Nitrogen partitioning among proteins in chloroplasts and mitochondria was examined in pea (Pisum sativum L.) and wheat (Triticum aestivum L.) grown hydroponically with different nitrogen concentrations. In pea leaves, chloroplast nitrogen accounted for 75 to 80% of total leaf nitrogen. We routinely found that 8% of total ribulose-1,5-bisphosphate carboxylase/oxygenase adhered to thylakoids during preparation and could be removed with Triton X-100. With this precaution, the ratio of stroma nitrogen increased from 53 to 61% of total leaf nitrogen in response to the nitrogen supply, but thylakoid nitrogen remained almost constant around 20% of total. The changes in the activities of the stromal enzymes and electron transport in response to the nitrogen supply reflected the nitrogen partitioning into stroma and thylakoids. On the other hand, nitrogen partitioning into mitochondria was appreciably smaller than that in chloroplasts, and the ratio of nitrogen allocated to mitochondria decreased with increasing leaf-nitrogen content, ranging from 7 to 4% of total leaf nitrogen. The ratio of mitochondrial respiratory enzyme activities to leafnitrogen content also decreased with increasing leaf-nitrogen content. These differences in nitrogen partitioning between chloroplasts and mitochondria were reflected in differences in the rates of photosynthesis and dark respiration in wheat leaves measured with an open gas-exchange system. The response of photosynthesis to nitrogen supply was much greater than that of dark respiration, and the CO2 compensation point decreased with increasing leaf-nitrogen content.Nitrogen is the most important element for higher plants, and plant productivity is to a large extent determined by nitrogen nutrition. Photosynthesis and respiration are two major physiological processes in plants that determine plant productivity, but there are few studies of the balance between photosynthesis and respiration in relation to nitrogen nutrition. Much attention has been paid to the relationship between photosynthesis, nitrogen nutrition, and the role of Rubisco in nitrogen use efficiency (7,15,30 thylakoids (24). We have taken precautions against this problem. Nitrogen allocation to mitochondria has not been examined in previous studies, even though enzymes of photorespiratory decarboxylation are major protein components of these organelles (6, 10, 28). We anticipate that even though mitochondrial nitrogen is probably a quantitatively smaller component of total leaf nitrogen, it might be responsive to factors associated with photorespiratory activities, such as Rubisco amount and activity, and therefore to nitrogen nutrition and CO2 concentration.In this study, we grew pea and wheat hydroponically with different nitrogen concentrations at ambient CO, and examined the effects on the nitrogen distribution in chloroplasts and mitochondria. Several enzyme activities located in these organelles were also measured, and the results were related to observations of photosynthesis and respiration measured by...

The amounts of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), total chlorophyll (Chi), and total leaf nitrogen were measured in fully expanded, young leaves of wheat (Triticum aestivum L.), rice (Oryza sativa L.), spinach (Spinacia oleracea L.), bean (Phaseolus vulgaris L.), and pea (Pisum sativum L.). In addition, the activities of whole-chain electron transport and carbonic anhydrase were measured. All plants were grown hydroponically at different nitrogen concentrations. Although a greater than proportional increase in Rubisco content relative to leaf nitrogen content and Chi was found with increasing nitrogen supply for rice, spinach, bean, and pea, the ratio of Rubisco to total leaf nitrogen or Chi in wheat was essentially independent of nitrogen treatment. In addition, the ratio of Rubisco to electron transport activities remained constant only in wheat. Nevertheless, gas-exchange analysis showed that the in vivo balance between the capacities of Rubisco and electron transport in wheat, rice, and spinach remained almost constant, irrespective of nitrogen treatment. The in vitro carbonic anhydrase activity in wheat was very low and strongly responsive to increasing nitrogen content. Such a response was not found for the other C3 plants examined, which had 10-to 30-fold higher carbonic anhydrase activity than wheat at any leafnitrogen content. These distinctive responses of carbonic anhydrase activity in wheat were discussed in relation to CO2-transfer resistance and the in vivo balance between the capacities of Rubisco and electron transport. ach, clarified the relation between nitrogen nutrition and nitrogen partitioning into the various photosynthetic components and activities. They found that although nitrogen supply increased the ratio of Rubisco activity to electron transport activity, ATPase, Chl, or total leaf nitrogen, the balance between the in vivo activities of Rubisco and electron transport remained constant. They concluded that this difference was compensated for by the presence of a C02-transfer resistance between intercellular air spaces and the carboxylation sites. As a result of this resistance, the in vivo Rubisco specific activity was reduced progressively with increasing amount of enzyme because the partial pressure of CO2 at the carboxylation sites was reduced and kept in a constant balance with electron transport activity. The increase in the ratio of Rubisco to total leaf nitrogen or Chl with nitrogen supply is frequently found for other C3 species, such as tobacco (1), cotton (32), Solanum (11), bean (26), and pea (18).However, in spite of the existence of significant C02-transfer resistance in wheat (5,8,23, 30), the ratio of Rubisco to total leaf nitrogen or Chl in fully expanded young leaves seems to be independent of nitrogen nutrition (5,17,18 Plant Physiol. Vol. 100, 1992 CO2 diffusion to the carboxylation sites remains uncertain. In addition, the response of CA activity to changing nitrogen content is not known.In this study, we used fully expanded, youn...

