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5 pages, 629 KiB

Open AccessEditorial

Adaptive Mechanisms of Tree Seedlings to Adapt to Stress

by Shaofei Jin, Bo Liu, Mulualem Tigabu and Jing Zhou

Forests 2024, 15(5), 846; https://doi.org/10.3390/f15050846 - 12 May 2024

Viewed by 941

Abstract

As the most critical stage in the plant life cycle, the seedling period assumes a crucial role in forest community succession and vegetation restoration [...] Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

Research

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14 pages, 3123 KiB

Open AccessArticle

Transcriptome Analysis Reveals the Impact of Arbuscular Mycorrhizal Symbiosis on Toona ciliata var. pubescens Seedlings

by Xue-Ru Jiang, Jian-Feng Pan, Ming Zhao, Xiao-Yan Guo, Qiong Wang, Lu Zhang and Wei Liu

Forests 2024, 15(4), 673; https://doi.org/10.3390/f15040673 - 8 Apr 2024

Cited by 1 | Viewed by 1148

Abstract

Toona ciliata var. pubescens, known as “Chinese mahogany”, has high commercial value and is classified as a level II priority protected wild plant in China. However, due to overexploitation and its poor natural regeneration capacity, natural T. ciliata var. pubescens forests show [...] Read more.

Toona ciliata var. pubescens, known as “Chinese mahogany”, has high commercial value and is classified as a level II priority protected wild plant in China. However, due to overexploitation and its poor natural regeneration capacity, natural T. ciliata var. pubescens forests show varying degrees of decline in habitat adaptability. Arbuscular mycorrhizal fungi (AMF) symbiosis presents a potential strategy to enhance its regeneration. In this study, T. ciliata var. pubescens seedlings were inoculated with Septoglomus viscosum, followed by RNA-Seq analysis to compare gene expression differences between AMF-inoculated (AMI) and non-mycorrhizal (NM) treatments three months post-inoculation. A total of 16,163 differentially expressed genes (DEGs) were upregulated by AMF colonization, constituting 96.46% of the total DEGs. Specifically, 14,420 DEGs were exclusively expressed in the AMI treatment, while 35 DEGs were completely silenced. Most of the upregulated DEGs were located on the cell membrane, nucleus, and cytoskeleton and functioned in protein binding, S-adenosylmethionine-dependent methyltransferase activity, and lipid binding during cellular/macromolecule/protein localization, intracellular/protein transport, the cell cycle, and signal transduction. Additionally, lots of key genes related to oxidative stress responses, nutrient transport, and small GTPase-mediated signal transduction were found to be upregulated. These results suggest that AMF inoculation may enhance root cell growth by activating genes involved in nutrient uptake, stress responses, signal transduction, and substance transportation. This study elucidates the molecular mechanisms underlying the growth promotion of T. ciliata var. pubescens through AMF symbiosis, laying a foundation for the future application of AMF in its natural forest regeneration. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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17 pages, 6648 KiB

Open AccessArticle

Responses of Soil Phosphorus Cycling-Related Microbial Genes to Thinning Intensity in Cunninghamia lanceolata Plantations

by Dongxu Ma, Jiaqi Wang, Kuaiming Chen, Weili Lan, Yiquan Ye, Xiangqing Ma and Kaimin Lin

Forests 2024, 15(3), 440; https://doi.org/10.3390/f15030440 - 26 Feb 2024

Cited by 1 | Viewed by 1519

Abstract

Background: Microorganisms are important regulators of soil phosphorus cycling and phosphorus availability in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations. However, the effects of thinning on soil phosphorus cycling by microbes in C. lanceolata plantations remain unclear. Methods: We performed a metagenomic [...] Read more.

