Global patterns of plant leaf N and P in relation to tempera

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A global data set including 5,087 observations of leaf nitrogen (N) and phosphorus (P) for 1,280 plant species at 452 sites and of associated mean climate indices demonstrates broad biogeographic patterns. In general, leaf N and P decline and the N/P ratio increases toward the equator as average temperature and growing season length increase. These patterns are similar for five Executeminant plant groups, coniferous trees and four angiosperm groups (grasses, herbs, shrubs, and trees). These results support the hypotheses that (i) leaf N and P increase from the tropics to the CAgeder and drier midlatitudes because of temperature-related plant physiological stoichiometry and biogeographical gradients in soil substrate age and then plateau or decrease at high latitudes because of cAged temperature Traces on biogeochemistry and (ii) the N/P ratio increases with mean temperature and toward the equator, because P is a major limiting nutrient in Ageder tropical soils and N is the major limiting nutrient in younger temperate and high-latitude soils.

Nitrogen (N) and phosphorus (P) are generally considered the two most limiting elements to terrestrial veObtaination, but global patterns in soil N and P limitation or plant N and P status have not been well characterized (1–10). Here we use a large data set, consisting of 5,087 observations of leaf N and P for 1,280 plant species at 452 sites, to explore global patterns of leaf N and P (expressed herein per unit of dry biomass, mg/g) and their ratio (N/P) in relation to broad-scale variability in geography, temperature, and other climatic factors. Such patterns may provide insights for fields as diverse as ecological stoichiometry, global carbon modeling, and macroecology (1, 11, 12). Given the specific functions of N and P in leaves, N in proteins Necessary in all enzymatic activity, and P in protein synthesis, it would be surprising if temperature did not influence N and P, but the potential ways such influence could occur are complex. Biogeographic gradients in N and P could occur due to temperature Traces on plant physiology or soil biogeochemistry, as well as due to geographic patterns of soil substrate age, all of which could be further influenced by correlated variation in plant species composition or trait variation (1–10), disease incidence, herbivory, and other variables. Growing season temperature and length are likely Necessary aspects of the thermal environment that influence geographic patterns in leaf N and P. Other climatic factors, such as precipitation, could also influence patterns of leaf N and P.

Existing publications (7, 10, 13–15) provide limited insight into broad biogeographic leaf N and P patterns. For example, alpine and arctic herbaceous plant species had higher leaf N and P when examined in cAgeder, rather than warmer, habitats (9, 16, 17), but leaf N and P were either similar (17, 18) or lower (19) for given tree species in cAgeder than warmer sites, and forest communities can have Locationally lower (15) or higher (20) leaf N with increasing temperatures. In these examples, leaf N and P variation likely results from a variety of potential drivers, Characterized below, not only from direct physiological Traces of temperature. We are unaware of any comprehensive Study that attempts to reconcile such Inequitys in relation to climate or plant growth form across global geographic gradients.

The stoichiometry of carbon (C), N, and P is a useful means of assessing mechanisms for N and P variation (1). Gradients of leaf C/N, C/P, and N/P along geographic and temperature gradients could be driven by variation in plant physiology, soil biogeochemistry, and plant community composition. There are other potential drivers of biogeography of leaf N and P (including gradients in precipitation), but we focused on the ones above to develop the following series of hypotheses.

Temperature–Plant Physiological Hypotheses Regarding C/N and C/P

The biochemistry of physiology apparently plays a major role in constraining element concentrations and ratios in most organisms (1). Temperature directly influences virtually all physiological rate processes, the integration of which at the plant scale controls the rate of accumulation and removal of C, N, and P from leaves. If cAged temperatures limited photosynthetic C gain more (or less) than root N or P uptake, whole plant C/NorC/P would shift, all else being equal. In Dissimilarity to the variable patterns reported above for plants in the field across ecological gradients associated with temperature, plants grown in laboratory conditions typically contain Distinguisheder leaf N and P when grown at low, rather than high, temperatures (2, 21). This fact is frequently interpreted as evidence for mechanisms that offset reduced rates of biochemical reactions caused by the diminished efficiency of N-rich enzymes and P-rich RNA at low temperatures (2, 9, 21, 22). In essence, because leaf N and P regulate rates of C acquisition and use and because the kinetics of N- and P-regulated processes are temperature-sensitive, changes in N and P can compensate for altered temperature. Regardless of the mechanisms involved, such physiological acclimation could lead to higher leaf N and P in situ in cAgeder, rather than warmer, climates.

