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Understanding leaf trait variation is critical for the prediction of plant responses to global climate changes. Leaf trichomes are derived from stomatal epidermal cells, which play critical roles in biotic defenses and against abiotic stress. Previous studies reported spatial variations in stomatal traits and their driving factors at the same sampling sites. However, it remains unclear how leaf trichome densities vary along large geographic gradients and whether trichomes and stomata co-vary under environmental changes. We measured the leaf trichome densities of 44 Quercus variabilis populations in situ across Eastern Asia (24 to 51.8 °N, 99 to 137 °E) and 15 populations grown in a common garden, and used structural equation modelling to evaluate their relationships with climatic factors and stomatal traits. Our results revealed that climatic factors not only had a direct effect on trichome density, but also had indirect effects on trichome density through stomatal density and leaf mass per area. Trichome density was positively correlated with stomatal density whether in situ or in the common garden, and both increased with drought, which implied that trichomes may impact stomatal behavior and both traits may co-vary under certain environmental conditions. Our results suggested that leaf trichomes possess highly adaptive variation and are in close coordination with stomata in response to climate changes. Our findings provide new insights toward elucidating the interactions between leaf traits and the adaptive strategies of plants under climate change.

Background Nutrient resorption is critical for plants toward balancing their nutritional requirements and adapting to environmental variabilities, which further impacts litter quality and nutrient cycling. However, the interannual variability of nutrient resorption under climate change remains unclear. Methods We investigated the five-year nutrient resorption efficiencies (NuRE, %) of 14 elements in three deciduous oak tree species (Quercus aliena var. acuteserrata, Q. glandulifera, and Q. variabilis) in a warm-temperate forest of Central China and assessed their relationships with interannual climate and soil factors. Results Nutrient resorption did not differ between species but varied significantly between different years. For each year, N, P, S, K, C, Mg, and Zn were preferentially resorbed in all of the oak species in contrast to Ca, Na, Mn, Ba, Al, Fe, Cu, which were to some extent discriminated. Among the 14 elements, the NuRE of C, N, P, S, Ca, and Mg was more sensitive to interannual climate variations in the three oak species. The carbon resorption efficiency was significantly increased during the driest year of the study (2014); N resorption efficiency was reduced with temperature; whereas N and P resorption efficiency initially decreased and then increased with precipitation. Moreover, the elements with higher NuREs typically had lower coefficient of variation (CV) in all three oak species. Conclusions Different oak species exhibited analogous nutrient conservation strategies in response to annual climate variabilities, and interannual climate variations strongly impacted plant nutrient resorption. Deciduous plants may establish a tradeoff mechanism to rebalance somatic nutrients for regrowth at the end of the growing season.

The middle reaches of the Yangtze River region (MRYRR) are China’s first trans-regional urban agglomeration, located in the center of the Yangtze River Economic Belt. The MRYRR is an important ecological reserve, and its land cover changes are affected by both socio-economic development and geographical environment. In this paper, Landsat ETM/TM/OLI remote sensing images were used to monitor land use and landscape patterns from 1990 to 2015. Through supervised classification, land use transfer matrix, landscape pattern metrics and correlation analysis, the spatial-temporal patterns of land use change and its relationship with socio-economic in the study area were revealed. The results showed that: (1) the main land use types in the study area were cropland (CL) and forestland (FL), accounting for more than three-quarters of the study area. During the study period, built-up land (BL) increased, CL decreased, FL increased first and then decreased, (2) the BL expanded mainly by occupying CL and FL, and regional landscape pattern was gradually fragmented, with complex patch shape and increasing diversity and heterogeneity. Among them, the BL is gradually gathered, and the FL and CL are gradually fragmented, (3) in the past 25 years, the urbanization process in this region has been obvious, and the Gross Domestic Product (GDP) has increased by 36 times. The socioeconomic variables were positively correlated with BL, orchard (OL) and Shannon diversity index (SHID), and negatively correlated with CL, Wasteland (WL), mean patch size (MPS) and contagion size (CONTAG). The results showed that the urbanization development has a great impact on the region, and the ecological protection task is still challenging. It is necessary to protect high-quality cropland and draw a red line for ecological protection. We should strengthen the construction of ecological corridors and ecological nodes to adapt to regional sustainable development.

The leaves and seeds of plants frequently function as the source and sink organs for distinct metabolites, which can interactively vary in response to adverse site conditions. Subtropical soils are typically characterized as having deficient phosphorus (P), calcium (Ca), and magnesium (Mg), with enriched aluminum (Al) and iron (Fe), while Al and manganese (Mn) are toxic at low pH. It remains largely unknown how leaf- and seed-sourced metabolites are synergistically linked to adapt to P-variable soils for trees in subtropical areas. Here we quantified the metabolic and elemental profiling in the mature leaves and immature seeds of Quercus variabilis at contrasting geologically-derived phosphorus sites in subtropical China. The results revealed that carbon (C) and nitrogen (N) based metabolites (primarily sugars and organic acids), as well as enzyme- and protein/nucleic acid-related elements (N, P, Mg, and Mn) played important roles toward characterizing the profiling of metabolites and ionomes in leaves and seeds at two site types, respectively. These metabolites (sugars, amino acids, and fatty acids) and elements (N, P, Mg, and Mn) of seeds were closely related to the sugars, organic acids, and elements (N, P, Mg, and Mn) of leaves at the two site types. For the most part, the content of N and P in the soil affected the accumulation of materials (such as, starchs and proteins) in seeds, as well as N and P assimilation in leaves, by influencing C- and N-containing metabolites in leaves. These results suggested that correlated disparities of C- and N-containing metabolites, along with enzyme- and protein/nucleic acid-related elements in both leaves and seeds played important roles in plants to facilitate their adaptation to nutrient-variable sites in subtropical zones.

