Surplus Carbon Drives Allocation and Plant-Soil Interactions

Plant growth is usually constrained by the availability of nutrients, water, or temperature, rather than photosynthetic carbon (C) fixation. Under these conditions leaf growth is curtailed more than C fixation, and the surplus photosynthates are exported from the leaf. In plants limited by nitrogen (N) or phosphorus (P), photosynthates are converted into sugars and secondary metabolites. Some surplus C is translocated to roots and released as root exudates or transferred to root-associated microorganisms. Surplus C is also produced under low moisture availability, low temperature, and high atmospheric CO2 concentrations, with similar below-ground effects. Many interactions among above- and below-ground ecosystem components can be parsimoniously explained by the production, distribution, and release of surplus C under conditions that limit plant growth.Non peer reviewe

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Litter production and nutrient resorption in western red cedar and western hemlock forests on northern Vancouver Island, British Columbia

Fine litter fall and concentrations of N and P in green foliage and foliar litter were measured in three species over 1 year in two forest types at three sites on northern Vancouver Island to explore the hypothesis that differences in nutrient use and cycling between the dominant tree species on each forest type contribute to differences in forest floor nutrient availability. Total annual aboveground fine litter fall was significantly higher in second-growth, windstorm-derived 85-year-old stands of western hemlock (Tsugaheterophylla (Raf.) Sarg.) and amabilis fir (Abiesamabilis (Dougl.) Forbes) forests (4137 kg•ha−1) than in adjacent old-growth forests of western red cedar (Thujaplicata Donn) and western hemlock (3094 kg•ha−1) occurring on similar sites. Cedar had significantly lower N concentration in green foliage (9.3 mg•g−1) and litter (4.3 mg•g−1) than the other species in each forest type. Hemlock had a higher litter N concentration in the hemlock–amabilis fir type (8.3 mg•g−1) than in the cedar–hemlock type (6.4 mg•g−1). Cedar resorbed a significantly higher percentage of N during leaf senescence (76%), than hemlock in the cedar–hemlock type (64%), hemlock in the hemlock–amabilis fir type (51%), or amabilis fir (18%). Nitrogen-use efficiency (litter-fall mass/litter N) was considerably higher in cedar (235 kg litter/kg N) than in the other species in either forest type (90–156 kg litter/kg N). These results suggest that differences within and between species in the two types in nutrient use and the amount of nutrients cycling through the litter fall and internal redistribution pathways are contributing to lower rates of nutrient cycling and forest floor nutrient availability in the cedar–hemlock type