[Changes in diversity of marsh plant communities under shrub encroachment in Sanjiang Plain and their soil control factors]. / çŒæœ¨æ‰©å¼ åŽ‹åŠ›ä¸‹ä¸‰æ±Ÿå¹³åŽŸæ²¼æ³½æ¤ç‰©ç¾¤è½å¤šæ ·æ€§å˜åŒ–åŠå ¶åœŸå£¤æŽ§åˆ¶å› å­.

In this study, we explored the changes in plant community diversity and their relationship with soil factors under shrub encroachment pressure by selecting four marsh areas in Sanjiang Plain with different degrees of shrub cover (a, 0≤a≤100%), including marsh with no shrub encroachment (a=0), light shrub encroachment (0

Impacts of permafrost thaw on streamflow recession in a discontinuous permafrost watershed of northeastern China.

Permafrost thaw due to climate change is altering terrestrial hydrological processes by increasing ground hydraulic conductivity and surface and subsurface hydrologic connectivity across the pan-Arctic. Understanding how runoff responds to changes in hydrologic processes and conditions induced by permafrost thaw is critical for water resources management in high-latitude and high-altitude regions. In this study, we analyzed streamflow recession characteristics for 1964-2016 for the Tahe watershed located at the southern margin of the permafrost region in Eurasia. Results reveal a link between streamflow recession and permafrost degradation as indicated by the statistical analyses of streamflow and the modeled ground warming and active layer thickening. The recession constant and the active layer temperatures at depths of 5, 40, 100, and 200 cm simulated by the backpropagation neural network model significantly increased during the study period from 1972 to 2020 due to intensified climate warming in northeastern China. The onset of seasonal active layer thaw was advanced by 10 days, and the modeled active layer thickness increased by 54 cm in this period. The average annual streamflow recession time increased by 11.5 days (+53 %) from the warming period (1972-1988) to the thawing period (1989-2016), with these periods determined from breakpoint analysis. These hydrologic changes arose from increased catchment storage and were correlated to increased active layer thickness and longer seasonal thawing periods. These results highlight that permafrost degradation can significantly extend the recession flow duration in a watershed underlain by discontinuous, sporadic, and isolated permafrost, and thereby alter flooding dynamics and water resources in the southern margin of the Eurasian permafrost region.

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.

Contribution of the nongrowing season to annual N2O emissions from the permafrost wetland in Northeast China.

Permafrost regions store large amounts of soil organic carbon and nitrogen, which are major sources of greenhouse gas. With climate warming, permafrost is thawing and releasing an abundance of greenhouse gases into the atmosphere and contributing to climate warming. Numerous studies have shown the mechanism of nitrous oxide (N2O) emissions from the permafrost region during the growing season. However, little is known about the temporal pattern and drivers of nongrowing season N2O emissions from the permafrost region. In this study, N2O emissions from the permafrost region were investigated from June 2016 to June 2018 using the static opaque chamber method. We aimed to quantify the seasonal dynamics of nongrowing season N2O emissions and their contribution to the annual budget. The results showed that the N2O emissions ranged from - 35.75 to 74.16 µg m-2 h-1 with 0.89 to 1.44 kg ha-1 being released into the atmosphere during the nongrowing season in the permafrost region. The permafrost wetland types had no significant influence on the nongrowing season N2O emissions due to the nitrate content. The cumulative N2O emissions during the nongrowing season contributed to 41.96-53.73% of the annual budget, accounting for almost half of the annual emissions in the permafrost region. The driving factors of N2O emissions were different among the nongrowing season, growing season, and entire period. The N2O emissions from the nongrowing season and total 2-year observation period were mainly affected by soil temperature, which could explain 3.01-9.54% and 6.07-14.48% of the temporal variation in N2O emissions, respectively. In contrast, the N2O emissions from the growing season were controlled by soil temperature, water table level, pH, NH4+-N, NO3--N, total nitrogen, total organic carbon, and C/N ratio, which could explain 14.51-45.72% of the temporal variation of N2O emissions. Nongrowing season N2O emissions are an essential component of annual emissions and cannot be ignored in the permafrost region.

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 Microbial Community Response Differently to the Frequency and Strength of Freeze-Thaw Events in a Larix gmelinii Forest in the Daxing'an Mountains, China.

Sustained climate warming increases the frequency and strength of soil freeze-thaw (FT) events, which strongly affect the properties of soil microbial communities. To explore the responses and mechanisms of the frequency and strength of freeze-thaw events on soil microbial communities, a lab-scale FT test was conducted on forest soil in permafrost region from the Daxing'an Mountains, China. The number of FT cycles (FTN) had a greater effect on microbial communities than FT temperature fluctuation (FTF). The FTN and FTF explained 20.9 and 10.8% of the variation in microbial community structure, respectively, and 22.9 and 11.6% of the variation in enzyme activities, respectively. The total and subgroup microbial biomass, the ratio of fungi to bacteria (F/B), and C- and N-hydrolyzing enzyme activities all decreased with an increase in FTN. Among microbial groups, arbuscular mycorrhizal fungi (AMF) were the most sensitive to FT events. Based on the changes of F/B and AMF, the reduction in soil carbon sequestration caused by frequent FT events can be explained from a perspective of microorganisms. Based on redundancy analysis and Mental Test, soil moisture, total organic carbon, and total nitrogen were the major factors affecting microorganisms in FT events. In the forest ecosystem, soil water and fertilizer were important factors to resist the damage of FT to microorganism, and sufficient water and fertilizer can lighten the damage of FT events to microorganisms. As a result of this study, the understanding of the responses of soil microorganisms to the variation in FT patterns caused by climate changes has increased, which will lead to better predictions of the effects of likely climate change on soil microorganisms.

