Chinese Pine Forest Research Articles

The Impacts of Phenological Stages within the Annual Cycle on Mapping Forest Stock Volume Using Multi-Band Dual-Polarization SAR Images in Boreal Forests

SAR images with two polarizations show strong potential for mapping forest stock volume (FSV) combined with limited samples. However, accurately mapping FSV still presents challenges in selecting the optimal acquisition date to obtain the SAR images during specific phenological stages within the annual forest cycle (growth and dormant stages). To clarify the impacts of phenological stages within the annual cycle on FSV mapping, SAR images with various polarization models and bands (Sentinel-1(S), GaoFen-3(GF-3 (G)) and ALOS-2(A)) were acquired within the growth and dormant stages of an annual cycle in a boreal evergreen coniferous forest (Chinese pine) and a deciduous coniferous forest (Larch). Subsequently, single-band (G, S, and A) and multi-band combined alternative variable sets (A + G, A + S, S + G, and A + S + G) were extracted within the same stage, respectively. Finally, the forward selection approach was utilized in conjunction with four different models (MLR, KNN, RF, and SVR) to obtain the most suitable variable sets and generate FSV mapping. The results demonstrated a strong correlation between the intensity of backscattering coefficients and the phenological stages of the forest. Within the dormant stage, there was a significant decrease in the gaps of backscattering coefficients obtained from the same polarization compared to those within the growth stage. Furthermore, the results also revealed that more signals from inside the canopy could be detected during the dormant stage in both evergreen coniferous forests and deciduous coniferous forests. Subsequently, the accuracy in mapping FSV obtained from single-band SAR images within the dormant stage are slightly higher than that within the growth stage, and the accuracy was still significantly affected by both overestimation and underestimation. Moreover, the combined effects of different bands significantly improve the reliability of mapped FSV. The rRMSE values in four multi-band combinations ranged from 22.37% to 29.40% for Chinese pine forests and from 21.27% to 34.38% for Larch forests, and the optimal result was observed from combinations of A + S + G acquired within the dormant stage. It is confirmed that SAR signal and their sensitivity to FSV depends on the stages of forest annual growth cycle. In comparison to the growth period, dual-polarization SAR data acquired during the dormant stage is more suitable for estimating FSV in boreal forests.

Mitochondrial genome provides species-specific targets for the rapid detection of early invasive populations of Hylurgus ligniperda in China

BackgroundHylurgus ligniperda, a major international forestry quarantine pest, was recently found to have invaded and posed a serious threat to the Pinus forests of the Jiaodong Peninsula in China. Continuous monitoring and vigilance of the early population is imperative, and rapid molecular detection technology is urgently needed. We focused on developing a single-gene-based species-specific PCR (SS-PCR) method.ResultsWe sequenced and assembled the mitochondrial genome of H. ligniperda to identify suitable target genes. We identified three closely related species for detecting the specificity of SS-PCR through phylogenetic analysis based on 13 protein-coding genes (PCGs). Subsequently, we analyzed the evolution of 13 PCGs and selected four mitochondrial genes to represent slow-evolving gene (COI) and faster-evolving genes (e.g. ND2, ND4, and ND5), respectively. We developed four species-specific primers targeting COI, ND2, ND4, and ND5 to rapidly identify H. ligniperda. The results showed that the four species-specific primers exhibited excellent specificity and sensitivity in the PCR assays, with consistent performance across a broader range of species. This method demonstrates the ability to identify beetles promptly, even during their larval stage. The entire detection process can be completed within 2–3 h.ConclusionsThis method is suitable for large-scale species detection in laboratory settings. Moreover, the selection of target genes in the SS-PCR method is not affected by the evolutionary rate. SS-PCR can be widely implemented at port and forestry workstations, significantly enhancing early management strategies and quarantine measures against H. ligniperda. This approach will help prevent the spread of the pest and effectively preserve the resources of Chinese pine forests.