There are growing concerns regarding the restoration of karst rocky desertification (KRD) areas. However, the soil conditions and its residing microorganisms, which are essential for the plants, remain largely unclear. We studied soil characteristics and microbial communities in natural forests (non-KRD) and shrubs with eroded soil and surface soil run-off, using Illumina Miseq sequencing. Our results showed that despite KRD reduced soil fertility and altered microbial community structures, microbial diversity did not diminish. Interestingly, bacterial OTU richness and diversity were greater in the KRD areas than in the non-KRD areas, which had relatively greater plant density and diversity. Fungal OTU richness and diversity remained unchanged by KRD. Although the KRD areas had been clear-cut and trees were mostly absent, ectomycorrhizal fungi did not differ in diversity and relative abundance between the two land types, indicating that the KRD shrubs hosted surprisingly diverse and abundant ectomycorrhizal fungi. Our results highlight the highly diverse microbes under environmental and anthropogenic stresses in KRD areas. Despite the fact that degraded soil properties and an altered microbial community structure remain, KRD did not erode ectomycorrhizal fungal species richness, which is crucial in the revegetation of trees in KRD areas.

Tree species and forest age are two key variables affecting timber production and carbon sequestration in forest ecosystems. In this study, in Jiangxi province of eastern China, by a thorough investigation of 179 subtropical forest stands in a 16.7 × 106 ha area with similar climatic conditions and past land-use history, we systematically examined biomass of live aboveground tree, forest floor litter, shrub and herb as well as soil organic carbon (SOC) content (0–10, 10–30 and 30–100 cm depths) to compare differences among five major vegetation types (Chinese fir, masson pine, single-species broadleaves, mixed conifers-broadleaves, and mixed-species broadleaves), and between age classes (below vs above 30 years of stand age). Tree species and stand age both had significant effects. Among the five forest types, mixed-species broadleaved forests had remarkably highest timber productivity, SOC content and storage in the 0–100 cm depth and total C store in the age group of above 30 years. Coniferous stands had generally higher forest floor biomass than broadleaved stands in the age group of below 30 years; this trend was opposite for mineral soil C in the age group of above 30 years. Stand age significantly affected aboveground timber production for all the tree species; this effect was weaker on belowground soil C, as broadleaves exhibited increases in SOC content with stand age while conifers did not. Our results suggest that long-term continuity (>30 years) of mixed-species broadleaves could be an optimal strategy for forests in subtropical region of China. This study contributes to a better understanding of the effects of management practices on forest ecosystems.

Background：Nutrient resorption is critical for plants toward balancing their nutritional requirements and adapting to environmental variabilities, which further impacts litter quality and nutrient cycling. However, the interannual variability of nutrient resorption under climate change remains unclear.Methods: We investigated the five-year nutrient resorption efficiencies (NuRE, %) of 14 elements in three deciduous oak tree species, Quercus aliena var. acuteserrata, Q. glandulifera, and Q. variabilis species in a warm-temperate forest of Central China, and assessed their relationships with interannual climate and soil factors. Results：Nutrient resorption did not differ between species but varied significantly between different years. For each year, nucleic acid-protein elements (N, P, S, and K) were preferentially resorbed in all of the oak species in contrast to photosynthesis-enzymic (C, Mg, and Zn) and structural (Ca, Na, Mn, and Ba) elements, which were to some extent discriminated, and toxic (Al and Fe) elements that were completely excluded. Among the 14 elements, the NuRE of N, P, S, Ca, and Mg was closely associated with interannual climate in the three oak species, showing N and S resorption efficiency were reduced with temperature, while N, P, and S resorption efficiency initially decreased and then increased with precipitation. Moreover, the elemental coefficient variations between different years generally decreased with higher NuREs in all three oak species.Conclusions: Different oak species have analogous nutrient conservation strategies in response to annual climate variability, and interannual climate variations strongly impacted plant nutrient resorption. Deciduous plants may establish a trade-off mechanism to rebalance somatic nutrients for regrowth at the end of growing season.

Subtropical soils are generally characterized by phosphorus (P), calcium (Ca) and magnesium (Mg) deficiency; extreme P-rich soils develop on phosphate rocks. How such contrasting geological-derived soils influence genetic diversity and structure of local plant populations have not been well documented, hindering our understanding of plant adaptive evolution in subtropical areas. In this study, we applied double digest restriction-site-associated DNA sequencing (ddRAD-seq) to investigate the genetic variation and differentiation of natural Quercus variabilis populations growing at geologically derived soil P-rich and P-deficient sites in subtropical China. Results showed that Q. variabilis populations had lower genetic diversity at P-rich sites than those at P-deficient sites, and genetic diversity was negatively correlated only with soil P content (p

