Leaf stomatal configuration and photosynthetic traits jointly affect leaf water use efficiency in forests along climate gradients.

Water use efficiency (WUE) represents the trade-off between carbon assimilation and water loss in plants. It remains unclear how leaf stomatal and photosynthetic traits regulate the spatial variation of leaf WUE in different natural forest ecosystems. We investigated 43 broad-leaf tree species spanning from cold-temperate to tropical forests in China. We quantified leaf WUE using leaf δ13C and measured stomatal traits, photosynthetic traits as well as maximum stomatal conductance ( G w max $$ {G}_{{\mathrm{w}}_{\mathrm{max}}} $$ ) and maximum carboxylation capacity ( V c max $$ {V}_{{\mathrm{c}}_{\mathrm{max}}} $$ ). We found that leaves in cold-temperate forests displayed 'fast' carbon economics, characterized by higher leaf nitrogen, Chl, specific leaf area, and V c max $$ {V}_{{\mathrm{c}}_{\mathrm{max}}} $$ , as an adaptation to the shorter growing season. However, these leaves exhibited 'slow' hydraulic traits, with larger but fewer stomata and similar G w max $$ {G}_{{\mathrm{w}}_{\mathrm{max}}} $$ , resulting in higher leaf WUE. By contrast, leaves in tropical forests had smaller and denser stomata, enabling swift response to heterogeneous light conditions. However, this stomatal configuration increased potential water loss, and coupled with their low photosynthetic capacity, led to lower WUE. Our findings contribute to understanding how plant photosynthetic and stomatal traits regulate carbon-water trade-offs across climatic gradients, advancing our ability to predict the impacts of climate changes on forest carbon and water cycles.

Global patterns and controlling factors of tree bark C : N : P stoichiometry in forest ecosystems consistent with biogeochemical niche hypothesis.

Bark serves crucial roles in safeguarding trees physically and chemically, while also contributing to nutrient cycling and carbon sequestration. Despite its importance, the broader biogeographical patterns and the potential factors influencing bark C : N : P stoichiometry in forest ecosystems remain largely unknown. In this study, we compiled a comprehensive dataset comprising carbon (C), nitrogen (N), and phosphorus (P) concentrations in bark with 1240 records from 550 diverse forest sites to systematically analyze the large-scale patterns and the factors controlling bark C : N : P stoichiometry. The geometric means of bark C, N, and P concentrations were found to be 493.17 ± 1.75, 3.91 ± 0.09, and 0.2 ± 0.01 mg g-1, respectively. Correspondingly, the C : N, C : P, and N : P mass ratios were 135.51 ± 8.11, 3313.19 ± 210.16, and 19.16 ± 0.6, respectively. Bark C : N : P stoichiometry exhibited conspicuous latitudinal trends, with the exception of N : P ratios. These patterns were primarily shaped by the significant impacts of climate, soil conditions, and plant functional groups. However, the impact of evolutionary history in shaping bark C : N : P stoichiometry outweigh climate, soil, and plant functional group, aligning with the biogeochemical niche (BN) hypothesis. These finding enhance our understanding of the spatial distribution of bark nutrient stoichiometry and have important implications for modeling of global forest ecosystem nutrient cycles in a changing environment.

Environmental versus phylogenetic controls on leaf nitrogen and phosphorous concentrations in vascular plants.

Global patterns of leaf nitrogen (N) and phosphorus (P) stoichiometry have been interpreted as reflecting phenotypic plasticity in response to the environment, or as an overriding effect of the distribution of species growing in their biogeochemical niches. Here, we balance these contrasting views. We compile a global dataset of 36,413 paired observations of leaf N and P concentrations, taxonomy and 45 environmental covariates, covering 7,549 sites and 3,700 species, to investigate how species identity and environmental variables control variations in mass-based leaf N and P concentrations, and the N:P ratio. We find within-species variation contributes around half of the total variation, with 29%, 31%, and 22% of leaf N, P, and N:P variation, respectively, explained by environmental variables. Within-species plasticity along environmental gradients varies across species and is highest for leaf N:P and lowest for leaf N. We identified effects of environmental variables on within-species variation using random forest models, whereas effects were largely missed by widely used linear mixed-effect models. Our analysis demonstrates a substantial influence of the environment in driving plastic responses of leaf N, P, and N:P within species, which challenges reports of a fixed biogeochemical niche and the overriding importance of species distributions in shaping global patterns of leaf N and P.

