[Effects of Simulated Acid Rain and Nitrogen Deposition on Soil Bacterial Community Structure and Diversity in the Masson Pine Forest].

By analyzing the effects of acid rain and nitrogen deposition on the structure and diversity of soil bacterial communities, the response mechanism of Masson pine forests to environmental stress was investigated, providing a theoretical reference basis for resource management and conservation in Tianmu Mountain National Nature Reserve. Four treatments of the simulated acid rain and nitrogen deposition were set up in 2017 to 2021 in Tianmu Mountain National Nature Reserve (pH value of 5.5 and 0 kg·(hm2·a)-1, CK; pH value of 4.5 and 30 kg·(hm2·a)-1, T1; pH value of 3.5 and 60 kg·(hm2·a)-1, T2; pH value of 2.5 and 120 kg·(hm2·a)-1, T3). The differences in soil bacterial community composition and structure among treatments and their influencing factors were analyzed by collecting soils from four treatments, using the Illumina MiSeq PE300 second-generation high-throughput sequencing platform. The results showed that acid rain and nitrogen deposition significantly reduced soil bacterial α-diversity (P<0.05) in a Masson pine forest. The Masson pine forest soils consisted of 36 phylum groups of mycota, with Acidobacteria, Proteobacteria, Actinobacteria, and Chloroflexi as the main bacterial phyla (relative abundance>1%) in the Masson pine forest soils. Flavobacterium, Nitrospira, Haliangium, Candidatus_Koribacter, Bryobacter, Occallatibacter, Acidipla, Singulisphaera, Pajaroellobacter, and Acidothermus, which showed significant changes in relative abundance under the four treatments, could be used as indicator species for changes in soil bacterial communities under acid rain and nitrogen deposition stress. Soil pH and total nitrogen were influential factors in the diversity of soil bacterial communities. As a result, acid rain and nitrogen deposition increased the potential ecological risk, and the loss of microbial diversity will change the ecosystem function as well as reduce the stability of the ecosystem.

The complete chloroplast genome sequence of Bambusa tuldoides f. swolleninternode (Poaceae: Bambuseae).

Bambusa tuldoides f. swolleninternode is an attractive ornamental bamboo species of southern China, with highly shortened and swollen at the base of internodes. In this study, the complete chloroplast genome of B. tuldoides was sequenced and reported for the first time. The complete genome size is 139,460 base pairs (bp), including a large single-copy (LSC) region of 82,996 bp, a small single-copy (SSC) region of 12,876 bp and a pair of invert repeats (IR) regions of 21,794 bp. The plastid genome contained 132 genes, including 86 protein-coding genes, 38 tRNA genes and 8 rRNA genes. The overall GC content of the genome is 39%. The phylogenetic analysis revealed that B. tuldoides is closely related to B. dolichoclada, B. pachinensis var. hirsutissima, and B. utilis, three species in Bambusa based on 16 chloroplast genomes.

[Effects of Simulated Acid Rain on Soil Fungi Diversity in the Transition Zone of Moso Bamboo and Broadleaf Forest].

Acid rain is an important phenomenon in the context of global climate change, and can strongly influence forest ecology. There have been many studies on the response of plants to acid rain. However, the effect of acid rain on soil microbial communities is still largely unknown. Studying the effects of acid rain on soil microbial community structure is of great significance for predicting the interactive effects of multiple climate factors on forest ecosystems in the future. Moso bamboo (Phyllostachys edulis) is often cultivated not only for its delicious shoots and versatile culms, but also as an important biomass resource in southern China. However, with its robust growth and strong rhizomes, Moso bamboo populations have been expanding rapidly into adjacent forests. Different perturbation regimes, including disturbance caused by simulated acid rain, can have significant effects on a soil fungal community in response to Moso bamboo invasion into native broadleaf forest. To explore the effect of acid rain on a mixed forest of Moso bamboo and broadleaf soil fungi diversity, and to understand the relationship between fungal community structure and acid rain stress, a mixed forest of Moso bamboo and broadleaf (transition forest) in Zhejiang Tianmu Mountain Nature Reserve was taken as the study site, and simulated acid rain was set at different acidity according to the acid rain component of Linan in recent years. The experiment consisted of three different treatments. Three gradients of simulated acid rain treatment[pH 2.5, 4.0, and CK (lake water)] were designed to determine the effects of simulated acid rain on soil bacterial community diversity in transition forest. Soil DNA was extracted from the soils for polymerase chain reaction amplification and high-throughput sequencing to study the effects of acid rain on the fungal communities of the mixed forest of Moso bamboo and broadleaf soil. We obtained 601 287 sequences across the three types of sampling sites. Sequences were affiliated to 13 different phyla throughout the dataset. The dominant fungal groups were Ascomycota, Basidiomycota, Mortierellomycota, and Mucoromycota. Simulated acid significantly increased the number of operational taxonomic units, Ace index, and Chao1 index of fungal communities (P<0.05). The results of principal coordinates analysis (PCoA) also revealed that acid rain significantly modified the structure. The changes in soil fungal community structure were mainly related to the abundance of genera Bifiguratu, Geminibasidium, Purpureocillium, and Oidiodendron, which could be utilized as indicator species to determine changes in soil fungal community structure. Redundancy and correlation analysis showed that changes in basic physicochemical factors in the soil, such as soil pH and total nitrogen, can significantly influence the composition of the fungal community (P<0.05).

