Quercus Liaotungensis Research Articles

Hydraulic conductivity regulates tree growth and drought resistance in semi-arid mixed forests of northern China

With the intensification of climate warming, drought has become increasingly severe. Drought seriously impacts tree growth and may even result in tree mortality. However, our understanding of how the hydraulic structure of xylem in different tree species regulates growth and drought resistance remains incomplete. Here, we collected tree-ring samples from three semi-arid natural Chinese pine (Pinus tabuliformis)-broadleaf mixed forests in northern China. We selected Chinese pine (non-porous wood), white birch (Betula platyphylla, diffuse-porous wood), and Liaodong oak (Quercus liaotungensis, ring-porous wood) as target tree species. Using dendrochronology and wood anatomy methods, we evaluated interspecies differences in tree growth, climate sensitivity, and drought resistance, and analyzed the relationships between tree growth, drought resistance, and theoretical xylem-specific hydraulic conductivity (Ks). Our findings revealed distinct differences in the hydraulic structure of xylem among these three tree species as well as their resilience to drought. Liaodong oak exhibited less sensitive to drought compared to Chinese pine and white birch. Meanwhile both Chinese pine and Liaodong oak demonstrated greater resistance to drought than white birch. The positive correlation between specific xylem hydraulic conductivity and both tree growth and drought resistance were observed for Chinese pine, but Liaodong oak was the opposite. This suggested that specific hydraulic conductivity of xylem cannot serve as a consistent or robust predictor of tree growth or drought resistance across different species. As climate warming intensifies, it is anticipated that white birch may experience severe and significant irreversible decline in growth, while Liaodong oak may exhibit the highest potential growth performance. Given the projected intensification of future warming trends along with more frequent extreme climate events, safeguarding biodiversity and productivity within semi-arid Chinese pine-broadleaf mixed forests may hinge on the prioritizing protection efforts for Chinese pine.

Effects of Pinus tabuliformis and Quercus liaotungensis mixture on morphological characteristics of ectomycorrhizae.

The mycorrhizal diversity and morphological plasticity determine the adaptability of host plants to habitat changes. To understand the effects of mixture between coniferous and broadleaf trees on the morphological characteri-stics of ectomyzorrhizal (EcM) associations, we examined the influences of environmental factors on changes in morphological characteristics based on a systematic investigation of the EcM morphological traits in Pinus tabuliformis Carr. and Quercus liaotungensis Koidz. grown in pure stands as well as in various levels of mixture (i.e., P. tabuliformis and Q. liaodongensis in a 3:1 mixture, a 1:1 mixture, and a 1:3 mixture) in Taiyue Mountains of Shanxi Province. Results showed that the EcM in both species are predominantly of the contact exploration type in all stand types. In P. tabuliformis, the root tip numbers of the contact and medium-distance exploration types in mixed stands were significantly greater by 3%-10% and 10%-16%, respectively, than in pure stands. In Q. liaotungensis, the root tip numbers of the contact exploration type in mixed stands were significantly higher by 5%-10% than in pure stands. In both species, the values of Simpson morphological diversity index were higher in mixed stands than in pure stands. Redundancy analysis indicated that the morphological variability of EcM was mostly affected by soil nitrogen to phosphorus ratio (explainable by 7.5%) and soil water content (explainable by 5.2%) in P. tabuliformis, while it was mostly affected by soil carbon content in Q. liaotungensis (explainable by 3.5%). Both P. tabuliformis and Q. liaotungensis are capable of adapting to conditions with competition for, and sharing of, soil nutrients in mixed forests through morphological variations of EcM.

