兴安落叶松林生长季土壤水势动态特征

兴安落叶松在大兴安岭分布广泛,土壤水分变化与其生长、发育关系密切,二者相互影响。通过测定兴安落叶松林不同深度土壤水势,研究兴安落叶松林生长季土壤水势的月、日变化特征。结果表明,土壤水势均值随深度增加而减小。20、80cm土壤水势变化程度大,40、60cm变化较为平缓。60cm土壤水势值较能反应林下土壤水势的大小。各深度土壤水势均采用三次函数拟合较好。生长季土壤水势在20cm呈整体下降趋势,40、60、80cm呈较快上升后平缓下降趋势。5、6月为土壤聚水期,水势上升迅速,土壤水势随深度增加而下降。7、8、9、10月为土壤失水期,水势下降平缓,土壤水势随深度增加而上升。土壤水势变化响应降水量、土壤温度的变化。土壤水势日变化特征:除5月20cm土壤水饱和外,各月20、40、60cm日变化特征一致,80cm在7、10月与其它深度特征不同。一天中,土壤水势极值常出现在7点左右与9点左右。

Driving force of soil microbial community structure in a burned area of Daxing'anling,China

Fires are an important factor impacting forest ecosystems of Daxing'anling and have a significant effect on soil microbial community structure.In this study,highthroughput sequencing for 16 S rDNA and ITS rDNA were applied to analyze the changing characteristics and driving factors of bacterial and fungal community structures in burned areas with different fire severity.PICRUSt2 software was used to predict the functional characteristics of burned areas with different fire severity.The purpose was to unveil the responsive relationships among the structure and function of bacterial and fungal communities,fire severity,and post-disturbance restoration times.After high severity fires,the destruction of surface vegetation and loss of soil nutrients reduced the diversity and abundance of soil bacteria and fungi.The soil bacteria community structure,which was dominated by Acidobacteria,Proteobacteria,and Actinobacteria,changed to be dominated by Proteobacteria and Chloroflexi.As well,soil fungal community changed from domination by Helotiales,Eurotiales and Russulales to domination by Archaeorhizomycetales and Helotiales.Over time,soil bacterial community was gradually restored to prefire levels 30 years after the fire.Soil fungal community changed and failed to restore to pre-fire levels after 30 years.After low/intermediate severity fires,environmental factors were relatively unchanged so that soil bacteria diversity and abundance increased,optimizing community composition.The diversity and abundance of soil fungi decreased and the community structure changed slightly.Over time,both bacterial and fungal communities were gradually restored to pre-fire levels 30 years after the fire.After fire disturbance,with increasing severity,soil carbon fixation,lignin degradation,mineralization of organic nitrogen and hydrolysis of organic phosphorus are enhanced.Denitrification is weakened.Therefore,forest fires have certain positive effects on carbon,nitrogen and phosphorus cycles where soil bacteria and fungi are involved.

Seasonal variations in temperature sensitivity of soil respiration in a larch forest in the Northern Daxing’an Mountains in Northeast China

Temperature sensitivity of respiration of forest soils is important for its responses to climate warming and for the accurate assessment of soil carbon budget. The sensitivity of temperature (T_(i)) to soil respiration rate (R_(s)), and Q_(10) defined by e^(10(lnRs−lna)/Ti) has been used extensively for indicating the sensitivity of soil respiration. The soil respiration under a larch (Larix gmelinii) forest in the northern Daxing’an Mountains, Northeast China was observed in situ from April to September, 2019 using the dynamic chamber method. Air temperatures (T_(air)), soil surface temperatures (T_(0cm)), soil temperatures at depths of 5 and 10 cm (T_(5cm) and T_(10cm), respectively), and soil-surface water vapor concentrations were monitored at the same time. The results show a significant monthly variability in soil respiration rate in the growing season (April–September). The Q_(10) at the surface and at depths of 5 and 10 cm was estimated at 5.6, 6.3, and 7.2, respectively. The Q_(10@10 cm) over the period of surface soil thawing (Q_(10@10 cm, thaw) = 36.89) were significantly higher than that of the growing season (Q_(10@10 cm, growth )= 3.82). Furthermore, the Rs in the early stage of near-surface soil thawing and in the middle of the growing season is more sensitive to changes in soil temperatures. Soil temperature is thus the dominant factor for season variations in soil respiration, but rainfall is the main controller for short-term fluctuations in respiration. Thus, the higher sensitivity of soil respiration to temperature (Q_(10)) is found in the middle part of the growing season. The monthly and seasonal Q_(10) values better reflect the responsiveness of soil respiration to changes in hydrometeorology and ground freeze-thaw processes. This study may help assess the stability of the soil carbon pool and strength of carbon fluxes in the larch forested permafrost regions in the northern Daxing’an Mountains.

