Influence of Precipitation on Soil and Foliar Nutrients Across Nine Costa Rican Forests

We explored patterns of soil and foliar nutrients across nine mature forest sites in Costa Rica, where mean annual precipitation (MAP) ranged between 3500 and 5500 mm, altitude ranged between 200 and 1200 m, and species composition varied among sites. Our objective was to investigate the relationship between rainfall and plant or soil nutrient characteristics to better understand the potential long‐term effects that alterations in MAP could have on the nutrient dynamics of wet forest plant communities. Indicators of soil N availability (net mineralization and nitrification) decreased with MAP but were not related to foliar N. Soil and foliar P, by contrast, were not correlated with MAP but were positively correlated with each other. Thus, across our gradient foliar P was a better predictor of soil nutrient availability than foliar N. There were wide differences in foliar nutrient concentrations and N:P ratios among species within sites. At each site, legumes had higher mean percent N than nonlegumes, resulting in higher N:P ratios for legumes. Taken together, these data suggest that, at least in these forests, a climate‐driven decrease in MAP could cause an increase in net N mineralization and nitrification for the wetter sites. However, this may not affect productivity at the community level because of low P availability, complex feedbacks between soil and foliar nutrients, and interactions with other biological and environmental factors such as elevation.     

RESPONSE OF A LENTIC PERIPHYTON COMMUNITY TO NUTRIENT ENRICHMENT AT LOW N:P RATIOS1

We examined the effect of nitrogen:phosphorus (N:P) ratios and nutrient concentrations on periphyton when nutrients (N and P) are provided in excess. A gradient of seven N:P ratios ranging from 7.5:1 to 1:7.5 and each at three absolute concentrations, was established using nutrient‐releasing substrata placed in a meso‐oligotrophic lake. Differences in total algal biovolume among nutrient ratios were significant (analysis of covariance [ANCOVA]) when P concentration was entered as the co‐variate. In addition, total algal biovolume was significantly correlated with N concentration but not P. To further evaluate the relationship between nutrient ratios and biovolume, we analyzed (using four 1‐way analysis of variances [ANOVAs]) four subsets of data defined as a series of treatments where one nutrient concentration remained relatively constant as the other changed creating different N:P ratios. Ratios of data subsets ranged from 1:1 to 7.5:1 and 1:1 to 1:7.5 with low and high concentrations of both series. Only diatom biovolume varied with ratio but these differences are most likely related to increased green algal abundance. Species richness and diversity differed among N:P ratios (ANCOVA) when P concentration was used as the co‐variate. Stigeoclonium tenue (Ag.) Gomont, which generally accounted for the increase in green algal abundance, varied with nutrient ratio (ANCOVA) when P was the co‐variate. Based on the ANCOVAs, correlations, and one‐way ANOVAs, periphyton in this system appears to be affected by N concentration but not by N:P treatment ratios under nutrient‐rich conditions. When compared with previous studies, these data also suggest that the response of periphyton to in situ treatments constructed with nutrient‐releasing substrata vary between years.     

Foliar C,N, and P stoichiometry characterize successful plant ecological strategies in the Sonoran Desert

Ecological processes are centered to water availability in drylands; however, less known nutrient stoichiometry can help explain much of their structure and ecological interactions. Here we look to the foliar stoichiometry of carbon (C), nitrogen (N), and phosphorus (P) of 38 dominant plant species from the Sonoran Desert, grouped in four different functional types to describe ecological characteristics and processes. We found that foliar N, C:N, C:P, and N:P stoichiometric ratios, but not P, were higher than those known to most other ecosystems and indicate P but not N limitations in leaves. Biological N fixers (BNF) had even higher leaf N concentrations, but bio-elemental concentrations and stoichiometry ratios were not different to other non-N-fixing legume species which underscores the need to understand the physiological mechanisms for high N, and to how costly BNF can succeed in P-limiting drylands environments. Stoichiometry ratios, and to lesser extent elemental concentrations, were able to characterize BNF and colonizing strategies in the Sonoran Desert, as well as explain leaf attribute differences, ecological processes, and biogeochemical niches in this dryland ecosystem, even when no direct reference is made to other water-limitation strategies.     

