Linkage of microbial living communities and residues to soil organic carbon accumulation along a forest restoration gradient in southern China

Background:Forest restoration has been considered an effective method to increase soil organic carbon(SOC),whereas it remains unclear whether long-term forest restoration will continuously increase SOC.Such large uncertainties may be mainly due to the limited knowledge on how soil microorganisms will contribute to SOC accumulation over time.Methods:We simultaneously documented SOC,total phospholipid fatty acids(PLFAs),and amino sugars(AS)content across a forest restoration gradient with average stand ages of 14,49,70,and>90 years in southern China.Results:The SOC and AS continuously increased with stand age.The ratio of fungal PLFAs to bacterial PLFAs showed no change with stand age,while the ratio of fungal AS to bacterial AS significantly increased.The total microbial residue-carbon(AS-C)accounted for 0.95-1.66% in SOC across all forest restoration stages,with significantly higher in fungal residue-C(0.68-1.19%)than bacterial residue-C(0.05-0.11%).Furthermore,the contribution of total AS-C to SOC was positively correlated with clay content at 0-10 cm soil layer but negatively related to clay content at 10-20 cm soil layer.Conclusions:These findings highlight the significant contribution of AS-C to SOC accumulation along forest restoration stages,with divergent contributions from fungal residues and bacterial residues.Soil clay content with stand age significantly affects the divergent contributions of AS-C to SOC at two different soil layers.

Temporal Variation in Sap-Flux-Scaled Transpiration and Cooling Effect of a Subtropical Schima superba Plantation in the Urban Area of Guangzhou

Agriculture could suffer the water stress induced by climate change. Because climate warming affects global hydrological cycles, it is vital to explore the effect of tree transpiration, as an important component of terrestrial evapotranspiration, on the environment. Thermal dissipation probes were used to measure xylem sap flux density of a Schima superba plantation in the urban area of Guangzhou City, South China. Stand transpiration was calculated by mean sap flux density times total sapwood area. The occurrence of the maximum sap flux density on the daily scale was later in wet season than in dry season. The peak of daily sap flux density was the highest of 59 g m-2 s^-1 in July and August, and the lowest of 28 g m-2 s-1 in December. In the two periods （November 2007-October 2008 and November 2008-October 2009）, the stand transpiration reached 263.2 and 291.6 ram, respectively. During our study period, stand transpiration in wet season （from April to September） could account for about 58.5 and 53.8% of the annual transpiration, respectively. Heat energy absorbed by tree transpiration averaged 1.4×10s and 1.6×10s kJ per month in this Schima superba plantation with the area of 2 885 m2, and temperature was reduced by 4.3 and 4.7℃ s^-1 per 10 m3 air.

Possibility of avoiding legumes-deriving boost of N 2 O emissions in tropical monoculture tree plantations

Recent reports warned that planting leguminous trees under monocultures elevates nitrous oxide(N2O)emissions through N-rich litter inputs.We hypothesized that planting trees on sandy soil can avoid the legume-derived boost of N2O emissions through limiting water availability for N2O production.Effects of planting legumes on methane(CH4)uptakes were also examined.N2O emissions and CH4uptakes were compared among five tropical tree plantation stands including three leguminous stands(Acacia auriculiformis,Acacia mangium,and Xylia xylocarpa)and two non-leguminous stands(Eucalyptus camaldulensis,and Hope a odorata).Due to lower water contents of the soil,the N2O fluxes in our study site were at the lower end of the tropical rain forests.As we hypothesized,no clear differences in N2O emissions were obs erved between leguminous and non-leguminous stands.CH4uptake rates in the present study were lower than those of other tropical forests.CH4uptakes in leguminous stands did not differ from those in non-leguminous stands.Overall,we demonstrated that planting leguminous trees on sandy soils has a potential to enable us to manage leguminous monoculture tree plantations without boosting N2O emissions or reducing CH4uptakes.

