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Experimental plant research and the discovery of carbon dioxide-mediated global greening: a tribute to Wilhelm Pfeffer (1845–1920)
Abstract
One century ago, the German chemist and botanist Wilhelm Pfeffer (1845–1920) died, shortly after finishing his last lecture at the University of Leipzig. Pfeffer was, together with Julius Sachs (1832–1897), the founder of modern plant physiology. In contrast to Sachs, Pfeffer’s work was exclusively based on the principles of physics and chemistry, so that with his publications, notably the ca. 1.600 pages-long Handbuch der Pflanzenphysiologie (2. ed., Vol. I/II; 1897/1904), experimental plant research was founded. Here we summarize Pfeffer’s life and work with special emphasis on his experiments on osmosis, plant growth in light vs. darkness, gravitropism, cell physiology, photosynthesis and leaf movements. We document that Pfeffer was the first to construct/establish constant temperature rooms (growth chambers) for seed plants. Moreover, he pioneered in outlining the carbon-cycle in the biosphere, and described the effect of carbon dioxide (CO2)-enhancement on assimilation and plant productivity. Wilhelm Pfeffer pointed out that, at ca. 0.03 vol% CO2 (in 1900), photosynthesis is sub-optimal. Accordingly, due to human activities, anthropogenic CO2 released into the atmosphere promotes plant growth and crop yield. We have reproduced Pfeffer’s classical experiments on the role of CO2 with respect to plant development, and document that exhaled air of a human (ca. 4 vol% CO2) strongly promotes growth. We conclude that Pfeffer not only acted as a key figure in the establishment of experimental plant physiology. He was also the discoverer of the phenomenon of CO2-mediated global greening and promotion of crop productivity, today known as the “CO2-fertilization-effect”. These topics are discussed with reference to climate change and the most recent findings in this area of applied plant research.
... It is obvious that the physiological-biochemical activity of green plants, which are, like algae and cyanobacteria, the sunlight-driven photoautotrophic producers of the biosphere, is the pre-requisite for the nutrition of humans, as well as all other heterotrophic organisms (Fig. 1). In two recent publications, we have analyzed these interrelationships between heterotrophs (bacteria, fungi, animals) and green plants, with reference to the evolutionary origin of chloroplasts [3,4]. In addition, we described the fact that both terrestrial and marine photoautotrophs contributed approximately equally to global primary production, as illustrated by the photosynthesis-equation in the Inset of Figure 2. The relationship between grossand net primary production (GPP vs. NPP) [5] is also illustrated in this Figure. ...
... Based on these facts we want to stress that L.S. Shashidhara and A. Joshi omit one key topic of major significance for the survival of humanity, to which an Indian plant biologist, -Govindjee ( Fig.1, Inset) -, has contributed more insights than most of his competitors: Photosynthesis research, i.e. the study of the mechanisms of light-driven carbon dioxide (CO2)assimilation in the green leaves of plants, as well as in algae and cyanobacteria, leading to the biosynthesis of energy-rich carbohydrates, and the concomitant release of molecular oxygen (O2) due to the splitting of water (H2O) [3,4,5]. ...
... As a scientist, Prof. Govindjee used, until 2017, only one name as author, speaker, referee, editor of the journal "Photosynthesis Research" etc. . Figure 1 shows Govindjee's portrait, placed close to a group of green, adult maize plants in a Greenhouse of the Carnegie Institution, where original research on plant growth and photosynthesis under defined conditions has been carried out [3]. Govindjee's pioneering experimental work on the mechanisms of oxygenic (O2-producing) photosynthesis and innovative use of biophysical techniques yielded more than 400 scientific publications, numerous invitations (to India etc.), and prestigious awards [6]. ...
The rejection of some US-science books by the Texas Board of Education because of their presentation of climate change and evolution, as discussed in The Wall Street Journal (Nov. 17, 2023), is very disturbing and reminiscent to the struggle for science education in India, on which we want to comment. We document that “parochial nationalism” may be the major cause of the rejection of Charles Darwin’s principle of evolution in India. In addition, we argue that an understanding of light-driven carbon dioxide (CO2)-assimilation (i.e., oxygenic photosynthesis of green leaves) is of equal importance and show that an Indian scientist, Govindjee, contributed much of our current knowledge on photosynthesis, inclusive of net primary production of plants, algae plus cyanobacteria, and the evolution of this key process of the biosphere. Finally, we come back to the situation in Texas-USA, with reference to rising carbon dioxide (CO2)-levels, global greening, and climate change.
... In a comprehensive bio-historical account on the discovery of carbon dioxide (CO2)-mediated "Global Greening", it is documented that the German plant physiologist Wilhelm Pfeffer (1845-1920) was the first to demonstrate that CO2 is a limiting factor for vegetative growth of crop-species, such as raspberries and horn beans [6]. The aim of the present investigation was to answer the question to what extent exhaled air of a human being is able to promote the growth of a representative flowering plant. ...
... 0,028 vol. % in 1903) is suboptimal for plant growth and crop yield (with respect to C3-Plants) [6], [9]. ...
The British Naturalist Alfred Russel Wallace (1823–1913), who was born 200 years ago, argued in a popular book of 1903 that carbon dioxide (CO2) is enriched in exhaled air of humans, and bad for our health, but essential to plant development. With reference to the 2023 World Climate Declaration, we document that exhaled CO2 drastically promotes the growth of a representative land pant. Using regenerated cuttings of Tradescantia geniculata, raised in moist soil, we show that, within 21 days of growth in a day-/night-cycle, CO2-enrichment (ca. 4 vol. % vs. 0.04 vol. % in the control) exerts the following effects: Average stem length is doubled, a three-fold enhancement in the number of branches occurs, and adventitious roots, plus flowers, develop. This CO2-fertilisation-experiment is discussed in the light of the “Global Greening”-phenomenon, documented as large increase in plant biomass since ca. 1850. We also address negative effects of further rising CO2-levels in the atmosphere on the global environment in the ongoing Anthropocene. Finally, we point out that A. R. Wallace was not only a theorizing explorer of nature, but also an expert in animal- and plant physiology.
