Chinese Temperate Forest Research Articles

Seasonality in embolism resistance and hydraulic capacitance jointly mediate hydraulic safety in branches and leaves of oriental cork oak (Quercus variabilis Bl.).

Seasonality in temperate regions is prominent during the era of increased climatic variability. A hydraulic trait that can adjust to seasonally changing climatic conditions is crucial for tree safety. However, little attention has been paid to the intraspecific seasonality of drought-related traits and hydraulic safety of keystone forest trees. We examined seasonal variations in the key morphological and physiological traits as well as multiple hydraulic safety margins (SMs) at the branch and leaf levels in oriental cork oak (Quercus variabilis Bl.), which is predominant in Chinese temperate forests. Pneumatic measurements indicated that, as seasons progressed, the water potential at which 50% of branch embolisms occur (P50_branch) decreased from -3.34 to -4.23MPa, with a coefficient of variation (CV) of 9.08%. Sapwood capacitance ranged from 48.19 to 248.08kgm-3MPa-1, peaking in autumn and reaching minimum in winter (CV 60.58%). Rehydration kinetics confirmed higher leaf embolism vulnerability (P50_leaf) in spring and autumn than those in summer, with values ranging from -1.06 to -3.02MPa (CV 39.85%). All leaf pressure-volume (PV) traits shifted with growth, with CVs ranging from 6.95% to 46.69%. Sapwood density had significant negative correlations with P50_branch and hydraulic capacitance for elastic water storage, whereas leaf mass per area was linearly associated with PV traits but not with P50_leaf. Furthermore, the branch typical SMs (difference between branch midday water potential and P50_branch) were consistently >1.84MPa, and vulnerability segmentation was prevalent throughout, implying a plausible hydraulic foundation for the dominance of Q. variabilis. Diverse hydraulic response patterns existed across seasons, leading to positive SMs mediated by the aforementioned physiological traits. Although Q. variabilis exhibits a high level of hydraulic safety, its susceptibility to sudden summer droughts may increase due to global climate change.

Climate Strengthens the Positive Effects of Stand Structure on Understory Plant Diversity in Chinese Temperate Forests

Stand structure, which links function and management, plays a crucial role in regulating forest ecosystems and influencing biodiversity. Nevertheless, knowledge of the effect of climate change on stand structure and plant diversity is still poorly understood on a large scale. To explore the effects of various climate conditions on stand structure–plant diversity, we conducted a comprehensive analysis of data from 1272 plots across China’s temperate and subtropical forests. Leveraging the structural equation model (SEM), we explored the direct and indirect effects of climate, topography, and tree diversity on understory woody and herbaceous plants with respect to stand structure. Furthermore, we evaluated the effect size of stand structure on understory vegetation diversity under different climatic zones. Our results showed that tree size variation (CV DBH) and stem density (SD) were the key drivers for understory woody plants, while the stand structure complexity index (SSCI) was more important for understory herbaceous diversity. Furthermore, the positive effects of stand structure differed across various climate zones and were enhanced with an increase in the climatic gradient. For instance, the impact of SD on understory woody plants, as well as the influence of the SSCI on the diversity of understory herbaceous vegetation, were both strengthened. These findings raise our awareness of the pressing need to manage stand structure heterogeneity differently across different climate zones, and different management also needs to be implemented among different understory plant types. It becomes evident that distinct forest management measures must be applied under future climate change and forest management practices in order to preserve biodiversity.

