Plant genome size modulates grassland community responses to multi-nutrient additions

Multiple Nutrient Additions Homogenize Multidimensional Plant Stoichiometry in a Meadow Steppe

Human activities are altering terrestrial ecosystem biogeochemistry globally by augmenting the availability of multiple biologically essential nutrients, thereby potentially altering plant internal concentrations (i.e., stoichiometry) across a diverse array of elements. These shifts in plant nutrient concentrations may subsequently impact crucial ecosystem processes, including litter decomposition, herbivory by insects and large animals, and ecosystem productivity. However, most work on the alteration of plant stoichiometry has focused on a few macronutrients (e.g., nitrogen or phosphorus), despite the potential importance of many other elements. In this study, we conducted a comprehensive field experiment in the Inner Mongolia Steppe, manipulating eight distinct nutrients to examine their effects on both soil and plant tissue concentrations. Our findings reveal that adding most nutrients increased their corresponding available contents in the soil. In most cases, the addition of nutrients also increased their corresponding concentrations in plant tissues at both species and community levels. Besides, multiple nutrient additions had greater effects on soil available nutrient contents than on plant internal nutrient concentrations. Notably, the concurrent addition of multiple nutrients led to a significant homogenization of plant stoichiometry among different species within the same community. This homogenization might influence interspecific interactions and coexistence within grassland ecosystems. Our findings advanced our comprehension of how anthropogenic nutrient enrichment may simplify plant nutrient profiles, thereby influencing grassland biodiversity and ecosystem functionality.

Mechanistic insights into plant community responses to environmental variables: genome size, cellular nutrient investments, and metabolic tradeoffs

Affecting biodiversity, plants with larger genome sizes (GS) may be restricted in nutrient-poor conditions. This pattern has been attributed to their greater cellular nitrogen (N) and phosphorus (P) investments and hypothesized nutrient-investment tradeoffs between cell synthesis and physiological attributes associated with growth. However, the influence of GS on cell size and functioning may also contribute to GS-dependent growth responses to nutrients. To test whether and how GS is associated with cellular nutrient, stomata, and/or physiological attributes, we examined > 500 forbs and grasses from seven grassland sites conducting a long-term N and P fertilization experiment. Larger GS plants had increased cellular nutrient contents and larger, but fewer stomata than smaller GS plants. Larger GS grasses (but not forbs) also had lower photosynthetic rates and water-use efficiencies. However, nutrients had no direct effect on GS-dependent physiological attributes and GS-dependent physiological changes likely arise from how GS influences cells. At the driest sites, large GS grasses displayed high water-use efficiency mostly because transpiration was reduced relative to photosynthesis in these conditions. We suggest that climatic conditions and GS-associated cell traits that modify physiological responses, rather than resource-investment tradeoffs, largely explain GS-dependent growth responses to nutrients (especially for grasses).

Nutrient effects on plant diversity loss arise from nutrient identity and decreasing niche dimension

Two hypotheses have been used to explain the loss of plant diversity with nutrient addition. The nutrient identity hypothesis posits that biodiversity loss is due to a specific limiting nutrient, such as nitrogen (N) or phosphorus (P), while the niche dimension hypothesis posits that adding a larger number of limiting nutrients, regardless of their identity, results in biodiversity loss. These two hypotheses have not previously been tested together simultaneously. Here, we conduct that analysis to enable their relative effect sizes to be compared. We manipulated the supply of eight nutrients in the same experimental meadow grassland site to isolate the effects of the identity of added nutrients versus the number of added nutrients on biodiversity loss. We found support for both hypotheses, with the largest negative effects on biodiversity measures being due to N, or N and P treatment, with additional more minor effects of the number of added nutrients. Structural equation models (SEMs) suggested both identity and number of added nutrients had direct negative effects on biodiversity, likely caused by species' innate ability to competitively respond to nutrients, especially in response to disease, herbivory, and stress. SEMs also suggested indirect effects arising from nutrient-driven increases in aboveground biomass, which resulted in intensified competition for light and the competitive exclusion of short-statured species. These effects were exacerbated by the nutrients N and P which caused a shift in biomass accumulation from belowground to aboveground. The results highlight that a multi-nutrient perspective will improve our ability to effectively manage, monitor, and restore ecosystems.

