Non-structural carbohydrates regulated by season and species in the subtropical monsoon broad-leaved evergreen forest of Yunnan Province, China

Divergent responses of woody plant leaf and root non-structural carbohydrates to nitrogen addition in China: Seasonal variations and ecological implications

Plant non-structural carbohydrates (NSCs), which largely comprise starch and soluble sugars, are essential energy reserves to support plant growth and physiological functions. While it is known that increasing global deposition of nitrogen (N) affects plant concentration of NSCs, quantification of seasonal responses and drivers of woody species leaf and root NSCs to N addition at larger spatial scales remains lacking. Here, we systematically analyzed data from 53 field experiments distributed across China, comprising 1202 observations, to test for effects of N addition on woody plant leaf and root NSCs across and within growing and non-growing seasons. We found (1) no overall effects of N addition on the concentrations of leaf and root NSCs, soluble sugars or starch during the growing season or the non-growing season for leaves. However, N addition decreased root NSC and starch concentrations by 13.8 % and 39.0 %, respectively, and increased soluble sugars concentration by 15.0 % during the non-growing season. (2) Shifts in leaf NSC concentration under N addition were driven by responses by soluble sugars in both seasons, while shifts in root NSC were driven by soluble sugars in the non-growing season and starch and soluble sugars in the growing season. (3) Relationships between N, carbon, and phosphorus stoichiometry with leaf and root NSCs indicated effects of N addition on woody plant NSCs allocation through impacts on plant photosynthesis, respiration, and growth. (4) Effects of N addition on leaf and root NSCs varied with plant functional types, where effects were more pronounced in roots than in leaves during the non-growing season. Overall, our results reveal divergent responses of woody plant leaf and root NSCs to N addition within non-growing season and highlight the role of ecological stoichiometry and plant functional types in woody plant allocation patterns of NSCs in response to ongoing N deposition under global change.

High-throughput Soxhlet extraction method applied for analysis of leaf lignocellulose and non-structural substances

The traditional Soxhlet extraction method is commonly employed to extract soluble components from non-soluble components in a solid matrix, for example, non-structural substances in biomass samples that can be separated from structural lignocellulosic compounds in biomass samples. Conventional laboratory procedures for such extractions typically involve a low sample throughput, with each run being performed individually, resulting in time-consuming and labour-intensive processes, making them impractical for analysing large sample sets. In research fields such as Earth Observation in Forest Ecosystems, extensive fieldwork sampling is required across large study areas, resulting in a substantial number of leaf samples, each with limited mass. In this study, an innovative adaptation of the conventional National Renewable Energy Laboratory (NREL) Soxhlet method is developed to create a high-throughput mini-Soxhlet apparatus that enables the simultaneous extraction of up to nineteen samples, each with a mass of 0.3 g per sample. With this adaptation, we measured the lignocellulose and extractive in 343 leaf samples collected from four temperate forest tree species. This modified approach enhances versatility and can be applied to all solid-liquid extractions and various types of vegetation tissues, such as tree leaves, shrubs, crops, feedstock, and other non-woody samples.•The solid-liquid extraction method has been implemented in a heating block facilitating 19 small flasks to measure multiple samples simultaneously while requiring only a small sample mass.•The apparatus set-up was constructed using an alumina heating block mounted on a standard laboratory heating plate. Boiling flask tubes were placed in the heating block and equipped with condenser caps and filters on glass rods on which the solid samples were placed.•The adjustments made the method suitable for application to diverse vegetation tissues and non-woody sample types. It holds particular appeal for research areas that necessitate a high sample number.

Alhagi sparsifolia acclimatizes to saline stress by regulating its osmotic, antioxidant, and nitrogen assimilation potential

BACKGROUND

Alhagi sparsifolia (Camelthorn) is a leguminous shrub species that dominates the Taklimakan desert's salty, hyperarid, and infertile landscapes in northwest China. Although this plant can colonize and spread in very saline soils, how it adapts to saline stress in the seedling stage remains unclear so a pot-based experiment was carried out to evaluate the effects of four different saline stress levels (0, 50, 150, and 300 mM) on the morphological and physio-biochemical responses in A. sparsifolia seedlings.