Factors driving native tree species restoration in plantations and tree structure conversion in Chinese temperate forests

Forests have been planted over large areas during forest restoration programs in Northeast China. An important challenge is transforming forest species structure by allowing colonization of native species in plantations, especially under the present policy of limited logging intensity and near-natural management practices. However, research on the entire process of native tree species restoration and conversion of tree species structure over time remains limited. Therefore, a multi-year field study was conducted to document native tree species restoration in plantations and different open land-cover types in Chinese temperate forests. We evaluated native tree species restoration in plantations (n = 30) and different types of natural recovery in open areas (n = 50) as controls. The first survey was conducted in 1990, with plots sampled in plantations of age 4–30 years, and repeat surveys were conducted in 1993, 2004, and 2016. We compared the importance of abiotic and biotic factors in the different survey periods using the Random Forest algorithm for restoration outcome (i.e., presence of ‘large trees’ (DBH ≥ 5 cm) of natural tree species in plantations) and the changes in plantation tree species composition during the survey periods. The aim was to test our hypothesis that abiotic and biotic factors, such as topography, habitat, and distance from nearest forest (i.e., seed source), differ in importance under different restoration periods. The results revealed that the basal area of large trees was the most important variable for native tree species restoration in plantations over the entire survey period. Abiotic factors, such as elevation and slope, differed in importance and relevance in the different recovery periods to the restoration outcomes in plantations and open areas. Increase in distance from seed source had a negative effect on natural tree species restoration in plantations and different types of open areas. Although the correlation of distance from seed source to restoration outcomes is consistent during the entire survey period, the importance of distance from seed source varied along a chronosequence. Different forest management measures require implementation. As succession progressed, the dominance of planted tree species in plantations gradually decreased. Compared with passive natural recovery, active planting of seedlings in open land not only promotes the restoration of coniferous species that no longer exist in an area owing to excessive logging, but also promotes the restoration of other native tree species.

Responses of soil microbial communities to freeze\u2013thaw cycles in a Chinese temperate forest

BackgroundFreeze–thaw events are common in boreal and temperate forest ecosystems and are increasingly influenced by climate warming. Soil microorganisms play an important role in maintaining ecosystem stability, but their responses to freeze–thaw cycles (FTCs) are poorly understood. We conducted a field freeze–thaw experiment in a natural Korean pine and broadleaf mixed forest in the Changbai Mountain Nature Reserve, China, to determine the dynamic responses of soil microbial communities to FTCs.ResultsBacteria were more sensitive than fungi to FTCs. Fungal biomass, diversity and community composition were not significantly affected by freeze–thaw regardless of the stage. Moderate initial freeze–thaw resulted in increased bacterial biomass, diversity, and copiotrophic taxa abundance. Subsequent FTCs reduced the bacterial biomass and diversity. Compared with the initial FTC, subsequent FTCs exerted an opposite effect on the direction of change in the composition and function of the bacterial community. Soil water content, dissolved organic carbon, ammonium nitrogen, and total dissolved phosphorus were important factors determining bacterial community diversity and composition during FTCs. Moreover, the functional potentials of the microbial community involved in C and N cycling were also affected by FTCs.ConclusionsDifferent stages of FTCs have different ecological effects on the soil environment and microbial activities. Soil FTCs changed the soil nutrients and water availability and then mainly influenced bacterial community composition, diversity, and functional potentials, which may disturb C and N states in this temperate forest soil. This study also improves our understanding of microbial communities regulating their ecological functions in response to climate change.

Effects of soil fauna on litter decomposition using field microcosms across 16 co-occurring temperate tree species

ABSTRACT Litter decomposition is an important part of the carbon and nutrient cycles in terrestrial ecosystems. However, understanding of the contribution of soil fauna to litter decomposition and the relationship between soil fauna and litter quality is limited. Using custom-made field microcosms, we conducted a two-year experiment to study the effects of soil fauna on litter decomposition and the relationship between soil fauna and litter quality for 16 co-occurring species in a Chinese temperate forest. Our results showed that soil fauna changed the litter decomposition rate by −13.0–34.0%, with an average of +13.1% across the 16 species studied. Moreover, the effects of soil fauna were correlated with initial litter quality. Fauna effects were positively correlated with concentrations of non-structural carbohydrates and nitrogen and negatively correlated with tannin and lignin concentrations. Our study suggests that soil fauna can significantly increase decomposition rates in temperate forest. Initial litter quality, especially in relation to non-structural carbohydrate, nitrogen, lignin and tannin concentrations, may largely explain the effects of soil fauna on decomposition.

