sheen (1990) demonstrated that, in photosynthetic cells, these sugars control the exp... more ... Indeed, Sheen (1990) demonstrated that, in photosynthetic cells, these sugars control the expression of the nuclear-encoded gene of the small subunit of Rubisco (rbcS). Moreover, abundant bio-chemical and molecular evidences ...

Water, Air, & Soil Pollution, 2011

We present here the effects of ambient ozone (O3)-induced decline in carbon availability, acceler... more We present here the effects of ambient ozone (O3)-induced decline in carbon availability, accelerated foliar senescence, and a decrease in aboveground biomass accumulation in the Aleppo pine (Pinus halepensis Mill.). Aleppo pine seedlings were continuously exposed in open-top chambers for 39 months to three different types of O3 treatments, which are as follows: charcoal-filtered air, nonfiltered air (NFA), and nonfiltered air

Tree Physiology, 2008

Soil nitrogen can alter storage and remobilization of carbon and nitrogen in forest trees and aff... more Soil nitrogen can alter storage and remobilization of carbon and nitrogen in forest trees and affect growth responses to elevated carbon dioxide concentration ([CO 2 ]). We investigated these effects in oak saplings (Quercus robur L.) exposed for two years to ambient or twice ambient [CO 2 ] in combination with low-(LN, 0.6 mmol N l -1 ) or high-nitrogen (HN, 6.1 mmol N l -1 ) fertilization. Autumn N retranslocation efficiency from senescing leaves was less in HN saplings than in LN saplings, but about 15% of sapling N was lost to the litter. During the dormant season, nonstructural carbohydrates made up 20 to 30% of the dry mass of perennial organs. Starch was stored mainly in large roots where it represented 35-46% of dry mass. Accumulation of starch increased in large roots in response to LN but was unaffected by elevated [CO 2 ]. The HN treatment resulted in high concentrations of N-soluble compounds, and this effect was reduced by elevated [CO 2 ], which decreased soluble protein N (-17%) and amino acid N (-37%) concentrations in the HN saplings. Carbon and N reserves were labeled with 13 C and 15 N, respectively, at the end of the first year. In the second year, about 20% of labeled C and 50% of labeled N was remobilized for spring growth in all treatments. At the end of leaf expansion, 50-60% of C in HN saplings originated from assimilation versus only 10-20% in LN saplings. In HN saplings only, N uptake occurred, and some newly assimilated N was allocated to new shoots. Through effects on the C and N content of perennial organs, elevated [CO 2 ] and HN increased remobilization capacity, thereby supporting multiple shoot flushes, which increased leaf area and subsequent C acquisition in a positive feedback loop.

Physiologia Plantarum, 1999

determined by the decrease in the large subunit (LSU). On the The effects of ozone exposure on ca... more determined by the decrease in the large subunit (LSU). On the The effects of ozone exposure on carbon-fixation-related processes in Pinus halepensis Mill. needles were assessed over 3 other hand, 200-ppb ozone fumigation induced a strong increase in both activity and quantity of another carboxylating months under controlled conditions. Ozone fumigation (200 ppb) did not induce a modification of either net CO 2 assimila-enzyme, phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), generally considered in C 3 plants to participate in tion or stomatal conductance in 1-year-old needles, whereas ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, carbon catabolism processes. Ozone induced a significant EC 4.1.1.39) activity was shown to be reduced by a half.

Physiologia Plantarum, 2000

Young trees of European beech (Fagus syl7atica L.) were phate carboxylase/oxygenase activity, whi... more Young trees of European beech (Fagus syl7atica L.) were phate carboxylase/oxygenase activity, while the summer and exposed in a phytotron to different levels of ozone and CO 2 early autumn harvests showed strong reductions in these under the climatic simulation of one vegetation period. High parameters. Only phosphoenolpyruvate carboxylase (PEPozone levels were simulated similar to high ozone concentra-case) activity remained higher under high ozone. The effects of high CO 2 appeared in general as a small stimulation in tion in the field (up to 110 ppb), while CO 2 was added as 300 ppm to the present level of ca 380 ppm. Our study describes enzyme activity like PEPcase in spring. However, with indifferent aspects of photosynthesis from the leaf level to the creasing time of fumigation, reductions of all parameters were observed. Especially chlorophylls showed strong reduc-reactions of selected thylakoid components at different hartions under high CO 2 . The combined treatment with high vest times during growth of the beech trees under the different fumigation regimes. Ozone effects appeared in the first weeks ozone plus high CO 2 resulted mostly in an amelioration of the of the treatment as a stimulation of chlorophyll fluorescence negative ozone effects, although control levels were not (F v /F m ), in oxygen production and in ribulose-1,5-bisphos-reached.

