Long-term thinning decreases the contribution of heterotrophic respiration to soil respiration in subalpine plantations

Interest in the dynamics of soil respiration(R_(S))in subalpine forest ecosystems is increasing due to their high soil carbon density and potential sensitivity to environmental changes.However,as a principal silvicultural practice,the long-term impacts of thinning on R_(S) and its heterotrophic and autotrophic respiration components(R_(h) and Ra,respectively)in subalpine plantations are poorly understood,espe-cially in winter.A 3-year field observation was carried out with consideration of winter CO_(2) efflux in middle-aged sub-alpine spruce plantations in northwestern China.A trench-ing method was used to explore the long-term impacts of thinning on R,Rn and Ra.Seventeen years after thinning,mean annual Rs,Rn and R_(a) increased,while the contribu-tion of R_(h) to R_(s) decreased with thinning intensity.Thinning significantly decreased winter R,because of the reduction in Rn but had no significant effect on Ra.The temperature sensitivity(Q_(10))of R_(h) and R_(a) also increased with thinning intensity,with lower Q_(10) values for R_(h)(2.1-2.6)than for Ra(2.4-2.8).The results revealed the explanatory variables and pathways related to Rn and R_(a) dynamics.Thinning increased soil moisture and nitrate nitrogen(NO_(3)^(-)-N),and the enhanced nitrogen and water availability promoted R_(h) and R_(a) by improving fine root biomass and microbial activity.Our results highlight the positive roles of NO_(3)^(-)-N in stimulating R_(s) components following long-term thinning.Therefore,applications of nitrogen fertilizer are not recommended while thinning subalpine spruce plantations from the perspective of reducing soil CO_(2) emissions.The increased Q_(10) values of R_(s) components indicate that a large increase in soil CO_(2) emissions would be expected following thinning because of more pronounced climate warming in alpineregions.

Unveiling evapotranspiration patterns and energy balance in a subalpine forest of the Qinghai-Tibet Plateau:observations and analysis from an eddy covariance system

Evapotranspiration is an important parameter used to characterize the water cycle of ecosystems.To under-stand the properties of the evapotranspiration and energy balance of a subalpine forest in the southeastern Qinghai-Tibet Plateau,an open-path eddy covariance system was set up to monitor the forest from November 2020 to October 2021 in a core area of the Three Parallel Rivers in the Qing-hai-Tibet Plateau.The results show that the evapotranspira-tion peaked daily,the maximum occurring between 11:00 and 15:00.Environmental factors had significant effects on evapotranspiration,among them,net radiation the greatest(R^(2)=0.487),and relative humidity the least(R^(2)=0.001).The energy flux varied considerably in different seasons and sensible heat flux accounted for the main part of turbulent energy.The energy balance ratio in the dormant season was less than that in the growing season,and there is an energy imbalance at the site on an annual time scale.

An Assessment of Storage Terms in the Surface Energy Balance of a Subalpine Meadow in Northwest China

The heat storage terms in the soil-vegetation-atmosphere system may play an important role in the surface energy budget.In this paper,we evaluate the heat storage terms of a subalpine meadow based on a ficld experiment conducted in the complex terrain of the eastern Qilian Mountains of Northwest China and their impact on the closure of the surface energy balance under such non-ideal conditions.During the night, the average sum of the storage terms was -5.5 W m,which corresponded to 10.4%of net radiation.The sum of the terms became positive at 0730 LST and negative again at about 1500 LST,with a maximum value of 19 W mobserved at approximately 0830 LST.During the day,the average of the sum of the storage terms was 6.5 W m,which corresponded to 4.0%of net radiation.According to the slopes obtained when linear regression of the net radiation and partitioned fluxes was forced through the origin,there is an imbalance of 14.0%in the subalpine meadow when the storage terms are not considered in the surface energy balance.This imbalance was improved by 3.4%by calculating the sum of the storage terms.The soil heat storage flux gave the highest contribution(1.59%),while the vegetation enthalpy change and the rest of the storage terms were responsible for improvements of 1.04%and 0.77%,respectively.