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Scaling is a naturally iterative and bi-directional component of problem solving in ecology and in climate science. Ecosystems and climate systems are unquestionably the sum of all their parts, to the smallest imaginable scale, in genomic processes or in the laws of fluid dynamics. However, in the process of scaling-up, for practical purposes the whole usually has to be construed as a good deal less than this. This essay demonstrates how controlled large-scale experiments can be used to deduce key mechanisms and thereby reduce much of the detail needed for the process of scaling-up. Collection of the relevant experimental evidence depends on controlling the environment and complexity of experiments, and on applications of technologies that report on, and integrate, small-scale processes. As the role of biological feedbacks in the behavior of climate systems is better appreciated, so the need grows for experimentally based understanding of ecosystem processes.We argue that we cannot continue as we are doing, simply observing the progress of the greenhouse gas-driven experiment in global change, and modeling its future outcomes. We have to change the way we think about climate system and ecosystem science, and in the process move to experimental modes at larger scales than previously thought achievable.

. (2017). Relative functional and optical absorption cross-sections of PSII and other photosynthetic parameters monitored in situ, at a distance with a time resolution of a few seconds, using a prototype light induced fluorescence transient (LIFT) device. Functional Plant Biology: an international journal of plant function, 44 (10), 985-1006 See next page for additional authorsRelative functional and optical absorption cross-sections of PSII and other photosynthetic parameters monitored in situ, at a distance with a time resolution of a few seconds, using a prototype light induced fluorescence transient (LIFT) device AbstractThe prototype light-induced fluorescence transient (LIFT) instrument provides continuous, minimally intrusive, high time resolution (~2 s) assessment of photosynthetic performance in terrestrial plants from up to 2 m. It induces a chlorophyll fluorescence transient by a series of short flashes in a saturation sequence (180 1μs flashlets inμs) to achieve near-full reduction of the primary acceptor QA, followed by a relaxation sequence (RQA; 90 flashlets at exponentially increasing intervals over ~30 ms) to observe kinetics of QA reoxidation. When fitted by the fast repetition rate (FRR) model (Kolber et al. 1998) the QA flash of LIFT/ FRR gives smaller values for FmQA from dark adapted leaves than FmPAM from pulse amplitude modulated (PAM) assays. The ratio FmQA/FmPAM resembles the ratio of fluorescence yield at the J/P phases of the classical O-J-I-P transient and we conclude that the difference simply is due to the levels of PQ pool reduction induced by the two techniques. In a strong PAM-analogous WL pulse in the dark monitored by the QA flash of LIFT/FRR φPSIIWL ≈ φPSIIPAM. The QA flash also tracks PQ pool reduction as well as the associated responses of ETR QA → PQ and PQ → PSI, the relative functional (σPSII) and optical absorption (aPSII) cross-sections of PSII in situ with a time resolution of ~2 s as they relax after the pulse. It is impractical to deliver strong WL pulses at a distance in the field but a longer PQ flash from LIFT/FRR also achieves full reduction of PQ pool and delivers φPSIIPQ ≈ φPSIIPAM to obtain PAM-equivalent estimates of ETR and NPQ at a distance. In situ values of σPSII and aPSII from the QA flash with smaller antenna barley (chlorinaf2) and Arabidopsis mutants (asLhcb2-12, ch1-3 Lhcb5) are proportionally similar to those previously reported from in vitro assays. These direct measurements are further validated by changes in antenna size in response to growth irradiance. We illustrate how the QA flash facilitates our understanding of photosynthetic regulation during sun flecks in natural environments at a distance, with a time resolution of a few seconds. A new approach to monitoring leaf photosynthesis in situ using 30 ms chlorophyll fluorescence transients at ~ 2 s intervals at distances up to 2 m is described. By monitoring fluorescence with near full reduction of Q A (the primary quinone acceptor of PSII) these transients deliver parameters not directly av...

