Nitrogen addition promotes foliar litterfall and element return in a subtropical forest,southwestern China

Nitrogen deposition has a considerable impact on biogeochemical cycling in terrestrial ecosystems.However,how litter production and element return respond to N addition remains poorly understood in nitrogen-rich subtropical regions.In this study,a 4-year nitrogen addition experiment explored its eff ects on foliar litter production and carbon,nitrogen and phosphorus in a subtropical Michelia wilsonii forest.A clear seasonal pattern in foliar litterfall was observed,regardless of nitrogen treatments,with a peak in spring and a smaller one in autumn.Foliar litter increased with increasing nitrogen but did not aff ect litter carbon concentrations and often decreased nitrogen and phosphorous concentrations.The eff ect of nitrogen addition was dependent on time(month/year).Carbon,nitrogen and phosphorous return showed similar bimodal seasonal patterns.Nitrogen addition increased carbon and nitrogen return but did not aff ect phosphorous.Our results suggest that the addition of nitrogen stimulates carbon and nutrient return via litterfall.

Effects of litter quality and climate change along an elevational gradient on litter decomposition of subalpine forests, Eastern Tibetan Plateau, China

Temperature and freeze-thaw events are two key factors controlling litter decomposition in cold biomes.Predicted global warming and changes in freeze-thaw cycles therefore may directly or indirectly impact litter decomposition in those ecosystems. Here, we conducted a2-year-long litter decomposition experiment along an elevational gradient from 3000 to 3600 m to determine the potential effects of litter quality, climate warming and freeze-thaw on the mass losses of three litter types [dragon spruce（Picea asperata Mast.）, red birch（Betula albosinensis Burk.）, and minjiang fir（Abies faxoniana Rehd. et Wild）]. Marked differences in mass loss were observed among the litter types and sampling dates. Decay constant（k） values of red birch were significantly higher than those of the needle litters. However, mass losses between elevations did not differ significantly for any litter type.During the winter, lost mass contributed 18.3-28.8 % of the net loss rates of the first year. Statistical analysis showed that the relationships between mass loss and litter chemistry or their ratios varied with decomposition periods. Our results indicated that short-term field incubations could overestimate the k value of litter decomposition.Considerable mass was lost from subalpine forest litters during the wintertime. Potential future warming may not affect the litter decomposition in the subalpine forest ecosystems of eastern Tibetan Plateau.

Winter soil CO_2 efflux in two contrasting forest ecosystems on the eastern Tibetan Plateau, China

Significant CO2 fluxes from snow-covered soils occur in cold biomes. However, little is known about winter soil respiration on the eastern Tibetan Plateau of China. We therefore measured winter soil CO2 fluxes and estimated annual soil respiration in two contrasting coniferous forest ecosystems （a Picea asperata plantation and a natural forest）. Mean winter soil CO2 effluxes were 1.08 μmol m-2 s-1 in the plantation and 1.16 μmol m-2 s-1 in the natural forest. These values are higher than most reported winter soil CO2 efflux values for temperate or boreal forest ecosystems. Winter soil respiration rates were similar for our two forest ecosystems but mean soil CO2 efflux over the growing sea- son was higher in the natural forest than in the plantation. The estimated winter and annual soil effluxes for the natural forest were 176.3 and 1070.3 g m-2, respectively, based on the relationship between soil respiration and soil temperature, which were 17.2 and 9.7 % greater than their counterparts in the plantation. The contributions of winter soil respiration toannual soil efflux were 15.4 % tor the plantation and 16.5R for the natural forest and were statistically similar. Our results indicate that winter soil CO2 efflux from frozen soils in the alpine coniferous forest ecosystems of the eastern Tibetan Plateau was considerable and was an important component of annual soil respiration. Moreover, reforesta- tion （natural coniferous forests were deforested and refor- ested with P. asperata plantation） may reduce soil respiration by reducing soil carbon substrate availability and input.

Do root modules still exist after they die?

Background:The terminal branch orders of plant root systems are increasingly known as an ephemeral module.This concept is crucial to recognize belowground processes.However,it is unknown if root modules still exist after they die?Methods:The decomposition patterns of the first five root orders were observed for 3 years using a branch-order classification,a litter-bag method and sequential sampling in a common subalpine tree species(Picea asperata)of southwestern China.Results:Two root modules were observed during the 3-year incubation.Among the first five branch orders,the first three order roots exhibited temporal patterns of mass loss,nutrients and stoichiometry distinct from their woody mother roots throughout the experimental period.This study,for the first time,reported the decomposition pattern of each individual root order and found a similar decomposition dynamic among ephemeral root branches in a forest tree species.Conclusions:Results from this study suggest that root modules may also exist after death,while more data are needed for confirmation.The findings may further advance our understanding of architecture-associated functional heterogeneity in the fine-root system and also improve our ability to predict belowground processes.

