The relative controls of temperature and soil moisture on the start of carbon flux phenology and net ecosystem production in two alpine meadows on the Qinghai-Tibetan Plateau

Aims Variations in vegetation spring phenology are widely attributed to temperature in temperate and cold regions.However,temperature effect on phenology remains elusive in cold and arid/semiarid ecosystems because soil water condition also plays an important role in mediating phenology.Methods We used growing degree day(GDD)model and growing season index(GSI)model,coupling minimum temperature(T_(min))with soil moisture(SM)to explore the influence of heat requirement and hydroclimatic interaction on the start of carbon uptake period(SCUP)and net ecosystem productivity(NEP)in two alpine meadows with different precipitation regimes on the Qinghai-Tibet Plateau(QTP).One is the water-limited alpine steppe-meadow,and the other is the temperature-limited alpine shrub-meadow.Important Findings We observed two clear patterns linking GDD and GSI to SCUP:SCUP was similarly sensitive to variations in preseason GDD and GSI in the humid alpine shrub-meadow,while SCUP was more sensitive to the variability in preseason GSI than GDD in the semiarid alpine steppe-meadow.The divergent patterns indicated a balance of the limiting climatic factors between temperature and water availability.In the humid meadow,higher temperature sensitivity of SCUP could maximize thermal benefit without drought stress,as evidenced by the stronger linear correlation coefficient(R2)and Akaike’s information criterion(AIC)between observed SCUPs and those of simulated by GDD model.However,greater water sensitivity of SCUP could maximize the benefit of water in semiarid steppe-meadow,which is indicated by the stronger R2 and AIC between observed SCUPs and those of simulated by GSI model.Additionally,although SCUPs were determined by GDD in the alpine shrub-meadow ecosystem,NEP was both controlled by accumulative GSI in two alpine meadows.Our study highlights the impacts of hydroclimatic interaction on spring carbon flux phenology and vegetation productivity in the humid and semiarid alpine ecosystems.The results also suggest that water,together with temperature should be included in the models of phenology and carbon budget for alpine ecosystems in semiarid regions.These fi ndings have important implications for improving vegetation phenology models,thus advancing our understanding of the interplay between vegetation phenology,productivity and climate change in future.

Interannual Variation in Terrestrial Ecosystem Carbon Fluxes in China from 1981 to 1998

A dynamic biogeochemical model was used to estimate the responses of China's terrestrial net primary productivity (NPP), soil heterotrophic respiration (HR) and net ecosystem productivity (NEP) to changes in climate and atmospheric CO2 from 1981 to 1998. Results show that China's total NPP varied between 2.89 and 3.37 Gt C/a and had an increasing trend by 0.32% per year, HR varied between 2.89 and 3.21 Gt C/a and grew by 0.40% per year, Annual NEP varied between -0.32 and 0.25 Gt C but had no statistically significant interannual trend. The positive mean NEP indicates that China's terrestrial ecosystems were taking up carbon with a total carbon sequestration of 1.22 Gt C during the analysis period. The terrestrial NEP in China related to climate and atmospheric CO2 increases accounted for about 10% of the world's total and was similar to the level of the United States in the same period. The mean annual NEP for the analysis period was near to zero for most of the regions in China, but significantly positive NEP occurred in Northeast China Plain, the southeastern Xizang (Tibet) and Huang-Huai-Hai Plain, and negative NEP occurred in the Da Hinggan Mountains, Xiao Hinggan Mountains, Loess Plateau and Yunnan-Guizhou Plateau. China's climate at the time was warm and dry relative to other periods, so the estimated NEP is probably lower than the average level. China's terrestrial NEP may increase if climate becomes wetter but is likely to continue to decrease if the present warming and drying trend sustains.

京津风沙源治理区植被固碳能力估算及归因分析

植被固碳能力是陆地生态系统碳汇的基础,可通过净生态系统生产力(NEP)这一重要指标来反映。估算植被固碳能力是生态学和地表生态系统研究领域的共同科学问题,揭示其变化特征及其因素影响对于区域生态系统具有重要意义。以京津风沙源治理区为研究区,估算了2000—2020年京津风沙源治理区NEP,并利用趋势分析法和稳定性分析法等方法分析其时空变化特征,并利用地理探测器探究了影响NEP的自然因素与人类活动因素。结果显示:(1)2020年,京津风沙源治理区的NEP均值为110.09 gC m^(-2)a^(-1),碳汇区面积约为3.591×10~5 km^(2),占总面积的78.80%;(2)2000—2020年,京津风沙源治理区多年平均NEP为77.54 gC m^(-2)a^(-1),年际变化率为4.118 gC m^(-2)a^(-1),总体上呈上升趋势,研究区以NEP明显增加区为主,占比55.16%,主要分布在研究区南部,NEP呈下降趋势地区仅占比0.15%,主要分布在北部干旱草原沙地治理区,呈斑块状分布;(3)不同生态系统NEP从高到低依次为林地、农田和草地,林地固碳作用较强,未来林地固碳潜力较大,草地面积占研究区的70%,其总固碳量远超其他类型且呈增加趋势;(4)影响京津风沙源治理区NEP的主导因素为年降水量,其次,生态工程的实施也是NEP变化的重要影响因素,不同因素对京津风沙源治理区NEP的影响表现为双因子增强或非线性增强。围绕京津风沙源植被固碳能力估算以及影响因素的空间分异性,研究也在一定程度上提出了空间恢复的建议,以期为京津风沙源加强植被固碳能力以及生态修复等决策提供科学依据。

Comparing the seasonal variation of parameter estimation of ecosystem carbon exchange between alpine meadow and cropland in Heihe River Basin,northwestern China