Background: Microorganisms are important regulators of soil phosphorus cycling and phosphorus availability in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations. However, the effects of thinning on soil phosphorus cycling by microbes in C. lanceolata plantations remain unclear. Methods: We performed a metagenomic sequencing analysis to investigate how thinning intensities (weak, moderate, and heavy) alter phosphorus cycling related microbial genes and their regulatory effects on soil phosphorus availability in C. lanceolata plantations. Results: Following heavy thinning, the contents of available and labile phosphorus increased by 13.8% and 36.9%, respectively, compared to moderate and weak thinning. Moreover, the relative abundance of genes associated with inorganic phosphorus solubilization increased significantly with the increase in thinning intensity, whereas genes associated with phosphorus uptake and transport significantly decreased. The metagenomic analysis results indicate that Acidobacteria (47.6%–53.5%), Proteobacteria (17.9%–19.1%), and Actinobacteria (11.7%–12.8%) are the major contributors to the functional phosphorus cycling genes in the soil. The random forest analysis results suggested that gcd, plc, phoN, ugpA, and phoR were the critical genes involved in the transformation and use of phosphorus, which in turn increased soil phosphorus availability. Structural equation modeling revealed that soil pH was the primary factor influencing changes in functional genes associated with phosphorus cycling in C. lanceolata plantations. Specifically, soil pH (ranging from 4.3 to 4.9) were positively correlated with genes involved in inorganic phosphate solubilization and organic phosphate mineralization, while negatively correlated with genes related to phosphorus uptake and transport. Conclusions: Taken together, our results demonstrate that the enhanced microbe-mediated mineralization of organic phosphorus and solubilization of inorganic phosphorus are suppressed when uptake and transportation are the mechanisms responsible for the increased soil phosphorus availability under appropriate thinning intensities. Changes in the soil microbial community and phosphorus cycling genes in response to different thinning intensities may maintain soil functionality and nutrient balance in C. lanceolata plantations. These findings contribute to a better understanding of the mechanisms underlying the microbial mediation of phosphorus cycling in the soil of C. lanceolata plantations. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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19 pages, 2247 KiB

Open AccessArticle

Enhanced Seedling Growth and Physiological Performances of Melia azedarach L. by Foliar Application of 24-Epibrassinolide under Salt Stress

by Zin Myo Htet, Xiaoxian Li and Fangyuan Yu

Forests 2024, 15(3), 427; https://doi.org/10.3390/f15030427 - 23 Feb 2024

Cited by 1 | Viewed by 1339

Abstract

Salinity is a serious environmental problem following a worsening trend. This study investigates the role of 24-epibrassinolide(EBR) in regulating plant growth and physiological performances, particularly in alleviating the negative effects of salt stress. Melia azedarach L. seedlings from two seed sources, Sheyang (SY) [...] Read more.

Salinity is a serious environmental problem following a worsening trend. This study investigates the role of 24-epibrassinolide(EBR) in regulating plant growth and physiological performances, particularly in alleviating the negative effects of salt stress. Melia azedarach L. seedlings from two seed sources, Sheyang (SY) and Xiashu (XS), were exposed to sea salt and treated with different concentrations of EBR within a 60-day period. The results demonstrate that appropriate EBR application improved the seedlings’ stress tolerance by promoting growth and physiological systems. In terms of the relative increment, it showed that a difference of 1.45% and 1.13% in the SY and XS groups was the positive effect of the highest EBR treatment concentration. As for diameter growth, the difference observed was 2.51% and 1.80% for the SY and XS groups, respectively. In all physiological measurements, including the content of photosynthetic pigments, water relations, membrane stability, osmolytes and antioxidant enzymes, significant changes generally observed between salt stress alone and the highest EBR treatment concentration. A better performance was observed in the SY seed source, which is of a coastal nature. These findings contribute to our understanding of Melia azedarach’s adaptation to changing environments and provide potential for further molecular studies as well as valuable insights for forestry, agricultural and ecological research. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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16 pages, 4253 KiB

Open AccessArticle

The Genome-Wide Profiling of Alternative Splicing in Willow under Salt Stress

by Xue Wang, Longfeng Gong, Junkang Zhang, Lei Wang, Di Wu and Jichen Xu

Forests 2024, 15(1), 30; https://doi.org/10.3390/f15010030 - 22 Dec 2023

Cited by 2 | Viewed by 1133

Abstract

Alternative splicing (AS) is an important post-transcriptional regulatory model that can change the normal transcript expression level and possibly result in protein diversity. In this study, we conducted the full-length transcript sequencing of Salix matsudana Koidz 9901 leaves under salt treatment using the [...] Read more.

