Pinus Tabulaeformis Plantation Research Articles

Interactions between root and rhizosphere microbes mediate phosphorus acquisition in Pinus tabulaeformis

The Pinus tabulaeformis plantation is a major industrial forest in China. Phosphorus (P) deficiency seriously affected its growth and productivity. Root traits and rhizosphere microorganisms play essential roles in plant P acquisition. However, how root traits interact with microbial communities for P acquisition remains largely unclear. The responses of P. tabulaeformis root morphological characteristics, oxalic acid, soil P fractions and rhizosphere bacterial and fungal communities and potential functions to P addition were investigated using a pot experiment with three P levels (0, 20, and 80 mg P kg−1 soil). Additionally, we constructed a functional synthetic microbial community (SynCom) and verified their behaviors in promoting plant P acquisition and growth. P fertilization significantly increased the soil CaCl2-P, citrate-P, HCl-P and microbial biomass P (MBP) fractions and decreased oxalic acid, bacterial indicator genera in P deficiency and ectomycorrhizal fungi (ECM). Most of the bacterial indicator genera in P deficiency were negatively correlated with citrate-P and HCl-P but were positively correlated with alkaline phosphatase (ALP) and oxalic acid. According to structure equation models, soil total P could directly influence P acquisition efficiency and indirectly through its effects on ECM or by regulating oxalic acid, which regulated bacterial indicator genera in P deficiency and thus affected ALP production. Inoculation with SynCom significantly increased soil available P contents, ALP activities, root P concentrations and superoxide dismutase activities. Under low P conditions, P. tabulaeformis adopted a high carbon cost strategy for P acquisition, specifically moderating root secretion. Rhizosphere bacteria could accelerate soil P mobility and enhance the P absorption ability and systemic resistance of roots to alleviate P stress. This study provided the theoretical basis for the exploitation and utilization of microbial fertilizers, as well as for the cultivation and management of plantation.

Effects of Forest Gaps on Forest Floor Microbial Community Composition in Pinus tabulaeformis Forests in a Rocky Mountain Area, Beijing, China

Forest gaps induce environmental heterogeneity, but their effects on the local forest floor microbial communities are not fully understood. This research investigated the impact of forest gap positions on the forest floor microbial community composition to provide baseline information for projects to accelerate nutrient cycling and forest regeneration and enhance ecosystem services. A one-year-old forest gap and an area of 40–50 m2 in Pinus tabulaeformis plantations were selected in the Beijing mountainous area. Forest floor samples were collected from the following positions: gap center, gap border, and adjacent closed canopy. Our study demonstrated that gap positions significantly influenced the forest floor microbial community composition. The Gram-positive bacteria, Gram-negative bacteria, and total bacteria, as well as the fungi, were significantly greater in the forest gap center and gap border compared to those in the closed canopy, and the dissolved organic carbon, readily oxidized organic carbon, ammonia nitrogen, and nitrate nitrogen followed the same trend. Compared with those of the closed canopy, the Gram-positive bacteria, Gram-negative bacteria, total bacteria, and fungi in the gap center were markedly greater by 23%, 25%, 22%, and 24% and by 14%, 14%, 11%, and 16% in the gap border, respectively (p < 0.05). Redundancy analysis demonstrated that shifts in the litter microbial community composition were predominantly predicted by litter moisture and β-1,4-glucosidase. In addition, we discovered that the microbial community composition was greater in the undecomposed forest layer than that in the semi-decomposed layer. In summary, gap positions and forest floor layers have a significant impact on microbial community composition. Nevertheless, additional long-term investigations are needed. Our study provides a reference for the promotion of nutrient cycling to guide future ecological management.

