Carbon storage in evergreen broad-leaf forests in mid-subtropical region of China at four succession stages

To better understand the effect of forest succession on carbon sequestration, we investigated carbon stock and allocation of evergreen broadleaf forest, a major zonal forest in subtropical China.We sought to quantify the carbon sequestration potential.We sampled four forest types,shrub(SR), pine(Pinus massoniana) forest(PF), pine and broadleaf mixed forest(MF) and evergreen broadleaf forest(BF).A regression equation was constructed using tree height and diameter at breast height(DBH) and elements of total tree biomass.The equation was subsequently utilized to estimate tree carbon storage.The carbon storage of understory, litter, and soil was also estimated.Carbon storage in biomass increased significantly from the early succession stage SR(6.21 t ha-1) to the late stage BF(134.87 t ha-1).The biomass carbon stock of forest layers generally increased with succession except for the understory.The soil organic carbon storage for the total profile increased with forest succession, from 51.16 to 90.49 t ha-1, but the contribution of SOC to the carbon stock of the forest ecosystem declined from 89.18% to 40.15%.The carbon stock at ecosystem scale increased significantly with succession from SR(57.37 t ha-1), to PF(154.20 t ha-1), to MF(170.96 t ha-1)and to BF(225.36 t ha-1), with carbon stock of BF3.93 times that of SR.The forests in our study have great potential for increasing carbon sequestration, and large areas of secondary or degraded evergreen broadleaf forests in the subtropical zone of China could be a great carbon sink in future.

Microbial biomass in subtropical forest soils： effect of conversion of natural secondary broad-leaved forest to Cunninghamia lanceolata plantation

到 Cunninghamialanceolata 种植园的自然第二等的阔叶的森林的变换是在副热带的中国的一个普通管理惯例。在这研究，我们比较了土壤物理化学的性质，在一天赋的微生物引起的生物资源第二等的 broad-leavedforest 和二 C。在土壤上估计森林变换的效果的 lanceolata 种植园地点在林地生态学的 Huitong 试验性的车站的微生物引起的生物资源，中国科学院。器官的碳，总氮， NH_4^+-N 和微生物引起的生物资源碳和氮多是的土壤的集中在 C 下面降低。lanceolata 种植园作为与自然离开 secondarybroad 的森林相比。在 C 的第一和第二旋转玷污微生物引起的生物资源 C。lanceolataplantations 仅仅是 53% ，那中的 46% 个分别地在自然第二等的阔叶的森林，和微生物引起的生物资源 N 里是 97% 和 79% 。到器官的 Cwas 也在种植园地点降低的土壤的微生物引起的生物资源 C 的贡献。然而，到总氮和 NH_4^+-N 的微生物引起的 N 的贡献在 C 是更大的。lanceolata 种植园地点。因此，到 C 的自然第二等的阔叶的森林的变换。lanceolata 种植园并且 C 的连续的种。lanceolataled 到在土壤的衰落微生物引起的生物资源和在副热带的中国的森林土的降级。

Soil microbial activity and nutrients of evergreen broad-leaf forests in mid-subtropical region of China

To better understand the effects of forest succession on soil microbial activity, a comparison of soil microbial properties and nutrients was conducted between three forest types representing a natural forest succession chronosequence. The study compared a pine(Pinus massoniana) forest(P_F), a pine and broadleaf mixed forest(M_F) and an evergreen broadleaf forest(B_F), in the Yingzuijie Biosphere Reserve, Hunan Province, China.Results showed that soil nutrients in the M_Fand BFplots were higher than in the P_Fplots. The range in microbial biomass carbon followed a similar pattern with B_Fhaving the greatest values, 522–1022 mg kg^-1, followed by M_F368–569 mg kg^-1, and finally, P_F193–449 mg kg^-1. Soil nutrients were more strongly correlated with microbial biomass carbon than basal respiration or metabolic quotient. Overall, forest succession in the study site improved soil microbial properties and soil fertility, which in turn can increase primary productivity and carbon sequestration.

Composition and mineralization of soil organic carbon pools in four single-tree species forest soils

Forest soil carbon(C) is an important component of the global C cycle. However, the mechanism by which tree species influence soil organic C(SOC) pool composition and mineralization is poorly understood. To understand the effect of tree species on soil C cycling, we assessed total, labile, and recalcitrant SOC pools, SOC chemical composition by ^(13) C nuclear magnetic resonance spectroscopy, and SOC mineralization in four monoculture plantations. Labile and recalcitrant SOC pools in surface(0–10 cm) and deep(40–60 cm) soils in the four forests contained similar content. In contrast, these SOC pools exhibited differences in the subsurface soil(from 10 to20 cm and from 20 to 40 cm). The alkyl C and O-alkyl C intensities of SOC were higher in Schima superba and Michelia macclurei forests than in Cunninghamia lanceolata and Pinus massoniana forests. In surface soil, S.superba and M. macclurei forests exhibited higher SOC mineralization rates than did P. massoniana and C.lanceolata forests. The slope of the straight line between C_(60) and labile SOC was steeper than that between C_(60) and total SOC. Our results suggest that roots affected the composition of SOC pools. Labile SOC pools also affected SOC mineralization to a greater extent than total SOC pools.