The landscape patterns of plantations (PT) are the results of human disturbances on local vegetation, and in turn, differ greatly from natural forests (NF), since the patterns strongly influence the natural circulation of material and energy. There is a need to understand the differences of landscape patterns between PT and NF, to establish a near natural afforestation strategy. This study chose three typical silvicultural counties in the middle reaches of the Yangtze River as the research areas and compared the landscape patterns of NF and PT, with other land use types (grassland, GL, cropland, CL, shrubland, SL, orchard, OR, built-up land, BUL, bare land, BL, and water bodies, WB). The results revealed that the areas of PT accounted for 7.67%, 12.05%, and 18.97% of three counties, bigger than GL, OC, BUL, BL, and WB, as one of main land use types. The landscape patterns of PT (mean patch size between 2.06 to 6.05 ha) were more fragmented than NF (mean patch size between 5.83 to 53.91 ha). NF areas increased along the relative altitude gradient, from 0 to 2500 m, while PT areas peaked from 100–1000 m. The higher the altitude, the more typical the zonal distribution of PT, the more aggregated the NF. NF had significant negative correlations with BL, BUL, CL, PT, GL, and OC, which suggest that human activities had seriously interfered with NF. Although PT as an ecological protection strategy was increasing, the landscape patterns of PT were obviously different from NF. This may affect the material energy flow in the ecological environment. The results in the present study have great implications in the other regions in China and the relevant parts of the world where natural forests were heavily disturbed.

The stomatal traits influence ecosystem carbon-water fluxes and play essential roles that enable plants to adapt to changing environmental conditions. However, how stomatal traits vary along a large climate gradient and whether stomatal traits coordinated with other leaf functional traits in response to environmental changes remain unclear. We investigated the stomatal density (SD), stomatal size (SS), and leaf traits (leaf area (LA), leaf mass per area (LMA), and vein density (VD)) of 44 in situ Quercus variabilis populations across Eastern Asia (24 to 51.8°N, 99 to 137°E) and 15 populations grown in a common garden, and evaluated their relationships with environmental factors. Stepwise multiple regression showed that the SD was significantly associated with mean annual precipitation (MAP), LMA, and VD, and the SS with latitude, mean annual temperature (MAT), mean monthly solar radiation (MMSR), and VD. The SD was positively correlated with the LMA, while the SS was negatively correlated with the VD. The SD and LMA increased with decreasing precipitation, which indicated that they may coordinate to commonly enhance plant resistance against drought. The SS decreased; however, the VD increased with temperature. This implied that plants might further reduce their SS by increasing VD limitations under global warming. In the common garden, plants exhibited a higher SD and VD and lower SS and LA compared to those in the field; however, no relation between the stomatal and leaf traits was observed. Our results suggested that stomatal traits have high environmental plasticity and are highly coordinated with other leaf functional traits in response to environmental changes. Nevertheless, this coordination may have been formed through long-term adaptations, rather than over short time spans.

As an alternative for phospholipid fatty acid (PLFA) analysis, a simpler ester linked fatty acid (ELFA) analysis has been developed to characterize soil microbial communities. However, few studies have compared the two methods in forest soils where the contribution of nonmicrobial sources may be larger than that of microbial sources. Moreover, it remains unclear whether the two methods yield similar relationships of microbial biomass and composition with environmental variables. Here, we compared PLFA and ELFA methods with respect to microbial biomass and composition and their relationships with environmental variables in six oriental oak (Quercus variabilis) forest sites along a 1500-km latitudinal gradient in East China. We found that both methods had a low sample-to-sample variability and successfully separated overall community composition of sites. However, total, bacterial, and fungal biomass, the fungal-to-bacterial ratio, and the gram-positive to gram-negative bacteria ratio were not significantly or strongly correlated between the two methods. The relationships of these microbial properties with environmental variables (pH, precipitation, and clay) greatly differed between the two methods. Our study indicates that despite its simplicity, the ELFA method may not be as feasible as the PLFA method for investigating microbial biomass and composition and for identifying their dominant environmental drivers, at least in forest soils.

Parasites obtain energy and nutrients from the host, and their body size is also usually limited by host size. However, the regulatory mechanisms that control the plasticity of parasite body sizes and the stoichiometric relationships with their hosts remain unclear. Here we investigated the concentrations of 14 elements (C, H, O, N, P, S, K, Na, Ca, Mg, Al, Fe, Mn, and Zn) in the acorns of three oak species (Quercus spp.), in their endoparasitic weevil (Curculio davidi Fairmaire) (Coleoptera: Curculionidae) larvae and in the larval feces, and the weight of weevil larvae within different hosts in a warm-temperate zone of China. Our results showed that the three acorn species exhibited significant differences in C, H, O, P, K, Mg, and Mn concentrations. However, in the weevil larvae, only P, Mn, and C:P ratio revealed significant differences. Weevil larvae preferentially absorbed and retained N, Zn, Na, and P, whereas Mn, K, Ca, and O were passively absorbed and transported. The weevil larvae weight was associated with acorn stoichiometry, and positively correlated with acorn size. Weevil larvae P decreased, but Mn and C:P increased with their weight, implying highly variable in somatic stoichiometry are coupled with the plasticity of body size. Interestingly, weevil larvae weight was negatively correlated with acorn infection rate, indicating small-size parasitic insects might have higher fitness level in parasite–host systems than larger-size ones. Our results suggest that variation in P, Mn, and C:P in parasites may play critical roles in shaping their body size and in improving their fitness.

