Qingkui Wang

Leaf litter decomposition in the pure and mixed plantations of Cunninghamia lanceolata and Michelia macclurei in subtropical China

Leaf litter decomposition of Cunninghamia lanceolata, Michelia macclurei, and their mixture in the corresponding stands in subtropical China was studied using the litterbag method. The objective was to assess the influence of native evergreen broadleaved species on leaf litter decomposition. The hypotheses were: (1) M. macclurei leaf litter with lower C/N ratio and higher initial N concentration decomposed faster than C. lanceolata litter, (2) decomposition rates in litter mixtures could be predicted from single-species decay rates, and (3) litters decomposed more rapidly at the site that contained the same species as in the litterbag. The mass loss of leaf litter was positively correlated with initial N concentration and negatively correlated with C/N ratio. The decomposition rate of M. macclurei leaf litter was significantly higher than that of C. lanceolata needle litter in the pure C. lanceolata stand. Contrary to what would be predicted, the litter mixture decomposed more slowly than expected based on the results from component species decomposing alone. There was no significant difference in litter decomposition rate between different habitats.

Biogeographic Distribution Patterns of Bacteria in Typical Chinese Forest Soils

Microbes are widely distributed in soils and play a very important role in nutrient cycling and ecosystem services. To understand the biogeographic distribution of forest soil bacteria, we collected 115 soil samples in typical forest ecosystems across eastern China to investigate their bacterial community compositions using Illumina MiSeq high throughput sequencing based on 16S rRNA. We obtained 4,667,656 sequences totally and more than 70% of these sequences were classified into five dominant groups, i.e., Actinobacteria, Acidobacteria, Alphaproteobacteria, Verrucomicrobia, and Planctomycetes (relative abundance >5%). The bacterial diversity showed a parabola shape along latitude and the maximum diversity appeared at latitudes between 33.50°N and 40°N, an area characterized by warm-temperate zones and moderate temperature, neutral soil pH and high substrate availability (soil C and N) from dominant deciduous broad-leaved forests. Pairwise dissimilarity matrix in bacterial community composition showed that bacterial community structure had regional similarity and the latitude of 30°N could be used as the dividing line between southern and northern forest soils. Soil properties and climate conditions (MAT and MAP) greatly accounted for the differences in the soil bacterial structure. Among all soil parameters determined, soil pH predominantly affected the diversity and composition of the bacterial community, and soil pH = 5 probably could be used as a threshold below which soil bacterial diversity might decline and soil bacterial community structure might change significantly. Moreover, soil exchangeable cations, especially Ca2+ (ECa2+) and some other soil variables were also closely related to bacterial community structure. The selected environmental variables (21.11%) explained more of the bacterial community variation than geographic distance (15.88%), indicating that the edaphic properties and environmental factors played a more important role than geographic dispersal limitation in determining the bacterial community structure in Chinese forest soils.

Carbon Mineralization of Soils from Native Evergreen Broadleaf Forest and Three Plantations in Mid-subtropic China

Mineralization of soil organic carbon (C) plays a key role in supplying nutrient elements essential to plant growth. Changes of C mineralization of mixed stands of Chinese fir and Michelia macclurei (a broadleaf tree), pure M. macclurei stands, and pure Chinese fir (Cunninghamia lanceolata) stands established in 1983 after clear‐felling of a first‐generation Chinese fir forest were analyzed in Huitong, Hunan Province, China, and compared with those of a stand of native secondary evergreen broadleaf forest (NBF). The results showed that NBF soil had the greatest C mineralization. Mixture of Chinese fir and M. macclurei had no effect on total soil organic C in comparison with pure Chinese fir plantation, but significantly increased C mineralization from soils was detected in this study. This positive influence on C mineralization could be explained by the increase of soil labile C pools and soil microbial biomass and activity. From the analysis of C mineralization, soil microbial properties, and labile organic C, mixtures of broadleaf and Chinese fir can be considered to be an effective sustainable management model for a Chinese fir plantation. Given strong correlations with microbiological and biochemical characteristics of soils and an easier process of determination, hot water extraction, hot water–extractable C (HWC) could be used as an integrated measure of forest soil quality in mid‐subtropics.

Soil microbial properties and nutrients in pure and mixed Chinese fir plantations