Unraveling the drivers and impacts of leaf phenological diversity in a subtropical forest: A fine-scale analysis using PlanetScope CubeSats.

Leaf phenology variations within plant communities shape community assemblages and influence ecosystem properties and services. However, questions remain regarding quantification, drivers, and productivity impacts of intra-site leaf phenological diversity. With a 50-ha subtropical forest plot in China's Heishiding Provincial Nature Reserve (part of the global ForestGEO network) as a testbed, we gathered a unique dataset combining ground-derived abiotic (topography, soil) and biotic (taxonomic diversity, functional diversity, functional traits) factors. We investigated drivers underlying leaf phenological diversity extracted from high-resolution PlanetScope data, and its influence on aboveground biomass (AGB) using structural equation modeling (SEM). Our results reveal considerable fine-scale leaf phenological diversity across the subtropical forest landscape. This diversity is directly and indirectly influenced by abiotic and biotic factors (e.g. slope, soil, traits, taxonomic diversity; r2 = 0.43). While a notable bivariate relationship between AGB and leaf phenological diversity was identified (r = -0.24, P < 0.05), this relationship did not hold in SEM analysis after considering interactions with other biotic and abiotic factors (P > 0.05). These findings unveil the underlying mechanism regulating intra-site leaf phenological diversity. While leaf phenology is known to be associated with ecosystem properties, our findings confirm that AGB is primarily influenced by functional trait composition and taxonomic diversity rather than leaf phenological diversity.

Exploring the role of biotic factors in regulating the spatial variability in land surface phenology across four temperate forest sites.

Land surface phenology (LSP), the characterization of plant phenology with satellite data, is essential for understanding the effects of climate change on ecosystem functions. Considerable LSP variation is observed within local landscapes, and the role of biotic factors in regulating such variation remains underexplored. In this study, we selected four National Ecological Observatory Network terrestrial sites with minor topographic relief to investigate how biotic factors regulate intra-site LSP variability. We utilized plant functional type (PFT) maps, functional traits, and LSP data to assess the explanatory power of biotic factors for the start and end of season (SOS and EOS) variability. Our results indicate that PFTs alone explain only 0.8-23.4% of intra-site SOS and EOS variation, whereas including functional traits significantly improves explanatory power, with cross-validation correlations ranging from 0.50 to 0.85. While functional traits exhibited diverse effects on SOS and EOS across different sites, traits related to competitive ability and productivity were important for explaining both SOS and EOS variation at these sites. These findings reveal that plants exhibit diverse phenological responses to comparable environmental conditions, and functional traits significantly contribute to intra-site LSP variability, highlighting the importance of intrinsic biotic properties in regulating plant phenology.

A national-scale assessment of land subsidence in China's major cities.

China's massive wave of urbanization may be threatened by land subsidence. Using a spaceborne synthetic aperture radar interferometry technique, we provided a systematic assessment of land subsidence in all of China's major cities from 2015 to 2022. Of the examined urban lands, 45% are subsiding faster than 3 millimeters per year, and 16% are subsiding faster than 10 millimeters per year, affecting 29 and 7% of the urban population, respectively. The subsidence appears to be associated with a range of factors such as groundwater withdrawal and the weight of buildings. By 2120, 22 to 26% of China's coastal lands will have a relative elevation lower than sea level, hosting 9 to 11% of the coastal population, because of the combined effect of city subsidence and sea-level rise. Our results underscore the necessity of enhancing protective measures to mitigate potential damages from subsidence.

The scaling of elemental stoichiometry and growth rate over the course of bamboo ontogeny.