The Effects of Thinning on Tree Growth and Stand Biomass in a Chronosequence of Pinus tabulaeformis Plantations in the Loess Plateau of China

Thinning plays a vital role in controlling stand density of plantation forests to get quality wood and more ecological function. However, the specific effects of thinning on forest biomass connected with forest age are usually overlooked especially in semi-arid regions. Here, we examined the effects of thinning on individual tree growth and stand biomass in a chronosequence of 20-, 30-, 40-, and 50-year-old Chinese pine (Pinus tabulaeformis) plantations on the Loess Plateau, China. We found that under different thinning managements, both mean diameter at breast height (DBH) and tree height followed the logistic growth pattern, and thinning promoted tree radial growth more than height. The effects of thinning on tree biomass differed between the individual tree and stand level. Thinning could promote individual tree biomass irrespective of stand ages, while stand biomass did not differ between the thinned and unthinned stands at different stand ages. Furthermore, the multiple linear regression analysis and structure equation model showed that individual tree growth was the primary contributor of stand biomass. Thus, we infer that the stand biomass loss after thinning could be mainly compensated by enhanced tree growth, especially radial growth, after a period of recovery (no more than 20 years). The results could provide helpful guidance for forest management and highlighted that reasonable thinning treatment could result in both high individual tree product and stand level harvests in the long term.

Effects of long-term vegetation restoration on soil physicochemical properties mainly achieved by the coupling contributions of biological synusiae to the Loess Plateau

Large-scale vegetation restoration has been performed to improve the fragile ecological environment of the Loess Plateau in the last decades. At present, the effects and mechanism of long-term vegetation restoration on soil properties in ecosystems require further exploration to provide a reference for rational ecological construction. Hence, we investigated the differences in vegetation attributes and soil properties between three typical vegetation types (Pinus tabulaeformis plantation forest, PTPF; Robinia pseudoacacia plantation forest, RPPF; natural secondary forest, NSF) after long-term (30–40 years) vegetation restoration in the western Loess Region, China. Our results showed that (1) the arborous synusia biomass of the plantation forests was twice that of NSF, whereas NSF had almost 50% higher near-surface synusia biomass than the plantation forests; (2) the soil nutrient contents of the plantation forests were lower (30%) than those of NSF; (3) the soil bulk density, organic matter, total nitrogen, and phosphorus were positively related to arborous and shrub synusia biomass; (4) the coupling effects of four biological synusiae (with the contribution of 47.67%) were the dominant factors affecting soil physicochemical properties. Natural forests have the better vegetation attributes and soil properties than plantation forests, indicating that the close-to-nature restoration should be considered in ecological restoration. These findings can provide scientific support and theoretical basis for reforestation and ecological restoration in the Loess Plateau region and similar areas in the future.

Dynamic microbial community composition, co-occurrence pattern and assembly in rhizosphere and bulk soils along a coniferous plantation chronosequence

During plantation development, soil microbial communities in different soil compartments (e.g., rhizosphere and bulk soils) is critical for the establishment of plant diversity and multiple ecosystem functions. The assembly process shaped microbial communities. However, the assembly mechanisms of soil microbial communities have rarely been studied. Therefore, we investigated the bacterial and fungal community compositions, species cooccurrence, and assembly processes in rhizosphere and bulk soils along a Pinus tabulaeformis plantation chronosequence (15, 30 and 60 years old). Results showed that plantation development altered the soil properties and microbial community structures in the rhizosphere and bulk soils. The effect of stand age on the soil properties and microbial community structures was stronger than the effect of the soil compartment. Higher turnover rates of soil microbial communities were observed in rhizosphere soil than in bulk soil. Dispersal limitation governed the bacterial and fungal community assembly throughout plantation chronosequence, while the fungal community was more susceptible to dispersal limitation. The bacterial and fungal keystone species compositions in the rhizosphere had significant positive correlations with the soil total phosphorus and nitrite nitrogen and total nitrogen and total phosphorus, respectively, indicating their importance in soil nitrogen and phosphorus cycling. The complexity of bacterial networks increased along the chronosequence, whereas fungal network complexity did not show a clear age-related trend but higher in the rhizosphere than in bulk soils. These results indicated that during Pinus tabulaeformis plantation development, soil microbial assembly was less environmentally constrained due to an increase in resource availability.