The smallest angiosperm genomes may be the price for effective traps of bladderworts

BACKGROUND

Species of the carnivorous family Lentibulariaceae exhibit the smallest genomes in flowering plants. We explored the hypothesis that their minute genomes result from the unique mitochondrial cytochrome c oxidase (COX) mutation. The mutation may boost mitochondrial efficiency, which is especially useful for suction-bladder traps of Utricularia, but also increase DNA-damaging reactive oxygen species, leading to genome shrinkage through deletion-biased DNA repair. We aimed to explore the impact of this mutation on genome size, providing insights into genetic mutation roles in plant genome evolution under environmental pressures.

METHODS

We compiled and measured genome and mean chromosome sizes for 127 and 67 species, respectively, representing all three genera (Genlisea, Pinguicula and Utricularia) of Lentibulariaceae. We also isolated and analysed COX sequences to detect the mutation. Through phylogenetic regressions and Ornstein-Uhlenbeck models of trait evolution, we assessed the impact of the COX mutation on the genome and chromosome sizes across the family.

RESULTS

Our findings reveal significant correlations between the COX mutation and smaller genome and chromosome sizes. Specifically, species carrying the ancestral COX sequence exhibited larger genomes and chromosomes than those with the novel mutation. This evidence supports the notion that the COX mutation contributes to genome downsizing, with statistical analyses confirming a directional evolution towards smaller genomes in species harbouring these mutations.

CONCLUSIONS

Our study confirms that the COX mutation in Lentibulariaceae is associated with genome downsizing, probably driven by increased reactive oxygen species production and subsequent DNA damage requiring deletion-biased repair mechanisms. While boosting mitochondrial energy output, this genetic mutation compromises genome integrity and may potentially affect recombination rates, illustrating a complex trade-off between evolutionary advantages and disadvantages. Our results highlight the intricate processes by which genetic mutations and environmental pressures shape genome size evolution in carnivorous plants.

Exploring the phylogenetic framework and trait evolution of Impatiens through chloroplast genome analysis

BACKGROUND

The genus Impatiens, which includes both annual and perennial herbs, holds considerable ornamental, economic, and medicinal value. However, it posed significant challenges for taxonomic and systematic reconstruction. This was largely attributed to its high intraspecific diversity and low interspecific variation in morphological characteristics. In this study, we sequenced samples from 12 Impatiens species native to China and assessed their phylogenetic resolution using the complete chloroplast genome, in conjunction with published samples of Impatiens. In addition, a comparative analysis of chloroplast genomes were conducted to explore the evolution of the chloroplast genome in Impatiens.

RESULTS

The chloroplast genomes of 12 Impatiens species exhibited high similarity to previously published samples in terms of genome size, gene content, and sequence. The chloroplast genome of Impatiens exhibited a typical four-part structure, with lengths ranging from 146,987 bp(I. morsei)- 152,872 bp(I. jinpingensis). Our results identified 10 mutant hotspot regions (rps16, rps16-trnG, trnS-trnR, and rpoB-trnC) that could serve as effective molecular markers for phylogenetic analyses and species identification within the Impatiens. Phylogenetic analyses supported the classification of Impatiens as a monophyletic taxon. The identified affinities supported the taxonomic classification of the subgenus Clavicarpa within the Impatiens, with subgenus Clavicarpa being the first taxon to diverge. In phylogenetic tree,the Impatiens was divided into eight distinct clades. The results of ancestral trait reconstruction suggested that the ancestral traits of Impatiens included a perennial life cycle, four sepals and three pollen grooves. However, the ancestral morphology regarding fruit shape, flower colour, and spacing length remained ambiguous.

CONCLUDE

Our study largely supported the family-level taxonomic treatment of Impatiens species in China and demonstrated the utility of whole chloroplast genome sequences for phylogenetic resolution. Comparative analysis of the chloroplast genomes of Impatiens facilitated the development of molecular markers.The results of ancestral trait reconstruction showed that the ancestor type of habit was perennial, the number of sepals was 4, and morphology and number of aperture was 3 colpus. The traits of capsule shape, flower colour, and spur length underwent a complex evolutionary process. Our results provided data support for further studies and some important new insights into the evolution of the Impatiens.