Polycyclic aromatic hydrocarbons (PAHs) have toxic, teratogenic, mutagenic and carcinogenic effects on living organisms. Plants can function as pollutant bioindicators and bioaccumulators due to their wide surface distribution and specific responses to atmospheric pollutants. However, various plants exhibit significant differences in their capacities to accumulate PAHs. At present, research has mainly focused on the effects of leaf morphology and physiological characteristics, and few studies have evaluated the effects of the leaf surface on PAH accumulation. We aimed to assess the factors impacting the uptake and accumulation of PAHs by leaves. We selected 8 common tree species in Shanghai, China, and used supercritical fluid extraction technology to determine the content of PAHs in their leaves. Specific measurements of leaf area, width/length, wax content, and stomatal density were applied to index the morphological and physiological characteristics; surface roughness, surface free energy, polar components, and dispersion components were compiled into an adsorption performance index. Principal component analysis (PCA) and canonical correlation analysis (CCA) were used to assess the effects of different leaf characteristics on PAH accumulation. We found that the mean concentrations of ΣPAHs ranged from 300 to 2000 ng·g−1 and that the proportions of different benzene rings were significantly different among the different tree species. Leaf morphology and physiological characteristics had more significant effects compared to surface adsorption. CCA showed a significant negative correlation between leaf morphological characteristics and wax content, but had no significant correlation with surface adsorption. Low-molecular-weight PAHs were found to be mainly affected by the morphological characteristics, while medium- and high-molecular-weight PAHs were influenced by wax content and adsorption. Our conclusions provide a theoretical basis for the establishment of a reliable plant atmosphere-monitoring system and a method for screening tree species with strong PAH adsorption capacity.

Tree height is a key variable in forest monitoring studies and for forest management. However, tree height measurement is time consuming, and the recommended procedure is to use estimates from tree height (H) - diameter at breast height (DBH) models. Increasingly, H-DBH models are being developed for urban forests, providing tools to forest management and ecosystem services estimation. Here, we compared model forms and approaches for predicting H as a function of DBH and additional stand level covariates variables. Four model forms were evaluated: (i) basic models (which only used DBH as predictor variable); (ii) generalized models (which used DBH and other predictor variables based on the best basic model); (iii) a mixed-effects model based on the best basic model; and (iv) a mixed-effects model based on the generalized model. Several sampling designs aimed at minimizing height measurement were tested in terms of accuracy and applicability. Taking predicted accuracy and investigation cost into account, we recommend generalized non-linear mixed-effects model (NLME) when there were two or less tree height measurements taken in a given stand. The basic NLME model could be calibrated when there were 3 or more tree height measurements, depending on the required level of accuracy and investigation cost. Additionally, we first reported that soil pH as a covariate variable in H-DBH model and our generalized NLME model implied that the difference in the H-DBH relationship caused by pH varies among different stands. This finding may be attributable to differing biological properties of the similar alkaline tolerance species.

With the rapid advancement of urbanization and industrialization, the contradiction between the social economy and resources and the environment has become increasingly prominent. On the basis of limited land resources, the way to promote multi-objective comprehensive development such as economic, social development and ecological and environmental protection through structure and layout regulation, so as to maximize regional comprehensive benefits, is an important task of current land spatial planning. Our aim is to obtain land-use-change data in the study area using remote-sensing data inversion and multiple-model simulation. Based on land suitability evaluation, we predict and optimize the land use structure of the study area in 2030 and evaluate and compare ecosystem services. Based on remote-sensing images and eco-environmental data from 1985 to 2014 in the study area, land use/land cover change (LUCC) and future simulation data were obtained by using supervised classification, landscape metrics and the CA-Markov model. The ecosystem services were evaluated by the InVEST model. The analytic hierarchy process (AHP) method was used to evaluate the land suitability for LUCC. Finally, the LUCC in 2030 under two different scenarios, Scenario_1 (prediction) and Scenario_2 (optimization), were evaluated, and the ecosystem service functions were compared. In the last 30 years, the landscape in the study area has gradually fragmented, and the built-up land has expanded rapidly, increased by one-third, mainly at the cost of cropland, orchards and wasteland. According to the suitability evaluation, giving priority to the land use types with higher environmental requirements will ensure the study area has a higher ecosystem service value. The rapid development of urbanization has a far-reaching impact on regional LUCC. Intensive land resources need reasonable and scientific land use planning, and land use planning should be based on the suitability evaluation of land resources, which can improve the regional ecosystem service function.

Additional file 8: Table S5. Correlations (r, Pearson’s correlation coefficient) between differential metabolites and discriminating elements in acorns between P-rich and P-deficient sites in September. Significance, p value

Additional file 4: Table S1. All metabolites identified in acorns at P-rich and P-deficient sites in July, August and September (mg g− 1). --, not determined. All data are mean ± SE (in July, n = 4 of P-rich sites, n = 5 of P-deficient sites; in August and September, n = 8 of P-rich sites, of P-deficient sites, n = 12).

Additional file 2: Figure S2. Variation of the same metabolites in acorns during three developmental stages at P-rich and P-deficient sites. A, Overlap of all metabolites identified in acorns during three developmental stages. R&D, at P-rich and P-deficient sites. B, Heatmap analysis of the same metabolites identified in acorns during three developmental stages. Values were normalized with the Z-transformation. PR, P-rich sites; PD, P-deficient sites; J, July; A, August; S, September.