Seed traits and burial state affect plant seed secondary dispersal mediated by rodents

Seed dispersal is an important ecological process and has important implications for plant population expansion and regeneration. Seed dispersal not only reduces the probability of death due to seed density but also facilitates seedling establishment. Many studies have focused on the effect of one or two factors on seed dispersal. However, little is known about studies on the effect of multiple factors and their interactions on seed dispersal. Here, we conducted a field experiment to explore how seed size, soil burial, and seed peeling affect the dispersal and hoarding of seeds of Quercus liaotungensis in dispersal animals. We found that large seeds were preferentially selected by animals, and the predation after dispersal, hoarding after dispersal, predation distance after dispersal, and hoarding distance after dispersal of large seeds were significantly greater than small seeds, which is more beneficial to the plant expansion and regeneration. Soil burial increased the time of seed intact in situ, significantly increased predation in situ, and reduced predation after dispersal, predation distance after dispersal, and hoarding distance after dispersal, which is not beneficial to the plant population expansion and regeneration. Seed peeling reduced the time of seed intact in situ, and the predation after dispersal was significantly greater than that of unpeeled seeds, which is not beneficial to the plant population. We did not find the interactions between seed size, soil burial, and seed peeling on dispersal. The effects of a single factor may be more than their interactions between seed size, soil burial and seed peeling on dispersal. These results implied that seed size, soil burial and seed peeling may affect plant population expansion and regeneration by affecting the dispersal and hoarding of animals.

Characteristics of soil moisture limitation and non-limitation in the response of sap flow to transpiration driving factors

Transpiration is a significant part of water cycle in forest ecosystems, influenced by meteorological factors and potentially constrained by soil moisture. We used Granier-type thermal dissipation probes to monitor xylem sap flow dynamics of three tree species (Quercus liaotungensis, Platycladus orientalis, and Robinia pseudoacacia) in a semi-arid loess hilly region, and to continuously monitor the key meteorological factors and soil water content (SWC). We established the SWC thresholds delineating soil moisture-limited and -unlimited sap flow responses to transpiration drivers. The results showed that mean sap flux density (Js) of Q. liaotungensis and R. pseudoacacia was significantly higher during period with higher soil moisture compared to lower soil moisture, while the difference in Js for P. orientalis between the two periods was not significant. We used an exponential saturation function to fit the relationship between the Js of each tree species and the integrated transpiration variable (VT) which reflected solar radiation and vapor pressure deficit. The difference in the fitting curve parameters indicated that there were distinct response patterns between Js and VT under different soil moisture conditions. There was a threshold in soil moisture limitation on sap flow for each species, which was identified as 0.129 m3·m-3 for Q. liaotungensis, 0.116 m3·m-3 for P. orientalis, and 0.108 m3·m-3 for R. pseudoacacia. Below the thresholds, Js was limited by soil moisture. Above these points, the normalized sensitivity index (NSI) for Q. liaotungensis and P. orientalis reached saturation, while that of R. pseudoacacia did not reach saturation but exhibited a significant reduction in moisture limitation. Among the three species, P. orientalis was the most capable of overcoming soil moisture constraints.

Nitrogen Enrichment Regulates the Changes in Soil Aggregate-Associated Bacterial Community: Evidence from a Typical Temperate Forest

The nitrogen (N) enrichment induced by atmospheric N deposition affects both soil physicochemical properties and bacterial communities. However, how N enrichment affects soil aggregate-associated bacterial communities remains largely unclear. In this study, we conducted a two-year N addition experiment (four N levels: 0, 5, 10, and 20 g N m−2 year−1, corresponding to normal N, low N, medium N, and high N, respectively) in a Quercus liaotungensis Koidz–dominated forest. The distribution, nutrient content, and bacterial community composition of the soil aggregates were measured under various N enrichment conditions. N enrichment changed the aggregate distribution, increased the content of nutrients in aggregates, and altered the aggregate-associated bacterial community composition. N enrichment reduced the complexity of the bacterial co-occurrence network and degraded the interactions between bacteria compared with those observed under the normal N level. Aggregate-associated bacterial community was determined to be primarily affected by N enrichment level but not by aggregate size. The litter properties are the key factors affecting the composition of bacteria in aggregates. These findings improve our understanding of aggregate-associated bacterial responses to N enrichment and the related influencing factors.