Determining the spatial and temporal diversity of photosynthetic processes in forest canopies presents a challenge to the evaluation of biological feedbacks needed for improvement of carbon and climate models. Limited access with portable instrumentation, especially in the outer canopy, makes remote sensing of these processes a priority in experimental ecosystem and climate change research. Here, we describe the application of a new, active, chlorophyll fluorescence measurement system for remote sensing of light use efficiency, based on analysis of laser-induced fluorescence transients (LIFT). We used mature stands of Populus grown at ambient (380 ppm) and elevated CO 2 (1220 ppm) in the enclosed agriforests of the Biosphere 2 Laboratory (B2L) to compare parameters of photosynthetic efficiency, photosynthetic electron transport, and dissipation of excess light measured by LIFT and by standard on-the-leaf saturating flash methods using a commercially available pulse-modulated chlorophyll fluorescence instrument (Mini-PAM). We also used LIFT to observe the diel courses of these parameters in leaves of two tropical forest dominants, Inga and Pterocarpus, growing in the enclosed model tropical forest of B2L. Midcanopy leaves of both trees showed the expected relationships among chlorophyll fluorescence-derived photosynthetic parameters in response to sun exposure, but, unusually, both displayed an afternoon increase in nonphotochemical quenching in the shade, which was ascribed to reversible inhibition of photosynthesis at high leaf temperatures in the enclosed canopy. Inga generally showed higher rates of photosynthetic electron transport, but greater afternoon reduction in photosynthetic efficiency. The potential for estimation of the contribution of outer canopy photosynthesis to forest CO 2 assimilation, and assessment of its response to environmental stress using remote sensing devices such as LIFT, is briefly discussed.

This study examined the ability of the photochemical reflectance index (PRI) to track changes in effective quantum yield ( F/F m ), non-photochemical quenching (NPQ), and the xanthophyll cycle de-epoxidation (DPS) in an experimental mangrove canopy. PRI was correlated with ( F/F m ) and NPQ over the 4-week measurement period and over the diurnal cycle. The normalised difference vegetation index (NDVI) was not correlated with any aspect of photochemical efficiency measured using chlorophyll fluorescence or xanthophyll pigments. This study demonstrated that photochemical adjustments were responsible for controlling the flow of energy through the photosynthetic apparatus in this mangrove forest canopy rather than canopy structural or chlorophyll adjustments.

Abstract. Recognising that plant leaves are the fundamental productive units of terrestrial vegetation and the complexity of different environments in which they must function, this review considers a few of the ways in which these functions may be measured and potentially scaled to the canopy. Although canopy photosynthetic productivity is clearly the sum of all leaves in the canopy, we focus on the quest for 'economical insights' from measurements that might facilitate integration of leaf photosynthetic activities into canopy performance, to better inform modelling based on the 'insights of economics'. It is focussed on the reversible downregulation of photosynthetic efficiency in response to light environment and stress and summarises various xanthophyll-independent and dependent forms of photoprotection within the inner and outer canopy of woody plants. Two main themes are developed. First, we review experiments showing the retention of leaves that grow old in the shade may involve more than the 'payback times' required to recover the costs of their construction and maintenance. In some cases at least, retention of these leaves may reflect selection for distinctive properties that contribute to canopy photosynthesis through utilisation of sun flecks or provide 'back up' capacity following damage to the outer canopy. Second, we report experiments offering hope that remote sensing of photosynthetic properties in the outer canopy (using chlorophyll fluorescence and spectral reflectance technologies) may overcome problems of access and provide integrated measurements of these properties in the canopy as a whole. Finding appropriate tools to scale photosynthesis from the leaf to the landscape still presents a challenge but this synthesis identifies some measurements and criteria in the laboratory and the field that improve our understanding of inner and outer canopy processes.