C:N:P stoichiometry in Australian soils with respect to vegetation and environmental factors

Aims

We estimate organic carbon (C): total nitrogen (N): total phosphorus (P) ratios in soils under Australia’s major native vegetation groups.

Methods

We use digital datasets for climate, soils, and vegetation created for the National Land and Water Resources Audit in 2001. Analysis-of-variance is used to investigate differences in nutrient ratios between ecosystems. Linear discriminant analysis and logistic regression are used to investigate the relative importance of climatic variables and soil nutrients in vegetation patterns.

Results

We find that the N:P and C:P ratios have a greater range of values than the C:N ratio, although major vegetation groups tend to show similar trends across all three ratios. Some apparently homeostatic groupings emerge: those with very low, low, medium, or high N:P and C:P. Tussock grasslands have very low soil N, N:P, and C:P, probably due to frequent burning. Eucalypt woodlands have low soil N:P and C:P ratios, although their total P level varies. Rainforests and Melaleuca forests have medium soil N:P and C:P ratios, although their total P level is different. Heathlands, tall open eucalypt forests, and shrublands occur on soils with low levels of total P, and high N:P and C:P ratios that reflect foliar nutrient ratios and recalcitrant litter.

Conclusions

Certain plant communities have typical soil nutrient stoichiometries but there is no single Redfield-like ratio. Vegetation patterns largely reflect soil moisture but for several plant communities, eucalypt communities in particular, soil N and P (or N:P) also play a significant role. Soil N:P and the presence of Proteaceae appear indicative of nutrient constraints in ecosystems.     

The C:N:P stoichiometry of organisms and ecosystems in a changing world: A review and perspectives

This study examined the literature in ISI Web of Science to identify the effects that the main drivers of global change have on the nutrient concentrations and C:N:P stoichiometry of organisms and ecosystems, and examined their relationship to changes in ecosystem structure and function. We have conducted a meta-analysis by comparing C:N:P ratios of plants and soils subjected to elevated [CO₂] with those subjected to ambient [CO₂]. A second meta-analysis compared the C:N:P ratios of plants and soils that received supplemental N to simulate N deposition and those that did not receive supplemental N. On average, an experimental increase in atmospheric [CO₂] increased the foliar C:N ratios of C3 grasses, forbs, and woody plants by 22%, but the foliar ratios of C4 grasses were unaffected. This trend may be enhanced in semi-arid areas by the increase in droughts that have been projected for the coming decades which can increase leaf C:N ratios. The available studies show an average 38% increase in foliar C:P ratios in C3 plants in response to elevated atmospheric [CO₂], but no significant effects were observed in C4 grasses. Furthermore, studies that examine the effects of elevated atmospheric [CO₂] on N:P ratio (on a mass basis) are warranted since its response remains elusive. N deposition increases the N:P ratio in the plants of terrestrial and freshwater ecosystems, and decreases plants and organic soil C:N ratio (25% on average for C3 plants), reducing soil and water N₂ fixation capacity and ecosystem species diversity. In contrast, in croplands subjected to intense fertilization, mostly, animal slurries, a reduction in soil N:P ratio can occur because of the greater solubility and loss of N. In the open ocean, there are experimental observations showing an ongoing increase in P-limited areas in response to several of the factors that promote global change, including the increase in atmospheric [CO₂] which increases the demand for P, the warming effect that leads to an increase in water column stratification, and increases in the N:P ratio of atmospheric inputs. Depending on the type of plant and the climate where it grows, warming can increase, reduce, or have no effect on foliar C:N ratios. The results suggest that warming and drought can increase C:N and C:P ratios in warm-dry and temperate-dry terrestrial ecosystems, especially, when high temperatures and drought coincide. Advances in this topic are a challenge because changes in stoichiometric ratios can favour different types of species and change ecosystem composition and structure.     

