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...

No abstract

No abstract

Aim Floristic differentiation in the Ryukyu Archipelago has been explained primarily by geohistory, specifically landbridge formation and vicariance at the Tokara and Kerama Gaps, two deep-sea channels through the island arc. This ignores current environmental effects, which may also be important. We therefore tested whether the floristic differentiation pattern is explained primarily by the historical effect of the gaps as barriers, or whether a better understanding of floristic differentiation is achieved when both historical and current environmental factors are incorporated.Location Ryukyu Archipelago, Japan: an assemblage of continental islands.Methods We compiled a presence-absence matrix of 1815 plant species on 26 islands. Floristic dissimilarity distances between islands were calculated using Simpson's similarity index and analysed using cluster analysis. We also conducted multiple regression on distance matrices (MRM) to examine the significance of the historical factors of the gaps and current environmental factors: geographical distance among islands and differences in island area and maximum elevation. ResultsWe detected clear patterns of floristic differentiation across the gaps. Using the two gaps as explanatory variables, the MRM showed that both had significant effects on floristic dissimilarity distance. However, when geographical distance was added to the explanatory model, the Kerama Gap effect disappeared. When all five explanatory variables were used, the Tokara Gap and geographical distance had positive effects, but area difference had a negative effect. The Kerama Gap and difference in maximum elevation had no effect. Main conclusionsThe geographical pattern of floristic differentiation appears to indicate the influence of both gaps. However, the MRM indicates that the floristic differentiation across the Kerama Gap is no more than could be explained solely by geographical distance. Across the Tokara Gap, however, floristic differentiation is larger than geographical distance alone can explain. This additional differentiation is attributable to the effect of the historical barrier. To verify the significance of historical effects of vicariance on island biota, the confounding effects of geographical distance must be considered. The distance decay of floristic similarity and negative effect of area difference on floristic differentiation demonstrate that floristic differentiation is better understood by incorporating both historical and current environmental factors.

Phosphorous (P) fertilization is the major mineral nutrient yield determinant among legume crops. However, legume crops vary widely in the ability to take up and use P during deficiency. The aim here was to compare P uptake and translocation, biological nitrogen fixing ability and photosynthetic rate among mashbean (Vigna aconitifolia cv. 'Mash-88'), mungbean (Vigna radiata cv. 'Moong-6601') and soybean (Glycine max L. cv. 'Tamahomare') during deficiency in hydroponics. Two treatments, the withdrawal of P from the solution (Pdeprivation) and continued P at 160 lM (P sufficient) were effected at the pod initiation stage. Plants were grown for 20 days. Short-term labeling with 32 P showed the uptake and distribution of P into plant parts. Withdrawal of P from the solution reduced biomass, photosynthetic activity, and nitrogen fixing ability in mungbean, and mashbean more than in soybean. P deprivation decreased P accumulation more than N accumulation. The decrease was more severe in mungbean and mashbean than soybean. More P was translocated and distributed into leaves in soybean than in mungbean and mashbean. Leaf P amount was more correlated to leaf area than to photosynthetic rate per unit leaf area among all three legume species. The results indicate that selection for increased efficiency of P utilization and leaf area may be used to improve leguminous crops.

Allometric relationships for estimating the phytomass of aboveground organs (stem, branches, leaves and their sum) and the leaf area in the mangrove Kandelia candel (L.) Druce were investigated. The variable D 0.1 2 H (D 0.1 stem diameter at a height of H/10, H tree height) showed better accuracy of estimation than D 2 (D, DBH) or D 2 H. A moderate relationship was found when the branch weight, leaf weight and leaf area were plotted against D B 2 (D B stem diameter at a height of clear bole length). A strong linear relationship was found between leaf area and leaf weight (R 2 =0.979). The aboveground weight (w T ) showed a strong relationship when plotted against D 0.1 2 H (R 2 =0.958), but very weak relationships were obtained against D 2 (R 2 =0.300) and D 2 H (R 2 =0.316). The w T also showed a proportional relationship (R 2 =0.978) to D 0.1 2 H with a proportional constant of 0.04117 kg cm −2 m −1 (R 2 =0.978). Taking into account the allometric relationships of the weight of aboveground organs or leaf area per tree to different dimensions, such as D 2 , D 2 H, D B 2 and D 0.1 2 H, a standard procedure for estimating the biomass and leaf area index in the K. candel stand, including the shorter trees, is proposed.

Attempts were made to quantify the carbon and nitrogen pools in a monospecific and pioneer mangrove stand of Kandelia obovata Sheue, Liu & Yong, Okinawa Island, Japan. The leaf C and N concentrations on a leaf area basis decreased with increasing PPFD (Photosysthetic Photon Flux Density). The total C and N stocks in foliage were estimated as 3.55 Mg ha -1 and 0.105 Mg ha -1 , respectively. The bark (45.6-48.6% for C and 0.564-0.842% for N) contained significantly higher amount of C (P < 0.05) and N (P < 0.01) than wood (46.2-47.8% for C and 0.347-0.914% N). The total C stock of stem was 23.2 Mg ha -1 in wood and 8.33 Mg ha -1 in bark, and the total N stock was 0.222 Mg ha -1 in wood and 0.116 Mg ha -1 in bark. The root wood (37.1-45.0%) contained significantly higher amount of C than root bark (35.4-40.7%) (P < 0.01). The total C stock of root was 14.2 Mg ha -1 in wood and 12.6 Mg ha -1 in bark, and the total N stock of root was 0.157 Mg ha -1 in wood and 0.155 Mg ha -1 in bark. The soil organic C and total N stocks within 1 m soil depth were estimated as 57.3 Mg ha -1 and 2.73 Mg ha -1 , respectively. The C pool in aboveground biomass (35.1 Mg ha -1 ) was 1.3 times as large as that in belowground biomass (26.9 Mg ha -1 ). However, the soil organic C pool (57.3 Mg ha -1 ) was similar to the total C pool (62.0 Mg ha -1 ) of vegetation, indicating that the mangrove stored a large part of production in the soil. About 50% of the C was in the soil. The N pool in aboveground biomass (0.442 Mg ha -1 ) was 1.4 times as large as that in belowground biomass (0.312 Mg ha -1 ). The soil N stock was 3.3 times as large as the biomass N stock (0.754 Mg ha -1 ).

Barium (Ba)-induced phytotoxicity at 100, 1000, or 5000 microM Ba in soybean plants (Glycine max) was investigated under hydroponic culture conditions. Soybean growth and leaf photosynthetic activity were significantly inhibited by all three levels of Ba treatments. In the case of photosynthetic activity, 5000 microM Ba treatment shutdown stomatal opening and perturbed carbon fixation metabolism and translocation. However, 100 and 1000 microM Ba treatments shut down stomatal opening and inhibited carbon fixation, but without perturbation of leaf carbon fixation-related metabolism. Potassium (K) absorption by soybean roots was also reduced in all three Ba treatments. This decreased K absorption reduced K localization at guard cells. Barium accumulation in guard cells also inhibited K transport from epidermal cells to guard cells. This lack of K in guard cells resulted in stomatal closure. As a result of inhibition of K transport into guard cells and stomatal shutdown, photosynthetic activity and plant productivity were inhibited. Our experiment indicates that Ba has phytotoxic effects on soybean plants by inhibiting photosynthesis.