High-resolution community-level sodium variation on the Tibetan Plateau: Content, density, and storage.

Sodium (Na), a beneficial mineral element, stimulates plant growth through osmotic adjustment. Previous studies focused on Na content at the individual or species level, however, it is hard to link to ecosystem functions without exploring the characteristics (content, density, and storage) of Na at the community level. We conducted grid-plot sampling of different plant organs in 2040 natural plant communities on the Tibetan Plateau (TP) to comprehensively characterize community-level Na on a regional scale. The Na content was 0.57, 0.09, 0.07, and 0.71 mg g-1 in leaves, branches, trunks, and roots, respectively. Across biomes Na content was higher in deserts under drought stress. Oxygen partial pressure, radiation, precipitation, soil Na supply, and temperature significantly affected the spatial variation in Na content. Furthermore, we accurately simulated the spatial variation in Na density and produced a highly precise 1 km × 1 km spatial map of plant Na density on the TP using random forest algorithm, which demonstrated higher Na density in the southeast of TP. The total plant Na storage on the TP was estimated as 111.80 × 104 t. These findings provide great insights and references for understanding the plant community-level adaptation strategies and evaluating the mineral element status on a large scale, and provide valuable data for ecological model optimization in the future.

Spatial variation and allocation of sulfur among major plant organs in China.

Sulfur (S) is a functional element that plays an important role in abiotic stress resistance and environmental adaptation in plants. However, knowledge of the biogeographic patterns of S among major plant organs remains limited. We conducted a methodologically consistent field survey of 2745 plant species across 78 typical communities throughout China. From this, we constructed a new matched database of S content in leaves, twigs, trunks, and roots to explore S allocation strategies in plants to better understand the regulatory mechanisms on a large scale. The average S content in leaves, twigs, trunks, and roots of plants in China was 2.32 ± 0.04, 1.13 ± 0.02, 0.15 ± 0.01, and 1.23 ± 0.02 g kg-1, respectively. S content was significantly higher in leaves than in other organs, and S content of plants in deserts was higher than that of plants in forests and grasslands. S content changed faster in roots and showed divergent allocation relationships among organs across communities at different scales. Climate and soil properties jointly regulated the spatial variation and allocation relationships of S among different organs. This study further broadens our understanding of the biological functions of S and their role in the interactions between plants and the environment.

Allometry and Distribution of Nitrogen in Natural Plant Communities of the Tibetan Plateau.

Nitrogen (N) is an important element for most terrestrial ecosystems; its variation among different plant organs, and allocation mechanisms are the basis for the structural stability and functional optimization of natural plant communities. The nature of spatial variations of N and its allocation mechanisms in plants in the Tibetan Plateau-known as the world's third pole-have not been reported on a large scale. In this study, we consistently investigated the N content in different organs of plants in 1564 natural community plots in Tibet Plateau, using a standard spatial-grid sampling setup. On average, the N content was estimated to be 19.21, 4.12, 1.14, and 10.86 mg g-1 in the leaf, branch, trunk, and root, respectively, with small spatial variations. Among organs in communities, leaves were the most active, and had the highest N content, independent of the spatial location; as for vegetation type, communities dominated by herbaceous plants had higher N content than those dominated by woody plants. Furthermore, the allocation of N among different plant organs was allometric, and not significantly influenced by vegetation types and environmental factors; the homeostasis of N was also not affected much by the environment, and varied among the plant organs. In addition, the N allocation strategy within Tibet Plateau for different plant organs was observed to be consistent with that in China. Our findings systematically explore for the first time, the spatial variations in N and allometric mechanisms in natural plant communities in Tibet Plateau and establish a spatial-parameters database to optimize N cycle models.