Seasonal variability of dry matter content and its relationship with shoot growth and nonstructural carbohydrates

Calcium sulphate biomineralisation: Artefact of sample preparation?

Calcium biomineralisation is widely documented in plants. However, crystallisation of Ca-sulphate-containing minerals is closely related to water content, and sample processing, such as drying, alters the water balance of plant tissues. We hypothesised that common sample processing practices may favour the formation of crystals, leading to spurious crystallisation not observed in unaltered plant tissues. We selected three species (Ononis tridentata, Helianthemum squamatum and Gypsophila struthium) with reported gypsum biomineralisation. We used x-ray diffractometry on fresh intact or sliced leaves, and on the same leaves processed by subsequent drying, to address whether sample processing alters crystal formation. Ca-sulphate crystals were detected in dry samples of all species but not in fresh intact samples. Ca-sulphate crystallisation occurred in some cut fresh samples, although the accumulation greatly increased after drying. In addition, G. struthium exhibited Ca-oxalate crystals in both fresh and dry treatments, with a tendency for greater accumulation in dry treatments. Our results demonstrate that the Ca-sulphate crystals observed by x-ray diffractometry in these species are artefacts caused by common sample processing practices, such as excessive drying and slicing samples. We encourage future studies on the biomineral potential of plants to avoid the use of procedures that alter the water balance of tissues.

How can the analysis of reserve dynamics after fire support the phenological insight of Bulbostylis paradoxa (Spreng.) Lindm (Cyperaceae)?

Carbohydrate reserves are an essential key to plant survival from disturbance. Therefore, studying the different storage organs and types of reserves makes it possible to understand the dynamics of singular plants such as Bulbostylis paradoxa (Spreng.) Lindm, which presents flowering triggered by fire in the Cerrado. Physiological response to fire frequency is detailed by measuring the plant's reserves after a fire disturbance and which carbohydrates are more available for its use. It was measured the concentrations of starch, amino acids, total soluble carbohydrates and soluble proteins in leaves (control), flowers (burning) and caudex of B. paradoxa, in unburned individuals (control), and burned individuals (annually and biennially, obtained 48 h and 15 days after fire). Starch concentrations increased at both fire frequencies in all parts of the plant, as did carbohydrate concentrations. In amino acids, an increase in the concentration of flowers from individuals burned biennially 48 h after fire was observed. The protein concentration showed a decrease in burned plants. Furthermore, the two burning frequencies and the days following the fire can influence the storage of such reserves.

Rapid adaptive responses of rosette-type macrophyte Vallisneria natans juveniles to varying water depths: The role of leaf trait plasticity

Rosette-type submerged macrophytes are widely distributed across a range of water depths in shallow lakes and play a key role in maintaining ecosystem structures and functions. However, little is known about the rapid adaptive responses of such macrophytes to variations in water depth, especially at the juvenile stage. Here, we conducted a short-term in situ mesocosm experiment, in which the juveniles of Vallisneria natans were exposed to a water depth gradient ranging from 20 to 360 cm. Twenty-two leaf-related traits were examined after 4 weeks of growth in a shallow lake. Most (18) traits of V. natans generally showed high plasticity in relation to water depth. Specifically, juveniles allocated more biomass to leaves and had higher specific leaf area, leaf length-to-width ratio, chlorophyll content, and carotenoids content in deep waters, displaying trait syndrome associated with high resource acquisition. In contrast, V. natans juveniles in shallow waters had higher leaf dry matter content, leaf soluble carbohydrate content, carotenoids per unit chlorophyll, and peroxidase activity, pertaining to resource conservation. Notably, underwater light intensity was found to be the key factor explaining the trait plasticity along the water depth gradient, and 1.30 mol photons m-2 d-1 (at 270 cm) could be the optimal irradiance level based on the total biomass of V. natans juveniles. The present study highlights the significance of leaf trait plasticity for rosette-type macrophytes in response to variations in water depth and sheds new light on the differences between trade-offs in deep- and shallow-water areas.