Soil respiration following Chinese fir plantation clear-cut: Comparison of two forest regeneration approaches.

In response to ecological problems originating from long-term pure coniferous plantations, clear-cut, species mixing, and other forest regeneration practices have been proposed to develop into mixed conifer-broadleaved stand. However, the dynamic effects of these forest regeneration approaches on soil respiration have not been well investigated. In this study, we compared soil respiration for three continuous years from two completely different forest regeneration approaches in clear-cut areas with uncut as control in pure Chinese fir plantations in subtropical China. These two approaches were, I: ground vegetation cut and removal of slash in the first year followed by the second year's ground vegetation cut but retained on the site, and II: ground vegetation cut and slash burning in first year followed by second year's soil ploughing, replanting, ground vegetation cut but retained on the site. Soil respiration changed obviously as forest practices were applied in the both regeneration sites. Mean respiration rate for the first year was lower for the treatments of Approach I and Approach II than uncut control (-15.0% and -26.8%), indicating that soil respiration decreased with ground vegetation removal or slash burning after clear-cut. In contrast to the first year, mean respiration rate was higher for the treatments of Approach I and Approach II treatments than uncut control (+12.8% and +32.2% in the second year, 16.3% and 30.8% in the third year), indicating ground vegetation cut with retaining residuals or soil ploughing significantly increased soil respiration. These drastically changes were mainly due to the rapid growth of understory vegetation and new seedlings, the difference of species composition, the availability of respired organic matter and the intensity of soil disturbance induced by different specific forest practices of two regeneration approaches over time. In addition, the different species mixing and forest management practices enhance the uncertainty linked to the analyses of soil respiration. Our results suggest that high intensity forest regeneration approach has a higher soil CO2 emission and lower production of biomass. Forest regeneration approaches could decrease the temperature sensitivity of soil respiration. Our findings provide new insights into the effects of forest practices on soil CO2 flux following clear-cut.

Effects of forest regeneration practices on the flux of soil CO2 after clear-cutting in subtropical China.

Reforestation after clear-cutting is used to facilitate rapid establishment of new stands. However, reforestation may cause additional soil disturbance by affecting soil temperature and moisture, thus potentially influencing soil respiration. Our aim was to compare the effects of different reforestation methods on soil CO2 flux after clear-cutting in a Chinese fir plantation in subtropical China: uncut (UC), clear-cut followed by coppicing regeneration without soil preparation (CC), clear-cut followed by coppicing regeneration and reforestation with soil preparation, tending in pits and replanting (CCRP), and clear-cut followed by coppicing regeneration and reforestation with overall soil preparation, tending and replanting (CCRO). Clear-cutting significantly increased the mean soil temperature and decreased the mean soil moisture. Compared to UC, CO2 fluxes were 19.19, 37.49 and 55.93 mg m-2 h-1 higher in CC, CCRP and CCRO, respectively (P < 0.05). Differences in CO2 fluxes were mainly attributed to changes in soil temperature, litter mass and the mixing of organic matter with mineral soil. The results suggest that, when compared to coppicing regeneration, reforestation practices result in additional CO2 released, and that regarding the CO2 emissions, soil preparation and tending in pits is a better choice than overall soil preparation and tending.

Can native clonal moso bamboo encroach on adjacent natural forest without human intervention?

Native species are generally thought not to encroach on adjacent natural forest without human intervention. However, the phenomenon that native moso bamboo may encroach on surrounding natural forests by itself occurred in China. To certificate this encroaching process, we employed the transition front approach to monitor the native moso bamboo population dynamics in native Chinese fir and evergreen broadleaved forest bordering moso bamboo forest in Tianmu Mountain Nature Reserve during the period between 2005 and 2014. The results showed that the bamboo front moved toward the Chinese fir/evergreen broadleaved stand with the new bamboo produced yearly. Moso bamboo encroached at a rate of 1.28 m yr(-1) in Chinese fir forest and 1.04 m yr(-1) in evergreen broadleaved forest, and produced 533/437 new culms hm(-2) yr(-1) in the encroaching natural Chinese fir/evergreen broadleaved forest. Moso bamboo coverage was increasing while adjacent natural forest area decreasing continuously. These results indicate that native moso bamboo was encroaching adjacent natural forest gradually without human intervention. It should be considered to try to create a management regime that humans could selectively remove culms to decrease encroachment.

