Different variations in soil CO2, CH4, and N2O fluxes and their responses to edaphic factors along a boreal secondary forest successional trajectory.

Forest succession is an important process regulating the carbon and nitrogen budgets in forest ecosystems. However, little is known about how and extent by which vegetation succession predictably affects soil CO2, CH4, and N2O fluxes, especially in boreal forest. Here, a field study was conducted along a secondary forest succession trajectory from Betula platyphylla forest (early stage), then Betula platyphylla-Larix gmelinii forest (intermediate stage), to Larix gmelinii forest (late stage) to explore the effects of forest succession on soil greenhouse gas fluxes and related soil environmental factors in Northeast China. The results showed significant differences in soil greenhouse gas fluxes during the forest succession. During the study period, the average soil CO2 flux was greatest at mid-successional stage (444.72 mg m-2 h-1), followed by the late (341.81 mg m-2 h-1) and the early-successional (347.12 mg m-2 h-1) stages. The average soil CH4 flux increased significantly during succession, ranging from -0.062 to -0.036 mg m-2 h-1. The average soil N2O flux was measured as 17.95 µg m-2 h-1 at intermediate successional stage, significantly lower than that at late (20.71 µg m-2 h-1) and early-successional (20.85 µg m-2 h-1) stages. During forest succession, soil greenhouse gas fluxes showed significant correlations with soil and environmental factors at both seasonal and successional time scales. The seasonal variations of soil GHG fluxes were mainly influenced by soil temperature and water content. Meanwhile, soil MBN and soil NO3--N content were also important factors for soil N2O fluxes. Structural equation modelling showed that forest succession affected soil CO2 fluxes by changing soil temperature and microbial biomass carbon, affected soil CH4 fluxes mainly by changing soil water content and soil pH value, and affected soil N2O fluxes mainly by changing soil temperature, microbial biomass nitrogen, and soil NO3--N content. Our study suggests that forest succession mainly alters soil nutrient and soil environment/chemical properties affecting soil CO2 and N2O fluxes and soil CH4 fluxes, respectively, in the secondary forest succession process.

Understory species composition mediates soil greenhouse gas fluxes by affecting bacterial community diversity in boreal forests.

Introduction: Plant species composition in forest ecosystems can alter soil greenhouse gas (GHG) budgets by affecting soil properties and microbial communities. However, little attention has been paid to the forest types characterized by understory vegetation, especially in boreal forests where understory species contribute significantly to carbon and nitrogen cycling. Method: In the present study, soil GHG fluxes, soil properties and bacterial community, and soil environmental conditions were investigated among three types of larch forest [Rhododendron simsii-Larix gmelinii forest (RL), Ledum palustre-Larix gmelinii forest (LL), and Sphagnum-Bryum-Ledum palustre-Larix gmelinii forest (SLL)] in the typical boreal region of northeast China to explore whether the forest types characterized by different understory species can affect soil GHG fluxes. Results: The results showed that differences in understory species significantly affected soil GHG fluxes, properties, and bacterial composition among types of larch forest. Soil CO2 and N2O fluxes were significantly higher in LL (347.12 mg m-2 h-1 and 20.71 µg m-2 h-1) and RL (335.54 mg m-2 h-1 and 20.73 µg m-2 h-1) than that in SLL (295.58 mg m-2 h-1 and 17.65 µg m-2 h-1), while lower soil CH4 uptake (-21.07 µg m-2 h-1) were found in SLL than in RL (-35.21 µg m-2 h-1) and LL (-35.85 µg m-2 h-1). No significant differences between LL and RL were found in soil CO2, CH4, and N2O fluxes. Soil bacterial composition was mainly dominated by Proteobacteria, Actinobacteria, Acidobacteria, and Chloroflexi among the three types of larch forest, while their abundances differed significantly. Soil environmental variables, soil properties, bacterial composition, and their interactions significantly affected the variations in GHG fluxes with understory species. Specifically, structural equation modeling suggested that soil bacterial composition and temperature had direct close links with variations in soil GHG fluxes among types of larch forest. Moreover, soil NO3 --N and NH4 + - N content also affected soil CO2, CH4, and N2O fluxes indirectly, via their effects on soil bacterial composition. Discussion: Our study highlights the importance of understory species in regulating soil GHG fluxes in boreal forests, which furthers our understanding of the role of boreal forests in sustainable development and climate change mitigation.

Soil fungal and bacterial communities in southern boreal forests of the Greater Khingan Mountains and their relationship with soil properties.

Little is known about the relationship between soil microbial communities and soil properties in southern boreal forests. To further our knowledge about that relationship, we compared the soil samples in southern boreal forests of the Greater Khingan Mountains-the southernmost boreal forest biome in the world. The forests can be divided into boardleaf forests dominated by birch (Betula platyphylla) or aspen (Populus davidiana) and coniferous forests dominated by larch (Larix gmelinii) or pine (Pinus sylvestris var. mongolica). Results suggested different soil microbial communities and soil properties between these southern boreal forests. Soil protease activity strongly associated with soil fungal communities in broadleaf and coniferous forests (p < 0.05), but not with soil bacterial communities (p > 0.05). Soil ammonium nitrogen and total phosphorus contents strongly associated with soil fungal and bacterial communities in broadleaf forests (p < 0.05), but not in coniferous forests (p > 0.05). Soil potassium content demonstrated strong correlations with both soil fungal and bacterial communities in broadleaf and coniferous forests (p < 0.05). These results provide evidence for different soil communities and soil properties in southern boreal forest, and further elucidate the explicit correlation between soil microbial communities and soil properties in southern boreal forests.