Immediate and legacy effects of snow exclusion on soil fungal diversity and community composition

Background:Soil fungi play crucial roles in ecosystem functions.However,how snow cover change associated with winter warming affects soil fungal communities remains unclear in the Tibetan forest.Methods:We conducted a snow manipulation experiment to explore immediate and legacy effects of snow exclusion on soil fungal community diversity and composition in a spruce forest on the eastern Tibetan Plateau.Soil fungal communities were performed by the high throughput sequencing of gene-fragments.Results:Ascomycota and Basidiomycota were the two dominant fungal phyla and Archaeorhizomyces,Aspergillus and Amanita were the three most common genera across seasons and snow manipulations.Snow exclusion did not affect the diversity and structure of soil fungal community in both snow-covered and snow-free seasons.However,the relative abundance of some fungal communities was different among seasons.Soil fungal groups were correlated with environmental factors(i.e.,temperature and moisture)and soil biochemical variables(i.e.,ammonium and enzyme).Conclusions:These results suggest that the season-driven variations had stronger impacts on soil fungal community than short-term snow cover change.Such findings may have important implications for soil microbial processes in Tibetan forests experiencing significant decreases in snowfall.

Variations in root chemistry of three common forest species,southwestern China

Root chemistry varies with tree species and root diameter but little information is available about Tibetan forest species. The root chemistry of three root diameter classes (fine: 0–2 mm, medium: 2–5 mm, coarse: 5–10 mm) of three subalpine species (Abies faxoniana Rehd. and Wild, Picea asperata Mast., and Betula albosinensis Burkill) were investigated. Carbon concentrations, and carbon/nitrogen and carbon/phosphorus ratios increased but nitrogen, phosphorus and nitrogen/phosphorus ratios decreased with increasing root diameter. The roots of the conifers had higher carbon levels, and higher carbon/nitrogen and carbon/phosphorus ratios than birch roots. The opposite was found with nitrogen and phosphorus levels and nitrogen/phosphorus ratios. Lignin concentrations decreased but cellulose concentrations increased with greater root diameters. The results indicate that diameter-associated variations in root chemistry may regulate their contribution to detrital pools which has important implications for below-ground carbon and nutrient cycles in these subalpine forests.

双源CT双能量检查技术对痛风结晶的临床诊断价值分析

目的探究双源CT双能量检查技术对痛风结晶的临床诊断价值。方法选取2014年10月-2016年7月收治的34例痛风患者临床资料进行分析,将其分为研究组,另取同期30例非痛风患者设为对照组,两组均进行双源CT双能量检查,观察尿酸盐结晶检出情况以及发作期、缓解期结晶计数。结果研究组扫描发现33例尿酸盐结晶,检测敏感度达97.05%,对照组1例(3.33%)骨折检出尿酸盐结晶,差异比较具统计学上的意义(P<0.05);研究组发作期结晶计数为135处,高于缓解期128处,发作期3、4处例数高于缓解期,比较差异无统计学意义(P>0.05)。结论双源CT双能量检查技术能够清晰显示出尿酸盐结晶,检出敏感度高,且作为痛风结晶筛查手段操作简单,具临床推广和应用价值。

Soil fauna accelerated litter C and N release by improving litter quality across an elevational gradient

Background Soil fauna is an important driver of carbon(C)and nitrogen(N)release from decomposing litter in forest ecosystems.However,its role in C and N cycling concerning climate and litter traits remains less known.In a 4-year field experiment,we evaluated the effects of soil fauna on litter C and N release across an elevation gradient(453,945,3023,and 3582 m)and litter traits(coniferous vs.broadleaf)in southwestern China.Results Our results showed that N was retained by–0.4%to 31.5%,but C was immediately released during the early stage(156–516 days)of decomposition for most litter species.Soil fauna significantly increased the peak N content and N retention across litter species,but reduced the C/N ratio for certain species(i.e.,Juniperus saltuaria,Betula albosinensis,Quercus acutissima,and Pinus massoniana litter),leading to more C and N being released from decomposing litter across the elevation gradient.Contributions of soil fauna to C and N release were 3.87–9.90%and 1.10–8.71%,respectively,across litter species after 4 years of decomposition.Soil environment and initial litter quality factors caused by elevation directly affected litter C and N release.Changes in soil fauna resulting from elevation and fauna exclusion factors had a direct or indirect impact on C and N release during litter decomposition.Conclusions Our findings suggest that soil fauna promote C and N release from decomposing litter in different magnitudes,mainly controlled by environmental conditions(i.e.,temperature and moisture),litter quality(i.e.,lignin and cellulose content,and lignin/cellulose),and its diversity across the elevation gradient.

Soil C, N and P stocks and stoichiometry under different vegetation on the surface of the Leshan Giant Buddha

The accumulation of soil organic matter and nutrients is an important pathway in effectivelyunderstanding the mechanisms of plant settlement and rock weathering, while the characteristics ofsoil organic carbon (C), nitrogen (N) and phosphorus (P) under different vegetation remain unclear.In this study, the stocks and stoichiometry of soil organic C, N and P were determined in differentpositions and types of vegetation on the surface of the Leshan Giant Buddha. We found that the totalstocks of soil organic C, N and P were 1689.77, 134.6 and 29.48 kg, respectively, for the Buddha.The stocks of soil organic C, N and P under vascular plants were higher than those under othervegetation, with highest values observed under herb. Higher stocks per unit area (m2) of soil organicC, N and P were found on the left and right arms, shoulders, and two platforms. These results providea full primary picture in understanding soil organic C, N and P accumulation and distribution on thesurface of the Buddha, which could supply the fundamental data on weathering management of theBuddha and other similar open-air stone carvings.