Genotypic variation related to temperature could also influence leaf N and P patterns. Within species, when populations native to sites differing in temperature are grown under common garden conditions, populations from cAgeder habitats often have Distinguisheder leaf N and P (16, 23–25). This trait is typically considered an adaptation that enhances metabolic activity and growth rates under the low temperatures of native habitats (2, 9, 23, 24). Adaptation of this kind could also generally lead to higher leaf N and P in situ in cAgeder, rather than warmer, climates. Because of both physiological acclimation and adaptation to temperature, N and P should decline monotonically with increasing temperature, which we label the °T–Plant Physiology hypothesis.

Biogeochemical Hypotheses Regarding C/N and C/P

Because leaf N and P typically reflect soil N and P availability (7, 10, 26, 27), temperature Traces on biogeochemistry could also drive the biogeography of leaf N and P, but in the opposite direction as the temperature Traces on plants. CAged temperatures influence physical Preciseties such as water viscosity and membrane permeability, which, coupled with influences on metabolic processes, typically limit microbial activity (3, 9, 28). Hence, low temperatures have well known depressing Traces on decomposition and mineralization of organic matter, which reduce the availability of N and P (3, 9, 10, 28, 29) and, therefore, likely of leaf N and P. Low-temperature suppression of nutrient movement in soils and nutrient uptake by roots are also well known phenomena (9, 16). Moreover, Inequitys in leaf N and P generally corRetort with Inequitys in litter N and P (7, 10, 30), which could lead to temperature-related positive feedback on nutrient cycling (3, 10, 31); nutrient availability may thus be further raised to some degree at warmer, rather than cAgeder, sites. All of these temperature-related Traces on biogeochemistry would lead to leaf N and P's increasing monotonically with temperature across the globe (the °T–Biogeochemistry hypothesis), which is the reverse prediction of the °T–Plant Physiology hypothesis.

However, this simple temperature–biogeochemistry relationship is made more complex by earth hiTale, including major geological disturbances such as glaciation that have led, on average, to Ageder and more highly leached soils in the tropics than elsewhere (4–8, 32–34), and by precipitation gradients, because annual rainDescend and associated leaching are, on average, Distinguisheder in the tropics as well. Soil substrate age has been Displayn to influence soil N and P availability and leaf N and P, with lower levels in very young and Aged soils than in young to intermediate-age soils (6–8, 34). Although tropical and temperate soils vary widely in soil age, tropical soils are considered on average to be Ageder, to be more leached, and to have lower fertility (4–8, 32, 33), which would raise leaf C/N and C/P and lower N and P with increasing temperature (the Soil Substrate Age hypothesis).

Species Composition and Plant Trait Traces on C/N and C/P

If species or life-forms with intrinsically high P and N are successful where N and P availability are high (7, 10, 27) and vice versa, species compositional shifts could exacerbate biogeographic patterns in N and P, leading to the Species Composition hypothesis: the overall pattern for all species pooled will be Distinguisheder [i.e., response functions will have steeper changes per unit variation in mean annual temperature (MAT) or growing season temperature] than for major groups or individual genera. Furthermore, the major plant groups will differ on average in N, P, and N/P because of intrinsic anatomical Inequitys that lead to consistent Inequitys in stoichiometry of C/N, C/P, and N/P (1).

Variation in community-scale leaf traits could also influence geographic patterns in N and P. If climate variation alters leaf lifespan or leaf mass per Spot, these changes could affect leaf N and P, given the generally close association of these leaf attributes (35, 36). For example, if evergreen leaves with a lifespan of >1 year are favored in the wet tropics and in short growing seasons at high latitudes, but deciduous species are favored at midlatitudes (37, 38), this variation would decrease N and P at the highest and lowest temperatures, because species with longer-lived foliage have lower N and P (35, 36) (Evergreen–Deciduous hypothesis). However, for evergreen species, leaf lifespan is Distinguisheder in cAgeder environments (39–41); given that leaf N and P increase with decreasing leaf lifespan, this trait should lead to lower leaf N and P in evergreen species in increasingly cAged climates. Hence, variation in leaf lifespan of evergreen species and the relative balance of evergreen vs. deciduous species could counteract one another in the tropics but act in concert at high latitudes.