Longitudinal patterns of spring-intermonsoon phytoplankton biomass,species compositions and size structure in the Bay of Bengal

Vertical distributions of phytoplankton biomass, compositions and size structure were investigated during the spring-intermonsoon （April 22 to 30） of 2010 along transact 10°N of the Bay of Bengal, northern Indian Ocean. Surface phytoplankton biomass （Chl a） was （0.065±0.009） μg/L, being greater than 80% of which was contributed by pico-phytoplankton （〈3 μm）. The Chl a concen- tration vertically increased to the maximal values at deep chlorophyll maximum （DCM） layer that shoaled eastwards from 75 to 40 m. The Chl a biomass at DCM layer generally varied between 0.2 and 0.4 μg/L, reaching the maximum of 0.56 μg/L with micro-phytoplankton cells （~20 #m） accounting for 58% and nano- （3-20μm） or pico-cells for 15% and 27%, respectively. In particular, the cells concentration coupling well with phosphate level was observed at middle layer （75-100 m） of 87° to 89°E, dominated by micro-cells diatoms （e.g., Chaetoceros atlanticus v. neapolitana, Chaetoceros femur and Pseudonitzsehia sp.） and cyanobacteria （i.e., Trichodesmium hildebrandtii）, With the ceils concentration reached as high as 4.0 × 10^4 and 4.3 × 10^4 cells/L. At the rest of the trans- act however, dinoflagellates （e.g., Amphisdinium carterae and Prorocentrum sp.） were the dominant species, with the cells concentration varying from 0.3×10^3 to 6.8×10^3 cells/L. Our results also indicate that the regulation of large cells （micro-, nano-） on phytoplankton biomass merely occurred at DCM layer of the Bay.

The responses of carbon-and nitrogen-acquiring enzymes to nitrogen and phosphorus additions in two plantations in southern China

In tropical plantations,nutrients such as nitrogen(N)or phosphorus(P)are often applied as management practices.However,the effects of such nutrient additions on topsoil C-and N-acquiring enzymes activities are unclear.In this study,the impacts of fertilization onβ-1,4-glucosidase(BG),β-D-cellobiosidase(CBH),β-1,4-xylosidase(BX),β-1,4-N-acetyl-glucosaminidase(NAG),and leucine amino peptidase(LAP)enzymes activities from topsoil and litter layer of two tropical plantations(Acacia auriculiformis and Eucalyptus urophylla)were measured.The results showed that N addition had neutral impact on topsoil enzymes,while significantly elevating the activities of BG,CBH,BX,and NAG in the litter layer.P fertilization had no impacts except for an elevation of NAG in litter sample.There was no interactions found between N and P additions on these enzyme activities.The clearer impacts of N over P fertilization were unexpected because that the study site receives a high rate of atmospheric N deposition,and has low soil P availability.The impact of P fertilization on hydrolytic enzyme activities may be less important compared with that of N.

Effect of nitrogen addition on DOC leaching and chemical exchanges on canopy leaves in Guangdong Province, China

The impact of nitrogen(N)deposition on dissolved organic carbon(DOC)fractions in throughfall is not well understood.We performed a laboratory experiment and compared DOC leaching from canopy leaves after dipping leaves in pure water(control)and NH4NO3 solution(N-treatment)for 18 h.Net changes of DOC,NH4^+,NO3^-,SO4^2-,K^+,Mg^2+,Ca^2+and H^+contents after dipping leaves were determined by comparing solutions with and without leaves.We recorded no differences of DOC leaching between control and N-treatment,implying that N deposition had minor impacts on canopy DOC production.This confirmed that previous experiments testing the effects of N addition on DOC dynamics without considering the effects of the canopy reaction successfully described the real situation.We also confirmed the previously-reported canopy exchange process in spite of a high background N deposition at our study site.N-treatment significantly increased base cation leaching,especially K^+,and the increase was positively correlated with foliar NH4?retention.Net leaching of H^+and SO4^2-was not affected by the N-treatment.

