Nitrogen (N) and phosphorus (P) play crucial roles in tea planting, but information on how the long-term excessive application of chemical N fertilizer affected N and P in subtropical tea plantations remains limited. In this study, soil and leaf samples were collected along a chronosequence of tea plantations (0-, 5-, 10-, 18- and 23-year-old plantations) with excessive N input but no P application to investigate the effects of planting age on N and P availability. Diverse soil N forms and P fractions, and the concentrations of leaf N and P were measured. The results showed that (1) ${\mathrm{N}\mathrm{O}}_3^{-}$-N and dissolved organic nitrogen (DON) concentrations in both topsoil and subsoil, and the N concentration of mature leaf showed significant upward trends with tea plantation age; (2) the concentrations of available phosphorus (AP), NaHCO₃-P_i in labile P pool, NaOH-P_i and D.HCl-P_i in moderately labile P pool in both layers of soil and that the P concentration of mature leaf also increased with age; (3) the N concentration of mature leaves had closely significant logarithmic relations with ${\mathrm{N}\mathrm{O}}_3^{-}$-N concentration, while the TP (total P) concentration of mature leaves had significant positive correlations with AP; and (4) the ratio of N/P in tea leaves indicated a slightly P limitation in tea plantations. We concluded that the ${\mathrm{N}\mathrm{O}}_3^{-}$-N concentration, instead of TN (total N) of ${\mathrm{N}\mathrm{H}}_4^{+}$-N, would be a good indicator to reflect N availability for tea trees, and the increasing of ${\mathrm{N}\mathrm{O}}_3^{-}$-N concentration in soil has a diminishing promoting effect on the TN concentration of mature leaves. The long-term application of chemical N fertilizer had not lead to serious P limitation in subtropical tea plantations. Generally, our study could contribute to improving our understanding of N and P availability and optimizing fertilization management in subtropical tea plantations.

Phosphorus (P) is a pivotal element in plant energy metabolism and growth, and P limitation is widespread among plants in nature. However, our understanding of how epiphytes allocate P and adapt to P-deficient environments remains limited. We selected an obligate epiphyte Pyrrosia sheareri from a subtropical forest as our research subject. We compared its carbon (C)–nitrogen (N)–P ecological stoichiometry, P fractions, and morphological and physiological traits under the two habitats (trunk-epiphytic and rock-epiphytic). We also constructed a plant trait network method (PTN) that includes 62 traits to explore the co-variation characteristics of plant traits across the whole plant and identify the hub traits. We found that the following: (1) Habitat type significantly affects plant P concentration, with trunk-epiphytic plants having higher P concentration than rock-epiphytic plants. Pyrrosia sheareri may be more strongly limited by P according to the results of C-N-P ecological stoichiometry. (2) Epiphytic habitats significantly affect plant P fractions but do not influence the relative allocation of P fractions. (3) Compared with rock-epiphytic plants, trunk-epiphytic plants adopt a root resource-acquisition strategy rather than relying on leaves. (4) P-related indicators link ecological stoichiometry with morphological and physiological traits and are hub traits in PTN. Overall, P. plays a key functional role in the environmental acclimatization of Pyrrosia sheareri, highlighting the morphological and physiological adaptability of epiphytes to various habitats in terms of P availability, allocation, and storage.

Tea (Camellia sinensis (L.) Kuntze) plantations have been rapidly expanding in recent years in developing countries, but there is a lack of knowledge about the effects of woodland conversion to tea plantations and tea plantation aging on soil organic carbon (SOC) accumulation in subtropical regions, which may be a critical issue for accurately estimating the regional C balance in tea planting areas. Thus, in this study, we selected four tea plantations with ages ranging from 5 to 23 years, along with an adjacent mature pine forest (PF, more than 60 years of age), to investigate the effects of woodland conversion to tea plantations and stand age on SOC. Lignin phenols and amino sugars were used to distinguish the contributions of plant-derived C and microbial-derived C to SOC. The results showed that when PF is converted to a tea plantation, 54.12% of the SOC content in the topsoil is lost, with reductions of 84.77% in plant-derived C and 10.23% in microbial-derived C; however, there is a slight increase in microbial-derived C in the deep-layer soil. The tea planting age only has a negative effect on microbial-derived C in the topsoil. Additionally, the plant aboveground biomass, ratio of carbon to nitrogen, total nitrogen concentration, and clay–silt content are key environmental variables influencing SOC accrual, explaining 59.8% of the total variance. SOC and plant-derived C are thus implicated in the quick response to decreasing plant inputs with land conversion and do not accumulate with increasing tea plantation age under the current tea plantation management practices. Generally, more attention should be focused on SOC loss with woodland conversion to tea plantations at the regional scale, and more effective practices can be applied to enhance SOC accrual in subtropical tea plantations.