Dynamics of Betula ermanni population in subalpine vegetation in Changbai Mountain, Northeast China

Betula ermanni population was divided into three groups: the upper population (2 000–2 200 m), the middle population (1 700–2 000 m), and the down population (1 400–1 700 m) in Changbai Mountain. The dynamics ofBetula ermanni populations in subalpine vegetation are studied and the population life table, fecundity schedule, survival curves, age structure, and fecundity curves were established. The results showed that the, middle population is obviously, the transition from the upper population to the down population.

Soil seed banks along elevational gradients in tropical, subtropical and subalpine forests in Yunnan Province, southwest China

Soil seed banks are a vital part of ecosystems and influence community dynamics and regeneration.Although soil seed banks in different habitats have been reported, how soil seed banks vary with elevational gradients in different climatic zones is still unknown. This paper investigates seed density,species composition and nonconstituent species of forest soil seed banks in Yunnan Province, southwest China. Similarity between the soil seed bank and standing vegetation was also examined. We collected soil samples from sites spanning 12 elevations in tropical rain forests, subtropical evergreen broadleaved forests and subalpine coniferous forests, and transported them to a glasshouse for germination trials for species identification. The soil seed banks of tropical and subtropical forests had much higher seed densities and species richness than those of subalpine forests. Seeds of woody species dominated the soil seed banks of tropical and subtropical forests, while herbs dominated those of subalpine forests.The nonconstituent species in the soil seed banks were all herbs and were most abundant in tropical forests, followed by subtropical forests but were completely absent from subalpine forests.

Population structure and regeneration patterns of tree species in climate-sensitive subalpine forests of Indian western Himalaya

The population structure of tree species has been explored in order to elucidate regeneration potential of the subalpine forests of Indian western Himalaya. For this study, the subalpine forest area was divided into three strata, i.e., lower altitude （〈3000 m）; mid-altitude （3000-3200 m）; and high altitude （〉3200m）. Considering the major compositional attributes, an increase in altitude came with a significant decline in tree density and the total basal area for all the sites. However, no such clear trends were observed for recruits （i.e., seedlings and saplings）. Seedling density did not exhibit uniform patterns for sites and altitude strata. In general, overall seedling density was greater at the Pindari site compared to the Lata and Tungnath sites. By comparison, significant variation in seedling density along the altitude strata was recorded for the Tungnath and Pindari sites only. Likewise, sapling density patterns varied across the sites and altitude strata, and significant variation in sapling density along the altitude strata was recorded only for the Lata site. At the Pin- daft site, the continuous increase in sapling density along with increasing altitude was revealing. The Pindari forests of exhibited expanding population structure. In contrast, greater accumulation of individuals in the sapling class and sharp decline toward both higher tree classes and lower seedling classes was generally apparent for the Lata and Tungnath sites. This indicates that the replacement in tree size classes from sapling stage is not proportional and the population may decline in the long-term. Considerable variation in patterns of forest and dominant species popula- tion structure were evident across altitude strata. But in all cases irrespective of sites, we found growth at the high-altitude stratum, in the form of entire forests or dominant species. This trend deserves further investigation to explore its relevance under changing climate scenarios.

Streamwater chemistry and flow dynamics along vegetation-soil gradient in a subalpine Abies fabri forest watershed, China

