Biology subjects

Roques, S.

Publications and source records attributed to Roques, S..

5 recordsLinked to original sources

bioRxiv2022

Combining modelling and experimental approaches to assess the feasibility of developing rice-oil palm agroforestry system

Climatic hazards affecting the main rice producing regions of Indonesia increase the risk of annual production loss and encourage the development of innovative strategies to maintain stable production. Conversion of oil palm monocultures to rice-based intercropping systems is a strategy to be considered, but relies on the existence of suitable planting management that optimizes both palm productivity while providing enough light for undergrowth rice varieties tolerant to shady conditions. This paper proposes to couple a model of light interception on virtual canopies with indoor experiments to evaluate the feasibility of developing rice-oil palm agroforestry systems. We first selected a planting design that optimized the transmitted light available for rice using a functional-structural plant model (FSPM) of oil palm. Secondly, we reproduced the light regime simulated with specific changes in the intensity and the daily fluctuation of light in controlled conditions. Three light treatments were designed to test independently the effect of daily light quantity and the effect of diurnal fluctuation on contrasted rice subpopulations. Light quantity was the main factor driving changes in plant morphology and architecture, while light fluctuation only appeared to explain variations in yield components and phenology. This study highlighted the importance of light fluctuation in the grain filling process and resource reallocation. The conservation of relative change among varieties between treatments suggests that varietal responses to low light are likely to be heritable, and that varietal screening under full light can provide clue on varietal behavior under low light. However, the identification of specific traits such as a limited expansion of leaf area and a conservation of leaf senescence under shade and high light fluctuation paves the way for selecting varieties dedicated to agroforestry systems. Further investigations including light quality and larger genotypic population to screen are discussed.

plant biology↗

bioRxiv2021

How much the response of rice genotypes to water deficit at the reproductive phase is dependent from environmental conditions?

Rice crop is known as particularly sensitive to water deficit, especially during the reproductive phase when growth of vegetative organs and formation of spikelets are simultaneous. Many works have focused on the response of rice plants to water deficits varying in timing, duration and intensity. Oppositely, the impact of the environmental conditions on the response to a given water deficit remains largely unknown. In order to test it, two experiments under contrasted conditions of temperature, radiation and VPD were conducted on six genotypes in greenhouse in Brazil (S) and in growth chamber in France (GC). The plants were submitted to the same mild water deficit at the reproductive phase, by adjusting FTSW at 0.4. Under irrigation, plant growth rate was reduced and crop duration extended in GC in relation to S: ultimately, this trade-off resulted in similar plant height and biomass in both environments. Under water deficit and in both environments, elongation rate decreased and was associated with an increase in soluble sugars in stem and flag leaf, while starch was reduced in S and negligible in GC because of the low radiation. This common biochemical response displayed a large gradient of values across environments and genotypes, but differentially impacted the branch and spikelet formation on the developing panicle: in carbon limiting conditions (GC), the increase in soluble sugars was associated with the reduction in branch and spikelet number, and conversely in S. At the morphological level, the maintenance of spikelet number on the panicle was correlated with the maintenance of flag leaf width in all genotypes and conditions, that was discussed according to the maintenance of the apical meristem size. Genotypes were discriminated and the study underlined the global tolerance of Cirad 409 and sensitivity of IAC 25.

plant biology↗

bioRxiv2020

When to depart from a stopover site? Time-since-arrival matters more than weather conditions

On the journey to wintering sites, migratory birds usually alternate between flights and stopovers where they rest and refuel. Migration strategies are assumed to differ according to season: a time-minimization pre-breeding migration strategy towards breeding locations, and an energy-minimization post-breeding migration strategy to wintering ones. The duration of flights and stopovers determines the energy requirements and the total duration of the journey. Since migrating birds actually spend most of the time at stopovers, selection to minimize the amount of energy or time spent on migration is very likely to operate on the effectiveness of stopover rest and refueling. Here we address the relative contribution of factors to departure decisions from stopover sites during the post-breeding migration in a long-distance migratory songbird. When capture probability is low it is impossible to assess the variation in body condition over the entire duration of the stopover. To get around this, we use Time Since Arrival (TSA) as a proxy for the changes in the state of individuals during the stopover. We propose that TSA is an integrative proxy for resting, feeding and fattening efficiency. We develop a capture-recapture model to address the relationship between departure probability, estimated TSA, and weather conditions. Using a 20-year dataset from sedge warblers, we show that TSA has a larger effect on departure probability than weather conditions. Low humidity and an increase in atmospheric pressure in the days preceding departure are associated with higher departure probability, but these effects are smaller than that of TSA.

ecology↗

bioRxiv2019

Genotypic variation in morphological source and sink traits affects the response of rice photosynthesis and growth to elevated atmospheric CO2

This study aimed to understand the response of photosynthesis and growth to e-CO2 conditions (800 vs. 400 mol mol-1) of rice genotypes differing in source-sink relationships. A proxy trait called local C source-sink ratio was defined as the ratio of flag leaf area over the number of spikelets on the corresponding panicle, and five genotypes differing in this ratio were grown in a controlled greenhouse. Differential CO2 resources were applied either during the two weeks following heading (EXP1) or during the whole growth cycle (EXP2). Under e-CO2, low source-sink ratio cultivars (LSS) had greater gains in photosynthesis, and they accumulated less nonstructural carbohydrate in the flag leaf than high source-sink ratio cultivars (HSS). In EXP2, grain yield and biomass gain was also greater in LSS probably caused by their strong sink. Photosynthetic capacity response to e-CO2 was negatively correlated across genotypes with local C source-sink ratio, a trait highly conserved across environments. HSS were sink-limited under e-CO2, probably associated with low triose phosphate utilization (TPU) capacity. We suggest that the local C source-sink ratio is a potential target for selecting more CO2-responsive cultivars, pending validation for a broader genotypic spectrum and for field conditions.\n\nHighlightRice local carbon source-sink ratio and sink plasticity can drive genotypic responses of leaf photosynthesis and plant production in a CO2 elevation context.

physiology↗

bioRxiv2019

Role of Triose Phosphate Utilization in photosynthetic response of rice to variable carbon dioxide levels and plant source-sink relations

This study aimed to understand the physiological bases of rice photosynthesis response to C source-sink imbalances, with focus on dynamics of the photosynthetic parameter TPU (Triose Phosphate Utilization). A dedicated experiment was replicated twice on IR64 indica rice cultivar in controlled environments. Plants were grown under the current ambient CO2 concentration until heading, thereafter, two CO2 treatments (400 and 800 mol mol-1) were compared in the presence and absence of a panicle pruning treatment modifying the C sink. At two weeks after heading, photosynthetic parameters derived from CO2 response curves, and nonstructural carbohydrate content of flag leaf and internodes were measured 3-4 times of day. Spikelet number per panicle and flag leaf area on the main culm were recorded. Net C assimilation and TPU decreased progressively after midday in panicle-pruned plants, especially under 800 mol mol-1. This TPU reduction was explained by sucrose accumulation in the flag leaf resulting from the sink limitation. It is suggested that TPU is involved in rice photosynthesis regulation under elevated CO2 conditions, and that sink limitation effects should be considered in crop models.\n\nHighlightThis study provide new insights in the effect of C source-sink relationships on rice photosynthesis. TPU should be considered in photosynthesis studies under severe source-sink imbalance at elevated CO2.

plant biology↗