Effects of root dominate over aboveground litter on soil microbial biomass in global forest ecosystems

Background:Inputs of above-and belowground litter into forest soils are changing at an unprecedented rate due to continuing human disturbances and climate change.Microorganisms drive the soil carbon(C)cycle,but the roles of above-and belowground litter in regulating the soil microbial community have not been evaluated at a global scale.Methods:Here,we conducted a meta-analysis based on 68 aboveground litter removal and root exclusion studies across forest ecosystems to quantify the roles of above-and belowground litter on soil microbial community and compare their relative importance.Results:Aboveground litter removal significantly declined soil microbial biomass by 4.9%but root exclusion inhibited it stronger,up to 11.7%.Moreover,the aboveground litter removal significantly raised fungi by 10.1%without altering bacteria,leading to a 46.7%increase in the fungi-to-bacteria(F/B)ratio.Differently,root exclusion significantly decreased the fungi by 26.2%but increased the bacteria by 5.7%,causing a 13.3%decrease in the F/B ratio.Specifically,root exclusion significantly inhibited arbuscular mycorrhizal fungi,ectomycorrhizal fungi,and actinomycetes by 22.9%,43.8%,and 7.9%,respectively.The negative effects of aboveground litter removal on microbial biomass increased with mean annual temperature and precipitation,whereas that of root exclusion on microbial biomass did not change with climatic factors but amplified with treatment duration.More importantly,greater effects of root exclusion on microbial biomass than aboveground litter removal were consistent across diverse forest biomes(expect boreal forests)and durations.Conclusions:These data provide a global evidence that root litter inputs exert a larger control on microbial biomass than aboveground litter inputs in forest ecosystems.Our study also highlights that changes in above-and belowground litter inputs could alter soil C stability differently by shifting the microbial community structure in the opposite direction.These findings are useful for predicting microbe-mediated C processes in response to changes in forest management or climate.

Woody Debris Storage of Evergreen Broad-leaf Forest

In Yingzuijie National Nature Reserve,Pinus massoniana forest,mixed broadleaf-coniferous forest and evergreen broad-leaf forest were investigated to study the changing characteristics of woody debris( WD) during various succession stages of evergreen broad-leaf forest. The results showed that during various succession stages of evergreen broad-leaf forest in Yingzuijie National Nature Reserve,WD storage of each forest ranged from 1. 26 to 8. 82 t /hm2,with the order of P. massoniana forest <mixed broadleaf-coniferous forest < evergreen broad-leaf forest,that is,it increased from early to late stages of the succession. At different succession stages,coarse woody debris( CWD) storage was 2-9 times more than fine woody debris( FWD) storage,revealing that CWD was dominant in WD of each forest. CWD biomass accounted for 0. 66%-2. 21% of arbor biomass,so the forests were at the developmental stage.

Allocation patterns of nonstructural carbohydrates in response to CO_(2)elevation and nitrogen deposition in Cunninghamia lanceolata saplings

Stored nonstructural carbohydrates(NSC)indicate a balance between photosynthetic carbon(C)assimilation and growth investment or loss through respiration and root exudation.They play an important role in plant function and whole-plant level C cycling.CO_(2)elevation and nitrogen(N)deposition,which are two major environmental issues worldwide,aff ect plant photosynthetic C assimilation and C release in forest ecosystems.However,information regarding the eff ect of CO_(2)elevation and N deposition on NSC storage in diff erent organs remains limited,especially regarding the trade-off between growth and NSC reserves.Therefore,here we analyzed the variations in the NSC storage in diff erent organs of Chinese fi r(Cunninghamia lanceolata)under CO_(2)elevation and N addition and found that NSC concentrations and contents in all organs of Chinese fi r saplings increased remarkably under CO_(2)elevation.However,N addition induced diff erential accumulation of NSC among various organs.Specifi cally,N addition decreased the NSC concentrations of needles,branches,stems,and fi ne roots,but increased the NSC contents of branches and coarse roots.The increase in the NSC contents of roots was more pronounced than that in the NSC content of aboveground organs under CO_(2)elevation.The role of N addition in the increase in the structural biomass of aboveground organs was greater than that in the increase in the structural biomass of roots.This result indicated that a diff erent tradeoff between growth and NSC storage occurred to alleviate resource limitations under CO_(2)elevation and N addition and highlights the importance of separating biomass into structural biomass and NSC reserves when investigating the eff ects of environmental change on biomass allocation.