Microtopography mediates the climate-growth relationship and growth resilience to drought of Pinus tabulaeformis plantation in the hilly site.

Understanding the factors affecting the growth of plantation forests can reduce the loss of economic and ecological values caused by plantation forest subhealth. Plantation forests are widely distributed in hilly areas with microtopographic features. Microtopography influences climatic factors associated with plant growth, during not only general time but also extreme events like droughts. However, little research has been conducted on the effects of microtopography on the plantation forest growth. In this paper, we selected Pinus tabulaeformis planted in a hilly site, and studied the effect of microtopography on the climate-growth relationship and drought response of a typical plantation in Northeast China using dendroecological methods. We found: 1) Between hill positions, temperature caused a climatic growth difference. Compared to the hilltop, the correlation of annual growth on the hillside with monthly temperature was more negative in July-August and less positive in January-April. 2) Between aspects, precipitation intensities caused a climatic growth difference. Compared to the sunny slope, the correlation of annual growth on the shady slope with monthly total precipitation below 10 mm/day was less positive (May-June) or more negative (March-April and July), while that with monthly total precipitation above 10 mm/day was more positive in most months.3) Drought response varied significantly based on hill position and aspect. There was no significant difference in resistance between hill positions, while recovery and resilience on the hilltop were greater than those on the hillside.Resistance, recovery, and resilience were all lower on the sunny slope than those on the shady slope. Overall, microtopography exists the effects on the growth of plantation forests, both in terms of climate-growth relationships in general climate and in response to drought when extreme events. Meanwhile, the climatic factors that caused the difference in growth of plantation forests between hill positions and aspects differed. The difference in growth between hill positions was caused by temperature, while that between aspects was caused by precipitation intensity. Drought response difference reflected the legacy effect of drought on plantation growth, which could lead to subsequent changes in climate-growth relationships. These findings demonstrate that strengthening the research of forest trees on microtopography is necessary for accurate carbon sink assessment and precise forest management.

Canopy Interception of Different Rainfall Patterns in the Rocky Mountain Areas of Northern China: An Application of the Revised Gash Model

Canopy interception is an important part of forest ecosystem hydrological processes. It is the first stage of water distribution when rainfall reaches the canopy and has an important impact on nutrient inputs and water exchange. Pinus tabulaeformis is a main tree species in the rocky mountain areas of Northern China, and it is also a primary species for artificial afforestation. In previous studies of canopy interception, applications of the revised Gash model did not take rainfall characteristics into account. Therefore, in this study, rainfall patterns were divided according to the local rainfall characteristics in the rocky mountainous areas of Northern China. Rainfall was divided into three patterns. Rain pattern A was the main rainfall type. Rainfall patterns B and C were two types of rainstorms. Next, the revised Gash model was used to simulate Pinus tabulaeformis plantations under different rainfall patterns. The results showed that the canopy interception rate of Pinus tabulaeformis plantations in this area ranged from 14.7% to 17.9%. The revised Gash model can be used to simulate Pinus tabulaeformis plantations in the rocky mountainous areas of Northern China, with good simulation results for more than 80% of the conventional rainfall patterns. Furthermore, the canopy interception effect of simulated cumulative rainfall events was better than the individual rainfall event. The simulation effect for special rainfall patterns was not good, so it is necessary to improve the model parameters or collect more rainfall samples. These results can be used to explore the applicability of the revised Gash model in Pinus tabulaeformis plantations in the rocky mountain areas of Northern China. They also demonstrate different applicability of the model under different rainfall characteristics.

