Sensitivity of forest phenology in China varies with proximity to forest edges

Background:Shifts in forest phenological events serve as strong indicators of climate change.However,the sensitivity of phenology events to climate change in relation to forest origins has received limited attention.Moreover,it is unknown whether forest phenology changes with the proximity to forest edge.Methods:This study examined the green-up dates,dormancy dates,time-integrated NDVI(LiNDVI,a measure of vegetation productivity in growing season),and their sensitivities to climatic factors along the gradients of distance(i.e.proximity)to forest edge(0–2 km)in China's natural forests(NF)and planted forests(PF).For the analysis,field-surveyed data were integrated with Moderate Resolution Imaging Spectroradiometer(MODIS)NDVI from 2000 to 2022.Results:Our results reveal that PF had earlier green-up dates,later dormancy dates,and higher LiNDVI than NF.However,green-up sensitivities to temperature were higher at the edges of NF,whereas no such pattern was observed in PF.Conversely,the sensitivity of dormancy dates remains relatively stable from the inner to the edge of both NF and PF,except for a quadratic change in dormancy date sensitivity to precipitation found in NF.Additionally,we found that the green-up sensitivity to temperature increased with decreasing proximity to edge in NF evergreen forests,while it showed the opposite trend in PF evergreen forests.Furthermore,we observed that the precipitation impact on green-up dates shifts from postponing to advancing from the inner to the edge of NF,whereas precipitation dominantly postpones PF's green-up dates regardless of the proximity to edge.The LiNDVI exhibits higher sensitivity to precipitation at the edge areas,a phenomenon observed in NF but not in PF.Conclusions:These results suggest that the responses of forests to climate change vary with the distance to the edge.With increasing edge forests,which results from fragmentation caused by global changes,we anticipate that desynchronized phenological events along the distance to the edge could alter biogeochemical cycles and reshape ecosystem services such as energy flows,pollination duration,and the tourism industry.Therefore,we advocate for further investigations of edge effects to improve ecosystem modelling,enhance forest stability,and promote sustainable tourism.

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.

Forest management required for consistent carbon sink in China’s forest plantations

Background:Forest is the largest biomass carbon(C)pool in China,taking up a substantial amount of atmospheric carbon dioxide.Although it is well understood that planted forests(PFs)act as a large C sink,the contribution of human management to C storage enhancement remains obscure.Moreover,existing projections of forest C dynamics suffer from spatially inconsistent age and type information or neglected human management impacts.In this study,using developed PF age and type maps and data collected from 1371 forest plantation sites in China,we simulated biomass C stock change and quantified management impacts for the time period 2010-2050.Results:Results show that future forest biomass C increment might have been overestimated by 32.5%-107.5% in former studies.We also found that age-related growth will be by far the largest contributor to PF biomass C increment from 2010 to 2050(1.23±0.002 Pg C,1 Pg=10^(15) g=1 billion metric tons),followed by the impact of human management(0.57±0.02 Pg C),while the contribution of climate is slight(0.087±0.04 Pg C).Besides,an additional 0.24±0.07 Pg C can be stored if current PFs are all managed by 2050,resulting in a total increase of 2.13±0.05 Pg C.Conclusions:Forest management and age-related growth dominate the biomass C change in PFs,while the effect of climatic factors on the accumulation is minor.To achieve the ambitious goal of forest C stock enhancement by 3.5 Pg from 2020 to 2050,we advocate to improve the management of existing forests and reduce the requests for more lands for forest expansion,which helps mitigate potential conflicts with agricultural sectors.Our results highlight that appropriate planning and management are required for sustaining and enhancing biomass C sequestration in China’s PF.

Two Ultraviolet Radiation Datasets that Cover China

Ultraviolet（UV） radiation has significant effects on ecosystems, environments, and human health, as well as atmospheric processes and climate change. Two ultraviolet radiation datasets are described in this paper. One contains hourly observations of UV radiation measured at 40 Chinese Ecosystem Research Network stations from 2005 to 2015. CUV3 broadband radiometers were used to observe the UV radiation, with an accuracy of 5%, which meets the World Meteorology Organization＇s measurement standards. The extremum method was used to control the quality of the measured datasets. The other dataset contains daily cumulative UV radiation estimates that were calculated using an all-sky estimation model combined with a hybrid model. The reconstructed daily UV radiation data span from 1961 to 2014. The mean absolute bias error and root-mean-square error are smaller than 30% at most stations, and most of the mean bias error values are negative, which indicates underestimation of the UV radiation intensity. These datasets can improve our basic knowledge of the spatial and temporal variations in UV radiation. Additionally, these datasets can be used in studies of potential ozone formation and atmospheric oxidation, as well as simulations of ecological processes.