Jointly soil properties affect N and P uptakes and utilizations in Pinus tabuliformis Carr. and Quercus liaotungensis Koidz. subjected to growing media with decomposed litter

Monocultured pine plantation is suffering ecological degradation that is highly associated with low regeneration. Decomposed litter is an important soil amendment for enhancing regeneration through promoting nitrogen (N) and phosphorus (P) uptakes and utilizations. It is necessary to detect key soil attributes that contributed to this positive effect for regenerations in pine plantations. In this study, in-situ soils and litter were collected from local Chinese pine (Pinus tabuliformis Carr.) plantations (objective) and secondary forests dominated by Liaodong oak (Quercus liaotungensis Koidz.) (control). Soils were used for culturing one-year-old Chinese pine and Liaodong oak seedlings with a prolonged photoperiod in a greenhouse. Litter was composted with effective microorganisms and mixed to soils at ratios of 0% (control), 25%, and 50% (v/v). Compared to the control, the 25% ratio decreased shoot height and root-collar diameter, and the 50% ratio decreased the comprehensive seedling quality. Decomposed litter addition reduced shoot biomass and P content in pine seedlings and utilizations for N and P in both species. Multivariate linear regression indicated that high pH in growing media impaired root P content and biomass increments in shoot and root parts, and high organic matter content inhibited N content and concentration in shoots. Overall, the addition of decomposed litter resulted in overdoses of nutrient supply for both species. Our results contradict the argument that N and P released from decomposed litter are both beneficial for regenerations in plantations, neither did in secondary forests.

Daily and seasonal patterns of stem diameter micro-variations in three semiarid forest species in relation to water status and environmental factors

Understanding the relationship between stem diameter micro-variation (SDMV) and stem water status and revealing the mechanism regulating stem water are essential for elucidating environmental adaptation and water use strategies in forest trees. Here, we report the results of the year-round monitoring (November 2018–October 2019) of SDMV and xylem sap flow obtained using high-resolution dendrometers and Granier-type thermal dissipation probes, respectively, in mature trees of three species in the semiarid Loess Plateau region: Quercus liaotungensis, Platycladus orientalis, and Robinia pseudoacacia. The year-round trend for the variations in stem diameter can be divided into phases of a decreasing period and a relatively stable period in the non-growing season, and a progressive rise and fluctuating plateau throughout the growing season. The observed interspecific differences in the time to full recovery from the water deficit state corresponded to species phenology and soil moisture conditions. These differences were manifested as the responses of sap flux density (Fd) and tree water deficit (TWD) to variations in soil water content during the growing season. Q. liaotungensis implements stomatal regulation early to avoid drastic water loss in the trunk, P. orientalis maintains a relatively stable Fd at the expense of increased TWD under soil drought, and R. pseudoacacia maintains relatively low stomatal conductance under soil drought with an increase in TWD. The results revealed that SDMV is determined by the stem water status and species-specific strategies for water use, which could provide beneficial information for forestation practices in semiarid regions.

Disparities in soil and water conservation functions among different forest types and implications for afforestation on the Loess Plateau

Afforestation is widely acknowledged as an effective approach for enhancing ecological conditions. Considering the challenging ecological environment on the Loess Plateau, prioritizing soil and water conservation functions in stands is crucial. The study aimed to ascertain the future development direction of forestry on the Loess Plateau by examining two representative forest types: planted forest (Robinia pseudoacacia pure forest and Pinus tabulaeformis pure forest), and natural secondary forest (a mixed forest of Quercus liaotungensis and Populus davidiana). The assessment centered on the soil and water conservation functions of the two forest types, encompassing the water conservation function (rainfall distribution and changes in multi-year soil moisture storage (0–200 cm)), soil conservation function (soil physicochemical properties), and understory plant diversity and stability. The results indicated that natural secondary forests outperformed planted forests in terms of water conservation function by effectively converting more precipitation into soil moisture, reducing runoff, and maintaining higher soil moisture storage. Additionally, natural secondary forests exhibited superior soil conservation functions compared to planted forests, characterized by higher soil porosity and nutrient properties. The variation in community structure between the shrub and herbaceous layers was more significant among different forests than within each forest (P < 0.05). Natural secondary forests exhibited higher understory shrub and herb biodiversity and interspecific repeatability compared to planted forests. Therefore, natural secondary forests are a more suitable forest type considering the natural conditions and silvicultural objectives of the Loess Plateau. To enhance the quality of afforestation, it is recommended to adopt near-natural planting patterns that replicate the environmental conditions of natural forests. For instance, actively creating mixed forests that emulate the tree species composition of natural forests and gradually reducing dependence on a single dominant tree species. Furthermore, the arborous and litter layers had a more direct and substantial influence on soil and water conservation functions compared to the shrub and herb layers. Foresters should prioritize regulating stand structure, such as increasing canopy variability, to enhance the water conservation function of stands. Additionally, they should actively protect the understory litter to fulfill its role in enhancing soil quality. This study provides a theoretical foundation and practical guidance for the implementation of vegetation restoration in ecologically vulnerable areas, such as the Loess Plateau.