Interguild fungal competition in litter and soil inversely modulate microbial necromass accumulation during Loess Plateau forest succession

Microbial interactions determine ecosystem carbon (C) and nutrient cycling, yet it remains unclear how interguild fungal interactions modulate microbial residue contribution to soil C pools (SOC) during forest succession. Here, we present a region-wide investigation of the relative dominance of saprophytic versus symbiotic fungi in litter and soil compartments, exploring their linkages to soil microbial residue pools and potential drivers along a chronosequence of secondary Chinese pine (Pinus tabulaeformis) forests on the Loess Plateau. Despite minor changes in C and nitrogen (N) stocks in the litter or soil layers across successional stages, we found significantly lower soil phosphorus (P) stocks, higher ratios of soil C: N, soil N: P and soil C: P but lower ratios of litter C: N and litter C: P in old (>75 years) than young stands (<30 years). Pine stand development altered the saprotroph: symbiotroph ratios of fungal communities to favor the soil symbiotrophs versus the litter saprotrophs. The dominance of saprotrophs in litter is positively related to microbial necromass contribution to SOC, which is negatively related to the dominance of symbiotrophs in soils. Antagonistic interguild fungal competition in litter and soil layers, in conjunction with increased fungal but decreased bacterial necromass contribution to SOC, jointly contribute to unchanged total necromass contribution to SOC with stand development. The saprotroph: symbiotroph ratios in litter and soil layers are mainly driven by soil P stocks and stand parameters (e.g., stand age and slope), respectively, while substrate stoichiometries primarily regulate microbial necromass accumulation and fungal: bacterial necromass ratios. These results provide novel insights into how microbial interactions at local spatial scales modulate temporal changes in SOC pools, with management implications for mitigating regional land degradation.

Interpreting the Response of Forest Stock Volume with Dual Polarization SAR Images in Boreal Coniferous Planted Forest in the Non-Growing Season

Polarimetric Synthetic Aperture Radar (PolSAR) images with dual polarization modes have great potential to map forest stock volume (FSV) by excellent penetration capabilities and distinct microwave scattering processes. However, the response of these SAR data to FSV is still uncertain in the non-growing season. To further interpret the response of FSV to different dual polarization SAR images, three types of dual polarization SAR images (GF-3, Sentinel-1, and ALOS-2) were initially acquired in coniferous planted forest in the non-growing season. Then, sensitivity between FSV and all alternative features extracted from each type of SAR image was analyzed to express the response of FSV to dual polarization SAR images with bands and polarization modes in the non-growing season in deciduous (Larch) and evergreen (Chinese pine) forests. Finally, mapped FSV using single and combined dual polarization images were derived by optimal feature sets and four machine learning models, respectively. The combined effects were also analyzed to clarify the difference of bands and polarization modes in deciduous and evergreen forests in the non-growing season. The results demonstrated that the backscattering energy from different sensors is significantly different in Chinese pine, and the difference is gradually reduced in Larch forests. It is also implied that the polarization mode is more important than penetration capability in mapping forest FSV in deciduous forest in the non-growing season. By comparing the accuracy of mapped FSV using single and combined images, combined images have more capability to improve the accuracy and reliability of mapped FSV. Meanwhile, it is confirmed that compensation effects with bands and polarization modes not only have great potential to delay the saturation phenomenon, but also have the capability to reduce errors caused by overestimation.

Pine caterpillar occurrence modeling using satellite spring phenology and meteorological variables

Outbreaks of leaf-feeding Lepidopteran insects substantially weaken the quality of forest trees and strongly affect the ecosystem functions of plant photosynthesis and carbon uptake. The narrow phenological time window of leaf out about ten days, during which Lepidopteran larvae feed on high nutrient newly flushed leaves, may change the insect community and outbreak dynamics by determining the survival rate of larvae. The Chinese pine Caterpillar (Dendrolimus tabulaeformis Tsai et Liu) infestation of the northern Chinese pine (Pinus tabulaeformis) forest in China is a major concern, and accurately modeling the day of insect occurrence (DIO) in the spring remains challenging. With continuous in-situ observed insect activities of 20 plots and satellite and meteorological observations from 1983 to 2014, we found a strong synchronization (r = 0.54, p = 0.001) between the satellite-based vegetation spring phenology, i.e. the green-up day (GUD), and DIO of the pine caterpillar over time. We used partial least squares regression and ridge regression models, and identified that monthly preseason air temperature, wind speed, specific humidity, and downward radiation were key environmental cues that awakened the overwintering pine caterpillars. After removing the collinearity of multiple variables, we showed that the dimensionality reduction-based regression models substantially improved the accuracy of DIO modeling than commonly used models, such as interval and degree-day models. In particular, including GUD significantly enhanced the predictive strength of the models increasing the coefficient of determination (R 2) by 17.1% and consequently a decrease of 16.5% in the root mean square error. We further showed that evapotranspiration changed the environmental moisture content, which indirectly affected the activities of insects. Our results revealed a useful linkage between spring leaf development and insect occurrence, and therefore are of great importance for the large-scale monitoring of pest outbreaks with future remote sensing observations.