Additional file 1: Figure S1. Mean monthly temperature and mean monthly precipitation of Mouding and Kunming, from 1981 to 2010.

Additional file 3: Figure S3. Over-fitting of OPLS-DA model validation based on metabolomic and ionomic data of developing acorns.

Additional file 5: Table S2. Results of pathway analysis involving all identified metabolites in acorns during three developmental stages. All pathways shown in the table are potential target metabolic pathways with pathway impacts of above 0.1.

Although Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is an important species for wood production in subtropical China, it serious declines in soil nutrients and timber productivity in plantations have been reported, probably caused by successive rotation and inappropriate cutting time. Although the significant effect of stand age on soil properties has been widely recognized, research on soil enzymes and microbial communities is relatively rare. In this study, assuming that short rotation period is one important reason for soil degradation, we measured soil physicochemical properties, microbial community composition, and enzyme activity in 3-, 15-, 25- and 45-year Chinese fir forests in Jiangxi province of China. Soil organic carbon (SOC) content decreased from 3-year to 25-year stands and then increased in 45-year stands. Despite the significant relationship between SOC and the abundance of total phospholipid fatty acids (PLFAs), no notable changes in the abundance of PLFAs were detected with increasing tree ages, except for the abundances of arbuscular mycorrhizal fungi (AMF) which were significantly higher in 25-year stands. However, the ratios of gram-positive to gram-negative bacteria (G+/G&minus, ) and fungi to bacteria (F/B) both decreased with increasing stand age. 45-year stands showed the highest activities of both phosphatase and &beta, glucosidase. Total potassium (TK) content and net N mineralization rate both had significant links with soil microbial community structure. Collectively, our study emphasized that stand age could significantly affect soil physicochemical properties and the microbial community. In general, 25-year stands showed poorer soil status compared to that of 45-year stands. Thus, the cutting age of Chinese fir should be increased to over 25 years to maintain a better soil status.

Forest ecosystems contain large amounts of soil organic carbon (SOC), which is a major component of biogeochemical cycles that may be sensitive to environmental change. We used a combination of nuclear magnetic resonance (NMR) spectroscopy and elemental and isotopic composition to examine the influence of soil properties and climatic factors on the quantity and degree of decomposition of SOC for organic and surface mineral horizons in seven oriental oak (Quercus variabilis Blume) forest sites arranged across a 11o latitudinal gradient in East China. Lacking Oa horizons, the two southernmost sites contained lower amounts of SOC in the forest floor horizon, but otherwise, latitudinal trends were not consistent. The SOC stock in the 0–10 cm mineral horizon exhibited no clear trend along the gradient and had a negative association with clay + silt content. Based on a higher alkyl/O-alkyl (A/O) ratio and alkyl/methoxyl (A/M) ratio, the SOC at the 0–10 cm depth appeared to be relatively more decomposed in three of the four southern subtropical sites. However, the degree of SOC degradation also decreased strongly with increasing soil pH (R2 = 0.90, P = 0.001). Soil organic carbon exhibited increases in δ13C and δ15N and decreases in the C/N ratio with depth for all the seven sites, indicating an increase in its extent of decomposition. Our analysis indicated that the A/M ratio from NMR provided the best indication of the extent of SOC degradation along the latitudinal transect, whereas the elemental and isotopic composition better reflected patterns with soil depth.

Key message The variation ofQuercus variabilisleaf δ13C along latitude resulted primarily from phenotypic acclimation to climate.

Despite the important roles of microorganisms in soil organic matter (SOM) decomposition and nutrient cycling, how their biomass, community composition and function are driven by a joint effect of edaphic and environmental factors at a large spatial scale remains unclear. Moreover, a mechanistic understanding of the associations among microbial communities and SOM chemistry as a key indicator of substrate availability over large spatial scales has been lacking until now. To fill this knowledge gap, we examined how soil microbial community abundance and composition (via phospholipid fatty acid (PLFA) analysis) and function (via enzyme activities and net N mineralization) were associated with the edaphic and environmental factors from six oriental oak (Quercus variabilis) forest sites arranged across a 11° latitudinal gradient in East China. We found strong relationships between SOM chemistry as indicated by 13C nuclear magnetic resonance (NMR) spectroscopy and microbial community composition and function along this gradient. For example, the ratio of fungi to bacteria (F/B) decreased with increasing carboxyl C percentage; the lower abundance of arbuscular mycorrhizal fungi (AMF) and decreased invertase activity in the southern sites were possibly related to higher ratio of alkyl to O alkyl (A/O); urease activity increased with carboxyl C percentage. Microbial biomass (total PLFAs) had positive relationships with urease activity, net N mineralization rate, and soil pH. Mean annual precipitation (MAP) and pH were important for overall microbial community composition. Overall, our results indicate that SOM chemistry is closely related to microbial community composition and function along the latitudinal gradient and should be considered in future studies. Our study contributes to a better prediction of microbial responses to possible substrate changes brought by future environmental changes, which is urgently needed under the context of accelerating global change.