Variations in fine root dynamics and turnover rates in five forest types in northeastern China

Quantifying fine root (≤ 2.0 mm in diameter) distribution and turnover is essential for accurately estimating forest carbon budgets. However, fine root dynamics are poorly understood, possibly because of their inaccessibility. This study quantifies fine root distribution and turnover rates for five representative Chinese temperate forests types. Fine root number, diameter, biomass, necromass, production, mortality, and turnover rates were measured using a minirhizotron over a 12-month period. More than 90% of the fine roots were < 0.5 mm in diameter, with thin fine roots at shallow layers, and thicker ones in deeper soil layers. The fine root dynamics were significantly different among the forest types. Coniferous plantations had fewer fine roots, less biomass, necromass, production and mortality but greater average diameters than fine roots of broadleaved forests. All traits, except for diameter, decreased along the soil profile. Fine root numbers and production exhibited a unimodal seasonal pattern with peaks occurring in summer, whereas biomass, necromass and mortality progressively increased over the growing season. The turnover rates of roots < 0.5 mm varied from 0.4 to 1.0 a−1 for the five forest types, 0.5–1.0 a−1 for the soil layers and 0.2–1.1 a−1 for the seasons, with the largest turnover rate at the 0–10 cm depth in summer. The patterns of fine root numbers, biomass, necromass, production, mortality, and turnover rates varied with forest types, soil depths, growing season and diameter classes. This study highlights the importance of forest types and diameters in quantifying fine root turnover rates.

Contrasting dynamics and trait controls in first-order root compared with leaf litter decomposition

Decomposition is a key component of the global carbon (C) cycle, yet current ecosystem C models do not adequately represent the contributions of plant roots and their mycorrhizae to this process. The understanding of decomposition dynamics and their control by traits is particularly limited for the most distal first-order roots. Here we followed decomposition of first-order roots and leaf litter from 35 woody plant species differing in mycorrhizal type over 6 years in a Chinese temperate forest. First-order roots decomposed more slowly (k = 0.11 ± 0.01 years-1) than did leaf litter (0.35 ± 0.02 years-1), losing only 35% of initial mass on average after 6 years of exposure in the field. In contrast to leaf litter, nonlignin root C chemistry (nonstructural carbohydrates, polyphenols) accounted for 82% of the large interspecific variation in first-order root decomposition. Leaf litter from ectomycorrhizal (EM) species decomposed more slowly than that from arbuscular mycorrhizal (AM) species, whereas first-order roots of EM species switched, after 2 years, from having slower to faster decomposition compared with those from AM species. The fundamentally different dynamics and control mechanisms of first-order root decomposition compared with those of leaf litter challenge current ecosystem C models, the recently suggested dichotomy between EM and AM plants, and the idea that common traits can predict decomposition across roots and leaves. Aspects of C chemistry unrelated to lignin or nitrogen, and not presently considered in decomposition models, controlled first-order root decomposition; thus, current paradigms of ecosystem C dynamics and model parameterization require revision.

Microbial community composition regulates SOC decomposition response to forest conversion in a Chinese temperate forest