[Time lag effects of throughfall in natural Larix gmelinii forest in the north of Great Xing'an Mountains, China].

Based on a natural Larix gmelinii forest from Mohe Ecological Station, located in north of Great Xing' an Mountains, time lag effects of throughfall inside the Larix gmelinii forest were analyzed by measuring rainfall, throughfall and stemflow with the method of location observation. The result showed that forest throughfall, stemflow and canopy interception accounted for 76.5%, 2.6% and 20.9% of total rainfall, respectively. Time lag of rainfall inside L. gmelinii forest was found both in beginning and termination of rainfall compared to outside, and the higher the rainfall level, the shorter the time lag of throughfall. For throughfall and stemflow, variations of time lag were (67.8 ± 7.8)--(17.2 ± 3.9) min and (112.0 ± 38.8)--(48.3 ± 10.6) min, respectively. The time lag of throughfall decreased with the increasing rainfall intensity under the same rainfall level. When the rainfall intensity was greater than 2 mm · h(-1), the time lag of throughfall was shortened significantly, but it increased with prolonging the antecedent dry period before rainfall. Rainfall would be the critical factor to affect the time lag of throughfall when the antecedent dry period was longer than 48 h. Termination of throughfall also lagged when rainfall termination happened with a rainfall greater than 5.0 mm. The time lag of throughfall termination increased with increasing the rainfall intensity, but it had no significant relationship with the antecedent dry period before rainfall. However, the termination of stemflow occurred prior to rainfall, which was relevant to the rainfall level, and the smaller the rainfall level, the sooner the stemflow terminated.

[Distribution characteristics and seasonal dynamics of Cu and Zn in shrub-marsh plants in mountainous areas of northeast China].

The study on the distribution, accumulation, and seasonal dynamics of Cu and Zn in shrub-marsh plants Salix rosmarinifolia, Salix pentandra, Carex caespitosa and Carex schmidtii in mountainous areas of Northeast China showed that the Cu concentration in test plants varied from 6 to 12 mg x kg(-1), and its distribution was in the sequence of root > stem > leaf in S. rosmarinifolia and S. pentandra, and of stem > leaf > root in C. caespitosa and C. schmidtii, suggesting that Cu was mainly accumulated in the root of shrubs and the stem or leaf of Carex. Shrubs and Carex had less difference in their Cu concentration. The Zn concentration in test plants was 30-250 mg x kg(-1), and its distribution was in the sequence of leaf > stem > root in S. rosmarinifolia and S. pentandra, and of root > stem > leaf in C. caespitosa and C. schmidtii, indicating that Zn was mainly accumulated in the leaf of shrubs and the root of Carex. Shrubs had a higher Zn concentration than Carex. The accumulation coefficient of Zn in the organs of S. rosmarinifolia and S. pentandra was higher than 1.45, suggesting a good Zn-accumulation ability of these plants. The Cu and Zn concentrations in the aboveground parts of the four plants were higher during the initial growth period and then fluctuated to decrease with season, while those in roots were all higher both in the initial and in the late growth periods.

[Effects of forest and swamp on hydrochemical characteristics of streams].

With the upper reaches of Gongbiela River in the northeast part of Xiaoxing' an Mountains as test area, this paper studied the hydrochemical characteristics of the streams in forest and swamp during the period of June - September 2004. The results indicated that the hydrochemistry of forest and swamp streams belonged to calcium-bicarbonate type I (C1(Ca)). The pH value, mineralization rate, total hardness, and HCO3(-), SO4(2-), Ca(2+), Mg(2+) and Fe concentrations of forest streams were lower than those of swamp streams, while the concentrations of total N, total P, Cl-, K+, and Na+ were in adverse. In both of the streams, the contents of heavy metal elements such as Fe, Mn, Cu, Zn, Cd, Hg and Pb were lower than the class I in Environmental Quality Standards for Surface Water (EQSSW) of China. The concentrations of total N and P in forest streams were (0.27 +/- 0.04) mg x L(-1) and (0.040 +/- 0.005) mg x L(-1), respectively, being significantly higher than those ((0.21 +/- 0.02) mg x L(-1) and (0.025 +/- 0.004) mg x L(-1)) in swamp streams. Swamp wetland had a stronger ability in depositing and adsorbing N and P, with more NH4(+) -N adsorbed than NO3(-) -N, and also had a stronger ability on the reduction and release of Fe, with the Fe content ((0.26 +/- 0.05) mg x L(-1)) in its streams obviously higher than that in forest streams.

[Hydrochemical characteristics of three kinds of wetland in Gongbiela Basin].

The study on the hydrochemical characteristics of three representative kinds of wetland in Gongbiela Basin showed that in the water of test wetlands, HCO3 - was the dominant anion, accounting for 81.91% - 85.46% of total anions, and Ca2+ was the dominant cation, accounting for 56.80% - 69.32% of total cations. The hydrochemical type belonged to that of bicarbonate calcium. In the three kinds of wetland, water pH ranged from 6.2 to 7.1, mineralization degree ranged from 112.56 to 461.23 mg x L(-1), and hardness ranged from 14.31 to 148.53 mg x L(-1). On the whole, the water quality of the wetlands met the grade 1 and grade 2 national environmental water quality standards, but the Fe and Mn contents exceeding the standards influenced the water resource quality of this area. The spatial and temporal changes of hydochemical characteristics of the wetlands and the trace element contents in the water were also discussed and analyzed.