Try or Die: Dynamics of Plant Respiration and How to Survive Low Oxygen Conditions

Fluctuations in oxygen (O2) availability occur as a result of flooding, which is periodically encountered by terrestrial plants. Plant respiration and mitochondrial energy generation rely on O2 availability. Therefore, decreased O2 concentrations severely affect mitochondrial function. Low O2 concentrations (hypoxia) induce cellular stress due to decreased ATP production, depletion of energy reserves and accumulation of metabolic intermediates. In addition, the transition from low to high O2 in combination with light changes—as experienced during re-oxygenation—leads to the excess formation of reactive oxygen species (ROS). In this review, we will update our current knowledge about the mechanisms enabling plants to adapt to low-O2 environments, and how to survive re-oxygenation. New insights into the role of mitochondrial retrograde signaling, chromatin modification, as well as moonlighting proteins and mitochondrial alternative electron transport pathways (and their contribution to low O2 tolerance and survival of re-oxygenation), are presented.

Performance of Plain Concrete and Cement Blocks with Cement Partially Replaced by Cement Kiln Dust

The growth of the construction industry has led to the greater consumption of natural resources, which has a direct or indirect negative impact on the environment. To mitigate this, recycled or waste materials are being used as a partial substitute in the manufacture of concrete. Among these waste materials is cement kiln dust (CKD), which is produced during cement production. This study investigated the potential benefits of replacing part of the cement with CKD in two construction applications, i.e., plain concrete and cement blocks. This reflects positively on cost, energy, and the environment, since putting CKD in a landfill damages agricultural soil and plant respiration. In this study, an experimental program was carried out to study how replacing various percentages of ordinary portland cement (OPC) with CKD affected the compressive strengths, the tensile strengths, and the air contents of concrete and cement blocks. Although the results showed that the compressive and tensile strengths decreased as the amount of CKD increased, the air content of the concrete increased, which showed that 5% CKD was suitable for such applications. The results were used to propose two equations that approximate the concrete and cement block compressive strengths according to the CKD replacement percentage.

A Diagnosis of Students’ Misconceptions of Photosynthesis and Plant Respiration

This study aims to identify common misconceptions about photosynthesis and plant respiration among Form Four (Grade 10) students by developing two-tier multiple-choice test questions. This descriptive survey research was carried out using a quantitative approach, with 500 study samples. The items in Photosynthesis and Plant Respiration Diagnostic Test (PRDT) was designed in two parts; Part One tested the students’ knowledge of concepts, and Part Two tested the students’ understanding and reasoning. Rasch analysis was used to obtain the option probability curves for each item. The option probability curves present a visual image of the distribution of correct answers and misconceptions across the spectrum of student knowledge. The findings showed that students had 43 common misconceptions, which can be categorised into the inability to trace matter, energy as well as scale and location. The findings brought significant implications on the progress of the teaching and learning of Biology.

Plant uptake of CO2 outpaces losses from permafrost and plant respiration on the Tibetan Plateau

High-latitude and high-altitude regions contain vast stores of permafrost carbon. Climate warming may result in the release of CO2 from both the thawing of permafrost and accelerated autotrophic respiration, but it may also increase the fixation of CO2 by plants, which could relieve or even offset the CO2 losses. The Tibetan Plateau contains the largest area of alpine permafrost on Earth. However, the current status of the net CO2 balance and feedbacks to warming remain unclear, given that the region has recently experienced an atmospheric warming rate of over 0.3 °C decade−1. We examined 32 eddy covariance sites and found an unexpected net CO2 sink during 2002 to 2020 (26 of the sites yielded a net CO2 sink) that was four times the amount previously estimated. The CO2 sink peaked at an altitude of roughly 4,000 m, with the sink at lower and higher altitudes limited by a low carbon use efficiency and a cold, dry climate, respectively. The fixation of CO2 in summer is more dependent on temperature than the loss of CO2 than it is in the winter months, especially at higher altitudes. Consistently, 16 manipulative experiments and 18 model simulations showed that the fixation of CO2 by plants will outpace the loss of CO2 under a wetting–warming climate until the 2090s (178 to 318 Tg C y−1). We therefore suggest that there is a plant-dominated negative feedback to climate warming on the Tibetan Plateau.

