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Article

Altered Functional Traits in Larix principis-rupprechtii Mayr Seedlings: Responses and Divergence Across Altitudes

by
Jiayi Deng
1,2,
Jiangkai Xie
1,2,
Tairui Liu
1,2,*,
Jinping Guo
3,*,
Yunxiang Zhang
3 and
Meng Yang
1,2
1
Guangxi Key Laboratory of Forest Ecology and Conservation, College of Forestry, Guangxi University, Nanning 530004, China
2
Guangxi Colleges and Universities Key Laboratory for Forestry Science and Engineering, College of Forestry, Guangxi University, Nanning 530004, China
3
College of Forestry, Shanxi Agricultural University, Jinzhong 030801, China
*
Authors to whom correspondence should be addressed.
Forests 2025, 16(11), 1665; https://doi.org/10.3390/f16111665
Submission received: 16 September 2025 / Revised: 24 October 2025 / Accepted: 29 October 2025 / Published: 31 October 2025
(This article belongs to the Special Issue Drought Tolerance in ​Trees: Growth and Physiology)
Browse Figures
Versions Notes

Abstract

To elucidate the adaptive strategies of leaf functional traits of Larix principis-rupprechtii in the context of climate change, this study chose 2 and 3 year-old seedlings of Larix principis-rupprechtii as the focal research objects. The experiment entailed transplanting seedlings obtained from different sources into high and low altitudes: 1600 m, 1900 m, 2100 m, and 2400 m, respectively. With changes in transplant elevation, seedlings showed variable responses in photosynthesis, water-use efficiency, and leaf morphology, depending on the altitude. High-altitude seedlings transplanted to low altitudes increased SLA and branch extension, enhancing photosynthesis and C-N metabolism. Conversely, low-altitude seedlings transplanted to high altitudes improved cold resistance primarily via leaf thickening, adjusting the chlorophyll a/b ratio, and enhancing the redistribution of soluble proteins. For high-altitude sources, water-use efficiency and transpiration rate were strongly linked to leaf nitrogen and the carbon-to-nitrogen ratio, respectively, indicating the optimisation of photosynthetic and water-use efficiency through modulation of chlorophyll-a content and branch extension. Low-altitude seedlings chiefly adjusted the chla/b ratio, leaf morphological traits, and soluble protein to cope with altitudinal change. In summary, variation in leaf functional traits among seedlings of Larix principis-rupprechtii across elevational gradients did not reflect isolated changes in individual traits but rather arose from integrated adjustments of photosynthetic capacity, resource allocation, and metabolic coupling, thereby optimising the balance between light capture, water usage, and stress tolerance. These results, therefore, offer insights into adaptive strategies under climate change.

1. Introduction

According to the IPCC Sixth Assessment Report, the global climate pattern underwent profound changes over the past 50 years [1,2], not only reshaping the global climate regime but also exerting cascading impacts on terrestrial ecosystems [3,4]. As altitudinal gradients simulate large-scale climate variation within short distances, they are ideal for studying plant adaptation [5,6]. It has been confirmed that for every 1000 m increase in elevation, the air temperature decreases by approximately 5.5 °C, while ultraviolet radiation and the proportion of snowfall increase significantly, leading to systematic changes such as a reduction in soil nutrient availability [7]. This environmental gradient can roughly simulate the climatic heterogeneity spanning thousands of kilometres in latitude within a horizontal distance of less than 10 km.
Larix principis-rupprechtii is a dominant coniferous species in northern China, playing a crucial ecological role in soil conservation, carbon sequestration, and watershed stability [8,9]. Its “deciduous–rapid-growth” strategy is highly optimised: by shedding needles in winter, it effectively avoids extreme low-temperature stress (≤−30 °C) [10,11] and accumulates biomass rapidly within a short growing season, thereby enhancing its water conservation and carbon sink potential [12]. However, global warming has increasingly disrupted this established adaptive balance. Species distribution models (SDMs) predicted that by 2070, low-elevation suitable habitats (<1500 m) would shrink by 58% ± 7%, while high-elevation potential habitats (>2500 m) could only compensate by 12–18%, due to topographic constraints [13,14]. Consequently, understanding the changes and mechanisms of phenotypic plasticity regulation and physiological trait divergence in Larix principis-rupprechtii is essential.
Reciprocal transplant experiments have been recognised as a key approach to investigating physiological adaptation in Larix principis-rupprechtii [15,16]. Previous studies suggested that seedlings are significantly affected by the “ecological memory effect” of their native environment—a lasting influence of past conditions on current physiological or community responses, mediated by structural, physiological, or epigenetic mechanisms [17,18]. For instance, in the Pangquangou Reserve, low-elevation seedlings (1600–1800 m) transplanted to high elevations (2500–2800 m) showed a 62.8% reduction in SOD activity, a 21.3% decrease in crown expansion rate, and an approximately 28% increase in vessel diameter (p < 0.01), which markedly increased the risk of freeze–thaw embolism [19,20]. Therefore, an in-depth analysis of the photosynthetic and physiological adaptation mechanisms of Larix principis-rupprechtii across elevational gradients was deemed not only a scientific necessity for elucidating its climate-response patterns but also a practical prerequisite for high-quality forest cultivation and carbon-sequestration strategies [14].
Under altitudinal gradient changes, plants generally develop two adaptation strategies. Phenotypic plasticity allows the adjustment of leaf morphology and physiological functions to cope with changing environments. For high-elevation populations of Larix principis-rupprechtii, the leaf thickness increased by 20–40% with increasing elevation, the antioxidant enzyme activity intensified by 3–5 times, and the reductions in the leaf area coupled with thicker mesophyll and elevated enzymatic activity reduced the transpiration rate while improving the leaf temperature and photosynthetic capacity [21]. Physiological trait divergence represents a stable trend in physiological processes among populations at different elevations due to long-term adaptation to distinct climates. Dendrochronological studies have found that the relationship between radial growth and climate factors changed markedly with elevation gradients in trees of Larix principis-rupprechtii on the south-facing slopes of Luyashan [22]. On the global scale, Poorter et al. [23] found through meta-analysis that tree species at different elevations exhibited substantial differentiation in specific leaf area, leaf nitrogen content, and photosynthetic rate; Wright et al. [24] pointed out that coniferous species in high-elevation regions tend to increase leaf thickness and adjust nutrient allocation to enhance stress tolerance and the photosynthetic rate. Therefore, plants may rely on phenotypic plasticity and physiological divergence to cope with elevational changes, forming highly differentiated patterns of morphological integration and resource allocation under varying environmental pressures, thereby achieving sustained adaptation to complex mountainous environments.
Based on the above research, we asked the following questions: (1) When Larix principis-rupprechtii responds to altitudinal changes, is there a threshold in morphological plasticity regulation beyond which genetic adaptation becomes the primary driver? (2) Do seedlings from different native elevations exhibit distinct morphological and physiological responses after transplantation, indicating possible local adaptation and ecological memory? (3) Can Larix principis-rupprechtii seedlings transplanted along an altitudinal gradient maintain ecological function and stable growth via plastic morphological and physiological adjustments?