Streamwater chemistry and spatial flow dynamics from a subalpine Abies fabri forest in an experimental watershed located in the east slope of Gongga Mountain were analyzed to gain insights into the gradient effect of primary community succession on the stream biogeochemical process. Results showed that high sand content(exceeding 80%) and porosity in the soil(exceeding 20% in A horizon and 35% in B horizon), as well as a thick humus layer on the soil surface, made the water exchange quickly in the Huangbengliu(HBL) watershed. Consequently, no surface runoff was observed, and the stream discharge changed rapidly with the daily precipitation. The flow trends of base ions in the stream water were influenced by the Abies fabri succession gradient. Ca 2+ , HCO - 3 and SO 2- 4 were the dominant anions in the streamwater in this region. A significant difference of Ca 2+ , HCO - 3 and SO 2- 4 concentration exported between the succession stages in the watershed can be found. But they had the similar temporal change in the stream flow. Ca 2+ , HCO - 3 and SO 2- 4 showed significantly negative correlations with the daily precipitation and the stream discharge. \;Concentrations of Cl -, Na +, K +, and Mg 2+ were low in all streamwaters monitored and we observed no differences along the Abies fabri succession gradient. Low ratios of Na:(Na+Ca) (range from 0.1 to 0.2) implied cations were from bedrock weathering(internal source process in the soil system) in this region. But, a variance analysis showed there were almost no differences between rainwater and streamwaters for Mg 2+ , Na +, K +, and Cl - concentrations. This indicated that they might be come from rainfall inputs(external source). The highly mobile capacity, rapid water exchange between precipitation and discharge, and long-term export lead to this observed pattern were suggested.

Geoecological analysis of the Korea alpine and subalpine plants and landscapes

Present work aims to designate the alpine and subalpine plants and landscapes, and also to analyse the species composition, physiognomy, attitudinal ranges as well as formation processes of Korean alpine and subalpine belts and their geoecology. The alpine and subalpine floras of Korean mountains are evidently descended from immigrants from NE Asia during the epochs of the Ice Age. These plants, which are very intolerant of competition in warm and mild climates, have been able to persist in alpine and subalpine belts thanks to their harsh climatic conditions, sterile soil, rugged topography and cryoturbation. Continuing works on the palaeoenvironment and thermal amplitude of alpine and subalpine elements on Korea high mountains may be enabled to understand better on the geoecology and natural history of the Korean Peninsula, as well as the structures, functions, mechanism and dynamics of alpine and subalpine plants and landscapes.

Once upon a time biomass burning in the western Alps: Nesting effects of climate and local drivers on long-term subalpine fires

Background:The present article questions the relative importance of local-and large-scale processes on the long-term dynamics of fire in the subalpine belt in the western Alps.The study is based on soil charcoal dating and identification,several study sites in contrasting environmental conditions,and sampling of soil charcoal along the elevation gradient of each site.Based on local differences in biomass combustion,we hypothesize that local-scale or landscape-scale processes have driven the fire history,while combustion homogeneity supports the hypothesis of the importance of large-scale or macro-ecological processes,especially climate.Results:Biomass burning during the Holocene resulted from the nesting effects of climate,land use,and altitude,but was little influenced by slope exposure(north versus south),soil(dryness,pH,depth),and vegetation.The mid-Holocene(6500–2700 cal BP)was an important period for climate-driven biomass burning in the subalpine ecosystems of the western Alps,while fires over the last 2500 years appear much more episodic,prompting us to speculate that human activity has played a vital role in their occurrence.Conclusion:Our working hypothesis that the strength of local drivers should offset the effects of regional climate is not validated.The homogeneity of the fire regime between sites thus underscores that climate was the main driver during the Holocene of the western Alps.Long-term subalpine fires are controlled by climate at the millennial scale.Local conditions matter for little in determining variability at the century scale.The mid-Holocene was a chief period for climatic biomass burning in the subalpine zone,while fires during the late Holocene appear much more episodic,suggesting that social drivers has exercised key function on their control.

Susceptible conditions for debarking by deer in subalpine coniferous forests in central Japan

Background： Recently, deer have expanded their distribution to higher altitude ranges including subalpine forests However, culling deer and construction of deer fence in subalpine forests are difficult because of steep slopes and complex topography. Thus it is necessary to clarify the factors which are associated with debarking by deer for the effective protection of subalpine forests. In this study, we examined which factors are associated with debarking b： sika deer （Cervus nippon） in subalpine coniferous forests. Methods： We conducted our survey in Minami-Alps National Park, central Japan. We established 24 10 m × 40 m plots and surveyed the occurrence of debarking on saplings 〉30 cm in height and 〈3 cm in diameter at breast heigh （DBH） and on trees 〉3 cm in DBH, as well as sapling density within each plot. Minimum distances to nearest grasslan（ of plots were calculated （tentatively assuming grassland would attract deer and would cause high debarking pressure in the surrounding subaipine forests）. Results： The mean percentage of debarked live saplings was higher than that of live trees. The mean percentage of debarked saplings which had already died was 81.6 %. Debarking of saplings increased with lower elevation taller sapling size, and marginally increased near grassland. Sapling density was lower in plots with low basa area of conspecific trees near grassland and differed among species. Sapling density marginally decreased with decreasing elevation and increasing stand tree density. Debarking of trees was positively related to small DBH and Io~ elevation, and marginally increased near grassland and differed among species. Conclusions： Our results suggest that tall saplings in subalpine forests of low elevation or near subalpine grassland were susceptible to debarking by deer and monitoring of these areas may permit the early detection of the impacts of deer in subalpine coniferous forests.