The influence of soil compaction in explaining spatial heterogeneity of different larch forest types: a preliminary study

Compacted soil has an adverse effect on plant roots and affects water and nutrient availability.However,different degrees of soil compaction may be suitable for growth and development of different understory species.This study determined whether soil compaction could explain characteristics of 10 different Dahurian larch(Larix gmelinii Rupr.)forest types in the Daxing’anling area.The relationship of soil compaction to soil depth was also studied.Forty-five tests were conducted on soil compaction of the 10 forest types with multiple comparisons,of which five showed no significant differences.At different soil depths,there were significant differences in soil compaction among forest types.The correlation between the degree of soil compaction and depth was positive and significant.The Larix gmelinii—shrub forest type,L.gmelinii—herb forest type,and L.gmelinii—swamp forest type were significantly different in soil compaction according to soil depth.This research indicates that,as a physical property,soil compaction may.

Spatial heterogeneity of dead fuel moisture content in a Larix gmelinii forest in Inner Mongolia using geostatistics

Spatial heterogeneity of fuel moisture content determines the spread rate and direction of a forest fire.Research on the spatial heterogeneity of the moisture content of dead fuel of Larix gmelinii Rupr.showed that:(1)fuel moisture content in litter layer<semi-humus layer<humus layer,and the coefficient of variation decreased with sampling depth;(2)the sill value of the semi-humus layer was highest,the humus layer moderate,the litter layer the smallest,overall,the spatial heterogeneity of the semi-humus layer was the highest.The humus layer in the slant direction and three layers in a vertical direction showed strong spatial correlation with the lowest nugget coefficient of 0.0968;(3)the fuel moisture content of the humus layer showed strong spatial anisotropy;and,(4)estimating the total moisture content of the sampling site by stimulated sampling reasonable control of the sampling interval,and increasing the sampling intensity can reduce the error.When the sampling intensity is increased to more than 16 and the sampling interval 3 m,the standard error is<15%.The spatial heterogeneity of fuel moisture content is best revealed by increasing sampling density,sampling in different fire seasons,and in different slope directions and positions.The results can provide a scientific basis for forest fire prediction and prevention.

Diversity and Biomass of Understory Plants in Larix gmelinii Forest under Different Reconstruction Methods

The effects of different management measures on the undergrowth diversity of Larix gmelinii forests were determined.The undergrowth vegetation of Xing'an Larch forest under seven different transformation methods was investigated in the Chaocha Forest Farm of the Genhe Forestry Bureau in the northern Daxinganling Mountains.Community composition,structural characteristics,species diversity and biomass of seven different retrofitting methods and one control plot.The results showed that the species composition of Larix gmeliniii under 7 different transformation methods included 34 species of 30 genera and 21 families of shrubs,including 7 species,7 genera and 7 species of shrub layer,and 20 species,24 genera and 24 species of common species in the herb layer.The species with the largest proportion in the layer is bilberry,followed by Xing'an rhododendron,and the dominant species of herbaceous layer is quite different.In terms of diversity index,the diversity index of Xing'an larch forest under local tending artificial promotion natural regeneration and transformation measures was low(P<0.05);the study showed that the best tending thinning intensity was between 30%and 40%,different.The impact of the transformation method on the structure and diversity of understory vegetation in Larix gmelinii forest is not only related to the transformation,but also depends on the transformation measures taken.

Long-term mercury variations in tree rings of the permafrost forest,northeastern China

Permafrost is a potential mercury(Hg)pool released by thawing,which can raise the risk of Hg pollution under global warming.Tree rings are useful archives of environment-specific Hg exposure over long periods.We determined Hg concentrations in tree rings of two dominant tree species(Larix gmelinii Rupr.and Pinus sylvestris var.mongolica)at permafrost sites in northeastern China.The biweighted mean Hg concentrations ranged from 0.36 to 3.96 ng g^(-1) from 1840 to 2014.The tree-ring width had no significant influence on the Hg concentration.Larch Hg increased slightly before the 1970 s and peaked in the 1990 s.However,the pine Hg concentration increased continuously until the 1930 s,decreased rapidly until the 1970 s,then rose to a peak in the late 1980 s.The change of Hg concentrations in larch and pine revealed a time offset of 4 to 5 years,which implied possibly high mobility of Hg in pine tree rings.Higher Hg concentrations from 1920 to 1960 and subsequent decreases in isolated permafrost forests revealed the local geographical Hg cycling history.Lower Hg concentrations and faster increases in larch suggest the role of additional winter Hg loading for the evergreen pine and species-specific differences in root absorption in response to melting permafrost.Our results highlight possible geographical impacts on tree-ring Hg records,improve understanding of Hg cycles in permafrost forest,and suggest a need to sample additional species in a range of permafrost environments.