Effectiveness of Chinese pine (Pinus tabulaeformis) plantation at reducing runoff and erosion rates in Anjiagou Watershed in Semi-arid Region of Gansu, China.

China’s Loess Plateau regions have experienced severe soil erosion for many decades due to fragmented landscapes, steep slopes, and concentrated rainfall storm-events. Restoring sub-optimal or marginal farming fields, mostly on steep, hilly terrain, to plantation forests has been a long-standing strategic policy in China aimed at rehabilitating degraded environments and reducing soil and water erosion. While there are numerous studies that have focused on the effects of forests at controlling soil erosion at relatively short time scales, few have addressed longer-term effects of plantation forests on reducing runoff and the mechanisms that inhibit erosion. Chinese pine (Pinus tabulaeformis) has been widely planted in abandoned or reclaimed lands that were formerly farmed in Northwest China; however, there is limited knowledge about the effectiveness of the tree species at reducing soil and water erosion. In this study, we examined reduction rates of runoff and erosion by Chinese pine plantation in comparison with agricultural land as a control (i.e., wheat, a dominant agricultural commodity in the region), based on long-term monitoring of modified standard erosion plots with slopes of 10°, 15°, and 20°. Results showed that as the slope of the land increased, rates of erosion increased for both plantation and agricultural land use. However, the runoff and soil erosion rates under Chinese pine plantation forest were about 11% and 60% lower, respectively, than those under agricultural land use of the same slope. Scaling with the slope, the highest reduced runoff and erosion rates by Chinese pine forest were 17% and 72%, respectively, on 20° slope. Also, it was found that runoff rates from the forested land were positively related to erosive rainfall (i.e., rainfall when runoff generated), and varied with forest canopy coverage. The rates of runoff and erosion can be well model led with multiple regression models. Taken together, this study provides insight into the importance and potential of Chinese pine plantations in the conservation of soil and water in China’s Loess Plateau.

Biophysical regulations of transpiration and water use strategy in a mature Chinese pine (Pinus tabulaeformis) forest in a semiarid urban environment

AbstractUrban trees and forests provide multiple ecosystem services for urban dwellers. However, forest water use for these benefits has become one of the critical concerns in dryland regions where water is limited. Negative forest water use impacts could be reduced by selecting tree species with low rates of transpiration. However, the possible changes of urban tree transpiration and its biophysical controls are still unclear. This study monitored the sap flow of a 58‐year‐old Chinese pine (Pinus tabulaeformis) plantation in a semiarid urban environment of northern China. Soil moisture played an important role in stand transpiration (Ec). Ec had a strong positive relationship with vapour pressure deficit (VPD) and solar radiation (Rs) when soil water was sufficient. In addition, the sensitivity of leaf stomata to VPD was not related to leaf and branch water potential. Under soil water stress, Ec was significantly reduced by 63.1% (p &lt; 0.001) and was weakly related to VPD and Rs. Canopy conductance (gc) was reduced (p &lt; 0.001) by 74.3% due to leaf stomatal closure, and the sensitivity of leaf stomata to VPD was significantly increased (p &lt; 0.05) with increasing leaf and branch water potential. Wind speed had no significant effects on Ec. P. tabulaeformis tended to be isohydric with a relatively constant midday leaf water potential (i.e. −2.46 to −2.92 MPa) and strong stomatal regulation as a function of soil water stress. However, slopes (0.53–0.56) of the linear relationship between m (dgc/dlnVPD) and reference canopy conductance were significantly lower than the widely recognized 0.6 (p &lt; 0.001). Therefore, urban tree transpiration drivers and forest impacts need to be clarified to better understand the proper tradeoff between water consumption and ecological services for urban areas.