AbstractForest conversion influences soil organic carbon (SOC) decomposition through cascading effects on forest structure, soil properties, and soil microbial communities. However, interactive effects of these drivers and the key pathways that mediate forest SOC decomposition remain relatively unexplored. In this study, we compared relative importance of variables describing forest structure, soil properties, and soil microbial community on affecting SOC decomposition response to the conversion of a broadleaved Korean pine mixed forest into three other forests in the Changbai Mountains of China. We quantified SOC decomposition rate of these four forest types by measuring incubation soil respiration (SR). We then employed univariate regressions to quantify effect size of individual factor on SOC decomposition rate. A structural equation model (SEM) was developed to analyze pathways, relative importance, and interactive effects of these factors on SR. Our results showed strong marginal effects of dissolved organic carbon (DOC) content, fungal Phospholipid fatty acids (PLFAs) to bacterial PLFAs ratio (F/B), broadleaved to conifer ratio (B/C), and total PLFAs content (TPC) on SR. Measured SOC decomposition rate was most closely related to F/B, which was in turn influenced primarily by soil C/N ratio and fraction of non‐oxidized carbon (NOC%). Our study identified “Aboveground forest composition → SOC chemistry → Soil microbial composition → SOC decomposition” as the key pathway by which forest conversion affected SOC decomposition. This research work highlights the critical role of soil microbial community composition in altering SOC decomposition response to forest conversion.

Assessing the Effect of Leaf Litter Diversity on the Decomposition and Associated Diversity of Fungal Assemblages

Although the effect of litter mixture on decomposition has been well documented, few studies have examined the relationships between richness and relative abundance of leaf species in litter mixture and changes in universal fungal communities during the decomposition process in temperate forests. In this study, we used the litterbag method and included three leaf litter species, i.e., aspen (Populus davidiana Dode), birch (Betula platyphylla Sukaczev) and oak (Quercus mongolica Fischer ex Ledebour), to investigate the mass loss rate and diversity of universal fungal communities in each litter treatment, which were sampled in situ after 180, 240, 300 and 360 days of decomposition (between 2012 and 2013) in broadleaved mixed forests in Chinese temperate forests. Eight mixture proportions were examined: pure aspen litter (10A), pure birch litter (10B), pure oak litter (10O), 50% aspen litter mixed with 50% birch litter (5A:5B), 50% aspen litter mixed with 50% oak (5A:5O), 50% birch litter mixed with 50% oak litter (5B:5O), 10% birch litter mixed with 80% aspen litter and 10% oak litter (1B:8A:1O), 30% birch litter mixed with 40% aspen litter and 30% oak litter (3B:4A:3O). Over 360 days of decomposition, approximately 46.6%, 43.6%, 28.0%, 54.4%, 40.2%, 39.5%, 54.5% and 49.46% of litter mass was lost from 10A, 10B, 10O, 5A:5B, 5A:5O, 5B:5O, 1B:8A:1O and 3B:4A:3O, respectively. In addition, the number of fungal denaturing gradient gel electrophoresis (DGGE) bands showed a positive correlation with mass loss rate, indicating a positive feedback between leaf litter decomposition and universal fungal communities in the leaf litter. The results revealed that the 5A:5B, 1B:8A:1O and 3B:4A:3O litter mixtures had a synergistic effect on the litter mixture, while the 5A:5O and 5B:5O litter mixtures had a nearly neutral effect on the litter mixture. Thus, leaf litter species composition and relative abundance seem to be more important than leaf litter richness in driving the direction and magnitude of litter mixture decomposition.

Effects of natural and human-assisted regeneration on landscape dynamics in a Korean pine forest in Northeast China.

Improper forest harvesting can potentially degrade forest ecosystem functions and services. Human-assisted regeneration (e.g., planting) is often used to increase the rate of forest recovery and thereby reduce regeneration failure. Seed dispersal is a fundamental ecological process that can also influence spatio-temporal patterns of forest regeneration. In this study, we investigated the relative contribution of planting and seed dispersal on forest regeneration at landscape scales. Because such influences can be further complicated by timber harvest intensity and seed availability within and around harvested area, we also evaluated the effects of those factors on forest landscape dynamics. We used the forest landscape model LANDIS to simulate the dynamics of Korean pine-broadleaf mixed forests in Northeast China. We considered three factors: timber harvest intensity (3 levels), seed dispersal and whether or not planting was used. The results showed that planting was more important in maintaining the abundance of Korean pine (Pinus koraiensis), a climax keystone species in this region, under the high-intensity harvesting option during early succession. In contrast, seed dispersal was more important during late succession. Korean pine can be successfully regenerated through seed dispersal under low and medium harvest intensities. Our results also indicated that effective natural regeneration will require protecting seed-production trees (seed rain). This study results provide a basis for more effectively managing Chinese temperate forests and possibly other similar ecosystems.

