Soil phosphorus drives plant trait variations in a mature subtropical forest

Differences and driving factors of leaf functional traits between old tree and mature tree of Pinus tabulaeformis in the Loess Plateau

BACKGROUND

Study the leaf functional traits is highly important for understanding the survival strategies and climate adaptability of old trees. In this study, the old (over 100 years old) and mature trees (about 50 years old) of Pinus tabulaeformis in the Loess Plateau were studied, and the variation of 18 leaf functional traits (6 economic, 4 anatomical, 2 photosynthetic and 6 physiological traits) was analyzed to understand the differences of survival strategies between old and mature trees. Combined with transcriptome and simple sequence repeats (SSR) techniques, the effects of soil property factors and genetic factors on leaf functional traits and the potential molecular mechanisms of traits differences were studied.

RESULTS

Compared with mature trees, old trees presented greater economic traits (except leaf phosphorus content), anatomical traits (except the stomatal density), and physiological traits (except superoxide dismutase activity) and lower photosynthetic traits, and their survival strategies were more conservative. The difference was mainly driven by soil property and genetic factors (common explanation rate was 67.89%), and the independent effect of genetic factors (10.09%) was slightly higher than that of soil property factors (2.88%). In addition, by constructing weighted gene co-expression networks analysis WGCNA), this research identified 24 candidate hub genes that regulate leaf functional traits, most of which are related to plant growth and development and the stress response, and can be used for further regulatory mechanism analysis.

CONCLUSIONS

In conclusion, this study is helpful to understand the ecological adaptability of P. tabuliformis under the background of climate change in the Loess Plateau, and provides a theoretical basis related to leaf functional traits and molecular regulation for the protection of old trees.

Treatment effects of nitrogen and phosphorus addition on foliar traits in six northern hardwood tree species

Foliar traits can reflect fitness responses to environmental changes, such as changes in nutrient availability. Species may respond differently to these changes due to differences in traits and their plasticity. Traits and community composition together can influence forest nutrient cycling. We compared five traits-foliar N, foliar P, specific leaf area (SLA), leaf dry matter content (LDMC), and leaf carbon isotope ratio (δ13C)-in six northern hardwood tree species (Acer rubrum, Acer saccharum, Betula alleghaniensis, Betula papyrifera, Fagus grandifolia, and Prunus pensylvanica) in a nitrogen (N) and phosphorus (P) fertilization study across 10 mid- and late-successional forest stands in New Hampshire, USA. We also analyzed the response of tree growth to N and P addition. Nutrient addition shifted trait values towards the "acquisitive" side of the spectrum for all traits except δ13C, reflecting a tradeoff between water-use efficiency and nutrient-use efficiency. Treatment responses in relative basal area increment revealed that the Betula species were N-limited, but traits of all species responded to either or both N and P addition in ways that suggest N and P co-limitation. Two species displayed lower foliar P under N addition, and three species displayed lower foliar N under P addition, which also suggests co-limitation. These indications of co-limitation were reflected at the community level. Specific leaf area, LDMC, and δ13C differed with stand age within several species. Examining trait responses of tree species and communities to nutrient availability increases our understanding of biological mechanisms underlying the complex effects of nutrient availability on forests.

Leaf Phosphorus Fractions Are Coordinated with Leaf Functional Traits in Four Juvenile Tree Species from the Chinese Subtropics

Phosphorus (P) is essential for cellular processes, and P fractions within leaf tissues reflect distinct biochemical functions. However, the relationship among foliar P allocation, leaf functional traits, and soil properties in subtropical China remains poorly understood. Here, we investigated four tree species to examine the relationships among foliar P fractions (orthophosphate P, metabolic P, nucleic acid P, lipid P, and residual P), key leaf functional traits (LMA, Amass, and leaf [N], and P concentrations), and soil properties. A negative correlation between the relative allocation of metabolic P (rPM) and nucleic acid P (rPN) suggested a trade-off between metabolic activity and growth. LMA was positively correlated with rPM and residual P (rPR) but negatively associated with rPN and lipid P (rPL). Similarly, leaf [N] correlated positively with rPN and negatively with rPR. Structural equation modeling (SEM) revealed that foliar P allocation was primarily driven by leaf functional traits independent of soil properties. These findings underscore the critical role of leaf functional traits in shaping P allocation patterns and highlight the adaptive strategies of tree species to cope with P-deficient environments in subtropical ecosystems.

