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Browsing by Author "Machado, Jose-Luis"

Now showing 1 - 3 of 3
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    Below-ground resources limit seedling growth in forest understories but do not alter biomass distribution
    (2003) Machado, Jose-Luis; Walters, Michael B; Reich, Peter B
    We examined the long-term growth, morphology, biomass distribution, and survival response of seedlings of five conifer species varying widely in shade tolerance to an increase in soil resources in shaded forest understories in northern Wisconsin, USA. In a 4-year experiment, trenching treatment was used to increase soil resource supply to 1-year old seedlings planted across a range of low light microenvironments. Specifically we asked: (1) does an increase in soil resources alter whole-plant growth, biomass distribution patterns, and survival in lowlight, and (2) do species differ in their responses to increasing soil resources? Increased soil resource availability increased height (+11% on average) and dry mass (+23% on average) of all species regardless of light availability. However, there was no evidence that trenching affected biomass distribution for any species, as has been previously reported. Survivorship after four years was positively related to the species' reported shade tolerance ranking and was unaltered by trenching. We concluded that soil resource availability (supply-demand) can limit tree seedling growth in deeply shaded forest understories, but that increased resource availability of the magnitude caused by trenching does not favor tolerant rather than intolerant species, or vice-versa.
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    Biological scaling: Does the exception prove the rule? (Reply)
    (Nature Publishing Group, 2007) Reich, Peter B; Tjoelker, Mark G; Machado, Jose-Luis; Oleksyn, Jacek
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    Universal scaling of respiratory metabolism, size and nitrogen in plants
    (Nature Publishing Group, 2006) Reich, Peter B; Tjoelker, Mark G; Machado, Jose-Luis; Oleksyn, Jacek
    The scaling of respiratory metabolism to body size in animals is considered to be a fundamental law of nature1–11, and there is substantial evidence for an approximate 3 4-power relation. Studies suggest that plant respiratory metabolism also scales as the 3 4-power of mass12–14, and that higher plant and animal scaling follow similar rules owing to the predominance of fractal-like transport networks and associated allometric scaling8–14. Here, however, using data obtained from about 500 laboratory and fieldgrown plants from 43 species and four experiments, we show that whole-plant respiration rate scales approximately isometrically (scaling exponent < 1) with total plant mass in individual experiments and has no common relation across all data. Moreover, consistent with theories about biochemically based physiological scaling15–18, isometric scaling of whole-plant respiration rate to total nitrogen content is observed within and across all data sets, with a single relation common to all data. This isometric scaling is unaffected by growth conditions including variation in light, nitrogen availability, temperature and atmospheric CO2 concentration, and is similar within or among species or functional groups. These findings suggest that plants and animals follow different metabolic scaling relations, driven by distinct mechanisms.