Stoichiometric rules may explain the allometric scaling among biological traits and body size, a fundamental law of nature. However, testing the scaling of elemental stoichiometry and growth to size over the course of plant ontogeny is challenging. Here, we used a fast-growing bamboo species to examine how the concentrations and contents of carbon (C), nitrogen (N) and phosphorus (P), relative growth rate (G), and nutrient productivity scale with whole-plant mass (M) at the culm elongation and maturation stages. The whole-plant C content vs M and N content vs P content scaled isometrically, and the N or P content vs M scaled as a general 3/4 power function across both growth stages. The scaling exponents of G vs M and N (and P) productivity in newly grown mass vs M relationships across the whole growth stages decreased as a -1 power function. These findings reveal the previously undocumented generality of stoichiometric allometries over the course of plant ontogeny and provide new insights for understanding the origin of ubiquitous quarter-power scaling laws in the biosphere.

Weak transgenerational effects of ancestral nitrogen and phosphorus availabilities on offspring phenotypes in Arabidopsis thaliana.

Nutrient availability significantly regulates plant growth and metabolic functions, but whether and how the long-term exposure of ancestral plants to contrasting nutrient environments influences offspring phenotypic performance (i.e., transgenerational plasticity) remain poorly addressed. Here we conducted experimental manipulations using Arabidopsis thaliana with the ancestral plants grown in different nitrogen (N) and phosphorus (P) availabilities over eleven consecutive generations, and then examined the offspring phenotypic performance under the interactive effects of current and ancestral nutrient environments. We found that current rather than ancestral nutrient environments dominantly explained the variations in offspring plant traits (i.e., flowering time, aboveground biomass and biomass allocation fractions), suggesting the relatively weak transgenerational effects of ancestral N and P availabilities on offspring phenotypes. In contrast, increasing N and P availabilities in the offspring generation remarkably shortened the flowering time, increased the aboveground biomass, and altered biomass allocation fractions differentially among organs. Despite the overall weak transgenerational phenotypic plasticity, under the low nutrient environment, the offspring of ancestral plants from the low nutrient environment had a significantly higher fruit mass fraction than those from the suitable nutrient environment. Taken together, our findings suggest that A. thaliana exhibits a much stronger within- than trans-generational trait plasticity under contrasting nutrient availabilities, and may provide important insights into the understanding of plant adaptation and evolutionary processes under changing nutrient environments.

Application of the rapid leaf A-Ci response (RACiR) technique: examples from evergreen broadleaved species.

Using steady-state photosynthesis-intercellular CO2 concentration (A-Ci) response curves to obtain the maximum rates of ribulose-1,5-bisphosphate carboxylase oxygenase carboxylation (Vcmax) and electron transport (Jmax) is time-consuming and labour-intensive. Instead, the rapid A-Ci response (RACiR) technique provides a potential, high-efficiency method. However, efficient parameter settings of RACiR technique for evergreen broadleaved species remain unclear. Here, we used Li-COR LI-6800 to obtain the optimum parameter settings of RACiR curves for evergreen broadleaved trees and shrubs. We set 11 groups of CO2 gradients ([CO2]), i.e. R1 (400-1500 ppm), R2 (400-200-800 ppm), R3 (420-20-620 ppm), R4 (420-20-820 ppm), R5 (420-20-1020 ppm), R6 (420-20-1220 ppm), R7 (420-20-1520 ppm), R8 (420-20-1820 ppm), R9 (450-50-650 ppm), R10 (650-50 ppm) and R11 (650-50-650 ppm), and then compared the differences between steady-state A-Ci and RACiR curves. We found that Vcmax and Jmax calculated by steady-state A-Ci and RACiR curves overall showed no significant differences across 11 [CO2] gradients (P > 0.05). For the studied evergreens, the efficiency and accuracy of R2, R3, R4, R9 and R10 were higher than the others. Hence, we recommend that the [CO2] gradients of R2, R3, R4, R9 and R10 could be applied preferentially for measurements when using the RACiR technique to obtain Vcmax and Jmax of evergreen broadleaved species.

Decoupling of N and P aggravated upward along food chains in an urban river ecosystem.