RESULTS

Our results revealed that N-fixing A. sparsifolia has a variety of physio-biochemical anti-saline stress acclimations, including osmotic adjustments, enzymatic mechanisms, and the allocation of metabolic resources. Shoot-root growth and chlorophyll pigments significantly decreased under intermediate and high saline stress. Additionally, increasing levels of saline stress significantly increased Na⁺ but decreased K⁺ concentrations in roots and leaves, resulting in a decreased K⁺/Na⁺ ratio and leaves accumulated more Na + and K + ions than roots, highlighting their ability to increase cellular osmolarity, favouring water fluxes from soil to leaves. Salt-induced higher lipid peroxidation significantly triggered antioxidant enzymes, both for mass-scavenging (catalase) and cytosolic fine-regulation (superoxide dismutase and peroxidase) of H₂O₂. Nitrate reductase and glutamine synthetase/glutamate synthase also increased at low and intermediate saline stress levels but decreased under higher stress levels. Soluble proteins and proline rose at all salt levels, whereas soluble sugars increased only at low and medium stress. The results show that when under low-to-intermediate saline stress, seedlings invest more energy in osmotic adjustments but shift their investment towards antioxidant defense mechanisms under high levels of saline stress.

CONCLUSIONS

Overall, our results suggest that A. sparsifolia seedlings tolerate low, intermediate, and high salt stress by promoting high antioxidant mechanisms, osmolytes accumulations, and the maintenance of mineral N assimilation. However, a gradual decline in growth with increasing salt levels could be attributed to the diversion of energy from growth to maintain salinity homeostasis and anti-stress oxidative mechanisms.

Seasonal Variation in Selected Biochemical Traits in the Leaves of Co-Occurring Invasive and Native Plant Species under Mediterranean Conditions

The success of invasive alien species (IAS) is often linked to differences in functional traits in relation to other, either native or non-invasive, species. Two of the most problematic IAS in the Mediterranean area belong to Hakea and Acacia genera that often invade pine plantations. Therefore, the aim of this study was to assess the seasonal variations in photosynthetic pigments, total phenolics, and non-structural carbohydrates (NSC), including total soluble sugars (SS) and starch (St), and lipid peroxidation, in terms of malondialdehyde (MDA) in the leaves of evergreen species, two IAS (Hakea sericea and Acacia melanoxylon) and one native (Pinus pinaster), throughout 2019. All parameters showed a pronounced seasonal variability while also differing across species. Generally, the lowest contents of photosynthetic pigments, phenolics and SS were noted in early spring, along with the highest St and NSC values. On the other hand, higher photosynthetic pigment and lower NSC contents were measured in early autumn and early winter. When these parameters were compared across the three species, the IAS had significantly higher content of photosynthetic pigments, mainly chlorophyll b and total chlorophyll, and lower total phenolics and MDA concentrations in their leaves than Pinus pinaster. Differences in seasonal patterns were also observed. Hakea sericea and Acacia melanoxylon had considerably higher chlorophyll, SS and NSC contents in the early autumn, while Pinus pinaster had higher St and MDA contents in early summer. Overall, the biochemical characteristics of leaves of the studied IAS can explain their success in the Mediterranean area, in terms of tolerance to stressful environmental conditions.