Relationships between Nutrient-Related Plant Traits and Combinations of Soil N and P Fertility Measures

Soil fertility and nutrient-related plant functional traits are in general only moderately related, hindering the progress in trait-based prediction models of vegetation patterns. Although the relationships may have been obscured by suboptimal choices in how soil fertility is expressed, there has never been a systematic investigation into the suitability of fertility measures. This study, therefore, examined the effect of different soil fertility measures on the strength of fertility–trait relationships in 134 natural plant communities. In particular, for eight plot-mean traits we examined (1) whether different elements (N or P) have contrasting or shared influences, (2) which timescale of fertility measures (e.g. mineralization rates for one or five years) has better predictive power, and (3) if integrated fertility measures explain trait variation better than individual fertility measures. Soil N and P had large mutual effects on leaf nutrient concentrations, whereas they had element-specific effects on traits related to species composition (e.g. Grime''s CSR strategy). The timescale of fertility measures only had a minor impact on fertility–trait relationships. Two integrated fertility measures (one reflecting overall fertility, another relative availability of soil N and P) were related significantly to most plant traits, but were not better in explaining trait variation than individual fertility measures. Using all fertility measures together, between-site variations of plant traits were explained only moderately for some traits (e.g. 33% for leaf N concentrations) but largely for others (e.g. 66% for whole-canopy P concentration). The moderate relationships were probably due to complex regulation mechanisms of fertility on traits, rather than to a wrong choice of fertility measures. We identified both mutual (i.e. shared) and divergent (i.e. element-specific and stoichiometric) effects of soil N and P on traits, implying the importance of explicitly considering the roles of different elements to properly interpret fertility–trait relationships.     

Tight Coupling Between Shoot Level Foliar N and P,Leaf Area,and Shoot Growth in Arctic Dwarf Shrubs Under Simulated Climate Change

Nutrient availability limits productivity of arctic ecosystems, and this constraint means that the amount of nitrogen (N) in plant canopies is an exceptionally strong predictor of vegetation productivity. However, climate change is predicted to increase nutrient availability leading to increases in carbon sequestration and shifts in community structure to more productive species. Despite tight coupling of productivity with canopy nutrients at the vegetation scale, it remains unknown how species/shoot level foliar nutrients couple to growth, or how climate change may influence foliar nutrients–productivity relationships to drive changes in ecosystem carbon gain and community structure. We investigated the influence of climate change on arctic plant growth relationships to shoot level foliar N and phosphorus (P) in three dominant subarctic dwarf shrubs using an 18-year warming and nutrient addition experiment. We found a tight coupling between total leaf N and P per shoot, leaf area and shoot extension. Furthermore, a steeper shoot length-leaf N relationship in deciduous species (Vaccinium myrtillus and Vaccinium uliginosum) under warming manipulations suggests a greater capacity for nitrogen to stimulate growth under warmer conditions in these species. This mechanism may help drive the considerable increases in deciduous shrub cover observed already in some arctic regions. Overall, our work provides the first evidence at the shoot level of tight coupling between foliar N and P, leaf area and growth i.e. consistent across species, and provides mechanistic insight into how interspecific differences in alleviation of nutrient limitation will alter community structure and primary productivity in a warmer Arctic.     

Silicon application induces changes C:N:P stoichiometry and enhances stoichiometric homeostasis of sorghum and sunflower plants under salt stress