Alternative splicing (AS) is an important post-transcriptional regulatory model that can change the normal transcript expression level and possibly result in protein diversity. In this study, we conducted the full-length transcript sequencing of Salix matsudana Koidz 9901 leaves under salt treatment using the PromethION platform. A total of 4786 AS genes (9307 AS events) were determined, accounting for 7.45% of all the transcribed genes. Of them, intron retention (IR) events accounted for the most AS events (46.05%), followed by alternative 3′ splice sites (A3SS). During salt stress, the percentage of IR events decreased, and the percentage of the others increased. Statistical results showed that 5′GG was the most common motif at the 5′ end of the intron in the AS events, and GG3′ was the most common motif at the 3′ end. 5′GG-AG3′ was the most common splice mode in the AS events. The occurrence of AS events was significantly related to the exon number, exon length, intron length, GC content, and expression abundance of the genes. During salt stress, the number of AS genes gradually increased, and they mainly participated in purine and chlorophyll metabolism, RNA transport, and autophagy. Meanwhile, the AS sites of the gene increased during salt treatment, indicating the complexity of the AS events by salt stress. A comparison of differentially expressed genes (DEGs) and differentially alternative splicing (DAS) genes during salt stress revealed that they had a different mechanism of gene expression regulation when subjected to salt stress. These results expand our knowledge of AS events and shed light on and improve our understanding of plant resistance to salt tolerance in willow. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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18 pages, 2118 KiB

Open AccessArticle

Responses of Growth and Root Vitality of Fokienia hodginsii Seedling to the Neighbor Competition in Different Heterogeneous Nutrient Environments

by Bingjun Li, Mi Deng, Yanmei Pan, Wenchen Chen, Jundong Rong, Tianyou He, Liguang Chen and Yushan Zheng

Forests 2023, 14(12), 2278; https://doi.org/10.3390/f14122278 - 21 Nov 2023

Cited by 2 | Viewed by 1245

Abstract

Fokienia hodginsii is characterized by shallow and developed lateral roots with no obvious taproot. It can be used as a pioneer tree species for opening up barren land and as a mixed species for creating plantation forests. During the growth process of F. [...] Read more.

Fokienia hodginsii is characterized by shallow and developed lateral roots with no obvious taproot. It can be used as a pioneer tree species for opening up barren land and as a mixed species for creating plantation forests. During the growth process of F. hodginsii seedlings, they are often exposed to heterogeneous nutrient environments and competition for nutrients, water, and space from neighboring plants, which have significant impacts on the growth of F. hodginsii. These impacts are most directly reflected in the root vitality of F. hodginsii, whose physiological changes embody the plant’s adaptability to different heterogeneous nutrient environments and neighbor competition. Herein, high-quality one-year-old F. hodginsii seedlings were subjected to three planting patterns to simulate different competition patterns. The three planting patterns were also exposed to three heterogeneous nutrient environments and a homogeneous nutrient environment (control) to determine the differences in the F. hodginsii seedling growth and root vitality under different heterogeneous nutrient environments and planting patterns. The F. hodginsii seedling height, ground diameter (root neck diameter), and root biomass under the heterospecific neighbor condition were significantly higher than under the single-plant condition. Across heterogeneous nutrient environments, the average seedling height in the N heterogeneous environments was higher than in the P and K heterogeneous environments. The root biomass in the P heterogeneous environment was slightly higher than in the N heterogeneous environment and significantly higher than in the homogeneous and the K heterogeneous environments. Moreover, the average F. hodginsii seedling root vitality under the heterospecific neighbor was the highest, and the root vitality in the N heterogeneous environment was the highest under each planting pattern. The F. hodginsii root catalase (CAT) and peroxidase (POD) activities under the competition patterns were significantly higher than under the single-plant condition. Additionally, the superoxide dismutase (SOD) activity under single-plant was higher than under the competition patterns. At the same time, the F. hodginsii root malondialdehyde (MDA) content was the highest under the conspecific neighbor. Relative to the homogeneous environment, the root CAT, SOD, and POD activities were increased in the N and P heterogeneous environments. The CAT, SOD, and POD activities were highest in the P heterogeneous environment, while the K heterogeneous environment had the highest average MDA content. From the results of principal component analysis, when F. hodginsii seedlings were in N and P heterogeneous nutrient environments and heterospecific neighbor, their growth, root biomass accumulation, and root activity indexes reached better levels. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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19 pages, 5654 KiB

Open AccessArticle

Compensatory Growth and Physiological Protective Mechanisms of Populus talassica Kom. × Populus euphratica Oliv. in Response to Leaf Damage

by Meng-Xu Su, Zhan-Jiang Han, Ying Liu, Zhen Zhao and Jia-Ju Wu

Forests 2023, 14(9), 1713; https://doi.org/10.3390/f14091713 - 25 Aug 2023

Cited by 2 | Viewed by 1290

Abstract

The compensatory growth and defensive capabilities of woody plants after damage are crucial to their large-scale promotion and economic value. Here, Populus talassica × Populus euphratica were subjected to artificial defoliation treatments that simulated leaf damage [25% (D₂₅), 50% (D₅₀ [...] Read more.