Land use types have been strongly modified across mountainous areas. This has substantially altered the patterns and processes of ecosystems and the components of ecosystem services (ESs), and could in turn impact the sustainable development. In the mountainous Mentougou district of Beijing, we explored the changes in land use type (cropland, orchard, forested land, scrubland, grassland, bare land, water bodies, wasteland and built-up land), landscape patterns and ESs as well as their interactions during the past 30 years (1985&ndash, 2014). The ESs included water yield (WY), carbon stocks (CS) and soil retention rate (SR). The results showed that 23.65% of the land use changed and the wasteland decreased by 80.87%. As for ESs, WY decreased by 47.32% since the year 2000, probably due to the increases in temperature and evapotranspiration. Although the decrease of forested land led to the decrease of CS, the increase of vegetation coverage improved SR. CS decreased by 0.99%from 1990 to 2014, and SR increased by 1.38% from 1985 to 2014. Landscape patterns became fragmented and dispersed, and MPS and CS, SHDI and SR were significantly negatively correlated. IJI and CS was positively correlated. This indicated that landscape patterns were highly correlated with ESs. In order to maintain the sustainable development of ESs, we should not only plan land use types, but also consider the rationality of landscape patterns.

Flux of CO2 from the forest soil surface ( $${\text{F}}_{{{\text{CO}}_{ 2} }}$$ ) reflects the activity of roots and microbes responding to plant and soil properties that are influenced by global changes such as nitrogen deposition and increasing temperature and atmospheric CO2. We added low levels of N (3 g/m2-year), P (1 g/m2-year) or N + P to thirteen northern hardwood stands of different age and soil N cycling and measured soil respiration, microbial respiration and fine root turnover. We hypothesized that soil respiration would decline in response to nutrient addition, but that this response would vary depending on forest age and N cycling rate. Soil respiration was significantly higher in successional ( 90-year-old). Overall, no significant treatment effects or age x treatment interactions were observed. However, on an individual stand basis, significantly lower soil respiration was observed in nutrient addition plots at four of the most infertile sites. Over half of the variation in the response ratio (fertilized-control/control) of soil respiration to fertilization was explained by using pre-treatment N cycling rate as a predictor: i.e., the greatest reduction in soil respiration on N and N + P fertilized plots occurred on the sites with lowest pre-treatment soil N mineralization and litterfall N flux. Nutrient additions did not significantly affect either fine root turnover (minirhizotrons) or microbial respiration (laboratory incubations). Perhaps responses of fine root biomass or rhizosphere C flux influenced the response of soil respiration to increasing soil fertility.

The variability of leaf stoichiometry has been studied at different taxonomic levels across various geographic ranges. However, the intraspecific variations in leaf stoichiometry of widely distributed species are poorly understood. We characterize the biogeographical patterns and environmental controls of leaf nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) concentrations of Quercus variabilis Blume, a widely distributed tree species of significant economic and ecological value in China. The stoichiometry of Q. variabilis leaves exhibited substantial variation, which was strongly affected by climatic factors and respective concentrations of soil nutrients but had little association with leaf mass per area. Climate was the dominant driver, apart from P and Ca, which were also strongly related to soil P and Ca, respectively. Concentrations of leaf N, P, K, and Mg decreased significantly with mean annual temperature and increased with aridity, albeit at different magnitudes, resulting in positive latitudinal trends of all elements except for Ca and S. The results indicate that Q. variabilis leaf stoichiometry shows a relevant degree of flexibility and that alterations in climatic factors and soil nutrient availability have diverse influences on patterns of the different elements. Our findings provide an important contribution toward an understanding of how widespread species regulate their stoichiometry to adapt to heterogeneous environments.

It is well established that land use change can have a profound impact on soil physicochemical properties but the associated changes in soil microbial communities are poorly understood. We used long-term research sites in a subtropical alluvial island of eastern China to measure changes in soil physicochemical properties and microbial community abundance and composition (via phospholipid fatty acid (PLFA) analysis) and function (via extracellular enzyme activity) across different land use types developed on the same soil matrix, including a camphor (Cinnamomum camphora) plantation, a chronosequence of differently aged dawn redwood (Metasequoia glyptostroboides) plantings, a deforested land and a rice paddy. We hypothesized that afforestation could improve soil quality by enhancing carbon (C) and nitrogen (N) contents, microbial biomass and enzyme activities, but that this effect would vary depending on forest age and tree species. Soil C and N concentrations, PLFA abundances and activities of decomposition enzymes (β-glucosidase, urease, alkaline phosphatase and catalase) in older plantations all increased significantly compared to cropland. These variables changed little or decreased in deforested land compared to cropland. These variables also increased with planting age in the dawn redwood plantings. Soils under camphor plantations had higher soil nutrient contents, microbial biomass and lower enzyme activities than dawn redwood soils with similar age. We also found some significant relationships between soil chemical and biological properties: PLFA abundances were positively related to soil organic matter (SOM) contents; the fungal-to-bacterial ratio and fungal relative abundance were correlated positively with SOM contents and negatively with C/N ratio; both soil PLFA abundances and enzyme activities were positively linked with soil inorganic N content and potential net N mineralization rate; ratio of specific C, N and P (phosphorus) acquisition activities was limited to 10: 1: 10 across land use types. Our study underscores the fact that land use type can have a profound impact on soil microbial communities; in addition, tree species and planting age also play significant roles in afforestation.