Effects of prescribed burning on carbon accumulation in two paired vegetation sites in subtropical China

Background: Prescribed burning is a common practice of site preparation before afforestation in subtropical forests. However, the effects of prescribed burning on carbon (C) dynamics of an ecosystem are poorly understood. Therefore, a Eucalyptus urophylla plantation (EU) and a naturally recovered shrubland (NS), each treated with prescribed burning and no burning were examined in subtropical China. Methods: Biomass of trees and shrubs in the 1st, 3nd, 4th, and 6th year after treatments were estimated by quadrat survey and allometric equations. Biomass of herbs and forest floors were estimated by harvest method. Plant biomass C storage was calculated by plant biomass multiplying by its C concentration. Soil organic C (SOC) storage in the 6th year after treatments was estimated by SOC concentration multiplying by soil bulk density and soil volumes. Results: Tree biomass C storage was significantly higher in the burned EU (BEU) than in the unburned EU (UEU) in the 1st year after treatments, yet the difference decreased over time. Conversely, tree biomass C storage was lower in the burned NS (BNS) than in the unburned NS (UNS), although the difference was not significant. However, in the 6th year after treatments, the total plant biomass C storage was 14.56% higher in the BEU than that in the UEU, and 59.93% higher in the BNS than that in the UNS, respectively, although the significant difference was only found between UNS and BNS. In addition, neither SOC storage at 0-20 cm nor ecosystem C storage in either the EU or NS was significantly affected by prescribed burning. Conclusions: Prescribed burning has little impact on overall C storage of forest ecosystems, we consider that prescribed burning may be an option for forest site preparation regarding plant biomass C accumulation.

Subtropical forest macro-decomposers rapidly transfer litter carbon and nitrogen into soil mineral-associated organic matter

Background:Forest soils in tropical and subtropical areas store a significant amount of carbon.Recent framework to assess soil organic matter(SOM)dynamics under evolving global conditions suggest that dividing bulk SOM into particulate and mineral-associated organic matter(POM vs.MAOM)is a promising method for identifying how SOM contributes to reducing global warming.Soil macrofauna,earthworms,and millipedes have been found to play an important role in facilitating SOM processes.However,how these two co-existing macrofaunae impac the litter decomposition process and directly impact the formation of POM and MAOM remains unclear.Methods:Here,we set up a microcosm experiment,which consisted of 20 microcosms with four treatments earthworm and litter addition(E),millipedes and litter addition(M),earthworm,millipedes,and litter addition(E+M),and control(only litter addition)in five replicates.The soil and litter were sterilized prior to beginning the incubation experiment to remove any existing microbes.After incubating the samples for 42 days,the litte properties(mass,C,and N contents),soil physicochemical properties,as well as the C and N contents,and POM and MAOM^(13)C abundance in the 0–5 and 5–10 cm soil layers were measured.Finally,the relative influences o soil physicochemical and microbial properties on the distribution of C and N in the soil fractions were analyzed Results:The litter mass,C,and N associated with all four treatments significantly decreased after incubation especially under treatment E+M(litter mass:-58.8%,litter C:-57.0%,litter N:-75.1%,respectively),while earthworm biomass significantly decreased under treatment E.Earthworm or millipede addition alone showed no significant effects on the organic carbon(OC)and total nitrogen(TN)content in the POM fraction,but join addition of both significantly increased OC and TN regardless of soil depth.Importantly,all three macrofauna treatments increased the OC and TN content and decreased the^(13)C abundance in the MAOM fraction.More than65%of the total variations in the distribution of OC and TN throughout the two fractions can be explained by a combination of soil physicochemical and microbial properties.Changes in the OC distribution in the 0–5 cm soi layer are likely due to a decrease in soil pH and an increase in arbuscular mycorrhizal fungi(AMF),while those in the 5–10 cm layer are probably caused by increases in soil exchangeable Ca and Mg,in addition to fungi and gram-negative(GN)bacteria.The observed TN distribution changes in the 0–5 cm soil likely resulted from a decrease in soil pH and increases in AMF,GN,and gram-negative(GP)bacteria,while TN distribution changes in the 5–10 cm soil could be explained by increases in exchangeable Mg and GN bacteria.Conclusions:The results indicate that the coexistence of earthworms and millipedes can accelerate the litte decomposition process and store more C in the MAOM fractions.This novel finding helps to unlock the processe by which complex SOM systems serve as C sinks in tropical forests and addresses the importance of soil mac rofauna in maintaining C-neutral atmospheric conditions under global climate change.