The compensatory growth and defensive capabilities of woody plants after damage are crucial to their large-scale promotion and economic value. Here, Populus talassica × Populus euphratica were subjected to artificial defoliation treatments that simulated leaf damage [25% (D₂₅), 50% (D₅₀), and 75% (D₇₅) leaf removal] to study the growth, anatomical, and physiological characteristics. The results showed that D₂₅ and D₅₀ treatments significantly increased the growth parameters, such as leaf length, leaf area, and specific leaf area, but did not affect the distributions of root and stem biomasses compared with the CK. However, the D₇₅ treatment significantly decreased most growth parameters. The time required for the chlorophyll content to recover increased along with the damage intensity as follows: D₂₅, high-flat-high; D₅₀, low-high-flat; and D₇₅, low-flat-high. Furthermore, leaf damage significantly reduced stomatal density, whereas the stomatal width, area, opening, and Pn significantly increased by 8.59%, 8.40%, 23.27%, and 31.22%, respectively, under the D₅₀ treatment, generating a photosynthetic compensation response. The leaf anatomical parameters increased along with damage intensity, except spongy tissue thickness, which decreased, while the stem anatomical parameters showed trends of first increasing and then decreasing, reaching maxima under the D₅₀ treatment. The enzymes showed an increasing and then decreasing trend as the damage time increased. After 1 d of treatment, CAT, POD, and PAL activities peak at D₇₅, in contrast to a peak of SOD activity at D_50. Overall, these findings indicate that it is advisable to keep the amount of leaf damage within 50%. The leaf damage can have an impact on the growth of P. talassica × P. euphratica. They adjusted their resource allocation strategy and physiological defense capacity by increasing the chlorophyll content, improving photosynthetic capacity, changing stem and leaf anatomy, and increasing defense enzyme activity levels, thereby improving their damage tolerance and adaptability. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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15 pages, 4123 KiB

Open AccessArticle

Leaf Plasticity of the Subtropical Evergreen Tree Phoebe bournei Increases with Ontogeny in Response to Sun and Shade

by Xin-Bei Li, Cheng-Cheng Liu, Jia-Xin Chen, Meng-Meng Zhang, Jun-Hong Zhang, Zai-Kang Tong and Qi Yang

Forests 2023, 14(8), 1683; https://doi.org/10.3390/f14081683 - 20 Aug 2023

Cited by 3 | Viewed by 1509

Abstract

Variation in shade tolerance is a primary mechanism driving succession in subtropical forests. However, little attention has been given to ontogenetic variation in light tolerance of late succession tree species such as Phoebe bournei. To investigate the differences in adaptive strategies between [...] Read more.

Variation in shade tolerance is a primary mechanism driving succession in subtropical forests. However, little attention has been given to ontogenetic variation in light tolerance of late succession tree species such as Phoebe bournei. To investigate the differences in adaptive strategies between seedlings and saplings in response to sun and shade, we systematically studied the physiological and morphological leaf plasticity of P. bournei and how these variables are influenced by ontogeny. This study provided experimental evidence that leaf plasticity increases with the ontogeny of juvenile P. bournei adapting to the changing light resources. Investment in leaf construction increased with age and light resources in the evergreen P. bournei, as shown by leaf mass per unit area (LMA). Six-month-old seedlings lacked the adjustment of stomatal conductance (g_s) and stomatal density responding to sun and shade. For seedlings, maintaining high g_s under sun conditions increased stress risk instead of carbon gain. However, the leaves of 2-year-old saplings accumulated more soluble sugars and showed lower stomatal conductance and higher stomatal density under the sun than under shade conditions. The nonphotochemical quenching of sun leaves increased with plant age, indicating that the photoprotective capacity was enhanced with ontogeny. The leaf plasticity increasing along the ontogeny of juvenile P. bournei may contribute to the adaptation from shade to sun. Our study provides new insights into understanding the influence of ontogeny on shade responses of late succession trees in subtropical forests. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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15 pages, 6413 KiB

Open AccessArticle

Variations in Microbial Residue and Its Contribution to SOC between Organic and Mineral Soil Layers along an Altitude Gradient in the Wuyi Mountains

by Yiming Sun, Xunlong Chen, Anna Zhong, Shijie Guo and Houxi Zhang

Forests 2023, 14(8), 1678; https://doi.org/10.3390/f14081678 - 18 Aug 2023

Cited by 4 | Viewed by 1406

Abstract

Microbes are crucial components of soil, and their residue carbon plays a significant role in the formation and stabilization of soil carbon pools. However, current research on microbial residue carbon has predominantly focused on surface soils, with limited studies on deep soils. The [...] Read more.