Variations and Factors Characterizing Ecological Niches of Understory Herbaceous Species in Plantation Forests

Plant ecological niche characteristics are powerful representations of plant survival status. Understory herbaceous species in plantation forests are sensitive to local ecological environment changes; patterns of ecological niche changes of herbaceous plants under plantation forests are of great significance for maintaining the stability and sustainable development of plantation forest ecosystems. This study aims to explore the ecological niche characteristics of understory herbaceous species in plantation forests and their influencing factors. Six different site types of Pinus tabulaeformis plantations were selected from a stable plantation community in the feldspathic sandstone area of the Loess Plateau (China). The relative importance value and niche breadth were used as comprehensive quantitative indices to characterize the status, role, and degree of dominance of understory herbaceous species in plantation forests. We found few dominant species of understory herbaceous species in plantation forests, mostly companion species. The niche characteristics of understory herbaceous species in plantation forests varied significantly. For understory herbaceous species, the niche width was positively correlated with slopes and the niche overlap of the sunny slopes was positively relevant with slopes, while that of the shady slopes was negatively correlated. A canonical correspondence analysis indicated that several major factors influencing the niche breadth and niche overlap of understory herbaceous species in plantation forests were different. The canopy density and slope of plantation played a major role in the niche breadth and niche overlap of understory herbaceous species in plantation forests. In summary, the species distribution of understory herbaceous species in plantation forests was determined by site type. The canopy density and geographical slope were the dominant environmental factors for different ecological niche characteristics of understory herbaceous species. The ecological niche variation of different herbaceous species was the consequence of the integrated effects of the plantation and geographical environment.

Soil microbes-mediated enzymes promoted the secondary succession in post-mining plantations on the Loess Plateau, China

The diversity of vegetation configuration is the key to ecological restoration in open-pit coal mine dump. However, the recovery outcomes of different areas with the same vegetation assemblage pattern are completely different after long-term evolution. Therefore, understanding the causes of differential vegetation recovery and the mechanism of plant succession is of great significance to the ecological restoration of mines. Three Pinus tabulaeformis plantations with similar initial site conditions and restoration measures but with different secondary succession processes were selected from the open-pit coal mine dump that has been restored for 30 years. Soil physicochemical properties, enzyme activities, vegetation and microbial features were investigated, while the structural equation models were established to explore the interactions between plants, soil and microbes. The results showed that original vegetation configuration and soil nutrient conditions were altered due to secondary succession. With the advancement of the secondary succession process, the coverage of plants increased from 34.8% to 95.5% (P < 0.05), soil organic matter increased from 9.30 g kg−1 to 21.13 g kg−1 (P < 0.05), and total nitrogen increased from 0.38 g kg−1 to 1.01 g kg−1 (P < 0.05). The activities of soil urease and β-glucosidase were increased by 1.7-fold and 53.26%, respectively. Besides, the secondary succession also changed the soil microbial community structure and function. The relative abundance of Nitrospira genus which dominates the nitrification increased 5.2-fold. The results showed that urease and β-glucosidase promoted the increase of vegetation diversity and biomass by promoting the accumulation of soil organic matter and nitrate nitrogen, which promoted the ecological restoration of mine dumps.

Contributions of biotic and abiotic factors to soil aggregation under different thinning intensities

Soil aggregation is a hierarchical and complex process mediated by both abiotic and biotic factors, and is crucial for preventing erosion.This study aimed to providing new insights into the role of biotic and abiotic factors on soil aggregation amid various thinning intensities and exploring mechanisms of aggregation. A survey involving four thinning treatments (T0: no thinning, T10: low-intensity thinning, T20: medium-intensity thinning, and T50: high-intensity thinning) of Pinus tabulaeformis plantation was conducted to explore mechanisms of soil aggregation and quantify the significance of selected biotic and abiotic factors effects on aggregation using structural equation models. Comprehensive models that included soil physicochemical properties, microbial community, root, and microarthropods were established. Compared to no-thinning, medium-intensity thinning contained about 1.8 times more mean weight diameter (MWD). The levels of total phospholipid fatty acids (totPLFAs), arbuscular mycorrhizal fungi (AMF), mycorrhizal colonization rate (F), and total microarthropods were significantly higher in T20 than in other thinning treatments. The structural equation model indicated that the abiotic, biotic, and abiotic/biotic factors accounted for 35%, 82%, and 92% of the variation on MWD, respectively. MWD depended on the positive influence of F, totPLFAs, and AMF. Microorganisms were positively affected by total microarthropods and negatively affected by Diptera. Overall, the medium-intensity thinning (T20) was beneficial to the stability of soil aggregates. Also, biotic factors were more vital in determining soil aggregation than abiotic factors. Of note, soil microarthropods actd on aggregates by influencing microorganisms rather than directly affecting aggregation.

