From atoms to ecosystems: elementome diversity meets ecosystem functioning

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.