Microbes are crucial components of soil, and their residue carbon plays a significant role in the formation and stabilization of soil carbon pools. However, current research on microbial residue carbon has predominantly focused on surface soils, with limited studies on deep soils. The patterns of variation along soil profiles and their controlling factors remain unclear. Therefore, this study aimed to investigate the soils from different elevations in the Wuyi Mountains, specifically focusing on the organic layers (0–10 cm) and mineral layers (30–40 cm). Amino sugars were utilized as biomarkers for the microbial residue, and the RDA (redundancy analysis) method was employed to analyze the patterns of microbial residue carbon in different soil layers and to identify the factors that control them. The results indicate that there are significant differences in the microbial residue carbon content and its contribution to soil organic carbon (SOC) between the different soil layers. Specifically, between the organic layer and the mineral layer, the microbial residue carbon content exhibited an increasing trend, whereas its contribution to SOC decreased. This finding suggests that soil layer type has a notable impact on microbial residue carbon content and its contribution to SOC. Moreover, fungal residue carbon content was found to be higher than bacterial residue carbon content in both soil layers. However, the ratio of fungal residue carbon to bacterial residue carbon gradually decreased between the organic layer and the mineral layer. This implies that although fungal residue carbon remains dominant, the contribution of bacterial residue carbon to the soil carbon pool increases as the soil transitions to the mineral layer. The total soil carbon content, elevation, and C/N ratio exhibited positive correlations with fungal and bacterial residue carbon, indicating their significant roles in the accumulation of microbial residue carbon in soils. Notably, elevation emerged as a key regulating factor in the accumulation of microbial residue carbon, explaining 85.8% and 67.9% of the variations observed in the organic layer and the mineral layer respectively. These research findings contribute to a better understanding of the soil carbon cycling process and its mechanisms, providing a scientific basis for developing strategies to enhance soil carbon sequestration by manipulating micro-organisms. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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15 pages, 3310 KiB

Open AccessArticle

Effects of Shading on the Growth and Photosynthetic Fluorescence Characteristics of Castanopsis hystrix Seedlings of Top Community-Building Species in Southern Subtropical China

by Guangyu Xue, Junduo Wu, Bingjiang Zhou, Xueping Zhu, Ji Zeng, Yue Ma, Yanan Wang and Hongyan Jia

Forests 2023, 14(8), 1659; https://doi.org/10.3390/f14081659 - 16 Aug 2023

Cited by 3 | Viewed by 1250

Abstract

Castanopsis hystrix is a major community-building species in the top communities of southern subtropical China, with a high natural regeneration capacity. However, excessive logging and the introduction of exotic tree species have substantially reduced the area of natural forest patches of Castanopsis hystrix [...] Read more.

Castanopsis hystrix is a major community-building species in the top communities of southern subtropical China, with a high natural regeneration capacity. However, excessive logging and the introduction of exotic tree species have substantially reduced the area of natural forest patches of Castanopsis hystrix, and seedling regeneration is essential for the long-term continuation of Castanopsis hystrix populations. To explore the effects of light intensity on the seedling emergence and early growth of Castanopsis hystrix, shading experiments were conducted under four shading treatments (0%, 40%, 60%, and 80%). The growth, biomass accumulation, and distribution, the quality index of seedlings, the morphology and structure of the root systems of seedlings, and the leaf chlorophyll content and chlorophyll fluorescence properties of seedlings under different shading treatments were analyzed. The results displayed the following: (1) Shade intensity impacts growth of Castanopsis hystrix seedlings and biomass allocation, with optimal results observed at 60% shade, leading to the promotion of organic matter production in leaves and the limitation of stem growth. (2) Using a multi-indicator composite index, it was determined that seedling quality for Castanopsis hystrix peaks at 60% shade intensity. (3) Shade significantly impacts the morphology and structure of Castanopsis hystrix’s root system, with most root characteristics peaking at 60% shade, indicating a substantial increase in root development compared to no-shade conditions. (4) The D-values indicated the most suitable shade intensity for seedling growth to be 60%, suggesting that Castanopsis hystrix seedlings are sensitive to light and excessive light can be detrimental to their growth. (5) The 60% shade treatment showed the maximum values of chlorophyll fluorescence characteristics and photochemical activity, with variations in energy conversion efficiency and dissipation reflected in parameters like photochemical burst coefficient (qP), photochemical burst coefficient (qN), the actual photometric yield of PSII under light acclimation (YII), and the maximum photosynthetic electron transport rate in photoinhibition (ETR), thereby supporting seedling growth and maintaining the normal function of photosynthetic organs. In conclusion, 60% shade treatment can effectively improve the growth and photosynthetic characteristics of Castanopsis hystrix seedlings and promote the accumulation of nutrient elements, ultimately promoting their growth. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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12 pages, 2955 KiB

