Carbon neutrality is widely concerned and highly valued by many countries. Biosphere has always maintained the balance between oxidized organic substances and assimilated organic matter, resulting in ...net-zero carbon dioxide (CO
2
) emissions and maintaining its own carbon neutrality. Nature has set a good example for human beings to coordinate oxygen (O
2
) balance and CO
2
balance, and achieve carbon neutrality. How does photosynthetic oxygen evolution initiate carbon and water neutrality? My synthesis shows that photosystem II functions as carbonic anhydrase to catalyze the reaction of CO
2
hydration under physiological conditions, and CO
2
hydration coupled with chemical equilibrium, H
+
+HCO
3
−
→1/2 O
2
+ 2e
−
+2 H
+
+CO
2
, occurs in a photosystem II core-complex. Meanwhile, I focused on the revisiting of four classical heavy oxygen (O
18
) labeling experiments and found that bicarbonate can promote photosynthetic oxygen evolution, and that photosynthetic oxygen evolution can alternately come from bicarbonate and water, not only water. Bicarbonate photolysis and water photolysis account for half of the photosynthetic oxygen evolution respectively, which can well explain the bicarbonate effect, Dole effect and plants’ environmental adaptability. Photosynthetic oxygen evolution initiated the journey of water metabolism and carbon metabolism in nature, which led to the coupling as 1:1 (mol/mol) stoichiometric relationship between the reduction of CO
2
and oxidation of organic carbon, coordinated the evolution of the atmosphere, hydrosphere, lithosphere and biosphere, and realized “carbon neutrality” in the whole Earth system.
If the photosynthetic organisms assimilated only CO
2
in the Archean atmosphere, hydroxide ion in the Archean seawater would not increase. If plants would not consume bicarbonate as a direct ...substrate during photosynthesis, it is difficult to explain the evolution of Earth's environment. To date, it is generally accepted that photosynthetic O
2
evolution of plants come from water photolysis. However, it should be debated by evaluating the effect of bicarbonate in photosynthetic O
2
evolution, analyzing the role of carbonic anhydrase (CA) in photosynthetic O
2
evolution, and the relationship between thylakoid CA and photosynthetic O
2
evolution. In the paper, I propose that bicarbonate is directly used as substrate to participate in photosynthetic O
2
evolution. The rationality of bicarbonate photolysis of plants is discussed from the thermodynamics and evolution of Earth's environment. The isotopic evidence that bicarbonate is not the direct substrate of photosynthetic O
2
release is reexamined, and the new explanation of bicarbonate photolysis in photosynthetic O
2
evolution is proposed.
Photosynthesis is crucial to the reduction of carbon dioxide in the atmosphere. The key enzyme of photosynthesis, Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), has two mutably competing ...substrates, CO
2
and O
2.
It has features of carboxylase and oxygenase. Rubisco performs the function of carboxylase to reduce inorganic carbon to form organic substances, which precondition is that more carbon dioxide accumulates around it. Carbon dioxide concentrating mechanisms (CCMs) are vital to cope with the limit of carbon dioxide. Various bicarbonate use pathway has a differential contribution to inorganic carbon assimilation. Bicarbonate transport, extracellular bicarbonate dehydration, or H
+
-ATPase-driven bicarbonate uptake, which induced CCMs, can support a considerable share of photosynthesis in photosynthetic organisms. However, CCMs in thylakoid membranes may be the most important. The CCMs occurred in the plasma membrane were secondary, evolutionary, and inducible, while CCMs coupled with photosynthetic oxygen evolution in thylakoid membranes, were primitive, major, and indispensable. A hypothetical schematic model of CCMs occurred in the plasma membrane and thylakoid membranes being proposed.
Calcareous soils are characterized by low nutrient contents, high bicarbonate (HCO3-) content, and high alkalinity. The effects of HCO3- addition under zinc-sufficient (+Zn) and zinc-deficient (-Zn) ...conditions on the growth and photosynthetic characteristics of seedlings of two Moraceae species (Broussonetia papyrifera and Morus alba) and two Brassicaceae species (Orychophragmus violaceus and Brassica napus) were investigated. These four species were hydroponically grown in nutrient solution with 0 mM Zn (-Zn) or 0.02 mM Zn (+Zn) and 0 mM or 10 mM HCO3-. The photosynthetic response to HCO3- treatment, Zn deficiency, or both varied according to plant species. Of the four species, Broussonetia papyrifera showed the best adaptability to Zn deficiency for both the 0 mM and 10 mM HCO3- treatments due to its strong growth and minimal inhibition of photosynthesis and photosystem II (PS II). Brassica napus was sensitive to Zn deficiency, HCO3- treatment, or both as evidenced by the considerable inhibition of photosynthesis and high PS II activity. The results indicated different responses of various plant species to Zn deficiency and excess HCO3-. Broussonetia papyrifera was shown to have potential as a pioneer species in karst regions.