2. Materials and Methods

2.1. Study Area

The study was conducted in the Guandi Mountain National Nature Reserve, located in the midsection of the Lvliang Mountains, Shanxi Province (37°45′–37°55′ N, 111°22′–111°33′ E), situated in the eastern transitional zone of the Loess Plateau (Figure 1). Meteorological data are based on the numerical values from the references of Xiao Yang et al. [25]. The area is characterised by a warm temperate continental monsoon montane climate, with a mean annual temperature of 4.3 °C and pronounced seasonal variation in monthly mean temperature. The frost-free period lasts approximately 100–125 days. The mean annual precipitation is 822.6 mm, the annual evaporation is 1268 mm, and rainfall is concentrated from July to September, indicating a marked water–heat imbalance [26]. The topographic vertical differentiation is distinct, with an elevational range spanning 2080 m (from a minimum of 750 m to the main peak, Xiaowen Mountain, at 2830 m), forming a typical montane ecological sequence. The vegetation exhibits a clear vertical zonation: lower montane coniferous forest (800–1600 m), mixed conifer–broadleaf forest (1600–1800 m), cold–temperate coniferous forest (1800–2500 m), and subalpine shrub–meadow (2500–2830 m). Correspondingly, soil types change with elevation from mountain brown soils to mountain eluviated brown soils, mountain brown forest soils, and subalpine meadow soils. Larix principis-rupprechtii was mainly distributed within the cold–temperate coniferous forest zone [27,28].

2.2. Plot Selection and Experimental Design

Plots were established in Chailugou within the Xiaowen Mountain Forest Farm. Four 10 m × 20 m plots were set along an elevational gradient (1600 m, 1900 m, 2100 m, 2400 m) and were consecutively labelled AL-1600, AL-1900, AL-2100, and AL-2400, respectively. From the areas adjacent to each elevational plot (≤200 m), 120 naturally regenerated Larix principis-rupprechtii seedlings were selected per elevation provenance, approximately 2–3 years old, 50 cm ± 10 cm in height, and in good health condition. These were then divided into 4 groups (30 seedlings per group) according to a completely randomised design. A split-plot design was used: the main plot factor was transplant elevation and the subplot factor was seedling provenance elevation, producing 16 treatment combinations (including native control treatments). Seedlings were lifted after leaf fall at the end of September 2018, with intact root systems retained, and transplantation was completed within 24 h. After planting, seedlings were watered thoroughly to settle the roots and were covered with litter for thermal insulation [29].

2.3. Sample Collection and Measurements

2.3.1. Measurement of Physiological Functional Traits

Sampling was conducted from 09:00 to 11:00 on the morning of 20 July 2020. In each plot, five healthy seedlings were randomly selected from each provenance, and sun-facing mature needle leaves were sampled for light response measurements. Measurements were made with an LI-6800 (LI-COR Inc., Lincoln, NE, USA) equipped with a fluorescence leaf chamber and red–blue light source. Photosynthetic active radiation (PAR) was set to 1200 μmol·m−2·s−1 to simulate saturating light. The leaf chamber temperature was held at 25 °C, the relative humidity at 60%, and the CO2 concentration at approximately 380 ppm. From the obtained light-response curves, the light saturation point (LSP), light compensation point (LCP), water-use efficiency (WUE), transpiration rate (Tr), maximum net photosynthetic rate (Amax), and net photosynthetic rate (Pn) were determined for Larix principis-rupprechtii following standard physiological measurement protocols [30,31,32]. The water-use efficiency (WUE) was calculated as the ratio of the photosynthetic rate (Pn) to the transpiration rate (Tr) [33]:
WUE = Pn/Tr.