Beneficial effects of silicon (Si) on growth have been observed in some plant species, reportedly due to stoichiometric changes of C, N, and P. However, little is known about the effects on the stoichiometric relationships between C, N, and P when silicon is supplied via different modes in sorghum and sunflower plants under salt stress conditions. Therefore, the current study was performed to investigate the impact of differing modes of Si supply on shoot biomass production and C:N:P stoichiometry in sorghum and sunflower plants under salt stress. Two experiments were performed in a glass greenhouse using the strong Si-accumulator plant sorghum, as well as the intermediate type Si-accumulator sunflower, both of which were grown in pots filled with washed sand. Plant species were cultivated for 30 days in the absence or presence of salt stress (0 or 100 mM) and supplemented with one of four Si treatments: control plants (without Si), 28.6 mmol Si L⁻¹ via foliar application, 2.0 mmol Si L⁻¹ via nutrient solution, and combined application of foliar and nutrient solution, each group with five replications. The results revealed that supplied Si modified the C, N, and P concentrations, thereby enhancing the C:N:P stoichiometry and shoot dry matter of sorghum and sunflower plants under salt stress. Both application of Si via nutrient solution, as well as combined application via foliar and nutrient solution, increased the C:N ratio in both plant species under salt stress, but in sorghum plants decreased the C:P and N:P ratios and increased the shoot biomass production by 39%, while in sunflower plants increased the C:P and N:P ratios and increased the shoot biomass production by 24%. Our findings suggest that salt stress alleviation by Si impacts C:N:P stoichiometric relationships in a variable manner depending on the ability of the species to accumulate Si, as well as the route of Si administration.     

Ecosystem development in short‐term postglacial chronosequences: N and P limitation in glacier forelands from Santa Inés Island,Magellan Strait

Glacier foreland moraines provide an ideal model to examine the patterns of ecosystem development and the evolution of nitrogen and phosphorous limitation over successional time. In this paper, we focus on a 400‐year soil chronosequence in the glacier forelands of Santa Inés Island in the Magellan Strait, southern Chile by examining forest development on phosphorus (P)‐poor substrates in a uniquely unpolluted region of the world. Results show a steady increase in tree basal area and a humped trend in tree species richness over four centuries of stand development. The increase in basal area suggests that the late successional tree species were more efficient nutrient users than earlier successional ones. Total contents of carbon (C) and nitrogen (N) in soils increased during the chronosequence, reaching an asymptote in late succession. The net increases in soil C : N, C : P and N : P ratios observed over successional time suggest that nutrient limitation is maximal in 400‐year‐old substrates. Foliar C : N and C : P ratios also increased over time to reach an asymptote in old‐growth stages, following soil stoichiometric relationships; however the foliar N‐to‐P ratio remained constant throughout the chronosequence. Biological N fixation was greater in early postglacial succession, associated with the presence of the symbiotic N‐fixer Gunnera magellanica. Declining trends of δ¹⁵N in surface soils through the 400‐year chronosequence are evidence of decreasing N losses in old‐growth forests. In synthesis, glacier foreland chronosequences at this high South American latitude provide evidence for increasing efficiency of N and P use in the ecosystem, with the replacement of shade‐intolerant pioneers by more efficient, shade‐tolerant tree species. This pattern of ecosystem development produces a constant foliar N : P ratio, regardless of variation in soil N‐to‐P ratio over four centuries.     

Relationships between below-ground biomass and foliar N:P stoichiometry along climatic and altitudinal gradients of the Chinese grassland transect

N and P concentrations and their ratios were determined for 132 foliar and 120 below-ground biomass (BGB) samples obtained at 132 sites along the 4500 km Chinese Grassland Transect (CGT) across the Inner Mongolian and Qinghai–Tibet Plateaus. Patterns of foliar and BGB N, P and their ratio (N/P) at the community level were related to altitude, temperature, and precipitation gradients. Also, patterns of relative N and P foliar and BGB concentrations were determined (N_F/B, foliar N/BGB N; P_F/B, foliar P/BGB P). The relationship between foliar N concentrations and mean annual temperature (MAT) was negative, agreeing with the Temperature-Plant Physiological hypothesis, whereas BGB N decreased with decreasing MAT, supporting the Biogeochemical hypothesis. Patterns of BGB N varying with altitude, MAP and MAT differed from the patterns for leaf N, which may indicate differences in nutrient allocation and utilization by leaves and BGB. N_F/B and P_F/B may reflect trade-offs by plants for N and P in leaves and BGB. For the entire CGT, N_F/B and P_F/B increased as altitude increased. N_F/B was positively related with MAP but negatively related with MAT, while P_F/B showed no correlations with MAP and MAT. Results suggest that ecological stoichiometry at the community level is similar to that at the species level. Strategies of nutrient utilization by leaves and BGB are indicated to be different, and abiotic environmental conditions could influence the stoichiometric characteristics and nutrient allocation to leaves and BGB.     