Effects of litter mass on throughfall partitioning in a Pinus tabulaeformis plantation on the Loess Plateau, China

Litter accumulates annually since vegetation is widely planted for afforestation. There is little information about the effects of litter on the reallocation of rainfall processes, although it plays an important role in hydrologic cycling. To examine the ecohydrological functions of litter under field experiments, eight runoff plots of four needle-leaf litter masses (0, 0.6, 1.2 and 1.8 kg/m2) were established in a Pinus tabulaeformis plantation on the Loess Plateau. Evaporation (E), surface runoff (R), infiltration and soil moisture dynamics in the 0–100 cm soil layer were measured throughout the rainy season in 2020. The results show that E decreased by 26.1–53.8% in litter-covered treatments compared with that without litter. Litter hindered heat and water exchange between soil and atmosphere, especially in 0–10 cm soil layer. R was effectively reduced by 71.1–90.5% with an increase in litter mass, and litter was more effective in controlling the R generation at higher rainfall intensities than at lower rainfall intensities. Litter hindered infiltration at the beginning of the rainy season but increased the soil water storage (SWS) with deeper infiltration in the long term. Both proportions of R and E to throughfall (P) decreased with increasing litter mass, and R/P was generally less than 10% in litter-covered treatments. SWS nonlinearly increased with an increase in litter mass, and more than half of the rainfall was stored, even in bare soil. Excessive litter (> 1.33 kg/m2) caused relatively less rainwater to be stored below the 100 cm soil layer or consumed by trees. This study may help to better understand the effects of litter on hydrological processes and can provide theoretical references for the proper management of plantations.

Impact of competition on the growth of Pinus tabulaeformis in response to climate on the Loess Plateau of China

As climate changes, understanding tree responses to climate is important to predict tree growth, and plant competition as a nonnegligible biotic factor plays a key role in such responses. However, few studies have investigated how competition affects the response of Pinus tabulaeformis plantations to climate. In our study, we investigated nine 29-year-old P. tabulaeformis plantation plots (three density gradients: 1208 N/ha, 2275 N/ha, 2989 N/ha). The dendroecological method was used to analyze the impact of competition on tree responses to drought and interannual climate variation. The stand density index was used to indicate the intensity of competition. The results showed that competition modified the climate–growth relationship. Competition increased tree sensitivity to drought but the relationship between competition and sensitivity to drought was nonlinear, which suggested that the competition effect slightly increased under intense competition conditions. Additionally, competition reduced trees growth sensitivity to interannual climate variation. After 1999, the effect of competition was obvious. The sensitivity of small-diameter trees, especially those in middle- and high-density stands, declined. Thus, in future, these trees presumably may exhibit a reduced sensitivity to interannual climate variation and a greater sensitivity to drought.

Near-natural transformation of Pinus tabuliformis better improve soil nutrients and soil microbial community.