2.3.2. Measurement of Photosynthetic Traits

From each plot, five healthy seedlings were randomly sampled. Part of the collected leaves were wrapped in aluminium foil, flash-frozen in liquid nitrogen, and stored at −80 °C. Frozen samples were ground in pre-cooled 80% acetone for pigment extraction; chlorophyll a content (Chla), chlorophyll b content (Chlb), total chlorophyll content (Tchlab), chlorophyll a/b ratio (Chla/b), carotenoid content (Car), and the carotenoid-to-total chlorophyll ratio (CarChl) were calculated from the absorbance at A663, A645, and A470. Another portion of fresh leaves was dark-adapted for 30 min; chlorophyll fluorescence parameters were measured with the LI-6800 fluorescence leaf chamber to record Fo and Fm, calculate Fv/Fm, and, under actinic light, record the steady-state fluorescence to compute the non-photochemical quenching coefficient (NPQ), photochemical quenching (qP), and electron transfer rate (ETR) [34].
Fv = Fm − FO

2.3.3. Measurement of Morphological Structural Traits

In August 2020, five healthy and disease-free mature sun leaves were selected from each of the 4 transplanting plots, avoiding the main leaf vein area, for the determination of the plant morphological structure in the plots. The fresh leaves of the seedlings were measured using a vernier calliper to obtain the length of the new branches (BL) and the base diameter of the new branches (BD). During the measurement, it was necessary to ensure that the vernier calliper did not get stuck on the veins, and several needles were collected and brought back to the laboratory to measure the leaf length (LL), leaf width (LW), and leaf area (LA), thereby calculating the leaf length–width ratio (LWR). The needles were placed on the scanner using the scanning method, and the average projected area of the needles (PA) was calculated using ImageJ 1.53e software (National Institutes of Health, Bethesda, MD, USA). The needles were then oven-dried in a 65 °C for 48 h, until a constant weight was achieved, and the dry weight was weighed using an electronic balance to calculate the specific leaf area (SLA) [35].
LWR = LL/LW
SLA (mm2/mg) = LA (mm2)/DW (mg)

2.3.4. Measurement of Nutrient Utilisation Capacity

In each plot, five healthy seedlings were randomly selected, and the collected leaves were oven-dried at 68 °C to a constant weight (48 h). Soluble sugars (SS) were quantified by the anthrone–sulfuric acid method; starch was obtained after perchloric acid hydrolysis and quantified colorimetrically, and soluble protein (SP) was determined accordingly. The non-structural carbohydrate (NSC) content was calculated. The total carbon and total nitrogen of the leaf material were determined by elemental analysis (Vario EL III, Elementar Analysensysteme GmbH, Langenselbold, Germany) to obtain the carbon–nitrogen ratio (CNR).
NSC (%) = SS (%) + SP(%)

2.4. Data Analysis

Prior to applying the data for analysis and testing, we assessed the normality and consistency of the variance. SPSS 27.0 (SPSS Inc., Chicago, IL, USA) software was used for the multivariate analysis of variance (ANOVA) to determine whether the reciprocal transplanting of plants at different altitude gradients had significant effects. The Mantel test method was adopted to study the correlation analysis among functional traits. To understand the degree of the explanatory power of Larix principis-rupprechtii transplanting for physiological functional traits under different altitude gradients, a redundant analysis (RDA) of each functional trait was performed. These analyses and visualisations were achieved using R 4.4.3 (R Development Core Group).

3. Results

3.1. Altitudinal Adaptation of Leaf Physiological Traits in Larix principis-rupprechtii Seedlings from Different Provenances

3.1.1. Effects of Provenance Elevation and Transplant Elevation on Physiological Traits in Seedlings of Larix principis-rupprechtii

Transplantation of Larix principis-rupprechtii seedlings from their provenance elevations to different transplant elevations had significant effects on their physiological functional traits (Figure 2). The study showed that seedlings originating from high elevations and those from low elevations differed significantly in physiological characteristics, and the trends of their physiological indices varied with the transplant elevation. For high-elevation provenances, most photosynthetic and water-use indices exhibited a hump-shaped response, as the transplant elevation decreased, with LSP, Amax, and WUE peaking at intermediate elevations, while Pn showed an overall increase, as the elevation decreased. By contrast, for low-elevation provenances LSP, Amax, LCP, WUE, and Tr generally showed either an increasing-then-decreasing pattern or an overall increase with increasing elevation; LCP was highest at intermediate elevation and lowest at high elevation, and WUE reached its maximum at high elevation.

3.1.2. The Influence of Seed Source Altitude and Transplantation Altitude on Chlorophyll Content and Fluorescence of Larix principis-rupprechtii

As shown in Figure 3, for high-elevation provenances, the Car, Chl a/b, Car/Chl, and fluorescence efficiency generally exhibited a hump-shaped response as the transplant elevation decreased, with Chla, total chlorophyll (Tchlab), and qP relatively high at intermediate elevations, whereas Chlb was significantly higher at 2400 m. For low-elevation provenances, pigment contents, together with ETR and qP, peaked at mid-high elevations and then declined; some indices showed an overall hump-shaped or increasing-then-decreasing trend with increasing elevation (Figure 3).