Titanium dioxide nanoparticles (nano-TiO2) have been widely applied in daily life and subsequent problem on the potential health risk are raised. Studies on the toxicity of nano-TiO2 have shown that they could lead to toxic effects on human and environment. However, the mechanisms are still unclear. We investigated the change of amino acid levels in L929 cells after nano-TiO2 exposure using gas chromatography with time-of-flight mass spectrometry (GC/TOFMS)-based metabolomics approach. Spectral profiles were subjected to multivariate statistics, namely, Principal Component Analysis (PCA), and Orthogonal Projections to Latent Structures-Discriminant Analysis (OPLS-DA). Using MetaboAnalyst 2.0, it was found that 7 metabolic pathways (impact-value >0.10) among the regulated pathways were significantly perturbed. Twelve distinct amino acids are identified from these pathways, including L-α-alanine, β-alanine, glycine, L-aspartate, L-methionine, L-cysteine, glutamate, L-pyroglutamate, L-asparagine, L-glutamine, S-adenosylmethionine, and L-lysine. These results show that the disturbed amino acids played an important role in the nano-TiO2-induced cytotoxicity. Along with earlier findings, we successfully used the metabolomics approaches to manifest nano-TiO2 toxicity through triggering cellular oxidative stress, energy damage and the inhibition of DNA and RNA synthesis.

Soil organic carbon (SOC) stock in mountain ecosystems is highly heterogeneous because of differences in soil, climate, and vegetation with elevation. Little is known about the spatial distribution and chemical composition of SOC along altitude gradients in subtropical mountain regions, and the controlling factors remain unclear. In this study, we investigated the changes in SOC stock and chemical composition along an elevation gradient (219, 405, 780, and 1268 m a.s.l.) on Lushan Mountain, subtropical China. The results suggested that SOC stocks were significantly higher at high altitude sites (1268 m) than at low altitude ones (219, 405, and 780 m), but the lower altitude sites did not differ significantly. SOC stocks correlated positively with mean annual precipitation but negatively with mean annual temperature and litter C/N ratio. The variations in SOC stocks were related mainly to decreasing temperature and increasing precipitation with altitude, which resulted in decreased litter decomposition at high altitude sites. This effect was also demonstrated by the chemical composition of SOC, which showed lower alkyl C and higher O-alkyl C contents at high altitude sites. These results will improve the understanding of soil C dynamics and enhance predictions of the responses of mountain ecosystem to global warming under climate change.

Although there is an increasing interest in using infrared spectroscopy for the simple, rapid, and inexpensive prediction of soil organic carbon content, few studies have used this technique to measure organic carbon chemistry. In this paper, based on both near-infrared and mid-infrared diffuse reflectance spectroscopy, we compared the use of instrumentation, spectral pretreatment, and regression method for the prediction of three parameters related to organic carbon content, one related to isotopic composition, and five related to organic carbon chemistry. A total of 140 soil samples collected from seven oriental oak forest sites across East China were used as the data set for the calibration-validation procedure. Calibrations using sample set partitioning based on joint x-y distances method significantly outperformed those using Kennard-Stone method. Compared to models using linear method (i.e., partial least squares), those using non-linear regression method (i.e., support vector machines) greatly improved the prediction precision of the alkyl-to-O-alkyl ratio and performed slightly better for the other organic carbon chemical compositions. Instrumentation had a large effect as mid-infrared models had higher average prediction accuracies than near-infrared models. We finally proposed a model using second derivative preprocessing, joint x-y distances based sample set partitioning, mid-infrared spectra, and support vector machines regression to quantify organic carbon chemistry in this study. The results are helpful for the further study of soil composition measurement.

To develop a simple, accurate, and non-destructive method for estimating the groundwater level (GWL) in an unconfined sandy aquifer, field measurements of soil electrical resistivity were conducted at the Daqinggou Ecological Station (DES) in 2005 and the Experimental Base of the Institute of Wind-Sand Land Improvement and Utilization (IWLIU) in 2009. The resistivity data were acquired through a series of vertical electrical soundings (VES) using a Wenner array. For comparison with the VES method, the GWLs were also manually monitored in wells. The results showed that the thirty VES profiles decreased or first increased and then decreased with increasing electrode spacing (i.e., becoming more conductive with depth). The depth of the GWL was obtained by calculating the turning points, as inferred from inflections in the apparent resistivity profiles. The GWL variations between the VES method and manual measurement ranged from 0.22 to 1.03 m at the DES, with a mean value of 0.52 m, and from 0.03 to 0.82 m at the IWLIU, with a mean value of 0.10 m. The significant differences between the GWLs obtained by the VES method and manual measurement at the DES were due to the higher GWLs with capillary action; there were no significant differences in the GWLs obtained at the IWLIU. The linear regression coefficient of determination was 0.97 for the IWLIU GWL values, indicating a good agreement between the VES method and manual measurements. Therefore, we conclude that the VES method is a sound measuring tool for estimating GWLs in unconfined sandy aquifers when the GWL is sufficiently deep (e.g., GWL > 3.98 m).