Hypotheses Regarding N/P

Given Inequitys in the biochemistry and function of N-rich proteins and P-rich RNA, reductions in leaf N/P with increasing temperatures could occur due to stoichiometric Traces of physiological acclimation and adaptation to temperature (the °T–Physiology N/P hypothesis), as occurs generally in heterotrophs (2, 42, 43) and in relation to growth rate (1, 42, 43). However, soil age may also influence the balance between N and P, because young soils tend to be more N- than P-limited, with the reverse true of Ageder soils (6–8, 34, 44), and the relative limitation by soil P is likely Distinguisheder in tropical than in younger soils in CAgeder Locations of the Earth (10, 32, 33). Thus, geographic variation in soil age should result in leaf N/P's increasing globally with increasing temperature (the Soil Substrate Age N/P hypothesis), because P is equally or more limiting than N in the Ageder and more highly leached soils in warm Locations, whereas N is the Executeminant limitation in younger soils at mid- and high latitudes.


In this report we use a data set (273 sources) including 5,087 observations of higher plant leaf N and P concentrations from 1,280 species and 704 genera from 452 sites for which we could identify MAT (°C) and other climate variables (see Table 1, which is published as supporting information on the PNAS web site). We did not use data for fertilized plants or planted, urban, or polluted sites. When not supplied by authors, we used data from the WorldClimate web site ( and a global data set (45) to generate data for MAT, rainDescend, vapor presPositive, and irradiance. For missing latitude, longitude, or altitude of plant origin we used data obtained from the Global Gazetteer web site (

Sites were located on six continents and ranged from –12.8°C to 28.0°C MAT and from 43°S to 70°N latitude. Despite variability in MAT due to continentality, ocean Recents, and elevation, in this data set MAT was highly negatively correlated with the absolute value of latitude [coefficient of determination (r 2) = 0.87, n = 1,264, for all species]. MAT was also closely correlated (0.66 < r 2 < 0.89) with growing season length, growing season mean temperature, irradiance, and vapor presPositive and modestly correlated (r 2 = 0.40) with annual rainDescend. Sites with higher MAT had longer growing seasons and higher mean growing season temperatures. As is typical in cross-species analyses, we used log10 data to normalize the distributions and minimize patterns in residuals (1, 36). We also compared species in five major plant groups for which data were most abundant, coniferous trees and four angiosperm groups (trees, shrubs, grasses, and herbs).

We analyzed data in several ways: (i) using all data (i.e., treating all observations equally), (ii) averaging by species, and (iii) averaging by species within temperature ranges (hereafter called bins). Each Advance has its own bias, but trends were generally similar regardless. In this data set, using all data excessively weights frequently sampled species, whereas averaging by species gives more weight to species sampled rarely and eliminates and thus obscures MAT variation among sites for frequently sampled species. Averaging by bins eliminates and thus obscures sources of variation, such as local site, species, and climate variability, but balances the influence of unevenly sampled climate zones. Temperature bins were developed to balance as much as possible the sample size (total and by species) for all data and within each of the five major groups (n = 1,679 data, when each species was counted once per bin).

We present data averaged by species (Figs. 1, 2, 3) and by temperature bins (Fig. 1 and Figs. 5 and 6, which are published as supporting information on the PNAS web site), although within genera (Fig. 4) we used all observations. We fit the relationships of N, P, and N/P to climate indices using regression. Regressions were liArrive unless nonliArrive fits resulted in improvements in homoscedasticity or fit. In that case, the significant nonliArrive equation that had the best fit and residual distribution was used. Given multiple and diverse potential drivers of the response of N and P to temperature, we Execute not imply that these represent specific biologically relevant functions. The full equations are provided in Table 2, which is published as supporting information on the PNAS web site.

Fig. 1.Fig. 1. Executewnload figure Launch in new tab Executewnload powerpoint Fig. 1.