3.1.3. The Influence of Seed Source Altitude and Transplanting Altitude on Leaf Morphological Traits of Larix principis-rupprechtii

According to the results shown in Figure 4, the morphological and structural traits of Larix principis-rupprechtii seedlings exhibited significant elevational adaptive differences (Figure 4). For high-elevation provenances, LL, LW, LWR, BL, and other morphological traits decreased linearly, as the transplant elevation decreased, with peak values concentrated at high elevations; a few indices, such as BD, were instead highest at low elevation. For low-elevation provenances, growth traits (PA, LL, LW, BL, Slender, etc.) were optimal at mid-high elevations, while SLA and LWR showed relatively high values at low transplant elevations, overall following a hump-shaped pattern.

3.1.4. The Influence of Seed Source Altitude and Transplanting Altitude on the Nutrient Utilisation Ability of Larix principis-rupprechtii

Non-structural carbohydrates and nutrient traits of Larix principis-rupprechtii seedlings exhibited significant altitudinal responses (Figure 5). For high-elevation provenances, SP, C, CNR, and other nutrient indices mostly peaked at mid-high elevations, SS was highest at the provenance elevation, and overall, these traits tended to show a hump-shaped response or remain relatively stable across transplant elevations. In contrast, for low-elevation provenances SP, SS, NSC, C, and CNR generally increased or followed a hump-shaped pattern with increasing transplant elevation; N content was significantly lower at intermediate elevations. High-and low-elevation provenances therefore exhibited clear provenance-dependent differences in nutrient responses.

3.2. Correlation Analysis of Leaf Functional Traits of Larix principis-rupprechtii Across Elevational Gradients

By conducting a Mantel test on the Larix principis-rupprechtii at different altitude gradients, a systematic analysis was conducted on the correlations among the trait distance matrices (Figure 6). The results showed that high-elevation and low-elevation seedlings exhibited a highly consistent correlation structure. LWR was significantly positively correlated with LL, BL, and Slender; Slender was also significantly positively correlated with LL, and BL. CNR was highly significantly positively correlated with the C content, and the CNR and N content were highly significantly positively correlated with physiological functional traits (p < 0.01). SLA, C content, N content, and CNR were highly significantly positively correlated with photosynthetic pigment contents (p < 0.01). LL, SLA, and CNR were also highly significantly positively correlated with physiological functional traits, and several morphological indices were significantly positively correlated with pigment or functional traits (p < 0.05). SP was highly significantly negatively correlated with BL (significant in both high-and low-elevation seedlings). In low-elevation seedlings, NSC was significantly positively correlated only with the chlorophyll fluorescence parameters (p < 0.05).

3.3. Pathway Differences Among Functional Traits of Larix principis-rupprechtii at Different Elevational Gradients

Redundancy analysis was employed to determine relationships among leaf functional traits and to screen predictors that influence physiological functional traits. Prior to RDA, variance inflation factors (VIFs) were used to select the original predictor variables and exclude multicollinearity; all original predictors had VIFs < 10 (Table 1). The results indicated that leaf physiological traits could well explain the variation in photosynthetic characteristics and their components. The original predictor variables explained approximately 60% of physiological trait variation across the elevational gradients. For high-elevation seedlings, five factors, Chla, Tchlab, PA, LW, and SLA, had significant explanatory power. Among these, PA had the strongest explanatory power, accounting for 12.210%, which was the most important original predictor. Next were SLA, Chla, and LW, each explaining approximately 7.270–7.830% of total variance. Finally, Tchlab accounted for 3.510%. For low-elevation seedlings, LWR, LL, and SP exerted significant influence. SP had the strongest explanatory power, accounting for 35.420%, and was the most important original predictor; next were LWR and SLA, accounting for 7.950% and 8.670%, respectively. Overall, the measured leaf functional traits and physiological functional traits explained 61.240% and 62.400% of the total variation in trait contents for high-elevation and low-elevation seedlings, respectively (Figure 7).