Building Virtual Watersheds: A Global Opportunity to Strengthen Resource Management and Conservation.

Modern land-use planning and conservation strategies at landscape to country scales worldwide require complete and accurate digital representations of river networks, encompassing all channels including the smallest headwaters. The digital river networks, integrated with widely available digital elevation models, also need to have analytical capabilities to support resource management and conservation, including attributing river segments with key stream and watershed data, characterizing topography to identify landforms, discretizing land uses at scales necessary to identify human-environment interactions, and connecting channels downstream and upstream, and to terrestrial environments. We investigate the completeness and analytical capabilities of national to regional scale digital river networks that are available in five countries: Canada, China, Russia, Spain, and United States using actual resource management and conservation projects involving 12 university, agency, and NGO organizations. In addition, we review one pan-European and one global digital river network. Based on our analysis, we conclude that the majority of the regional, national, and global scale digital river networks in our sample lack in network completeness, analytical capabilities or both. To address this limitation, we outline a general framework to build as complete as possible digital river networks and to integrate them with available digital elevation models to create robust analytical capabilities (e.g., virtual watersheds). We believe this presents a global opportunity for in-country agencies, or international players, to support creation of virtual watersheds to increase environmental problem solving, broaden access to the watershed sciences, and strengthen resource management and conservation in countries worldwide.

[Rainfall redistribution traits of three main forest types in Dagangshan Mountains of Jiangxi Province, China].

The redistribution processes of rainfall due to the canopy were studied on three typical forest types (Chinese fir forest, evergreen broad-leaved forest and Phyllostachys pubescens forest) in Dagangshan Mountains of Jiangxi Province. The results showed that from April to June, 2012, the total precipitation was 531.6 mm, with the maximum single rainfall of 61.7 mm. The rainfall in this area was mainly light and moderate. During the research period, the total throughfall of P. pubescens forest was the greatest, and that of evergreen broad-leaved forest was the smallest. The throughfall of P. pubescens and Chinese fir forest were almost equal at the same rainfall intensity. However, the throughfall of evergreen broad-leaved forest was smaller than those of the other two types of forest at the same high rainfall intensity. Throughfall presented a distinct spatial variability within each forest. Stemflow of Chinese fir forest, evergreen broad-leaved forest and P. pubescens forest were 1.4%, 8.9% and 8.8%, respectively. There were significant differences (P < 0.01) in stemflow between the Chinese fir forest and the other two types of forests. In addition, the moisture degree of forests before a rain event greatly influenced the quantity of the stemflow. The effect was strongest in the Chinese fir plantation and weakest in the P. pubescens forest. The proportion of interception to rainfall was in a descending order of 30.5%, 25.5% and 19.2% for the Chinese fir forest, the evergreen broad-leaved forest and the P. pubescens forest, respectively. The Chinese fir forest had the obviously greater interception rate than the other two types of forests under usual rainfall in the study area.

Multi-model ensemble simulation and projection in the climate change in the Mekong River Basin. Part I: temperature.

This paper evaluates the performance of the Coupled Model Intercomparison Project phase 5 (CMIP5) in simulating annual and decadal temperature in the Mekong River Basin from 1950 to 2005. By use of Bayesian multi-model averaging method, the future projection of temperature variation under different scenarios are also analyzed. The results show, the performances of climate model are more accurate in space than time, the model can catch the warming characteristics in the Mekong river Basin, but the accuracy of simulation is not good enough. Bayesian multi-model averaging method can improve the annual and decadal temperature simulation when compared to a single result. The projected temperature in Mekong River will increase by 0.88 °C/100 year, 2.15 °C/100 year and 4.96 °C/100 year for the RCP2.6, RCP4.5, and RCP8.5 scenarios, respectively, over the twenty-first century. The findings will be beneficial for local people and policy-maker to formulate regional strategies against the potential menaces of warming scenarios.

Food availability and animal space use both determine cache density of Eurasian red squirrels.

