Biogeochemical niche conservatism relates to plant species diversification and life form evolution in a subtropical montane evergreen broad‐leaved forest

Abstract

The evolutionary mechanisms underlying the biogeochemical niche conservatism in forests remain incompletely understood. Here we aimed to determine how the strengths of biogeochemical niche conservatism vary among elements and between life forms. We measured leaf concentrations of basal elements (C, N, P, K, Ca, and Mg) in a wide range of life forms in a subtropical montane evergreen broad‐leaved forest. We found that differences in life forms such as evergreen/deciduous woody species and herbaceous/woody species significantly affected leaf elemental composition. The significant phylogenetic signal was present in leaf C, N, K, and Mg concentrations but absent in leaf P and Ca concentrations in all species. These contrasting strengths of biogeochemical niche conservatism were best generated by Ornstein–Uhlenbeck processes toward optima. Woody species were evolutionarily selected to show lower optimal leaf N, P, and K concentrations and higher optimal leaf C, Ca, and Mg concentrations than herbaceous species. The number of optima varied from the least in leaf C concentration to the most in leaf Ca concentration, suggesting the stronger convergent evolution of leaf Ca concentration. The positions of optima toward the tips were more selected in woody species, suggesting the more frequency of species‐specific adaptations in woody species. The positions of optima were also selected at the nodes towards the species groupings from certain life forms (e.g., the group of 12 Polypodiales ferns in leaf Ca evolution and the group of three evergreen Theaceae species in leaf P evolution) that were converged to present similar leaf elemental composition. During the evolution of biogeochemical niche, strong correlations were found among leaf C, N, P, and K concentrations and between leaf Ca and Mg concentrations. In conclusion, the strengths of biogeochemical niche conservatism can vary among elements and between life forms due to the different tempo and mode of Ornstein–Uhlenbeck processes.

Substantial variation of the two‐dimensional spectrum of senescent leaf in subalpine forest along elevational gradients

“…Second only to N, K is an essential element for plant growth and plays a vital role in maintaining the normal life cycle of plants (Li, He, et al, 2021). For example, leaf elemental composition with fresh leaves significantly differed among species (e.g., herbaceous vs. woody species), which was characterized by higher leaf N, P, and K; but the concentrations were flexible with the plant growth (Bai et al, 2022; Wang et al, 2014). As the most abundant cations, K located in cells solely exists in ionic form (K + ) or in weak complexes from which it is easily exchangeable (Ge et al, 2016; Laskowski et al, 1995).…”

“…This difference in functional traits between fresh and aged leaves could lead to dramatic changes in resource trade‐off strategies of various species at different life cycles (e.g., growth vs. aging) due to the alteration in leaves from anabolic growth phase to catabolic aging phase (Estiarte & Penuelas, 2015). However, previous studies have mainly focused on some nutrient dynamics of fresh leaves (Bai et al, 2022; Wang et al, 2014), but how these traits can be integrated to reflect the strategies of the senescent leaves in resource acquisition and allocation and response of plant aged leaves to environmental factors remains unclear.…”

“…Climate conditions on mountains reflect variations in temperature and precipitation at relatively small spatial scales, providing a useful location for assessing environmental responses of leaf functional traits (Bai et al, 2022; Chieppa et al, 2022; Hikosaka et al, 2021). Indeed, temperature and precipitation control the plant leaf economics spectrum by affecting plant nutrient demand for various functions, soil nutrient supply (e.g., weathering, leaching, and organic matter accumulation), and nutrient reabsorption during leaf senescence (Chávez‐Vergara et al, 2015; Estiarte & Penuelas, 2015).…”