Open AccessArticle

Differences in Root Endophytic Bacterial Communities of Chinese Cork Oak (Quercus variabilis) Seedlings in Different Growth Years

by Weilai Sha, Die Hong, Yuying Che, Yafei Xue, Yong Kong, Xianfeng Yi, Jing Zhou, Guohong Yu and Baoxuan Liu

Forests 2023, 14(7), 1489; https://doi.org/10.3390/f14071489 - 20 Jul 2023

Cited by 3 | Viewed by 1450 | Correction

Abstract

In forests, seedling renewal is influenced by many environmental factors, including climate change, seed size, wildfires, and ecological factors. It is unclear how different growth years of seedlings affect Chinese cork oak (Quercus variabilis) root endophyte communities. In this study, we [...] Read more.

In forests, seedling renewal is influenced by many environmental factors, including climate change, seed size, wildfires, and ecological factors. It is unclear how different growth years of seedlings affect Chinese cork oak (Quercus variabilis) root endophyte communities. In this study, we took a holistic approach, using Illumina sequencing, to study the composition and function of bacterial communities associated with root microorganisms in four Q. variabilis seedlings after 1, 2, and 3 years of growth. The bacterial alpha diversity indexes were highest in the second year and lowest in the third year, and age was the decisive factor for the differences found in the root endophytic bacterial communities. Total phosphorus had the greatest effect on bacterial communities. The abundance of beneficial bacteria Streptomyces (8.69%) and Novosphingobium (4.22%) was highest in the second-year samples, and their abundance decreased by 7.96% and 3.61% in the third year, respectively. Higher levels of plant disease inhibition and metabolism (23.80%) were in the roots of second-year Q. variabilis seedlings. The metabolic abundance of carbohydrate was 3.66% lower in the first year and 3.95% lower in the third year compared to the second year. Our results suggest that the structure and function of bacterial communities changed with increasing growth years. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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14 pages, 3059 KiB

Open AccessArticle

Effects of Different Trace Elements on Ecophysiological Characteristics of Ligustrum obtusifolium Saplings

by Wenqiu Cao, Muhammad Arif, Zhen Cui and Changxiao Li

Forests 2023, 14(5), 972; https://doi.org/10.3390/f14050972 - 8 May 2023

Cited by 6 | Viewed by 1628

Abstract

Phytoremediation is becoming more prevalent globally. Literature on phytoremediation strategies in western China is relatively scarce. The present research sought to fill this gap by examining the effects of trace elements such as Cd, Cr, Pb, and Zn on growth, physiological traits, tolerances, [...] Read more.

Phytoremediation is becoming more prevalent globally. Literature on phytoremediation strategies in western China is relatively scarce. The present research sought to fill this gap by examining the effects of trace elements such as Cd, Cr, Pb, and Zn on growth, physiological traits, tolerances, and accumulation characteristics in 2-year-old saplings of Ligustrum obtusifolium. The gradient of trace element concentration was determined by adding exogenous trace elements to the soil in a pot experiment: CK (no exogenous trace element), T1, T2, and T3 (Cd 0, 2, 5, and 10 mg/kg; Cr 0, 300, 500, and 700 mg/kg; Pb 0, 400, 800, and 1200 mg/kg; and Zn 0, 300, 500, and 1000 mg/kg, respectively). The results indicated that Chla, Chlb, and total Chls significantly decreased (p < 0.05) in the leaves of L. obtusifolium, with the lowest value obtained during soil treatment with T3. Along with the increase in trace element concentration, the net increase in height, root biomass, aerial biomass, and total biomass was reduced significantly. The net growth of L. obtusifolium under Cr stress did not differ significantly from that of CK at T1; however, the net growth of L. obtusifolium under Cr stress was considerably reduced at T2 and T3. The antioxidant enzyme activity of L. obtusifolium increased under different trace element stresses and first increased and then decreased as trace element levels increased. It was found that the SOD, POD, CAT, and APX activity of L. obtusifolium peaks at T2 under Cd and Zn stress in contrast to a peak at T1 under Cr and Pb stress. The contents of trace elements in L. obtusifolium roots, stems, and leaves increased along with the increase in soil trace element levels. Cr, Pb, and Zn threshold values can be set at 300 mg/kg, 400 mg/kg, and 300 mg/kg, respectively. This is carried out by using a reference index of the biomass of L. obtusifolium decreased by 10%, while the Cd threshold value needs to be further studied. L. obtusifolium would be an appropriate plant for phytoremediation of Cr-polluted soil, compared to Cd, Pb, and Zn absorption and accumulation. It showed optimal antioxidant enzyme activity and transfer ability under soil Cr contents of 300 mg/kg, and the growth of L. obtusifolium was not restricted. Therefore, L. obtusifolium was particularly suitable for phytoremediation of Cr pollution in areas in western China. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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12 pages, 1779 KiB