Pinus tabulaeformis plantations have been established around northern China to restore degraded land and provide timber or fuelwood. In recent years, widely distributed monoculture P. tabulaeformis forests have been transformed into mixed forests due to various ecological problems. However, the current research on the influence of near-natural transformation of P. tabulaeformis on soil microbial diversity and community composition remains limited. Therefore, we examined the effect of forest conversion from monoculture Pinus tabuliformis (PT) to P. tabuliformis-Armeniaca vulgaris (PTAU), P. tabuliformis - Robinia pseudoacacia (PTRP), P. tabuliformis - Vitex negundo L. var. heterophylla (PTVN) forests on soil microbial community diversity and composition. The results indicated that compared to PT, PTAU, PTVN, and PTRP could enhance the soil pH, TC, TN, AN, and AK in different degrees, the most obvious in PTAU. Near-natural transformation of P. tabuliformis could improve soil bacterial Pielou_e index, and Simpson index, as well as soil fungal Chao1 index. Proteobacteria and Ascomycota were the dominant soil microbial community at the phylum level. What’s more, both soil bacterial and fungal community among PT, PTAU, PTRP and PTVN showed clear different, and PTAU obviously altered the soil microbial community structure. Proteobacteria was the predominant group in PT, while, Gemmatimonadetes enriched in PTVN. Ascomycota was the predominant group in PTAU, while, Basidiomycota was the predominant group in PTRP. Near-natural transformation of P. tabuliformis could change soil microbial community via altering soil characteristics. In brief, our research results revealed the influence of tree composition and soil nutrient availability on soil microbial diversity and composition, and provided management guidance for introduction soil microbial community in forest protection and management.

Climate-growth pattern of Pinus tabulaeformis plantations and their resilience to drought events in the Loess Plateau

Large-scale plantations were established under the Grain for Green project to improve the ecological environment of the Loess Plateau (LP) of China. However, there are increasing concerns regarding the sustainability of plantation ecosystems under climate change. In this study, we developed tree-ring width chronologies of Pinus tabulaeformis at seven sites along a precipitation gradient from south to north in the LP. Correlation analysis was performed to investigate the climate (temperature, precipitation, self-calibrating Palmer Drought Severity Index)-growth relationship. Moreover, the tree resilience components were computed to study the adaptability of trees to extreme drought during the growth periods. The results showed that the differences in radial growth to climate change along the precipitation gradient and the cluster analysis of the tree ring width index (RWI)-scPDSI correlation coefficient illustrated that the climate-growth response pattern along the LP was divided into southern and northern regions. Tree growth in the southern region is limited by humid environment conditions, while tree growth in the early and middle growing seasons of the northern region is limited by warming-induced drought. As the temperature rising over the past fifty years, the growth was found to be negatively correlated with temperature, especially in the spring and autumn seasons of the northern region. In contrast, the effect of precipitation on tree growth became more negative in the southern region, but more positive in the middle and late growing seasons of the northern region. Moreover, tree resilience analysis showed that the high resistance of Pinus tabulaeformis in the southern region, whereas high recovery in the northern region. It was difficult for the growth of Pinus tabulaeformis to recover from drought in the southern region, but stronger adaptability to extreme drought events in the northern region. Our study illustrated that there are different climate response patterns and limiting factors of Pinus tabulaeformis along the precipitation gradient in the LP; thus, different ecological restoration and regional forestry management strategies should be initiated in the LP.

The production and nutrients in the fine roots of fertilized Pinus tabulaeformis plantation forests in the Loess Plateau in China

ABSTRACT Fine roots (FRs; <2 mm in diameter) might act as substantial pools of underground carbon and nutrients in the forest ecosystem. Since nutrient availability directly impacts plant growth, any changes in soil fertilization and subsequent changes in nutrients would alter the production of FRs. Here, we investigated the impact of fertilization with nitrogen (N) and phosphorus (P) [control, N (200 kg/ha/y), P (100 kg/ha/y), and N + P (200 kg N/ha/y + 100 kg P/ha/y)] on the FR production, biomass, turnover rate, N:P ratio in young (10-year) and nearly mature (40-year) Pinus tabulaeformis forest stands in the Loess Plateau in China. The production and biomass of FRs were evaluated using the ingrowth core and the soil core methods, respectively. The results showed that during the first growing season after N or P fertilization, neither the production, biomass nor the turnover rate of FRs responded significantly to the treatments. A substantial increase in the TN content was observed after fertilization with N, P, and N + P in the FR of the young forest stand, but not in the mature forest stand. The ratio of N:P in FRs increased after N addition but did not respond to P addition significantly in either the young or mature forest stands, indicating that FR N:P ratio was affected more by N availability than by P availability in P. tabulaeformis forests on the Loess Plateau.