Analysis of the Misconceptions of Class XII High School Students in Pekanbaru by Using the Certainty of Response Index (CRI)

One of the misconceptions can be identified by using CRI (Certainty of Response Index). The purpose of this study was to identify the misconceptions of class XII high school students in the city of Pekanbaru on the material of Photosynthesis and Plant Respiration using the Certainty of Response Index (CRI) method. This research is a survey research. The location of this research was carried out at two high schools in Pekanbaru, namely SMA N 15 Pekanbaru and SMA IT Az-Zuhra Pekanbaru. The number of samples in this study is the total population of the two SMAs. The data collection technique was carried out using a written test instrument in the form of a multiple choice test accompanied by CRI. The average percentage of students' misconceptions of SMA IT AZ-ZUHRA and SMAN 15 Pekanbaru on the concept of photosynthesis, the highest percentage is in the sub-concept of the benefits of photosynthesis for plants by 96.15% and the lowest percentage is in the sub-concept of photosynthetic pigments at 53.19%. The average percentage of students' misconceptions at SMA IT AZ-ZUHRA and SMAN 15 Pekanbaru on the concept of plant respiration, the highest percentage is found in the sub-concept of understanding respiration in plants of 84.62%. The lowest percentage is found in the sub-concept of understanding breathing and the sub-concept of when plants breathe, each of which is 67.58%.

Diagnostic Test to Assess Misconceptions on Photosynthesis and Plant Respiration: Is It Valid and Reliable?

High percentage of secondary school students was found that they were lack of understanding of the relationship between photosynthesis and respiration in plants. They did not fully understand the importance and function about plant respiration. Thus, this study designed to develop a valid and reliable instrument in two- tier multiple choice questions format which called Photosynthesis and Plant Respiration Diagnostic Test (PRDT) to assess the common types of misconceptions related to this topic among form four students (Grade 10) in Malaysia. Survey research method was applied in this study. There were 500 participants from 15 secondary schools were involved. 45 minutes were given to the participants in answering 18 two- tier diagnostic test items. The psychometric properties of the instrument had been tested using Rasch analysis. The result found that the newly developed instrument was valid and reliable. It brought the significant contribution in teaching and learning, especially classroom assessment practice in Biology subject.

Plant gross primary production, plant respiration and carbonyl sulfide emissions over the globe inferred by atmospheric inverse modelling

Carbonyl Sulphide (COS), a trace gas showing striking similarity to CO2 in terms of biochemical diffusion pathway into leaves, has been recognized as a promising indicator of the plant gross primary production (GPP), the amount of carbon dioxide that is absorbed through photosynthesis by terrestrial ecosystems. However, large uncertainties about the other components of its atmospheric budget prevent us from directly relating the atmospheric COS measurements to GPP. The largest uncertainty comes from the closure of its atmospheric budget, with a source component missing. Here, we explore the benefit of assimilating both COS and CO2 measurements into the LMDz atmospheric transport model to obtain consistent information on GPP, plant respiration and COS budget. To this end, we develop an analytical inverse system that optimizes biospheric fluxes for the 15 plant functional types (PFTs) defined in the ORCHIDEE global land surface model. Plant uptake of COS is parameterized as a linear function of GPP of the leaf relative uptake (LRU), which is the ratio of COS to CO2 deposition velocities in plants. A possible scenario for the period 2008–2019 leads to a global biospheric sink of 800 GgS.yr−1, with higher absorption in the high latitudes and higher oceanic emissions between 400 and 600 GgS.yr−1 most of which is located in the tropics. As for the CO2 budget, the inverse system increases GPP in the high latitudes by a few GtC.yr−1 without modifying the respiration compared to the ORCHIDEE fluxes used as a prior. In contrast, in the tropics the system tends to weaken both respiration and GPP. The optimized components of the COS and CO2 have been evaluated against independent measurements over Northern America, the Pacific Ocean, at three sites in Japan and at one site in France. Overall, the posterior COS concentrations are in better agreement with the COS retrievals at 250 hPa from the MIPAS satellite and with airborne measurements made over North America and the Pacific Ocean. The system seems to have rightly corrected the underestimated GPP over the high latitudes. However, the change in seasonality of GPP in the tropics disagrees with Solar Induced Fluorescence (SIF) data. The decline in biospheric sink in the Amazon driven by the inversion also disagrees with MIPAS COS retrievals at 250 hPa, highlighting the lack of observational constraints in this region. Moreover, the comparison with the surface measurements in Japan and France suggests misplaced sources in the prior anthropogenic inventory, emphasizing the need for an improved inventory to better partition oceanic and continental sources in Asia and Europe.