An investigation on soil organic carbon, total N and P, NO3−-N, available P, microbial biomass C, N and P, basal respiration and metabolic quotients (qCO2) was conducted to compare differences in soil microbial properties and nutrients between 15-year-old pure Chinese fir (Cunninghamia lanceolata) and two mixed Chinese fir plantations (mixed plantations with Alnus cremastogyne, mixed plantations with Kalopanax septemlobus) at Huitong Experimental Station of Forest Ecology (26°45′N latitude and 109°30′E longitude), Chinese Academy of Sciences in May, 2005. Results showed that the concentrations of soil organic carbon, total N, NO3−-N, total P and available P in mixed plantations were higher than that in pure plantation. Soil microbial biomass N in two mixed plantations was averagely higher 69% and 61% than that in pure plantation at the 0–10 cm and 10–20 cm soil depth, respectively. Soil microbial biomass C, P and basal respiration in mixed plantations were higher 11%, 14% and 4% at the 0–10 cm soil depth and 6%, 3% and 3% at the 10–20 cm soil depth compared with pure plantation. However, soil microbial C: N ratio and qCO2 were averagely lower 34% and 4% in mixed plantations than pure plantation. Additionally, there was a closer relation between soil microbial biomass and soil nutrients than between basal respiration, microbial C: N ratio and qCO2 and soil nutrients. In conclusion, introduction of broad-leaved tree species into pure coniferous plantation improved soil microbial properties and soil fertility, and can be helpful to restore degraded forest soil.

Microbial Biomass in Subtropical Forest Soils: Effect of Conversion of Natural Secondary broad-leaved Forest to Cunninghamia lanceolata Plantation

Conversion of natural secondary broad-leaved forest to Cunninghamia lanceolata plantation is a common management practice in subtropical China. In this study, we compared soil physico-chemical properties, microbial biomass in one natural secondary broad-leaved forest and two C. lanceolata plantation sites to estimate the effects of forest conversion on soil microbial biomass at the Huitong Experimental Station of Forestry Ecology, Chinese Academy of Sciences. Concentrations of soil organic carbon, total nitrogen, NH4+-N and microbial biomass carbon and nitrogen were much lower under C. lanceolata plantations as compared to natural secondary broad-leaved forest. Soil microbial biomass C in the first and second rotation of C. lanceolata plantations was only 53%, 46% of that in natural secondary broad-leaved forest, and microbial biomass N was 97% and 79%, respectively. The contribution of microbial biomass C to soil organic C was also lower in the plantation sites. However, the contribution of microbial N to total nitrogen and NH4+-N was greater in the C. lanceolata plantation sites. Therefore, conversion of natural secondary broad-leaved forest to C. lanceolata plantation and continuous planting of C. lanceolata led to the decline in soil microbial biomass and the degradation of forest soil in subtropical China.

Forest conversion induces seasonal variation in microbial β-diversity: Seasonal shifts in ecological processes

World-wide conversion of natural forests to other land uses has profound effects on soil microbial communities. However, how soil microbial β-diversity responds to land-use change and its driving mechanisms remains poorly understood. In this study, therefore, we examined the effect of forest conversion from native broad-leaved forest to coniferous plantation on soil microbial β-diversity and its underlying mechanisms in both summer and winter in subtropical China. Microbial communities increasingly differed in structure as geographical distance between them increased, and the slope of the relationship among distances and community similarity differed among forest covers. In general, as with microbial β-diversity, slopes also shifted across seasons. Finally, null deviations of bacterial and fungal communities were lower in coniferous plantation and presented opposing seasonal variations with greater influences of deterministic processes in summer for soil fungi and in winter for soil bacteria. Integrating previous frameworks with our β-null model results, we propose a conceptual model to link microbial secondary succession to stochastic/deterministic shifts in forest ecosystems. Overall, forest conversion induced significant increases in stochastic processes in both bacterial and fungal community assemblies. Therefore, our results highlight the importance of spatiotemporal scales to assess the influence of land-use change on microbial β-diversity.

Nitrogen Addition Altered the Effect of Belowground C Allocation on Soil Respiration in a Subtropical Forest.

The availabilities of carbon (C) and nitrogen (N) in soil play an important role in soil carbon dioxide (CO2) emission. However, the variation in the soil respiration (Rs) and response of microbial community to the combined changes in belowground C and N inputs in forest ecosystems are not yet fully understood. Stem girdling and N addition were performed in this study to evaluate the effects of C supply and N availability on Rs and soil microbial community in a subtropical forest. The trees were girdled on 1 July 2012. Rs was monitored from July 2012 to November 2013, and soil microbial community composition was also examined by phospholipid fatty acids (PLFAs) 1 year after girdling. Results showed that Rs decreased by 40.5% with girdling alone, but N addition only did not change Rs. Interestingly, Rs decreased by 62.7% under the girdling with N addition treatment. The reducing effect of girdling and N addition on Rs differed between dormant and growing seasons. Girdling alone reduced Rs by 33.9% in the dormant season and 54.8% in the growing season compared with the control. By contrast, girdling with N addition decreased Rs by 59.5% in the dormant season and 65.4% in the growing season. Girdling and N addition significantly decreased the total and bacterial PLFAs. Moreover, the effect of N addition was greater than girdling. Both girdling and N addition treatments separated the microbial groups on the basis of the first principal component through principal component analysis compared with control. This indicated that girdling and N addition changed the soil microbial community composition. However, the effect of girdling with N addition treatment separated the microbial groups on the basis of the second principal component compared to N addition treatment, which suggested N addition altered the effect of girdling on soil microbial community composition. These results suggest that the increase in soil N availability by N deposition alters the effect of belowground C allocation on the decomposition of soil organic matter by altering the composition of the soil microbial community.

