HS Johnson

Bio: HS Johnson is an academic researcher. The author has contributed to research in topics: Photosynthesis & Carbon fixation. The author has an hindex of 1, co-authored 1 publications receiving 230 citations.

Further studies on a new pathway of photosynthetic carbon dioxide fixation in sugar-cane and its occurrence in other plant species.

Abstract: 1. The pathway of photosynthesis in sugar-cane, which gives most of the radio-activity fixed during short periods in (14)CO(2) in C-4 of oxaloacetate, malate and aspartate, was examined under varied conditions. 2. The pattern of labelling was essentially the same with leaves of different ages and with leaves equilibrated at carbon dioxide concentrations in the range 0-3.8% (v/v) and light-intensities in the range 1400-9000ft.-candles before adding (14)CO(2). 3. Radioactive products were examined after exposing leaves of 33 different plant species to (14)CO(2) for 4sec. under standard conditions. 4. A labelling pattern typical of sugar-cane was found in several species of Gramineae but not in others. Of 16 species from other Families only a species of Cyperaceae contained a large proportion of the fixed radioactivity in oxaloacetate, malate and aspartate.

Compositions and fluxes of particulate organic material in the Amazon River1

Abstract: Lignin, elemental, and stable carbon isotope compositions are reported for local plants and for coarse (>63 µm) and fine (<63 µm) suspended particulate materials collected along a 1,950-km reach of the lower Amazon River during four contrasting stages of the 1982–1983 hydrograph. Fluxes of chemically recognizable lignin in the two size classes generally parallel each other along the mainstem with the fine fraction usually predominating. Particulate organic matter transported in the coarse size fraction of the mainstem and its major tributaries is composed of recently formed and well preserved tree leaf debris along with some wood. Organic matter in the fine size fraction is comparatively old, degraded, and rich in immobilized nitrogen and derives primarily from soils. C-4 grasses, which are abundant in the mainstem floodplain (varzea), are not major components of either the coarse or fine particulate material in the river. Particulate organic matter in both size fractions is introduced largely from upstream sources within the Rio Solimoes and Rio Madeira drainage basins. Most of this organic matter is unreactive and is transported conservatively with mineral particles along the Amazon mainstem. However, some downstream compositional trends are seen in both size fractions which reflect the addition or exchange of highly degraded, 13C-depleted, and lignin-poor organic materials from lower basin sources.

Crop Water Deficits

Abstract: Publisher Summary This chapter emphasizes the measurement of plant water potential following the realization of the importance of atmospheric demand in determining plant water deficits. The total water potential concept determines the movement of water through the soil-plant-atmosphere continuum in response to gradients in water potential and of the soil, plant, and atmospheric factors that influence the development of water deficits in plants. A water deficit occurs whenever water loss exceeds absorption. The use of total water potential as the best single indicator of plant water status has its limitations while attempting to understand the effect of water deficits on the various physiological processes involved in plant growth. The chapter discusses the effects of water deficits on crop growth, crop development, and crop yield. The differences in response of plants grown under controlled conditions and in the field are discussed. Some difficulties in extrapolating from controlled environments to the field are presented in the chapter.

Isotopic Evidence of Early Maize Cultivation in New York State

Abstract: Plants metabolize carbon dioxide photosynthetically either through a 3-carbon (Calvin) or 4-carbon pathway. Most plants are of the C-3 type; C-4 plants are primarily grasses adapted to hot, arid environments. Since C-4 plants have a higher 13C/12C ratio than C-3 plants, animals and humans with a significant C-4 plant food-intake will have higher 13C/12C ratios as well. Maize is a C-4 plant, hence maize cultivators living in predominantly C-3 plant environments should show significant isotopic differences from local hunter-gatherers in their skeletal remains; the importance of maize in their diet should also be measurable. The practicability of this method is demonstrated for New York State archaeological materials and wider implications are mentioned.