Steroidal glycoalkaloids (SGAs), the nitrogen-containing compounds produced primarily by Liliaceae and Solanaceae species, are toxic to animals and humans and have putative roles in defense against pests. UDP-glycosyltransferases (UGTs) catalyze the final glycosylation steps of SGA biosynthesis. Although previously published studies focused on the effect of UGT proteins on SGA biosynthesis, research to understand the effects of constitutive overexpression of UGTs on plant phenotype and fruit development is limited. The constitutive overexpression of a UGT encoding gene, GAME 17, may provide an alternative method to study the role of UGTs on the fruit development. In this study, we have identified 162 SlUGT proteins in tomato that are classified into t 23 groups. Gene structure and motif analyses have demonstrated that all SlUGTs have similar intron/exon distribution and motif compositions. RNA-seq data analysis has shown that SlUGTs exhibit differential expression patterns in different organs or different stages of fruit development. When the constitutive promoter 35S is used to control the expression of GAME 17, we have observed significant differences in growth parameters (i.e., plant height, leaf length, leaf width, internode length, and stem diameter) between WT and transgenic plants under high-CO2 conditions, and slight differences in growth parameters between WT and transgenic plants have beendetected. In addition, the contents of glucose, fructose, and soluble sugar of transgenic plants are significantly higher than those of WT plants. The increases in glucose, fructose, and soluble sugar in transgenic tomato fruits at three developmental stages under high-CO2 conditions are significantly higher than under natural conditions. This study provides additional evidence that the GAME 17 gene plays an important role in controlling plant phenotype and sugar homeostasis, especially in environments with high concentration of CO2.
One century ago (Jan. 9, 1921), the Russian biologist Constantin S. Merezhkowsky, who proposed the endosymbiotic origin of plastids, committed suicide at the age of 66 years. Here, we provide Merezhkowsky’s original observations on chloroplast development in seedlings and recount the career and achievements of the “founding father” of this Anti-Darwinian symbiogenesis-theory of cell evolution via cooperation and functional integration. In his phylogenetic tree published in 1910, Merezhkowsky distinguished between organisms that belong to all five Kingdoms of Life (Monera, Protoctista, Fungi, Animalia and Plantae), proposed a hypothesis concerning the origin of life, and argued that chloroplasts are descendants of once free-living cyanobacteria. A few years later, the American biologist Ivan E. Wallin (1883–1969) proposed that mitochondria evolved from ancient bacteria. The Merezhkowsky-Wallin-principle of organelle origin is summarized, and its current status critically evaluated. In addition, the contributions of Lynn Margulis (1938–2011), who died ten years ago, are outlined and evaluated in the light of Merezhkowsky’s pioneering work that led to the establishment of “evolutionary cell biology” as an independent research agenda.
The enhanced vegetation productivity driven by increased concentrations of carbon dioxide (CO2)
[i.e., the CO2 fertilization effect (CFE)] sustains an important negative feedback on climate warming, but the temporal dynamics of CFE remain unclear. Using multiple long-term satellite- and ground-based datasets, we showed that global CFE has declined across most terrestrial regions of the globe from 1982 to 2015, correlating well with changing nutrient concentrations and availability of soil water. Current carbon cycle models also demonstrate a declining CFE trend, albeit one substantially weaker than that from the global observations. This declining trend in the forcing of terrestrial carbon sinks by increasing amounts of atmospheric CO2 implies a weakening negative feedback on the climatic system and increased societal dependence on future strategies to mitigate climate warming.
Abstract
In 1821, the Swiss botanist A. P. de Candolle (1788–1841) introduced the term ‘‘Arabidopsis’’ to denote a group of dicotyledonous plants (family Brassicaceae). Here, we recount the history of Arabidopsis research from 1588 to 2020, with a focus on light and plant development. We document that plant stem cell research, with commercial applications, is essentially based on Arabidopsis-thaliana. Then, we discuss scoto- and photomorphogenesis in this model plant and introduce the light-auxin connection. Based on these insights, we argue that an as yet unknown ‘‘hidden signal’’ must be involved in the phenomenon of scotomorphogenesis, also known under the name etiolation. We conclude that Arabidopsis will serve in the foreseeable future as the model organism of choice with respect to the causal analysis of the actions of light and phytohormones during plant development.
One century ago (1920), Otto Warburg (1883–1970) discovered that in liquid cultures of unicellular green algae (Chlorella sp.) molecular oxygen (O2) exerts an inhibitory effect on photosynthesis. Decades later, O2 dependent suppression of photosynthetic carbon dioxide (CO2) assimilation (the “green” Warbur geffect) was confirmed on the leaves of seed plants. Here, we summarize the history of this discovery and elucidate the consequences of the photorespiratory pathway in land plants with reference to unpublished CO2 exchange data measured on the leaves of sunflower (Helianthus annuus) plants. In addition, we discuss the inefficiency of the key enzyme Rubisco and analyze data concerning the productivity of C3 vs. C4 crop species (sunflower vs. maize, Zea mays). Warburg’s discovery inaugurated a research agenda in the biochemistry of photosynthetic CO2 assimilation that continues to the present. In addition, we briefly discuss Warburg’s model of metabolic processes in cancer, net primary production (global photosynthesis) with respect to climate change, trees and other land plants as CO2 removers, and potential climate mitigators in the Anthropocene.
The year 2020 marks the 150th anniversary of the elucidation of the process of plant organ growth at the cellular level by Julius Sachs (1870). In this Addendum to a Review Article in Molecular Plant, we describe this fundamental discovery and argue that the etiolated grass coleoptile still represents the system of choice for the experimental analysis of auxin (indole-3-acetic acid, IAA)-action. With reference to the phenomenon of ‘tissue tension’, we discuss the acid-growth hypotheses of IAA-induced wall loosening and the process of vacuolar expansion, respectively. IAA-mediated elongation appears to be independent of wall acidification, and may be regulated via the secretion of glycoproteins into the outer epidermal wall, whereby turgor (and tissue) pressure provides the ‘driving force’ for growth. As predicted by the “acid growth-hypothesis”, the fungal phytotoxin Fusicoccin (Fc) induces organ elongation via the rapid secretion of protons. We conclude that “cell elongation” can only be understood at the level of the entire organ that displays biomechanical features not established by single cells. This systems-level approach can be traced back to the work of Sachs (1870).