Nitrogen addition mediates the response of foliar stoichiometry to phosphorus addition: a meta-analysis

Background:Changes in foliar nitrogen(N)and phosphorus(P)stoichiometry play important roles in predicting the efects of global change on ecosystem structure and function.However,there is substantial debate on the efects of P addition on foliar N and P stoichiometry,particularly under diferent levels of N addition.Thus,we conducted a global meta-analysis to investigate how N addition alters the efects of P addition on foliar N and P stoichiometry across different rates and durations of P addition and plant growth types based on more than 1150 observations.Results:We found that P addition without N addition increased foliar N concentrations,whereas P addition with N addition had no efect.The positive efects of P addition on foliar P concentrations were greater without N addition than with N addition.Additionally,the efects of P addition on foliar N,P and N:P ratios varied with the rate and duration of P addition.In particular,short-term or low-dose P addition with and without N addition increased foliar N concentration,and the positive efects of short-term or low-dose P addition on foliar P concentrations were greater without N addition than with N addition.The responses of foliar N and P stoichiometry of evergreen plants to P addition were greater without N addition than with N addition.Moreover,regardless of N addition,soil P availability was more efective than P resorption efciency in predicting the changes in foliar N and P stoichiometry in response to P addition.Conclusions:Our results highlight that increasing N deposition might alter the response of foliar N and P stoichiometry to P addition and demonstrate the important efect of the experimental environment on the results.These results advance our understanding of the response of plant nutrient use efciency to P addition with increasing N deposition.

Effects of snow absence on available N pools and enzyme activities within soil aggregates in a spruce forest on the eastern Tibetan Plateau

Winter climate change has great potential to affect the functioning of terrestrial ecosystems.In particular,increased soil frost associated with reduced insulating snow cover may impact the soil nitrogen(N)dynamics in cold ecosystems,but little is known about the variability of these effects among the soil aggregates.A snow manipulation experiment was conducted to investigate the effects of snow absence on N cycling within soil aggregates in a spruce forest on the eastern Tibetan Plateau of China.The extractable soil available N(ammonium and nitrate),net N mineralization rate,and N cycling-related enzyme activities(urease,nitrate reductase,and nitrite reductase)were measured in large macroaggregate(>2 mm),small macroaggregate(0.25–2 mm),and microaggregate(<0.25 mm)during the early thawing period in the years of 2016 and 2017.Snow absence increased soil N availabilities and nitrite reductase activity in microaggregate,but did not affect net N mineralization rate,urease or nitrate reductase activities in any of the aggregate fractions.Regardless of snow manipulations,both soil inorganic N and nitrate reductase were higher in small macroaggregate than in the other two fractions.The effect of aggregate size and sampling year was significant on soil mineral N,net N mineralization rate,and nitrite reductase activity.Our results indicated that snow cover change exerts the largest impact on soil N cycling within microaggregate,and its effect is dependent on winter conditions(e.g.,snow cover and temperature).Such findings have important implications for soil N cycling in snow-covered subalpine forests experiencing pronounced winter climate change.

Physiological and biomass partitioning shifts to water stress under distinct soil types in Populus deltoides saplings

Aims Although soil environments exist extensive heterogeneity for many plants with a wide range of distribution,researches about effects of soil conditions on plants’tolerance and adaptation are particularly inadequate.In our study,the aims are to reveal physiological strategies of Populus deltoides against drought stress under different soil conditions and to select the most suitable soil type for P.deltoides plantation.Methods Under controlled conditions,we used P.deltoides as a model species to detect differences in gas exchange rate,antioxidative capacity,nitrogen metabolism and biomass accumulation and partitioning in response to drought stress under three mineral soil types with distinct physicochemical characters,i.e.red soil(RS),yellow soil(YS)and yellow-brown soil(BS).Important Findings Exposure to 25%of field water holding capacity in soil for 3 months had significantly decreased biomass of all organs,photosynthetic rate,enzyme activities related to N assimilation,but increased H2O2,malondialdehyde and content of both NO3−and NH4+,when P.deltoides was planted in both RS and YS.In contrast,under BS,there are slightly negative effects exerted by water deficit on total biomass,gas exchange rate,activities of enzymes related to nitrogen metabolism and membrane damage caused by reactive oxygen species,which can be associated with a consistent increase in superoxide dismutase,peroxidase and catalase,and a higher ratio of root mass to shoot mass.It is concluded that,such higher capacity in tolerance and adaptation against drought stress under BS relative to both RS and YS could be accounted for more sufficient nutrient provision in soil parental materials and better soil aeration conditions which play a vital role in plant acclimation to water shortage.Our study also revealed that,distribution areas of BS might be preferable for cultivation of P.deltoides,when compared with those of RS and YS.