Leaf nutrient traits exhibit greater environmental plasticity compared to resource utilization traits along an elevational gradient

Studying key leaf functional traits is crucial for understanding plant resource utilization strategies and growth. To explore the patterns and driving factors of key leaf functional traits in forests along elevational gradients under global change, we collected survey data from 697 forests across China from 2008 to 2020. This study examined the elevational patterns of Specific Leaf Area (SLA, m²/kg), Leaf Dry Matter Content (LDMC, g/g), Leaf Nitrogen (LN, mg/g), and Leaf Phosphorus (LP, mg/g), and their responses to climate, soil nutrients, and stand factors. The results showed distinct differences in these key leaf traits at different elevational gradients. Generally, as elevation increased, SLA decreased, while LDMC significantly increased (P < 0.001), and LN first increase and then decreased (P < 0.001). The direct influence of elevation on the spatial variation of key leaf traits was greater than its indirect effects (through environmental and stand factors). The elevational patterns of leaf traits related to resource utilization strategies (SLA and LDMC) were mainly influenced by climate (temperature and precipitation) and soil nutrient factors, showing opposite trends in response to environmental changes. The patterns of leaf nutrient traits (LN and LP) along elevational gradients were primarily influenced by climatic factors, with LN exhibiting greater environmental plasticity. Compared to other stand factors, forest age predominantly influenced the spatial variation of key leaf traits, especially SLA. These findings have significant theoretical implications for revealing how plants adapt to global change.

Nutrient Addition Enhances the Temperature Sensitivity of Soil Carbon Decomposition Across Forest Ecosystems

Atmospheric nitrogen (N) and phosphorus (P) depositions have been shown to alter nutrient availability in terrestrial ecosystems and thus largely influence soil carbon cycling processes. However, the general pattern of nutrient-induced changes in the temperature response of soil carbon decomposition is unknown. Yet, understanding this pattern is crucial in terms of its effect on soil carbon-climate feedback. Here, we report that N and P additions significantly increase the temperature sensitivity of soil organic carbon decomposition (Q10) by sampling soils from 36 sites across China's forests. We found that N, P, and their co-addition (NP) significantly increased the Q10 by 11.3%, 11.5%, and 23.9%, respectively. The enhancement effect of nutrient addition on Q10 was more evident in soils from warm regions than in those from cold regions. Moreover, we found that nutrient-induced changes in substrate availability and initial substrate and nutrient availability mainly regulated nutrient addition effects. Our findings highlight that N and P deposition enhances the temperature response of soil carbon decomposition, suggesting that N and P deposition should be incorporated into Earth system models to improve the projections of soil carbon feedback to climate change.

Climate factors dominate the elevational variation in grassland plant resource utilization strategies

Specific leaf area (SLA) and leaf dry matter content (LDMC) are key leaf functional traits often used to reflect plant resource utilization strategies and predict plant responses to environmental changes. In general, grassland plants at different elevations exhibit varying survival strategies. However, it remains unclear how grassland plants adapt to changes in elevation and their driving factors. To address this issue, we utilized SLA and LDMC data of grassland plants from 223 study sites at different elevations in China, along with climate and soil data, to investigate variations in resource utilization strategies of grassland plants along different elevational gradients and their dominant influencing factors employing linear mixed-effects models, variance partitioning method, piecewise Structural Equation Modeling, etc. The results show that with increasing elevation, SLA significantly decreases, and LDMC significantly increases (P < 0.001). This indicates different resource utilization strategies of grassland plants across elevation gradients, transitioning from a "faster investment-return" at lower elevations to a "slower investment-return" at higher elevations. Across different elevation gradients, climatic factors are the main factors affecting grassland plant resource utilization strategies, with soil nutrient factors also playing a non-negligible coordinating role. Among these, mean annual precipitation and hottest month mean temperature are key climatic factors influencing SLA of grassland plants, explaining 28.94% and 23.88% of SLA variation, respectively. The key factors affecting LDMC of grassland plants are mainly hottest month mean temperature and soil phosphorus content, with relative importance of 24.24% and 20.27%, respectively. Additionally, the direct effect of elevation on grassland plant resource utilization strategies is greater than its indirect effect (through influencing climatic and soil nutrient factors). These findings emphasize the substantive impact of elevation on grassland plant resource utilization strategies and have important ecological value for grassland management and protection under global change.