Physiologia Plantarum, 1993

1993 Physical, immunological and kinetic properties of ribulose-l,5-bisphosphate carboxylase/oxyg... more 1993 Physical, immunological and kinetic properties of ribulose-l,5-bisphosphate carboxylase/oxygetiase from fir (Abies alba) and spruce (Picea abies). -Physiol. Plant. 88: 113-122. Ribulose-1.5.^bisphosphate carboxylase/oxygenase {Rubisco; EC 4.1.1.39) from fir (Abies alba Mill.) and spruce (Picea abies [L.] Karst.) needles was purified to homogeneity. The enzyme was isolated from crude extracts through quantitative precipitation in 40-55% and 40-60% (NHJ^SOj for fir and spruce, respectively, followed by linear sucrose gradient centrifugation. Using two dimensional gel eiectrophoresis, the isoelectric points were determined. For the large subunit (LSU) it was 6.7 for both species, and for the small subunit (SSU) it was 7.1 and 7.7 for fir and spruce, respectively. Very few differences in tt7ptic peptides and amino acid composition of Rubisco LSU were observed between fir and spruce. By contrast, marked differences characterized the same analyses for the Rubisco SSU of the two species. Moreover, substitution of residues was observed in the sequenced N-terminal region when comparing fir and spruce SSU. The Ouchterlony technique showed no immunochemical difference between Rubisco of fir and spruce when a rabbit antiserum to spinach Rubisco was used. The Eadie-Hofstee plots of carboxyiase activity indicated that the apparent K^(CO;) were 31 and 36 uM for the fir and spruce enzymes, respectively.

Journal of Plant Physiology, 1984

The uncommon amino acid 3,4-dihydroxyphenylalanine (DOPA) was determined colorimetrically using i... more The uncommon amino acid 3,4-dihydroxyphenylalanine (DOPA) was determined colorimetrically using isonicotinic acid hydrazide (IAH) in the crude extracts obtained from fresh material of Vicia faba minor. DOPA was found to accumulate at concentrations inconsistent with its solubility in water. Other orthodiphenols do not interfere in DOPA determination. The accumulated DOPA was only of the L-form. The DOPA content in the dry material of Vicia faba was significantly lower than that from the corresponding fresh material, suggesting some kind of DOPA oxidation during drying. Subsequent analyses designed to evaluate the actual potential of V. faba minor in the accumulation of DOPA were performed with fresh material. It was observed that the DOPA concentration in the tissues of V. faba minor is reproducible when expressed on a fresh matter weight basis. In young seedlings L-DOPA production is significantly enhanced by light via an increased fresh matter yield. The DOPA content was found to be increased in mature plants grown on media enriched with low concentrations of NaCl (up to 25 mM) that showed a positive effect on their growth. NaCl induced an overproduction of L-DOPA even when growth was restricted by ion excess. On the contrary, the DOPA level dropped in mature plants submitted to water stress. Nodulated plants were found to contain higher content of L-DOPA than the non-nodulated ones grown with NO(3)(-) and NH(4)(+). It is suggested that DOPA hyperproduction by Vicia faba minor might be optimized by growing plants in mild saline conditions and by inoculating them with efficient salt tolerant strains of R. leguminosarum.

Journal of Plant Physiology, 1996

ABSTRACT Since several years, accelerated decline of Aleppo pine (Pinus halepensis) forests has b... more ABSTRACT Since several years, accelerated decline of Aleppo pine (Pinus halepensis) forests has been observed in mediterranean areas. In fact, the combination of various environmental factors (photochemical oxidants, drought, high light, ...) was suspected to cause this decline. In this study, three year-old Aleppo pines were exposed during 3 months to ozone fumigation (100 ppb) combined or not with mild drought to study the effects of these combined factors on some sequences linked to carbon partitioning and primary carbon metabolism within the tree. After a cumulative ozone exposure of 132ppm·h, ozone induced a significant decrease in specific activity of the whole-plant (−38%) combined with a disequilibrium of the carbon transfer between root and shoot in favour of the shoots (non significant). Moreover, while the same cumulative dose of ozone had no effect on total Rubisco activity in one year-old needles, mitochondfial NAD malic enzyme activity increased significantly (+32%). By combining ozone with mild drought, the ozone-induced responses of all the parameters were significantly amplified and Rubisco activity was significantly decreased (by 44%). These results allowed us to conclude that at 132ppm·h, ozone alone led to an increase in dark respiration. Moreover, by the combination of ozone and mild drought, a decrease carbon fixation capacity was associated to a decrease of the carbon transfered to the toots, leading to a reduced root growth. Thus, there are indications that high levels of ozone during the summer months may impair the ability of Pinus halepensis to withstand severe water stress in its natural environment.

Under temperate latitudes, soil respiration is responsible for the reemission of almost half of t... more Under temperate latitudes, soil respiration is responsible for the reemission of almost half of the carbon assimilated by the forest vegetation. Soil respiration is well-known to be very sensitive to environmental factors such as temperature and moisture and has been shown to widely vary during the growing season. The main difficulty when studying the impact of environment on this process is to differentiate the sources of CO2 in the soil and their specific response to environmental factors. With regard to this drawback, high frequency measurements of 13C in the respiratory flux of the different compartments would help in differentiating emission compartments with short residence time (i.e. using photosynthates as respiratory carbon sources) from compartments with longer residence time (i.e. using soil organic matter as respiratory carbon sources). A tunable diode laser spectrophotometer (TDLS) was installed in the Hesse forest (northeast of France) early during the 2007 growing sea...