4. Discussion

4.1. Responses of Leaf Functional Traits in Seedlings of Larix principis-rupprechtii to Transplant Elevation

The results support the ecological memory hypothesis, where seedlings retain functional imprints from their native environment [36]. When high-elevation seedlings were moved downslope, Tr and Amax both followed a rise-then-fall pattern, with maxima at 2100 m. This trend matched observed altitudinal responses of leaf photosynthetic traits in Himalayan plants and suggested that mid-elevations provide an optimal balance of light, temperature, and water. At lower transplant elevations, initial warming induced stomatal opening to increase CO2 uptake, but excessive transpiration eventually caused water deficits, leading to concurrent declines in Tr and Amax—consistent with the widely observed “photosynthesis transpiration co-regulation” mechanism [37,38,39]. The dynamic change in SLA reflects structural memory: the warmer environment at medium altitudes induces leaf thinning to reduce photosynthetic construction costs, while low-temperature stress at high altitudes promotes leaf thickening. The subsequent recovery in plant adaptability reflects the photosynthetic structure adjustment strategy of the native high-altitude population, aligning with the global altitudinal adaptation pattern of leaf thickness in alpine plants [40]. Regarding chlorophyll composition, Chla and Car content initially increased and then decreased with decreasing altitude, while Chlb showed the opposite response. This optimises light energy transfer by increasing the Chla/b ratio and reduces damage from high UV radiation, consistent with the cross-species consistency of photoprotection strategies in alpine plants [27,29,41]. BD returned to its peak at the native altitude but decreased significantly in the non-original environment, further verifying the constraints of long-term ecological memory, such as light energy utilisation, water economy, and structural construction on ex situ adaptation [18].
Low-altitude seedlings show response patterns similar to high-altitude ones, but this pattern reflects the low-altitude seedlings’ legacy of optimising growth rate under warm moist climates, which conflicts with the light- and water-economy strategies required at high altitude. Initially, when transplanted to higher altitudes, low-altitude seedlings compensated for CO2 diffusion limitations by increasing stomatal conductance to maintain photosynthetic efficiency. However, persistent low temperatures and high radiation led to stomatal closure, ultimately reducing the photosynthetic and transpiration rates. This is consistent with the physiological response characteristics of Himalayan poplars along altitudinal gradients [29,42]. The SLA is generally on a downward trend, reflecting the strategic shift from “resource acquisition” to “stress defence”, which is consistent with the conservative adjustment trend of warm-adapted species in the research on the thermal plasticity of alpine plants. Changes in the pigment content reflect the trade-off between light harvesting capacity and antioxidant systems; under prolonged stress, pigment synthesis is restricted, consistent with metabolic regulation logic of alpine plants in extreme environments. At the same time, the altitudinal response of BD highlights the low-altitude provenance’s growth-nutrient allocation memory: high-altitude cold stress markedly suppresses cambial activity, aligning with the adaptation strategy observed in high-latitude conifers of “first suppress growth to maintain metabolic stability, then gradually develop adaptive differentiation” [43].
In conclusion, this study answered the first research question. Larix principis-rupprechtii seedlings from different native altitudes showed a highly consistent differentiation pattern in terms of physiological functional traits, chlorophyll content and fluorescence, morphological structure, and nutrient utilisation capacity in response to their growth memory. This regular difference is highly consistent with the “memory effect differentiation hypothesis”. It indicates that the long-term memory of its native environment has a profound impact on the adaptation to a different environment.

4.2. Correlations Among Leaf Functional Traits of Larix principis-rupprechtii Seedlings Across Elevational Gradients

The Mantel test showed that seedlings from different provenances exhibited significant and systematic differences in the structure of trait correlations along the transplant altitude gradient, and these differences consistently point to “carbon–nitrogen coupling plus morphological adjustment” as the principal rapid-response pathway. Morphologically, LWR was strongly positively correlated with LL, BL, and Slender, and Slender was strongly correlated with LL and BL, indicating a coordinated strategy of reallocating biomass to leaves and branches, elongating shoots, and expanding the crown to increase light interception. In terms of resource allocation, the significant negative correlation between SP and BL suggests that soluble protein is preferentially invested in photosynthetic and growth-related structures to support rapid morphological construction. Physiologically, N and CNR showed strong positive correlations with multiple physiological traits and photosynthetic pigments, and SLA, C, N, and CNR were likewise closely related to the pigment content; this implies the synchronised investment of structural carbon and functional nitrogen that enhances light reactions and assimilation efficiency. This pattern agrees with the global leaf economics spectrum linking high SLA to high photosynthetic potential [24] and with mechanisms by which leaf N positively regulates photosynthesis. Moreover, the observed differences in trait networks indicate that adaptation to altitude does not follow a single pathway but rather a “training–adaptation” sequence: local adaptation and provenance-specific histories substantially affect the strength and centrality of trait linkages, thereby determining the scope of plastic adjustment [44,45]. The evidence supports the phenotypic-plasticity hypothesis: for plants under environmental change, rapid morphological expansion combined with carbon–nitrogen coupling serves as the primary adaptive response, whereas, when stress exceeds plastic limits, the trait network shifts toward genetic control [46]. In short, successful establishment of Larix principis-rupprechtii in a new site depends on the coordinated coupling of morphology and nitrogen-driven upgrades of the photosynthetic apparatus.
When low-altitude seedlings were transplanted to high-altitude environments, LWR was positively correlated with LL, BL, and Slender, as well as Slender with LL and BL; CNR was positively correlated with C content; and SP was negatively correlated with BL. In addition, LL, SLA, CNR, and C content were positively correlated with each other and with physiological functional traits (p < 0.01), and N content was positively correlated with CNR and photosynthetic pigment content (p < 0.05), while NSC content was only positively correlated with chlorophyll fluorescence parameters (p < 0.05). These results indicated that low-altitude seedlings tended to enhance their resistance to low-temperature stress by increasing the leaf thickness and the structural carbon allocation in the high-altitude environment, then promoting the recovery of morphology and functional traits on the basis of stable physiological traits [47]. Regardless of the direction of transplantation, the leaf N content, CNR, and C content were significantly correlated with the functional trait matrix, and the CNR and C content have a long-term positive correlation, indicating the stability of carbon–nitrogen metabolic coupling in the new environment. Moreover, according to the “phenotypic-plasticity hypothesis”, the plasticity adjustment of low-altitude source seedlings under high-altitude stress conditions showed a preliminary rapid adaptive ability; if the environmental stress exceeds the threshold of plasticity regulation, genetic adaptation will become the dominant mechanism [29]. This viewpoint was in line with previous studies on the role of phenotypic plasticity in the context of climate change and the adaptation of plants along elevation gradients [48], aimed to illustrate that the adaptability of Larix principis-rupprechtii is predictable. That is, the initial stage dominated by phenotypic plasticity may be succeeded by genetic adaptation, thereby influencing the future distribution and community structure [49]. Moreover, this study also answered the second research question. Different source seedlings achieved initial adaptation dominated by plasticity regulation through the rapid reconfiguration of carbon–nitrogen metabolism and functional traits at different elevation gradients and transformed to a strategy of genetic adaptation when environmental changes exceeded the threshold.