Different transpiration and growth patterns of the black locust plantation and natural oak forest on China's Loess Plateau

AbstractRestoration of natural secondary forests and afforestation of introduced tree species are major effective measures for revegetation. The semiarid Loess Plateau region, characterised by fragile ecosystems and severe soil erosion, is a key area for ecological restoration and protection in China. To illustrate water use characteristics and adaptation to drought in the main forests in this area, we monitored the xylem sap flow of two typical adjacent forest communities with similar climatic characters, a secondary natural forest dominated by oak (Quercus liaotungensis) and a pure plantation of black locust (Robinia pseudoacacia), during 2011–2019 using Granier‐type thermal dissipation probes. Solar radiation (RS), air temperature, relative humidity (RH), precipitation and soil water content (SWC) were measured simultaneously. Throughout the whole study period, the mean diameter at breast height (DBH) and total sapwood area increased by 4.5 cm and 1.10 m2 ha−1, respectively in the oak forest and by 1.0 cm and 0.22 m2 ha−1, respectively in the black locust plantation. The monthly stand transpiration was jointly determined by phenological and meteorological factors. At the annual timescale, transpiration of the oak stand was significantly correlated with potential reference evapotranspiration (ET0) and rainfall in the previous year, whereas a significant positive relationship was detected between stand transpiration and SWC in the black locust stand. The analyses of differences between dry and wet years showed that the oak forest exhibited significantly different parameters in the regression analysis of stand transpiration to vapour pressure deficit (VPD), whereas only one parameter was clearly distinct in the black locust plantation, suggesting that its transpiration status did not fully recover even in wet years. The management of black locust plantations with weakened growth conditions should be adjusted under prolonged drought conditions. In contrast, oak forest can maintain the water balance and stable growth by efficiently controlling stomatal behaviour.

Optimization of Solid-State Fermentation Conditions of Quercus liaotungensis by Bacillus subtilis

The current study aimed to investigate the solid-state fermentation process of Quercus liaotungensis (QL) by Bacillus subtilis (BS). The parameters included the inoculation amount, the soybean meal addition amount, the fermentation temperature and the ratio of material to water. The optimal process was determined based on the nutritional value, tannin content and DPPH clearance of QL after fermentation. The results showed that: (1) The parameters of the optimal process included inoculating 106 BS per gram of QL, then adding 10% soybean meal, the ratio of material to the water of 100:80, and temperature at 33 °C for 72 h. (2) In the optimum fermentation conditions, the crude fiber content, and the ether extract content of QL decreased by 66.94% and 66.96%, respectively (p &lt; 0.05). Moreover, the crude protein content and the ash content increased by 65.81% and 4.63%, respectively, after fermentation (p &lt; 0.05). Additionally, the tannin content decreased by 62.77% (p &lt; 0.05), and the DPPH scavenging rate decreased by 45.45% (p &lt; 0.05) after fermentation, respectively. In summary, the QL significantly improved the nutritional value after the solid-state fermentation with BS.

