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In forest ecosystems, the onset of spring photosynthesis may have an important influence on the annual carbon balance. However, triggers for the onset of photosynthesis have yet to be clearly identified, especially for temperate evergreen conifers. The effects of climatic factors on recovery of photosynthetic capacity in a Korean pine forest were investigated in the field. No photosynthesis was detectable when the soil temperature was below 0°C even if the air temperature was far beyond 15°C. The onset of photosynthesis and sap flow was coincident with the time of soil thawing. The rates of recovery of photosynthetic capacity highly fluctuated with air temperature after onset of photosynthesis, and intermittent frost events remarkably inhibited the photosynthetic capacity of the needles. The results suggest that earlier soil thawing is more important than air temperature increases in triggering the onset of photosynthesis in Korean pine in temperate zones under global warming scenarios.

Oxygen is a chemical element with symbol O and atomic number 8

Theodor Wilhelm Engelmann (DE) described the accumulation of, a small, rod-shaped, polarly flagellated putrefactive bacterium, in regions of high oxygen tension surrounding cells of higher and lower plants undergoing photosynthesis. This is one of the earliest recorded examples of chemotaxis ().

Etymology and changes in classification

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The timing of annual onset of photosynthesis ranged from DOY 99 to DOY 117, with an average starting date of DOY 107. The earliest start of photosynthesis appeared in April 2008 (), coinciding with the highest monthly mean air temperature. The latest signs of photosynthesis appeared in April 2006, coinciding with the appearance of the lowest monthly mean air temperature. However, data analysis suggests that air temperature is not the main trigger of the onset of tree photosynthesis, as observed from seasonal evolutions of air and soil temperature and synchronous variations in the daytime net ecosystem carbon exchange (). The onset of photosynthesis coincided with the end of soil thawing, and the maximum lag of onset of photosynthesis related to the end of soil thawing was generally within one day. After onset of photosynthesis, photosynthetic rates obviously fluctuated with daily and seasonal evolutions of air temperature throughout the study period.

The photosynthetic capacity of deciduous trees in boreal and temperate forests varies considerably with the annual cycle of presence and absence of foliage. Therefore, for deciduous trees, the onset of photosynthesis in spring is linked to the easily observable growth of leaves. Several studies report that air temperature triggers the recovery of boreal and temperate deciduous forest photosynthesis in spring (e.g., –), and the effects of air temperature on the onset of photosynthesis have been well modeled . Accordingly, an earlier onset of photosynthesis in spring for these forests is reported following global warming –.

9,000 B.C. - 3,000 B.C. - Mirror H

Strange Science: What is Evolution?

Based on global scale correlations between NDVI and environmental factors, Schultz and Halpert (1993) found that onset of spring photosynthesis is mainly influenced by temperature in cold regions, by both precipitation and temperature in temperate regions, and by precipitation in regions where the amplitude of the annual temperature cycle is small. Such responses have been verified by investigations at the ecosystem scale and individual plant level . Overall, the site-based research results are generally consistent with regional scale findings, but each dataset presents special properties. Suni et al. (2003) reported that air temperature triggers the recovery of evergreen boreal forest photosynthesis in spring. Ensminger et al. (2006) also considered that air temperature is responsible for the onset of photosynthesis in spring. However, onset of photosynthesis in plants has been mostly attributed to soil temperature-related triggers. For example, by using eddy covariance technique, Hollinger et al. (1999) found that significant ecosystem carbon uptake of an evergreen coniferous in the Howland Forest site began with the thawing of the soil in early April, and hence concluded that the threshold for the regulation of photosynthetic carbon assimilation is the spring thawing of forest soil. Control experiments on soil temperature also suggest that the timing of onset of photosynthesis is delayed by delayed soil thawing and advanced by earlier soil thawing .