4.3. Pathway Differences in Which Leaf Traits Affect Physiological Traits Across Elevational Gradients

Under high-elevation conditions, where irradiance is strong, temperatures are low, and diurnal temperature range is large, plants often exhibit a pronounced “training–adaptive differentiation strategy”. This strategy refers to the process by which plants, after long-term exposure to specific environmental conditions, form stable functional trait combinations along both physiological and morphological pathways through the combined action of phenotypic plasticity and natural selection, thereby enhancing adaptation to such environments [50]. In the present study, high-altitude seedlings exhibited a “structure–function coordination” adaptive pathway centred on the optimisation of photosynthesis. The main explanatory variables included Chla, Tchlab, PA, LW, and SLA, among which PA had the highest explanatory power, indicating that high-altitude seedlings prioritise increasing photosynthetic rates to offset the reduction in enzymatic reaction rates caused by low temperatures. This is consistent with the findings of Körner in studies of alpine plants, namely that alpine species tend to maintain high photosynthetic capacity to cope with the short growing season. In addition, morphological traits such as low SLA and greater LW contribute to enhanced tolerance to cold, intense radiation, and wind exposure [51].
In contrast to the adaptive strategy of high-altitude seedlings, low-altitude seedlings displayed a “rapid response” pathway dominated by physiological plasticity. The primary explanatory variables were SP, LWR, and SLA, of which SP accounted for approximately 35.420% of the explained variance, indicating that in warm, humid, and highly variable environments, plants rely more heavily on stomatal and protein regulation to rapidly respond to fluctuations in light and water availability. This finding is in agreement with Hepworth et al. and Lawson and Vialet-Chabrand [52,53], who reported that, in resource-rich environments, stomatal dynamics play a critical role in optimising water-use efficiency and photosynthetic responsiveness. Combined with high SLA traits, this low-altitude seedling strategy aligns with the “fast investment–fast return” model of the leaf economics spectrum [24,54,55].
Therefore, our study answered the third research question. Although the overall explanatory rates of high-altitude seedlings and low-altitude seedlings are similar, there are significant differences in the leading factors and the mechanism of related trait effects, respectively, manifesting as two adaptation paths dominated by photosynthetic optimisation and nutrient metabolism. This difference not only reflects the historical imprint of the original environment’s long-term training but also reveals the differences in resource allocation priorities formed by plants under different local environmental pressures.

5. Conclusions

This study revealed that 2–3 years old seedlings of Larix principis-rupprechtii transplanted across different elevational gradients employ diversified leaf adaptive strategies by adjusting photosynthetic pigment contents, leaf morphology, and nutrient allocation. High-elevation seedlings rely on increases in Chla content and SLA to lower the LCP and enhance Amax, thereby optimising the carbon–nitrogen metabolic balance to tolerate harsh environments. By contrast, low-elevation seedlings regulate the Chla/b ratio and SP content to enhance photosynthetic efficiency and WUE, thus maintaining physiological homeostasis under strong irradiance and fluctuating water availability. Simultaneously, the findings answered the three research questions, with evidence for both phenotypic plasticity and memory effects. These findings not only provide important theoretical support for predicting distribution patterns and community succession of montane forest species under climate change but also offer scientific guidance for near-provenance introduction, cultivation management, and the maintenance of ecosystem function [36].

Author Contributions

Conceptualisation, Formal analysis, Investigation, Data curation, Writing—original draft, Writing—review and editing, J.D.; Investigation, Data curation, Visualisation, J.X.; Conceptualisation, Resources, Supervision, Project administration, Funding acquisition, T.L.; Resources, Supervision, Project administration, Funding acquisition, J.G.; Resources, Y.Z.; Data curation, Writing—review and editing, M.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Guangxi Natural Science Foundation (2025GXNSFBA069250) and the National Key Research and Development Program of China (2024YFD2201002-03).

Data Availability Statement

Data are contained within the article.

Acknowledgments

We gratefully acknowledge the support of the Xiaowenshan Forest Farm for fieldwork. We also thank our colleagues for their assistance with field measurements and laboratory work. We are extremely grateful to Diego Rodriguez Hernandez for revising and polishing the article.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
LSPLight Saturation Point
LCPLight Compensation Point
WUEWater-Use Efficiency
TrTranspiration Rate
PnNet Photosynthetic Rate
AmaxMaximum Net Photosynthetic Rate
ChlaChlorophyll a
ChlbChlorophyll b
TchlabTotal Chlorophyll ab
Chla/bChlorophyll ab ratio
CarCarotenoids
CarChlThe Ratio of Carotenoids to Chlorophyll
NPQNon-Photochemical Quenching Coefficient
ETRElectron Transfer Rate
qPPhotochemical Quenching
BLNew Branch Length
BDNew Branch Diameter
LLLeaf Length
LWLeaf Width
LWRLeaf Length-to-width Ratio
PAProject Area
SLASpecific Leaf Area
SSSoluble Sugar
SPSoluble Protein
NSCNon-Structural Carbohydrates
CNRCarbon–Nitrogen Ratio