Natural revegetation over ∼ 160 years alters carbon and nitrogen sequestration and stabilization in soil organic matter on the Loess Plateau of China

Natural revegetation has been reported to play a very active role in ecosystem carbon (C) and nitrogen (N) sinks in degenerated ecosystems. However, the responses of C and N sequestration and stabilization in soil organic matter (SOM) to natural revegetation remain inadequately understood. In this study, we analyzed C and N contents and δ13C and δ15N values of SOM, free light fraction (FLF), intra-aggregate particulate organic matter (IPOM) and mineral-associated organic matter (MAOM) along ∼ 160 years of natural revegetation on the Loess Plateau of China. The results showed that natural revegetation significantly (P < 0.05) enhanced soil C and N contents in FLF, IPOM, MAOM, SOM in the surface soil (0–20 cm) during the later stages of revegetation, which exhibited smaller impact on the deeper soil (20–60 cm). Natural revegetation significantly increased distribution proportions of C and N in FLF (i.e., 18.00–36.00%, 8.46–22.57%, respectively), and that in IPOM (i.e., from 11.60 to 25.38%, 10.89–26.92%, respectively), while it decreased that in MAOM (i.e., from 56.25 to 37.00%, 67.69–50.24%, respectively) in the surface soil, thereby altering C and N stabilization in SOM (0–20 cm). The climax Quercus liaotungensis forest exhibited the highest C distribution proportion in FLF and IPOM, and the lowest C distribution proportion in MAOM in the surface soil. The δ13C and δ15N were enriched with the decomposition of SOM and soil profile depths at each revegetation stage. The highest δ13C and δ15N values (0–60 cm) and the lowest C:N ratio (0–20 cm) of SOM, FLF, and IPOM were found in the farmland. In conclusion, ∼160 years of natural revegetation substantially promoted C and N sequestration in SOM, whereas altered C and N stabilization in SOM of the surface soil through shifting C and N towards more non-protected and pure physically protected SOM fractions rather than the most stable MAOM. Meanwhile, soil δ13C and δ15N in SOM and its fraction were changed along with natural revegetation. The most enriched soil δ15N in the farmland implied that soil N cycle in the farmland was more open to N losses relative to the other revegetation stages.

Characterization of dominant factors on evapotranspiration with seasonal soil water changes in two adjacent forests in the semiarid Loess Plateau

Evapotranspiration is an essential process of ecosystem water consumption and is controlled by meteorological factors and soil water conditions. In this study, evapotranspiration based on soil water budget was investigated with respect to major influencing factors during the growing seasons of 2012–2015 for two adjacent forest communities in the semiarid Loess Plateau region: a natural secondary forest dominated by oak (Quercus liaotungensis) and a plantation of exotic black locust (Robinia pseudoacacia). Based on the combination of precipitation, soil water storage, and evapotranspiration dynamics, four distinct periods were differentiated to explore the evapotranspiration response to the main meteorological factors. The correlation matrixes showed that, in most investigated days, evapotranspiration was limited by soil water storage, while an increase in soil water storage shifted dominance from water-related to energy-related factors. The stepwise regression of ≥5-day dry events in each period had a better fitness when paired with the relationship between the summations of evapotranspiration and dominant factors (R2 > 0.7, p < 0.01 for all) than the stepwise results for daily averages. A receiver operating characteristic (ROC) curve was applied to validate the division and determine thresholds. All divisions were thoroughly validated, and the soil water storage thresholds of the black locust (120.2 mm and 150.7 mm) were higher than those of the oak (105.8 mm and 137.9 mm). Our results suggest that the oak had an adaptive water consumption strategy, while the black locust had a higher sensitivity to soil water insufficiency. The method for determining the threshold of soil water storage to separate the dominant factors of evapotranspiration was validated. The approach may be applied to other semiarid forest communities with distinct evapotranspiration response patterns.

Responses of soil fungal communities and functional guilds to ~160 years of natural revegetation in the Loess Plateau of China.