Genome size influences plant growth and biodiversity responses to nutrient fertilization in diverse grassland communities

Experiments comparing diploids with polyploids and in single grassland sites show that nitrogen and/or phosphorus availability influences plant growth and community composition dependent on genome size; specifically, plants with larger genomes grow faster under nutrient enrichments relative to those with smaller genomes. However, it is unknown if these effects are specific to particular site localities with speciifc plant assemblages, climates, and historical contingencies. To determine the generality of genome size-dependent growth responses to nitrogen and phosphorus fertilization, we combined genome size and species abundance data from 27 coordinated grassland nutrient addition experiments in the Nutrient Network that occur in the Northern Hemisphere across a range of climates and grassland communities. We found that after nitrogen treatment, species with larger genomes generally increased more in cover compared to those with smaller genomes, potentially due to a release from nutrient limitation. Responses were strongest for C3 grasses and in less seasonal, low precipitation environments, indicating that genome size effects on water-use-efficiency modulates genome size-nutrient interactions. Cumulatively, the data suggest that genome size is informative and improves predictions of species' success in grassland communities.

Bigger genomes provide environment-dependent growth benefits in grasses

Increasing genome size (GS) has been associated with slower rates of DNA replication and greater cellular nitrogen (N) and phosphorus demands. Despite most plant species having small genomes, the existence of larger GS species suggests that such costs may be negligible or represent benefits under certain conditions. Focussing on the widespread and diverse grass family (Poaceae), we used data on species' climatic niches and growth rates under different environmental conditions to test for growth costs or benefits associated with GS. The influence of photosynthetic pathway, life history and evolutionary history on grass GS was also explored. We found that evolutionary history, photosynthetic pathway and life history all influence the distribution of grass species' GS. Genomes were smaller in annual and C4 species, the latter allowing for small cells necessary for C4 leaf anatomy. We found larger GS were associated with high N availability and, for perennial species, low growth-season temperature. Our findings reveal that GS is a globally important predictor of grass performance dependent on environmental conditions. The benefits for species with larger GS are likely due to associated larger cell sizes, allowing rapid biomass production where soil fertility meets N demands and/or when growth occurs via temperature-independent cell expansion.

Repeatome evolution across space and time: Unravelling repeats dynamics in the plant genus Erythrostemon Klotzsch (Leguminosae Juss)

Fluctuations in genomic repetitive fractions (repeatome) are known to impact several facets of evolution, such as ecological adaptation and speciation processes. Therefore, investigating the divergence of repetitive elements can provide insights into an important evolutionary force. However, it is not clear how the different repetitive element clades are impacted by the different factors such as ecological changes and/or phylogeny. To discuss this, we used the Neotropical legume genus Erythrostemon (Caesalpinioideae) as a model, given its ancient origin (~33 Mya), lineage-specific niche conservatism, macroecological heterogeneity, and disjunct distribution in Meso- and South American (MA and SA respectively) lineages. We performed a comparative repeatomic analysis of 18 Erythrostemon species to test the impact of environmental variables over repeats diversification. Overall, repeatome composition was diverse, with high abundances of satDNAs and Ty3/gypsy-Tekay transposable elements, predominantly in the MA and SA lineages respectively. However, unexpected repeatome profiles unrelated to the phylogeny/biogeography were found in a few MA (E. coccineus, E. pannosus and E. placidus) and SA (E. calycinus) species, related to reticulate evolution and incongruence between nuclear and plastid topology, suggesting ancient hybridizations. The plesiomorphic Tekay and satDNA pattern was altered in the MA-sensu stricto subclade with a striking genomic differentiation (expansion of satDNA and retraction of Tekay) associated with the colonization of a new environment in Central America around 20 Mya. Our data reveal that the current species-specific Tekay pool was the result of two bursts of amplification probably in the Miocene, with distinct patterns for the MA and SA repeatomes. This suggests a strong role of the Tekay elements as modulators of the genome-environment interaction in Erythrostemon, providing macroevolutionary insights about mechanisms of repeatome differentiation and plant diversification across space and time.