Comparisons of carbon storages in Cunninghamia lanceolata and Michelia macclurei plantations during a 22-year period in southern China

Tree species composition was important for carbon storage within the same climate range.To quantify the dynamics of ecosystem carbon allocation as affected by different tree species,we measured the above-and below-ground biomass accumulation in 22 years,as well as the tissue carbon concentrations of trees in Cunninghamia lanceolata plantation and Michelia macclurei plantation.Results indicated that M.macclurei plantation significantly stored more carbon(174.8 tons/hm2) than C.lanceolata plantation(154.3 tons/hm2).Most of the carbon was found in the soil pool(57.1% in M.macclurei plantation,55.2% in C.lanceolata plantation).Tree and soil component of M.macclurei plantation possessed significantly higher carbon storage than that of C.lanceolata plantation(p < 0.05).No significant difference was found in the carbon storage of understory and forest floor.These results suggest that the broadleaved species(M.macclurei) possesses greater carbon sequestration potential than the coniferous species(C.lanceolata) in southern China.

Stability of soil organic carbon changes in successive rotations of Chinese fir(Cunninghamia lanceolata(Lamb.) Hook) plantations

The importance of soil organic carbon(SOC) under forests in the global carbon cycle depends on the stability of the soil carbon and its availability to soil microbial biomass.We investigated the effects of successive rotations of Chinese fir(Cunninghamia lanceolata(Lamb.) Hook) plantations on the stability of SOC and its availability to microbes by adopting the two-step hydrolysis with H2SO4 and density fractionation.The results showed that successive rotations of Chinese fir decreased the quantity of total SOC,recalcitrant fraction,and carbohydrates in Labile Pool I(LP Ⅰ),and microbial properties evidently,especially at 0-10 cm horizon.However,cellulose included in Labile Pool II(LP Ⅱ) and the cellulose/total carbohydrates ratio increased in successive rotations of Chinese fir.The non-cellulose of carbohydrates included in LP I maybe highly available to soil microbial biomass.Hence the availability of SOC to microbial biomass declined over the successive rotations.Although there was no significant change in recalcitrance of SOC over the successive rotations of Chinese fir,the percentage of heavy fraction to total SOC increased,suggesting that the degree of physical protection for SOC increased and SOC became more stable over the successive rotations.The degradation of SOC quality in successive rotation soils may be attributed to worse environmental conditions resulted from disturbance that related to "slash and burn" site preparation.Being highly correlated with soil microbial properties,the cellulose/total carbohydrates ratio as an effective indicator of changes in availability of SOC to microbial biomass brought by management practices in forest soils.

Effects of phenolic acids on soil nitrogen mineralization over successive rotations in Chinese fir plantations

Phenolic acids are secondary metabolites of plants that significantly affect nutrient cycling processes.To investigate such effects,the soil available nitrogen(N)content,phenolic acid content,and net N mineralization rate in three successive rotations of Chinese fir plantations in subtropical China were investigated.Net N mineralization and nitrification rates in soils treated with phenolic acids were measured in an ex situ experiment.Compared with first-rotation plantations(FCP),the contents of total soil nitrogen and nitrate in second(SCP)-and third-rotation plantations(TCP)decreased,and that of soil ammonium increased.Soil net N mineralization rates in the second-and third-rotation plantations also increased by 17.8%and 39.9%,respectively.In contrast,soil net nitrification rates decreased by 18.0%and 25.0%,respectively.The concentrations of total phenolic acids in the FCP soils(123.22±6.02 nmol g^-1)were 3.0%and 17.9%higher than in the SCP(119.68±11.69 nmol g^-1)and TCP(104.51±8.57 nmol g^-1,respectively).The total content of phenolic acids was significantly correlated with the rates of net soil N mineralization and net nitrification.The ex situ experiment showed that the net N mineralization rates in soils treated with high(HCPA,0.07 mg N kg^-1 day^-1)and low(LCPA,0.18 mg N kg^-1 day^-1)concentrations of phenolic acids significantly decreased by 78.6%and 42.6%,respectively,comparing with that in control(0.32 mg N kg^-1 day^-1).Soil net nitrification rates under HCPA and LCPA were significantly higher than that of the control.The results suggested that low contents of phenolic acids in soil over successive rotations increased soil net N mineralization rates and decreased net nitrification rates,leading to consequent reductions in the nitrate content and enhancement of the ammonium content,then resulting in enhancing the conservation of soil N of successive rotations in Chinese fir plantation.