Vegetation greenness has been increasing globally since at least 1981, when satellite technology enabled large-scale vegetation monitoring. The greening phenomenon, together with warming, sea-level rise and sea-ice decline, represents highly credible evidence of anthropogenic climate change. In this Review, we examine the detection of the greening signal, its causes and its consequences. Greening is pronounced over intensively farmed or afforested areas, such as in China and India, reflecting human activities. However, strong greening also occurs in biomes with low human footprint, such as the Arctic, where global change drivers play a dominant role. Vegetation models suggest that CO2 fertilization is the main driver of greening on the global scale, with other factors being notable at the regional scale. Modelling indicates that greening could mitigate global warming by increasing the carbon sink on land and altering biogeophysical processes, mainly evaporative cooling. Coupling high temporal and fine spatial resolution remote-sensing observations with ground measurements, increasing sampling in the tropics and Arctic, and modelling Earth systems in more detail will further our insights into the greening of Earth.
Growing evidence suggests that environmentally relevant elevations in CO2 (<5,000 ppm) may pose direct risks for human health. Increasing atmospheric CO2 concentrations could make adverse exposures more frequent and prolonged through increases in indoor air concentrations and increased time spent indoors. We review preliminary evidence concerning the potential health risks of chronic exposure to environmentally relevant elevations in ambient CO2, including inflammation, reductions in higher-level cognitive abilities, bone demineralization, kidney calcification, oxidative stress and endothelial dysfunction. This early evidence indicates potential health risks at CO2 exposures as low as 1,000 ppm—a threshold that is already exceeded in many indoor environments with increased room occupancy and reduced building ventilation rates, and equivalent to some estimates for urban outdoor air concentrations before 2100. Continuous exposure to increased atmospheric CO2 could be an overlooked stressor of the modern and/or future environment. Further research is needed to quantify the major sources of CO2 exposure, to identify mitigation strategies to avoid adverse health effects and protect vulnerable populations, and to fully understand the potential health effects of chronic or intermittent exposure to indoor air with higher CO2 concentrations.
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The potential for global forest cover
The restoration of forested land at a global scale could help capture atmospheric carbon and mitigate climate change. Bastin et al. used direct measurements of forest cover to generate a model of forest restoration potential across the globe (see the Perspective by Chazdon and Brancalion). Their spatially explicit maps show how much additional tree cover could exist outside of existing forests and agricultural and urban land. Ecosystems could support an additional 0.9 billion hectares of continuous forest. This would represent a greater than 25% increase in forested area, including more than 200 gigatonnes of additional carbon at maturity.Such a change has the potential to store an equivalent of 25% of the current atmospheric carbon pool.
Science , this issue p. 76 ; see also p. 24
Satellite data show increasing leaf area of vegetation due to direct factors (human land-use management) and indirect factors (such as climate change, CO2 fertilization, nitrogen deposition and recovery from natural disturbances). Among these, climate change and CO2 fertilization effects seem to be the dominant drivers. However, recent satellite data (2000–2017) reveal a greening pattern that is strikingly prominent in China and India and overlaps with croplands world-wide. China alone accounts for 25% of the global net increase in leaf area with only 6.6% of global vegetated area. The greening in China is from forests (42%) and croplands (32%), but in India is mostly from croplands (82%) with minor contribution from forests (4.4%). China is engineering ambitious programmes to conserve and expand forests with the goal of mitigating land degradation, air pollution and climate change. Food production in China and India has increased by over 35% since 2000 mostly owing to an increase in harvested area through multiple cropping facilitated by fertilizer use and surface- and/or groundwater irrigation. Our results indicate that the direct factor is a key driver of the ‘Greening Earth’, accounting for over a third, and probably more, of the observed net increase in green leaf area. They highlight the need for a realistic representation of human land-use practices in Earth system models.
Cyanobacteria and plants carry out oxygenic photosynthesis. They use water to generate the atmospheric oxygen we breathe and carbon dioxide to produce the biomass serving as food, feed, fibre and fuel. This paper scans the emergence of structural and mechanistic understanding of oxygen evolution over the past 50 years. It reviews speculative concepts and the stepped insight provided by novel experimental and theoretical techniques. Driven by sunlight photosystem II oxidizes the catalyst of water oxidation, a hetero-metallic Mn 4 CaO 5 (H 2 O) 4 cluster. Mn 3 Ca are arranged in cubanoid and one Mn dangles out. By accumulation of four oxidizing equivalents before initiating dioxygen formation it matches the four-electron chemistry from water to dioxygen to the one-electron chemistry of the photo-sensitizer. Potentially harmful intermediates are thereby occluded in space and time. Kinetic signatures of the catalytic cluster and its partners in the photo-reaction centre have been resolved, in the frequency domain ranging from acoustic waves via infra-red to X-ray radiation, and in the time domain from nano- to milli-seconds. X-ray structures to a resolution of 1.9 Å are available. Even time resolved X-ray structures have been obtained by clocking the reaction cycle by flashes of light and diffraction with femtosecond X-ray pulses. The terminal reaction cascade from two molecules of water to dioxygen involves the transfer of four electrons, two protons, one dioxygen and one water. A rigorous mechanistic analysis is challenging because of the kinetic enslaving at millisecond duration of six partial reactions (4e ⁻ , 1H ⁺ , 1O 2 ). For the time being a peroxide-intermediate in the reaction cascade to dioxygen has been in focus, both experimentally and by quantum chemistry. Homo sapiens has relied on burning the products of oxygenic photosynthesis, recent and fossil. Mankind's total energy consumption amounts to almost one-fourth of the global photosynthetic productivity. If the average power consumption equalled one of those nations with the highest consumption per capita it was four times greater and matched the total productivity. It is obvious that biomass should be harvested for food, feed, fibre and platform chemicals rather than for fuel.
One hundred and fifty years ago, Julius von Sachs’ (1832–1897) monumental Lehrbuch der Botanik (Textbook of Botany) was published, which signified the origin of physiological botany and its integration with evolutionary biology. Sachs regarded the physiology of photoautotrophic organisms as a sub-discipline of botany, and introduced a Darwinian perspective into the emerging plant sciences. Here, we summarize Sachs’ achievements and his description of sexuality with respect to the cellular basis of plant and animal biparental reproduction. We reproduce and analyze a forgotten paper (Gutachten) of Sachs dealing with Die Akademische Frau (The Academic Woman), published during the year of his death on the question concerning gender equality in humans. Finally, we summarize his endorsement of woman’s rights to pursue academic studies in the natural sciences at the University level, and conclude that Sachs was a humanist as well as a great scientist.