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Figure 1. Geographic location of the study area.
Figure 1. Geographic location of the study area.
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Figure 2. Differences in physiological functional traits of Larix principis-rupprechtii seedlings under different elevation gradients. (a) The changes in photosynthetic characteristics of plants when they are transplanted between different altitude gradients; (b) The changes in physiological metabolism of plants when they are transplanted among different altitude gradients. See abbreviation table for all abbreviations. LSP represents the Light Saturation Point, LCP represents the Light Compensation Point, Amax represents the Maximum Net Photosynthetic Rate, WUE represents the Water-Use Efficiency, Tr represents the Transpiration Rate, Pn represents the Net Photosynthetic Rate. Note: LSP/(μmol·m−2·s−1); LCP/(μmol·m−2·s−1); Amax/(μmol·m−2·s−1); WUE/(mmol/mol); Tr/(mmol·m−2·s−1); Pn/(μmol CO2·m−2·s−1).
Figure 2. Differences in physiological functional traits of Larix principis-rupprechtii seedlings under different elevation gradients. (a) The changes in photosynthetic characteristics of plants when they are transplanted between different altitude gradients; (b) The changes in physiological metabolism of plants when they are transplanted among different altitude gradients. See abbreviation table for all abbreviations. LSP represents the Light Saturation Point, LCP represents the Light Compensation Point, Amax represents the Maximum Net Photosynthetic Rate, WUE represents the Water-Use Efficiency, Tr represents the Transpiration Rate, Pn represents the Net Photosynthetic Rate. Note: LSP/(μmol·m−2·s−1); LCP/(μmol·m−2·s−1); Amax/(μmol·m−2·s−1); WUE/(mmol/mol); Tr/(mmol·m−2·s−1); Pn/(μmol CO2·m−2·s−1).
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Figure 3. Differences in chlorophyll content and fluorescence of Larix principis-rupprechtii seedlings under different altitude gradients. (a) The changes in pigments of plants when they are transplanted between different altitude gradients; (b) The changes in the ratio of pigments among plants when they are transplanted between different altitude gradients. See abbreviation table for all abbreviations. Chla represents the Chlorophyll a, Chlb represents the Chlorophyll b, Tchlab represents the Total Chlorophyll ab, Car represents the Carotenoids, Chla/b represents Chlorophyll ab ratio, CarChl represnets the Ratio of Carotenoids to Chlorophyll, qP represents the Photochemical Quenching, ETR represents the Electron Transfer Rate. Note: Chla/(mg/g); Chlb/(mg/g); Tchllab/(mg/g); Car/(mg/g).
Figure 3. Differences in chlorophyll content and fluorescence of Larix principis-rupprechtii seedlings under different altitude gradients. (a) The changes in pigments of plants when they are transplanted between different altitude gradients; (b) The changes in the ratio of pigments among plants when they are transplanted between different altitude gradients. See abbreviation table for all abbreviations. Chla represents the Chlorophyll a, Chlb represents the Chlorophyll b, Tchlab represents the Total Chlorophyll ab, Car represents the Carotenoids, Chla/b represents Chlorophyll ab ratio, CarChl represnets the Ratio of Carotenoids to Chlorophyll, qP represents the Photochemical Quenching, ETR represents the Electron Transfer Rate. Note: Chla/(mg/g); Chlb/(mg/g); Tchllab/(mg/g); Car/(mg/g).
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Figure 4. Effects of different altitude gradients on morphological and structural traits of Larix principis-rupprechtii seedlings. (a) The changes in the leaf morphology of plants when they are transplanted between different altitude gradients; (b) The changes in the leaf characteristics of plants when they are transplanted between different altitude gradients. See abbreviation table for all abbreviations. LL represents the Leaf Length, LW represents the Leaf Width, BL represents the New Branch Length, BD represents the New Branch Diameter, PA represents Project Area, LWR represnets the Leaf Length-to-width Ratio, SLA represents the Specific Leaf Area. Note: LL/(mm); LW/(mm); BL/(mm); BD/(mm); PA/(mm2); SLA/(mm2/mg).
Figure 4. Effects of different altitude gradients on morphological and structural traits of Larix principis-rupprechtii seedlings. (a) The changes in the leaf morphology of plants when they are transplanted between different altitude gradients; (b) The changes in the leaf characteristics of plants when they are transplanted between different altitude gradients. See abbreviation table for all abbreviations. LL represents the Leaf Length, LW represents the Leaf Width, BL represents the New Branch Length, BD represents the New Branch Diameter, PA represents Project Area, LWR represnets the Leaf Length-to-width Ratio, SLA represents the Specific Leaf Area. Note: LL/(mm); LW/(mm); BL/(mm); BD/(mm); PA/(mm2); SLA/(mm2/mg).
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Figure 5. Effects of different altitudinal gradients on the nutrient utilisation capacity of Larix principis-rupprechtii seedlings. (a) The changes in the transfer of nutrients among plants at different altitude gradients; (b) The changes in the carbon-nitrogen ratio of plants when they are transplanted between different altitude gradients. See table for all abbreviations. SP represents the Soluble Protein, SS represents the Soluble Sugar, NSC represents the Non-Structural Carbohydrates, CNR represnets the Carbon–Nitrogen Ratio. Note: SP/(%); SS/(%); NSC/(%); C/(g/kg); N/(g/kg); SLA/(mm2/mg).