Mechanisms of biodiversity loss under nitrogen enrichment: unveiling a shift from light competition to cation toxicity

The primary mechanisms contributing to nitrogen (N) addition induced grassland biodiversity loss, namely light competition and soil cation toxicity, are often examined separately in various studies. However, their relative significance in governing biodiversity loss along N addition gradient remains unclear. We conducted a 4-yr field experiment with five N addition rates (0, 2, 10, 20, and 50 g N m-2 yr-1) and performed a meta-analysis using global data from 239 observations in N-fertilized grassland ecosystems. Results from our field experiment and meta-analysis indicate that both light competition and soil cation (e.g. Mn2+ and Al3+) toxicity contribute to plant diversity loss under N enrichment. The relative importance of these mechanisms varied with N enrichment intensity. Light competition played a more significant role in influencing species richness under low N addition (≤ 10 g m-2 yr-1), while cation toxicity became increasingly dominant in reducing biodiversity under high N addition (>10 g m-2 yr-1). Therefore, a transition from light competition to cation toxicity occurs with increasing N availability. These findings imply that the biodiversity loss along the N gradient is regulated by distinct mechanisms, necessitating the adoption of differential management strategies to mitigate diversity loss under varying intensities of N enrichment.

Genome size is positively correlated with extinction risk in herbaceous angiosperms

Angiosperms with large genomes experience nuclear-, cellular-, and organism-level constraints that may limit their phenotypic plasticity and ecological niche, which could increase their risk of extinction. Therefore, we test the hypotheses that large-genomed species are more likely to be threatened with extinction than those with small genomes, and that the effect of genome size varies across three selected covariates: life form, endemism, and climatic zone. We collated genome size and extinction risk information for a representative sample of angiosperms comprising 3250 species, which we analyzed alongside life form, endemism, and climatic zone variables using a phylogenetic framework. Genome size is positively correlated with extinction risk, a pattern driven by a signal in herbaceous but not woody species, regardless of climate and endemism. The influence of genome size is stronger in endemic herbaceous species, but is relatively homogenous across different climates. Beyond its indirect link via endemism and climate, genome size is associated with extinction risk directly and significantly. Genome size may serve as a proxy for difficult-to-measure parameters associated with resilience and vulnerability in herbaceous angiosperms. Therefore, it merits further exploration as a useful biological attribute for understanding intrinsic extinction risk and augmenting plant conservation efforts.

Transcriptomic insights into the potential impacts of flavonoids and nodule-specific cysteine-rich peptides on nitrogen fixation in Vicia villosa and Vicia sativa

Vicia villosa (VV) and Vicia sativa (VS) are legume forages highly valued for their excellent nitrogen fixation. However, no research has addressed the mechanisms underlying their differences in nitrogen fixation. This study employed physiological, cytological, and comparative transcriptomic approaches to elucidate the disparities in nitrogen fixation between them. Our results showed that the total amount of nitrogen fixed was 60.45% greater in VV than in VS, and the comprehensive nitrogen response performance was 94.19% greater, while the nitrogen fixation efficiency was the same. The infection zone and differentiated bacteroid proportion in mature VV root nodules were 33.76% and 19.35% greater, respectively, than those in VS. The size of the VV genome was 15.16% larger than that of the VS genome, consistent with its greater biomass. A significant enrichment of the flavonoid biosynthetic pathway was found only for VV-specific genes, among which chalcone-flavonone isomerase, caffeoyl-CoA-O-methyltransferase and stilbene synthase were extremely highly expressed. The VV-specific genes also exhibited significant enrichment in symbiotic nodulation; genes related to nodule-specific cysteine-rich peptides (NCRs) comprised 61.11% of the highly expressed genes. qRT‒PCR demonstrated that greater enrichment and expression of the dominant NCR (Unigene0004451) were associated with greater nodule bacteroid differentiation and greater nitrogen fixation in VV. Our findings suggest that the greater total nitrogen fixation of VV was attributed to its larger biomass, leading to a greater nitrogen demand and enhanced fixation physiology. This process is likely achieved by the synergistic effects of high bacteroid differentiation along with high expression of flavonoid and NCR genes.