Niche convergence and biogeographic history shape elevational tree community assembly in a subtropical mountain forest

Niche convergence or conservatism have been proposed as essential mechanisms underlying elevational plant community assembly in tropical mountain ecosystems. Subtropical mountains, compared to tropical mountains, are likely to be shaped by a mixing of different geographic affinities of species and remain somehow unclear. Here, we used 31 0.1-ha permanent plots distributed in subtropical forests on the eastern and western aspects of the Gaoligong Mountains, southwest China between 1498 m and 3204 m a.sl. to evaluate how niche-based and biogeographic processes shape tree community assembly along elevational gradients. We analyzed the elevational patterns of taxonomic, phylogenetic and functional diversity, as well as of individual traits, and assessed the relative importance of environmental effects on these diversity measures. We then classified tree species as being either tropical affiliated or temperate affiliated and estimated their contribution to the composition of biogeographic affinities. Species richness decreased with elevation, and species composition showed apparent turnover across the aspects and elevations. Most traits exhibited convergent patterns across the entire elevational gradient. Phylogenetic and functional diversity showed opposing patterns, with phylogenetic diversity increasing and functional diversity decreasing with elevation. Soil nutrients, especially phosphorus and nitrogen, appeared to be the main abiotic variables driving the elevational diversity patterns. Communities at lower elevations were occupied by tropical genera, while highlands contained species of tropical and temperate biogeographic affinities. Moreover, the high phylogenetic diversity at high elevations were likely due to differences in evolutionary history between temperate and tropical species. Our results highlight the importance of niche convergence of tropical species and the legacy of biogeographic history on the composition and structure of subtropical mountain forests. Furthermore, limited soil phosphorus caused traits divergence and the partitioning for different forms of phosphorus may explain the high biodiversity found in phosphorus-limited subtropical forests.

Assessing leaf physiological traits in response to flooding among dominant riparian herbs along the Three Gorges Dam in China

Dams worldwide have significantly altered the composition of riparian forests. However, research on the functional traits of dominant herbs experiencing flooding stress due to dam impoundment remains limited. Given the high plasticity of leaf traits and their susceptibility to environmental influences, this study focuses on riparian herbs along the Three Gorges Hydro-Fluctuation Zone (TGHFZ). Specifically, it investigates how six leaf physiological traits of leading herbs-carbon, nitrogen, phosphorus, and their stoichiometric ratios-adapt to periodic flooding in the TGHFZ using cluster analysis, one-way analysis of variance (ANOVA), multiple comparisons, Pearson correlation analysis, and principal component analysis (PCA). We categorized 25 dominant herb species into three plant functional types (PFTs), noting that species from the same family tended to fall into the same PFT. Notably, leaf carbon content (LCC) exhibited no significant differences across various PFTs or altitudes. Within riparian forests, different PFTs employ distinct adaptation strategies: PFT-I herbs invest in structural components to enhance stress resistance; PFT-II, mostly comprising gramineous plants, responds to prolonged flooding by rapid growth above the water; and PFT-III, encompassing nearly all Compositae and annual plants, responds to prolonged flooding with vigorous rhizome growth and seed production. Soil water content (SWC) emerges as the primary environmental factor influencing dominant herb growth in the TGHFZ. By studying the response of leaf physiological traits in dominant plants to artificial flooding, we intend to reveal the survival mechanisms of plants under adverse conditions and lay the foundation for vegetation restoration in the TGHFZ.

Drought shortens subtropical understory growing season by advancing leaf senescence

Subtropical forests, recognized for their intricate vertical canopy stratification, exhibit high resistance to extreme drought. However, the response of leaf phenology to drought in the species-rich understory remains poorly understood. In this study, we constructed a digital camera system, amassing over 360,000 images through a 70% throughfall exclusion experiment, to explore the drought response of understory leaf phenology. The results revealed a significant advancement in understory leaf senescence phenology under drought, with 11.75 and 15.76 days for the start and end of the leaf-falling event, respectively. Pre-season temperature primarily regulated leaf development phenology, whereas soil water dominated the variability in leaf senescence phenology. Under drought conditions, temperature sensitivities for the end of leaf emergence decreased from -13.72 to -11.06 days °C-1, with insignificance observed for the start of leaf emergence. Consequently, drought treatment shortened both the length of the growing season (15.69 days) and the peak growth season (9.80 days) for understory plants. Moreover, this study identified diverse responses among intraspecies and interspecies to drought, particularly during the leaf development phase. These findings underscore the pivotal role of water availability in shaping understory phenology patterns, especially in subtropical forests.

Response of tree growth to nutrient addition is size dependent in a subtropical forest

Understanding how nutrient addition affects the tree growth is critical for assessing forest ecosystem function and processes, especially in the context of increased nitrogen (N) and phosphorus (P) deposition. Subtropical forests are often considered N-rich and P-poor ecosystems, but few existing studies follow the traditional "P limitation" paradigm, possibly due to differences in nutrient requirements among trees of different size classes. We conducted a three-year fertilization experiment with four treatments (Control, N-treatment, P-treatment, and NP-treatment). We measured soil nutrient availability, leaf stoichiometry, and relative growth rate (RGR) of trees across three size classes (small, medium and large) in 64 plots. We found that N and NP-treatments increased the RGR of large trees. P-treatment increased the RGR of small trees. RGR was mainly affected by N addition, the total effect of P addition was only 10 % of that of N addition. The effect of nutrient addition on RGR was mainly regulated by leaf stoichiometry. This study reveals that nutrient limitation is size dependent, indicating that continuous unbalanced N and P deposition will inhibit the growth of small trees and increase the instability of subtropical forest stand structure, but may improve the carbon sink function of large trees.