Figure 5. Effects of different altitudinal gradients on the nutrient utilisation capacity of Larix principis-rupprechtii seedlings. (a) The changes in the transfer of nutrients among plants at different altitude gradients; (b) The changes in the carbon-nitrogen ratio of plants when they are transplanted between different altitude gradients. See table for all abbreviations. SP represents the Soluble Protein, SS represents the Soluble Sugar, NSC represents the Non-Structural Carbohydrates, CNR represnets the Carbon–Nitrogen Ratio. Note: SP/(%); SS/(%); NSC/(%); C/(g/kg); N/(g/kg); SLA/(mm2/mg).
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Figure 6. Correlation analysis of functional traits in Larix principis-rupprechtii seedlings under different elevation gradients. (a) The correlations of various functions of plants when transplanted to high-altitude areas; (b) The correlations of various functions of plants after transplantation to lower-altitudes. See abbreviation table for all abbreviations. PA represents the Project Area, LL represents the Leaf Length, LW represents the Leaf Width, LWR represents the Leaf Length-to-width Ratio, BL represents the New Branch Length, BD represents the New Branch Diameter, SLA represents the Specific Leaf Area, SP represents the Soluble Protein, SS represents the Soluble Sugar, NSC reprresents the Non-Structural Carbohydrates, CNR represents the Carbon-Nitrogen Ratio. Asterisk represents statistical significance, in which, * p < 0.05; ** p < 0.01; *** p < 0.001.
Figure 6. Correlation analysis of functional traits in Larix principis-rupprechtii seedlings under different elevation gradients. (a) The correlations of various functions of plants when transplanted to high-altitude areas; (b) The correlations of various functions of plants after transplantation to lower-altitudes. See abbreviation table for all abbreviations. PA represents the Project Area, LL represents the Leaf Length, LW represents the Leaf Width, LWR represents the Leaf Length-to-width Ratio, BL represents the New Branch Length, BD represents the New Branch Diameter, SLA represents the Specific Leaf Area, SP represents the Soluble Protein, SS represents the Soluble Sugar, NSC reprresents the Non-Structural Carbohydrates, CNR represents the Carbon-Nitrogen Ratio. Asterisk represents statistical significance, in which, * p < 0.05; ** p < 0.01; *** p < 0.001.
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Figure 7. Redundancy analysis (RDA) for the first two RDA axes showing differences between leaf traits of high-altitude seedlings (a) and low-altitude seedlings (b). Arrows indicate trait loadings with grouping colours, where pink represents 1600 m, green represents 1900 m, yellow represents 2100 m, and blue represents 2400 m. See the abbreviation table for all abbreviations.
Figure 7. Redundancy analysis (RDA) for the first two RDA axes showing differences between leaf traits of high-altitude seedlings (a) and low-altitude seedlings (b). Arrows indicate trait loadings with grouping colours, where pink represents 1600 m, green represents 1900 m, yellow represents 2100 m, and blue represents 2400 m. See the abbreviation table for all abbreviations.
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Table 1. Variation differences of each index across different altitude gradients. See abbreviation table for all abbreviations.
Table 1. Variation differences of each index across different altitude gradients. See abbreviation table for all abbreviations.
High ElevationInterpretation Amount (%)Fp
Model48.1103.520<0.001
Chla7.3203.2400.037
Tchlab3.5103.3300.032
PA12.21010.690<0.001
LW7.2702.1900.109
SLA7.8302.8700.040
SS5.6900.9500.417
NSC4.2801.3400.262
Low ElevationInterpretation Amount (%)Fp
Model58.6504.850<0.001
Chla2.1103.7100.029
Chlb1.9403.7400.025
LL1.2002.8100.048
LW1.3602.4800.067
LWR7.9503.0700.031
SLA8.6703.3200.032
SP35.42014.820<0.001
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Deng, J.; Xie, J.; Liu, T.; Guo, J.; Zhang, Y.; Yang, M. Altered Functional Traits in Larix principis-rupprechtii Mayr Seedlings: Responses and Divergence Across Altitudes. Forests 2025, 16, 1665. https://doi.org/10.3390/f16111665

AMA Style

Deng J, Xie J, Liu T, Guo J, Zhang Y, Yang M. Altered Functional Traits in Larix principis-rupprechtii Mayr Seedlings: Responses and Divergence Across Altitudes. Forests. 2025; 16(11):1665. https://doi.org/10.3390/f16111665

Chicago/Turabian Style

Deng, Jiayi, Jiangkai Xie, Tairui Liu, Jinping Guo, Yunxiang Zhang, and Meng Yang. 2025. "Altered Functional Traits in Larix principis-rupprechtii Mayr Seedlings: Responses and Divergence Across Altitudes" Forests 16, no. 11: 1665. https://doi.org/10.3390/f16111665

APA Style

Deng, J., Xie, J., Liu, T., Guo, J., Zhang, Y., & Yang, M. (2025). Altered Functional Traits in Larix principis-rupprechtii Mayr Seedlings: Responses and Divergence Across Altitudes. Forests, 16(11), 1665. https://doi.org/10.3390/f16111665

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