Karst habitats are uniquely characterized by high bicarbonate, high nitrate, and low ammonium, which are in-conducive to their growth and biodiversity. The occurrence of inorganic carbon and nitrogen ...in karst soil profoundly affects the carbon/nitrogen metabolism and adaptability of plants. However, there has been no final conclusion to the joint interactions of carbon and nitrogen metabolism in plants under karst habitats. In this study, we selected a karst-adaptable plant Orychophragmus violaceus (Ov), and a non-karst-adaptable plant Brassica napus (Bn) as experimental plants, and compared their joint effects of carbon and nitrogen metabolism under simulated karst habitats. It was found that the two species had different joint effects of carbon and nitrogen metabolisms. Bicarbonate and nitrate joint promoted photosynthetic activity and glucose metabolism, facilitating the carbon/nitrogen metabolism and growth of Ov, but their impacts on the carbon and nitrogen metabolism were insignificant in Bn. Bicarbonate and ammonium joint inhibited the photosynthesis and nitrogen metabolism, but promoted water use efficiency in Ov, leading to its enhance of growth reduction, ammonium toxicity alleviation, and drought resistance, while they inhibited the water use efficiency of Bn. In general, bicarbonate and nitrate/ammonium more significantly joint affected the carbon and nitrogen metabolism in Ov than Bn, which is vital for Ov to adapt to karst habitats.
The worldwide demand for Romaine lettuce (Lactuca sativa L.) is increasing. Regulation measures of supplementary or shading light are often used in the production of lettuce in some regions. However, ...inconsistent results on light saturation point of lettuce from previous studies did not facilitate the regulation of light intensity. In the present study, the effects of different light intensities on chlorophyll fluorescence characteristics and yield in lettuce were investigated. The results show that in the 100 and 800μmolm−2s−1 treatments, the values of qP, ΦPSII, and ETR were low, resulting in low light use efficiency and plant yield in lettuce. In the 200, 400, and 600μmolm−2s−1 treatments, the values of qP, ΦPSII, and ETR were high, resulting in high light use efficiency and plant yield in lettuce. Light-use efficiency in the 200μmolm−2s−1 treatment was the highest, whereas plant yield in the 600μmolm−2s−1 treatment was the highest. No significant difference in plant yield was observed between the 400 and 600μmolm−2s−1 treatment. In addition, judging by the values of Fv/Fm, the lettuce samples were under rather serious stress in the 800μmolm−2s−1 treatment, whereas they were under mild stress in the 600μmolm−2s−1 treatment. Based on these results, an optimal regulation strategy of light intensity that can maximize economic benefits for lettuce growers in some regions of the world is proposed. That is the range of 400–600μmolm−2s−1 is a recommendable light intensity for production of certain types of lettuce, and light intensity of 400μmolm−2s−1 can be an optimal value of supplementary light for winter greenhouse production of certain types of lettuce in higher latitudes, while light intensity of 600μmolm−2s−1 can be an optimal value of shading light for late spring and early autumn production of certain types of lettuce in lower latitudes.
Two of the most important CO2 sequestration processes on Earth are plant photosynthesis and rock chemical dissolution. Photosynthesis is undoubtedly the most important biochemical reaction and carbon ...sink processes on Earth. Karst geological action does not produce net carbon sinks. Photosynthesis and karstification in nature are coupled. Karstification–photosynthesis coupling can stabilize and increase the capacity of karstic and photosynthetic carbon sinks. Bidirectional isotope tracer culture technology can quantify the utilization of different inorganic carbon sources by plants. Bicarbonate utilization by plants is a driver of karstification–photosynthesis coupling, which depends on plant species and the environment. Carbonic anhydrase, as a pivot of karstification–photosynthesis coupling, can promote inorganic carbon assimilation in plants and the dissolution of carbonate rocks. Karst-adaptable plants can efficiently promote root-derived bicarbonate and atmospheric carbon dioxide use by plants, finally achieving the conjugate promotion of karstic carbon sinks and photosynthetic carbon sinks. Strengthening karstification–photosynthesis coupling and developing karst-adaptable plants will greatly improve the capacity of carbon sinks in karst ecosystems and better serve the “Carbon peak and Carbon neutralization” goals of China.