Diversity of Methanotrophic Bacteria Community between Different Development Stages in Chinese Temperate Forest

The method of terminal restriction fragment length polymorphism (T-RFLP) was used to study the community structures and diversities of aerobic methanotrophs by the key functional genes pmoA in the forest land soils of Changbai Mountains in China. And the effects of soil factors on them were also evaluated, and then the mechanism of microbiological communities in forest land soils response to the forest succession were discussed. The results showed that the diversity indices of aerobic methanotrophs were higher, and community structures appeared more complicated at the later plots. Their similarity coefficients gradually declined from the middle of the forest succession to the adjacent forest, indicating communities dynamic succession. During succession process, soil moisture and organic matter content had significant influence on it. The microbial communities were under the stress of succession process, which led to more emission of other greenhouse-gas from forest soils.

Seasonality of soil CO2 efflux in a temperate forest: Biophysical effects of snowpack and spring freeze–thaw cycles

Changes in characteristics of snowfall and spring freeze–thaw-cycle (FTC) events under the warming climate make it critical to understand biophysical controls on soil CO2 efflux (RS) in seasonally snow-covered ecosystems. We conducted a snow removal experiment and took year-round continuous automated measurements of RS, soil temperature (T5) and soil volumetric water content at the 5cm depth (W5) with a half-hour interval in a Chinese temperate forest in 2010–2011. Our objectives were to: (1) develop statistical models to describe the seasonality of RS in this forest; (2) quantify the contribution of seasonal RS to the annual budget; (3) examine biophysical effects of snowpack on RS; and (4) test the hypothesis that an FTC-induced enhancement of RS is jointly driven by biological and physical processes. Empirical RS–T5–W5 models explained 65.3–94.1% of the variability in the RS data, but the number of the regression terms and their coefficients varied with season. This indicates that the model should be fitted to the seasonal data sets separately to explicitly describe the seasonality of RS. The RS during the winter, spring FTC period, and growing season contributed 5.7%, 3.5%, and 91.1%, respectively, to the total annual RS. The relative enhancement of RS due to snowpack and FTCs averaged 3.4 and 2.5, respectively. The snowpack-induced enhancement of RS exponentially increased with T5 (R2=0.83) and snow depth (R2=0.16), while the FTC-induced enhancement of RS exponentially decreased with T5 (R2=0.45) and W5 (R2=0.67). These results suggest that the snowpack-induced enhancement mainly results from the snow-depth-dependent insulation of soil from low air temperatures, while the FTC-induced enhancement is dominantly driven by biological processes. Accumulatively, the snowpack and spring FTCs made a minor net contribution (2.3% and 1.2%, respectively) to the annual RS budget.

Time and litter species composition affect litter-mixing effects on decomposition rates

Purpose Litter decomposition is a fundamental process of biogeochemical cycles. Mixing litter of different species can induce non-additive effect (NAE) on decomposition processes. A better understanding of the factors influencing the direction and magnitude of NAE is important for quantification of ecosystem carbon and nutrient cycling. Methods Litter mixing effects on leaf litter decomposition were examined using two parallel experiments (each with leaf litter of four tree species combined into four diversity levels) conducted in Chinese temperate forests for 2 years. Results A significant diversity effect in both experiments demonstrated NAEs of litter mixing on the mass remaining. Separating the diversity effect into species richness and composition showed that composition was statistically significant in both experiments whereas an effect of species richness was only detected in Experiment 2. In both experiments, the NAE on decomposition changed with incubation time and showed a declining trend during decomposition process. However, a slight difference of the NAE in the two experiments was observed in our study. Decomposition in the litter mixtures differed from the predictions based on single species, and the presence/absence of poplar, pine and oak in the litter mixture significantly influenced the direction and magnitude of the NAE. Presence of coniferous species litter significantly reduced decomposition rates even within the same species richness level. The coefficient of variation of remaining litter mass was lower in the treatments with higher number of litter species. Conclusions Our findings showing of changes in the direction and magnitude of NAE with decomposition time and litter species composition indicate that tree species composition and decomposition duration should be considered in predicting biodiversity effect on biogeochemical cycling in temperate forests.

