Aims The emergence and application of ecosystem process models have provided useful tools for studying carbon and water balances of terrestrial ecosystems at large spatiotemporal scales, but the accuracy of model simulations is affected by the parameterization of key variables among many factors. Sensitivity analysis is commonly used to screen the critical parameters that have predominant influences on model simulations. The objective of this study was to identify the critical ecophysiological parameters in Biome-BGC model in simulating annual net primary productivity (NPP) and evapotranspiration (ET) of broadleaved-Korean pine forests in Northeast China.

Methods We simulated carbon and water fluxes of broadleaved-Korean pine forests with the Biome-BGC (version 4.2) at a daily time step based on site- and species-specific parameters. Daily meteorological data for the period 1958-2015 was obtained from the China Meteorological Administration. Initialization parameters such as geographical position, soil depth, and soil texture of the site were obtained from field measurements. Among the 43 ecophysiological parameters represented in the model, 30 were derived either from field measurements or from published data for the study sites in literature, and the default values were used for 13 of the parameters. The modeled forest NPP was compared with the tree-ring width index to test the model’s ability to simulate the inter-annual variations in forest productivity. The modeled NPP and ET were also compared with existing remote sensing products for the period 2000-2014 for validation purpose. Sensitivity analysis was conducted using a variance-based sensitivity analysis method—Extended Fourier Amplitude Sensitivity Test (EFAST) to acquire the first order and total order sensitivity index of the parameters.

Important findings Our locally parameterized Biome-BGC model well simulated the carbon and water fluxes of the broadleaved-Korean pine forests. The uncertainty of simulated NPP is higher for Korean pine trees than for broad-leaved trees, while that of ET was small for both tree types. Both NPP and ET of broad-leaved trees were generally less sensitive to ecophysiological parameters than Korean pine. Leaf carbon to nitrogen ratio, fine root carbon to nitrogen ratio, specific leaf area (SLA), and water interception coef?cient were among the highly sensitive parameters affecting the modeled NPP; while fine root carbon to new leaf carbon allocation, new stem carbon to new leaf carbon allocation and SLA were the highly sensitive parameters influencing ET. In addition, fraction of leaf N in Rubisco, leaf and fine root turnover, ratio of all sided to projected leaf area are also critical parameters affecting the output of Biome-BGC simulations. The degree of sensitivity of the critical parameters varied with species and sites, highlighting the need to adopt local parametrization of Biome-BGC model in simulating regional forest carbon and water fluxes. For other non-sensitive parameters, model default value can be readily used.

Aims Spatial segregations between male and female populations of dioecious plants has been increasingly reported in recent years. However, the drivers underlying these segregations have not been fully discussed. Here, we explored the factors driving the spatial segregation between male and female populations of Populus cathayanadistributed in Xiaowutai Mountains of Hebei Province, China.

Methods The male and female P. cathayana trees with diameter at breast height (DBH) larger than 9 cm (representing individuals with sexual maturity) were investigated and the soil physical and chemical properties of each individual were analyzed. The methods of average nearest neighbor index, kernel density estimation and analysis of variance (ANOVA) were employed to analyze the aggregation degree, population density and distribution pattern of male and female P. cathayana populations and their relationships with distance from the river, altitude and soil properties.

Important findings Firstly, P. cathayanapopulation was distributed along the Jinhegou River in a long and narrow belt, with the largest number of individuals and the highest density in the middle altitude area. Secondly, both the number and density of female and male trees increased first and then decreased with the increase of altitude, whereas the change of average DBH was opposite. Thirdly, altitude had a significant effect on sex ratio. The sex ratio was female biased in the low altitude area (1 300-1 400 m), male biased in middle-low altitude areas (1 400-1 500 m), and close to 1:1 in other areas. Fourthly, with the increase of distance from the river, the number, density and average DBH of females or males gradually decreased. Moreover, the content of organic matter and total nitrogen in the dominant distribution area of female trees was significantly higher than that of males. Lastly, because the variation of altitude and distance from the river changed soil physical and chemical properties and growth environment of P. cathayana trees in some areas, the sex ratio was biased. These results indicated that the spatial distribution, dynamic variation and sex ratio of male and female P. cathayana populations were greatly affected by altitude, distance from the river and soil physical and chemical properties. Because of the differences in resource demand and environmental adaptability between male and female populations, the sex ratio will be biased in some area.