Anthropogenic input of nutrient has profoundly influenced water quality and aquatic organisms, however, large and unbalanced nitrogen (N) and phosphorus (P) inputs (decoupling) can lead to a range of ecological health problems such as eutrophication. Whether and how the decoupling varies along the aquatic food chain remains poorly addressed. Here we chose an urban river ecosystem in the cosmopolis region of Beijing, with reclaimed water as the entire replenishment water source over 20 years, to demonstrate the decoupling pattern of N vs P across trophic levels. Results showed that organism C, N and P concentration increased, but N:P ratio decreased upward along the food chains, suggesting that this decoupling of N and P increased as trophic level ascends. Compared with natural freshwater ecosystem, the decoupling of N and P was aggravated in the reclaimed water river. Moreover, the homeostasis of N and P were higher at higher relative to lower trophic levels, and higher in macro-food chain relative to planktonic food chain. This study, for the first time, revealed the increasing decoupling of N vs P upward along the major food chains in an urban aquatic ecosystem, and could improve the understanding of nutrient cycling at the food chain level under human disturbance, and provide useful information for ecological restoration and eutrophication control of urban wetlands replenished with reclaimed water.

Above- and belowground biomass allocation and its regulation by plant density in six common grassland species in China.

Above- and belowground biomass allocation is an essential plant functional trait that reflects plant survival strategies and affects belowground carbon pool estimation in grasslands. However, due to the difficulty of distinguishing living and dead roots, estimation of biomass allocation from field-based studies currently show large uncertainties. In addition, the dependence of biomass allocation on plant species, functional type as well as plant density remains poorly addressed. Here, we conducted greenhouse manipulation experiments to study above- and belowground biomass allocation and its density regulation for six common grassland species with different functional types (i.e., C3 vs C4; annuals vs perennials) from temperate China. To explore the density regulation on the biomass allocation, we used five density levels: 25, 100, 225, 400, and 625 plant m-2. We found that mean root to shoot ratio (R/S) values ranged from 0.04 to 0.92 across the six species, much lower than those obtained in previous field studies. We also found much lower R/S values in annuals than in perennials (C. glaucum and S. viridis vs C. squarrosa, L. chinensis, M. sativa and S. grandis) and in C4 plants than in C3 plants (C. squarrosa vs L. chinensis, M. sativa and S. grandis). In addition to S. grandis, plant density had significant effects on the shoot and root biomass fraction and R/S for the other five species. Plant density also affected the allometric relationships between above- and belowground biomass significantly. Our results suggest that R/S values obtained from field investigations may be severely overestimated and that R/S values vary largely across species with different functional types. Our findings provide novel insights into approximating the difficult-to-measure belowground living biomass in grasslands, and highlight that species composition and intraspecific competition will regulate belowground carbon estimation.

Spectroscopy outperforms leaf trait relationships for predicting photosynthetic capacity across different forest types.

Leaf trait relationships are widely used to predict ecosystem function in terrestrial biosphere models (TBMs), in which leaf maximum carboxylation capacity (Vc,max ), an important trait for modelling photosynthesis, can be inferred from other easier-to-measure traits. However, whether trait-Vc,max relationships are robust across different forest types remains unclear. Here we used measurements of leaf traits, including one morphological trait (leaf mass per area), three biochemical traits (leaf water content, area-based leaf nitrogen content, and leaf chlorophyll content), one physiological trait (Vc,max ), as well as leaf reflectance spectra, and explored their relationships within and across three contrasting forest types in China. We found weak and forest type-specific relationships between Vc,max and the four morphological and biochemical traits (R2 ≤ 0.15), indicated by significantly changing slopes and intercepts across forest types. By contrast, reflectance spectroscopy effectively collapsed the differences in the trait-Vc,max relationships across three forest biomes into a single robust model for Vc,max (R2 = 0.77), and also accurately estimated the four traits (R2 = 0.75-0.94). These findings challenge the traditional use of the empirical trait-Vc,max relationships in TBMs for estimating terrestrial plant photosynthesis, but also highlight spectroscopy as an efficient alternative for characterising Vc,max and multitrait variability, with critical insights into ecosystem modelling and functional trait ecology.

Scaling the leaf nutrient resorption efficiency: Nitrogen vs phosphorus in global plants.