A global study of relationships between leaf traits, climate and soil measures of nutrient fertility

Aim This first global quantification of the relationship between leaf traits and soil nutrient fertility reflects the trade‐off between growth and nutrient conservation. The power of soils versus climate in predicting leaf trait values is assessed in bivariate and multivariate analyses and is compared with the distribution of growth forms (as a discrete classification of vegetation) across gradients of soil fertility and climate. Location All continents except for Antarctica. Methods Data on specific leaf area (SLA), leaf N concentration (LNC), leaf P concentration (LPC) and leaf N:P were collected for 474 species distributed across 99 sites (809 records), together with abiotic information from each study site. Individual and combined effects of soils and climate on leaf traits were quantified using maximum likelihood methods. Differences in occurrence of growth form across soil fertility and climate were determined by one‐way ANOVA. Results There was a consistent increase in SLA, LNC and LPC with increasing soil fertility. SLA was related to proxies of N supply, LNC to both soil total N and P and LPC was only related to proxies of P supply. Soil nutrient measures explained more variance in leaf traits among sites than climate in bivariate analysis. Multivariate analysis showed that climate interacted with soil nutrients for SLA and area‐based LNC. Mass‐based LNC and LPC were determined mostly by soil fertility, but soil P was highly correlated to precipitation. Relationships of leaf traits to soil nutrients were stronger than those of growth form versus soil nutrients. In contrast, climate determined distribution of growth form more strongly than it did leaf traits. Main conclusions We provide the first global quantification of the trade‐off between traits associated with growth and resource conservation ‘strategies’ in relation to soil fertility. Precipitation but not temperature affected this trade‐off. Continuous leaf traits might be better predictors of plant responses to nutrient supply than growth form, but growth forms reflect important aspects of plant species distribution with climate.     

WHY DOES A TRAIT EVOLVE MULTIPLE TIMES WITHIN A CLADE? REPEATED EVOLUTION OF SNAKELINE BODY FORM IN SQUAMATE REPTILES

Abstract Why does a trait evolve repeatedly within a clade? When examining the evolution of a trait, evolutionary biologists typically focus on the selective advantages it may confer and the genetic and developmental mechanisms that allow it to vary. Although these factors may be necessary to explain why a trait evolves in a particular instance, they may not be sufficient to explain phylogenetic patterns of repeated evolution or conservatism. Instead, other factors may also be important, such as biogeography and competitive interactions. In squamate reptiles (lizards and snakes) a dramatic transition in body form has occurred repeatedly, from a fully limbed, lizardlike body form to a limbreduced, elongate, snakelike body form. We analyze this trait in a phylogenetic and biogeographic context to address why this transition occurred so frequently. We included 261 species for which morphometric data and molecular phylogenetic information were available. Among the included species, snakelike body form has evolved about 25 times. Most lineages of snakelike squamates belong to one of two ecomorphs, either short‐tailed burrowers or long‐tailed surface dwellers. The repeated origins of snakelike squamates appear to be associated with the in situ evolution of these two ecomorphs on different continental regions (including multiple origins of the burrowing morph within most continents), with very little dispersal of most limb‐reduced lineages between continental regions. Overall, the number of repeated origins of snakelike morphology seems to depend on large‐scale biogeographic patterns and community ecology, in addition to more traditional explanations (e.g., selection, development).     