A starting guide to root ecology: strengthening ecological concepts and standardising root classification, sampling, processing and trait measurements

In the context of a recent massive increase in research on plant root functions and their impact on the environment, root ecologists currently face many important challenges to keep on generating cutting-edge, meaningful and integrated knowledge. Consideration of the below-ground components in plant and ecosystem studies has been consistently called for in recent decades, but methodology is disparate and sometimes inappropriate. This handbook, based on the collective effort of a large team of experts, will improve trait comparisons across studies and integration of information across databases by providing standardised methods and controlled vocabularies. It is meant to be used not only as starting point by students and scientists who desire working on below-ground ecosystems, but also by experts for consolidating and broadening their views on multiple aspects of root ecology. Beyond the classical compilation of measurement protocols, we have synthesised recommendations from the literature to provide key background knowledge useful for: (1) defining below-ground plant entities and giving keys for their meaningful dissection, classification and naming beyond the classical fine-root vs coarse-root approach; (2) considering the specificity of root research to produce sound laboratory and field data; (3) describing typical, but overlooked steps for studying roots (e.g. root handling, cleaning and storage); and (4) gathering metadata necessary for the interpretation of results and their reuse. Most importantly, all root traits have been introduced with some degree of ecological context that will be a foundation for understanding their ecological meaning, their typical use and uncertainties, and some methodological and conceptual perspectives for future research. Considering all of this, we urge readers not to solely extract protocol recommendations for trait measurements from this work, but to take a moment to read and reflect on the extensive information contained in this broader guide to root ecology, including sections I-VII and the many introductions to each section and root trait description. Finally, it is critical to understand that a major aim of this guide is to help break down barriers between the many subdisciplines of root ecology and ecophysiology, broaden researchers' views on the multiple aspects of root study and create favourable conditions for the inception of comprehensive experiments on the role of roots in plant and ecosystem functioning.

A starting guide to root ecology: strengthening ecological concepts and standardising root classification, sampling, processing and trait measurements

In the context of a recent massive increase in research on plant root functions and their impact on the environment, root ecologists currently face many important challenges to keep on generating cutting-edge, meaningful and integrated knowledge. Consideration of the below-ground components in plant and ecosystem studies has been consistently called for in recent decades, but methodology is disparate and sometimes inappropriate. This handbook, based on the collective effort of a large team of experts, will improve trait comparisons across studies and integration of information across databases by providing standardised methods and controlled vocabularies. It is meant to be used not only as starting point by students and scientists who desire working on below-ground ecosystems, but also by experts for consolidating and broadening their views on multiple aspects of root ecology. Beyond the classical compilation of measurement protocols, we have synthesised recommendations from the literature to provide key background knowledge useful for: (1) defining below-ground plant entities and giving keys for their meaningful dissection, classification and naming beyond the classical fine-root vs coarse-root approach; (2) considering the specificity of root research to produce sound laboratory and field data; (3) describing typical, but overlooked steps for studying roots (e.g. root handling, cleaning and storage); and (4) gathering metadata necessary for the interpretation of results and their reuse. Most importantly, all root traits have been introduced with some degree of ecological context that will be a foundation for understanding their ecological meaning, their typical use and uncertainties, and some methodological and conceptual perspectives for future research. Considering all of this, we urge readers not to solely extract protocol recommendations for trait measurements from this work, but to take a moment to read and reflect on the extensive information contained in this broader guide to root ecology, including sections I-VII and the many introductions to each section and root trait description. Finally, it is critical to understand that a major aim of this guide is to help break down barriers between the many subdisciplines of root ecology and ecophysiology, broaden researchers' views on the multiple aspects of root study and create favourable conditions for the inception of comprehensive experiments on the role of roots in plant and ecosystem functioning.