Rates of litter decomposition in terrestrial ecosystems:global patterns and controlling factors

Aims We aim to construct a comprehensive global database of litter decomposition rate(k value)estimated by surface floor litterbags,and investigate the direct and indirect effects of impact factors such as geographic factors(latitude and altitude),climatic factors(mean annual tempePlrature,MAT;mean annual precipitation,MAP)and litter quality factors(the contents of N,P,K,Ca,Mg and C:N ratio,lignin:N ratio)on litter decomposition.Methods We compiled a large data set of litter decomposition rates(k values)from 110 research sites and conducted simple,multiple regression and path analyses to explore the relationship between the k values and impact factors at the global scale.Important findings The k values tended to decrease with latitude(LAT)and lignin content(LIGN)of litter but increased with temperature,precipitation and nutrient concentrations at the large spatial scale.Single factor such as climate,litter quality and geographic variable could not explain litter decomposition rates well.However,the combination of total nutrient(TN)elements and C:N accounted for 70.2%of the variation in the litter decomposition rates.The combination of LAT,MAT,C:N and TN accounted for 87.54%of the variation in the litter decomposition rates.These results indicate that litter quality is the most important direct regulator of litter decomposition at the global scale.This data synthesis revealed significant relationships between litter decomposition rates and the combination of climatic factor(MAT)and litter quality(C:N,TN).The global-scale empirical relationships developed here are useful for a better understanding and modeling of the effects of litter quality and climatic factors on litter decomposition rates.

Effects of precipitation on soil organic carbon fractions in three subtropical forests in southern China

Aims The aim of this study was to investigate the effects of precipitation changes on soil organic carbon(SOC)fractions in subtropical forests where the precipitation pattern has been altered for decades.Methods We conducted field manipulations of precipitation,including ambient precipitation as a control(CK),double precipitation(DP)and no precipitation(NP),for 3 years in three forests with different stand ages(broadleaf forest[BF],mixed forest[MF]and pine forest[PF])in subtropical China.At the end of the experiment,soil samples were collected to assay SOC content,readily oxidizable organic carbon(ROC)and non-readily oxidizable organic carbon(NROC),as well as soil microbial biomass carbon(MBC),pH and total nitrogen content.Samples from the forest floors were also collected to analyze carbon(C)functional groups(i.e.alkyl C,aromatic C,O-alkyl C and carbonyl C).Furthermore,fine root biomass was measured periodically throughout the experiment.Important Findings Among the forests,ROC content did not exhibit any notable differences,while NROC content increased significantly with the stand age.This finding implied that the SOC accumulation observed in these forests resulted from the accumulation of NROC in the soil,a mechanism for SOC accumulation in the mature forests of southern China.Moreover,NP treatment led to significant reductions in both ROC and NROC content and therefore reduced the total SOC content in all of the studied forests.Such decreases may be due to the lower plant-derived C inputs(C quantity)and to the changes in SOC components(C quality)indicated by C functional groups analyses under NP treatment.DP treatment in all the forests also tended to decrease the SOC content,although the decreases were not statistically significant with the exception of SOC and ROC content in PF.This finding indicated that soils in MF and in BF may be more resistant to precipitation increases,possibly due to less water limitations under natural conditions in the two forests.Our results therefore highlight the different responses of SOC and its fractions to precipitation changes among the forests and suggest that further studies are needed to improve our understanding of SOC dynamics in such an important C sink region.

Changes in leaf nutrient traits and photosynthesis of four tree species: effects of elevated [CO_(2)], N fertilization and canopy positions