Forest management practices of Pinus tabulaeformis plantations alter soil organic carbon stability by adjusting microbial characteristics on the Loess Plateau of China

Sustainable management practices can enhance the capacity and potential for soil carbon (C) sequestration, significantly contributing towards mitigating regional climate change. Here, we investigated how the microbial characteristics of a Pinus tabulaeformis plantation responded to different management practices to identify the role of microbial characteristics in influencing the stability of soil organic carbon (SOC). We chose a Pinus tabulaeformis plantation on the Loess Plateau where forest management practices had been conducted since 1999. Five forest management practices were implemented: two at the forest level (P. tabulaeformis with and without ground litter), and three using different vegetation restoration approaches after clear-cutting (P. tabulaeformis seedlings, abandoned grassland, and natural shrub regeneration). Microbial biomass, soil respiration, microbial community structure, microbial metabolic function, and soil oxidizable organic carbon (OC) fractions were evaluated. Forest management practices changed SOC stability by adjusting the microbial characteristics (e.g. soil microbial community diversity and microbial metabolic function diversity). The result of path analysis was that the direct path coefficient of microbial biomass on soil oxidizable OC fractions was the largest, which was 1.499. Path analysis and redundancy analysis showed that microbial biomass had the largest direct influence on soil oxidizable OC fractions. Compared with other forest management practices, natural shrub regeneration increased the nonlabile carbon fraction by increasing soil microbial characteristics, and contributed the most towards stabilizing SOC, which enhanced the stability of the soil ecosystem on the plateau. In conclusion, microbial biomass was the biggest influence factor of SOC stability. In contrast, the stability of SOC may be most stable in the area of natural shrub regeneration.

Effects of vegetation type, fine and coarse roots on soil microbial communities and enzyme activities in eastern Tibetan plateau

Microbial communities and enzyme activity in soil are the functional link through which the vegetation type occupying a site, may alter soil processes fundamental to nutrient cycling. Roots are known to regulate soil carbon (C) input, but the impacts of different classes of roots on soil microbial community (as indexed by PLFAs) and enzyme activity are uncertain. Thus, the aim of this study was to assess how different classes of woody roots (fine roots ≤ 2 mm and coarse roots > 2 mm) in Pinus tabulaeformis (PT) and Cercidiphyllum japonicum (CJ) plantations influence the microbial community and enzyme potential activity, as compared to natural shrubland.In the fine root rhizosphere soil, the PT and CJ plantations had lower abundances of fungal and gram-positive bacterial PLFAs, and the PT plantation had significantly lower acid phosphatase, dehydrogenase, and higher invertase activities compared to the shrubland. The shrubland and CJ plantation had distinctly higher soil microbial parameters (total, fungal, and arbuscular mycorrhizal fungal PLFAs) and enzyme activities (urease, acid phosphatase, invertase, β-glucosidase, and dehydrogenase) in the fine root rhizosphere than in the coarse root rhizosphere and bulk soils. We concluded that soil organic carbon (SOC) (much more significant) and total nitrogen (TN) were the main factors in regulating soil microbial community and enzymes.Our findings demonstrate the importance of fine roots in regulating microbial community and function. Our results also highlight that differences between fine root rhizosphere and coarse root rhizosphere, or bulk soil are dependent on vegetation type.