The year 2018 marks the 150th anniversary of the first publication of Julius von Sachs' (1832–1897) Lehrbuch der Botanik (Textbook of Botany), which provided a comprehensive summary of what was then known about the plant sciences. Three years earlier, in 1865, Sachs produced the equally impressive Handbuch der Experimental‐Physiologie der Pflanzen (Handbook of Experimental Plant Physiology), which summarized the state of knowledge in all aspects of the discipline known today as plant physiology. Both of these books provided numerous insights based on Sachs' seminal experiments. By virtue of a reliance on detailed empirical observation and the rigorous application of chemical and physical principles, it is fair to say that the publication of these two monumental works marked the beginning of what can be called “modern‐day” plant science. Moreover, Sachs' Lehrbuch der Botanik prefigured the ascendance of plant molecular biology and the systems biology of photoautotrophic organisms. Regrettably, many of the insights of this great scientist have been forgotten by the generations who followed. It is only fitting, therefore, that the anniversary of the publication of the Lehrbuch der Botanik and the career of “the father of plant physiology” should be honored and reviewed, particularly because Sachs established the physiology of green organisms as an integral branch of botany and incorporated a Darwinian perspective into plant biology. Here we highlight key insights, with particular emphasis on Sachs' detailed discussion of sexual reproduction at the cellular level and his endorsement of Darwinian evolution.
Assessing human impacts on climate and biodiversity requires an understanding of the relationship between the concentration of carbon dioxide (CO2) in the Earth’s atmosphere and global temperature (T). Here I explore this relationship empirically using comprehensive, recently-compiled databases of stable-isotope proxies from the Phanerozoic Eon (~540 to 0 years before the present) and through complementary modeling using the atmospheric absorption/transmittance code MODTRAN. Atmospheric CO2 concentration is correlated weakly but negatively with linearly-detrended T proxies over the last 425 million years. Of 68 correlation coefficients (half non-parametric) between CO2 and T proxies encompassing all known major Phanerozoic climate transitions, 77.9% are non-discernible (p > 0.05) and 60.0% of discernible correlations are negative. Marginal radiative forcing (ΔRFCO2), the change in forcing at the top of the troposphere associated with a unit increase in atmospheric CO2 concentration, was computed using MODTRAN. The correlation between ΔRFCO2 and linearly-detrended T across the Phanerozoic Eon is positive and discernible, but only 2.6% of variance in T is attributable to variance in ΔRFCO2. Of 68 correlation coefficients (half non-parametric) between ΔRFCO2 and T proxies encompassing all known major Phanerozoic climate transitions, 75.0% are non-discernible and 41.2% of discernible correlations are negative. Spectral analysis, auto- and cross-correlation show that proxies for T, atmospheric CO2 concentration and ΔRFCO2 oscillate across the Phanerozoic, and cycles of CO2 and ΔRFCO2 are antiphasic. A prominent 15 million-year CO2 cycle coincides closely with identified mass extinctions of the past, suggesting a pressing need for research on the relationship between CO2, biodiversity extinction, and related carbon policies. This study demonstrates that changes in atmospheric CO2 concentration did not cause temperature change in the ancient climate.
As atmospheric levels of carbon dioxide continue to escalate far beyond the range that was present in the evolutionary period of humans, the safe level for long-term breathing is not clear given that CO2 is known to be toxic for short-duration exposures at high concentrations. There is now substantial evidence that permanent exposure, to the current elevated and future predicted CO2 levels, will have significant effects on humans. Carbon dioxide overload, already detected in human population blood chemistry, is identified by ongoing changes to bicarbonate, calcium and phosphorous levels in the body and the trends, towards unhealthy levels, predict global breathing toxicity by around mid-century. In common indoor environments, mental impairment, altered brainwaves and health symptoms have been observed at levels of CO2 above 600 ppm for relatively short-term exposures. Although humans and animals are generally able to deal with breathing elevated levels of CO2 in the short-term due to compensation mechanisms in the body, long-term perpetual increased exposure, with no change in respiration rate, causes build-up of CO2 and a range of potentially severe physiological consequences. Protein malfunctions in cells due to elevated CO2 and associated low pH has the potential to cause threats to life including cancer, neurological disorders, lung disease, diabetes, etc. In particular excess CO2 causes the overexpression of carbonic anhydrase, the enzyme that catalyses CO2 in the body, and this produces calcification in the kidneys, arteries and tissues, along with other diseases. Although there is very low awareness of this risk, it is likely that human physical and mental health will be progressively impacted in the near-future with the severity dependant on CO2 emissions.
In 1963, a monograph by Thomas D. Luckey entitled Germfree Life and Gnotobiology was published, with a focus on animals treated with microbes and reference to the work of Louis Pasteur (1822–1895). Here, we review the history and current status of plant gnotobiology, which can be traced back to the experiments of Jean-Baptiste Boussingault (1801–1887) published in 1838. Since the outer surfaces of typical land plants are much larger than their internal areas, embryophytes “wear their guts on the outside.” We describe the principles of gnotobiological analyses, with reference to epiphytic metylobacteria, and sunflower (Helianthus annuus) as well as Arabidopsis as model dicots. Finally, a Californian field experiment aiming to improve crop yield in strawberries (Fragaria ananassa) is described to document the practical value of this novel research agenda.
Global environmental change is rapidly altering the dynamics of terrestrial vegetation, with consequences for the functioning of the Earth system and provision of ecosystem services. Yet how global vegetation is responding to the changing environment is not well established. Here we use three long-term satellite leaf area index (LAI) records and ten global ecosystem models to investigate four key drivers of LAI trends during 1982-2009. We show a persistent and widespread increase of growing season integrated LAI (greening) over 25% to 50% of the global vegetated area, whereas less than 4% of the globe shows decreasing LAI (browning). Factorial simulations with multiple global ecosystem models suggest that CO2 fertilization effects explain 70% of the observed greening trend, followed by nitrogen deposition (9%), climate change (8%) and land cover change (LCC) (4%). CO2 fertilization effects explain most of the greening trends in the tropics, whereas climate change resulted in greening of the high latitudes and the Tibetan Plateau. LCC contributed most to the regional greening observed in southeast China and the eastern United States. The regional effects of unexplained factors suggest that the next generation of ecosystem models will need to explore the impacts of forest demography, differences in regional management intensities for cropland and pastures, and other emerging productivity constraints such as phosphorus availability.
Background:
One of the best-known plant movements, phototropic solar tracking in sunflower (Helianthus annuus), has not yet been fully characterized. Two questions are still a matter of debate. (1) Is the adaptive significance solely an optimization of photosynthesis via the exposure of the leaves to the sun? (2) Is shade avoidance involved in this process? In this study, these concepts are discussed from a historical perspective and novel insights are provided.