Natural revegetation has been widely confirmed to be an effective strategy for the restoration of degraded lands, particularly in terms of rehabilitating ecosystem productivity and soil nutrients. Yet the mechanisms of how natural revegetation influences the variabilities and drivers of soil residing fungal communities, and its downstream effects on ecosystem nutrient cycling are not well understood. For this study, we investigated changes in soil fungal communities along with ~160 years of natural revegetation in the Loess Plateau of China, employing Illumina MiSeq DNA sequencing analyses. Our results revealed that the soil fungal abundance was greatly enhanced during the later stages of revegetation. As revegetation progresses, soil fungal richness appeared first to rise and then decline at the climax Quercus liaotungensis forest stage. The fungal Shannon and Simpson diversity indexes were the lowest and highest at the climax forest stage among revegetation stages, respectively. Principal component analysis, Bray–Curtis similarity indices, and FUNGuild function prediction suggested that the composition, trophic modes, and functional groups for soil fungal communities gradually shifted along with natural revegetation. Specifically, the relative abundances of Basidiomycota, Agaricomycetes, Eurotiomycetes, and ectomycorrhizal fungi progressively increased, while that of Ascomycota, Sordariomycetes, Dothideomycetes, Tremellomycetes, saprotrophic, pathotrophic, arbuscular mycorrhizal fungi, and endophyte fungi gradually decreased along with natural revegetation, respectively. The most enriched members of Basidiomycota (e.g., Agaricomycetes, Agaricales, Cortinariaceae, Cortinarius, Sebacinales, Sebacinaceae, Tricholomataceae, Tricholoma, Russulales, and Russulaceae) were found at the climax forest stage. As important carbon (C) sources, the most enriched symbiotic fungi (particularly ectomycorrhizal fungi containing more recalcitrant compounds) can promote organic C and nitrogen (N) accumulation in soils of climax forest. However, the most abundant of saprotrophic fungi in the early stages of revegetation decreased soil organic C and N accumulation by expediting the decomposition of soil organic matter. Our results suggest that natural revegetation can effectively restore soil fungal abundance, and modify soil fungal diversity, community composition, trophic modes, and functional groups by altering plant properties (e.g., plant species richness, diversity, evenness, litter quantity and quality), quantity and quality of soil nutrient substrates, soil moisture and pH. These changes in soil fungal communities, particularly their trophic modes and functional groups along with natural revegetation, impact the accumulation and decomposition of soil C and N and potentially affect ecosystem C and N cycling in the Loess Plateau of China.

High Level of Ammonium Nitrogen Increases Net Ecosystem Productivity in a Quercus liaotungensis Forest in Northern China

Forest ecosystems are vital to the terrestrial ecosystem’s carbon (C) cycle. The effects of nitrogen (N) addition on C sequestration in forest ecosystems are critical for better understanding C dynamics when facing an increase in N availability. We conducted a six-year field experiment to examine the effects of N addition on C sequestration and net ecosystem productivity (NEP) in a Quercus liaotungensis forest in northern China. N addition resulted in a significant increase in biomass C storage (17.54–48.62%) and changed the distribution patterns of above and belowground biomass C storage, resulting in a 9.64 to 23.23% reduction in the proportion of belowground biomass C compared with the control. The annual average heterotrophic respiration was significantly increased by the additional N (by 0.06–0.94 Mg C ha−1 yr1). In comparison with the control, the C sequestration efficiency driven by N addition ranged from 7.12 to 33.50 kg C/kg N. High-level N addition exerted stronger effects on ecosystem C sequestration than low-level N addition. NH4+-N, rather than NO3−-N, dominated the increase in ecosystem C sequestration. We found that Q. liaotungensis forest acted as a C sink. The increase in NEP in the study forest in northern China was mainly due to an increase in net primary productivity (NPP) caused by N addition. Atmospheric N deposition increased the C sequestration efficiency depending on the rate and form of N deposition.

Differences in the short-term responses of soil nitrogen and microbial dynamics to soil moisture variation in two adjacent dryland forests