Rainfall Partitioning in Chinese Pine (Pinus tabuliformis Carr.) Stands at Three Different Ages

Chinese pine (Pinus tabuliformis Carr.) is the main forest species in northern China, with the potential to dramatically affect biotic and abiotic aspects of ecosystems in this region. To discover the rainfall partitioning patterns of different growth periods of Chinese pine forest, we studied the throughfall (Tf), stemflow (Sf) and canopy interception (I) in three stand ages (40-, 50-, 60-year-old) in Liaoheyuan Natural Reserve of Hebei Province during the growing seasons of 2013 and 2014, and analyzed effect of rainfall amount, rainfall intensity, and canopy structure on rainfall partitioning in Chinese pine forest. The results showed that throughfall decreased with the stand age, accounting for 78.8%, 74.1% and 66.7% of gross rainfall in 40-, 50- and 60-year-old Chinese pine forests, respectively. Canopy interception, on the other hand, increased with the stand age (20.4%, 24.8%, and 32.8%, respectively), while the pattern in stemflow was less clear (0.8%, 1.1%, and 0.6%, respectively). As rainfall intensity increased, the Tf and Sf increased and I declined. Additionally, our results showed that leaf area index (LAI) and the diameter at breast height (DBH) increased with age in Chinese pine stands, probably explaining the similar increase in canopy interception (I). On the other hand, the mean leaf angle, openness, gap fraction all decreased with the stand age. Stepwise regression analysis showed that the rainfall amount and LAI were the major determinants influencing the rainfall partition. Our study highlights the importance of stand age in shaping different forest canopy structures, and shows how age-related factors influence canopy rainfall partitioning. This study also significantly adds to our understanding the mechanisms of the hydrological cycle in coniferous forest ecosystems in northern China.

Effects of freeze-thaw cycles and initial soil moisture content on soil aggregate stability in natural grassland and Chinese pine forest on the Loess Plateau of China

Ongoing global warming is decreasing the thickness of snow covers and increasing initial soil moisture content (SMC), which increase the number of freeze-thaw cycles (FTCs) at mid-high latitudes and high elevations, especially at temperate regions. FTCs substantially affect the stability of soil aggregates, which may increase soil erosion. A comprehensive understanding of aggregate stability under different types of vegetation restoration in response to FTCs, however, has not yet been attained. We evaluated the effects of number of FTCs (0, 1, 3, and 9) and initial SMC (40, 60, and 80% field capacity) on aggregate distribution and stability in cropland, natural grassland, and Chinese pine forestland, the three typical types of vegetation on the Loess Plateau in China. The experiment was conducted under simulated conditions in the laboratory using disturbed soil samples. Most aggregate-size fractions and mean weight diameters (MWDs) were significantly (P < 0.05) affected by FTCs, initial SMC, and vegetation types. FTCs significantly decreased MWD by 3.6–18.1% through disrupting larger macro-aggregates, which increased with SMC. Increased SMC increased MWD by 2.0–53.0% through binding soil particles, the effect of which was much larger than the disruptive effects under the freeze-thaw conditions, especially at high SMC. MWD was in the order of cropland < Chinese pine forestland < natural grassland under each freeze-thaw condition. The results indicated that natural vegetation succession was better than Chinese pine forest plantation for resisting seasonal FTCs and that aggregate stability may increase due to increased initial SMC under scenarios of future global warming.

Soil organic matter and glomalin-related soil protein contents do not explain soil aggregate stability after freeze-thaw cycles at contrasting soil moisture contents

ABSTRACT Soil organic carbon (SOC) and glomalin-related soil protein (GRSP) contributes to the formation and stability of soil aggregates, but it remains unknown whether the frequency of freeze-thaw cycles (FTCs) and soil moisture content (SMC) at freezing changes aggregate stability and whether SOC and GRSP regulate these changes. Effects of FTCs (0, 1, 3 and 9 times) and initial SMC (40% and 80% field capacity) on aggregate distribution, SOC, and easily extractable, difficultly extractable and total GRSP content in soil aggregates (> 2000 μm, 250–2000 μm, and <250 μm) were evaluated in Chinese pine forest soil. FTCs significantly reduced MWD by disrupting large macro-aggregates. On the other hand, higher SMC increased MWD by binding soil particles, the effect of which was much greater than the disruptive effects of FTCs. SOC in bulk soil and aggregate fractions slightly decreased with the frequency of FTCs. Bulk and aggregate-associated GRSP fractions first decreased, and then increased with the frequency of FTCs. SOC and GRSP fractions correlated insignificantly with MWD. Our results indicated that increasing SMC could augment soil aggregate stability, and that SOC and GRSP might not be the primary control on aggregate stabilization during freeze-thaw conditions in Chinese pine forest soil.