Nutrient resorption from senescent leaves is one essential plant nutrient strategy. Allocation of nitrogen (N) and phosphorus (P) reflects the influences of evolution and ecological processes on plant functional traits, and thus is related to functional types and environmental factors. However, we know little about the pattern among plant functional types (PFTs) and the driving factors of the allometric relationship of N resorption efficiency (NRE) against P resorption efficiency (PRE) in plant leaves (NRE ~ PREb; b, scaling exponent). We compiled N and P resorption data from the literature, including 2541 records, 894 plant species, and 488 sites worldwide, and then explored the allometric relationships between NRE and PRE across different PFTs and environmental factors (i.e. climate and soil nutrients). The scaling exponent for overall species was 0.88, suggesting that plants generally re-absorb P from senesced leaves at a higher rate than N. Among diverse PFTs, the scaling exponents of broadleaved (0.91), deciduous (0.92), non-leguminous (0.88), and woody plants (0.90) were higher than those of coniferous (0.81), evergreen (0.89), leguminous (0.74), and herbaceous plants (0.76), respectively. The scaling exponents increased with increasing latitude and soil nutrient (N and P) availability, and decreased with increasing mean annual temperature. Our results suggest that terrestrial plants utilize P relative to N more effectively through resorbing a higher proportion of P than N from senescent leaves. However, the differential resorption efficiency between N and P may vary among diverse plant types, and displayed a biogeographic pattern at global scale through the plant-environment interactions. These findings can broaden our understanding of the nutrient recycling processes within plants, and help in better prediction of nutrient balance in response to global changes.

[Nitrogen and phosphorus stoichiometry of aquatic macrophytes in Kaidu River of Xinjiang and the potential influencing factors].

Nitrogen (N) and phosphorus (P) are two common mineral elements constraining plant growth. Nutrients in aquatic macrophytes are mainly absorbed from water and sediments, and thus elemental composition in plant tissues can reflect the nutritional status in freshwater ecosystems. Kaidu River is an important river flowing through the alpine meadows, deserts, and desert oases in Xinjiang. Herein, samples of aquatic macrophytes, water, and sediments across the Kaidu River were collected. Foliar stoichiometric characteristics of N and P in plants were examined among life forms and phylogeny. The differences and correlations among the stoichiometric characteristics of plants, water bodies, and sediments in the upstream and downstream and across different land use types were elaborated. Results showed that the means of leaf N and P concentrations and N/P mass ratio were 24.9 mg·g-1, 2.49 mg·g-1, and 12.6, respectively. There were significant differences in the leaf N and P stoichiometry among various life forms. Specifically, leaf N and P concentrations in submerged species were significantly higher than that in floating-leaved species and emergent species. The N/P of floating-leaved species was 19.2 and significantly higher than that in other two life-forms, indicating that their growth might be limited by P. Leaf N and P concentrations were higher in the upstream than in the downstream. Nitrogen contents in water and sediment were the higher in the upstream of the river. Compared with the river reaches in farming areas, the higher N and P concentrations of aquatic macrophytes in the grassland regions might be related to the higher contents of organic matter in grassland soils and of animal slurries from flocks and herds, suggesting that grazing exerted larger impact on the stoichiometric characteristics of the Kaidu River ecosystem. Our findings highlighted that overgrazing might accelerate the deterioration of water quality in the upstream of the Kaidu River, disturb the balance of N and P in the aquatic ecosystem, and potentially influence the biogeochemical cycling.

Family-level leaf nitrogen and phosphorus stoichiometry of global terrestrial plants.