Stem and leaf traits as co-determinants of canopy water flux

However,the empirical relationship between leaf stomata anatomy and canopy stomatal conductance(Gs)is surprisingly rare,thereby the underlying biological mechanisms of terrestrial water flux are not well elucidated.To gain further insight into these mechanisms,we reanalyzed the dataset of Gs previously reported by Gao et al.(2015)using a quantile regression model.The results indicated that the reference Cs(Gsref.Gs at 1 kPa)was negatively correlated with wood density at each quantile,which confirmed previous data;however,Gsref was significantly correlated with stomatal density at the 0.6 quantile,i.e.,450 stomata mm-2.This highlighted the potential of using stomatal density as a trait to predict canopy water flux.A conceptual model of co-determinants of xylem and stomatal morphology suggests that these traits and their coordination may play a critical role in determining tree growth,physiological homeostatic response to environmental variables,water use efficiency,and drought resistance.

Effects of planting dates, densities, and varieties on ecophysiology of pigeonpea in the Southeastern United States

Pigeonpea [Cajanus cajan (L.) Millsp.] is an important legume crop widely cultivated in tropical and subtropical climates of the world. Interest in this crop is growing in many countries because of its multiple uses as a source of food, feed, fuel, and fertilizer. However, the performance of pigeonpea in Southeastern US has not been well investigated. We conducted an experiment in Nashville, Tennessee to test the effects of two planting dates, three densities, and four varieties on pigeonpea ecophysiology that included leaf photosynthesis, stomatal conductance, transpiration, water use efficiency (WUE), leaf area index (LAI) and soil respiration. Results indicated that the plants in the late planting plots had higher photosynthetic rate, stomatal conductance and transpiration. There were significant differences in the levels of leaf photosynthesis, stomatal conductance, transpiration, WUE and LAI among all four varieties. W3 and G1 showed higher photosynthetic rate and LAI than W1, and W3 had higher WUE than G2 and W1. Planting densities had no significant effect on all variables studied. This study indicated that late planting of variety G1 or W3 resulted in higher WUE and yield, but did no significant influence soil CO2 emission.

Plant above-ground biomass and litter quality drive soil microbial metabolic limitations during vegetation restoration of subtropical forests

Changes in litter quality(carbon:nitrogen,C:N)and above-ground biomass(AGB)following vegetation restoration significantly impact soil physicochemical properties,yet their effects on soil microbial metabolic limitations remain unclear.We measured litter quality,AGB,soil physicochemical properties,and extracellular enzyme activity(EEA)along a vegetation restoration gradient(7,14,49,70 years,and nearly climax evergreen broadleaved forests)in southern China.We also evaluated soil microbial metabolic limitations by a vector analysis of the EEA.Results revealed the soil microbial metabolisms were co-limited by C and phosphorus(P).The microbial C limitation initially decreased(before 14 years)and then increased,while the microbial P limitation initially increased(before 49 years)and then decreased.Partial least squares path modeling(PLS-PM)showed that the microbial C limitation was mainly attributed to microbial C use efficiency induced by litter quality,suggesting that microorganisms may transfer cellular energy between microbial growth and Cacquiring enzyme production.The microbial P limitation was primarily correlated with AGB-driven change in soil elements and their stoichiometry,highlighting the importance of nutrient stoichiometry and balance in microbial metabolism.The shifts between microbial C and P limitations and the strong connections of plant–soil-microbe processes during vegetation restoration revealed here will provide us with helpful information for optimal management to achieve forest restoration success.

Reduced turnover rate of topsoil organic carbon in old-growth forests:a case study in subtropical China