Aims Leaf carbon (C), nitrogen (N), and phosphorus (P) concentrations and their stoichiometry can provide a basis for plant nutrient status and element limitation. Our objective was to explore variations of leaf C:N:P stoichiometry in plants of different growth forms.

Methods We analyzed leaf C, N, and P concentrations in three graminoids (Eriophorum vaginatum, Carex globularis, Deyeuxia angustifolia), five deciduous shrubs (Betula fruticosa, Salix myrtilloides, Salix rosmarinifolia, Vaccinium vitis-idaea, Vaccinium uliginosum), and three evergreen shrubs (Ledum palustre, Chamaedaphne calyculata, Rhododendron capitatum) across 18 peatland sites in the Da Hinggan Ling, northeastern China.

Important findings (1) Leaf C, N, and P concentrations were higher, and the leaf C:N, C:P, and N:P values were lower, in deciduous and evergreen shrubs than in graminoids, indicating that plants of different growth forms had different nutrient utilization strategies. Shrubs had higher C, N and P storage and lower N and P use efficiency than graminoids. (2) Leaf N:P values in Deyeuxia angustifolia and R. capitatum were less than 10, and their leaf N concentrations were lower than the global mean leaf N concentration, indicating that those species were limited by N more than other plants. (3) The sampling sites explained 12.8%-40.8% of the variations in leaf C, N, and P stoichiometry, and plant species explained 9.3%-25.5%. (4) Graminoids had greater inter-site coefficient of variance (CV) values in leaf C, N, and P variables than deciduous and evergreen shrubs, indicating greater sensitive to site factors. (4) The inter-species CV values in leaf N were greater in graminoids than in deciduous and evergreen shrubs, and the inter-species CV values in leaf P were greater in deciduous shrubs than in graminoids and evergreen shrubs, indicating greater physiological differentiation in N and P use strategies in graminoids and deciduous shrubs than in evergreen shrubs.

Aims Cerasus dielsianais a wild cherry species endemic to the subtropical forest of China, and was regarded as a promising ornamental resource. Our objectives were to determine the leaf phenotypic variation, adaptation and patterns in eight natural C. dielsiana populations.

Methods We analyzed eleven leaf phenotypic traits from five provinces of China in eight natural populations of C. dielsianaby using multiple comparisons, nested analysis of variance, correlation analysis, principal component analysis (PCA), principal coordinate analysis (PCoA) and unweighted pair-group method with arithmetic mean (UPGMA) cluster analysis.

Important findings Results showed that 1) Rich leaf phenotypic variation existed among and within populations, and the average coefficient of variation (CV) was 22.44%, the maximum and the minimum were leaf area (CV = 50.83%) and primary lateral veins (CV = 7.96%), respectively. The mean differentiation coefficient (V_st) for all traits was 30.78%, and the variation within populations (51.55%) was higher than that among populations (22.55%). 2) The principal component analysis showed that the cumulative contribution rate of the first three main components of variation from leaf phenotypic traits of C. dielsiana made a major contribution reached to 92.400%, and can be comprehensively summarized and sorted as “size traits” (73.242%) and “shape traits” (19.158%). 3) Leaf width (r = -0.641), leaf area (r = -0.658) and primary lateral veins (r = 0.659) showed significant negative or positive correlation with longitude, and the temperature seasonality and precipitation of wettest quarter were showed more influence on leaf phenotype variation. 4) The eight natural populations of C. dielsiana could be divided into four groups according to principal coordinate analysis (PCA) and UPGMA cluster analysis. To sum up, leaf phenotypic variation in C. dielsiana is abundant, with a certain of continuity in quantity, and “size trait” is the main source of inter-trait variation. The mean differentiation coefficient at a moderate level, the phenotypic variation within populations was the main source of leaf traits variation. The results of phenotypic differentiation among populations were found to be consistent with the geographical location, and presented a gradient variation pattern dominated by longitude geographically. Meanwhile, the “climate variability” and “leaf-expansion period” are the main climatic factors that drive leaf phenotypic variation. We speculate the phenomena results from a long evolutionary adaptation of C. dielsiana to the subtropical monsoon climate.

Aims Accurate simulation of canopy stomatal conductance (G_S) is quite important for the assessment of regional evapotranspiration.

Methods In this study, two planted broad-leaved tree species, Eucalyptus urophylla (exotic species) and Schima superba (native species), were chosen to estimate their G_S with two different methods of K?stner (G_S1) and inversed Penman-Monteith equation (G_S2). The effect of environmental factors on canopy decoupling coefficient (Ω) was evaluated before they were adopted to assess the reasonability of G_Ssimulated by the two methods.

