The scaling of respiratory metabolism with body mass is one of the most pervasive phenomena in biology. Using a single allometric equation to characterize empirical scaling relationships and to evaluate alternative hypotheses about mechanisms has been controversial. We developed a method to directly measure respiration of 271 whole plants, spanning nine orders of magnitude in body mass, from small seedlings to large trees, and from tropical to boreal ecosystems. Our measurements include the roots, which have often been ignored. Rather than a single power-law relationship, our data are fit by a biphasic, mixed-power function. The allometric exponent varies continuously from 1 in the smallest plants to 3/4 in larger saplings and trees. The transition from linear to 3/4-power scaling may indicate fundamental physical and physiological constraints on the allocation of plant biomass between photosynthetic and nonphotosynthetic organs over the course of ontogenetic plant growth.allometry | metabolic scaling | mixed-power function | whole-plant respiration | simple-power function F rom the smallest seedlings to giant trees, the masses of vascular plants span 12 orders of magnitude in mass (1). The growth rates of most plants, which are generally presented in terms of net assimilation rates of CO 2 , are believed to be controlled by respiration (2, 3). Furthermore, many of the CO 2 -budget models of plant growth and carbon dynamics in terrestrial ecosystems are based on whole-plant respiration rates in relation to plant size (2, 4-7). Thus far, however, there have been few studies of wholeplant respiration over the entire range of plant size from tiny seedlings to large trees. The purpose of the present study was to quantify the allometric scaling of metabolism by directly measuring whole-plant respiration over a representative range of sizes.For the past century, the scaling of metabolic rate with body size has usually been described using an allometric equation, or simple power function, for the form (8-17)where Y is the respiratory metabolic rate (μmol s −1 ), F is a constant (μmol s −1 kg -f ), M is the body mass (kg), and f is the scaling exponent. The exponent f has been controversial, and various values have been reported based on studies of both animals and plants (15). Recently, it was suggested that f = 1 for relatively small plants, based on data for a 10 6 -fold range of body mass (16), including measurements using a whole-plant chamber (18,19). If f = 1, this means that whole-plant respiration scales isometrically with body mass, which may be reasonable in the case of herbaceous plants and small trees because nearly all of their cells, even those in the stems, should be active in respiration. However, it was suggested that f = 3/4 based originally on empirical studies of animal metabolism (8). This idea is consistent with the mechanistic models of resource distribution in vascular systems (10, 11), including the pipe model (20, 21) and models based on space-filling, hierarchical, fractal-like networks of br...

One-half of the total deaths in chronic dialysis patients are due to cardiovascular disease; however, the precise incidence and relative risk of those compared to normals are not known. Therefore, we sought to determine the annual incidence of cardiovascular disease and relative risk of those on chronic dialysis to the general population. Both the general population (1.2 million, Census 1990) and chronic dialysis patients (N = 1,609) in Okinawa, Japan were studied prospectively from April, 1988, to March, 1991. Diagnosis of stroke was made by symptoms and brain CT scan, and acute myocardial infarction was done by changes in electrocardiogram and serum enzymes. The relative risk (observed/expected ratio) was calculated by using the standardized morbidity rate obtained in both sexes and age-class every 10 years in the general population. Forty-one stroke (8 cerebral infarction, 31 cerebral hemorrhage, and 2 subarachnoid hemorrhage) and four acute myocardial infarction cases were registered during the study period in chronic dialysis patients. The incidence per 1,000 person-year was 11.5 in stroke, 2.2 in cerebral infarction, 8.7 in cerebral hemorrhage, 0.6 in subarachnoid hemorrhage, and 1.1 in acute myocardial infarction. The relative risk compared to normals was 5.2 in stroke, 2.0 in cerebral infarction, 10.7 in cerebral hemorrhage, 4.0 in subarachnoid hemorrhage, and 2.1 in acute myocardial infarction. Cerebral hemorrhage occurred at 10 years younger than that of the general population (P < 0.001) and was associated with high prevalence of hypertension and low levels of serum albumin and cholesterol. Our results confirm the importance of blood pressure control and nutritional status in chronic dialysis patients.

Allometric theory on mechanisms of the self—thinning rule was tested for Nothofagus solandri populations from the Craigieburn Range, New Zealand and for Pinus densiflora stands from northern Japan. The self—thinning rule describes a consistent relationship of mean plant mass to the approximately —3/2 power of plant density in evenaged monocultures. Although his rule has been described for various species, mechanisms that produce certain relationships have not been well understood. We tested an allometric theory of Long and Smith of the self—thinning rule that assumes constant foliage mass density and allometry for mean dimensions of populations that represent dense conditions for given mean plant sizes. Only stands at maximum crowding were selected for analysis. The self—thinning boundary of N. solandri showed an exponent —1.13 with a 95% ci of —1.25 to —1.02 for mean stem mass. This was significantly shallower than the conventional value of the exponent —3/2, but was identical to the predicted exponent from the allometric theory. The thinning coefficient was also explained numerically by this hypothesis. In contrast, analysis of published data for P. densiflora indicated that the thinning exponent did not differ from the proposed —3/2. Empirical thinning lines varied substantially depending on species and plant parts considered; however, the allometric theory consistently provided predictions that agreed with the observed thinning relationships. Implications for the geometry of self—thinning populations and generality of the allometric theory are discussed.

Circumboreal forest ecosystems are exposed to a larger magnitude of warming in comparison with the global average, as a result of warming-induced environmental changes. However, it is not clear how tree growth in these ecosystems responds to these changes. In this study, we investigated the sensitivity of forest productivity to climate change using ring width indices (RWI) from a tree-ring width dataset accessed from the International Tree-Ring Data Bank and gridded climate datasets from the Climate Research Unit. A negative relationship of RWI with summer temperature and recent reductions in RWI were typically observed in continental dry regions, such as inner Alaska and Canada, southern Europe, and the southern part of eastern Siberia. We then developed a multiple regression model with regional meteorological parameters to predict RWI, and then applied to these models to predict how tree growth will respond to twenty-first-century climate change (RCP8.5 scenario). The projections showed a spatial variation and future continuous reduction in tree growth in those continental dry regions. The spatial variation, however, could not be reproduced by a dynamic global vegetation model (DGVM). The DGVM projected a generally positive trend in future tree growth all over the circumboreal region. These results indicate that DGVMs may overestimate future wood net primary productivity (NPP) in continental dry regions such as these; this seems to be common feature of current DGVMs. DGVMs should be able to express the negative effect of warming on tree growth, so that they simulate the observed recent reduction in tree growth in continental dry regions.

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