Leaf photosynthetic plasticity does not predict biomass responses to growth irradiance in rice

Trait variation and performance across varying levels of drought stress in cultivated sunflower (Helianthus annuus L.)

Drought is a major agricultural challenge that is expected to worsen with climate change. A better understanding of drought responses has the potential to inform efforts to breed more tolerant plants. We assessed leaf trait variation and covariation in cultivated sunflower (Helianthus annuus L.) in response to water limitation. Plants were grown under four levels of water availability and assessed for environmentally induced plasticity in leaf stomatal and vein traits as well as biomass (performance indicator), mass fractions, leaf area, leaf mass per area, and chlorophyll content. Overall, biomass declined in response to stress; these changes were accompanied by responses in leaf-level traits including decreased leaf area and stomatal size, and increased stomatal and vein density. The magnitude of trait responses increased with stress severity and relative plasticity of smaller-scale leaf anatomical traits was less than that of larger-scale traits related to construction and growth. Across treatments, where phenotypic plasticity was observed, stomatal density was negatively correlated with stomatal size and positively correlated with minor vein density, but the correlations did not hold up within treatments. Four leaf traits previously shown to reflect major axes of variation in a large sunflower diversity panel under well-watered conditions (i.e. stomatal density, stomatal pore length, vein density, and leaf mass per area) predicted a surprisingly large amount of the variation in biomass across treatments, but trait associations with biomass differed within treatments. Additionally, the importance of these traits in predicting variation in biomass is mediated, at least in part, through leaf size. Our results demonstrate the importance of leaf anatomical traits in mediating drought responses in sunflower, and highlight the role that phenotypic plasticity and multi-trait phenotypes can play in predicting productivity under complex abiotic stresses like drought.

Plasticity of mesophyll cell density and cell wall thickness and composition play a pivotal role in regulating plant growth and photosynthesis under shading in rapeseed

BACKGROUND AND AIMS

Plasticity of leaf growth and photosynthesis is an important strategy of plants to adapt to shading stress; however, their strategy of leaf development to achieve a simultaneous increase in leaf area and photosynthesis under shading remains unknown.

METHODS

In the present study, a pot experiment was conducted using three rapeseed genotypes of Huayouza 50 (HYZ50), Zhongshuang 11 (ZS11) and Huayouza 62 (HYZ62), and the responses of plant growth, leaf morphoanatomical traits, cell wall composition and photosynthesis to shading were investigated.

KEY RESULTS

Shading significantly increased leaf area per plant (LAplant) in all genotypes, but the increase in HYZ62 was greater than that in HYZ50 and ZS11. The greater increment of LAplant in HYZ62 was related to the larger decrease in leaf mass per area (LMA) and leaf density (LD), which were in turn related to less densely packed mesophyll cells and thinner cell walls (Tcw). Moreover, shading significantly increased photosynthesis in HYZ62 but significantly decreased it in HYZ50. The enhanced photosynthesis in HYZ62 was related to increased mesophyll conductance (gm) due primarily to thinner cell walls.

CONCLUSIONS

The data presented indicate that the different plasticity of mesophyll cell density, cell wall thickness and cell wall composition in response to shading can dramatically affect leaf growth and photosynthesis.

Leaf physiological and morphological constraints of water-use efficiency in C3 plants

The increasing evaporative demand due to climate change will significantly affect the balance of carbon assimilation and water losses of plants worldwide. The development of crop varieties with improved water-use efficiency (WUE) will be critical for adapting agricultural strategies under predicted future climates. This review aims to summarize the most important leaf morpho-physiological constraints of WUE in C3 plants and identify gaps in knowledge. From the carbon gain side of the WUE, the discussed parameters are mesophyll conductance, carboxylation efficiency and respiratory losses. The traits and parameters affecting the waterside of WUE balance discussed in this review are stomatal size and density, stomatal control and residual water losses (cuticular and bark conductance), nocturnal conductance and leaf hydraulic conductance. In addition, we discussed the impact of leaf anatomy and crown architecture on both the carbon gain and water loss components of WUE. There are multiple possible targets for future development in understanding sources of WUE variability in plants. We identified residual water losses and respiratory carbon losses as the greatest knowledge gaps of whole-plant WUE assessments. Moreover, the impact of trichomes, leaf hydraulic conductance and canopy structure on plants' WUE is still not well understood. The development of a multi-trait approach is urgently needed for a better understanding of WUE dynamics and optimization.

Rice (Oryza sativa) alleviates photosynthesis and yield loss by limiting specific leaf weight under low light intensity

The physiological mechanisms of shade tolerance and trait plasticity variations under shade remain poorly understood in rice (Oryza sativa L.). Twenty-five genotypes of rice were evaluated under open and shade conditions. Various parameters to identify variations in the plasticity of these traits in growth irradiance were measured. We found wide variations in specific leaf weight (SLW) and net assimilation rate measured at 400µmolm-2 s-1 photosynthetic photon flux density (PPFD; referred to as A 400 ) among the genotypes. Under shade, tolerant genotypes maintained a high rate of net photosynthesis by limiting specific leaf weight accompanied by increased intercellular CO2 concentration (C i ) compared with open-grown plants. On average, net photosynthesis was enhanced by 20% under shade, with a range of 2-30%. Increased accumulation of biomass under shade was observed, but it showed no correlation with photosynthetic plasticity. Chlorophyll a /b ratio also showed no association with photosynthetic rate and yield. Analysis of variance showed that 11%, 16%, and 37% of the total variance of A 400 , SLW, and C i were explained due to differences in growth irradiance. SLW and A 400 plasticity in growth irradiance was associated with yield loss alleviation with R 2 values of 0.37 and 0.16, respectively. Biomass accumulation was associated with yield loss alleviation under shade, but no correlation was observed between A 400 and leaf-N concentration. Thus, limiting specific leaf weight accompanied by increased C i rather than leaf nitrogen concentration might have allowed rice genotypes to maintain a high net photosynthesis rate per unit leaf area and high yield under shade.

Stomatal Ratio Showing No Response to Light Intensity in Oryza

Stomata control carbon and water exchange between the leaves and the ambient. However, the plasticity responses of stomatal traits to growth conditions are still unclear, especially for monocot leaves. The current study investigated the leaf anatomical traits, stomatal morphological traits on both adaxial and abaxial leaf surfaces, and photosynthetic traits of Oryza leaves developed in two different growth conditions. Substantial variation exists across the Oryza species in leaf anatomy, stomatal traits, photosynthetic rate, and stomatal conductance. The abaxial stomatal density was higher than the adaxial stomatal density in all the species, and the stomatal ratios ranged from 0.35 to 0.46 across species in two growth environments. However, no difference in the stomatal ratio was observed between plants in the growth chamber and outdoors for a given species. Photosynthetic capacity, stomatal conductance, leaf width, major vein thickness, minor vein thickness, inter-vein distance, and stomatal pore width values for leaves grown outdoors were higher than those for plants grown in the growth chamber. Our results indicate that a broad set of leaf anatomical, stomatal, and photosynthetic traits of Oryza tend to shift together during plasticity to diverse growing conditions, but the previously projected sensitive trait, stomatal ratio, does not shape growth conditions.