Effects of moso bamboo encroachment into native, broad-leaved forests on soil carbon and nitrogen pools.

Across southern China, Moso bamboo has been encroaching on most neighboring secondary broad-leaved forests and/or coniferous plantations, leading to the land cover changes that alter abiotic and biotic conditions. Little is known about how this conversion alters soil carbon (C) and nitrogen (N). We selected three sites, each with three plots arrayed along the bamboo encroachment pathway: moso bamboo forest (BF); transition zone, mixed forest plots (MF); and broad-leaved forest (BLF), and examined how bamboo encroachment affects soil organic C (SOC), soil total N, microbial biomass C (MBC), microbial biomass N (MBN), water-soluble organic C (WSOC), and water-soluble organic N (WSON) in three forests. Over nine years, moso bamboo encroachment leads to a decrease in SOC and total soil N, an increase in MBC and WSOC, and a decrease in MBN and WSON. Changes in soil C and N occurred mainly in the topsoil. We conclude that moso bamboo encroachment on broadleaved forest not only substantially altered soil C and N pools, but also changed the distribution pattern of C and N in the studied forest soils. Continued bamboo encroachment into evergreen broadleaved forests seems likely to lead to net CO2 emissions to the atmosphere as ecosystem C stocks decline.

Cadmium accumulation and tolerance of Lagerstroemia indica and Lagerstroemia fauriei (Lythraceae) seedlings for phytoremediation applications.

Contamination by heavy metals is one of the most serious environmental problems generated from human activities. Because phytoremediation utilizes plants to uptake contaminants, it could potentially be used to remediate metal-contaminated areas. A pot culture experiment with four levels of cadmium (Cd) (0, 20, 40, and 80 mg of Cd/kg dry soil) was conducted to investigate Cd accumulation and tolerance of roots, shoots, and leaves of Lagerstroemia indica and Lagerstroemia fauriei as well as their potential for phytoremediation. Experimental results indicated that Cd inhibited seedling growth only at the higher Cd exposure concentration (40 and 80 mg/kg). The tolerance index revealed that on average L. indica is more tolerant of Cd than L. fauriei. Moreover, plants in the experiment accumulated Cd differentially. In comparisons between L. indica and L. fauriei, the leaves of the former had higher concentrations of Cd, while the roots of latter had higher concentrations of Cd. Furthermore, the roots, shoots, and leaves had very high bioaccumulation factors that markedly exceeded 1.0 (exceptional only in shoots of 80 mg/kg for L. fauriei), indicating that the seedlings extracted Cd from the soil. The leaves' translocation factor of L. indica was greater than 1.0, being significantly higher than that of L. fauriei. Chlorophyll a, Chlorophyll b and total declined in both species significantly as Cd concentrations exceeded 40 mg/kg in the soil. In contrast, lipid peroxidation and proline content was found to increase with increasing Cd concentration. From the assessments of biomass production, Cd tolerance and uptake L. indica and L. fauriei could stand as excellent species for remediating Cd-contaminated soils.

[Instant response of individual size inequality indices to thinning regimes in plantation].

Four kinds of thinning treatments were designed including thinning from below, thinning from above, mechanical thinning and crop tree release with the same thinning intensity on the 14-year-old pure Cunninghamia laceolata and Pinus massoniana plantations in Guangxi, and 6 kinds of size inequality indices were applied including stand deviation, variation coefficient, skewness, Gini coefficient, Kuznetz coefficient and Lorenz asymmetry coefficient to evaluate the change of individual volume inequality after the 4 kinds of thinning regimes applied. The results showed that stand deviation, variation coefficient, Gini coefficient and Kuznetz coefficient decreased and skewness increased after thinning from below or above compared with before thinning, while after crop tree release these four indices increased and skewness was uncertain. Lorenz asymmetry coefficient increased after thinning from below while it decreased after thinning from above or crop tree release compared with before thinning. There was no distinct rule for the 6 kinds of size inequality indices after mechanical thinning. The size inequality increased after crop tree release while it decreased af- ter thinning from above or below. The study suggested that Lorenz curve, Gini coefficient and Lorenz asymmetry coefficient could be used to compare the size inequality statically and dynamically among different stands, and could be discriminated the difference of size inequality caused by the different thinning regimes. Lorenz asymmetry coefficient even could be applied to tell the size inequality was mainly from the larger or smaller individuals. Crop tree release method in close-to-nature management could lessen the competition pressures of crop trees and increase the size inequality of the stand effectively which would be helpful to maintain the dominant position of crop trees.