The stoichiometric composition of plant reproductive organs varies with environmental conditions at a large geographical scale, which has potentially important consequences both for plant reproductive success and for the nutrition of consumers. In the study reported here, we investigated variations in the concentrations of macronutrients in acorns of the oriental oak (Quercus variabilis) in relation to environmental variables across a geographic gradient spanning temperate and subtropical latitudes. Across this gradient, nitrogen (N) and calcium (Ca) concentrations of the acorns had higher coefficients of variance (CV 18–23 %) than the other elements (CV 8–14 %). With increasing latitude (LAT), acorn N, potassium (K), and magnesium (Mg) concentrations increased, whereas those of sulfur (S) and Ca and the carbon:nitrogen (C:N) and S:N ratios decreased. The K and Mg concentrations of the acorns were positively correlated with the concentrations of these elements in the soil, whereas N and Ca concentrations were inversely correlated with soil concentrations. The C:N:P (phosphorus) molar ratio of the acorns was 1,008:17:1. A low temperature and short growing season stimulated seeds to accumulate more macronutrient elements in the north to ensure reproductive success, while high soil Ca in the north led plants to allocate less Ca to their acorns. The pattern of variation in acorn stoichiometric traits along LAT may be the result of interacting effects of plant reproduction strategy and environmental factors. Our results can help improve our understanding of the effects of global changes on the chemical compositions of plant reproductive organs and advance our knowledge of global patterns of ecological stoichiometry in reproductive organs.

The leaf vein traits of plants result partially from adaptations to environmental factors during the long-term evolution. However, no general conclusion on the variation trend of the vein density along a climate gradient or the response of such vein density–climate relationship pattern to climate changes has been made. We examined the variations in leaf vein density and other leaf traits of oriental oak (Quercus variabilis) in 10 in situ populations (in situ populations) across temperate-subtropical biomes and the response of the leaf vein density to environmental changes in 7 populations grown in a common garden (garden populations). The results show that the minor vein density of the in situ populations (≥3rd order) significantly decreased with increasing latitude (r 2 = 0.44 and P = 0.04). This pattern remained unchanged for the garden populations (r 2 = 0.67 and P = 0.02). The minor vein densities of both the garden and in situ populations were positively correlated to the mean annual temperature (MAT) of the origins (r 2 = 0.66 and P = 0.03 for the garden populations; r 2 = 0.37 and P = 0.06 for the in situ populations), but their correlation to the mean annual precipitation (MAP) of the origins was not significant. Compared with the MAT and MAP, the vein density displayed a significantly lower correlation to climate variables in the current year or the current-year growing seasons. For the garden populations, the minor vein density significantly increased with leaf dry mass per area and decreased with petiole length and leaf length. These results imply that leaf vein density is genotypically fixed and is therefore not responsive to temporal changes in the growing conditions.

The patterns of variation in natural abundance of foliar and soil ( 15 N) (expressed as δ 15 N) related to geographical and climatic variables frequently vary over plant species or plant function groups. It is essential to identify the pattern of foliar δ 15 N for specific plant species which has a widespread distribution and to explore the underlying mechanisms in the context of environmental change such as global warming and anthropogenic nitrogen deposition. Oriental oak ( Quercus variabilis Bl.), characterized by cork bark, is a widely distributing deciduous broadleaf tree species that can be found in temperate and subtropical areas of East Asia. In this study, the variations in foliar and soil 15 N were investigated based on the data of leaf and soil samples collected in 22 stands over eastern China (from 24 to 41° N in latitude and 102 to 123° E in longitude), and the mechanisms were discussed. The results showed that for oriental oak stands, mean foliar and soil δ 15 N were − 4.8‰ and 2.0‰, respectively, indicating an evident 15 N enrichment in the soils. The average foliar δ 15 N value of oriental oak in warm temperate forest was significantly lower ( p 15 N increased linearly and significantly with increasing mean annual precipitation (MAP) (R 2 = 0.481 and p 2 = 0.285 and p = 0.01) and decreasing pH value of rain water (R 2 = 0.333 and p = 0.005). With these results in eastern China, there are great implications in understanding how nitrogen dynamics of ecosystems responds to warming, drought and acid rain.

Nitrogen (N) and phosphorus (P) and N:P ratio in terrestrial plants and the patterns at a large geographical scale are an important issue in ecological stoichiometry. In particular, it is essential to know that for a single species, how the N:P stoichiometry varies with climatic factors in the context of global warming. Our analysis was based on a data set including 2583 observations at 441 sites on nutritional status of Norway spruce ( Picea abies L.) located in European counties (including Austria, Belgium, Bulgaria, Czech Rep., Finland, Germany, Ireland, Italy, Lithuania, Norway, Slovak Rep., Slovenia, United Kingdom). Our objectives are to demonstrate how leaf N and P concentration and N:P ratio in Norway spruce vary with altitude (ALT), latitude (LAT), longitude (LON), mean annual temperature (MAT) and mean annual precipitation (MAP) across Europe. The results showed that for 1-year-old needles of Norway spruce, the N and P concentration were 13.28 mg g −1 , 1.41 mg g −1 and the N:P ratio was 9.76. Leaf N displayed a convex curve pattern with increasing MAT and decreasing LAT from the boreal Europe to the Mediterranean area. The N concentration and N:P generally reached peak at about 7 °C in MAT or 53° N in LAT. The N:P ratio varied non-linearly with LAT and MAP, but linearly with MAT. Leaf N concentration and N:P ratio decreased linearly with increasing ALT in temperate European area. Across Europe, that the patterns of leaf N and N:P ratio were mainly driven by climate-related geochemistry and plant physiology, but also greatly impacted by anthropogenic N deposition.