Inter-specific and seasonal variations in photosynthetic capacity and water use efficiency of five temperate tree species in Northeastern China

Photosynthetic capacity (P max) and water use efficiency (WUE) are useful indices for describing CO2 uptake and H2O loss of trees. Inter-specific and seasonal variations in P max and WUE of five tree species were quantified in a Chinese temperate forest. The study included pioneer (white birch), mid-successional (Amur cork-tree, Manchurian walnut, Mongolian oak), and late-successional (Amur linden) species. The P max and WUE differed significantly among species, but the inter-specific variations were smaller than previously reported. Leaf-area-based P max varied from 5.1 for linden to 11.0 µmol m−2s−1 for birch, whereas leaf-mass-based P max ranged from 154 for linden to 252 µmol kg−1s−1 for walnut. Linden had the highest WUE, whereas walnut had the lowest. The seasonal patterns of P max and WUE were significantly different between species. The P max of birch increased as the season proceeded, whereas the P max of the other four species was lowest in May, and peaked in June. The seasonality of P max was influenced by stomatal conductance, apparent carboxylation efficiency, and specific leaf area, but the determining factor varied with species and leaf development. This study suggests that a deeper understanding of inter-specific and seasonal variations of gas exchange parameters would improve our ability to predict the carbon metabolism in the temperate forests.

Carbon density and distribution of six Chinese temperate forests

Quantifying forest carbon (C) storage and distribution is important for forest C cycling studies and terrestrial ecosystem modeling. Forest inventory and allometric approaches were used to measure C density and allocation in six representative temperate forests of similar stand age (42-59 years old) and growing under the same climate in northeastern China. The forests were an aspen-birch forest, a hardwood forest, a Korean pine plantation, a Dahurian larch plantation, a mixed deciduous forest, and a Mongolian oak forest. There were no significant differences in the C densities of ecosystem components (except for detritus) although the six forests had varying vegetation compositions and site conditions. However, the differences were significant when the C pools were normalized against stand basal area. The total ecosystem C density varied from 186.9 tC hm(-2) to 349.2 tC hm(-2) across the forests. The C densities of vegetation, detritus, and soil ranged from 86.3-122.7 tC hm(-2), 6.5-10.5 tC hm(-2), and 93.7-220.1 tC hm(-2), respectively, which accounted for 39.7% +/- 7.1% (mean +/- SD), 3.3% +/- 1.1%, and 57.0% +/- 7.9% of the total C densities, respectively. The overstory C pool accounted for > 99% of the total vegetation C pool. The foliage biomass, small root (diameter < 5mm) biomass, root-shoot ratio, and small root to foliage biomass ratio varied from 2.08-4.72 tC hm(-2), 0.95-3.24 tC hm(-2), 22.0%-28.3%, and 34.5%-122.2%, respectively. The Korean pine plantation had the lowest foliage production efficiency (total biomass/foliage biomass: 22.6 g g(-1)) among the six forests, while the Dahurian larch plantation had the highest small root production efficiency (total biomass/small root biomass: 124.7 g g(-1)). The small root C density decreased with soil depth for all forests except for the Mongolian oak forest, in which the small roots tended to be vertically distributed downwards. The C density of coarse woody debris was significantly less in the two plantations than in the four naturally regenerated forests. The variability of C allocation patterns in a specific forest is jointly influenced by vegetation type, management history, and local water and nutrient availability. The study provides important data for developing and validating C cycling models for temperate forests.