Gap edge canopy buffering of throughfall deposition in a subalpine natural forest

Base cation loads are rarely considered in forest gap edge canopies,but they can play critical roles in capturing or buffering atmospheric deposition in forests with frequent gap disturbances,such as subalpine forests.We selected an expanded gap edge canopy and a closed canopy in a subalpine natural forest on the eastern Tibetan Plateau.The throughfall deposition and canopy exchange processes of common base cations(K^(+),Ca^(2+),Na^(+),and Mg^(2+))were continuously studied over two years.The results showed that the enrichment ratio and fluxes had lower levels of base cations in the gap-edge canopy than in the closed canopy,which indicated that base cations were concentrated more in the closed canopy than in the gap-edge canopy.Although Ca^(2+)in the gap-edge canopy showed a higher net throughfall flux,the annual net throughfall fluxes of K^(+),Na^(+) and Mg^(2+) within the gap-edge canopy were 1.83,6.75 and 2.95 times lower than those in the closed canopy,respectively.Moreover,dry deposition fluxes of base cations significantly decreased in the gap edge canopy compared to those in the closed canopy,and the decreasing tendency was more significant during the snowy season than during the rainy season.Overall,these results suggest that the amount of base cations in subalpine natural forest ecosystems may be overestimated when the throughfall deposition of ions in gap edge canopies is ignored.

Host-environment mismatches associated with subalpine fir decline in Colorado

Subalpine fir decline （SFD） has killed more trees in Colorado＇s high elevation forests than any other insect or disease problem. The widespread nature of this disorder suggests that the cause involves climatic factors. We examined the influence of varying combinations of average annual temperature and precipitation on the incidence and distribution of SFD. Climatic transition matrices generated in this study indicate that most healthy trees are found in climatic zones with moderate to low temperatures and high precipitation; whereas, SFD occurs mostly in zones of moderate temperatures and moderate precipitation. The contrasting distributions define an environmental mismatch. Forests matched with favorable climatic conditions thrive; those that are mismatched can become vulnerable to decline disease.

CO2Emissions from Soils in Subalpine Dark Coniferous Forest Region of Gongga Mountain

A field experiment was carried out to examine the soil respiration rate in Abies fabri forests in Gongga Mountain National Nature Reserve using LI-6400-09 portable soil respiration chamber.The results showed that the soil respiration rate and soil temperature of mature and middle-aged A.fabri forests were different in each month.The soil CO2 emission rates of the two stands had obvious seasonal variation characteristics,which were arranged: summer > autumn > spring > winter;the monthly average soil CO2 emission rate of the mature aged forest ranged from 0.82 to 5.88 μmol/(s·m^2),with the coefficient of seasonal variation of 50.6%;and the average monthly soil respiration rate of middle-aged forest was in the range of 0.52-3.52 μmol/(s·m^2),with the coefficient of seasonal variation of 48.5%.The seasonal variation of soil CO2 emission rate was positively correlated with the 5 cm soil temperature.And the Q10 values of the soil CO2 emission rates in the mature and middle-aged A.fabri forests were 3.2 and 2.6,respectively,and the sensitivity index of CO2 emission to temperature in the mature A.fabri forest was higher than that in the middle-aged forest.