Important findings Results showed that the G_S of the two tree species was well coupled with meteorological conditions (Ω = 0.10 ± 0.03 for E. urophylla and 0.17 ± 0.03 for S. superba). Principal component analysis showed that photosynthetically active radiation (PAR) and vapor pressure deficit (D) significantly dominated the variations of Ω, while the effect of wind speed (u) was very weak. Multivariate correlation analysis also found weak relations between those environmental factors and Ω. Boundary line analysis revealed that the increase of D and PAR would eventually force Ω approaching a constant value as determined by tree species (S. superba ≈ 0.20, E. urophylla ≈ 0.05), while Ω decreases exponentially with the increase of u. Compared with S. superba, E. urophylla has higher G_S. The annual averages G_S2 of E. urophylla and S. superba were (33.42 ± 9.37) mmol·m^-2·s^-1 and (23.40 ± 2.03) mmol·m^-2·s^-1, respectively. Linear fitting showed that the G_S2/G_S1 ratio of E. urophylla and S. superba was 0.92 (R² ≈ 0.70) and 0.98 (R² ≈ 0.76), respectively, implying the overestimated canopy stomatal conductance for G_S1 (p < 0.01). In addition, the ratio of the sensitivity of canopy stomatal conductance to vapor pressure deficit to stomatal conductance at D = 1 kPa (G_Siref) for G_S1 and G_S2 is closely related to Ω. Based on the estimation, G_S1 was relatively reliable when Ω = 0.05-0.15 (83.1% of all the data) and 0.10-0.20 (47.8% of all the data) for E. urophylla and S. superba.

Aims The aim of this study is to investigate the effect of different light qualities on circumnutation of cowpea (Vigna unguiculata) seedlings.

Methods The behaviors of cowpea seedlings were observed in a black box, which fixed with two infrared cameras on the top and a side, respectively. The motion was recorded as photos taken at an interval of 5 min, in a 3-dimensional space coordinate under different light qualities (such as white, red, blue, and red-blue with opposite direction) for 48 h. The coordinate values of cowpea seedling growth point (CPGP) were read on a computer screen.

Important findings The results showed that in the dark condition, the CPGP movements had two types, one was a spiral rising anticlockwise circulation, and the other was swinging up irregularly. The spiral rising anticlockwise circulation lasted 18.3 h, then turned to swing up irregularly. It takes (82.7 ± 4.2) min spiraling a circle on average, with the maximum range of swing 2.0 cm and the minimum 0.5 cm. Under white light condition, the CPGP movements tended toward light source with a swing up irregularly. The range of swing changed from decrease to increase, with the maximum range of swing 0.6 cm and the minimum 0.1 cm. Under red light condition, the CPGP movements showed two stages, in which one was a tending toward light source directly for (21.9 ± 1.6) h, the other was swing up perpendicular to light direction for (8.8 ± 0.5) h. The maximum range of swing was 3.5 cm, and the minimum was 2.0 cm. Under blue light condition, the CPGP movements showed a swing up with “Z” trajectory tending toward light source, alternating 2 durations with (110.0 ± 5.8) min and (223.5 ± 4.9) min. under red-blue light with opposite direction conditions, the CPGP movements tended toward blue light source for (12.0 ± 3.8) h, then toward red light source slowly. The order of CPGP within 48 h decreased under different light quality with red, dark, blue, white and red-blue. The seedlings of cowpea could move with circumnutation in dark conditions, suggesting that circumnutation does not need light induction. However, the light quality could change the movement direction and speed. CPGP movements showed different patterns under different light qualities, but the movements tended toward light source in general.

Aims Microorganisms play a crucial role in the litter decomposition process in terrestrial ecosystems. Understanding the independent and interactive relationship between fine root decomposition and bacteria community related to substrate characteristics can help to predict the consequences of changes on ecosystem function. Therefore, the aim of this study was to identify fine roots’ influences on rhizosphere microbial structure and diversity.

Methods The decomposition of root litters of four dominant tree species of Mount Taishan (Robinia pseudoacacia(RP), Quercus acutissima(QA), Pinus tabulaeformis(PT) and Pinus densiflora(PD)) was tested in a Yaoxiang Forest Farm. Using Illumina high-throughput sequencing of 16S rRNA genes, bacterial community composition was determined. Composition, diversity and relative abundance of bacteria were calculated for per fine root litter.