Tea plantations in Karst regions suffer from the serious effects of frequent temporary karst droughts, leading to a decline in tea production and quality in the region. The close relationship between ...growth and electrical parameters of plants, including physiological capacitance, resistance and impedance, can be used to accurately monitor their plant water status online, quickly, accurately, timely and nondestructively. In this study, three tea tree cultivars of Zhonghuang No.2 (ZH), Wuniuzao (WNZ), and Longjing 43 (LJ) with different levels of drought resistance were selected as experimental materials, and experiments were carried out under controlled conditions according to control (soil water content of 40-45%, D0), (keeping D0 no watering to 5 days, D5), (keeping D0 no watering to 10 days, D10), (the first day after D10 is rehydrated to D0 is regarded as R1) and (the fifth day after D10 rehydration to D0 is regarded as R5), to determine intracellular water metabolism and nutrient translocation characteristics based on intrinsic electrical parameters. The photosynthetic characteristics and chlorophyll fluorescence parameters were also determined to investigate the response of water metabolism to simulated karst drought in the three tea tree cultivars. The results indicated that the water metabolism patterns responded to environmental water changes with a medium water-holding capacity, medium water transport rate, and low water-use efficiency, and the nutrient patterns in those tea tree varieties demonstrated with a high nutrient flux per unit area, low nutrient transfer rate, and high nutrient transport capacity. After rehydration, only the electrical characteristics of WNZ returned to the D0 levels, but the net photosynthetic rate of all varieties returned to or even exceeded the D0 levels. The chlorophyll fluorescence parameters could not be used to characterize the recoverability of metabolism in tea trees. The electrical characteristics quickly reflected the response of the water metabolism in plants to environmental changes, and the fusion of electrical characteristics and photosynthetic characteristics was able to more quickly, accurately, and comprehensively reflect the response of water metabolism to temporary karst drought.
Karstification forms tremendous karst carbon sinks in the Earth. Whether terrestrial higher plants can absorb and utilize bicarbonate, there is a key testimony that karst carbon sinks can be ...transformed into carbon sequestrations by terrestrial higher plants. The uptake and use of root-derived bicarbonate, photosynthesis, phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase contents of Broussonetia papyrifera (Bp) and Morus alba L. (Ma) were measured. This study provides the most direct and primary evidence for the transformation using the bidirectional isotope tracer technique. The transformation may result from the synergism in the absorption and utilization of photosynthetic and nonphotosynthetic pathway, and simultaneously strengthen karst carbon sink and carbon sequestrations of plants, while it had no effect on photosynthetic CO
2
assimilation in leaves. Differences in the transformation result in the discrepancies of Bp and Ma in the adaptation to karst environments. Karst-adaptable plants can more regulate the entire carbon cycle.
Photosynthesis is the most important biochemical reaction on Earth. It has co-evolved and developed with the Earth, driving the biogeochemical cycle of all elements on the planet and serving as the ...only chemical process in nature that can convert light energy into chemical energy. Some heavy oxygen isotopic (
18
O) labeling experiments have “conclusively” demonstrated that the oxygen released by photosynthesis comes only from water and are written into textbooks. However, it is not difficult to find that bicarbonate has never been excluded from the direct substrate of photosynthesis from beginning to end during the history of photosynthesis research. No convincing mechanism can be used to explain photosynthetic oxygen evolution solely from water photolysis. The bicarbonate effect, the Dole effect, the thermodynamic convenience of bicarbonate photolysis, the crystal structure characteristics of photosystem II, and the reinterpretation of heavy oxygen isotopic labeling (
18
O) experiments all indicate that the photosynthetic oxygen evolution does not exclude the important role and contribution of bicarbonate photolysis. The recently proposed view that bicarbonate photolysis is the premise of water photolysis, bicarbonate photolysis and water photolysis work together with a 1:1 (mol/mol) stoichiometric relationship, and the stoichiometric relationship between oxygen and carbon dioxide released during photosynthetic oxygen evolution is also 1:1, has excellent applicability and objectivity, which can logically and reasonably explain the precise coordination between light and dark reactions during photosynthesis, the bicarbonate effect, the Dole effect, the Kok cycle and the neutrality of water and carbon in nature. This is of great significance for constructing the bionic artificial photosynthetic reactors and scientifically answering the question of the source of elemental stoichiometric relationships in nature.
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