Warming Stimulated Soil Respiration in a Subalpine Meadow in North China

In order to explore the response of soil respiration in grassland to global warming,we carried out a warming experiment with open top chambers(OTCs)in the subalpine meadow,Mount Wutai in north China.Our results showed in the subalpine meadow across 2500-2700 m above the sea level(ASL),with OTCs,soil respiration increased by 2.00μmol·m^(-2)·s^(-1)as soil temperature increased by 1.25℃on average.Warming decreased soil moisture over the experiment periods except in October 2019 when snow melted in OTCs.Warming effect on soil respiration peaked at 178.31%in October 2019.In control and warming treatment,based on exponential regression equations,soil temperature alone accounted for 85.3%and 61.2%of soil respiration variation,respectively.In control treatment soil moisture alone explained 23.2%of soil respiration variation based on the power regression equation while in warming treatment they were not significantly correlated with each other.The response of soil respiration to warming relied on altitudes as well as the time of the year,but was not inhibited by soil moisture,labile carbon pool,and available nitrogen.We concluded soil temperature was the main factor influencing soil respiration,and global warming would stimulate soil respiration in the subalpine meadows of Mount Wutai in the future.Our analysis provided new data on characteristics and mechanisms of the response of soil respiration to warming,and helped to further understand the relationship between carbon cycle and climate change.

Vegetation types and climate conditions reflected by the modern phytolith assemblages in the subalpine Dalaoling Forest Reserve, central China

This research describes modern phytolith records and distributions from subalpine surface soils in the Dalaoling Forest Reserve, and reveals its implications for local climate conditions with respect to the altitude gradient. Well-preserved phytolith morpho-types, assem- blages, and climatic indices were used to study the relationship between local vegetation and climate condi- tions. The phytolith classification system is mainly based on the characteristics of detailed morpho-types described for anatomical terms, which are divided into seven groups： long cells, short cells, bulliform cells, hair cells, pterido- phyte type, broad-leaved type, and gymnosperm type. Phytoliths originating from the Poaceae are composed of Pooideae （rondel and trapeziform）, Panicoideae （bilobate, cross, and polylobate）, Chloridoideae （short/square sad- dle）, and Bambusoideae （oblong concave saddle）. Based on the altitudinal distribution of the phytolith assemblages and the indices of aridity （Iph）, climate （Ic）, and tree cover density （D/P）, five phytolith assemblage zones have revealed the five types of climatic conditions ranging from 1,169 m to 2,005 m in turn： warm-wet, warm-xeric to warm-mesic, warm- xeric to cool-mesic, cool-xeric, and cool-mesic to cool-xeric. The Bambusoideae, Panicoideae, and Chloridoideae are the dominant vegetation at the lower-middle of the mountains, while Pooideae is mainly distributed in the higher mountains. The close relationship between phytolith assembleages and changes of altitude gradient suggest that vegetation distribution patterns and plant ecology in the Dalaoling mountains are controlled by temperature and humidity conditions. Our results highlight the importance ofphytolith records as reliable ecoclimatic indicators for vegetation ecology in subtropical regions.

Stem CO_(2) efflux of Abies fabri in subalpine forests in the Gongga Mountains,Eastern Tibetan Plateau

Aims Despite the importance of stem cO_(2)efflux(Es)in ecosystem carbon cycling and energy balance,little is known about temporal variation in the temperature coefficient(Q10)and sapwood nitrogen concen-trations([N])and their intrinsic links with Es.The objectives of this study were:(i)to examine the response of Es to temperature in a subalpine region and(ii)to explore the influence of stem diameter and[N]on Es.Also,we will test the hypothesis that(i)Es in trees has thermal acclimation and(ii)Es will be well correlated with diameter at breast height(DBH)and[N].Methods Here,a horizontally oriented soil chamber technique was applied to measure Es of Abies fabri in two subalpine forest stands in Southwestern china from May to December 2014.We also exam-ined the variability in Es,Q10 and[N]in trees and monitored the relationship between temperature,[N],DBH and Es.Important Findings During the measurement period,Es showed an apparent seasonal trend,following the change in air temperature,increasing from May and peaking in July,then continuously decreasing until December.The mean Es for the growing and dormant seasons were 1.45 and 0.25μmol·m^(−2)·s^(−1),respectively,and Es in the mature forest was sig-nificantly higher than in the immature forest.The area-based Es was positively correlated with DBH and sapwood width(SW),while volume-based Es showed negative relationship with DBH and SW.Across the five diameter classes,69.8-89.0%of the variation in Es could be explained by air temperature.The temperature sensitiv-ity(Q10)of Es ranged from 2.98 to 5.61 during the measurement period,with a higher Q10 appearing in the growing season than in the dormant season.There was a significant linear relationship(P<0.01)between[N]and Es(expressed based on two different units).Additionally,exponential models of Es against[N]and air temperature were applied to estimate Es.