Background:Old-growth forests are irreplaceable with respect to climate change mitigation and have considerable carbon(C)sink potential in soils.However,the relationship between the soil organic carbon(SOC)turnover rate and forest development is poorly understood,which hinders our ability to assess the C sequestration capacity of soil in old-growth forests.Methods:In this study,we evaluated the SOC turnover rate by calculating the isotopic enrichment factor β(defined as the slope of the regression between ^(13)C natural abundance and log-transformed C concentrations)along 0-30 cm soil profiles in three successional forests in subtropical China.A lower β(steeper slope)is associated with a higher turnover rate.The three forests were a 60-year-old P.massoniana forest(PF),a 100-year-old coniferous and broadleaved mixed forest(MF),and a 400-year-old monsoon evergreen broadleaved forest(BF).We also analyzed the soil physicochemical properties in these forests to examine the dynamics of SOC turnover during forest succession and the main regulators.Results:The β value for the upper 30-cm soils in the BF was significantly(p<0.05)higher than that in the PF,in addition to the SOC stock,although there were nonsignificant differences between the BF and MF.The β value was significantly(p<0.05)positively correlated with the soil recalcitrance index,total nitrogen,and available nitrogen contents but was significantly(p<0.01)negatively correlated with soil pH.Conclusions:Our results demonstrate that SOC has lower turnover rates in old-growth forests,accompanied by higher soil chemical recalcitrance,nitrogen status,and lower soil pH.This finding helps to elucidate the mechanism underlying C sequestration in old-growth forest soils,and emphasizes the important value of old-growth forests among global C sinks.

Variations in silicate concentration affecting photosynthetic carbon fixation by spring phytoplankton assemblages in surface water of the Strait of Malacca

The Strait of Malacca （SoM）, the world＇s busiest sea-route, is increasingly polluted as the rapid develop- ment of world trades, affecting phytoplankton primary productivity therein. The variations of surface phy- toplankton biomass, size-structure and carbon fixation were investigated across the SoM during the spring period （May 4 to 9, 2011）. Chlorophyll a concentration increased from 0.12 ptg/L at the northwest entrance of the SoM to a maximal 0.63 #g/L at narrowest section, and decreased to 0.10/.tg/L at the southeast entrance. Photosynthetic carbon fixation by phytoplankton coincided well with Chl a biomass, and increased from 10.8 to 22.3 pg C/（L.d）, then decreased to 9.21/zg C/（L.d）; while the carbon fixation rate showed an inverse pattern to the changes of Chl a, and decreased from 87.1 to 35.5 #g C/（#g Chl a.d） and increased thereafter to 95.3 btg C/（/2g Chl a.d）. Picophytoplankton cells （〈3/2m） contributed to more than 60% and 50% of the total Chl a and carbon fixation at both the entry waters; while the contributions of pico-cells decreased sharply to the minimum of 18.3% and 27.5% at the narrowest part of the SoM. In particular, our results showed that the silicate concentration positively regulated Chl a biomass and carbon fixation, reflecting that the higher silicate favoured the growth of phytoplankton and thus led to higher primary production in this strait.

Introduction of Dalbergia odorifera enhances nitrogen absorption on Eucalyptus through stimulating microbially mediated soil nitrogen-cycling

Background:There is substantial evidence that Eucalyptus for nitrogen(N)absorption and increasing the growth benefit from the introduction of N-fixing species,but the underlying mechanisms for microbially mediated soil N cycling remains unclear.Methods:We investigated the changes of soil pH,soil water content(SWC),soil organic carbon(SOC),total N(TN),inorganic N(NH_(4)^(+)-N and NO_(3)^(-)-N),microbial biomass and three N-degrading enzyme activities as well as the biomass and N productivity of Eucalyptus between a pure Eucalyptus urophylla×grandis plantation(PP)and a mixed Dalbergia odorifera and Eucalyptus plantation(MP)in Guangxi Zhuang Autonomous Region,China.Results:Compared with the PP site,soil pH,SWC,SOC and TN in both seasons were significantly higher at the MP site,which in turn enhanced microbial biomass and the activities of soil N-degrading enzymes.The stimulated microbial activity at the MP site likely accelerate soil N mineralization,providing more available N(NH_(4)^(+)-N in both seasons and NO_(3)^(-)-N in the wet-hot season)for Eucalyptus absorption.Overall,the N productivity of Eucalyptus at the MP site was increased by 19.7% and 21.9%,promoting the biomass increases of 15.1% and 19.2% in the drycold season and wet-hot season,respectively.Conclusion:Our results reveal the importance of microbially mediated soil N cycling in the N absorption on Eucalyptus.Introduction of D.odorifera enhances Eucalyptus biomass and N productivity,improve soil N availability and increased soil C and N concentration,which hence can be considered to be an effective sustainable management option of Eucalyptus plantations.