Interactive effects of grassland utilization and climatic factors govern the plant diversity-soil C relationship in steppe of North China

The relationship between plant diversity and the ecosystem carbon pool is important for understanding the role of biodiversity in regulating ecosystem functions. However, it is not clear how the relationship between plant diversity and soil carbon content changes under different grassland use patterns. In a 3-year study from 2013 to 2015, we investigated plant diversity and soil total carbon (TC) content of grasslands in northern China under different grassland utilization methods (grazing, mowing, and enclosure) and climatic conditions. Shannon-Wiener and Species richness index of grassland were significantly decreased by grazing and mowing. Plant diversity was positively correlated with annual precipitation (AP) and negatively correlated with annual mean temperature (AMT). AP was the primary regulator of plant diversity. Grazing and mowing decreased TC levels in grasslands compared with enclosures, especially in topsoil (0-20 cm). The average TC content was decreased by 58 % and 36 % in the 0-10 cm soil layer, while it was decreased by 68 % and 39 % in 10-20 cm soil layer. TC was positively correlated with AP and negatively correlated with AMT. Principal component analysis (PCA) showed that plant diversity was positively correlated with soil TC, and the correlation decreased with an increase in the soil depth. Overall, this study provides a theoretical basis for predicting soil carbon storage in grasslands under human disturbances and climate change impacts.

The global distribution of angiosperm genome size is shaped by climate

Angiosperms, which inhabit diverse environments across all continents, exhibit significant variation in genome sizes, making them an excellent model system for examining hypotheses about the global distribution of genome size. These include the previously proposed large genome constraint, mutational hazard, polyploidy-mediated, and climate-mediated hypotheses. We compiled the largest genome size dataset to date, encompassing 16 017 (> 5% of known) angiosperm species, and analyzed genome size distribution using a comprehensive geographic distribution dataset for all angiosperms. We observed that angiosperms with large range sizes generally had small genomes, supporting the large genome constraint hypothesis. Climate was shown to exert a strong influence on genome size distribution along the global latitudinal gradient, while the frequency of polyploidy and the type of growth form had negligible effects. In contrast to the unimodal patterns along the global latitudinal gradient shown by plant size traits and polyploid proportions, the increase in angiosperm genome size from the equator to 40-50°N/S is probably mediated by different (mostly climatic) mechanisms than the decrease in genome sizes observed from 40 to 50°N northward. Our analysis suggests that the global distribution of genome sizes in angiosperms is mainly shaped by climatically mediated purifying selection, genetic drift, relaxed selection, and environmental filtering.

Multi-elemental stoichiometric ratios of atmospheric wet deposition in Chinese terrestrial ecosystems

Intense human activities have significantly altered the concentrations of atmospheric components that enter ecosystems through wet and dry deposition, thereby affecting elemental cycles. However, atmospheric wet deposition multi-elemental stoichiometric ratios are poorly understood, hindering systematic exploration of atmospheric deposition effects on ecosystems. Monthly precipitation concentrations of six elements-nitrogen (N), phosphorus (P), sulfur (S), potassium (K), calcium (Ca), and magnesium (Mg)-were measured from 2013 to 2021 by the China Wet Deposition Observation Network (ChinaWD). The multi-elemental stoichiometric ratio of atmospheric wet deposition in Chinese terrestrial ecosystems was N: K: Ca: Mg: S: P = 31: 11: 67: 5.5: 28: 1, and there were differences between vegetation zones. Wet deposition N: S and N: Ca ratios exhibited initially increasing then decreasing inter-annual trends, whereas N: P ratios did not exhibit significant trends, with strong interannual variability. Wet deposition of multi-elements was significantly spatially negatively correlated with soil nutrient elements content (except for N), which indicates that wet deposition could facilitate soil nutrient replenishment, especially for nutrient-poor areas. Wet N deposition and N: P ratios were spatially negatively correlated with ecosystem and soil P densities. Meanwhile, wet deposition N: P ratios were all higher than those of ecosystem components (vegetation, soil, litter, and microorganisms) in different vegetation zones. High input of N deposition may reinforce P limitations in part of the ecosystem. The findings of this study establish a foundation for designing multi-elemental control experiments and exploring the ecological effects of atmospheric deposition.

Nano-fibre matrix loaded with multi-nutrients to achieve balanced crop nutrition in greengram (Vigna radiata L.)

