Optimal Allocation Strategies of Plant Calcium on Qinghai-Tibetan Plateau

Calcium (Ca) is an essential nutrient for plant growth and development. As Ca plays crucial roles in plant structure and signaling, its allocation strategies among organs can reflect the optimization of plant functions and responses to the environment. However, the allocation strategies and spatial variation of plant Ca at the community level have not been systematically determined on a large scale despite their potential link to ecosystem functions. Here, we mapped community-level Ca content and density (1 x 1 km) using grid-investigated data on leaves, branches, trunks, and roots from 680 sampling sites on the Qinghai-Tibetan Plateau (TP). Specifically, the Ca content and density of the leaves, branches, trunks, and roots of TP plants were 10.90, 6.09, 1.85, and 15.62 mg g-1 and 3.29, 17.10, 12.27, and 12.06 g m-2, respectively. Importantly, plant adopted optimal allocation strategies with allocating more Ca to roots in stressed ecosystems to maintain survival while more Ca to leaves in suitable forests for growth, that is the proposed survival/growth-driven allocation hypothesis. Furthermore, plants optimally absorbed more nutrients in stressed environments for defense, as demonstrated by the higher Ca content and lower Ca use efficiency in deserts and grasslands than in forests. Furthermore, the strong evidence for the proposed hypothesis was the spatial pattern of plant Ca content decreasing from the northwest to the southeast. Our findings reveal the optimal nutrient allocation strategies and provide data support (Ca content and density) for assessing plant nutrient status in different types of ecosystems. Calcium (Ca) is a vital nutrient that plays a significant role in the growth and development of plants, contributing to their structure and signaling processes. The way plants distribute Ca among their different organs can give us insights into how they adapt and respond to their environment. However, there hasn't been a large-scale, systematic study on how plants allocate Ca at the community level and how this might relate to the functions of an ecosystem. In our study, we focused on the Qinghai-Tibetan Plateau (TP) and used data from 680 sampling sites to map out the Ca content and density of the local plant communities. Our findings suggest that plants adopt optimal allocation strategies, distributing more Ca to their roots in stressful ecosystems to ensure survival, and more Ca to their leaves in suitable forest environments to support growth. Additionally, we observed that plants in stressed environments, such as deserts and grasslands, absorb more nutrients for defense, as indicated by their higher Ca content and lower Ca use efficiency compared to plants in forests. Systematically explored plant Ca spatial variation and allocation in Tibetan Plateau Stressed ecosystems allocate more Ca to roots for survival Low soil Ca availability led to high plant Ca use efficiency in forests