Coordination of photosynthetic traits across soil and climate gradients

"Least-cost theory" posits that C3 plants should balance rates of photosynthetic water loss and carboxylation in relation to the relative acquisition and maintenance costs of resources required for these activities. Here we investigated the dependency of photosynthetic traits on climate and soil properties using a new Australia-wide trait dataset spanning 528 species from 67 sites. We tested the hypotheses that plants on relatively cold or dry sites, or on relatively more fertile sites, would typically operate at greater CO2 drawdown (lower ratio of leaf internal to ambient CO2 , Ci :Ca ) during light-saturated photosynthesis, and at higher leaf N per area (Narea ) and higher carboxylation capacity (Vcmax 25 ) for a given rate of stomatal conductance to water vapour, gsw . These results would be indicative of plants having relatively higher water costs than nutrient costs. In general, our hypotheses were supported. Soil total phosphorus (P) concentration and (more weakly) soil pH exerted positive effects on the Narea -gsw and Vcmax 25 -gsw slopes, and negative effects on Ci :Ca . The P effect strengthened when the effect of climate was removed via partial regression. We observed similar trends with increasing soil cation exchange capacity and clay content, which affect soil nutrient availability, and found that soil properties explained similar amounts of variation in the focal traits as climate did. Although climate typically explained more trait variation than soil did, together they explained up to 52% of variation in the slope relationships and soil properties explained up to 30% of the variation in individual traits. Soils influenced photosynthetic traits as well as their coordination. In particular, the influence of soil P likely reflects the Australia's geologically ancient low-relief landscapes with highly leached soils. Least-cost theory provides a valuable framework for understanding trade-offs between resource costs and use in plants, including limiting soil nutrients

Hydrological regime and plant functional traits jointly mediate the influence of Salix spp. on soil organic carbon stocks in a High Arctic tundra

Evidence points out that increasing plant productivity associated with greater erect shrub abundance alters soil organic carbon (SOC) stocks in the Arctic. However, the underlying plant economic traits remain poorly examined, which limits our understanding of plant–environment interactions driving tundra carbon cycling. We explored how erect shrub abundance leads to SOC variation in a High Arctic tundra (Bylot Island, Nunavut, Canada), where the only erect shrub, Salix richardsonii, has settled along currently active and abandoned channel zones of alluvial fans. The effects of vegetation and local environmental changes on SOC were evaluated through a paired sampling of soil materials and plant aboveground functional traits associated with plant carbon supply and nutrient demand processes. The occurrence of S. richardsonii, characterized by a tenfold increase in aboveground biomass, induced a 28% increase in SOC compared to adjacent plots dominated by prostrate shrubs and graminoids. Yet, this vegetation effect was solely observed along active channels, where higher SOC was associated with greater leaf and stem biomass. A path analysis showed that shrub leaf area index and total leaf nutrient content best represented plant carbon supply and nutrient demand dynamics, respectively, and jointly regulated SOC variation. This study underscores that vegetation structural changes associated with increasing erect shrub abundance in the Arctic can promote soil organic carbon storage, but that this pattern may be mediated by strong plant–environment interactions. Accounting for changes in functional traits driving plant carbon supply and nitrogen demand proves important for a better mechanistic understanding of how shrubification impacts tundra carbon cycling

Carboxylation capacity is the main limitation of carbon assimilation in High Arctic shrubs

Abstract Increases in shrub height, biomass and canopy cover are key whole-plant features of warming-induced vegetation change in tundra. We investigated leaf functional traits underlying photosynthetic capacity of Arctic shrub species, particularly its main limiting processes such as mesophyll conductance. In this nutrient-limited ecosystem, we expect leaf nitrogen concentration to be the main limiting factor for photosynthesis. We measured the net photosynthetic rate at saturated light (Asat) in three Salix species throughout a glacial valley in High-Arctic tundra and used a causal approach to test relationships between leaf stomatal and mesophyll conductances (gsc, gm), carboxylation capacity (Vcmax), nitrogen and phosphorus concentration (Narea, Parea) and leaf mass ratio (LMA). Arctic Salix species showed no difference in Asat compared to a global data set, while being characterized by higher Narea, Parea and LMA. Vcmax, gsc and gm independently increased Asat, with Vcmax as its main limitation. We highlighted a nitrogen-influenced pathway for increasing photosynthesis in the two prostrate mesic habitat species. In contrast, the erect wetland habitat Salix richardsonii mainly increased Asat with increasing gsc. Overall, our study revealed high photosynthetic capacities of Arctic Salix species but contrasting regulatory pathways that may influence shrub ability to respond to environmental changes in High Arctic tundra

Mise en place de consultations pharmaceutiques en oncohématologie dans un centre hospitalo-universitaire : résultats à plus d’un an

International audienceThe development of Oral Cancer Therapies (OAT) raises the question of the therapeutic adherence of patients, put in difficulty by the isolation of the patient in the management of treatment and adverse reactions. Accompanying processes are developing, such as Pharmaceutical Consultations (PC), whose monitoring and education objectives are multiple. The PCs and their implementation are presented here, as well as the first results at 15months. The scope of the PCs was first defined, as well as their organization and supporting documents. A patient's medication history is carried out before the PC, then analyzed. The initial PC incorporates a discussion about patient's health habits, followed by information on the OAT, which is closed by the delivery of a follow-up diary. The follow-up PCs, distributed over the course of the first year following the initiation, allow to correct the erroneous knowledge of the patient, to support him in his difficulties and to detect any adverse effects. From May 2019 to August 2020, 81.2% of the 32 patients who initiated OAT took part in CP. A pharmacotherapeutic problem is encountered in 65.4% of them and a drug interaction with alternative or complementary medicines in 62.5% of patients which consuming. The PCs developed provide new elements compared to the recommendations and provide support for patients with toxicities that weaken their medical care throughout their care pathway

Caravane: la base de données sur les essences.

National audienc

When and where soil is important to modify the carbon and water economy of leaves.

Photosynthetic “least‐cost” theory posits that the optimal trait combination for a given environment is that where the summed costs of photosynthetic water and nutrient acquisition/use are minimised. The effects of soil water and nutrient availability on photosynthesis should be stronger as climate‐related costs for both resources increase. Two independent datasets of photosynthetic traits, Globamax (1509 species, 288 sites) and Glob13C (3645 species, 594 sites), were used to quantify biophysical and biochemical limitations of photosynthesis and the key variable Ci/Ca (CO2 drawdown during photosynthesis). Climate and soil variables were associated with both datasets. The biochemical photosynthetic capacity was higher on alkaline soils. This effect was strongest at more arid sites, where water unit‐costs are presumably higher. Higher values of soil silt and depth increased Ci/Ca, likely by providing greater H2O supply, alleviating biophysical photosynthetic limitation when soil water is scarce. Climate is important in controlling the optimal balance of H2O and N costs for photosynthesis, but soil properties change these costs, both directly and indirectly. In total, soil properties modify the climate‐demand driven predictions of Ci/Ca by up to 30% at a global scale

Caravane: la base de données sur les essences.

National audienc