Open AccessArticle

Effect of Cork Flour Supplementation on the Growth Indices and Rhizosphere Bacterial Communities of Quercus variabilis Seedlings

by Yuying Che, Yong Kong, Shangwen Song, Xianfeng Yi, Jing Zhou and Baoxuan Liu

Forests 2023, 14(5), 892; https://doi.org/10.3390/f14050892 - 26 Apr 2023

Cited by 2 | Viewed by 1278

Abstract

Substrate and rhizosphere microorganisms are key factors affecting seedling growth; however, the effects of seedling substrates and rhizosphere bacteria on the growth of Quercus variabilis are not completely understood. Here, Q. variabilis seedlings were grown in substrates with and without cork flour, as [...] Read more.

Substrate and rhizosphere microorganisms are key factors affecting seedling growth; however, the effects of seedling substrates and rhizosphere bacteria on the growth of Quercus variabilis are not completely understood. Here, Q. variabilis seedlings were grown in substrates with and without cork flour, as follows: H substrate (charcoal soil/cork flour/perlite, 1:1:2), S substrate (cork flour/perlite, 1:1), and the control (CK) substrate (charcoal soil/perlite, 3:2). High-throughput sequencing and qPCR were used to investigate the effects of these substrates on seedling growth, physiological indices, and rhizosphere bacterial communities. Root and shoot weights of seedlings grown in H and S substrates were significantly higher than those of seedlings grown in CK. Moreover, H was conducive to chlorophyll synthesis in seedling leaves, and the transpiration rate and intercellular CO₂ concentration of the leaves of seedlings grown in H were higher than those of seedlings grown in CK. The number of rhizosphere bacterial 16S rRNA copies was significantly greater in the case of seedlings grown in S than for those grown in H and CK. As well, rhizosphere bacterial richness was higher in seedlings grown in H and S than in those grown in CK. Thus, cork-flour-supplemented substrates are beneficial for seedling growth and development, seedling rhizosphere bacterial abundance and diversity, and the abundance of nitrogen and phosphorus metabolism-promoting microbial taxa. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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12 pages, 1721 KiB

Open AccessArticle

Effects of Light Intensity on Seedling Emergence and Early Growth of Liquidambar formosana Hance

by Hang Chen, Lei Wang, Si Guo, Mengqi Li, Zhifang Tian, Biao Han, Xinghao Tang and Bo Liu

Forests 2023, 14(5), 867; https://doi.org/10.3390/f14050867 - 24 Apr 2023

Cited by 4 | Viewed by 4504

Abstract

Liquidambar formosana Hance is a common deciduous broad-leaved tree known for its fast growth rate and adaptability. However, excessive logging has substantially reduced the area of natural forest patches of L. formosana, and seedling regeneration is essential for the long-term continuation of L. [...] Read more.

Liquidambar formosana Hance is a common deciduous broad-leaved tree known for its fast growth rate and adaptability. However, excessive logging has substantially reduced the area of natural forest patches of L. formosana, and seedling regeneration is essential for the long-term continuation of L. formosana populations. To explore the effects of light intensity on the seedling emergence and early growth of L. formosana, a controlled experiment was conducted under three light-intensity treatments (20%, 60%, and 100% of full sunlight, i.e., the photosynthetic photon flux densities (PPFDs) were 223.93 ± 7.54, 670.94 ± 30.14, and 1119.61 ± 23.19 μmol·m⁻²·s⁻¹, respectively). The seedling emergence percentage, mean germination time, germination synchrony, vitality index, survival percentage, emergence index, morphological characteristics, and biomass allocation under different light intensities were analyzed. The seedling vitality index and survival percentage significantly differed among the treatments and were the lowest under 20% light intensity. With increased light intensity, the seedling mean germination time and germination synchrony increased and then decreased, and the opposite was true for the emergence index. With the increased light intensity, the seedling height, stem diameter, and root length significantly increased. The total, root, stem, and leaf biomasses reached maximum values under full sunlight. With the increased light intensity, the leaf biomass ratio increased, whereas the root biomass, stem biomass, and root–shoot ratios decreased. Our results indicated that the poor light environment under the canopy is not conducive to the survival and growth of L. formosana seedlings and may be among the primary reasons for low seedling establishment. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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13 pages, 3092 KiB