Scatter hoarders are not able to defend their caches. A longer hoarding distance combined with lower cache density can reduce cache losses but increase the costs of hoarding and retrieving. Scatter hoarders arrange their cache density to achieve an optimal balance between hoarding costs and main cache losses. We conducted systematic cache sampling investigations to estimate the effects of food availability on cache patterns of Eurasian red squirrels (Sciurus vulgaris). This study was conducted over a five-year period at two sample plots in a Korean pine (Pinus koraiensis)-dominated forest with contrasting seed production patterns. During these investigations, the locations of nest trees were treated as indicators of squirrel space use to explore how space use affected cache pattern. The squirrels selectively hoarded heavier pine seeds farther away from seed-bearing trees. The heaviest seeds were placed in caches around nest trees regardless of the nest tree location, and this placement was not in response to decreased food availability. The cache density declined with the hoarding distance. Cache density was lower at sites with lower seed production and during poor seed years. During seed mast years, the cache density around nest trees was higher and invariant. The pine seeds were dispersed over a larger distance when seed availability was lower. Our results suggest that 1) animal space use is an important factor that affects food hoarding distance and associated cache densities, 2) animals employ different hoarding strategies based on food availability, and 3) seed dispersal outside the original stand is stimulated in poor seed years.

[Seasonal dynamics of hydrochemical characteristics of streams under different forest types].

Stream water samples under the Korean pine broad-leaved forest, spruce-fir forest, and larch plantation in Liangshui Nature Reserve of Xiaoxing' an Mountains were collected monthly from March to October 2006 to study the dynamic changes of their hydrochemical characteristics. The results indicated that the content of major cations in the streams was in the sequence of Ca2+ > Na+ > K+ > Mg2+, and that of anions was HCO3(-) > SO4(2-) > NO3(-) > Cl(-). The average content of Na+, Ca2+, Mg2+, Fe2+ and Fe3+ was in the order of spruce-fir forest > larch plantation > Korean pine broad-leaved forest, while that of K+ was in the order of larch plantation > spruce-fir forest > Korean pine broad-leaved forest. The average monthly content of anions in stream water was the highest under larch plantation.

[Estimation of forest canopy closure by using partial least square regression].

Based on remote sensing and forest resources inventory data, this paper approached the feasibility of using Bootstrap approach to select optimal variables and using partial least square (PLS) regression to build a model for estimating forest canopy closure. The results showed that whether using a model built with all variables or a model with the optimal variables selected by Bootstrap approach, the relative deviation in estimating forest canopy closure was about 5%. The optimal variables selected in this paper differed greatly with those in the studies for other areas, suggesting that besides selection method, zonal vegetation and terrain could also induce the differences of selected optimal variables for the estimation of forest canopy closure.

[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.

[Effects of forest harvesting on river runoff in Xiaoxing'anling].

By the method of runoff determination in large basin combined with contrast experiment in small watershed, and based on the runoff and forest resources data in past 35 years, this paper studied the serial changes of river runoff in Xiaoxing'anling after forest harvesting. The results showed that the river flow was increased in the early 10 years after forest harvesting, but decreased gradually with the growth and crown closure of artificial larch forest, tended towards or even lower than the level before harvesting. The river runoff had a close correlation with annual rainfall and the areas of forest harvesting and regeneration. Significant positive correlation was observed between annual flow and forest harvesting area, which resulted in the increase of river runoff after forest harvesting. Forest harvesting could also significantly increase the peak flood and snowmelt runoff. There was a negative correlation between regenerated forest area and annual flow, and thus, forest regeneration would decrease annual

[Quantitative estimation of vegetation coverage in Mu Us sandy land based on RS and GIS].

On the basis of oriented field investigation data and corresponding RS and GIS information, and by the method of ridge estimation, this paper studied the estimation model of vegetation coverage and its affecting factors in Yijinholo County of northeast Mu Us sandy land. The results showed that the vegetation coverage was affected by NDVI, and closely linked with such RS and GIS information as, TM7, TM2, TM 4/3 and gradient. Ridge estimation method could obviously improve the limitation of Least Square method, eliminate the adverse effects caused by existing complex estimation relation towards uncoiling undetermined parameter among the variables, and improve the estimate precision. The vegetation coverage estimation model taking pixel as unit was established, and its test precision could reach 98.7%. In addition, a regional vegetation coverage GIS was established, which could realize the inquiry, regeneration, and drawing of any spot (pixel) or any land unit of vegetation coverage automatically.

[Preliminary research on environmental characteristics of oasis-desert ecotone].

Taking Minqin Oasis in the downstream of Shiyanghe Rivers as example, the shrub characteristics of sand dune, which was closely related to the vegetation of the interface between the outside of oasis and desert, was studied in this paper. The change of vegetation coverage and dune density indicated that the vegetation coverage in the ecotone was obviously higher than that in the outside of oasis and in drift desert. There existed an area outside oasis that was obviously affected by human activies and 0-600 m away from the outside of oasis. Meanwhile, the appearing position of area outside oasis was different in different place. The naked area ratio of dune in the area outside oasis was the biggest, so that the area outside oasis was the main resource of drift sand resulting in desertification of oasis. Over extracting ground water in oasis district resulted in a forming of dropping funnel of ground water there, and resulted in a fluid of ground water from desert to oasis. Ultimately, human activites aggravated those processes to some extent.