The timing and rate of recovery of photosynthetic capacity in spring influence the potential carbon balance of boreal and temperate forests. Several approaches have been used to define the seasonal start of ecosystem photosynthesis. Tanja et al. (2003) defined the onset of photosynthesis in five boreal coniferous forests as the date when the half-hourly NEE first falls below 20% of the maximum summer NEE. Moore et al. (2006) defined the onset of photosynthesis in a temperate bog as the date when the estimated daily photosynthesis (GPP) first becomes greater than zero. In the current study, the onset of photosynthesis in Korean pine forest was defined as a cumulative daytime NEE less than zero. This definition avoids the uncertainties in GPP estimations, considering potential errors in estimating daytime ecosystem respiration fluxes because of the light inhibition of leaf respiration . Besides, without consideration of the high nighttime ecosystem respiration of forests with high biomass, NEEd can more sensitively reflect the development of plant photosynthesis. It has to been mentioned that for this proposed method, the onset of photosynthesis will be detected only when the daytime photosynthesis will exceed daytime ecosystem respiration, which could lead to biases, depending on the strength of ecosystem respiration in the spring season. However, from another perspective, this method can effectively prevent the misjudgment caused by the disturbance of earlier onset of photosynthesis of early-spring herbs growing on the forest floor. According to the investigation conducted on April 21, 2005 , there were 12 herb species (including Anemone amurensis, Adonis amurensis, Corydalis repens, and so on) growing on the floor of this pine forest and their biomass was 588.7 kg·hm−2.

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9,000 B.C. - 3,000 B.C. - 1page Mirror Intro

In temperate forests, the onset of spring photosynthesis may have an important influence on the carbon assimilation of trees , and hence influence the carbon balance of forest ecosystems . The onset of photosynthesis is a crucial process in plant phenology. Accurate evaluation of the starting date of photosynthesis and its connections with future climatic factors are essential for understanding and modeling the ecosystem carbon balance. For example, enhanced warming at high northern latitudes has been reported to result in the earlier onset of plant photosynthesis and therefore an increase in forest productivity –.

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Led by Tim White, the research team that identified as a candidate for earliest hominin also proposed it was the ancestor of a later member of that genus: Dated at about 4.4 million years old, this species, nicknamed Ardi, showed signs of tree climbing — including an opposable toe — and bipedalism — evidenced by hip and leg bones. But Ardi held a surprise for the science community; the fossil was strangely unlike a chimpanzee. Ardi served as a reminder that, like humans, chimps have continued evolving away from our last common ancestor too.

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Ozone’s Effects on Plants
Because ozone formation requires sunlight, periods of high ozoneconcentration coincide with the growing season. Just as in damage to people,ozone damage to plants can occur without any visible signs. Many farmers areunaware that ozone is reducing their yields. Ozone enters the plant’sleaves through its gas exchange pores (stomata), just as other atmospheric gasesdo in normal gas exchange. It dissolves in the water within the plant andreacts with other chemicals, causing a variety of problems. Plant physiologistsare still trying to understand the specific pathways and locations ofozone’s effects within plant cells. Physiologists know that some cellmembranes become leaky, possibly because of ozone’s ability to interactwith lipid (fatty) components and/or membrane proteins. Photosynthesis slows,resulting in slower plant growth. Compounds resulting from oxidation by ozoneinterfere with the cell’s energy production in the mitochondria. Suchozone-induced compounds also decrease the numbers of flowers and fruits a plantwill produce, and they impair water use efficiency and other functions. Plantsweakened by ozone may be more susceptible to pests, disease, and drought.

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Further data analysis suggests the existence of a threshold value of accumulated growing degree days (GDD, which is defined as a cumulative sum of daily mean air temperatures above 0°C from the beginning of the soil isothermal stage period) related to the timing of onset of photosynthesis. As observed from , photosynthesis began when the GDD had accumulated to 105°C in all of the observed years. The GDD was significantly higher in 2008 and 2009 than in 2006 and 2007, obviously contributing to the earlier onset of photosynthesis in the latter two years.

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