Leaf nitrogen (N) and phosphorus (P) concentrations are critical for photosynthesis, growth, reproduction and other ecological processes of plants. Previous studies on large-scale biogeographic patterns of leaf N and P stoichiometric relationships were mostly conducted using data pooled across taxa, while family/genus-level analyses are rarely reported. Here, we examined global patterns of family-specific leaf N and P stoichiometry using a global data set of 12,716 paired leaf N and P records which includes 204 families, 1,305 genera, and 3,420 species. After determining the minimum size of samples (i.e., 35 records), we analyzed leaf N and P concentrations, N:P ratios and N∼P scaling relationships of plants for 62 families with 11,440 records. The numeric values of leaf N and P stoichiometry varied significantly across families and showed diverse trends along gradients of mean annual temperature (MAT) and mean annual precipitation (MAP). The leaf N and P concentrations and N:P ratios of 62 families ranged from 6.11 to 30.30 mg g-1, 0.27 to 2.17 mg g-1, and 10.20 to 35.40, respectively. Approximately 1/3-1/2 of the families (22-35 of 62) showed a decrease in leaf N and P concentrations and N:P ratios with increasing MAT or MAP, while the remainder either did not show a significant trend or presented the opposite pattern. Family-specific leaf N∼P scaling exponents did not converge to a certain empirical value, with a range of 0.307-0.991 for 54 out of 62 families which indicated a significant N∼P scaling relationship. Our results for the first time revealed large variation in the family-level leaf N and P stoichiometry of global terrestrial plants and that the stoichiometric relationships for at least one-third of the families were not consistent with the global trends reported previously. The numeric values of the family-specific leaf N and P stoichiometry documented in the current study provide critical synthetic parameters for biogeographic modeling and for further studies on the physiological and ecological mechanisms underlying the nutrient use strategies of plants from different phylogenetic taxa.

A global database of paired leaf nitrogen and phosphorus concentrations of terrestrial plants.

Nitrogen (N) and phosphorus (P) are essential components of the basic cell structure of plants. In particular, leaf N and P concentrations and their stoichiometric relationship largely determine the photosynthesis, growth, reproduction, and ecophysiological processes of plants. As important leaf functional traits, leaf N and P concentrations and their stoichiometric relationship play vital roles in indicating plant nutrient-use strategies and their evolution in terrestrial ecosystems. They also influence physiological and ecological processes in leaves (e.g., growth rate and energy metabolism) and productivity (e.g., net primary production and net ecosystem production) at ecosystem level. However, the lack of a comprehensive data set containing paired leaf N and P concentration records has distinctly limited research on nutrient stoichiometry and leaf functional traits. Here, we provide a global database of paired records of leaf N and P concentrations. A total of 11,354 individual records were acquired spanning 1,291 sites worldwide, including 201 families, 1,265 genera, and 3,227 species. The records span a latitudinal range of 45.28 °S to 68.35 °N and a longitudinal range of 155.5 °W to 168.0 °E. The variables provided for each individual record are (1) geographical location (longitude, latitude, and altitude); (2) matched leaf N and P concentrations and N:P ratio; (3) taxonomic information (family, genera, and species); (4) life form (angiosperm/gymnosperm, monocotyledonous/dicotyledonous and woody plants/herbaceous plants; note that woody plants were further divided into coniferous, deciduous broad-leaved, and evergreen broad-leaved woody species and that herbaceous plants were further divided into annual and perennial species); (5) mean annual temperature (MAT) and mean annual precipitation (MAP); and (6) soil N and P concentrations and pH value in some records. To date, this database is the world's largest database of paired leaf N and P concentrations, which contains matched information of geographical location, environmental factors, and taxa. We believe that the database will play a fundamental and crucial part of ecological stoichiometric studies. There are no copyright restrictions. When using this database, we kindly request that you cite this article, respecting all the authors' hard work during sample collection and data compilation.

Biomass Allocation in Response to Nitrogen and Phosphorus Availability: Insight From Experimental Manipulations of Arabidopsis thaliana.