On the Physicochemical Characteristics and Applications of an "Undesirable" Pyrenean Thorny Cushion Dwarf: Echinospartum horridum (Vahl) Roth

Small evergreen shrubs of the family Fabaceae represent a large proportion of current Mediterranean mountain vegetation. Their low pastoral value and tendency for encroachment makes these plants undesirable. In this paper, the thermal and chemical characteristics of Echinospartum horridum, a thorny cushion-shaped dwarf shrub native to the French Central Massif and the Pyrenees (particularly dominant in the shrublands of the Pyrenees), have been analyzed with a view to its valorization. Although the higher and lower heating values of the biomass from E. horridum met the ISO 17225-2:2014 requirements for its use in pellets, the ash content was slightly above the upper limit, so it would not comply with the normative for its acceptable use as a fuel. Nevertheless, the presence of high added-value flavonoids and lignans in its extracts, which are receiving increasing recent interest as efficient anti-tumor drugs and antivirals, may open the door to the valorization of this shrub for pharmacological applications.

Is the scaling relationship between carbohydrate storage and leaf biomass in meadow plants affected by the disturbance regime?

BACKGROUND AND AIMS

Below-ground carbohydrate storage is considered an adaptation of plants aimed at regeneration after disturbance. A theoretical model by Iwasa and Kubo was empirically tested which predicted (1) that storage of carbohydrates scales allometrically with leaf biomass and (2) when the disturbance regime is relaxed, the ratio of storage to leaf biomass increases, as carbohydrates are not depleted by disturbance.

METHODS

These ideas were tested on nine herbaceous species from a temperate meadow and the disturbance regime was manipulated to create recently abandoned and mown plots. Just before mowing in June and at the end of the season in October, plants with below-ground organs were sampled. The material was used to assess the pool of total non-structural carbohydrates and leaf biomass.

KEY RESULTS

In half of the cases, a mostly isometric relationship between below-ground carbohydrate storage and leaf biomass in meadow plants was found. The ratio of below-ground carbohydrate storage to leaf biomass did not change when the disturbance regime was less intensive than that for which the plants were adapted.

CONCLUSIONS

These findings (isometric scaling relationship between below-ground carbohydrate storage and leaf biomass; no effect of a relaxed disturbance regime) imply that storage in herbs is probably governed by factors other than just the disturbance regime applied once in a growing season.

Endogenous rhythmic growth in oak trees is regulated by internal clocks rather than resource availability

Common oak trees display endogenous rhythmic growth with alternating shoot and root flushes. To explore the mechanisms involved, microcuttings of the Quercus robur L. clone DF159 were used for (13)C/(15)N labelling in combination with RNA sequencing (RNASeq) transcript profiling of shoots and roots. The effect of plant internal resource availability on the rhythmic growth of the cuttings was tested through inoculation with the ectomycorrhizal fungus Piloderma croceum. Shoot and root flushes were related to parallel shifts in above- and below-ground C and, to a lesser extent, N allocation. Increased plant internal resource availability by P. croceum inoculation with enhanced plant growth affected neither the rhythmic growth nor the associated resource allocation patterns. Two shifts in transcript abundance were identified during root and shoot growth cessation, and most concerned genes were down-regulated. Inoculation with P. croceum suppressed these transcript shifts in roots, but not in shoots. To identify core processes governing the rhythmic growth, functions [Gene Ontology (GO) terms] of the genes differentially expressed during the growth cessation in both leaves and roots of non-inoculated plants and leaves of P. croceum-inoculated plants were examined. Besides genes related to resource acquisition and cell development, which might reflect rather than trigger rhythmic growth, genes involved in signalling and/or regulated by the circadian clock were identified. The results indicate that rhythmic growth involves dramatic oscillations in plant metabolism and gene regulation between below- and above-ground parts. Ectomycorrhizal symbiosis may play a previously unsuspected role in smoothing these oscillations without modifying the rhythmic growth pattern.