Aims Leaf traits of trees exposed to elevated[CO_(2)]in association with other environmental factors are poorly understood in tropical and subtropical regions.Our goal was to investigate the impacts of elevated[CO_(2)]and N fertilization on leaf traits in southern China.Methods Four tree species,Schima superba Gardn.et Champ.(S.superba),Ormosia pinnata(Lour.)Merr(O.pinnata),Castanopsis hystrix AC.DC.(C.hystrix)and Acmena acuminatissima(Blume)Merr.et Perry(A.acuminatissima)were studied in a factorial combination of atmospheric[CO_(2)](ambient at~390μmol mol^( -1)and elevated[CO_(2)]at~700μmol mol ^(-1))and N fertilization(ambient and ambient+100 kg N ha ^(-1)year^( -1))in open-top chambers in southern China for 5 years.Leaf mass per unit leaf area(LMA),leaf nutrient concentration and photosynthesis(A_(sat))were measured.Important Findings Results indicated that leaf traits and photosynthesis were affected differently by elevated[CO_(2)]and N fertilization among species.Elevated[CO_(2)]decreased LMA in all species,while N fertilization did not affect LMA.Leaf mass-based N concentration(N_(M))was significantly greater in O.pinnata and C.hystrix grown in elevated[CO_(2)]but was lower in S.superba.Leaf mass-based P concentration(P_(M))was significantly greater in C.hystrix and A.acuminatissima exposed to elevated[CO_(2)]but was lower in S.superba.N fertilization significantly increased P_(M) in O.pinnata but decreased P_(M) in S.superba.Photosynthetic stimulation in O.pinnata,C.hystrix and A.acuminatissima was sustained after 5 years of CO_(2)fumigation.N fertilization did not modify the effects of elevated[CO_(2)]on photosynthesis.Leaf traits(N_(M),N_(A),P_(M),P_(A))and light-saturated photosynthesis were decreased from the upper to lower canopy.Canopy position did not alter the responses of leaf traits and photosynthesis to elevated[CO_(2)].Results suggest that photosynthetic stimulation by elevated[CO_(2)]in native species in subtropical regions may be sustained in the long term.

Not vegetation itself but mis-revegetation reduces water resources

Increasing greening of planet Earth to slow down the rise of atmospheric CO_(2) concentrations is certainly desirable;however,its consequences on water resources are less affirmative and thus are a matter of wide concern.China,as the largest and most successful country of the world in terms of artificial revegetation,is naturally the focus of the concerns and warnings.Based on previous studies,we analyzed the mechanism for the effects of climate and watershed characteristics on water resources,explained various hydrological results and phenomena,and considered the ways in which water consumption by artificial revegetation projects can be reduced.Moreover,some guidelines are suggested for artificial revegetation at watershed scale with consideration of water resource sustainability.The findings of this study highlight the need for more top-down approaches when studying the mechanism of"forest and water".

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.

环境因子对叶氮、磷含量异速生长关系的属水平差异的影响

植物叶片中氮(N)、磷(P)含量的异速生长关系表明了植物对这两种元素的相对投入。而,现有的研究很少关注这一关系在分类单元之间的差异及其成因。本研究基于来自全国1733个样地,属于46个木本被子植物属的2483个叶片样品,利用异速生长方程([N]=α[P]β)分别计算了各属的叶氮、磷含量异速生长指数(β_(L))。然后利用谱系路径分析检验了这些属的气候和土壤生态位条件如何影响属间的β_(L)的差异。生活在贫磷土壤中的属更可能表现出更高的β_(L),即相对于氮而言更强的磷积累,这可能表明了植物对磷限制的抵抗倾向。此外,各属的β_(L)与相对应的土壤氮、磷含量异速生长指数(β_(S))正相关,这可能表明了叶养分的变化受制于作为来源的土壤养分的变化。最后,包括温度和湿度在内的气候因子不会直接影响β_(L)的属间变化,但可能通过调节土壤养分水平发挥间接的作用。谱系关系不会影响各属β_(L)随环境梯度的变化。这些结果揭示了植物对氮、磷摄取的权衡关系可能受属生态位,特别是土壤生态位的影响,表明了β_(L)可以作为一项反映植物养分利用特征如何响应生态位差异的功能属性。

Soil microbial biomass and community responses to experimental precipitation change:A meta-analysis

The activity of soil microbes is strongly constrained by water availability.However,it is unclear how microbial activity responds to spatial and temporal changes in precipitation,particularly to long-term precipitation changes.To identify the spatiotemporal patterns of microbial responses to precipitation changes of differing durations,we conducted a meta-analysis of data from 95 field studies with drought treatments and 109 field studies with elevated precipitation treatments.Our results indicated that microbial biomass carbon(MBC)decreased by 17% under drought and increased by 18% under elevated precipitation.Across all studies,the phospholipid fatty acid(PLFA)biomarkers for fungi and bacteria decreased significantly under drought but increased under elevated precipitation.In addition,the negative effect of drought on MBC tended to be greater at sites with a high aridity index,but the effect of elevated precipitation on MBC did not differ among sites.More importantly,the responses of MBC,fungal and bacterial PLFA abundance did not vary with treatment duration under drought,but under elevated precipitation,they increased in the first five years of treatment and declined thereafter.These results are important for our prediction of microbial responses to long-term precipitation change,because they imply that microbes acclimate to long-term elevated precipitation.