Experimental and modeling evidence of carbon limitation of leaf appearance rate for spring and winter wheat.

Maeva Baumont,Bertrand Muller,Boris Parent,Pierre Martre,Steven M Driever,Loïc Manceau,Hamish E Brown

doi:10.1093/jxb/erz012

Abstract

Accurate predictions of the timing of physiological stages and the development rate are crucial for predicting crop performance under field conditions. Plant development is controlled by the leaf appearance rate (LAR) and our understanding of how LAR responds to environmental factors is still limited. Here, we tested the hypothesis that carbon availability may account for the effects of irradiance, photoperiod, atmospheric CO2 concentration, and ontogeny on LAR. We conducted three experiments in growth chambers to quantify and disentangle these effects for both winter and spring wheat cultivars. Variations of LAR observed between environmental scenarios were well explained by the supply/demand ratio for carbon, quantified using the photothermal quotient. We therefore developed an ecophysiological model based on the photothermal quotient that accounts for the effects of temperature, irradiance, photoperiod, and ontogeny on LAR. Comparisons of observed leaf stages and LAR with simulations from our model, from a linear thermal-time model, and from a segmented linear thermal-time model corrected for sowing date showed that our model can simulate the observed changes in LAR in the field with the lowest error. Our findings demonstrate that a hypothesis-driven approach that incorporates more physiology in specific processes of crop models can increase their predictive power under variable environments.

Highlights

The rate at which plants develop strongly affects canopy and root structure, radiation interception, and, through the cumulative effects of these factors, biomass production, partitioning, and yield
Three independent experiments were carried out on wheat (Triticum aestivum) under controlled environment conditions using winter and spring cultivars (Table 1, Supplementary Table S1 at JXB online).The first experiment studied the response of leaf appearance rate (LAR) to different combinations of temperature, irradiance, and photoperiod; the second studied the response of LAR to elevated CO2 at two temperatures; and the third studied the genetic variability of the response of LAR to the photothermal quotient (PTQ, mol m−2 °Cd−1)
The dynamics of leaf appearance was first analysed for three contrasting cultivars (Fig. 1), Paragon, Récital, and Renan, grown in four treatments with stable environmental conditions differing in temperature, photoperiod, and light intensity (Experiment 1;Table 1) in such a way that we could compare treatments differing in temperature only (LT.LD.280 versus HT.LD.280), irradiance only (HT.LD.280 versus HT.LD.170), or both irradiance and photoperiod but with a similar daily irradiance (HT.SD.170 versus HT.LD.170)

Summary

Introduction

The rate at which plants develop strongly affects canopy and root structure, radiation interception, and, through the cumulative effects of these factors, biomass production, partitioning, and yield. It is essential to understand how this rate is determined and how it can be modeled in order to accurately predict crop responses to their environment in the field.A widely used metric to quantify plant development rate is the phyllochron, i.e. the time-interval between successive organs at the same stage (Wilhelm and McMaster, 1995), or its reciprocal, the leaf appearance rate (LAR) Expressed in (or per) thermal-time unit (i.e. in cumulative temperature above a base temperature, classically expressed in degree-days, °Cd).The phyllochron has been used for decades in the plant science community and many growth simulation models use it to model both vegetative and reproductive development (Rickman and Klepper, 1995; Fournier et al, 2005; Evers et al, 2006). The success of the phyllochron as a straightforward concept relies on the linear relationship between LAR and temperature, and its constancy when expressed in thermal time. In several grasses, including wheat, LAR increases with photoperiod (Baker et al, 1980; Cao and Moss, 1989a;Masle et al.,1989;Slafer et al.,1994),irradiance (Rickman et al, 1985;Volk and Bugbee, 1991; Bos and Neuteboom, 1998; Birch et al, 1998), and atmospheric CO2 concentration (Boone et al, 1990; McMaster et al, 1999), whilst it decreases with plant density (Abichou et al, 2018), red/far-red ratio and blue light (Gautier and Varlet‐Grancher, 1996), and nitrogen or water deficit (Longnecker and Robson, 1994)

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Conclusion