Dark Respiration In Light Research Articles

Parameter sensitivity analysis for a biochemically-based photosynthesis model

A challenge for the development of Land Surface Models (LSMs) is improving transpiration of water exchange and photosynthesis of carbon exchange between terrestrial plants and the atmosphere, both of which are governed by stoma in leaves. In the photosynthesis module of these LSMs, variations of parameters arising from diversity in plant functional types (PFTs) and climate remain unclear. Identifying sensitive parameters among all photosynthetic parameters before parameter estimation can not only reduce operation cost, but also improve the usability of photosynthesis models worldwide. Here, we analyzed 13 parameters of a biochemically-based photosynthesis model (FvCB), implemented in many LSMs, using two sensitivity analysis (SA) methods (i.e., the Sobol’ method and the Morris method) for setting up the parameter ensemble. Three different model performance metrics, i.e., Root Mean Squared Error (RMSE), Nash Sutcliffe efficiency (NSE), and Standard Deviation (STDEV) were introduced for model assessment and sensitive parameters identification. The results showed that among all photosynthetic parameters only a small portion of parameters were sensitive, and the sensitive parameters were different across plant functional types: maximum rate of Rubisco activity (Vcmax25), maximum electron transport rate (Jmax25), triose phosphate use rate (TPU) and dark respiration in light (Rd) were sensitive in broad leaf-evergreen trees (BET), broad leaf-deciduous trees (BDT) and needle leaf-evergreen trees (NET), while only Vcmax25 and TPU are sensitive in short vegetation (SV), dwarf trees and shrubs (DTS), and agriculture and grassland (AG). The two sensitivity analysis methods suggested a strong SA coherence; in contrast, different model performance metrics led to different SA results. This misfit suggests that more accurate values of sensitive parameters, specifically, species specific and seasonal variable parameters, are required to improve the performance of the FvCB model.

(13) CO2 /(12) CO2 exchange fluxes in a clamp-on leaf cuvette: disentangling artefacts and flux components.

Leaks and isotopic disequilibria represent potential errors and artefacts during combined measurements of gas exchange and carbon isotope discrimination (Δ). This paper presents new protocols to quantify, minimize, and correct such phenomena. We performed experiments with gradients of CO2 concentration (up to ±250 μmol mol(-1) ) and δ(13) CCO2 (34‰), between a clamp-on leaf cuvette (LI-6400) and surrounding air, to assess (1) leak coefficients for CO2 , (12) CO2 , and (13) CO2 with the empty cuvette and with intact leaves of Holcus lanatus (C3 ) or Sorghum bicolor (C4 ) in the cuvette; and (2) isotopic disequilibria between net photosynthesis and dark respiration in light. Leak coefficients were virtually identical for (12) CO2 and (13) CO2 , but ∼8 times higher with leaves in the cuvette. Leaks generated errors on Δ up to 6‰ for H. lanatus and 2‰ for S. bicolor in full light; isotopic disequilibria produced similar variation of Δ. Leak errors in Δ in darkness were much larger due to small biological : leak flux ratios. Leak artefacts were fully corrected with leak coefficients determined on the same leaves as Δ measurements. Analysis of isotopic disequilibria enabled partitioning of net photosynthesis and dark respiration, and indicated inhibitions of dark respiration in full light (H. lanatus: 14%, S. bicolor: 58%).

Estimation of daytime ecosystem respiration to determine gross primary production of a mountain meadow

Gross primary production ( F GPP) may be calculated from net ecosystem CO 2 exchange ( F NEE), measured, for example, by means of the eddy covariance method, provided an estimate of daytime ecosystem respiration is available. The latter is now often estimated by extrapolating functional relationships between nighttime F NEE, when F GPP is zero, and temperature to daytime conditions. The present paper deals with one problem associated with this approach, namely the reduction of leaf respiration in light relative to darkness, which causes an overestimation of daytime ecosystem respiration, and hence F GPP. The overestimation of F GPP is quantified for a mountain meadow in the Austrian Alps using a coupled model of the reduction of leaf dark respiration as a function of light intensity and within-canopy radiative transfer. For the two study years analysed in the present paper, model simulations suggest a reduction of F GPP by 11–13% and 13–17%, for a low and a high estimate of the maximum leaf-level reduction of dark respiration, respectively. This reduction is shown to be most sensitive to the ratio between F GPP and total ecosystem respiration, as well as to the ratio between leaf and total ecosystem respiration. The largest factors of uncertainty in this modelling approach are the cause for and the actual level of the reduction of leaf dark respiration in light. The significance of the present findings for estimating F GPP of other sites is discussed.