Contrasting Responses of Soil Respiration Components in Response to Five-Year Nitrogen Addition in a Pinus tabulaeformis Forest in Northern China

Increasing atmospheric nitrogen (N) deposition has profound effects on carbon (C) cycling in forest ecosystems. As an important part of belowground C dynamics, soil respiration is potentially affected by changing N availability. However, the responses of total soil respiration (RST) and its three components, soil respiration derived from plant roots (RSR), root-free soil (RSS) and the litter layer (RSL), to such N enrichment remains poorly understood. To assess the effects of N enrichment on soil respiration components, three levels of N addition, namely low (LN, 50 kg N ha−1 year−1), medium (MN, 100 kg N ha−1 year−1) and high (HN, 150 kg N ha−1 year−1), were conducted over five growing seasons from 2011 to 2015 in a temperate Chinese pine (Pinus tabulaeformis) forest in northern China. A control plot without N addition (CK) was also established. The five-year mean annual rate of RST was 2.18 ± 0.43 μmol m−2 s−1, and the contributions of RSR, RSS and RSL were 8.8 ± 3.1%, 82.2 ± 4.5% and 9.0 ± 5.5%, respectively. Compared with CK, RST was significantly increased by 16.5% in the HN plots, but not in the LN or MN treatments. RSS was significantly decreased by 18.1%, 26.6% and 18.4% in the LN, MN and HN plots, respectively, due to the reduction of both microbial biomass carbon (MBC) and enzyme activity. In contrast, RSR was increased by more than twice under the MN treatment, which promoted root growth and activity (higher fine root biomass and N concentration). A significant elevation in RSL was only detected in the HN plots, where the increased litter input enhanced litter decomposition and hence RSL. Our findings clearly demonstrated that N addition of different intensities had different effects on soil components. In particular, the above- and belowground components of heterotrophic respiration, RSL and RSR, showed contrasting responses to high level addition of N. Thus, we highlight that the response of soil respiration components to N addition should be examined individually. Our results may contribute to a better understanding of soil respiration dynamics under future N scenarios, and have important implications in forest management.

Effects of freeze-thaw cycles on aggregate-associated organic carbon and glomalin-related soil protein in natural-succession grassland and Chinese pine forest on the Loess Plateau

Glomalin-related soil protein (GRSP) is a hydrophobic glycoprotein that can protect soil organic carbon (SOC) from decomposition by promoting the formation of soil aggregates. Few studies, however, have evaluated the response of aggregate-associated SOC and GRSP to freeze-thaw cycles (FTs) under different patterns of vegetation restoration. Soil samples were collected from three typical natural-succession grasslands (dominated by Artemisia capillaris, A. sacrorum, and Bothriochloa ischaemum) and a Chinese pine (Pinus tabuliformis) forest before and after natural FTs during a winter-spring season on the Loess Plateau in China. The soil aggregate stability and concentrations of SOC, easily extractable GRSP (EE-GRSP) and total GRSP (T-GRSP) in different aggregate fractions were measured. The FTs decreased the proportion of >5.0 mm wet-sieved fractions, increased the proportion of <0.25 mm wet-sieved fractions, and decreased the mean weight diameters by 8.7, 9.5, 2.9, and 9.4% in the soils of A. capillaris, A. sacrorum, B. ischaemum, and P. tabuliformis, respectively. The SOC, T-GRSP, and EE-GRSP concentrations in each aggregate fraction generally decreased after FTs in the four vegetation types. The SOC, T-GRSP, and EE-GRSP concentrations did not differ significantly in the larger aggregate fractions before the FTs in the soils for B. ischaemum and P. tabuliformis, but their concentrations were significantly higher for B. ischaemum than P. tabuliformis after FTs. The SOC and GRSP concentrations were significantly and linearly correlated in most aggregate fractions both before and after the FTs. These results indicated that the FTs decreased SOC by decreasing the GRSP concentration in each aggregate fraction and that SOC was more sensitive to FTs in forest than in natural-succession grassland.