N concentration of old leaves and twigs is more sensitive to stand density than that of young ones in Chinese fir plantations： a case study in subtropical China

Young leaves are conventionally used in the analysis to study the nutrient status of evergreen plants and their responses to environmental changes, but the role of old leaves remains poorly understood. We selected two stand types in 31-year-old Chinese fir(Cunninghamia lanceolata) plantations with similar soil conditions but different stand densities, to test the hypothesis that nitrogen(N) concentration of old leaves and twigs is more sensitive to stand density than that of young ones. Leaves and twigs were sampled and sorted into young(one-year-old) and old(two-and three-year-old) groups. Significant differences in N concentration and carbon: nitrogen ratio between the low-density stand and high-density stand were only found in the old leaves and twigs but not in the young ones.Although the N resorption efficiency did not vary significantly with stand density, the annual N resorption rates were increased in old leaves and relatively young twigs at high stand density. These results show the potential use of old tissues in the nutrient analysis in Chinese fir plantations. Testing the generality of these results could improve the use of foliar analysis as an indicator of nutrient status and environmental changes in evergreen tree species.

Temporal shifts in the explanatory power and relative importance of litter traits in regulating litter decomposition

Background:Litter traits critically affect litter decomposition from local to global scales.However,our understanding of the temporal dynamics of litter trait-decomposition linkages,especially their dependence on plant functional type remains limited.Methods:We decomposed the leaf litter of 203 tree species that belong to two different functional types(deciduous and evergreen)for 2 years in a subtropical forest in China.The Weibull residence model was used to describe the different stages of litter decomposition by calculating the time to 10%,25%and 50%mass loss(Weibull t_(1/10),t_(1/4),and t_(1/2)respectively)and litter mean residence time(Weibull MRT).The resulting model parameters were used to explore the control of litter traits(e.g.,N,P,condensed tannins and tensile strength)over leaf litter decomposition across different decomposition stages.Results:The litter traits we measured had lower explanatory power for the early stages(Weibull t_(1/10)and t_(1/4))than for the later stages(Weibull t_(1/2)and MRT)of decomposition.The relative importance of different types of litter traits in influencing decomposition changed dramatically during decomposition,with physical traits exerting predominant control for the stages of Weibull t_(1/10)and MRT and nutrient-related traits for the stages of Weibull t_(1/4),and t_(1/2).Moreover,we found that litter decomposition of the early three stages(Weibull t_(1/10),t_(1/4),and t_(1/2))of the two functional types was controlled by different types of litter traits;that is,the litter decomposition rates of deciduous species were predominately controlled by nutrient-related traits,while the litter decomposition rates of evergreen species were mainly controlled by carbon-related traits.Conclusions:This study suggests that litter trait-decomposition linkages vary with decomposition stages and are strongly mediated by plant functional type,highlighting the necessity to consider their temporal dynamics and plant functional types for improving predictions of litter decomposition.

Nitrogen addition reduced carbon mineralization of aggregates in forest soils but enhanced in paddy soils in South China

Background:Despite the crucial role of nitrogen(N)availability in carbon(C)cycling in terrestrial ecosystems,soil organic C(SOC)mineralization in different sizes of soil aggregates under various land use types and their responses to N addition is not well understood.To investigate the responses of soil C mineralization in different sized aggregates and land use types to N addition,an incubation experiment was conducted with three aggregate-size classes(2000,250,and 53μm)and two land use types(a Chinese fir plantation and a paddy land).Results:Cumulative C mineralization of the<53-μm fractions was the highest and that of microaggregates was the lowest in both forest and paddy soils,indicating that soil aggregates enhanced soil C stability and reduced the loss of soil C.Cumulative C mineralization in all sizes of aggregates treated with N addition decreased in forest soils,but that in microaggregates and the<53-μm fraction increased in paddy soils treated with 100μgNg−1.Moreover,the effect sizes of N addition on C mineralization of forest soils were below zero,but those of paddy soils were above zero.These data indicated that N addition decreased SOC mineralization of forest soils but increased that of paddy soils.Conclusions:Soil aggregates play an important role in soil C sequestration,and decrease soil C loss through the increase of soil C stability,regardless of land use types.N addition has different effects on soil C mineralization in different land use types.These results highlight the importance of soil aggregates and land use types in the effects of N deposition on the global terrestrial ecosystem C cycle.

Current knowledge of COVID-19:Advances,challenges and future perspectives

The pandemic of coronavirus disease 2019(COVID-19)has already evoked massive influence.The global pandemic has been ravaging the whole world for a year,with the number of confirmed human infection cases over 150 million and a death toll exceeding 3 million.Although the genomic sequence of the cognate pathogen SARS-CoV-2(severe acute respiratory syndrome coronavirus 2)has been quickly determined,there are still many unknown aspects,including the virus origin and evolution trend,and the effectiveness of current vaccines and drugs against the mutating virus.This review summarizes current knowledge and advances about COVID-19,including virus origin,transmission and infection,with the aim to improve the understanding of COVID-19 and provide a new perspective for future studies.