Scope and methods:
Results from the primary literature on heliotropic growth movements led to the conclusion that these responses cease before anthesis, so that the flowering heads point to the East. Based on observations on 10-week-old plants, the diurnal East-West oscillations of the upper fifth of the growing stem and leaves in relation to the position of the sun (inclusive of nocturnal re-orientation) were documented, and photon fluence rates on the leaf surfaces on clear, cloudy and rainy days were determined. In addition, the light-response curve of net CO2 assimilation was determined on the upper leaves of the same batch of plants, and evidence for the occurrence of shade-avoidance responses in growing sunflower plants is summarized.
Conclusions:
. Only elongating, vegetative sunflower shoots and the upper leaves perform phototropic solar tracking. Photon fluence response and CO2 assimilation measurements cast doubt on the 'photosynthesis-optimization hypothesis' as the sole explanation for the evolution of these plant movements. We suggest that the shade- avoidance response, which maximizes light-driven CO2 assimilation, plays a major role in solar tracking populations of competing sunflower plants, and an integrative scheme of these growth movements is provided.
In 1865, the German botanist Julius Sachs published a seminal monograph entitled Experimental-Physiologie der Pflanzen (Experimental Physiology of Plants) and hence became the founder of a new scientific discipline that originated 150 years ago. Here, we outline the significance of the achievements of Sachs. In addition, we document, with reference to his Vorlesungen über Pflanzen-Physiologie (Lectures on the Physiology of Plants, 1882), that Sachs was one of the first experimentalists who proposed the functional unity of all organisms alive today (humans, animals, plants and other "vegetable" organisms, such as algae, cyanophyceae, fungi, myxomycetes, and bacteria).
The German biologist Julius Sachs was the first to introduce controlled, accurate, quantitative experimentation into the botanical sciences, and is regarded as the founder of modern plant physiology. His seminal monograph Experimental-Physiologie der Pflanzen (Experimental Physiology of Plants) was published 150 years ago (1865), when Sachs was employed as a lecturer at the Agricultural Academy in Poppelsdorf/Bonn (now part of the University). This book marks the beginning of a new era of basic and applied plant science. In this contribution, I summarize the achievements of Sachs and outline his lasting legacy. In addition, I show that Sachs was one of the first biologists who integrated bacteria, which he considered to be descendants of fungi, into the botanical sciences and discussed their interaction with land plants (degradation of wood etc.). This "plant-microbe-view" of green organisms was extended and elaborated by the laboratory botanist Wilhelm Pfeffer (1845-1920), so that the term "Sachs-Pfeffer-Principle of Experimental Plant Research" appears to be appropriate to characterize this novel way of performing scientific studies on green, photoautotrophic organisms (embryophytes, algae, cyanobacteria).
Significance
Feedbacks from terrestrial ecosystems to atmospheric CO 2 concentrations contribute the second-largest uncertainty to projections of future climate. These feedbacks, acting over huge regions and long periods of time, are extraordinarily difficult to observe and quantify directly. We evaluated in situ, atmospheric, and simulation estimates of the effect of CO 2 on carbon storage, subject to mass balance constraints. Multiple lines of evidence suggest significant tropical uptake for CO 2 , approximately balancing net deforestation and confirming a substantial negative global feedback to atmospheric CO 2 and climate. This reconciles two approaches that have previously produced contradictory results. We provide a consistent explanation of the impacts of CO 2 on terrestrial carbon across the 12 orders of magnitude between plant stomata and the global carbon cycle.
J H van’ t Hoff is considered as one of the greatest chemists of all time. He started his career as an organic chemist. He solved the vexing problem of optical isomerism by proposing an asymmetric tetrahedral carbon bonded to form different groups. He extended this to include geometric isomerism, and to compounds with heteroatoms in place of asymmetric carbon. Thus he established the ‘chemistry in space’ or stereochemistry. He moved on to work on reaction kinetics, equilibria, thermodynamic properties of dilute solutions and related areas. He laid the foundation for physical chemistry through these discoveries and was awarded the first Nobel Prize in Chemistry in 1901. van’ t Hoff died of tuberculosis at a relatively early age of 59.
Significance
Photosynthesis by cyanobacteria, algae, and plants sustains life on Earth by oxidizing water to the O 2 we breathe and by converting CO 2 into biomass we eat, burn, or use otherwise. Although O 2 production and CO 2 reduction are functionally and structurally well separated in photosynthetic organisms, there is a long debated role of CO 2 / in water oxidation. Here we demonstrate that acts as mobile acceptor and transporter of protons produced by photosystem II, and that depletion of leads to a reversible down-regulation of O 2 production. These findings add a previously unidentified component to the regulatory networks in higher plants, algae, and cyanobacteria and conclude the long quest for the function of CO 2 / in photosynthetic water oxidation.
Increasing paleoclimatic evidence suggests that the Little Ice Age (LIA)
was a global climate change event. Understanding the forcings and
associated climate system feedbacks of the LIA is made difficult by the
scarcity of Southern Hemisphere paleoclimate records. We use a new
glaciochemical record of a coastal ice core from Mt. Erebus Saddle,
Antarctica, to reconstruct atmospheric and oceanic conditions in the
Ross Sea sector of Antarctica over the past five centuries. The LIA is
identified in stable isotope (δD) and lithophile element records,
which respectively demonstrate that the region experienced 1.6 ±
1.4 °C cooler average temperatures prior to 1850 AD than during the
last 150 yr and strong (>57 m s-1) prevailing katabatic
winds between 1500 and 1800 AD. Al and Ti concentration increases of an
order of magnitude (>120 ppb Al) are linked to enhanced aeolian
transport of complex silicate minerals and represent the strongest
katabatic wind events of the LIA. These events are associated with three
12-30 yr intervals of cooler temperatures at ca. 1690 AD, 1770 AD and
1840 AD. Furthermore, ice core concentrations of the biogenic sulphur
species MS- suggest that biological productivity in the Ross
Sea polynya was ~80% higher prior to 1875 AD than at any subsequent
time. We propose that cooler Antarctic temperatures promoted stronger
katabatic winds across the Ross Ice Shelf, resulting in an enlarged Ross
Sea polynya during the LIA.