Important findings (1) Fine root litter decomposition differed significantly among different root types. There was no difference in decomposition rate between broad-leaved species and conifer species. In all species, fine roots of RP and QA were more strongly decomposed than that of PT and PD, and these differences were significant (RP > QA > PT > PD). (2) The number of observed species, operational taxonomic units, Ace index and phylogenetic diversity in broad-leaved species were significantly lower than that in coniferous species. Bacterial community structure differed significantly among four species for root decomposition. Initial carbon (C), lignin:nitrogen (N) and C:N in fine root had a great influence on the bacterial community structure. (3) At the phylum level, a total of 4 phyla were dominant (>5% across all species). Based on the average relative abundance, the most abundant phyla were Proteobacteria, Actinomyces, Bacteroidetes and Acidobacteria. Proteobacteria’s and Acidbacteria’s abundance were significantly different among the four species. Particularly, the Proteobacteria of broad-leaved species was significantly higher than that of coniferous species. At the class level, a wide range of classes dominated. Based on the average relative abundance, the most abundance classes were Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, unidentified-Actinobacteria and Sphingobacteriia. Alphaproteobacteria and unidentified-Actinobacteria had significant differences among the four species. (4) Pearson correlation analysis showed that the relative abundance of dominant phylum and class was affected by the initial properties of root litter, especially the Proteobacteria and Alphaproteobacteria. In addition, there was a significant positive correlation between fine root decomposition rate and relative abundance of Proteobacteria and Alphaproteobacteria. Redundancy analysis (RDA) also demonstrated that the initial properties of fine root litter (initial N, P, C:N) had significant effects on the structures of bacterial community. These results can improve understanding the links between fine root litter decomposition and functional microbial communities.

Aims Soil organic carbon (SOC) mineralization and its controlling factors are critical for understanding the mechanisms that regulate C storage and loss processes. Our objectives were to accurately assess the impacts of vegetation restoration on SOC mineralization and to illustrate the underlying mechanism of changes in SOC stability with vegetation restoration in the mid-subtropical region of China.

Methods Four types of vegetation communities (Loropetalum chinense-Vaccinium bracteatum-Rhododendron mariesiiscrub-grass-land (LVR), Loropetalum chinense-Cunninghamia lanceolata-Quercus fabri shrubbery (LCQ), Pinus massoniana-Lithocarpus glaber-Loropetalum chinense coniferous-broad leaved mixed forest (PLL) and Lithocarpus glaber-Cleyera japonica-Cyclobalanopsis glauca evergreen broad-leaved forest (LAG) ) were selected for a successional sequence of the secondary forest in a hilly region of eastern Hunan Province, China. Soil samples (0-40 cm) were collected from four depths (0-10, 10-20, 20-30 and 30-40 cm). SOC mineralization was determined by the laboratory incubation method (alkali absorption method). Principal component analysis and stepwise regression were applied to analyze the relationships between SOC cumulative mineralization (C_m), the percentage of C_m to SOC content and vegetation factors and soil factors.

Important findings 1) SOC mineralization rate displayed similar trends during the four restoration stages: during the early incubation period, SOC mineralization was high and decreased fast, and then the rate decreased slowly and tend to stabilize during the middle and late periods. The pattern was well fitted with the reciprocal equation. 2) SOC mineralization rate and C_m increased significantly with the vegetation restoration stage with the LAG having both the highest SOC mineralization rate and the highest C_m. In 0-40 cm soil layer, C_m in LAG soil was 359.06%-716.31%, 112.38%-232.61%, 94.40%-105.74% higher than that in LVR, LCQ, PLL soils, respectively. 3) The percentage of C_m to SOC content were 2.13%-4.99%, 3.42%-4.18%, 4.05%-4.64%, and 4.02%- 5.64% in 0-10, 10-20, 20-30, 30-40 cm soil layers, respectively. However, there was no significant difference in the percentage of C_m to SOC content among the different restoration stages. 4) Among different vegetation restoration stages, total nitrogen (TN) content and root biomass (RB) were the key factors affecting C_m. TN content and RB together explained 97.8% variations in C_m, of which TN content explained 96.9%. However, C:N was the dominant factor affecting the percentage of C_m to SOC content and it alone explained 49.4% variation. Vegetation restoration promoted SOC mineralization rate and reduced the percentage of C_m to SOC content in our study, which might be related to the changes in RB and soil nutrient during vegetation restoration.