A New Index Developed for Fast Diagnosis of Meteorological Roles in Ground-Level Ozone Variations

China experienced worsening ground-level ozone(O_(2)) pollution from 2013 to 2019. In this study, meteorological parameters, including surface temperature(T_(2)), solar radiation(SW), and wind speed(WS), were classified into two aspects,(1) Photochemical Reaction Condition(PRC = T_(2)× SW) and(2) Physical Dispersion Capacity(PDC = WS). In this way, a Meteorology Synthetic Index(MSI = PRC/PDC) was developed for the quantification of meteorology-induced ground-level O_(2)pollution. The positive linear relationship between the 90 th percentile of MDA8(maximum daily 8-h average) O_(2)concentration and MSI determined that the contribution of meteorological changes to ground-level O-3 varied on a latitudinal gradient, decreasing from ~40% in southern China to 10%–20% in northern China. Favorable photochemical reaction conditions were more important for ground-level O_(2)pollution. This study proposes a universally applicable index for fast diagnosis of meteorological roles in ground-level O_(2)variability, which enables the assessment of the observed effects of precursor emissions reductions that can be used for designing future control policies.

Traffic Pollution Influences Leaf Biochemistries of <i>Broussonetia papyrifera</i>

Paper mulberry (Broussonetia papyrifera) is one of multifunctional species in agroforestry systems as well as one of traditional forages in many countries of Asia. Fully expanded tender leaves of B. papyrifera wildly growing under two traffic densities (a high traffic loads bearing more than 1000 vehicles per hour, HT;and a relatively clear section with almost no traffic loads, NT) were collected for carbohydrates, amino acids and phytohormones analysis. Leaves exposed to traffic pollutants were revealed to have significant lower amounts of carbohydrates and total amino acids than those growing at relatively clear environment. The levels of abscisic acid in the leaves significantly increased, while gib-berellin acid, indoleaetic acid, and zeatin riboside in the leaves significantly decreased, with the traffic densities. The results indicated that the contents of carbohydrates, amino acids and phytohormones in the leaves of B. papyrifera could be adversely affected by traffic pollution. Variations of the leaf biochemistries of B. papyrifera exposed to traffic pollutants implied that B. papyrifera could physiologically regulate itself to adapt or resist traffic stress.

Environmental selection and evolutionary process jointly shape genomic and functional profiles of mangrove rhizosphere microbiomes

Mangrove reforestation with introduced species has been an important strategy to restore mangrove ecosystem functioning.However,how such activities affect microbially driven methane(CH4),nitrogen(N),and sulfur(S)cycling of rhizosphere microbiomes remains unclear.To understand the effect of environmental selection and the evolutionary process on microbially driven biogeochemical cycles in native and introduced mangrove rhizospheres,we analyzed key genomic and functional profiles of rhizosphere microbiomes from native and introduced mangrove species by metagenome sequencing technologies.Compared with the native mangrove(Kandelia obovata,KO),the introduced mangrove(Sonneratia apetala,SA)rhizosphere microbiome had significantly(p<0.05)higher average genome size(AGS)(5.8 vs.5.5 Mb),average 16S ribosomal RNA gene copy number(3.5 vs.3.1),relative abundances of mobile genetic elements,and functional diversity in terms of the Shannon index(7.88 vs.7.84)but lower functional potentials involved in CH4 cycling(e.g.,mcrABCDG and pmoABC),N2 fixation(nifHDK),and inorganic S cycling(dsrAB,dsrC,dsrMKJOP,soxB,sqr,and fccAB).Similar results were also observed from the recovered Proteobacterial metagenome-assembled genomes with a higher AGS and distinct functions in the introduced mangrove rhizosphere.Additionally,salinity and ammonium were identified as the main environmental drivers of functional profiles of mangrove rhizosphere microbiomes through deterministic processes.This study advances our understanding of microbially mediated biogeochemical cycling of CH_(4),N,and S in the mangrove rhizosphere and provides novel insights into the influence of environmental selection and evolutionary processes on ecosystem functions,which has important implications for future mangrove reforestation.