Effects of Management Measures on Soil Water-soluble Carbon and Nitrogen and Their Three-Dimensional Fluorescence Characteristics of Pinus tabulaeformis Plantations on Loess Plateau

The Pinus tabulaeformis plantation on the Loess Plateau was selected as the research site to study the changes of soil water-soluble carbon and nitrogen content and components of soil dissolved organic matter (SDOM) under different management measures (litter removal, young Pinus tabulaeformis forest, shrubs, grassland). The uncleared Pinus tabulaeformis plantation was used as the control. Results show that the soil water-soluble organic carbon content of shrubs and young Pinus tabulaeformis forests was significantly higher than that in other management measures. The content of soil water-soluble organic carbon decreased with an increase in soil depth, whereas soil water-soluble organic carbon/soil organic carbon (WSOC/SOC) increased. The change of soil water-soluble nitrogen content corresponded to that of water-soluble carbon. The content of soil water-soluble nitrogen content in the young Pinus tabulaeformis forest was higher than that of other management measures, and generally decreased with an increase in depth. Different management measures have significant effects on SDOM components. Based on three-dimensional fluorescence spectroscopy combined with parallel factor (EEM-PARAFAC) analysis, four components of SDOM are identified, which are mainly divided into categories, humus, protein-like, and soluble microbial metabolites in three major categories, among which the main component of the SDOM is the rich acid humus, and the highest content in the soil of the young forest of Pinus tabulaeformis is rich acid. The results suggested that management measures had certain effects on soil water-soluble carbon and nitrogen content as well as SDOM components, especially in young Pinus tabulaeformis forests and shrubs. The young Pinus tabulaeformis forest and shrubs increased the content of soil water-soluble organic carbon and water-soluble nitrogen, enhanced their ability to migrate and transform in the soil, and changed the structural composition of soil organic matter, hence enhancing the degree of humification and further improving soil quality.

Variations in the growth response of Pinus tabulaeformis to a warming climate at the northern limits of its natural range

Higher temperatures are changing the geographical locations in which Pinus tabulaeformis plantations thrive. Future plantations should be located in the warmer, wetter regions of northern China. The adaptability of fragile plantation ecosystems to environmental change, especially in our currently warming climate, has become an important issue. We studied the growth of Pinus tabulaeformis, a tree species endemic to China and widely used in plantations, along a climate–latitude gradient. We established a regional tree ring data network for P. tabulaeformis based on 1340 cores from 28 plantations at the northern limits of its natural range in China and studied the association between the radial growth of the pines and climate factors in a changing environment. Our results show that increasing temperatures have led to changes in the distribution of P. tabulaeformis, with plantations expanding in the southern sub-regions and shrinking in the northern sub-regions. An increase in temperature and the subsequent effect on the availability of water is the most important factor in the different responses of P. tabulaeformis growth to climate change. Relatively wetter regions, such as the southern part of our study area, may be better locations to develop future P. tabulaeformis plantations.

Designing near-natural planting patterns for plantation forests in China

BackgroundChina has a long tradition of managing planted forests. Different species of Populus, Eucalyptus, Larix, Cunninghamia and Pinus are planted to satisfy the local demand for wood products and provide ecological services at the same time. Evidence of the greater resilience of natural forests provides the motivation to develop asymmetric planting patterns, which is the focus of this study. We present a new method for designing plantation patterns that follow those observed in natural ecosystems and to maintain some regularity for operational convenience.MethodsBased on the uniform angle index, we analyzed the spatial structure of six natural forests in different regions of China. The uniform angle index describes the degree of spatial uniformity of the n nearest neighbors of a given reference tree. Accordingly, we identified all possible patterns of a neighborhood group within a regular planting pattern and developed a method to optimize planting point arrangements that contain some randomness as well as a minimum degree of regularity.Results(1) There are 13 types of structural units in a regular planting, including seven random units, five even units and one cluster unit; (2) Five near-natural arrangements are presented with a minimum proportion of 50% of random units. These five arrangements represent a combination of regularity for operational convenience and asymmetry.ConclusionsThe new planting patterns developed in this study are expected to increase the asymmetric competition and resilience of these important ecosystems. Some experimental plantings, based on our findings, have already been established, e.g., in Pinus tabulaeformis plantations in Tianshui, Gansu Province, and in a Populus deltoides plantation in Fangshan near Beijing.