Spatial structural characteristics of forests dominated by Pinus tabulaeformis Carr.

The Chinese pine (Pinus tabulaeformis Carr.) is an ecologically and economically important evergreen coniferous tree which dominates warm temperate forests throughout northern China. We established two permanent plots within the Chinese pine forest in the Jiulong Mountains, Beijing, China. To understand the structural characteristics and dynamics of these plots, we analyzed the spatial structural characteristics within nearest-neighbor relationships using the bivariate distributions of the stand spatial structural parameters: uniform angle index, W; mingling index, M; dominance index, U; and crowding index, C. Results revealed that most trees in the forest were randomly distributed. The predominant individuals and randomly arranged trees were in very dense areas and surrounded by the same species. In addition, both plots exhibited a uniform size differentiation pattern. The two plots differed mainly in the level of species mixture and dominance. The majority of reference trees in the pure Chinese pine forest (plot 1) exhibited poor species mingling and low dominance, whereas trees in the mixed Chinese pine forest (plot 2) were evenly distributed in each mingling class and most trees were of intermediate dominance. The study results are useful for optimizing forest management activities in the studied stands, promoting tree growth, regeneration and habitat diversity, and improving forest quality at a fine scale.

Variability after 15 Years of Vegetation Recovery in Natural Secondary Forest with Timber Harvesting at Different Intensities in Southeastern China: Community Diversity and Stability

The mixed Cunninghamia lanceolata (Lamb.) Hook., Pinus massoniana Lamb., and hardwood forest in southeastern China is a major assemblage in natural secondary forests, and of national and international importance in terms of both timber and ecosystem services. However, over-harvesting has threatened its long-term sustainability, and there is a knowledge gap relating to the effect of harvesting on the ecosystem. After conifer species were selected for harvesting, the mixed Chinese fir, pine, and hardwood forest was changed into mixed evergreen broadleaf forest. In this context, we observed the restoration dynamics of plant communities over a period of 15 years (1996 to 2011) with different levels of harvesting intensity, including selective harvesting at low (13.0% removal of growing stock volume), medium (29.1%), high (45.8%), and extra-high (67.1%) intensities, as well as clear-cut harvesting (100.0%), with non-harvesting as the control, based on permanent sample plots established in a randomized block design in these forests in southeastern China. The impact on the richness, diversity, and evenness of plant species derived from descriptive statistical analyses was shown to initially increase, and then decrease, with an increase in harvesting intensity. The most critical impacts were on the richness, diversity, and evenness of shrub and herb species. Richness, diversity, and evenness of plant species recovered and increased under selective harvesting at low and medium intensities, while these parameters had not recovered and significantly decreased under selective harvesting at high and extra-high intensities, as well as with clear-cut harvesting. The impact on the plant community stability was derived from the stability test method of the improved Godron M. The plant community stability was closest to the point of stability (20/80) under selective harvesting at medium intensity, followed by selective harvesting at low intensity. The plant community stability was far from the point of stability (20/80) under selective harvesting at high and extra-high intensities, as well as with clear-cut harvesting. Of these treatments, clear-cut harvesting had the greatest effect with regard to reducing stability. Therefore, these results indicate that the selective harvesting at low and medium intensities is conducive to preserve or increase the species diversity and community stability. In order to prioritize promoting plant species diversity, clear-cut harvesting and selective harvesting at high and extra-high intensities should be avoided with regard to this type of forest in this region. This study sheds light on the practice of forest operation in the study region and subtropical forests with the same environment.

Agricultural non-point source pollution management in a reservoir watershed based on ecological network analysis of soil nitrogen cycling.