Altered N,P and C dynamics with absence of fire in Eucalyptus forests affected by premature decline

Absence of fire is increasingly recognized as an important driver of soil nutrient budgets in Eucalyptus forest, especially in forests affected by premature Eucalyptus decline, due to the effects of soil nutrient accumulation on nutrient balances and forest community dynamics. In this study, we present a dataset of soil and foliar nutrient analyses, and vegetation measurements from a fire chronosequence survey in native E. delegatensis forest. Measured indices include total soil and extractable soil nitrogen (N), or phosphorus (P), soil organic carbon (C), soil acid‐phosphatase (PME) activity, foliar N and foliar P, and understorey and overstorey vegetation canopy height. We show that in some cases indices are strongly linked to time since fire (2–46 years). Time since fire correlated positively with foliar N, total and extractable soil N, soil organic C, and also soil PME activity; the latter an indicator of biotic P demand. Differences in the strength of these relationships were apparent between two geology types, with stronger relationships on the potentially less‐fertile geology. The strong positive correlation with time since fire and understorey canopy height reflected increasing shrub biomass and thickening of the shrub layer. The strong positive correlation for soil or foliar N, but not P, with time since fire, indicates that P does not increase relative to N over time. P may, therefore, become limiting to growth in this plant community. Similarly, the significantly higher concentrations of soil N but not P, also found in both older and long‐unburnt forest stands (>100 years since management), may exacerbate a situation of soil nutrient limitation over several decades. A characteristic feature of long unmanaged stands is a developing tea tree (Leptospermum sp.) understorey, which may benefit from elevated soil N availability and increasing organic C accumulation with prolonged fire absence. This increased shrub biomass would outcompete Eucalyptus for resources, including soil nutrients and water.     

N and P in New Zealand Soil Chronosequences and Relationships with Foliar N and P

The growth of forest species in soil development chronosequences becomes increasingly phosphorus (P)-limited with time, as P is weathered, eroded and leached from soil. Foliar nitrogen (N) concentrations also tend to decrease with soil age when vegetation may be limited in both N and P. Here we report on soil development in temperate rain forests along three New Zealand chronosequences that have minimal pollution and disturbance from human activities, at Franz Josef, Waitutu and Central Volcanic Plateau, and on factors influencing soil net N mineralization (aerobic; 56 days) and foliar N and P concentrations. Except in very young soils (<500 years), at least 85% of total-P in mineral soil (0–10 cm) was transformed to organic-P. In each chronosequence, total-P declined with time, and foliar N:P ratios (mass) generally increased from 8 to 15–18, suggesting P was more limiting than N in the oldest soils of the chronosequence. There was a negative relationship between net N mineralization and C:N ratio for mineral soil. For the FH (organic) layer, net N mineralization had the strongest relationships with total-N concentration (positively) and C:organic-P ratio (negatively); however, relationships varied with forest group, suggesting that other factors were also important. Foliar P of kamahi (Weinmannia racemosa Linn. f.), a dominant canopy species, was related to soil organic-P, suggesting mineralization was an important process for tree nutrition.Foliar N was positively related to N concentration in the FH layer, but was not significantly related to any measured property in mineral soil, possibly because of the wide range of soils. The consistent declines in both soil and foliar P across the contrasting chronosequences strongly suggest that vegetation becomes progressively P-limited during long-term ecosystem development.     

Nutrient resorption patterns of plant functional groups in a tropical savanna: variation and functional significance

Green and senesced leaf nitrogen (N) and phosphorus (P) concentrations of different plant functional groups in savanna communities of Kruger National Park, South Africa were analyzed to determine if nutrient resorption was regulated by plant nutritional status and foliar N:P ratios. The N and P concentrations in green leaves and the N concentrations in senesced leaves differed significantly between the dominant plant functional groups in these savannas: fine-leaved trees, broad-leaved trees and grasses. However, all three functional groups reduced P to comparable and very low levels in senesced leaves, suggesting that P was tightly conserved in this tropical semi-arid savanna ecosystem. Across all functional groups, there was evidence for nutritional control of resorption in this system, with both N and P resorption efficiencies decreasing as green leaf nutrient concentrations increased. However, specific patterns of resorption and the functional relationships between nutrient concentrations in green and senesced leaves varied by nutrient and plant functional group. Functional relationships between N concentrations in green and senesced leaves were indistinguishable between the dominant groups, suggesting that variation in N resorption efficiency was largely the result of inter-life form differences in green leaf N concentrations. In contrast, observed differences in P resorption efficiencies between life forms appear to be the result of both differences in green leaf P concentrations as well as inherent differences between life forms in the fraction of green leaf P resorbed from senescing leaves. Our results indicate that foliar N:P ratios are poor predictors of resorption efficiency in this ecosystem, in contrast to N and P resorption proficiencies, which are more responsive to foliar N:P ratios.     