Dynamics of fine roots in five Chinese temperate forests

We used a minirhizotron method to investigate spatial and temporal dynamics of fine roots (diameter < or =2 mm) in five Chinese temperate forests: Mongolian oak forest, aspen-birch forest, hardwood forest, Korean pine plantation and Dahurian larch plantation. Fine root dynamics were significantly influenced by forest type, soil layer, and sampling time. The grand mean values varied from 1.99 to 3.21 mm cm(-2) (root length per minirhizotron viewing area) for the fine root standing crop; from 6.7 to 11.6 microm cm(-2) day(-1) for the production; and from 3.2 to 6.1 microm cm(-2) day(-1) for the mortality. All forests had a similar seasonal "sinusoidal" pattern of standing crop, and a "unimodal" pattern of production. However, the seasonal dynamics of the mortality were largely unsynchronized with those of the production. The minimum values of standing crop, production and mortality occurred in March for all forests, whereas the maximum values and occurrence time differed among forest types. The standing crop, production and mortality tended to decrease with soil depth. The different spatiotemporal patterns of fine roots among the forests highlight the need for forest-specific measurements and modeling of fine root dynamics and forest carbon allocation.

Rhizospheric and heterotrophic components of soil respiration in six Chinese temperate forests

AbstractPartitioning soil respiration (RS) into heterotrophic (RH) and rhizospheric (RR) components is an important step for understanding and modeling carbon cycling in forest ecosystems, but few studies on RR and RH exist in Chinese temperate forests. In this study, we used a trenching plot approach to partition RS in six temperate forests in northeastern China. Our specific objectives were to (1) examine seasonal patterns of soil surface CO2 fluxes from trenched (RT) and untrenched plots (RUT) of these forests; (2) quantify annual fluxes of RS components and their relative contributions in the forest ecosystems; and (3) examine effects of plot trenching on measurements of RS and related environmental factors. The RT maximized in early growing season, but the difference between RUT and RT peaked in later summer. The annual fluxes of RH and RR varied with forest types. The estimated values of RH for the Korean pine (Pinus koraiensis Sieb. et Zucc.), Dahurian larch (Larix gmelinii Rupr.), aspen‐birch (Populous davidiana Dode and Betula platyphylla Suk.), hardwood (Fraxinus mandshurica Rupr., Juglans mandshurica Maxim. and Phellodendron amurense Rupr.), Mongolian oak (Quercus mongolica Fisch.) and mixed deciduous (no dominant tree species) forests averaged 89, 196, 187, 245, 261 and 301 g C m−2 yr−1, respectively; those of RR averaged 424, 209, 628, 538, 524 and 483 g C m−2 yr−1, correspondingly; calculated contribution of RR to RS (RC) varied from 52% in the larch forest to 83% in the pine forest. The annual flux of RR was strongly correlated to biomass of roots &lt;0.5 cm in diameter, while that of RH was weakly correlated to soil organic carbon concentration at A horizon. We concluded that vegetation type and associated carbon metabolisms of temperate forests should be considered in assessing and modeling RS components. The significant impacts of changed soil physical environments and substrate availability by plot trenching should be appropriately tackled in analyzing and interpreting measurements of RS components.