Importance of the cytochrome pathway of mitochondrial electron transport over the alternative pathway during the Kok effect in leaf discs of pea (Pisum sativum).

The Kok effect refers to the progressive light-induced inhibition of dark respiration at low light intensities, which saturates around the light compensation point. This appears as a sudden break around the light compensation point in the plot of photosynthesis versus light intensity. The magnitude of the break can be considered as a measure of the Kok effect. In the present work, the importance of different components of dark respiration during the Kok effect was investigated by using low concentrations of mitochondrial inhibitors in leaf discs of pea (Pisum sativum L. cv. Azad P1). The effects of glucose (stimulates respiration) and 0.8 M sorbitol (imposes osmotic stress and inhibits photosynthesis) were also studied for comparison. The magnitude of the break decreased significantly in the presence of antimycin A or oligomycin (inhibitors of cytochrome pathway of mitochondrial electron transport and ATP synthase, respectively). In contrast, there was no significant change with salicylhydroxamic acid (SHAM; an inhibitor of alternative pathway of mitochondrial electron transport). The magnitude of the break increased significantly with glucose, and decreased on exposure to osmotic stress. Our results suggest that the Kok effect (inhibition of dark respiration in light) is modulated by inhibitors of cytochrome pathway and ATP synthesis, but not that of the alternative pathway.

Variability of photosynthetic gas exchange parameters, dark respiration, and stomatal numbers in species of Polygonum

Within the genus Polygonum a large variation was found between species with regard to stomatal number, gas phase resistance, intracellular resistance and dark respiration. Interspecific variation in CO2 compensation concentration and intercellular CO2 concentration at constant external concentration were comparatively small. Correlations were found between stomatal number and gas phase resistance, stomatal number and Γ, and Γ and the product of dark respiration rate and intracellular resistance. The influence of dark respiration and stomatal number on photosynthetic gas exchange is discussed. It was concluded that dark respiration in light was enhanced by 22% as a mean value in 9 Polygonum species and by 62% in Polygonum lapathifolium.

Dark Leaf Respiration in Light and Darkness of an Evergreen and a Deciduous Plant Species.

Dark respiration in light as well as in dark was estimated for attached leaves of an evergreen (Heteromeles arbutifolia Ait.) and a deciduous (Lepechinia fragans Greene) shrub species using an open gas-exchange system. Dark respiration in light was estimated by the Laisk method. Respiration rates in the dark were always higher than in the light, indicating that light inhibited respiration in both species. The rates of respiration in the dark were higher in the leaves of the deciduous species than in the evergreen species. However, there were no significant differences in respiration rates in light between the species. Thus, the degree of inhibition of respiration by light was greater in the deciduous species (62%) than in the evergreen species (51%). Respiration in both the light and darkness decreased with increasing leaf age. However, because respiration in the light decreased faster with leaf age than respiration in darkness, the degree of inhibition of respiration by light increased with leaf age (from 36% in the youngest leaves to 81% in the mature leaves). This suggests that the rate of dark respiration in the light is related to the rate of biosynthetic processes. Dark respiration in the light decreased with increasing light intensity. Respiration both in the light and in the dark was dependent on leaf temperature. We concluded that respiration in light and respiration in darkness are tightly coupled, with variation in respiration in darkness accounting for more than 60% of the variation in respiration in light. Care must be taken when the relation between respiration in light and respiration in darkness is studied, because the relation varies with species, leaf age, and light intensity.

Photosynthesis and light and dark respiration in freshwater algae

Rates of gas exchange were measured for cultures of Chlorella pyrenoidosa, Chlamydomonas reinhardtii, and Anabaena flos-aquae, which were suspended in moist air on an artificial leaf made with nylon bolting cloth. A 14CO2–12CO2 technique was used to measure net and gross photosynthesis and light and dark respiration in air or nitrogen. Rates of gas exchange on the artificial leaf were equal to maximum rates obtainable for the same algae suspended in culture medium. Rates were stable, and the artificial leaf could be maintained for many hours.The algae did not exhibit conventional photorespiration. However, they did have a variable rate of light respiration that frequently equalled, but did not exceed, the rate of dark respiration. This light respiration appeared to be a continuation of normal dark respiration in light. It was affected by CO2 concentration, declining to zero if the cells were illuminated in the absence of CO2. Unlike higher plants, recent photosynthate is not a substrate of light respiration in these algae.