Temporal variability of foliar nutrients: responses to nitrogen deposition and prescribed fire in a temperate steppe

Plant nutrient concentrations and stoichiometry drive fundamental ecosystem processes, with important implications for primary production, diversity, and ecosystem sustainability. While a range of evidence exists regarding how plant nutrients vary across spatial scales, our understanding of their temporal variation remains less well understood. Nevertheless, we know nutrients regulate plant function across time, and that important temporal controls could strongly interact with environmental change. Here, we report results from a 3-year assessment of inter-annual changes of foliar nitrogen (N) and phosphorus (P) concentrations and stoichiometry in three dominant grasses in response to N deposition and prescribed fire in a temperate steppe of northern China. Foliar N and P concentrations and their ratios varied greatly among years, with this temporal variation strongly related to inter-annual variation in precipitation. Nitrogen deposition significantly increased foliar N concentrations and N:P ratios in all species, while fire significantly altered foliar N and P concentrations but had no significant impacts on N:P ratios. Generally, N addition enhanced the temporal stability of foliar N and decreased that of foliar P and of N:P ratios. Our results indicate that plant nutrient status and response to environmental change are temporally dynamic and that there are differential effects on the interactions between environmental change drivers and timing for different nutrients. These responses have important implications for consideration of global change effects on plant community structure and function, management strategies, and the modeling of biogeochemical cycles under global change scenarios.     

Imaging spectroscopy reveals the effects of topography and logging on the leaf chemistry of tropical forest canopy trees

Logging, pervasive across the lowland tropics, affects millions of hectares of forest, yet its influence on nutrient cycling remains poorly understood. One hypothesis is that logging influences phosphorus (P) cycling, because this scarce nutrient is removed in extracted timber and eroded soil, leading to shifts in ecosystem functioning and community composition. However, testing this is challenging because P varies within landscapes as a function of geology, topography and climate. Superimposed upon these trends are compositional changes in logged forests, with species with more acquisitive traits, characterized by higher foliar P concentrations, more dominant. It is difficult to resolve these patterns using traditional field approaches alone. Here, we use airborne light detection and ranging‐guided hyperspectral imagery to map foliar nutrient (i.e. P, nitrogen [N]) concentrations, calibrated using field measured traits, over 400 km² of northeastern Borneo, including a landscape‐level disturbance gradient spanning old‐growth to repeatedly logged forests. The maps reveal that canopy foliar P and N concentrations decrease with elevation. These relationships were not identified using traditional field measurements of leaf and soil nutrients. After controlling for topography, canopy foliar nutrient concentrations were lower in logged forest than in old‐growth areas, reflecting decreased nutrient availability. However, foliar nutrient concentrations and specific leaf area were greatest in relatively short patches in logged areas, reflecting a shift in composition to pioneer species with acquisitive traits. N:P ratio increased in logged forest, suggesting reduced soil P availability through disturbance. Through the first landscape scale assessment of how functional leaf traits change in response to logging, we find that differences from old‐growth forest become more pronounced as logged forests increase in stature over time, suggesting exacerbated phosphorus limitation as forests recover.     

Hidden patterns of phylogenetic non‐stationarity overwhelm comparative analyses of niche conservatism and divergence

