From atoms to ecosystems: elementome diversity meets ecosystem functioning

Coral elementomes diverge for colonies persisting in vegetative lagoons versus reef environments

Climate change, in tandem with localised stressors, continues to drive global declines in coral cover worldwide. Identifying where and how corals survive in present day extreme environments, characterised by suboptimum abiotic conditions, has become a key tool to better resolve coral stress tolerance and in turn future reef trajectories. Whilst several reef forming coral species routinely extend their ecological niche into extreme environments, whether corals have a distinct biogeochemical niche reflected by unique elementomes (the stoichiometry and quantity of elements) remains unknown. Here, through quantitative assessment and elemental mapping, we demonstrate that two functionally important Great Barrier Reef coral species, Acropora millepora and Porites lutea and their algal symbionts (Symbiodiniaceae) exhibit unique elementomes, that reflect a unique biogeochemical niche of species in the extreme mangrove lagoon compared to a neighbouring reef. Coral elementomes were distinct over multiple years, as were the elementomes of the seawater of each habitat. Furthermore, particulate organic matter was elevated in the mangrove lagoon which could support enhanced rates of heterotrophy. Collectively these findings reveal that vegetative mangrove island waters provide a unique biogeochemical environment for resident corals and that resident corals undergo bioelemental reorganisation, particularly via elevated micronutrient content, when living in extreme vegetative mangrove island lagoons. Results here reaffirm the importance of vegetative island systems in the survival of coral reefs and thus the critical need to ensure conservation efforts consider cross ecosystem protection measures.

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.

Plant species determine elementome differentiation and element coupling during deadwood decay

The elemental dynamics and interactions within deadwood profoundly influence carbon sequestration and nutrient cycling in forest ecosystems. Recent studies have investigated macronutrient cycling during deadwood decay of specific plants, yet the dynamics and interactions of micronutrients, trace elements, and the elementome across species and decay stages remain unexplored. Here, we investigated the elementome and their coupling relationships across five decay stages of downed deadwood (DDW) from four dominant species (Hippophae rhamnoides, Populus purdomii, Abies fabri, and Picea brachytyla) along the Hailuogou Glacier primary successional chronosequence. Element coupling was evaluated following the framework of mean correlation of all elements in absolute value and null modeling. We observed species-specific elementome differentiation during DDW decay, with interspecific distances greater in the initial and later decay stages and lower in the intermediate stage. Notably, shrub H. rhamnoides exhibited distinct initial elementomes and remained robust multi-element coupling throughout decay. Conversely, element couplings for tree species declined with decay, particularly for P. purdomii and A. fabri, reaching decoupling from Stage III. Non-essential elements of Al, V, and Ti remained robust coupling, while key nutrients of N, P, and Ca decoupled as decay progressed. The individual element coupling was negatively correlated with their enrichment levels, with lower coupling observed for anthropogenically enriched metals. Our results reveal the importance of plant species in elementome differentiation and element coupling during deadwood decay, while atmospheric heavy metal deposition mediates individual element coupling, underscoring species-specific deadwood management strategies and monitoring of heavy metal deposition to optimize forest ecosystem functions and stability.

The Plant Ionome as a Functional Trait: Variation across Bioclimatic Regions and Functional Groups

Plant chemical composition is a trait gaining increasing importance in plant ecology. However, there is limited research on the patterns and drivers of its variation among different plant functional groups and bioclimatic regions. We conducted an analysis of ionomes utilising X-ray fluorescence on 83 plant species from four distinct functional groups (grasses, legumes, forbs and woody species); we marked plots across 15 sites located in both the desert and Mediterranean bioclimatic regions. The primary factors influencing variations in ionomes are predominantly attributed to bioclimatic factors rather than soil composition. Across all functional groups, plants from the Mediterranean region are characterised by greater association with calcium, whereas desert plants exhibit a higher affinity for strontium (Sr), suggesting its potential role in drought tolerance. Among functional groups, grasses uniquely exhibit distinct ionomic features, primarily due to their higher silicon (Si) concentrations. Plant species' affinities for certain elements and their interactions are likely driven by physiological constraints, whereas variations within a functional group are mostly driven by environmental conditions. We conclude that interactions among elements form physiological phenotypes shaped by natural selection under large-scale environmental variability, making plant ionome composition an important plant functional trait.