This research paper focuses on exploring the possibility of delivering macro, micro and trace elements using seed encapsulation through nano-fibres that are known to improve the nutrient use efficiencies while reducing the loss of nutrients. The nano-fibres were developed using an electrospinning machine by subjecting the polymer solution (10% polyvinyl alcohol PVA) loaded with recommended quantities of nutrients under optimal solution (pH, concentration, viscosity) and process (voltage, flow rate, tip-to-collector distance) parameters. The nano-fibres were characterized using SEM, TEM, FT-IR, XRD, TGA and Impedance spectra besides nutrient release pattern by ICP-MS. The data have clearly shown that nano-fibres retained nutrients and released slowly up to 35 days. After the characterization, green gram (Vigna radiata L) seeds were encapsulated with nano-fibres loaded with multi-nutrients and each seed was coated with approximately 20-25 mg of nano-fibres, dibbled into the soil and the physiological, nutritional, growth and yield responses were assessed. Seeds encapsulated with nano-fibres fortified with nutrients (NF) had registered significantly higher crop emergence percentage (C 62%; NF 99.8%), root length (C 12.3; NF 27.1 cm), shoot length (C 28.7; NF 47.7 cm), dry matter production (C 16.2; NF 27.5 g) and grain yield (C 621.6; NF 796.3 kg ha-1). All the parameters measured in nano-fibre encapsulated seeds fortified with 100% of recommended dose of nutrients (NF) were higher than uncoated control (C) seeds but comparable with 100 % conventional fertilizer applied ones (RDF). Such phenomenal increase in growth and yield parameters associated with the extensive surface area of nano-fibres that is capable of retaining and releasing nutrients in a regulated pattern and assist in improving the pulses productivity by achieving balance crop nutrition which alleviating multi-nutrient deficiencies.

Testing the large genome constraint hypothesis in tropical rhizomatous herbs: life strategies, plant traits and habitat preferences in gingers

Plant species with large genomes tend to be excluded from climatically more extreme environments with a shorter growing season. Species that occupy such environments are assumed to be under natural selection for more rapid growth and smaller genome size (GS). However, evidence for this is available only for temperate organisms. Here, we study the evolution of GS in two subfamilies of the tropical family Zingiberaceae to find out whether species with larger genomes are confined to environments where the vegetative season is longer. We tested our hypothesis on 337 ginger species from regions with contrasting climates by correlating their GS with an array of plant traits and environmental variables. We revealed 16-fold variation in GS which was tightly related to shoot seasonality. Negative correlations of GS with latitude, temperature and precipitation emerged in the subfamily Zingiberoidae, demonstrating that species with larger GS are excluded from areas with a shorter growing season. In the subfamily Alpinioideae, GS turned out to be correlated with the type of stem and light requirements and its members cope with seasonality mainly by adaptation to shady and moist habitats. The Ornstein-Uhlenbeck models suggested that evolution in regions with humid climates favoured larger GS than in drier regions. Our results indicate that climate seasonality exerts an upper constraint on GS not only in temperate regions but also in the tropics, unless species with large genomes find alternative ways to escape from that constraint.

Applied phosphorus is maintained in labile and moderately occluded fractions in a typical meadow steppe with the addition of multiple nutrients

Phosphorus (P) is a limiting nutrient second only to nitrogen (N) in the drylands of the world. Most previous studies have focused on N transformation processes in grassland ecosystems, particularly under artificial fertilization with N and atmospheric N deposition. However, P cycling processes under natural conditions and when P is applied as an inorganic P fertilizer have been understudied. Therefore, it is essential to examine the fate of applied P in grassland ecosystems that have experienced long-term grazing and, under certain circumstances, continuous hay harvest. We conducted a 3-year field experiment with the addition of multiple nutrient elements in a typical meadow steppe to investigate the fate of the applied P in various fractions of P pools in the top soil. We found that the addition of multiple nutrients significantly increased P concentrations in the labile inorganic P (Lab-Pi) and moderately occluded inorganic P (Mod-Pi) fractions but not in the recalcitrant inorganic P (Rec-Pi) fraction. An increase in the concentration of total inorganic P was found only when P and N were applied together. However, the addition of other nutrients did not change P concentrations in any fraction of the mineral soil. The addition of P and N significantly increased the total amount of P taken up by the aboveground plants but had no effect on the levels of organic and microbial P in the soil. Together, our results indicate that the P applied in this grassland ecosystem is taken up by plants, leaving most of the unutilized P as Lab-Pi and Mod-Pi rather than being immobilized in Rec-Pi or by microbial biomass. This implies that the grassland ecosystem that we studied has a relatively low P adsorption capacity, and the application of inorganic P to replenish soil P deficiency in degraded grasslands due to long-term grazing of livestock or continuous harvest of forage in the region could be a practical management strategy to maintain soil P fertility.