Open AccessArticle

Natural Physiological Changes on Overwintering and Spring Recovery of Needles of Pinus densiflora Siebold & Zucc.

by Dongxue Yue, Erkun Chao, Yiheng Deng, Kerui Chen, Zhengning Wang, Nianwei Qiu and Hongxia Zhang

Forests 2023, 14(2), 168; https://doi.org/10.3390/f14020168 - 17 Jan 2023

Cited by 2 | Viewed by 1861

Abstract

Overwintering and spring recovery of pine needles have important ecological significance. The natural changes in physiological state, photosynthetic function, and material metabolism in needles of Pinus densiflora Siebold & Zucc. from the autumn of 2020 to the spring of 2021 were assessed. The [...] Read more.

Overwintering and spring recovery of pine needles have important ecological significance. The natural changes in physiological state, photosynthetic function, and material metabolism in needles of Pinus densiflora Siebold & Zucc. from the autumn of 2020 to the spring of 2021 were assessed. The photosynthetic rate (Pn) of P. densiflora needles decreased first and then increased, with the maximum Pn observed in the autumn. After experiencing sub-zero temperatures in the winter, needles of P. densiflora still performed weak photosynthesis at a temperature above zero. In the spring, the Pn gradually recovered but could not recover to the maximum. Under sub-zero temperatures in the winter of 2020, the plasma membrane permeability and MDA content of needles increased, whereas the chlorophyll content and Fv/Fm decreased significantly. The needles showed obvious characteristics of freezing injury. During the whole process, the water content of needles remained at a low level (about 60%), which gradually decreased with the increase of leaf age. The cell sap concentration and soluble sugar content of needles decreased with the decrease in air temperature and recovered in spring. Therefore, P. densiflora needles do not improve frost resistance through osmotic adjustment. However, the increasing carotenoid content is helpful for needles to tide over the winter. The soluble sugar and protein contents increased, implying they are important for the recovery of needles in spring. This study expands our understanding of the mechanism and ecological contribution of overwintering and spring recovery of pine needles. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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12 pages, 1675 KiB

Open AccessReview

Adaptive Strategies Employed by Clonal Plants in Heterogeneous Patches

by Pan Yang, Li Huang, Suni He, Xianghua Zeng, Yinyi Chen and Haimiao Wang

Forests 2023, 14(8), 1648; https://doi.org/10.3390/f14081648 - 15 Aug 2023

Cited by 2 | Viewed by 1558

Abstract

Heterogeneity is widespread in natural environments; as a result, connected clonal ramets often live in areas characterized by patches of different resources. Specifically, clonal plants are frequently affected by conditions of heterogeneous water stress. This raises the question of how clonal plants grow [...] Read more.

Heterogeneity is widespread in natural environments; as a result, connected clonal ramets often live in areas characterized by patches of different resources. Specifically, clonal plants are frequently affected by conditions of heterogeneous water stress. This raises the question of how clonal plants grow and reproduce in areas with patches of different resources. In this study, we investigated the adaptation mechanisms of clonal plants under heterogeneous environmental conditions. On the one hand, we bore in mind that phenotypic plasticity is abundantly exhibited in clonal plants. Clonal plants respond to water stress mainly through regulation of the size of individuals, the allocation of population biomass, and the number of daughter plants, as well as the extension ability and branching intensity of clonal organs, which directly affect reproduction and population stability in clonal plants. On the other hand, we also considered the physiological integration in clonal plants which has been shown in many studies. Ramets of clonal plants normally stay connected to each other through horizontal connectors (stolons or rhizomes). Communicated substances and resources such as water, mineral nutrition, photosynthetic products, and secondary metabolites are translocated between ramets; by such means, the plant relieves stress caused by heterogeneous patches. In this study, we sought to obtain scientific references to improve our understanding of how clonal plants in natural environments acclimate to stresses caused by soil heterogeneity. Full article

(This article belongs to the Special Issue Adaptive Mechanisms of Tree Seedlings to Adapt to Stress)

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