Combined effects of defoliation and water stress on pine growth and non-structural carbohydrates

Climate change is expected to increase both pest insect damage and the occurrence of severe drought. There is therefore a need to better understand the combined effects of biotic and abiotic damage on tree growth in order to predict the multi-factorial effect of climate change on forest ecosystem productivity. Indeed, the effect of stress interactions on tree growth is an increasingly important topic that greatly lacks experiments and data, and it is unlikely that the impact of combined stresses can be extrapolated from the outcomes of studies that focused on a single stress. We developed an original manipulative study under real field conditions where we applied artificial defoliation and induced water stress on 10-year-old (∼10 m high) maritime pine trees (Pinus pinaster Ait.). Tree response to combined stresses was quantitatively assessed following tree secondary growth and carbohydrate pools. Such a design allowed us to address the crucial question of combined stresses on trees under stand conditions, sharing soil supplies with neighboring trees. Our initial hypotheses were that (i) moderate defoliation can limit the impact of water stress on tree growth through reduced transpiration demand by a tree canopy partly defoliated and that (ii) defoliation results in reduced non-structural carbohydrate (NSC) pools, affecting tree tolerance to drought. Our results showed additive effects of defoliation and water stress on tree growth and contradict our initial hypothesis. Indeed, under stand conditions, we found that partial defoliation does not limit the impact of water stress through reduced transpiration. Our study also highlighted that, even if NSC in all organs were affected by defoliation, tree response to water stress was not triggered. We found that stem NSC were maintained or increased during the entire growing season, supporting literature-based hypotheses such as an active maintenance of the hydraulic system or another limiting resource for tree growth under defoliation. We also observed a significant decrease in root carbohydrates, which suggests a shift in the root carbon balance under defoliation. The decrease in carbohydrate supply under defoliation may not counterbalance the carbon use for mineral and water uptakes or a translocation to other tissues.

Contrasting seasonal overlaps between primary and secondary growth are linked to wood anatomy in Mediterranean sub-shrubs

Whole-plant approaches allow quantification of the temporal overlap between primary and secondary growth. If the amount of time available to grow is short, there may be a high temporal overlap between shoot growth and wood formation. We hypothesise that such overlap depends on the duration of the growing season and relates to wood anatomy. We evaluated wood anatomy, shoot longitudinal and radial growth rates, fine root production and the concentrations of non-structural carbohydrates (NSC) in the wood of six sub-shrub species growing in sites with contrasting climatic conditions (Lepidium subulatum, Linum suffruticosum, Salvia lavandulifolia, Satureja montana, Ononis fruticosa, Echinospartum horridum). Sub-shrub species living in sites with a short growing season displayed a high overlap between aboveground primary and secondary growth and formed wide vessels, whereas species from the warmest and driest sites presented the reverse characteristics. The highest overlap was linked to a rapid shoot extension and thickening through the enhanced hydraulic conductivity provided by wide vessels. The reductions in NSC concentrations when growth peaked were low or moderate, indicating that sub-shrubs accumulate NSC in excess, as do trees. The temporal overlap among primary and secondary growth in woody plants may be connected to the duration and rates of shoot and wood growth, which in turn depend on the vessel lumen area.

Short-term dynamics of nonstructural carbohydrates and hemicelluloses in young branches of temperate forest trees during bud break

Nonstructural carbohydrates (NSC) are the most important C reserves in the tissues of deciduous and evergreen tree species. Besides NSC, cell-wall hemicelluloses as the second most abundant polysaccharides in plants have often been discussed to serve as additional mobile carbon (C) reserves during periods of enhanced carbon-sink activities. To assess the significance of hemicelluloses as mobile carbon reserves, branches of two deciduous (Carpinus betulus L. and Fagus sylvatica L.) and two evergreen (Picea abies L. and Pinus sylvestris L.) tree species were sampled in a mature mixed forest stand in short intervals before and during bud break to assess NSC and hemicellulose concentrations in response to the increased carbon demand during bud break. Starch concentrations in branch sapwood of deciduous trees strongly decreased immediately before bud break and increased after bud break. In both evergreen species, only small changes of NSC were found in branch sapwood. However, 1-year-old needles exhibited a significant increase in starch concentration shortly before bud break which declined again after flushing. Hemicellulose concentrations (on an NSC-free dry matter basis) in branch sapwood of Carpinus decreased significantly shortly before bud break, but increased again after bud break. Contrarily, in Fagus branch sapwood, hemicellulose concentrations remained constant during bud break. Moderate increases of total hemicellulose concentrations before bud break were found in 1-year-old needles of both conifers, which could be explained by an accumulation of glucose units within the hemicellulose fraction. Overall, cell-wall hemicelluloses appeared to respond in a species-specific manner to the enhanced carbon demand during bud break. Hemicelluloses in branch sapwood of Carpinus and in 1-year-old needles of conifers likely act as additional carbon reserves similar to starch.