Stable nutrient utilization of trees promotes community biomass accumulation in Korean pine and broad-leaved mixed forests after logging

The recovery of community productivity in disturbed temperate forests is affected by fluctuating nutrient environments. How plant growth achieves high biomass accumulation in a limited nutrient environment remains unclear but may be attributed to the flexibility of plant nutrient utilization. Nutrient homeostasis (H) reflects the ability of plant tissues to maintain a relatively constant N and P content under nutrient fluctuations and represents flexible or stable plant nutrient utilization. We aim to reveal the influence of plant nutrient utilization mechanisms on community biomass accumulation after logging. We chose 28 post-logged Korean pine and broad-leaved mixed forests after seven recovery periods (6, 14, 25, 36, 45, and 55 years after logging) with six low-intensity selective logged treatments and one unlogged treatment (100 years after logging). We then estimated the H value of leaf N (HN), leaf P (HP), and leaf N:P ratio (HN:P) and the biomass of 234 plant species with different functional groups, soil nutrient, and species diversity. The leaf HN of 13.19 and the leaf HP of 9.87 reached the maximum at 36 and 45 years after logging, respectively. The HN:P at the community level reached the maximum at 36 years after logging. The robust linear trend between nutrient H and biomass suggests the accumulation of biomass benefits from stable nutrient utilization after logging. Considering the soil nutrient and species diversity, nutrient H showed the major explanation of biomass accumulation in trees, herbs, and whole community. The stable N utilization of tree species accounts for the maximum independent contribution (25.05%) to the community biomass accumulation. Herb species with flexible P utilization had major contribution (37.97%) to herb biomass accumulation. Our study highlights the vital role of high HN in promoting community biomass accumulation in logged forest to assess forest sustainability.

Shading and Water Addition Alleviate the Elemental Limitations of the Early Restoration Community in a Stressful Environment

Shading and water addition are essential management measures to improve seed germination and early seedling survival; however, little is known about their effects on leaf stoichiometry and nutrient status. We established 90 plant communities with shading and water addition gradients on a rocky hill; leaves of their dominant woody plant species were collected to measure elemental concentrations, and then, stoichiometric variation and nutrient status were analysed. The results showed that the overall effects of shading and water addition significantly altered the concentrations and ratios of nutrient elements; shading largely affected leaf K and P, while water addition mainly affected leaf N and P. The interactions between shading and water addition were significant for most species but disappeared at the community level. Consequently, the nutrient status in leaves was improved by promoting the concentrations and balances of nutrient elements. However, the responses to shading and water addition were marked by species-specific differences, with some plants forming a sensitive group and others distinguished by conservatism. Our findings show that management of the physical environment could improve nutrient element utilization in leaves and alleviate the nutrient limitations. For our site conditions, mild shading (25-35%) and adequate water addition (30 L·m-2) in the early stage of vegetation restoration is recommended to advance community assembly by improving nutrient physiology, directly diminishing the stress of water scarcity and excessive irradiation. These findings explore the underlying mechanisms of shading and water addition that could promote community development and provide guidance for restoration practice.