Numerous botanists of the early 19th century investigated the effect of sunlight on plant development, but no clear picture developed. One hundred and fifty years ago, Julius Sachs () systematically analysed the light-plant relationships, using developing garden nasturtium (Tropaeolum majus) and seedlings of buckwheat (Fagopyron esculentum) as experimental material. From these studies, Sachs elucidated the phenomenon of photomorphogenesis (plant development under the influence of daylight) and the associated 'shade-avoidance response'. We have reproduced the classical buckwheat experiments of Sachs () and document the original shade-avoidance syndrome with reference to hypocotyl elongation and cotyledon development in darkness (skotomorphogenesis), white light and shade induced by a canopy of green leaves. In subsequent publications, Sachs elaborated his concepts of 1863 and postulated the occurrence of 'flower-inducing substances'. In addition, he argued that the shade-avoidance response in cereals, such as wheat and maize, is responsible for lodging in crowded plant communities. We discuss these processes with respect to the red- to far-red light/phytochrome B relationships. Finally, we summarise the phytochrome B-phytohormone (auxin, brassinosteroids) connection within the cells of shaded Arabidopsis plants, and present a simple model to illustrate the shade-avoidance syndrome. In addition, we address the relationship between plant density and health of the corresponding population, a topic that was raised for the first time by Sachs () in his seminal paper and elaborated in his textbooks.
Five decades ago, a novel mode of CO2 assimilation that was later described as C4-photosynthesis was discovered on mature leaves of maize (Zea mays L.) plants. Here we show that 3- to 5-day-old developing maize leaves recapitulate the evolutionary advance from the ancient,
inefficient C3 mode of photosynthesis to the C4 pathway, a mechanism for overcoming the wasteful process of photorespiration. Chlorophyll fluorescence measurements documented
that photorespiration was high in 3-day-old juvenile primary leaves with non-specialized C3-like leaf anatomy and low in 5-day-old organs with the typical “Kranz-anatomy” of C4 leaves. Photosynthetic gas (CO2)-exchange measurements on 5-day-old leaves revealed the characteristic features of C4 photosynthesis, with a CO2 compensation point close to zero and little inhibition of photosynthesis by the normal oxygen concentration in the air. This
indicates a very low photorespiratory activity in contrast to control experiments conducted with mature C3 sunflower (Helianthus annuus L.) leaves, which display a high rate of photorespiration.
Additional key wordsleaf development–maize seedlings–photorespiration–photosynthesis
In roots, the "hidden half" of all land plants, gravity is an important signal that determines the direction of growth in the soil. Hence, positive gravitropism has been studied in detail. However, since the 19th century, the response of roots toward unilateral light has also been analyzed. Based on studies on white mustard (Sinapis alba) seedlings, botanists have concluded that all roots are negatively phototropic. This "Sinapis-dogma" was refuted in a seminal study on root phototropism published a century ago, where it was shown that less then half of the 166 plant species investigated behave like S. alba, whereas 53% displayed no phototropic response at all. Here we summarize the history of research on root phototropism, discuss this phenomenon with reference to unpublished data on garden cress (Lepidium sativum) seedlings, and describe the effects of blue light on the negative bending response in Thale cress (Arabidopsis thaliana). The ecological significance of root phototropism is discussed and the relationships between gravi- and phototropism are outlined, with respect to the starch-statolith-theory of gravity perception. Finally, we present an integrative model of gravi- and blue light perception in the root tip of Arabidopsis seedlings. This hypothesis is based on our current view of the starch-statolith-concept and light sensing via the cytoplasmic red/blue light photoreceptor phytochrome A and the plasma membrane-associated blue light receptor phototropin-1. Open questions and possible research agendas for the future are summarized.
As a student of theology at Cambridge University, Charles Darwin (1809-1882) attended the lectures of the botanist John S. Henslow (1796-1861). This instruction provided the basis for his life-long interest in plants as well as the species question. This was a major reason why in his book On the Origin of Species, which was published 150 years ago, Darwin explained his metaphorical phrase 'struggle for life' with respect to animals and plants. In this article, we review Darwin's botanical work with reference to the following topics: the struggle for existence in the vegetable kingdom with respect to the phytochrome-mediated shade avoidance response; the biology of flowers and Darwin's plant-insect co-evolution hypothesis; climbing plants and the discovery of action potentials; the power of movement in plants and Darwin's conflict with the German plant physiologist Julius Sachs; and light perception by growing grass coleoptiles with reference to the phototropins. Finally, we describe the establishment of the scientific discipline of Plant Biology that took place in the USA 80 years ago, and define this area of research with respect to Darwin's work on botany and the physiology of higher plants.
A pioneer in the study of the effect of light on plant development, Wilhelm Pfeffer (1845–1920), outlined both modes of plant development in darkness and in light– today known as skoto- and photo- morphogenesis, respectively. By exploring the current understanding of these pathways in Arabidopsis, we speculate on the possible mechanisms of cell and organ elongation in darkness. We present a thought experiment, which highlights the need for a yet unknown (hidden) external signal, we call aleph (ℵ), and its possible sensor “etioreceptor”. Here we propose for the first time that this system is required for growth and developmental patterning to continue in localized spacetime under minimal growth environments, particularly in the absence of light. If true, this mechanism may have played a fundamental role in organism’s survival during Darwinian (adaptive) evolution (“survival of the fittest”). We present our working model whereby the hidden signal acting through its etioreceptor, increases auxin biosynthesis to facilitate organ expansion, and suggest a function for this system in the auxin biosynthesis pathway.
Secondary agriculture plays a significant role in making a positive impact on the country’s economy. It has potential to increase the value of primary agriculture. It ensures better utilization of renewable agro-bioresources either through value addition or waste utilization. Nurseries, bio-fertilizers, bio-pesticides, compost, fruit-processed products, agro-tourism, weaving, flavours, and dyes are some of the avenues of secondary agriculture. By-products from agricultural crops like wheat and rice bran, corn gluten meal and germ, pulses meal and husk, and sugarcane bagasse, if processed appropriately for deriving industrial products could pave a way in getting better economic returns from agriculture rather using them as livestock feed. Among food crops, major post-harvest losses (30–40%) occurs in fruits and vegetables; their waste being rich in several bioactive compounds possess great potential to be added as a polyphenol rich and fibre source in food products or for the synthesis of food-grade industrial products like ethanol, citric acid and pectin etc. Wastes from floriculture industries can also be utilised for the production of several value-added products such as biofuels, bio-ethanol, compost, organic acids, pigments and dyes, incense sticks, handmade paper production, and sugar syrup. Around the world, 80% of population is dependent on traditional medicine for health care needs. The secondary metabolites from medicinal plants possess pharmaceutical properties and advancement in extraction techniques can lead to novel range of herbal products of high economic value. The market potential of agro-produce seems to be naïve but opportunistic in near future. The advancement in technologies, equipments, and processes would enable enhanced secondary agriculture practices giving range of materials of better quality, yield, nutrition, and convenience. Hence, the potential of secondary agriculture and bioprocessing could be strong boost to the economy, societal status and environmental protection. In this article we have made an effort to understand the secondary agriculture, its potential to uplift the economy and strategies for value addition in different agricultural domains such as horticulture, floriculture and medicinal plants.