The future of high-quality Ceylon tea seems bleak in the face of climate change

Understanding the interactive effects and relationships between biochemical elements of tea leaves and the related factors, particularly climatic, cultivar, and geographic, is key for high-quality Ceylon tea production. The objectives of this study were to (1) investigate the effects of season × cultivar × agro-ecological regions (AERs) on the four tested biochemicals in fresh tea leaves, total polyphenol content (TPC), free sugar, protein, and theanine; (2) determine the relationships between, and develop a model to estimate, the biochemicals and their related factors; and (3) project the potential concentrations and distributions of four tested biochemicals in tea leaves with respect to the current and future climate. This study primarily uses inferential statistics via the Statistical Package for the Social Sciences (SPSS), cross-validation using R software, and the inverse distance weighting (IDW) approach in ArcGIS. The results demonstrate that the season, cultivar (Ceylon tea cultivars of TRI 2025 and TRI 4053), and AER and their interactions on biochemicals have significant effects (p < 0.05). The models derived in the regression analysis demonstrate the strong relationships between the independent variables and the biochemicals, with multiple correlation coefficients (R) around 0.8 and coefficient of determination (R2) around 0.6. The low standard deviation of error of prediction (SDEP < 0.1) and the high correlation coefficient of leave-one-out cross-validation (Q2) for all four biochemicals ranged from 0.56 to 0.61, which signifies the predictive ability of the models. The future projections show a considerable increase in the thresholds of all tested biochemicals. The distribution category with 'very high' concentrations of TPC and theanine is predicted to increase in the future by averages of 10% and 14%, respectively, while reducing the classes of protein and free sugar by 14% and 12%, respectively. Overall, the changing concentrations of the thresholds of relevant biochemicals and their distribution will negatively affect the final quality of tea, and these variations indicate that climate change has started to diminish Ceylon tea quality.

Effects of Soil Properties and Plant Diversity on Soil Microbial Community Composition and Diversity during Secondary Succession

Soil microbial communities play an important role in maintaining the ecosystem during forest secondary succession. However, the underlying mechanisms that drive change in soil microbial community structures during secondary succession remain poorly defined in species-rich subtropical coniferous forests. In this study, Illumina high-throughput sequencing was used to analyze the variations in soil microbial community structures during forest secondary succession in subtropical coniferous forests in China. The role of soil properties and plant diversity in affecting soil bacterial and fungal communities was determined using random forest and structural equation models. Highly variable soil microbial diversity was observed in different stages of secondary succession. Bacterial community diversity rose from early to middle and late successional stages, whereas fungal community diversity increased from early to middle successional stages and then declined in the late stage. The relative abundance of Acidobacteria, Gemmatimonadetes, Eremiobacterota(WPS-2), Rokubacteria, and Mortierellomycota increased during succession, whereas the relative abundance of Ascomycota and Mucoromycota decreased. The community composition and diversity of the soil microbial community were remarkably influenced by plant diversity and soil properties. Notably, tree species richness (TSR) displayed a significant and direct correlation to the composition and diversity of both bacterial and fungal communities. The carbon-to-nitrogen (C:N) ratio had a direct impact on the bacterial community composition and diversity, and pH had a marked impact on the fungal community composition and diversity. Furthermore, succession stage and plant diversity indirectly impacted the composition and diversity of soil bacterial and fungal communities via soil properties. Overall, it can be concluded that soil intrinsic properties and plant diversity might jointly drive the changes in soil microbial community composition and diversity during secondary succession of subtropical coniferous forests.

Species-Specific Responses of Root Morphology of Three Co-existing Tree Species to Nutrient Patches Reflect Their Root Foraging Strategies