Unforeseen plant phenotypic diversity in a dry and grazed world

Earth harbours an extraordinary plant phenotypic diversity1 that is at risk from ongoing global changes2,3. However, it remains unknown how increasing aridity and livestock grazing pressure-two major drivers of global change4-6-shape the trait covariation that underlies plant phenotypic diversity1,7. Here we assessed how covariation among 20 chemical and morphological traits responds to aridity and grazing pressure within global drylands. Our analysis involved 133,769 trait measurements spanning 1,347 observations of 301 perennial plant species surveyed across 326 plots from 6 continents. Crossing an aridity threshold of approximately 0.7 (close to the transition between semi-arid and arid zones) led to an unexpected 88% increase in trait diversity. This threshold appeared in the presence of grazers, and moved toward lower aridity levels with increasing grazing pressure. Moreover, 57% of observed trait diversity occurred only in the most arid and grazed drylands, highlighting the phenotypic uniqueness of these extreme environments. Our work indicates that drylands act as a global reservoir of plant phenotypic diversity and challenge the pervasive view that harsh environmental conditions reduce plant trait diversity8-10. They also highlight that many alternative strategies may enable plants to cope with increases in environmental stress induced by climate change and land-use intensification.

Heterogeneity of leaf stoichiometry of different life forms along environmental transects in typical ecologically fragile areas of China

The coupling between carbon (C):nitrogen (N):phosphorus (P) stoichiometry in plant leaves is closely related to ecological functions such as photosynthesis, growth, and biogeochemical cycling. To explore the biogeographic patterns, nutrient limitations, and the relationships between leaf and soil stoichiometry, as well as the factors influencing leaf stoichiometry, we quantified community-level leaf C:N:P stoichiometry in trees, shrubs, and herbs along transects with a total length of about 4300 km. The leaf C:N:P ratios of trees, shrubs, and herbs were approximately 349:13:1, 267:14:1, and 226:12:1, respectively. Leaf C:N:P stoichiometry differed significantly (p < 0.05) among the life forms. Compared with global and Chinese scales, the C, N, and P concentrations were higher and C:N, C:P, and N:P ratios were lower. The leaf C:N:P stoichiometry patterns along a latitude gradient differed among life forms. There was no significant correlation between leaf N and soil total N, whereas leaf P of all three life forms increased significantly with increasing soil total P. Those results suggested a community-level N limitation for trees, shrubs, and herbs growth. Environmental factors explained 43.9, 26.5, and 6.1 % of leaf stoichiometric variations for trees, shrubs, and herbs, respectively. However, the key environmental driving factors gradually changed from climatic factors for trees and shrubs to soil factors for herbs. The results provide new insights into community-level biogeographical patterns and potential factors of leaf stoichiometry among plant life forms.

Uncovering the significance of the ratio of food K:Na in bee ecology and evolution

Bees provide important ecological services, and many species are threatened globally, yet our knowledge of wild bee ecology and evolution is limited. While evolving from carnivorous ancestors, bees had to develop strategies for coping with limitations imposed on them by a plant-based diet, with nectar providing energy and essential amino acids and pollen as an extraordinary, protein- and lipid-rich food nutritionally similar to animal tissues. Both nectar and pollen display one characteristic common to plants, a high ratio of potassium to sodium (K:Na), potentially leading to bee underdevelopment, health problems, and death. We discuss why and how the ratio of K:Na contributes to bee ecology and evolution and how considering this factor in future studies will provide new knowledge, more accurately depicting the relationship of bees with their environments. Such knowledge is essential for understanding how plants and bees function and interact and is needed to effectively protect wild bees.

The essential role of biodiversity in the key axes of ecosystem function

Biodiversity is essential for maintaining the terrestrial ecosystem multifunctionality (EMF). Recent studies have revealed that the variations in terrestrial ecosystem functions are captured by three key axes: the maximum productivity, water use efficiency, and carbon use efficiency of the ecosystem. However, the role of biodiversity in supporting these three key axes has not yet been explored. In this study, we combined the (i) data collected from more than 840 vegetation plots across a large climatic gradient in China using standard protocols, (ii) data on plant traits and phylogenetic information for more than 2,500 plant species, and (iii) soil nutrient data measured in each plot. These data were used to systematically assess the contribution of environmental factors, species richness, functional and phylogenetic diversity, and community-weighted mean (CWM) and ecosystem traits (i.e., traits intensity normalized per unit land area) to EMF via hierarchical partitioning and Bayesian structural equation modeling. Multiple biodiversity attributes accounted for 70% of the influence of all the variables on EMF, and ecosystems with high functional diversity had high resource use efficiency. Our study is the first to systematically explore the role of different biodiversity attributes, including species richness, phylogenetic and functional diversity, and CWM and ecosystem traits, in the key axes of ecosystem functions. Our findings underscore that biodiversity conservation is critical for sustaining EMF and ultimately ensuring human well-being.