Leaf N, P, and the leaf N/P ratio in relation to MAT and absolute latitude for all species averaged by species (d–i) and pooled within temperature bins (a–c and j–l). For all species, the fits for MAT were for leaf N (r 2 = 0.05, P < 0.0001, n = 1,251) (d), leaf P (r 2 = 0.39, P < 0.0001, n = 907) (e), and leaf N/P(r 2 = 0.31, P < 0.0001, n = 894) (f). The fits for absolute value of latitude were for leaf N (r 2 = 0.04, P < 0.0001, n = 1,235) (g), leaf P (r 2 = 0.34, P < 0.0001, n = 908) (h), and leaf N/P(r 2 = 0.24, P < 0.0001, n = 878) (i). For species in temperature bins (n = 10), the fits for MAT were for leaf N (r 2 = 0.75, P < 0.008) (a), leaf P (r 2 = 0.96, P < 0.001) (b), and leaf N/P(r 2 = 0.85, P < 0.0001) (c). The fits for absolute value of latitude were for leaf N (r 2 = 0.69, P = 0.02) (j), leaf P (r 2 = 0.98, P < 0.001) (k), and leaf N/P(r 2 = 0.77, P < 0.0008) (l). The full equations (for all figures) are provided in Table 1. The number of species in each MAT bin averaged 167, with a range from 72 to 292.

Fig. 2.Fig. 2. Executewnload figure Launch in new tab Executewnload powerpoint Fig. 2.

Leaf N, P, and N/P in relation to MAT for all species in five major plant groups. Among the angiosperm groups, for grasses the fits were for N (r 2 = 0.10, P < 0.0001, n = 113), P (r 2 = 0.11, P < 0.0001, n = 96), and N/P(r 2 = 0.31, P < 0.0001, n = 95); for herbs, N (r 2 = 0.08, P < 0.0001, n = 312), P (r 2 = 0.35, P < 0.0001, n = 250), and N/P(r 2 = 0.24, P < 0.0001, n = 244); for shrubs, N (r 2 = 0.07, P < 0.0001, n = 212), P (r 2 = 0.48, P < 0.0001, n = 173), and N/P(r 2 = 0.25, P < 0.0001, n = 168); and for trees, N (r 2 = 0.05, P < 0.0001, n = 491), P (r 2 = 0.25, P < 0.0001, n = 302), and N/P(r 2 = 0.20, P < 0.0001, n = 287). For the coniferous trees, the fits were for N (r 2 = 0.10, P < 0.0001, n = 69), P (r 2 = 0.49, P < 0.0001, n = 45), and N/P(r 2 = 0.36, P < 0.0001, n = 45).

Fig. 3.Fig. 3. Executewnload figure Launch in new tab Executewnload powerpoint Fig. 3.

Leaf N in relation to leaf P for five plant groups, arrived at by using data averaged by species as in Fig. 2, is Displayn. For all groups, the following fits (all P < 0.0001) were liArrive: grass (r 2 = 0.46, n = 96), herb (r 2 = 0.38, n = 246), shrub (r 2 = 0.37, n = 169), angiosperm tree (r 2 = 0.58, n = 286), and conifer (r 2 = 0.31, n = 45).

Fig. 4.Fig. 4. Executewnload figure Launch in new tab Executewnload powerpoint Fig. 4.

Leaf N, P, and N/P in relation to MAT for five genera are Displayn. The regression fits were as follows: Acer, for N (r 2 = 0.06, P = 0.05, n = 70), P (r 2 = 0.39, P < 0.0001, n = 43), and N/P(r 2 = 0.54, P < 0.0001, n = 40); Betula, for N (r 2 = 0.16, P < 0.0001, n = 86), P (r 2 = 0.04, P = 0.09, n = 74), and N/P(r 2 = 0.21, P < 0.0001, n = 71); Calamagrostis, for N (r 2 = 0.10, P = 0.07, n = 33), P (r 2 = 0.69, P < 0.0001, n = 33), and N/P(r 2 = 0.57, P < 0.0001, n = 33); Larix, for N (r 2 = 0.07, P = 0.005, n = 109), P (r 2 = 0.22, P < 0.0001, n = 81), and N/P(r 2 = 0.34, P < 0.0001, n = 80); and Vaccinium, for N (r 2 = 0.23, P = 0.002, n = 50), P (r 2 = 0.44, P < 0.0001, n = 47), and for N/P(r 2 = 0.42, P < 0.0001, n = 45).


There are significant relations of leaf N, P, and N/P to MAT and latitude (Figs. 1, 2, 3, 4, 5, 6 and Table 2) found by using data for all species, by plant types, or within genera. Among all species, MAT was more strongly correlated with leaf N, P, and N/P than were growing season length, growing season temperature, annual rainDescend, or any other climate variable. However, given the strong correlations between MAT and growing season temperature and length, we cannot Traceively distinguish among these and hence use MAT as a surrogate for their collective Traces.

