Soil Abiotic Properties and Plant Functional Traits Mediate Associations Between Soil Microbial and Plant Communities During a Secondary Forest Succession on the Loess Plateau

In the context of secondary forest succession, aboveground-belowground interactions are known to affect the dynamics and functional structure of plant communities. However, the links between soil microbial communities, soil abiotic properties, plant functional traits in the case of semi-arid and arid ecosystems, are unclear. In this study, we investigated the changes in soil microbial species diversity and community composition, and the corresponding effects of soil abiotic properties and plant functional traits, during a ≥150-year secondary forest succession on the Loess Plateau, which represents a typical semi-arid ecosystem in China. Plant community fragments were assigned to six successional stages: 1–4, 4–8, 8–15, 15–50, 50–100, and 100–150 years after abandonment. Bacterial and fungal communities were analyzed by high-throughput sequencing of the V4 hypervariable region of the 16S rRNA gene and the internal transcribed spacer (ITS2) region of the rRNA operon, respectively. A multivariate variation-partitioning approach was used to estimate the contributions of soil properties and plant traits to the observed microbial community composition. We found considerable differences in bacterial and fungal community compositions between the early (S1–S3) and later (S4–S6) successional stages. In total, 18 and 12 unique families were, respectively, obtained for bacteria and fungi, as indicators of microbial community succession across the six stages. Bacterial alpha diversity was positively correlated with plant species alpha diversity, while fungal diversity was negatively correlated with plant species diversity. Certain fungal and bacterial taxa appeared to be associated with the occurrence of dominant plant species at different successional stages. Soil properties (pH, total N, total C, NH4-N, NO3-N, and PO4-P concentrations) and plant traits explained 63.80% and 56.68% of total variance in bacterial and fungal community compositions, respectively. These results indicate that soil microbial communities are coupled with plant communities via the mediation of microbial species diversity and community composition over a long-term secondary forest succession in the semi-arid ecosystem. The bacterial and fungal communities show distinct patterns in response to plant community succession, according to both soil abiotic properties and plant functional traits

Root phosphatase activity is a competitive trait affiliated with the conservation gradient in root economic space

Background: The diversity of resource acquisition strategies of plant roots determines the species coexistence patterns to a certain extent. However, few root physiological traits have been investigated, such as root phosphatase activity (PA) that affects plant phosphorus (P) uptake. Methods: Root PA and classical root functional traits were investigated for 21 coexisting species in a deciduous broad-leaved forest in warm temperate-subtropical transition zone, China. We analyzed the root order variation of absorptive fine root PA, clarified the attribution of root PA in root economic space (RES) and the different P acquisition strategies of co-occurring species based on the multidimensional RES theory, and determined the dominant factors affecting interspecific variation in root PA. Results: There was no distinct pattern of PA variation with root order in the first three root orders of absorptive fine roots, and root PA was constrained by phylogeny. Root PA is a competitive trait affiliated with the conservation gradient in RES. The tight linkages among root PA, mycorrhizal colonization, diameter, specific root length, and nitrogen concentration suggested trade-offs among P acquisition strategies of co-occurring species, i.e. species with long and fine roots acquire inorganic P by actively exploring the soil and secreting phosphatase to mineralize and hydrolyze organic P, while species with short and thick roots obtain P mainly by investing C in mycorrhizal partners. Conclusions: Collectively, our study provides an insight into the forest species coexistence in climatic transition zones, i.e. species coexistence mechanisms based on diverse phosphorus acquisition strategies

Spatial Distribution and Species Association of Dominant Tree Species in Huangguan Plot of Qinling Mountains, China

The spatial distribution pattern and population structure of trees are shaped by multiple processes, such as species characteristics, environmental factors, and intraspecific and interspecific interactions. Studying the spatial distribution patterns of species, species associations, and their relationships with environmental factors is conducive to uncovering the mechanisms of biodiversity maintenance and exploring the underlying ecological processes of community stability and succession. This study was conducted in a 25-ha Qinling Huangguan forest (warm-temperate, deciduous, broad-leaved) dynamic monitoring plot. We used univariate and bivariate g(r) functions of the point pattern analysis method to evaluate the spatial distribution patterns of dominant tree species within the community, and the intra- and interspecific associations among different life-history stages. Complete spatial randomness and heterogeneous Poisson were used to reveal the potential process of community construction. We also used Berman’s test to determine the effect of three topographic variables on the distribution of dominant species. The results indicated that all dominant species in this community showed small-scale aggregation distribution. When we excluded the influence of environmental heterogeneity, the degree of aggregation distribution of each dominant species tended to decrease, and the trees mainly showed random or uniform distribution. This showed that environmental heterogeneity significantly affects the spatial distribution of tree species. Dominant species mainly showed positive associations with one another among different life-history stages, while negative associations prevailed among different tree species. Furthermore, we found that the associations between species were characterized by interspecific competition. Berman’s test results under the assumption of complete spatial randomness showed that the distribution of each dominant species was mainly affected by slope and convexity