Changes in root chemical diversity along an elevation gradient of Changbai Mountain, China

Root chemical traits play a critical role in plant resource use strategies and ecosystem nutrient cycling; however, the chemical diversity of multiple elements of fine root and community chemical assembly belowground are poorly understood. Here, we measured 13 elements (C, N, K, Ca, Mg, S, P, Al, Fe, Na, Mn, Zn, and Cu) in the fine roots of 204 plant species along elevational transect from 540 to 2357 m of Changbai Mountain, China to explore the variation, diversity, and community assembly of root chemical traits. At the species level, the concentrations of macronutrients (N, K, Ca, Mg, S, and P) decreased, whereas the trace metals (Fe, Mn, and Zn) increased with elevation. Root chemical traits at the community level systematically shifted along elevational gradients showing a pattern similar to that at the species level, which were mainly influenced by climate and soil rather than species diversity. In general, the interactions of climate and soil were the main drivers of root chemical assembly for woody layers, whereas soil factors played significant role for root chemical assembly for herb layer. The chemical assembly of rock-derived element P was mainly driven by soil factors. Meanwhile, root chemical diversities were mainly regulated by species diversity, the interactions of climate and soil, and soil factors in the tree, shrub, and herb layers, respectively. A better understanding of plant root chemical diversity and community chemical assembly will help to reveal the role of chemical traits in ecosystem functioning.

The conserved and high K-to-Na ratio in sunflower pollen: Possible implications for bee health and plant-bee interactions

Sodium (Na) concentrations are low in plant tissues, and its metabolic function in plants is minor; however, Na is a key nutrient for plant consumers. Previous studies have thus far focused on Na concentration. Nevertheless, a balanced potassium (K) to Na ratio (K:Na) is more important than Na concentration alone since food with high K:Na has detrimental effects on consumers irrespective of Na concentration. Therefore, plants may actively regulate K:Na in their tissues and products, shaping plant-insect interactions. Studies considering nutritional aspects of plant-insect interactions have focused on nonreproductive tissues and nectar. In this study, we consider pollen as serving a primary reproductive function for plants as well as a food of pollinivores. Plants might regulate K:Na in pollen to affect their interactions with pollinivorous pollinators. To investigate whether such a mechanism exists, we manipulated Na concentrations in soil and measured the proportion of K, Na, and 13 other nutrient elements in the pollen of two sunflower (Helianthus annuus) cultivars. This approach allowed us to account for the overall nutritional quality of pollen by investigating the proportions of many elements that could correlate with the concentrations of K and Na. Of the elements studied, only the concentrations of Na and K were highly correlated. Pollen K:Na was high in both cultivars irrespective of Na fertilization, and it remained high regardless of pollen Na concentration. Interestingly, pollen K:Na did not decrease as pollen increased the Na concentration. We hypothesize that high K:Na in pollen might benefit plant fertilization and embryonic development; therefore, a tradeoff might occur between producing low K:Na pollen as a reward for pollinators and high K:Na pollen to optimize the plant fertilization process. This is the first study to provide data on pollen K:Na regulation by plants. Our findings broaden the understanding of plant-bee interactions and provide a foundation for a better understanding of the role of the soil-plant-pollen-pollinator pathway in nutrient cycling in ecosystems. Specifically, unexplored costs and tradeoffs related to balancing the K:Na by plants and pollinivores might play a role in past and current shaping of pollination ecology.