Shrub interactions drive vegetation succession of subalpine grasslands under two climatic conditions

Aims The abandonment of agronomic practices in subalpine systems has led to shrub encroachment,which has transformed grasslands into woodlands.The competitive and facilitative interactions among incoming shrub species might influence vegetation succession and might be affected by climate change.This study aimed to identify the nature of shrub species interactions between an early colonizer and a secondary succession shrub in the successional encroach-ment process and whether it differs between two contrasting cli-matic conditions.Methods The interactions between the two main encroaching shrub spe-cies in the Central Pyrenees(Spain),Buxus sempervirens and Echinospartum horridum,were studied at the current upper limit of the altitudinal range of B.sempervirens,where it coexists with E.horridum(high site),and in a milder location at lower eleva-tion(low site).in the studied areas,E.horridum is the first shrub species that encroaches upon the abandoned grasslands and B.sempervirens enters the system after E.horridum has become established.A neighbor-removal experiment was used to assess the bidirectional interactions between both species,and whether those interactions differed among the life stages of B.sempervirens(seed-lings,juveniles and adults),at the two study sites.Survival,annual crown growth and developmental instability(error in development caused by stress)were the performance indices used to quantify plant responses.Differences in air temperatures and soil nutrient amelioration were evaluated as possible mechanisms of facilitation of E.horridum on B.sempervirens.Important Findings E.horridum enhanced the survival of B.sempervirens seedlings under its crown,whereas,B.sempervirens adults outcompeted E.horridum.Therefore,the invasion of the grasslands by E.horridum facilitated the settlement and expansion of B.sempervirens,pro-moting vegetation succession at the Pyrenees.in addition,climatic differences associated with elevation affected shrub interactions.Under low temperatures at the upper limit of B.sempervirens alti-tudinal range,the presence of E.horridum enhanced the growth of B.sempervirens juveniles.At low elevation,under a milder climate,B.sempervirens exerted a high degree of competition toward E.hor-ridum.An increase in temperatures associated with climate change would benefit B.sempervirens juveniles growth which might affect the successional process because it would increase their competi-tive ability when B.sempervirens juveniles become adults.

Response of clonal plasticity of Fargesia nitida to different canopy conditions of subalpine coniferous forest

The aim of this study is to explore the effects of canopy conditions on clump and culm numbers,and the morphological plasticity and biomass distribution patterns of the dwarf bamboo species Fargesia nitida.Specifically,we investigated the effects of canopy conditions on the growth and morphological characteristics of F.nitida,and the adaptive responses of F.nitida to different canopy conditions and its ecological senses.The results indicate that forest canopy had a significant effect on the genet density and culm number per clump,while it did not affect the ramet density.Clumps tended to be few and large in gaps and forest edge plots,and small under forest understory plots.The ramets showed an even distribution under the closed canopy,and cluster distribution under gaps and forest edge plots.The forest canopy had a significant effect on both the ramets’biomass and biomass allocation.Favourable light conditions promoted ramet growth and biomass accumulation.Greater amounts of biomass in gaps and forest edge plots were shown by the higher number of culms per clump and the diameter of these culms.Under closed canopy,the bamboos increased their branching angle,leaf biomass allocation,specific leaf area and leaf area ratio to exploit more favourable light conditions in these locations.The spacer length,specific spacer length and spacer branching angles all showed significant differences between gaps and closed canopy conditions.The larger specific spacer length and spacer branching angle were beneficial for bamboo growth,scattering the ramets and exploiting more favourable light conditions.In summary,this study shows that to varying degrees,F.nitida exhibits both a wide ecological amplitude and high degree of morphological plasticity in response to differing forest canopy conditions.Moreover,the changes in plasticity enable the plants to optimize their light usage efficiency to promote growth and increase access to resources available in heterogeneous light environments.