Our study quantified the global tree restoration potential and its associated carbon storage potential under existing climate conditions. We received multiple technical comments, both supporting and disputing our findings. We recognize that several issues raised in these comments are worthy of discussion. We therefore provide a detailed common answer where we show that our original estimations are accurate.
Human-caused CO2 emissions over the past century have caused the climate of
the Earth to warm and have directly impacted on the functioning of terrestrial
plants. We examine the global response of terrestrial gross primary production
(GPP) to the historic change in atmospheric CO2. The GPP of the terrestrial
biosphere has increased steadily, keeping pace remarkably in proportion to the
rise in atmospheric CO2. Water-use efficiency, namely the ratio of CO2 uptake
by photosynthesis to water loss by transpiration, has increased as a direct leaf-
level effect of rising CO2. This has allowed an increase in global leaf area,
which has conspired with stimulation of photosynthesis per unit leaf area to
produce a maximal response of the terrestrial biosphere to rising atmospheric
CO2 and contemporary climate change.
Highlights
Global climate change caused by CO2 emissions can stress terrestrial vegetation, potentially decreasing production. On the other hand, CO2 interacts directly with plants, stimulating leaf-level photosynthesis and water-use efficiency.
The rise in atmospheric CO2 concentration over the past century presents an opportunity for gauging the strength of the terrestrial biosphere response to these potential impacts.
Atmospheric proxy and model analysis both suggest that global terrestrial photosynthesis has increased in nearly constant proportion to the rise in atmospheric CO2 concentration, a maximal response by the terrestrial biosphere.
An accurate understanding of the impacts of climate change on terrestrial vegetation is essential for managing risks associated with human-caused climate change: gauging the historic response of terrestrial photosynthesis is an important step in this direction.
When fossil fuels are extracted from the earth, they are naturally replaced by a layer of water. Water has high thermal conductivity as compared to coal, oil, and gas. This will increase the heat transfer rate from the underground in all directions but most importantly towards the surface of the earth and seas due to the greater temperature difference. Additionally, heat losses and thermal emissions from boreholes will be even higher and given that there are more than 4 million onshore hydrocarbon wells (producing and non-producing) around the world, the heat emissions could be significant. Added to this is the heat from thousands of coal mines across the world. We review the literature and report on temperature trends observed in areas subject to fossil fuel extraction. We find that land and sea areas subject to fossil fuel extraction are experiencing relatively high rates of temperature rise. We examine the case of the Arctic in some detail and compare sea-ice extent change in both the Arctic and Antarctica. We find that despite increasing levels of CO2 observed in the Polar Regions, sea-ice extent is shrinking in the Arctic and expanding in the Antarctic. We believe that a possible cause of shrinking sea-ice in the Arctic could be geothermal heat rising to the surface as a direct result of fossil fuel extraction in regions such as Siberia and Alaska. To provide a crude approximation of the heat released from the earth’s interior and subsequent impact on global average temperature as a result of earth insulation loss, we use worldwide oil and gas production data from 2007 until 2017. We find the subsequent impact on global surface temperature over this period to be 0.026°C compared with an observed temperature rise of 0.15°C. This amounts to 17% of total warming observed over the period attributable to earth insulation loss, which is significant. We end by making some suggestions on further research necessary to fully understand the possible effect of earth insulation loss on rising global temperature.
Growth in terrestrial gross primary production (GPP)—the amount of carbon dioxide that is ‘fixed’ into organic material through the photosynthesis of land plants—may provide a negative feedback for climate change1, 2. It remains uncertain, however, to what extent biogeochemical processes can suppress global GPP growth3. As a consequence, modelling estimates of terrestrial carbon storage, and of feedbacks between the carbon cycle and climate, remain poorly constrained4. Here we present a global, measurement-based estimate of GPP growth during the twentieth century that is based on long-term atmospheric carbonyl sulfide (COS) records, derived from ice-core, firn and ambient air samples5. We interpret these records using a model that simulates changes in COS concentration according to changes in its sources and sinks—including a large sink that is related to GPP. We find that the observation-based COS record is most consistent with simulations of climate and the carbon cycle that assume large GPP growth during the twentieth century (31% ± 5% growth; mean ± 95% confidence interval). Although this COS analysis does not directly constrain models of future GPP growth, it does provide a global-scale benchmark for historical carbon-cycle simulations.
Terrestrial ecosystems play a significant role in the global carbon cycle and offset a large fraction of anthropogenic CO 2 emissions. The terrestrial carbon sink is increasing, yet the mechanisms responsible for its enhancement, and implications for the growth rate of atmospheric CO 2 , remain unclear. Here using global carbon budget estimates, ground, atmospheric and satellite observations, and multiple global vegetation models, we report a recent pause in the growth rate of atmospheric CO 2 , and a decline in the fraction of anthropogenic emissions that remain in the atmosphere, despite increasing anthropogenic emissions. We attribute the observed decline to increases in the terrestrial sink during the past decade, associated with the effects of rising atmospheric CO 2 on vegetation and the slowdown in the rate of warming on global respiration. The pause in the atmospheric CO 2 growth rate provides further evidence of the roles of CO 2 fertilization and warming-induced respiration, and highlights the need to protect both existing carbon stocks and regions, where the sink is growing rapidly.