[Allelopathic potential of Phyllostachys edulis on two dominant tree species of evergreen broad-leaved forest in its invasive process].

In order to explore the influence of Phyllostachys edulis invasion on the surrounding forest environment,the effects of aqueous extracts from P. edulis on two dominant species (Castanopsis sclerophylla and Cyclobalanopsis glaunca)in southern China were assessed by germination bioassays. The results showed that seed germination effects depended on the concentration of aqueous extracts and the extract sources. The highest extract concentration showed significant inhibitory effects on seed germination percentage, which was 82. 3% -102. 2% of control for C. sclerophylla and 80% -90. 9% of control for C. glauca, while in the treatment with lowest extract concentration the values were 101.7% - 107.6% of control for C. sclerophylla and 94.9% - 109. 1% of control for C. glauca, respectively. The extracts had inhibitory effects on the germination speed of both species (P < 0.05) , except that no effects on C. sclerophylla were observed in the low concentration treatment. Extracts at the highest concentration reduced the root activity of C. sclerophylla by 41. 1% -62. 4% (P <0.05). There were obvious different effects among the treatments with different extract sources. Seed germination percentage was the lowest in root extract treatments. There was no obvious difference for shoot height of C. sclerophylla in different treatments(P >0.05) , while there was significant difference for C. glauca, its shoot height was higher in the leaf, root, and litter extracts treatments than in the soil extracts treatments. P. edulis possesses allelopathic potential that could possibly facilitate its invasion and monoculture formation, and does harm to the surrounding forest environment.

[Effects of UV-B radiation on the decomposition of Cunninghamia lanceolata leaf litter].

A litterbag experiment was conducted to study the decomposition of Cunninghamia lanceolata leaf litter under ambient and reduced UV-B radiation (22.1% below ambient). Comparing with ambient treatment, the reduced treatment decreased the decomposition rate of C. lanceolata leaf litter by 69.6% (P<0.001), making the relative contents of nitrogen (N), phosphorus (P), and lignin in the litter increased by 150%, 83.3%, and 13.8%, respectively, and the release of potassium (K) and carbon (C) slowed down. In the process of litter decomposition, photo-degradation of lignin didn't play crucial role. The results suggested that UV-B radiation could accelerate the decomposition rate of C. lanceolata leaf litter, promote the release of N, P, K, and C from it, and increase the nutrients turnover rate in litter layer as well as the carbon flux on the ground, giving potential effects on the function of C. lanceolata forest as a carbon source or sink in humid subtropical China.

[Effects of nitrogen forms on nutrient uptake and growth of trees].

Forest tree species take up both NH4(+)-N and NO3(-)-N forms of nitrogen (N) during their growth. However, the effects of N form on nutrition uptake and tree growth are different due to the different N forms. Generally, trees show preference to N source, and most conifers prefer to NH4(+)-N while the preference to N form of broadleaved trees is unclear. The preference may be correlated with the pH value of the site on which the trees grown. The trees grown on acid soil generally appear preference to NH4(+)-N while trees grown on litmusless or alkaline soil prefer to NO3(-)-N. Fungus also can alter the tree uptake characteristic to NH4(+)-N and NO3(-)-N. In some species, the NO3(-)-N uptake capacity increased remarkably while uptake capacity of NH4(+)-N keep consistent when fungus were inoculated. NH4(+)-N and NO3(-)-N have different effects on other nutrient ions uptake because of the difference charge of NH4(+)-N and NO3(-)-N. In general, NH4(+)-N accelerates the anion absorption while inhibits cation absorption. The effects of nitrogen forms on nutrition uptake are related with not only the charge of NH4(+)-N and NO3(-)-N, but also the restrain effects among other ions. Sometimes, NH4(+)-N inhibits NO3(-)-N uptake, but the mechanism is not very clear now. The form of which nitrogen is taken up by trees will induce the change of rhizospheric pH value. Uptake of NH4(+)-N results in the decrease of rhizospheric pH value. Contrary, uptake of NO3(-)-N will cause the increase of rhizospheric pH value. The change of rhizospheric pH value will affect nutrient availability and thus affect nutrition uptake and utilization by trees. Trees grow differently after NH4(+)-N and NO3(-)-N uptake. When supplied with NH4(+)-N, some confers that prefer to NH4(+)-N grow better while a few ammonium-preference conifers hardly show the better growth. Nevertheless, most plants grow better when both forms of N supplied simultaneously than either of N source supplied alone. For few similar studies were carried out with tree species, it needs to do more researches.