Root foraging strategies of plants may be critical to the competition for nutrient resources in the nutrient patches, but little is known about these of co-existing tree species in subtropical regions. This study aimed to elucidate root foraging strategies of three co-existing tree species in nutrient heterogeneous soils by exploring their root distribution, root morphology, photosynthates allocation and nutrient accumulation. Seedlings of the three tree species [moso bamboo (Phyllostachys edulis), Chinese fir (Cunninghamia lanceolata), and masson pine (Pinus massoniana)] were grown for 8months under one homogeneous soil [uniform nitrogen (N) plus phosphorus (P)] and three heterogeneous soils (localized N supply, localized P supply, or localized N plus P supply). The biomass, root morphological parameters (i.e., root length and root surface area), specific root length (SRL), non-structural carbohydrates (NSCs, i.e., mobile sugar and starch) in roots, total N and total P of plants were measured. The plasticity and distribution of root system were analyzed by calculating the root response ratio (RRR) and root foraging precision (FP), respectively. The results are as follows (i) Chinese fir tended to forage more N by promoting root proliferation in the N-rich patch, while root proliferation of bamboo and pine did not change. For P, bamboo absorbed more P by promoting root proliferation in the P-rich patch. The total P content of Pine and Chinese fir under localized P supply treatment remain the same despite the fact that the root length in the P-rich patch and the FP increased. (ii) Chinese fir foraged more N by increasing root length and decreasing SRL in the NP-rich patch; bamboo foraged more N and P by increasing root length and SRL in the NP-rich patch. The FP and foraging scale (FS) of both bamboo and Chinese fir were significantly improved under localized N plus P treatment. (iii) The concentrations of NSC were positively correlated with root morphological plasticity for moso bamboo and Chinese fir. Our results indicated that higher morphological plasticity is exhibited in moso bamboo and Chinese fir than masson pine in nutrient heterogeneous soils, allowing them to successfully forage for more nutrients.

A Non-destructive Method to Quantify Leaf Starch Content in Red Clover

Grassland-based ruminant livestock production provides a sustainable alternative to intensive production systems relying on concentrated feeds. However, grassland-based roughage often lacks the energy content required to meet the productivity potential of modern livestock breeds. Forage legumes, such as red clover, with increased starch content could partly replace maize and cereal supplements. However, breeding for increased starch content requires efficient phenotyping methods. This study is unique in evaluating a non-destructive hyperspectral imaging approach to estimate leaf starch content in red clover for enabling efficient development of high starch red clover genotypes. We assessed prediction performance of partial least square regression models (PLSR) using cross-validation, and validated model performance with an independent test set under controlled conditions. Starch content of the training set ranged from 0.1 to 120.3 mg g-1 DW. The best cross-validated PLSR model explained 56% of the measured variation and yielded a root mean square error (RMSE) of 17 mg g-1 DW. Model performance decreased when applying the trained model on the independent test set (RMSE = 29 mg g-1 DW, R 2 = 0.36). Different variable selection methods did not increase model performance. Once validated in the field, the non-destructive spectral method presented here has the potential to detect large differences in leaf starch content of red clover genotypes. Breeding material could be sampled and selected according to their starch content without destroying the plant.

Leaf nonstructural carbohydrate concentrations of understory woody species regulated by soil phosphorus availability in a tropical forest

Leaf soluble sugars and starch are important components of nonstructural carbohydrates (NSCs), which are crucial for plant growth, development, and reproduction. Although there is a large body of research focusing on the regulation of plant NSC (soluble sugars and starch) concentrations, the response of foliar NSC concentrations to continuous nitrogen (N) and phosphorus (P) addition is still unclear, especially in tropical forests. Here, we used a long-term manipulative field experiment to investigate the response of leaf NSC concentrations to continuous N and P addition (3-, 5-, and 8-year fertilization) in a tropical forest in southern China. We found significant species-specific variation in leaf NSC concentrations in this tropical forest. Phosphorus addition dramatically decreased both leaf soluble sugar and starch concentrations, while N addition had no significant effects on leaf soluble sugar and starch concentrations. These results suggest that, in plants growing in P-limiting tropical soil, leaf NSC concentrations are regulated by soil P availability rather than N availability. Moreover, the negative relationships between NSC concentrations and leaf mass per area (LMA) revealed that NSCs could supply excess carbon (C) for leaf expansion under P addition. This was further supported by the increased structural P fraction after P fertilization in our previous study at the same site. We conclude that soil P availability strongly regulates leaf starch and soluble sugar concentrations in the tropical tree species included in this study. The response of leaf NSC concentrations to long-term N and P addition can reflect the close relationships between plant C dynamics and soil nutrient availability in tropical forests. Maintaining relatively higher leaf NSC concentrations in tropical plants can be a potential mechanism for adapting to P-deficient conditions.