Allocation of biomass to different organs is a fundamental aspect of plant responses and adaptations to changing environmental conditions, but how it responds to nitrogen (N) and phosphorus (P) availability remains poorly addressed. Here we conducted greenhouse fertilization experiments using Arabidopsis thaliana, with five levels of N and P additions and eight repeat experiments, to ascertain the effects of N and P availability on biomass allocation patterns. N addition increased leaf and stem allocation, but decreased root and fruit allocation. P addition increased stem and fruit allocation, but decreased root and leaf allocation. Pooled data of the five levels of N addition relative to P addition resulted in lower scaling exponents of stem mass against leaf mass (0.983 vs. 1.226; p = 0.000), fruit mass against vegetative mass (0.875 vs. 1.028; p = 0.000), and shoot mass against root mass (1.069 vs. 1.324; p = 0.001). This suggested that N addition relative to P addition induced slower increase in stem mass with increasing leaf mass, slower increase in reproductive mass with increasing vegetative mass, and slower increase in shoot mass with increasing root mass. Further, the levels of N or P addition did not significantly affect the allometric relationships of stem mass vs. leaf mass, and fruit mass vs. vegetative mass. In contrast, increasing levels of N addition increased the scaling exponent of shoot to root mass, whereas increasing levels of P addition exerted the opposite influence on the scaling exponent. This result suggests that increasing levels of N addition promote allocation to shoot mass, whereas the increasing levels of P addition promote allocation to root mass. Our findings highlight that biomass allocation of A. thaliana exhibits a contrasting response to N and P availability, which has profound implications for forecasting the biomass allocation strategies in plants to human-induced nutrient enrichment.

Morphological traits of submerged macrophytes reveal specific positive feedbacks to water clarity in freshwater ecosystems.

Positive feedbacks are generally related to the interactions between biotic processes and abiotic drivers and may lead to the emergence of alternative stable states in ecosystems. Understanding the mechanisms of self-reinforcing feedbacks in a macrophyte-dominant clear state is critical for lake management. Based on a survey of 35 lakes in the Yangtze River floodplain and canonical correspondence analysis (CCA) with forward selection, the results showed that water clarity is the most limiting factor that influences the community structure and biomass of submerged macrophytes. The canopy length of tall macrophytes (i.e., Myriophyllum spicatum L. and Potamogeton malaianus Miq.) showed positive allometry with plant height, while the canopy length of small macrophytes (e.g., Potamogeton maackianus A. Benn.) showed isometry. Our results indicated the existence of positive feedbacks between macrophyte vegetation and water clarity in a "more vegetation, higher water clarity" pattern. We found that the relationships between monospecific community biomass and water clarity differed among community types, indicating that the strength of the positive feedback was interspecific. Furthermore, we found significant differences in the Secchi depth (SD), chlorophyll a (Chl a), light attenuation coefficient (K) and dissolved oxygen (DO) associated with monospecific macrophyte patches. Plant height had significant relationships with the mean values of SD, Chl a, total phosphorus (TP) and K, suggesting that plant height was one of the mechanisms underlying the positive feedbacks. In management practices, efforts to build and maintain the resilience of an ecosystem should be trait-based rather than merely focusing on vegetation abundance.

Effects of body size and root to shoot ratio on foliar nutrient resorption efficiency in Amaranthus mangostanus.

PREMISE OF THE STUDY: Nutrient resorption is essential for plant nutrient conservation. Large-bodied plants potentially have large nutrient sink pools and high nutrient flux. Whether and how nutrient resorption can be regulated by plant size and biomass allocation are yet unknown. METHODS: Using the herbaceous plant Amaranthus mangostanus in greenhouse experiments for two consecutive years, we measured plant biomass, height, and stem diameter and calculated the root to shoot biomass ratio (R/S ratio) and nutrient resorption efficiency (NuRE) to assess the effects of plant body size and biomass allocation on NuRE. NuRE was calculated as the percentage reduction in leaf nutrient concentration from green leaf to senesced leaf. KEY RESULTS: NuRE increased with plant biomass, height, and stem diameter, suggesting that the individuals with larger bodies, which led to a larger nutrient pool, tended to resorb proportionally more nutrients from the senescing leaves. NuRE decreased with increasing root to shoot ratio, which might have reflected the nutrient acquisition trade-offs between resorption from the senescent leaves and absorption from the soil. Increased root biomass allocation increased the proportion of nutrient acquisition through absorption more than through resorption. CONCLUSIONS: This study presented the first experimental evidence of how NuRE is linked to plant size (indicated by biomass, height, and stem diameter) and biomass allocation, suggesting that nutrient acquisition could be modulated by the size of the nutrient sink pool and its partitioning in plants, which can improve our understanding of a conservation mechanism for plant nutrients. The body size and root to shoot ratio effects might also partly explain previous inconsistent reports on the relationships between environmental nutrient availability and NuRE.