Periodic droughts and extreme rainfall are predicted to become more common in the future; therefore, it is important to understand how soil N transformation processes driven by soil microbes respond to rainfall events. Differences in forest type, including those in the predominant mycorrhizal type, can have varying effects on soil N transformation. Therefore, we hypothesised that the response of the N transformation processes to rainfall events would differ between forest types, even those that are adjacently located. In this study, we generated a soil moisture gradient in adjacent dryland black locust (Robinia pseudoacacia, non-ectomycorrhizal [ECM]-type) and oak (Quercus liaotungensis, ECM-type) forests and measured the abundance and community composition of fungi and prokaryotes (including ammonia-oxidisers), extractable N content, and net N transformation rates in the soil. Increasing moisture was found to increase nitrate N content in the black locust forest but not in the oak forest. In the oak forest, the abundance of ECM fungi increased with increasing moisture, subsequently enhancing ECM fungal ammonium N uptake and limiting the N availability for ammonia oxidisers, which may reduce the nitrate N production by ammonia-oxidisers. Increased nitrate N uptake by ECM fungi may also result in low soil nitrate N content. The findings of this study indicate that the responses of the nitrate N dynamics to rainfall events can differ between adjacent forests and that this difference may be attributable to the presence of ECM fungi. Therefore, considering the forest mycorrhizal type is vital for predicating the response of forest N cycling under climate change.

The influence of microhabitat factors on the regeneration and species composition of understory woody plants in Pinus tabuliformis plantations on the Loess Plateau

Chinese pine (Pinus tabuliformis) is one of the main tree species for water and soil conservation on the Loess Plateau. However, most of these plantations face a series of ecological problems, such as low diversity of understory plants and difficulty in natural regeneration. Our study focused on the microhabitat factors that affected the species composition of understory woody plants and the distribution and growth of regeneration in Chinese pine plantations. Plots of 50 × 50 m were randomly established in three typical mature plantations, and then each plot was divided into 100 5 × 5 m microplots to investigate the characteristics of canopy trees, Chinese pine regeneration, other understory woody plants, the light environment, litter and soil. The involved microhabitat factors jointly explained 37.68% of the variation in the species composition of understory woody plants, among which soil total phosphorus (2.66%) and available potassium (2.19%) were the main factors. In the regeneration layer, Chinese pine regeneration (7,261 stems·ha−1, 124.6 cm), Quercus liaotungensis (3,114 stems·ha−1, 117.0 cm) and Betula platyphylla (953 stems·ha−1, 305.7 cm) were considered the canopy replacement species with the most potential. Additionally, we found that the regeneration density was significantly affected by soil total nitrogen, available potassium and shrub density, while the differences in regeneration height growth mainly resulted from the density of other understory trees and shrubs, soil total phosphorus and diffuse non-interceptance. The density of saplings and juvenile trees of Chinese pine was more affected by microhabitat factors than that of seedlings, but the effect of the microenvironment on the former two was less different, indicating that the sapling stage may be the critical period for successful recruitment of the plantations. Therefore, gap creation or thinning is suggested to promote the growth of saplings and juvenile trees, thus increasing the opportunity for them to enter the canopy. At the stand scale, soil resources and interspecies interactions were the dominant microhabitat factors influencing the regeneration of Chinese pine, which inspired us to deeply explore the vegetation-soil-microbial systems and the relationship between regeneration and their neighbors in the future. Moreover, managers should pay more attention to the survival and growth of saplings and juvenile trees to promote the sustainable development of Chinese pine plantations. We believe that these plantations will be transformed into coniferous and broad-leaved mixed forests with high stability and species diversity (e.g., P. tabuliformis × B. platyphylla or P. tabuliformis × Q. liaotungensis).

Changes in soil organic carbon and nitrogen pool sizes, dynamics, and biochemical stability during ∼160 years natural vegetation restoration on the Loess Plateau, China