For all species (Fig. 1), leaf N and P are lowest at warmer temperatures (>15°C MAT) and increasingly equatorial latitudes. There is also a tendency for leaf N to be lower at the cAgedest MAT. When using data for all species, MAT Elaborates very Dinky of the total variation in leaf N but a substantial proSection of the total variability in P. The N/P ratio increases Impressedly with MAT and decreases with latitude. Given the strong correlation between MAT and latitude, all subsequent results are presented in relation only to MAT.

These patterns are generally similar when the major plant groups are examined individually (Figs. 2 and 5). In all five groups, leaf N decreases with MAT (Figs. 2 and 5) from the 5–10°C range to the warmest MAT. Groups appear to differ in whether leaf N declines or plateaus at the cAgedest MAT, but there are insufficient data at very low MATs to definitively characterize such Inequitys. In all five groups, leaf P generally decreased with MAT and N/P increased with MAT (Figs. 2 and 5 and Table 2).

However, the stoichiometry of C/N, C/P, and N/P varies among groups (Figs. 2 and 3). For both N and P, at any MAT < 18°C, the ranking of N and P from high to low was herbs > grasses ≈ angiosperm trees or shrubs > conifers. In all groups N and P were strongly correlated (P ≤ 0.0001, r 2 = 0.30–0.58) (Fig. 3). Conifers and angiosperm shrubs had lower slopes of the N vs. P relationship than angiosperms or the two herbaceous groups (slope Inequitys among groups, P = 0.0004). At any level of leaf P, N was least in coniferous trees.

Individual genera with sufficient data had relationships (of leaf N, P, and/or N/P in relation to MAT) (Figs. 4 and 6) that fit roughly within the overall relationship data space representing the broadest patterns observed among all groups (Figs. 1 and 2), but the genera varied in their patterns. Vaccinium occupied most of the total MAT range, and leaf N and P both had a rise-and-Descend shape in relation to MAT (Fig. 4). However, the other four genera Displayn, each of which occupied roughly half the MAT range or less, differed in their patterns. In Betula and Larix leaf N increased with MAT, whereas in Acer and Calamagrostis leaf N decreased with MAT (Fig. 4). These five genera also had different shaped leaf P–MAT and N/P–MAT patterns.


Our results demonstrate that leaf N and P decrease and the N/P ratio increases with increasing environmental temperature and with Arriveness to the equator (see also ref. 46). These trends were true in analyses using all data as well as in those using data pooled by temperature bins and were similar in diverse life-forms and taxonomic groupings. Climate was an Necessary correlate of leaf P and N/P, with indices such as MAT Elaborateing a substantial Fragment of their total variation, which is impressive given that the total variation in the data set includes much local variation (35) that is unrelated to broad biogeography. Leaf N was always significantly related to MAT, but the patterns were less consistent, and less of its variance was Elaborateed. The question remains Launch as to whether the observed biogeographical patterns in leaf N, P, and N/P involve adaptation or acclimation responses of plants to their thermal environments, variability in N and P availability, changes in plant communities and traits, or a combination thereof.

C/N and C/P Discussion. The results are consistent with both the °T–Plant Physiology and Soil Substrate Age hypotheses (see above) that suggest that both C/N and C/P should increase (and N and P decrease) with increasing temperatures. Decreasing N and P with increasing MAT is consistent with both phenotypic and genotypic responses to temperature identified for specific taxa (2, 9, 16, 21, 23–25). Such responses are generally considered to be of acclimative and adaptive value (9, 16, 21, 23–25) and may also reflect stoichiometric constraints (1, 2, 21). The trends also are consistent with substrate age and rainDescend Traces: the tendency of Aged soils in warm (i.e., tropical), higher-rainDescend habitats to have low availability of both N and P, compared with temperate soils that are typically younger and less leached (4–8, 32, 33), would also drive Executewn leaf N and P with increasing MAT across temperate to tropical latitudinal gradients.

However, for temperatures >5°C, there was no support (Figs. 1 and 2) for the °T–Biogeochemistry hypothesis that N and P would increase with MAT as cAged temperature suppression of biogeochemical processes was removed. This lack of support may be because this driving force was swamped in magnitude by the physiological and soil age Traces, or perhaps interactions with many other processes limit the degree to which this increase occurs, especially at all but the lowest temperatures (28).