Effects of Seasonal Freeze-Thaw Cycles on Quantity of Soil Microbes in Subalpine Fir Forest

Fir(Abies faxoniana) distributes widely in the alpine and subalpine region of western Sichuan.To understand effects of freeze-thaw events on soil microbial community,microbial number was investigated monthly in a fir forest,employing the method of lab freeze/thaw cycles in combination with field soil sampling.Bacterial and actinomycete number in soil decreased and fungal count increased after a seasonal freeze-thaw season cycle.Bacterial and fungal counts increased with the decreased altitude,while actinomycete count decreased with the decreased altitude.Different microbes had various change patterns with altitude in humus layer(AL), illuvial layer(BL) and parent material layer(CL). Compared with the 3 582 m altitude,bacterial count in the AL and CL at the 3 298 m altitude increased 4.2%and 7.0%,respectively,but that in the BL decreased 0.6%.Meanwhile,bacterial count increased 11.5%,3.5%and 2.1%in the AL,BL and CL at the 3 023 m altitude in comparison with the 3 298 m altitude,respectively.Fungi count in the AL,BL and CL increased by 10.5%,10.3%and 16.4%at the 3 298 m altitude in comparison with 3 582 m altitude,respectively,while it increased by 2.4%,1.7%and 3.5%at the 3 023 m altitude in comparison with 3 298 m altitude,respectively. Actinomycete count in the AL at the 3 298 m altitude increased by 0.7%than that at the 3 582 m altitude, but decreased 5.9%and 13.9%in the BL and CL.In the AL and BL,it increased 5.2%and 5.2% respectively at the 3 023 m altitude than that at the 3 298 m altitude,while in the CL it decreased 12.4%.These results were in agreement with the simulation freeze/thaw cycle experiment in lab.The results also revealed that the seasonal freeze-thaw cycle increased the ratio of soil fungi to bacteria. These results demonstrated that different microbial groups responded differentially to the seasonal freeze-thaw cycle,which may be an important ecological mechanism for maintaining the seasonal frozen ecosystem.

Grazing impact on forage quality and macronutrient content of rangelands in Qilian Mountains, NW China

An important indicator of the rangeland health, associated with land degradation, is the ability of semi-natural rangelands to provide forage of sufficient quality for livestock production. In Qilian Mountains(Gansu Province, NW China) biomass production and forage quality are dependent on the seasonality of precipitation and temperature; most of the precipitation falls during summer season, when sheep, goats and yaks graze mountain rangelands. To sustain the rangelands and to improve the management strategies, the assessment of the forage quality should be implemented. The purpose of this research was to study the response of biomass, forage quality and macronutrient content different levels of grazing intensity in Qilian rangelands. We sampled aboveground biomass in the growing seasons in 2012 and 2013 within spring/autumn or summer grazing regimes in two altitudinal zones below and above 3000 m a.s.l.(montane-subalpine and subalpine-alpine respectively). In order to estimate forage quality, biomass was sampled in 1 m × 1 m plots, assigned to the center of 10 ×10 m sites, fromwhich we collected different indicator parameters of rangeland health. Mineral and fiber content of forage biomass was estimated under different levels of grazing intensity with regard to the growing period. It was found that an increase in grazing intensity led to a decrease in dry matter weight. No linearity was observed in the relationship between nutritive value and grazing intensity. The highest fiber content(59.20 %) was found in plots mostly disturbed by grazing. The highest protein(16.30 %) and the lowest fiber(51.30 %) contents were associated with slightly grazing intensity. Concentrations of the mineral elements, such as Zn, P, K and S varied significantly and showed maximum values under low grazing intensity.