The Miyun Reservoir plays a pivotal role in providing drinking water for the city of Beijing. In this research, ecological network analysis and scenario analysis were integrated to explore soil nitrogen cycling of chestnut and Chinese pine forests in the upper basin of the Miyun Reservoir, as well as to seek favorable fertilization modes to reduce agricultural non-point source pollution. Ecological network analysis results showed that (1) the turnover time was 0.04 to 0.37year in the NH4+ compartment and were 15.78 to 138.36years in the organic N compartment; (2) the Finn cycling index and the ratio of indirect to direct flow were 0.73 and 11.92 for the chestnut forest model, respectively. Those of the Chinese pine forest model were 0.88 and 29.23, respectively; and (3) in the chestnut forest model, NO3- accounted for 96% of the total soil nitrogen loss, followed by plant N (2%), NH4+ (1%), and organic N (1%). In the Chinese pine forest, NH4+ accounted for 56% of the total soil nitrogen loss, followed by organic N (34%) and NO3- (10%). Fertilization mode was identified as the main factor affecting soil N export. To minimize NH4+ and NO3- outputs while maintaining the current plant yield (i.e., 7.85e0kgN/year), a fertilization mode of 162.50kgN/year offered by manure should be adopted. Whereas, to achieve a maximum plant yield (i.e., 3.35e1kgN/year) while reducing NH4+ and NO3- outputs, a fertilization mode of 325.00kgN/year offered by manure should be utilized. This research is of wide suitability to support agricultural non-point source pollution management at the watershed scale.

Different winter soil respiration between two mid-temperate plantation forests

Abstract Larch and Chinese pine plantation forests are important carbon (C) sinks in the temperate regions, especially in China. However, their soil respiration in winter is still poorly studied. Here we explored the different microbial characteristics and winter soil respiration in larch and Chinese pine plantation forests in northeastern China, which has similar climate and basic soil characteristics. Results showed that both mean and cumulative winter soil CO2 fluxes were significantly higher in Chinese pine forest (0.45 µmol m−2 s−1 and 46.39 g C m−2, respectively) than in larch forest (0.25 µmol m−2 s−1 and 25.92 g C m−2, respectively). Snow depth and inorganic nitrogen (N) could not explain the differences in winter soil respiration between the two sites. Instead, Chinese pine forest had higher soil microbial biomass, fungi abundance, F/B (ratio of fungi to bacteria), and extracellular enzymatic activities (EEAs) than larch forest, which could lead to higher winter soil respiration in Chinese pine forest than in larch forest. Our findings indicated that the thermal insulation effect of litter cover was important to winter soil respiration, especially when the snow cover depth was less than 30 cm. Soil microbes played a more important role in soil respiration than soil nutrient status and should be carefully considered for better estimation of the C budget in different forest ecosystems. Although soil respiration was higher in Chinese pine forest, soil organic C content was also higher, suggesting its better C sequestration capacity than larch forest.

Construction of compatible and additive individual-tree biomass models forPinustabulaeformisin China

Current biomass models for Chinese pine (Pinus tabulaeformis Carr.) fail to accurately estimate biomass in large geographic regions because they were usually based on limited sample trees on local sites, incompatible with stem volume, and not additive among components and total biomass. This study was based on mensuration data of individual-tree biomass from large samples of Chinese pine. The purpose was to construct compatible and additive biomass models using the nonlinear error-in-variable simultaneous equations and dummy variable modeling approach. This approach could ensure compatibility of an aboveground biomass model with a biomass conversion factor (BCF) and a stem volume model and compatibility of a belowground biomass model with a root-to-shoot ratio (RSR) model. Also, stem, branch, and foliage biomass models were additive to the aboveground biomass model. Results showed that mean prediction errors (MPEs) of the developed one- and two-variable aboveground biomass models were less than 4% and MPEs of the three-component (stem, branch, and foliage) and belowground biomass models were less than 10%. Furthermore, the effects of main climate variables on above- and below-ground biomass were analyzed. Aboveground biomass was related to mean annual temperature (MAT), while belowground biomass had no significant relationship with either MAT or mean annual precipitation (MAP). The developed models provide a good basis for estimating biomass of Chinese pine forests.