Litter input decreased the response of soil organic matter decomposition to warming in two subtropical forest soils.

Interaction effect of temperature and litter input on SOM decomposition is poor understood, restricting accurate prediction of the dynamics and stocks of soil organic carbon under global warming. To address this knowledge gap, we conducted an incubation experiment by adding 13C labeled leaf-litter into a coniferous forest (CF) soil and a broadleaved forest (BF) soil. In this experiment, response of the temperature sensitivity (Q10) of SOM decomposition to the increase in litter input was investigated. The temperature dependences of priming effect (PE) and soil microbial community were analyzed. The Q10 for CF soil significantly decreased from 2.41 in no-litter treatment to 2.05 in litter-added treatment and for BF soil from 2.14 to 1.82, suggesting that litter addition decreases the Q10. PE in the CF soil was 24.9% at 20 °C and 6.2% at 30 °C, and in the BF soil the PE was 8.8% at 20 °C and −7.0% at 30 °C, suggesting that PE decreases with increasing temperature. Relative PE was positively related to the concentrations of Gram-negative bacterial and fungal PLFAs. This study moves a step forward in understanding warming effect on forest carbon cycling by highlighting interaction effect of litter input and warming on soil carbon cycling.

Contrasting dynamics and trait controls in first-order root compared with leaf litter decomposition

Significance Decomposition of plant roots and associated fungal mutualists is a dominant process in ecosystem carbon cycles, yet is woefully understudied compared with decomposition of leaf litter, particularly for the finest order roots that have the highest turnover. In a field experiment, we compared decomposition of the finest, most distal roots and leaf litter among 35 cooccurring temperate forest species over 6 years. We found that decomposition rates of root tips were considerably lower than those of leaf litter and were controlled by nonlignin carbon compounds in contrast to lignin:nitrogen ratio control over leaf litter decomposition. Our study suggests that models of terrestrial carbon cycling based on aboveground patterns are inadequate to describe decomposition of the finest plant roots. Decomposition is a key component of the global carbon (C) cycle, yet current ecosystem C models do not adequately represent the contributions of plant roots and their mycorrhizae to this process. The understanding of decomposition dynamics and their control by traits is particularly limited for the most distal first-order roots. Here we followed decomposition of first-order roots and leaf litter from 35 woody plant species differing in mycorrhizal type over 6 years in a Chinese temperate forest. First-order roots decomposed more slowly (k = 0.11 ± 0.01 years−1) than did leaf litter (0.35 ± 0.02 years−1), losing only 35% of initial mass on average after 6 years of exposure in the field. In contrast to leaf litter, nonlignin root C chemistry (nonstructural carbohydrates, polyphenols) accounted for 82% of the large interspecific variation in first-order root decomposition. Leaf litter from ectomycorrhizal (EM) species decomposed more slowly than that from arbuscular mycorrhizal (AM) species, whereas first-order roots of EM species switched, after 2 years, from having slower to faster decomposition compared with those from AM species. The fundamentally different dynamics and control mechanisms of first-order root decomposition compared with those of leaf litter challenge current ecosystem C models, the recently suggested dichotomy between EM and AM plants, and the idea that common traits can predict decomposition across roots and leaves. Aspects of C chemistry unrelated to lignin or nitrogen, and not presently considered in decomposition models, controlled first-order root decomposition; thus, current paradigms of ecosystem C dynamics and model parameterization require revision.

Differences in root-associated bacterial communities among fine root branching orders of poplar ( Populus × euramericana (Dode) Guinier.)

Background and AimsRoot branching leads to morphological and functional heterogeneity of fine roots. However, the structure of soil microbiota associated with root branching orders has never been investigated. Deep insights into rhizosphere microbial community could provide a better understanding of the plant-microbe relationship.MethodsFine roots of poplar (Populus × euramericana (Dode) Guinier.) were sampled and sorted into three groups according to their branching orders. Scanning electron microscopy (SEM) was used to observe the surface features of different orders of fine roots. Illumina MiSeq was employed to analyze the bacterial community structure of soil compartments from different root orders (i.e., R1, R2, and R3) and bulk soil compartment (NR).ResultsSEM showed that the first-order root with smaller diameter had dense coverage of vigorous root hairs, whereas higher order roots with larger diameter had sloughed-off cortical tissues on the rhizoplane. The diversity of bacterial communities was higher in the R1 and R2 compartment than in R3 or NR. There were 80 genera with a relative abundance above 0.05% in soils. Ternary plot revealed that bacterial genera were significantly enriched in R1 than in R2 or R3. Redundant analysis (RDA) showed that 12 dominant bacterial genera with a relative abundance over 1% were significantly correlated with P and NH4+-N content of soils.ConclusionsRoot orders could influence the inhabitation of bacterial communities. The core groups of bacterial communities inhabiting the rhizosphere were correlated with soil nutrients. The root order-dependent interactions of plant-microbe provided a new model about the association between roots and soils.