Improving tree carbon use efficiency for climate-adapted more productive forests (iCUE-Forest)

<p>The rate at which forests take up atmospheric CO<sub>2</sub> is critical with regard to their potential to mitigate climate change as well as their value for wood production. The allocation of carbon fixed through photosynthesis into biomass is crucially dependent on tree carbon use efficiency (CUE), which is determined by gross primary production (GPP) and plant respiration (Ra) via the relation CUE=(GPP-Ra)/GPP. The effect of future climate on CUE is unclear due to the unknown response of plant respiration to more severe increases in temperature. This motivates assessing spatial patterns in CUE across climatic gradients with marked temperature variations.  </p><p>Within the ”Improving tree carbon use efficiency for climate-adapted more productive forests” (iCUE-Forest) project, we aim to develop novel data-driven estimates of plant respiration, net primary production (NPP=GPP-Ra) and tree CUE covering the northern hemisphere boreal and temperate forests. These will be based on recent satellite-driven maps of tree living biomass, databases of N concentration measurements in tree compartments (leaves, stem/branches, roots) and the relationships between respiration rates and tissue N concentrations and temperature. Such estimates will enable the detection of spatial relationships between CUE and environmental conditions and facilitate the parameterization of dynamic global vegetation models which allow predicting the change in CUE in response to future climate and forest management.</p><p>Here we will present an extensive database of N concentration measurements in tree stems/branches and roots that we have compiled in addition to data available mainly for leaves from databases like TRY. More than 5000 measurements have been collected from the literature covering all common boreal and temperate tree species. Currently, we are exploring how the variation in tissue N concentrations is influenced by climate and tree species. Subsequently, we apply the derived tree-level relationships between tissue N concentrations and underlying drivers in combination with tree species distribution maps and estimates of tree compartment biomass based on satellite remote sensing products. In this way, we will derive novel estimates of the spatial distribution of N content in northern boreal and temperate forests that will in turn be used to assess CUE variations.</p>

Spatiotemporal dynamics of CO2 flux in Basel city centre

<p>Independent, timely and accurate monitoring of urban CO<sub>2</sub> emissions is important to assess the progress towards the Paris Agreement goals, evaluate the mitigation potential of the implemented actions and support urban planning, policy- and decision-making processes. However, there are several challenges towards achieving comprehensive urban emission monitoring at the required scales, which are mainly related to the complexities in the urban form, the urban function and their interactions with the atmosphere. Cities are highly heterogeneous mosaics of CO<sub>2</sub> sources and sinks. Typically, the main emission sources in an urban neighbourhood are vehicles and buildings, while the contribution of human, plant and soil respiration can be also significant depending on population density and green area fraction. At the same time, urban vegetation acts as carbon sink, mitigating urban emissions locally. This study attempts to unravel the complex urban CO<sub>2</sub> flux dynamics by modelling each component separately (i.e. building emissions, traffic emissions, human metabolism, photosynthetic uptake, plant respiration, soil respiration) based on high resolution geospatial, meteorological and population activity datasets. The case study is the city centre of Basel, Switzerland. The models are calibrated and evaluated using Eddy Covariance measurements of CO<sub>2</sub> flux from two permanent tower sites in the city centre, covering a significant part of the study area. Moreover, an extended field campaign for the measurement of the biogenic components (i.e. photosynthetic uptake, plant respiration, soil respiration) has been active since the summer of 2020, involving regular chamber flux measurements and soil stations across the study area. The study reveals the spatial and temporal complexity of the urban CO<sub>2</sub> flux dynamics both diurnally and seasonally. The relative contribution of each flux component to the seasonal cycle is presented, while the mitigation potential of urban vegetation is evaluated. Cross-comparison between model outputs and Eddy Covariance measurements are discussed in respect to source area variability, airflow complexity in the urban canopy layer and irregular unrecognized emission sources.</p>