Soil respiration in six temperate forests in China

AbstractScaling soil respiration (RS), the major CO2 source to the atmosphere from terrestrial ecosystems, from chamber‐based measurements to ecosystems requires studies on variations and correlations of RS from various biomes and across geographic regions. However, few studies on RS are available for Chinese temperate forest despite the importance of this forest in the national and global carbon budgets. In this study, we conducted 18‐month RS measurements during 2004–2005 in six temperate forest types, representing the typical secondary forest ecosystems across various site conditions in northeastern China: Mongolian oak (Quercus mongolica Fisch.), aspen‐birch (Populous davidiana Dode and Betula platyphylla Suk.), mixed deciduous (no dominant tree species), hardwood (dominated by Fraxinus mandshurica Rupr., Juglans mandshurica Maxim., and Phellodendron amurense Rupr.) forests, Korean pine (Pinus koraiensis Sieb. et Zucc.) and Dahurian larch (Larix gmelinii Rupr.) plantations. Our specific objectives were to: (1) explore relationships of RS against soil temperature and water content for the six forest ecosystems, (2) quantify annual soil surface CO2 flux and its relations to belowground carbon storage, (3) examine seasonal variations in RS and related environmental factors, and (4) quantify among‐ and within‐ecosystem variations in RS. The RS was positively correlated to soil temperature in all forest types, and was significantly influenced by the interactions of soil temperature and water content in the pine, larch, and mixed deciduous forests. The sensitivity of RS to soil temperature at 10 cm depth (Q10) ranged from 2.61 in the oak forest to 3.75 in the aspen‐birch forests. The Q10 tended to increase with soil water content until reaching a threshold, and then decline. The annual RS for the larch, pine, hardwood, oak, mixed deciduous, and aspen‐birch forests averaged 403, 514, 781, 785, 786, and 813 g C m−2 yr−1, respectively. The annual RS of the broadleaved forests was 72% greater than that of the coniferous forests. The annual RS was positively correlated to soil organic carbon (SOC) concentration at O horizon (R2=0.868) and total biomass of roots &lt;0.5 cm in diameter (R2=0.748). The coefficient of variation (CV) of RS among forest types averaged 25% across the 18‐month measurements. The CV of RS within plots varied from 20% to 27%, significantly (P&lt;0.001) greater than those among plots (9–15%), indicating the importance of the fine‐scaled heterogeneity in RS. This study emphasized that variations in soil respiration and potential sampling bias should be appropriately tackled for accurate soil CO2 flux estimates.

Biomass allometric equations for 10 co-occurring tree species in Chinese temperate forests

The temperate forest in northeastern China accounts for more than one-third of Chinese forest resources (both area and stocking volume), and plays a key role in the national and global carbon budgets and climatic system. However, few allometric equations exist for accurately estimating biomass and carbon budgets of the forest. In this study, allometric equations were developed relating component biomass to diameter at breast height (DBH) and tree height ( H) to DBH for 10 co-occurring tree species in the Chinese temperate mixed forest. The 10 species were Korean pine ( Pinus koraiensis Sieb. et Zucc.), Dahurian larch ( Larix gmelinii Rupr.), Mongolian oak ( Quercus mongolica Fisch.), white birch ( Betula platyphylla Suk.), Amur cork-tree ( Phellodendron amurense Rupr.), Manchurian walnut ( Juglans mandshurica Maxim.), Manchurian ash ( Fraxinus mandshurica Rupr.), aspen ( Populous davidiana Dode), maple ( Acer mono Maxim.), and Amur linden ( Tilia amurensis Rupr.). The biomass components included stem, current-year branch, older branch, current-year foliage, older foliage, stump, and coarse root (diameter ≥5 mm). Harvested tree DBH ranged from 2.4 to 57.1 cm. Generalized biomass allometric equations that ignored tree species, based on DBH and fitted on a log–log scale, explained more than 90% of variability in woody component biomass, but the species effect was significant ( α = 0.05). Including tree height as the second independent variable in the allometric equations improved the accuracy of biomass estimates, especially for foliage biomass. The relative differences in biomass estimated from the generalized, DBH-only, and DBH– H combined equations varied from −50.6% to 43.9% depending upon model form, species, and biomass component. Foliage biomass was more variable than other component biomass both across and within tree species. Some potential sources of error in biomass estimation were also discussed.