Effects of gaps in the forest canopy on soil microbial communities and enzyme activity in a Chinese pine forest

Gaps in the forest canopy play an important role in forest ecology, affecting biological dynamics, nutrient cycling, and plant succession. The influence of gap size on soil microbial communities and soil enzyme activity is poorly understood. Chinese pine (Pinus tabulaeformis) is one of the main afforestation species in northern China, and the creation of artificial gaps in Chinese pine forests is a common silvicultural practice to reduce forest density. We compared the microbial communities and the activity levels of several key enzymes in a Chinese forest among sites with closed canopies and canopies with small gaps (40–50m2) and large gaps (100–120m2) in October 2015, one year after the gaps were created. Soil samples from a depth of 0–10cm were collected, and soil microbial community composition was evaluated using phospholipid fatty acid analysis. The activity levels of soil enzymes were also analyzed. Overall, the amounts of phospholipid fatty acids and the activity level of soil enzymes were highest in the sites with small gaps, followed by sites with closed canopies and sites with large gaps. Gram-positive bacteria were mainly responsible for the difference between microbial communities in sites with small gaps and sites with closed canopies. The activity levels of soil β-glucosidase and l-leucineaminopeptidase were also highest in sites with small gaps and lowest in those with large gaps. Soil acid phosphatase activity was similar in sites with small gaps and closed canopies and was lowest in sites with large gaps. Redundancy analysis indicated that dissolved organic carbon was the common driving factor affecting the variations in microbial communities and enzyme activity. Our results suggest that small gaps are beneficial for microbial communities. Further study of gap treatments is needed to determine the proper gap size for forest management.

Combined effects of nitrogen addition and organic matter manipulation on soil respiration in a Chinese pine forest.

The response of soil respiration (Rs) to nitrogen (N) addition is one of the uncertainties in modelling ecosystem carbon (C). We reported on a long-term nitrogen (N) addition experiment using urea (CO(NH2)2) fertilizer in which Rs was continuously measured after N addition during the growing season in a Chinese pine forest. Four levels of N addition, i.e. no added N (N0: 0gNm-2year-1), low-N (N1: 5gNm-2year-1), medium-N (N2: 10gNm-2year-1), and high-N (N3: 15gNm-2year-1), and three organic matter treatments, i.e. both aboveground litter and belowground root removal (LRE), only aboveground litter removal (LE), and intact soil (CK), were examined. The Rs was measured continuously for 3days following each N addition application and was measured approximately 3-5 times during the rest of each month from July to October 2012. N addition inhibited microbial heterotrophic respiration by suppressing soil microbial biomass, but stimulated root respiration and CO2 release from litter decomposition by increasing either root biomass or microbial biomass. When litter and/or root were removed, the "priming" effect of N addition on the Rs disappeared more quickly than intact soil. This is likely to provide a point of view for why Rs varies so much in response to exogenous N and also has implications for future determination of sampling interval of Rs measurement.

Long‐term effects of vegetational restoration on soil microbial communities on the Loess Plateau of China

AbstractSoil microbial communities are important indicators for evaluating the effectiveness of vegetational restoration. The ability of soil microbial communities to recover under six types of restoration was examined using Biolog, phospholipid fatty acid (PLFA), and denaturing gradient gel electrophoresis (DGGE). Soil samples were collected from eroded loessial soils that had been restored for 30 years on the Loess Plateau with natural grass, black locust, korshinsk peashrub, Chinese pine, and mixed forest of Chinese pine‐indigo and black locust‐indigo. Part of sloped farmland that had not been restored represented pre‐restoration conditions. An 80‐year‐old forest of Chinese arborvitae represented the end point of restoration. Soils that were originally farmed but have been under restoration treatments for the past 30 years had significantly higher average well‐color development, total PLFAs, bacterial PLFAs, fungal PLFAs, and Shannon indices of catabolic diversity, structural diversity, and bacterial phylogenetic diversity. These indicators, though, were lower than those for the native forest. Principal component analysis significantly separated the sloped farmland, Chinese arborvitae, and the six types of restoration. Redundancy analysis indicated that pH, total organic carbon, total nitrogen, available nitrogen, and available phosphorus were the most important environment factors in affecting soil functional diversity, and C/N ratio and available nutrients were the main properties in determining microbial community structure. Vegetational restoration substantially increased microbial biomass and microbial physiological activity, and shifted microbial community structure, but the community structures and compositions did not recover to the status of the natural forest during the early stage (&lt;30 years) of vegetational restoration.