The complete chloroplast genome sequence of Phoebe puwenensis

The first complete chloroplast genome (cpDNA) sequence of Phoebe puwenensis was determined from Illumina HiSeq pair-end sequencing data in this study. The cpDNA is 152,746 bp in length, contains a large single-copy region (LSC) of 93,685 bp and a small single-copy region (SSC) of 18,909 bp, which were separated by a pair of inverted repeats (IR) regions of 20,076 bp. The genome contains 127 genes, including 82 protein-coding genes, 8 ribosomal RNA genes, and 36 transfer RNA genes. The overall GC content of the whole genome is 39.1%, and the corresponding values of the LSC, SSC, and IR regions are 37.9%, 33.9%, and 44.4%, respectively. Further phylogenomic analysis showed that P. puwenensis and Phoebe neurantha clustered in a clade in Phoebe genus.

Photosynthesis, Ecological Stoichiometry, and Non-Structural Carbohydrate Response to Simulated Nitrogen Deposition and Phosphorus Addition in Chinese Fir Forests

Phosphorus (P) deficiency in soil affects plant growth and primary production. Accelerated nitrogen (N) deposition can cause ecological carbon:nitrogen:phosphorus (C:N:P) stoichiometry imbalance and increase the degree of relative P deficiency in the soil. However, it remains unclear how N deposition affects P uptake and C:N:P stoichiometry in coniferous timber forests, and whether P addition diminishes the effect of N-induced P limitation on plant growth. From January 2017 to April 2018, we investigated the effects of nine different N and P addition treatments on 10-year old trees of Chinese fir, Cunninghamia lanceolata (Lamb.) Hook. Our results demonstrated that N and P additions at a high concentration could improve the photosynthetic capacity in Chinese fir by increasing the chlorophyll content and stimulating the photosynthesis activity. The C:N:P stoichiometry varied with the season under different N and P addition treatments, indicating that N addition at a moderate concentration could diminish the effect of the P limitation on the growth of Chinese fir. The soluble sugar content in the leaves displayed more stable seasonal variations, compared with those of starch. However, the non-structural carbohydrate (NSC) content in the leaves did not vary with the season under both P and N addition treatment. The data suggested that N and P combination treatment at moderate concentrations promoted carbon assimilation by accelerating the photosynthetic rate. Thus, our results provide new insights into the adaptation mechanisms of coniferous timber forest ecosystems to the effects of N deposition under P deficiency and can help to estimate the ecological effects of environmental changes linked to human management practices.

Interannual variability of leaf area index of an evergreen conifer stand was affected by carry-over effects from recent climate conditions

Despite the relevance of leaf area index (LAI) to forest productivity, few studies have focused on the interannual variability of LAI of an evergreen stand and its relationship with stand growth and meteorological factors. We estimated the change in LAI of an evergreen conifer (Chamaecyparis obtusa) stand over 19 years from a dataset using allometric methods. The LAI varied between 7.1 and 8.8 m2 m-2, with a 95% confidence interval of <1.1 m2 m-2 over the 19 years. This LAI range was maintained such that the gradual increase in leaf area (LA) of the largest trees counterbalanced the gradual loss in LA of the smallest trees. Meanwhile, more trees showed a temporary decrease in LA in years with low summer precipitation. The LAI and current-year mean temperature for July and August (TJA) were weakly correlated, whereas the correlation coefficient increased (r = 0.93) when LAI was correlated with the moving average TJA over the previous 6 years, which agreed with the estimated turnover time of canopy foliage. The annual stem biomass growth rate was significantly positively correlated with summer precipitation, but not with LAI. These results will be useful for refining models in studies on forest growth and global climate change.