Genome-material costs and functional trade-offs in the autopolyploid Solidago gigantea (giant goldenrod) series

PREMISE

Increased genome-material costs of N and P atoms inherent to organisms with larger genomes have been proposed to limit growth under nutrient scarcities and to promote growth under nutrient enrichments. Such responsiveness may reflect a nutrient-dependent diploid versus polyploid advantage that could have vast ecological and evolutionary implications, but direct evidence that material costs increase with ploidy level and/or influence cytotype-dependent growth, metabolic, and/or resource-use trade-offs is limited.

METHODS

We grew diploid, autotetraploid, and autohexaploid Solidago gigantea plants with one of four ambient or enriched N:P ratios and measured traits related to material costs, primary and secondary metabolism, and resource-use.

RESULTS

Relative to diploids, polyploids invested more N and P into cells, and tetraploids grew more with N enrichments, suggesting that material costs increase with ploidy level. Polyploids also generally exhibited strategies that could minimize material-cost constraints over both long (reduced monoploid genome size) and short (more extreme transcriptome downsizing, reduced photosynthesis rates and terpene concentrations, enhanced N-use efficiencies) evolutionary time periods. Furthermore, polyploids had lower transpiration rates but higher water-use efficiencies than diploids, both of which were more pronounced under nutrient-limiting conditions.

CONCLUSIONS

N and P material costs increase with ploidy level, but material-cost constraints might be lessened by resource allocation/investment mechanisms that can also alter ecological dynamics and selection. Our results enhance mechanistic understanding of how global increases in nutrients might provide a release from material-cost constraints in polyploids that could impact ploidy (or genome-size)-specific performances, cytogeographic patterning, and multispecies community structuring.

β-diversity in temperate grasslands is driven by stronger environmental filtering of plant species with large genomes

Elucidating mechanisms underlying community assembly and biodiversity patterns is central to ecology and evolution. Genome size (GS) has long been hypothesized to potentially affect species' capacity to tolerate environmental stress and might therefore help drive community assembly. However, its role in driving β-diversity (i.e., spatial variability in species composition) remains unclear. We measured GS for 161 plant species and community composition across 52 sites spanning a 3200-km transect in the temperate grasslands of China. By correlating the turnover of species composition with environmental dissimilarity, we found that resource filtering (i.e., environmental dissimilarity that includes precipitation, and soil nitrogen and phosphorus concentrations) affected β-diversity patterns of large-GS species more than small-GS species. By contrast, geographical distance explained more variation of β-diversity for small-GS than for large-GS species. In a 10-year experiment manipulating levels of water, nitrogen, and phosphorus, adding resources increased plant biomass in species with large GS, suggesting that large-GS species are more sensitive to the changes in resource availability. These findings highlight the role of GS in driving community assembly and predicting species responses to global change.

Enhanced foliar 15 N enrichment with increasing nitrogen addition rates: Role of plant species and nitrogen compounds

Determining the abundance of N isotope (δ¹⁵ N) in natural environments is a simple but powerful method for providing integrated information on the N cycling dynamics and status in an ecosystem under exogenous N inputs. However, whether the input of different N compounds could differently impact plant growth and their ¹⁵ N signatures remains unclear. Here, the response of ¹⁵ N signatures and growth of three dominant plants (Leymus chinensis, Carex duriuscula, and Thermopsis lanceolata) to the addition of three N compounds (NH₄ HCO₃ , urea, and NH₄ NO₃ ) at multiple N addition rates were assessed in a meadow steppe in Inner Mongolia. The three plants showed different initial foliar δ¹⁵ N values because of differences in their N acquisition strategies. Particularly, T. lanceolata (N₂ -fixing species) showed significantly lower ¹⁵ N signatures than L. chinensis (associated with arbuscular mycorrhizal fungi [AMF]) and C. duriuscula (associated with AMF). Moreover, the foliar δ¹⁵ N of all three species increased with increasing N addition rates, with a sharp increase above an N addition rate of ~10 g N m^-2  year^-1 . Foliar δ¹⁵ N values were significantly higher when NH₄ HCO₃ and urea were added than when NH₄ NO₃ was added, suggesting that adding weakly acidifying N compounds could result in a more open N cycle. Overall, our results imply that assessing the N transformation processes in the context of increasing global N deposition necessitates the consideration of N deposition rates, forms of the deposited N compounds, and N utilization strategies of the co-existing plant species in the ecosystem.