Natural vegetation restoration has been reported as an effective strategy for the enhancement of soil organic carbon (SOC) and nitrogen (SON) sequestration in degraded ecosystems. However, changes in SOC and SON pool sizes, dynamics, and biochemical stability to natural vegetation restoration remain inadequately addressed. For this study, we investigated carbon (C) and nitrogen (N) contents and δ13C and δ15N values of SOC and SON pools, their labile C and N (LSOC and LSON, respectively), and recalcitrant C and N (RSOC and RSON, respectively) along 0–60 cm soil depths spanning ∼160 years of natural vegetation restoration on the Loess Plateau, China. Our results revealed that natural vegetation restoration greatly enhanced SOC, SON, LSOC, LSON, RSOC, total N, water-soluble organic C, and mineralizable organic C in the topsoil (0–20 cm), while it had little influence on the deeper soil layers (20–60 cm). The concentrations and stocks of SOC and SON in the topsoil increased significantly during the later restoration stages. The recalcitrant index for C at the 0–40 cm soil depths was highest in climax Quercus liaotungensis forest, while the recalcitrant index for N was unchanged at 0–20 and 40–60 cm soil depths between vegetation restoration stages. The δ13C values of SOC, LSOC, and RSOC, and δ15N values of SON and LSON were more enriched in the deeper soil layers relative to the topsoil, for the majority of restoration stages. The δ15N values of SON, LSON, and RSON in the topsoil were more enriched during the early restoration stages compared to the later restoration stages. Our results suggested that long-term natural vegetation restoration enhanced SOC and SON sequestration, increased biochemical stability of SOC, altered the dynamics of SOC and SON in the topsoil of degraded ecosystems through the increased inputs of plant residuals, and reduced the decomposition soil organic matter.

Quercus liaotungensis

This datasheet on Quercus liaotungensis covers Identity.

Survival Rate, Chemical and Microbial Properties of Oak Seedlings Planted with or without Oak Forest Soils in a Black Locust Forest of a Dryland

Native tree species are frequently unable to effectively grow in non-native tree cultivation scenarios. In the Loess Plateau, China, it is difficult to find native oak (Quercus liaotungensis) seedlings in non-native black locust forests. Black locust is an arbuscular mycorrhizal (AM) tree, but oak is an ectomycorrhizal (ECM) tree. Plants highly depend on their symbiotic mycorrhizal fungi to take up water, nitrogen (N) and other nutrients. We hypothesized that black locust forests would not provide ECM inoculum to oak seedlings, limiting their water and nutrient uptake, which would be improved by ECM inoculum. Here, we (1) sowed seeds, with or without oak forest soils, (2) transplanted seedlings collected in oak forests, with or without oak forest soils, and (3) planted seedlings germinated in autoclaved or unautoclaved oak forest soils. We measured the survival and growth rate for all three experiments, along with chemical properties, and root ECM colonization. Oak seeds sowed with oak forest soils had higher mycorrhizal colonization, leaf N concentrations and survival rate, and lower root δ13C than the seeds sowed without oak forest soils. Planting with oak forest soils also increased the survival rate of the germinated seedlings, but not the transplanted seedlings. Overall, our study suggested that the use of oak forest soils in the black locust forest to improve the water and N uptake of oak seedlings by providing the ECM inoculum, resulting in a high survival rate. Our study also implies that the method of sowing seeds was effortless and effectively compared to transplanting wild/nursery seedlings.

Dynamics and influencing factors of stem diameter micro-variations during the growing season in two typical forestation species in the loess hilly region, China.

Using DC3 high-resolution dendrometer and Granier-type thermal dissipation probes, we measured stem diameter micro-variations and xylem sap flow of two typical forestation species, Quercus liaotungensis and Robinia pseudoacacia, for a growing season in the loess hilly region of China. The main environmental factors (soil water content, solar radiation, air temperature and relative humidity) were monitored. The linkage between diameter micro-variations and transpiration water use were analyzed with respect to their responses to environmental factors. The results showed that the variations in stem diameter and sap flux density of both species had obvious diurnal rhythms. The maximum daily shrinkage was positively correlated with daily sap flux density. The micro-variation of stem diameter at the daily scale was affected by transpiration during the day. The maximum daily shrinkage of stem diameter was positively correlated and well fitted with transpiration driving factors (solar radiation, vapor pressure deficit, and the integrated variable VT). The difference in slopes of regression curves suggested that the daily variation of stem diameter in Q. liaotungensis was greater and more sensitive to meteorological factors than that in R. pseudoacacia. The sap flux densities of both tree species were higher during the period with relatively higher soil water content than that with lower soil water content. The difference of maximum daily diameter shrinkage between different soil water conditions was statistically significant in Q. liaotungensis, but not in R. pseudoacacia. These differences may be related to water use strategies, including transpiration regulation and stem water replenishment.