Water-use efficiency of four native trees under CO_(2) enrichment and N addition in subtropical model forest ecosystems

Aims We aimed to evaluate the changes in water-use efficiency(WuE)in native tree species in forests of subtropical China,and determine how coexisting species would be responding to increases in atmospheric carbon dioxide(CO_(2))concentrations and nitrogen(N)deposition.Methods We used model forest ecosystems in open-top chambers to study the effects of elevated CO_(2)(ca.700μmol mol−1)alone and together with N addition(NH4No3 applied at 100 kg N ha−1year−1)on WuE of four native tree species(Schima superba,Ormosia pin-nata,Castanopsis hystrix and Acmena acuminatissima)from 2006 to 2010.Important findingsour result indicated that all species increased their WuE when they were exposed to elevated CO_(2).although higher WuE was shown in faster-growing species(S.superba and O.pinnata)than that of slower-growing species(C.hystrix and Acmena acuminatissima),the increased extent of WuE induced by elevated CO_(2) was higher in the slower-growing species than that of the faster-growing species(P<0.01).the N treatment decreased WuE of S.superba,while the effects on other species were not significant.the interactions between elevated CO_(2) and N addition increased intrinsic WuE of S.superba significantly(P<0.001),however,it did not affect WuE of the other tree species significantly.We conclude that the responses of native tree species to elevated CO_(2) and N addition are different in subtropical China.the species-specific effects of elevated CO_(2) and N addition on WuE would have important implications on species composition in China’s subtropics in response to global change.

Advances in the reintroduction of rare and endangered wild plant species

Human disturbance and climate change have increased the risk of extinction for rare and endangered wild plant species.One effective way to conserve these rare and endangered species is through reintroduction.In this review,we summarize the advances in wild plant reintroduction from five perspectives:the establishment of reintroduction biology as an important tool for biodiversity conservation;the importance of genetic diversity in reintroduction;reintroduction under global climate change;recruitment limitation in reintroduction;and reintroduction and ecological restoration.In addition,we consider the future of plant reintroduction strategies.

Phosphorus limitation on photosynthesis of two dominant understory species in a lowland tropical forest

Aims Elevated nitrogen(N)deposition in tropical regions may accelerate ecosystem phosphorus(P)limitation.However,it is not explicitly addressed that how changes in soil N and P availability affect foliar nutrients and photosynthesis of plants in tropical forests.In this study,we examined the effects of N and P additions on foliar nutrients and net photosynthesis of two dominant understory species,Randia can-thioides(R.canthioides)and Cryptocarya concinna(C.concinna)in an N-saturated old-growth tropical forest(>400-year-old)in south-ern China.Methods A full factorial NP addition experiment(2×2)was established in 2007 and continued through August 2010.Four treatments,including control,N addition(150 kg N ha^(−1) year^(−1)),P addi-tion(150 kg P ha^(−1) year^(−1))and NP addition(150 kg N ha^(−1) year^(−1) plus 150 kg P ha^(−1) year^(−1))were set up in this experiment.Photosynthetic traits maximum photosynthetic CO_(2) assimilation(Amax),stomatal conductance(gs),leaf transpiration(E),light satu-rating point,concentrations of chlorophyll a/b and foliar nutri-ents(N and P)of the two species were measured with standard methods.Important Findings Three years of N addition had no significant effects on any measured photosynthetic parameter of either species.However,N addition significantly elevated foliar N and P concentrations of one species(R.canthioides),resulting in lower photosynthetic nitrogen use effi-ciency(PNUE).N treatments decreased foliar P concentration of the other(C.concinna),resulting in increased photosynthetic phos-phorus use efficiency,which was potentially related to N-induced P shortage.In contrast,positive effects of P treatments on gs of R.can-thioides,Amax and chlorophyll a+b of C.concinna were observed.P treatments also elevated foliar P and PNUE of both species,imply-ing P induced more efficient use of N.Our results suggested a more important role of P than N on influencing photosynthetic traits of these two understory species.Alleviation of P shortage through P addition may enhance photosynthetic performances of some under-story species in N-rich tropical forests.