Microplastics could alter invasive plant community performance and the dominance of Amaranthus palmeri

The increase in alien plant invasions poses a major threat to global biodiversity and ecosystem stability. However, the presence of microplastics (MPs) as an environmental stressor could impact the interactions between invasive and native species in an invasive plant community. Nevertheless, the community alterations and underlying mechanisms resulting from these interactions remain unclear. Herein, we systematically investigated the impacts of polyethylene (PE) and polypropylene (PP) on invasive plant communities invaded by Amaranthus palmeri through soil seed bank. The results illustrated that MPs markedly declined community height and biomass, and altered community structure, low-dose MPs could prominently increase community invasion resistance, but reduced community stability. The niche width and niche overlap of A. palmeri and S. viridis declined when exposed to high-dose MPs, but MPs elicited a significant rise in the niche width of S. salsa. PP had the potential to reduce the diversity of invasive plant community. Structural equation model revealed that PP addition could change soil total phosphorus content, thereby leading to a reduction of the community stability. Our study helps to fill the knowledge gap regarding the effects of MPs on invasive plant communities and provide new perspectives for invasive plant management.

Coordinated variation in root and leaf functional traits of Hippophae rhamnoides treated at different stump heights in feldspathic sandstone areas of Inner Mongolia

This study was aimed to clarify the effects of stumping on root and leaf traits as well as the tradeoffs and synergies of decaying Hippophae rhamnoides in feldspathic sandstone areas, and to select the optimal stump height that contributed to the recovery and growth of H. rhamnoides. variations and coordination between leaf traits and fine root traits of H. rhamnoides were studied at different stump heights (0, 10, 15, 20 cm, and no stumping) in feldspathic sandstone areas. All functional traits of the leaves and roots, except the leaf C content (LC) and the fine root C content (FRC), were significantly different among different stump heights. The total variation coefficient was the largest in the specific leaf area (SLA), which is therefore the most sensitive trait. Compared to non-stumping, SLA, leaf N content (LN), specific root length (SRL) and fine root N content (FRN) all improved significantly at stump height of 15 cm, but leaf tissue density (LTD), leaf dry matter content (LDMC), leaf carbon to nitrogen ratio (LC : LN), fine root tissue density (FRTD), fine root dry matter content (FRDMC) and fine root carbon to nitrogen ratio (FRC : FRN) all decreased significantly. The leaf traits of H. rhamnoides at different stump heights follow the leaf economic spectrum, and the fine roots show a similar trait syndrome to the leaves. SLA and LN are positively correlated with SRL and FRN and negatively with FRTD and FRC : FRN. LDMC and LC : LN are positively correlated with FRTD and FRC : FRN, and negatively correlated SRL and RN. The stumped H. rhamnoides changes to the 'rapid investment-return type' resource trade-offs strategy, and the growth rate is maximized at the stump height of 15 cm. Our findings are critical to the prevention and control of vegetation recovery and soil erosion in feldspathic sandstone areas.

Plant photosynthetic overcompensation under nocturnal warming: lack of evidence in subtropical evergreen trees

BACKGROUND AND AIMS

Increased plant photosynthesis under nocturnal warming is a negative feedback mechanism to overcompensate for night-time carbon loss to mitigate climate warming. This photosynthetic overcompensation effect has been observed in dry deciduous ecosystems but whether it exists in subtropical wet forest trees is unclear.

METHODS

Two subtropical evergreen tree species (Schima superba and Castanopsis sclerophylla) were grown in a greenhouse and exposed to ambient and elevated night-time temperature. The occurrence of the photosynthetic overcompensation effect was determined by measuring daytime and night-time leaf gas exchange and non-structural carbohydrate (NSC) concentration.

KEY RESULTS

A reduction in leaf photosynthesis for both species and an absence of persistent photosynthetic overcompensation were observed. The photosynthetic overcompensation effect was transient in S. superba due to respiratory acclimation and stomatal limitation. For S. superba, nocturnal warming resulted in insufficient changes in night-time respiration and NSC concentration to stimulate overcompensation and inhibited leaf stomatal conductance by increasing the leaf-to-air vapour pressure deficit.

CONCLUSIONS

The results indicate that leaf stomatal conductance is important for the photosynthetic overcompensation effect in different tree species. The photosynthetic overcompensation effect under nocturnal warming may be a transient occurrence rather than a persistent mechanism in subtropical forest ecosystems.