Aim Despite the importance of the niche concept in ecological and evolutionary theory, there are still many discussions about its definition and operational evaluation, especially when dealing with niche divergence and conservatism in an explicit phylogenetic context. Here we evaluate patterns of niche evolution in 67 New World Carnivora species, measured using Hellinger distances based on MAXENT models of species distribution. We show how inferences on niche conservatism or divergence depend on the way phylogenetic patterns are analysed using matrix comparison techniques. Innovation Initially we used the simplest approach of Mantel tests to compare Hellinger distances ( N ) derived from MAXENT and phylogenetic distances ( P ) among species. Then we extended the Mantel test to generate a multivariate correlogram, in which phylogenetic patterns are analysed at multiple levels in the phylogeny and can reveal nonlinearity in the relationship between divergence and time. Finally, we proposed a new approach to generate ‘local’ (or ‘specific’) leverages of components for Mantel correlation, evaluating the non‐stationarity in the relationship between N and P for each species. This new approach was used to show if some lineages are more prone to niche shift or conservatism than others. Main conclusions Standard Mantel tests indicated a poor correspondence between N and P matrices, discarding the idea of niche conservatism for Carnivora, but the correlogram supports that closely related species tend to be more similar than expected by chance. Moreover, the variance among Hellinger distances between pairs of closely phylogenetically related species is much larger than for the entire clade. Phylogenetic non‐stationarity analysis shows that in some Carnivora families the niche tends to divergence (Mustelidae and Canidae), whereas in others it tends to conservatism (Procyonidae and Mustelidae) at short phylogenetic distances. Our analyses clearly show that misleading results may appear if niche divergence is analysed only by simple matrix correlations not taking into account complex patterns of phylogenetic nonlinearity and non‐stationarity.     

N:P stoichiometry in Ficus racemosa and its mutualistic pollinator

Aims Nitrogen (N) and phosphorus (P) are limiting nutrients to life across a variety of ecosystems. N:P stoichiometry, concerning the balance of these two elements, has recently received great attention. However, little is known about the nature of N:P stoichiometry in obligate mutualism.Methods N:P stoichiometry of Ficus racemosa and its pollinating wasp Ceratosolen fusciceps, an example of coevolving obligate mutualism, was investigated, and the N:P stoichiometric traits of male versus female wasps were compared.Important findings Nutrient concentrations in C. fusciceps were much higher than in its host. N enrichment in fig wasp was evidently stronger than phosphorus. N concentrations of male fig wasps were significantly higher than those of females, while P concentrations of female fig wasps were remarkably higher than those of male ones. Therefore, N:P ratios in male fig wasps were significantly greater than in female fig wasps. N:P ratio in fig-pollinating wasp displayed linear functions to fig N contents, suggesting that N limitation in fig wasps may dominate the nutritional relationship between fig pollinator and its host. Fig wasp population size had significant influences on N concentrations in host fig and female wasp per se. Driven by the nutritional stress of pollinating and parasite insects, fig fruit preferred increasing its diameter first but not nutrient richness. Values for N and P contents of fig pollinators showed seasonal differences with greater N:P ratios in dry season than in rainy season. The observations suggest that tropical climate change would result in more severe N limitation to fig-pollinating wasp and may further influence the stability of fig–fig wasp mutualism.     

SEASONAL NUTRIENT DYNAMICS,NUTRIENT RESORPTION,AND MYCORRHIZAL INFECTION INTENSITY OF TWO PERENNIAL FOREST HERBS

Patterns of mycorrhizal infection, seasonal foliar nutrient concentrations, nutrient allocation to shoots and rhizomes, and nutrient resorption were measured in relation to soil nutrient availability in two species of perennial forest herbs, Geranium maculatum L. and Polygonatum pubescens Pursh., in four forest stands in southern and central Ohio. The percentage of plants with V-A mycorrhizae and the proportion of root length colonized by VAM structures increased with decreasing nutrient availability in both species. Foliar N and P concentrations in plants from lower fertility sites were as high, or higher, than those in plants from higher fertility sites; as a result, tissue nutrient enrichment ratios (foliar concentration/soil available concentration) increased with decreasing fertility. Proportional resorption of N and P generally decreased with decreasing nutrient availability, a pattern inconsistent with those exhibited by woody plants in these forest stands. We hypothesize that the inverse relationship between nutrient uptake efficiency (via mycorrhizae) and nutrient use efficiency (resorption) exhibited by these forest understory herbs, but not by trees or herbs from high-light environments, may be related to low-light limitation of energy reserves in the forest understory.