Shrubs Should Be Valued: The Functional Traits of Lonicera fragrantissima var. lancifolia in a Qinling Huangguan Forest Dynamics Plot, China

Previous studies have focused on the functional traits of trees, while undergrowth shrubs have not received the same attention. We collected 97 shrubs from 6 habitats in 3 diameter classes to measure the functional traits of Lonicera fragrantissima var. lancifolia, which is one of the dominant species in the shrub layer of the Qinling Huangguan plot. We found that leaf thickness (LT) decreased with an increase in diameter classes. Other functional traits did not change significantly with the diameter classes. Most of the functional traits changed with the habitats, which may be influenced by topography and soil. On the whole, Lonicera fragrantissima var. lancifolia showed low variation, which indicates that its growth was stable and good. The relationships between functional traits within species was in accordance with the leaf economic spectrum. The positive correlation between soil total nitrogen (STN) and C:N verified the “nutrition luxury hypothesis”

Shrubs Should Be Valued: The Functional Traits of <i>Lonicera fragrantissima</i> var. <i>lancifolia</i> in a Qinling Huangguan Forest Dynamics Plot, China

Previous studies have focused on the functional traits of trees, while undergrowth shrubs have not received the same attention. We collected 97 shrubs from 6 habitats in 3 diameter classes to measure the functional traits of Lonicera fragrantissima var. lancifolia, which is one of the dominant species in the shrub layer of the Qinling Huangguan plot. We found that leaf thickness (LT) decreased with an increase in diameter classes. Other functional traits did not change significantly with the diameter classes. Most of the functional traits changed with the habitats, which may be influenced by topography and soil. On the whole, Lonicera fragrantissima var. lancifolia showed low variation, which indicates that its growth was stable and good. The relationships between functional traits within species was in accordance with the leaf economic spectrum. The positive correlation between soil total nitrogen (STN) and C:N verified the “nutrition luxury hypothesis”

How do mountain ecosystem services respond to changes in vegetation and climate? An evidence from the Qinling Mountains, China

Ecosystem services (ESs) have been widely used in the management and protection of regional ecosystems. Among the numerous influencing factors, climate and vegetation are important factors affecting ESs. Nevertheless, unraveling the intricate and non-linear relationship between ESs and the fluctuations in climate and fractional vegetation cover (FVC) remains an elusive task, particularly within the intricate and dynamic context of mountainous terrains. Therefore, the Qinling Mountains (QL) was selected as the study area, four major ESs (habitat quality, water yield, carbon sequestration and soil conservation) were quantified, and two key points (threshold point and critical point of high ESs supply) were determined by elastic analysis and constraint line respectively. The results showed that the influence thresholds of temperature and FVC on ESs were 13.2 °C and 57%, respectively. The results of constraint line showed that ESs is maintained at a high level when the temperature  840 mm, and the FVC > 57%. According to the threshold points and critical points of high ESs supply, sensitive areas and high ESs supply areas were divided respectively. In addition, based on the above two regional divisions, we obtained an ecosystem management planning map of the study area and put forward corresponding practical suggestions for different regions. This study satisfies the docking of the research results and practical decision-making requirements and provides a theoretical scientific basis for the restoration and sustainable management of ecological environments

Functional Traits of <i>Quercus aliena</i> var. <i>acuteserrata</i> in Qinling Huangguan Forest Dynamics Plot: The Relative Importance of Plant Size and Habitat

Variation in intraspecific functional traits is one of the important components of community variation, and has drawn the attention of researchers. Studying the variation of traits under different plant sizes and habitats helps to reveal the adaptation mechanism of plants. We explored intraspecific trait variations by focusing on the widespread species Quercus aliena var. acuteserrata in a 25 ha warm, temperate, deciduous broadleaved forest plot in the Qinling Mountains. We measured nine morphological and chemical traits for 90 individuals from different plant sizes and habitats. In addition, we evaluated the relative impact of plant size and environment on Q. aliena var. acuteserrata with multiple regression models. We found that plant size explained the most variance of traits. As plant size increased, the trees tended to have lower leaf nitrogen concentrations, lower leaf phosphorus concentrations, higher leaf carbon concentrations, higher leaf dry matter content (LDMC), and thinner leaves, indicating the transformation from rapid resource acquisition strategy to conservative resource-use strategy. Habitats could only explain the changes in chemical traits. Leaf carbon concentration was principally affected by topographical factors and was significant different among habitats. Leaf nitrogen concentration and LPC were significantly limited by soil N and P. In conclusion, shifts in size-dependent traits met the growth requirements of Q. aliena var. acutiserrata; the high tolerance traits associated with this tree species might elucidate important mechanisms for coping with changing environments