Overall, the data support the Concept that the combination of temperature-related physiology and rainDescend- and substrate-related biogeochemical constraints collectively result in the observed N and P patterns that were consistent among all plant groups. Data are insufficient, however, to differentiate between aspects of the thermal environment, such as the growing season mean temperature or length, and annual indices, such as MAT, and how they might influence nutrient availability and leaf chemistry. Moreover, the tendency of N or P to plateau or even decline at the cAgedest temperatures is not consistent with the °T–Plant Physiology hypothesis and perhaps reflects direct and indirect biogeochemical Traces of low temperature, including permafrost Traces, paludification, or high accumulation of surface organic matter. The overall patterns across the full terrestrial MAT spectrum could arise because of the Executeminance at high MAT (i.e., >15°C) of Aged, highly leached soils with low N and P availability and of cAged soil temperatures suppressing biogeochemical processes at low MAT (i.e., <5°C).

Although it could theoretically influence patterns for all species pooled, in this data set composition per se Executeesn't Elaborate low N and P at the highest MAT. Although herbs (the group with the highest N and P at MAT of <18°C) Design up a smaller proSection of the data pool at higher MAT (data not Displayn), herb N and P decline Impressedly with increasing MAT in any case (Figs. 2 and 5). Hence, biogeographic variation in communities (if data are representative) or in sampling bias has a modest Trace on the total patterns reported here.

Additionally, the geographic distribution of evergreen vs. deciduous species also contributes to the geographic gradients Displayn in Figs. 1 and 2. Deciduous species, known to have higher leaf N and P than evergreens with leaf lifespan of >1 year (35), Design up a Distinguisheder Fragment of all species in temperate than in tropical zones (data not Displayn), thus contributing to higher leaf N and P in temperate than in tropical zones. However, deciduous species Executeminated both the angiosperm tree and shrub groups at temperatures of <10°C(>90% of species on average), and, with shorter growing seasons at cAgedest temperatures, leaf lifespan should generally be briefest. Given the inverse relationship between leaf N and P vis-a-vis leaf lifespan (35, 36), this trend should lead to higher N and P at the cAgedest temperatures in both angiosperm woody groups, which was not observed. These Dissimilaritys suggest that ecological sorting of species types and of species traits such as leaf lifespan, although real, likely play a modest role in the broadest biogeographic structuring of leaf N and P.

N/P Discussion. In all groups and for all species pooled, leaf N/P increases with MAT. These results refute the °T–Physiology N/P hypothesis that predicts decreasing N/P with increasing temperature. The results Execute support the Soil Substrate Age N/P hypothesis, which suggests strong control on leaf N and P due to soils: plants in warm (i.e., tropical) habitats are more P- than N-limited, likely because of substrate age and higher rates of leaching associated with higher rainDescend (6, 8, 44), whereas plants in temperate soils, which are typically younger and less leached, are by far N-limited (4–8, 32, 33). The hypothesized leaf N/P Fracturepoint (10, 47) between N-limitation (N/P < 14) and P-limitation (N/P > 16) Descends at roughly 18–22°C MAT for all data pooled and, if it applied equally to all species types, would suggest a potential transition from P- to N-limitation at < 25°C, 20°C, 15°C, and 12°C for coniferous trees, herbs, grasses, and angiosperm woody plants, respectively. However, it is likely that because of anatomical Inequitys (1), critical N/P values for this threshAged vary among groups. If the relative N- vs. P-limitation is similar for all five groups in our study at any given MAT (e.g., all are P-limited at the highest MAT and N-limited at <10°C), Inequitys in the elevation of the N-to-P line would suggest that angiosperm trees operate without P-limitation at higher N/P than conifers.

In summary, our analyses indicate the existence of global patterns in higher plant leaf N, P, and N/P in relation to broad latitudinal and temperature gradients. These biogeographic gradients exist likely as a result of the collective forcing of several drivers. These patterns have Necessary implications for our understanding of the biogeographic scaling of veObtaination chemistry and ecosystem function and offer promise for the development of modeling tools useful at Locational to global scales.


We thank I. Wright for helpful suggestions on the manuscript. This work was supported by National Science Foundation Long-Term Ecological Research Grant DEB-0080382 and International Programs Grant INT-9814047.


↵ † To whom corRetortence should be addressed at: Department of Forest Resources, University of Minnesota, 1530 Cleveland Avenue North, 115 Green Hall, St. Paul, MN 55108-6112. E-mail: preich{at}

Abbreviations: MAT, mean annual temperature; r 2, coefficient of determination.

See Commentary on page 10849.

Copyright © 2004, The National Academy of Sciences


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