In recent years, increased awareness of the potential interactions between rising atmospheric CO2 concentrations ([ CO2 ]) and temperature has illustrated the importance of multifactorial ecosystem manipulation experiments for validating Earth System models. To address the urgent need for increased understanding of responses in multifactorial experiments, this article synthesizes how ecosystem productivity and soil processes respond to combined warming and [ CO2 ] manipulation, and compares it with those obtained in single factor [ CO2 ] and temperature manipulation experiments. Across all combined elevated [ CO2 ] and warming experiments, biomass production and soil respiration were typically enhanced. Responses to the combined treatment were more similar to those in the [ CO2 ]-only treatment than to those in the warming-only treatment. In contrast to warming-only experiments, both the combined and the [ CO2 ]-only treatments elicited larger stimulation of fine root biomass than of aboveground biomass, consistently stimulated soil respiration, and decreased foliar nitrogen (N) concentration. Nonetheless, mineral N availability declined less in the combined treatment than in the [ CO2 ]-only treatment, possibly due to the warming-induced acceleration of decomposition, implying that progressive nitrogen limitation (PNL) may not occur as commonly as anticipated from single factor [ CO2 ] treatment studies. Responses of total plant biomass, especially of aboveground biomass, revealed antagonistic interactions between elevated [ CO2 ] and warming, i.e. the response to the combined treatment was usually less-than-additive. This implies that productivity projections might be overestimated when models are parameterized based on single factor responses. Our results highlight the need for more (and especially more long-term) multifactor manipulation experiments. Because single factor CO2 responses often dominated over warming responses in the combined treatments, our results also suggest that projected responses to future global warming in Earth System models should not be parameterized using single factor warming experiments.
A critical uncertainty in climate forecasts stems from our poor
understanding of the extent to which increasing CO2 concentrations will
cause growth in gross primary production (GPP). This GPP-CO2 sensitivity
varies widely among different carbon-climate models, field studies, and
plant chamber experiments. Recent work suggests that GPP is
quantitatively related to spatial and temporal gradients of atmospheric
carbonyl sulfide (COS) concentrations. Here we investigate past changes
in global GPP using the long-term atmospheric COS record and simulations
of global atmospheric COS concentrations. The atmospheric COS
simulations, driven by a wide range of source and sink estimates, only
successfully captured the observed COS trends for simulations that
included the quantitative relationship between COS plant uptake and GPP.
The COS observations were most consistent with the COS simulations that
were driven by high GPP-CO2 sensitivity, rather than low GPP-CO2
sensitivity. Since the assumption of low GPP-CO2 sensitivity in
carbon-climate models results in anomalous temperature forecasts, the
COS constraint may help improve climate forecasts. Furthermore,
continued COS monitoring could be used to examine ongoing primary
production changes and their relation to climate feedbacks.
The fact that a mould fungus will thrive in a solution, from which, with the exception of certain inorganic acids, it can obtain nothing but sugar, affords proof that the elaboration of these food substances in metabolism not only provides the numerous carbon compounds which are concerned in the construction of the plant, but also serves as a sufficient source of energy for the performance of its functions. For in the plant, as in the animal, vital activity comes to a standstill if the conditions and the energy necessary for the discharge of its functions are not constantly provided by means of profound chemical decompositions. Just as in animals, a great amount of internal and external work has to be accomplished, in order to carry on and maintain the action of the organism. Hence the greater part, and in the mature plant even the whole, of the food absorbed is devoted to this functional metabolism, so that only a certain fraction of the sugar which has disappeared from the solution is to be found in the resulting crop of fungi, in the form of various carbon compounds.
The polar-orbiting satellite, Seasat, had been designed as an
oceanographic satellite with little advance thought being given to
atmospheric uses. However, the microwave instruments provided a rich
source of data for studying atmospheric conditions. The simultaneous
sampling by several instruments generated special benefits, a situation
which to date has not been repeated. In this review we emphasize studies
of midlatitude and tropical cyclones and regional weather and climate
analyses. We also touch upon studies of long swell, sea ice, and
continental ice sheets with Seasat data.Many of these results of the
Seasat mission were serendipitous. In preparation for the major NASA
initiative for the next decade, the Earth Observing Satellite (EOS)
program, we thought it timely to bring some of the Seasat experiences to
the fore, since valuable lessons can be learned from the successes and
the failures (or omissions) of the Seasat program. We have learned of:
1) the synergistic value of integrated, overlapping sampling by several
instruments, 2) the invaluable contribution of carefully planned surface
measurements, and 3) the importance of retaining flexibility in the
system (enough data retention) to allow unexpected and innovative
analysis techniques.
summaryForests have a prominent role in the global carbon cycle, but their response to a changing atmosphere cannot be measured directly. Experimental observations of small trees in CO2-enriched atmospheres must be interpreted carefully if they are to be relevant to the potential responses of forest trees. We grew1 white oak (Quercus alba L.) saplings for four complete growing seasons in open-top chambers with different partial pressures of atmospheric CO2 White oak saplings produced 58% more dry mass in 50 Pa CO2 and 135% more in 65 Pa, compared with plants in ambient (35 Pa) CO2 Although this result might suggest a substantial potential for increased carbon storage in forests, the large difference in growth rate could be attributed to a stimulation of growth very early in the experiment. There was not a sustained effect of C2 on relative growth rate after the first year, and the increased absolute growth rate could persist only so long as leaf area could increase, a condition that would not occur indefinitely in a forest. Nevertheless, annual stem wood production per unit area (growth efficiency) was 37 %, greater in elevated CO2. This increase in growth efficiency, a response that is consistent across diverse studies, implies a potential increase in carbon sequestration by forests, subject to critical assumptions about forest canopy development in a CO2-enriched atmosphere
The first inklings of an understanding of the role played by infraredabsorbing gases in maintaining the warmth of the surface of our planet were voiced early in the 19th century, and by the turn of this century quantitative calculations had been carried out that demonstrated how a change in atmospheric carbon dioxide would alter the earth's mean temperature. However, it was not until the 1960s that much attention was paid to this matter, and in the early 1970s two important summer studies dealing with environmental change fired the imagination of the scientific community. Since then the science (or art) of modeling the climate system has made great strides, aided by faster computers, greater knowledge of the factors involved, and global observations from space of the atmosphere, oceans, and biosphere. This effort has also been bolstered by studies of the behavior of the climate system in the past. There is now a strong consensus that the observed increase in the atmospheric concentrations of carbon dioxide and other infrared-absorbing trace gases is indeed warming the earth, and that this change is caused by mankind. The next set of questions are now being seriously addressed in national and international forums: what are the regional patterns of the changes to be anticipated, especially in terms of rainfall and soil moisture? And what should the countries of the world do about the situation? There is already a sharp debate between the activists, who would take action worldwide to avoid the climate change (or at least slow its advance), and those who would simply wait and see what happens and perhaps take what local measures are necessary to mitigate the effects.
Göttingen, Univ., Phil. Diss.