Functional Traits of Quercus aliena var. acuteserrata in Qinling Huangguan Forest Dynamics Plot: The Relative Importance of Plant Size and Habitat

Variation in intraspecific functional traits is one of the important components of community variation, and has drawn the attention of researchers. Studying the variation of traits under different plant sizes and habitats helps to reveal the adaptation mechanism of plants. We explored intraspecific trait variations by focusing on the widespread species Quercus aliena var. acuteserrata in a 25 ha warm, temperate, deciduous broadleaved forest plot in the Qinling Mountains. We measured nine morphological and chemical traits for 90 individuals from different plant sizes and habitats. In addition, we evaluated the relative impact of plant size and environment on Q. aliena var. acuteserrata with multiple regression models. We found that plant size explained the most variance of traits. As plant size increased, the trees tended to have lower leaf nitrogen concentrations, lower leaf phosphorus concentrations, higher leaf carbon concentrations, higher leaf dry matter content (LDMC), and thinner leaves, indicating the transformation from rapid resource acquisition strategy to conservative resource-use strategy. Habitats could only explain the changes in chemical traits. Leaf carbon concentration was principally affected by topographical factors and was significant different among habitats. Leaf nitrogen concentration and LPC were significantly limited by soil N and P. In conclusion, shifts in size-dependent traits met the growth requirements of Q. aliena var. acutiserrata; the high tolerance traits associated with this tree species might elucidate important mechanisms for coping with changing environments

rpoB and efp are stable candidate reference genes for quantitative real-time PCR analysis in Saccharopolyspora spinosa

Spinosad (spinosyn A and spinosyn D), the secondary metabolite produced by Saccharopolyspora spinosa, is a potent insecticide with low effects on the environment and mammals. Strategies such as metabolic engineering, mutagenesis and fermentation process optimization have been employed for its production enhancement. Quantitative real-time polymerase chain reaction(qRT-PCR) is one of the preferred methods for the evaluation of gene transcript levels, whose accuracy and sensitivity depend on the normalization using optimal reference genes. However, no single reference gene is universally appropriate for all strains under various conditions. In this study, the transcriptional stability of 35 candidate reference genes, including 23 traditionally used reference genes and 12 novel reference genes identified in S. spinosa homologous species, was analysed in S. spinosa ATCC 49460 and spinosad high-yield strain S. spinosa S3-3 under three fermentation phases. The transcriptional stability of these genes was assessed by three statistical algorithms, geNorm, NormFinder and BestKeeper. The overall rankings suggested that rpoB and efp were the most stable candidate reference genes, and they may be the most promising reference genes for further study on the measurement of expression levels of target genes involved in the biosynthetic process of spinosad

Neighbouring tree effects on leaf herbivory: Insect specialisation matters more than host plant leaf traits

Insect herbivory plays a critical role in the regulation of plant populations and community structures. Although the strength of insect herbivory varies with neighbouring tree diversity and identity, it is not clear to what extent insect guilds and leaf traits of host plants mediate the relationships, particularly in diverse natural forests. In this study, we measured leaf herbivory by chewing and mining insect herbivores in 442 saplings of nine species of deciduous trees in a warm‐temperate montane forest. We censused neighbouring trees and measured five leaf traits known to influence herbivory (i.e. specific leaf area‐SLA, thickness, carbon: nitrogen ratio‐C:N ratio, sodium‐Na and silicon‐Si content) on a subset of saplings. Only herbivory by leaf‐mining insects was influenced by the identity and diversity of neighbouring trees. Specifically, the incidence of leaf‐miners decreased with the phylogenetic diversity of neighbouring trees and increased with conspecific adult density in the vicinity of focal trees. Furthermore, leaf mining herbivory was positively correlated with the amount of Si in the leaves of focal saplings, and leaf chewing herbivory decreased with increasing C:N ratio in the leaves. In contrast to our hypothesis, the leaf traits of focal saplings did not serve as a functional link between tree diversity and insect herbivory. Synthesis : Overall, this study highlights the importance of considering the specialisation of insect herbivores in understanding the impacts of the diversity and identity of neighbouring trees on the strength of insect herbivory