Tea plantations are one of the most intensive land-use systems in subtropical China, but the long-term effects on soil microbial functioning remain insufficiently understood. This study combined extracellular enzyme activity, ecoenzymatic stoichiometry, and partial least squares path modeling (PLS-PM) to assess the impacts of forest-to-tea conversion and plantation age on microbial nutrient acquisition and metabolic limitations. The results showed that tea plantations had significantly higher activities of carbon (C)-, nitrogen (N)-, and phosphorus (P)-acquiring hydrolases compared to adjacent pine forests, and oxidase activity increased significantly with plantation age, reaching a fivefold higher level in the oldest plantation. Soil acidification, decreased soil organic carbon, and shifts in microbial composition (decline in bacteria and actinomycetes, increase in fungi) were the main drivers of these changes. The study indicates that tea planting intensifies microbial limitations on carbon and phosphorus and shifts microbial metabolism toward oxidative pathways, which may destabilize soil carbon pools and reduce long-term fertility. These findings highlight the importance of balanced nutrient management in tea plantation practices. However, the study is limited by the short duration of field sampling. Future research should focus on long-term monitoring to better understand the sustained impacts of tea cultivation on soil microbial functions and explore the role of different management practices in mitigating these effects.

The coordinated variation between plant size and functional traits is a critical link connecting individual ecological strategies and community assembly. However, unlike angiosperms, the drivers of trait–size coordination in coexisting fern species remain unclear. This study sampled seven coexisting fern species in a subtropical secondary forest, measuring biomass (an indicator of plant size) and functional traits related to leaf and root morphology and elemental composition. The coordinated relationship between plant individual size and functional traits was investigated using regression and principal component analysis, while the relative contributions of phylogeny, species identity, and individual biomass to trait variation were quantified via Bayesian phylogenetic generalized linear mixed models. Results indicated that there is a clear trait–size coordination relationship. Specifically, significant linear or nonlinear relationships were identified between plant size and multiple functional traits (e.g., elemental concentrations, specific leaf area, and specific root length), indicating a transition from “fast-acquisitive” to “conservative” strategies. However, variance partitioning indicated that phylogeny and species identity together explained the majority of variation in leaf and root traits (71.4% on average), whereas the independent contribution of individual biomass was minimal (7.1% on average). The results suggest that although significant trait–size coordination exists in understory fern communities, this coordination is statistically dominated by evolutionary history (phylogeny and species identity), though the ecological significance of plant size remains evident in significant trait–size coordination patterns. Overall, the coordinated variation between plant size and functional traits is pivotal in forging resource-allocation strategies and fostering fern species coexistence, highlighting that evolutionary background must be foregrounded when disentangling the mechanisms of functional community assembly.

Phosphorus (P) availability critically limits plant growth in ecosystems. Plants adapt by regulating internal P fractions, yet how these fractions underpin ecological strategies in wild plants remains unclear. We investigated the allocation of P fractions in Yushania shuichengensis along a natural soil total P (TP) gradient (Low-P: 0.66, Moderate-P: 1.60, High-P: 2.73 g kg⁻¹) in the Yunnan-Guizhou Plateau. In leaves, concentrations of metabolic P (P_M) and lipid P (P_L) showed a unimodal response, peaking at the Moderate-P site (e.g., P_M increased by approximately 45% compared to the Low-P site), whereas the High-P site favored the storage of inorganic P (P_i) and residual P (P_R). In roots, P_i concentration increased linearly with soil TP, indicating a tight coupling with geochemical supply. Phosphorus resorption efficiency (PRE) decreased with increasing green leaf TP and P_M concentration but was unrelated to the relative allocation of P fractions. Net photosynthetic rate was governed by the absolute concentrations of P fractions rather than their reallocation. Conversely, root morphological traits were positively correlated with nucleic acid P allocation (rP_N), underscoring its role in promoting root elongation. Our findings reveal that Y. shuichengensis relies on regulating the concentrations of key P fractions in a context-dependent manner, rather than reallocating internal P, to adapt to soil P heterogeneity, with significant implications for its distribution and nutrient management.