Grasslands and agro-ecosystems occupy one-third of the global terrestrial area. However, great uncertainty still exists about their contributions to the global carbon cycle. This study used various combinations of a simple ecosystem respiration model and a photosynthesis model to simulate the influence of different climate factors, specifically radiation, temperature, and moisture, on the ecosystem carbon exchange at two dissimilar study sites. Using a typical alpine meadow site in a cold region and a typical cropland site in an arid region as cases, we investigated the response char- acteristics of productivity of grasslands and croplands to different environmental factors, and analyzed the seasonal change patterns of different model parameters. Parameter estimations and uncertainty analyses were performed based on a Bayesian approach. Our results indicated that： （1） the net ecosystem exchange （NEE） of alpine meadow and seeded maize during the growing season presented obvious diurnal and seasonal variation patterns. On the whole, the alpine meadow and seeded maize ecosystems were both apparent sinks for atmospheric CO2; （2） in the daytime, the mean NEE of the two ecosystems had the largest values in July and the lowest values in October. However, overall carbon uptake in the cropland was greater than in the alpine meadow from June to September; （3） at the alpine meadow site, temperature was the main limiting factor influencing the ecosystem carbon exchange variations during the growing season, while the sensitivity to water limitation was relatively small since there is abundant of rainfall in this region; （4） at the cropland site, both temperature and moisture were the most important limiting factors for the variations of ecosystem carbon exchanges during the growing season; and （5） some parameters had an obvious characteristic of seasonal patterns, while others had only small seasonal variations.

Analyzing the spatiotemporal evolution and driving forces of gross ecosystem product in the upper reaches of the Chaobai River Basin

The Chaobai River Basin,which is a crucial ecological barrier and primary water source area within the Beijing-Tianjin-Hebei region,possesses substantial ecological significance.The gross ecosystem product(GEP)in the Chaobai River Basin is a reflection of ecosystem conditions and quantifies nature’s contributions to humanity,which provides a basis for basin ecosystem service management and decision-making.This study investigated the spatiotemporal evolution of GEP in the upper Chaobai River Basin and explored the driving factors influencing GEP spatial differentiation.Ecosystem patterns from 2005 to 2020 were analyzed,and GEP was calculated for 2005,2010,2015,and 2020.The driving factors influencing GEP spatial differentiation were identified using the optimal parameter-based geographical detector(OPGD)model.The key findings are as follows:(1)From 2005 to 2020,the main ecosystem types were forest,grassland,and agriculture.Urban areas experienced significant changes,and conversions mainly occurred among urban,water,grassland and agricultural ecosystems.(2)Temporally,the GEP in the basin increased from 2005 to 2020,with regulation services dominating.At the county(district)scale,GEP exhibited a north-west-high and south-east-low pattern,showing spatial differences between per-unit-area GEP and county(district)GEP,while the spatial variations in per capita GEP and county(district)GEP were similar.(3)Differences in the spatial distribution of GEP were influenced by regional natural geographical and socioeconomic factors.Among these factors,gross domestic product,population density,and land-use degree density contributed significantly.Interactions among different driving forces noticeably impacted GEP spatial differentiation.These findings underscore the necessity of incorporating factors such as population density and the intensity of land-use development into ecosystem management decision-making processes in the upper reaches of the Chaobai River Basin.Future policies should be devised to regulate human activities,thereby ensuring the stability and enhancement of GEP.

Findings through the AsiaFlux network and a view toward the future

The preliminary results of long-term CO_(2)flux measurements at forest sites in East Asia are explained and compared with each other.The features of seasonal variation of CO_(2)fluxes are different among deciduous-broadleaf,evergreen-coniferous,deciduous-coniferous and tropical forests in East Asia,and the causes of difference are discussed.The integrated yearly NEP(net ecosystem production)estimated from the CO_(2)flux by eddy covariance method in various forests of East Asia has a notable difference in the range of 2 to 8 tC ha^(-1)yr^(-1).The main factors of this difference are the annual mean temperature and tree species.Furthermore,the remaining issues are discussed,such as the quantitative estimation of the CO_(2)flux by the eddy covariance method and the synthetic analysis of the carbon budget under collaborations with biological survey.

A process model for simulating net primary productivity (NPP) based on the interaction of water-heat process and nitrogen: a case study in Lantsang valley

Terrestrial carbon cycle and the global atmospheric CO2 budget are important foci in global climate change research. Simulating net primary productivity （NPP） of terrestrial ecosystems is important for carbon cycle research. In this study, a plant-atmosphere-soil continuum nitrogen （N） cycling model was developed and incorporated into the Boreal Ecosystem Productivity Simulator （BEPS） model. With the established database （leaf area index, land cover, daily meteorology data, vegetation and soil） at a 1 km resolution, daily maps of NPP for Lantsang valley in 2007 were produced, and the spatial-temporal patterns of NPP and mechanisms of its responses to soil N level were further explored. The total NPP and mean NPP of Lantsang valley in 2007 were 66.5 Tg C and 416 g？m-2？a-1 C, respectively. In addition, statistical analysis of NPP of different land cover types was conducted and investigated. Compared with BEPS model （without considering nitrogen effect）, it was inferred that the plant carbon fixing for the upstream of Lantsang valley was also limited by soil available nitrogen besides temperature and precipitation. However, nitrogen has no evident limitation to NPP accumulation of broadleaf forest, which mainly distributed in the downstream of Lantsang valley.

Effects of Environmental Conditions and Aboveground Biomass on CO2 Budget in Phragmites australis Wetland of Jiaozhou Bay,China

Estuarial saline wetlands have been recognized as a vital role in CO_2 cycling.However,insufficient attention has been paid to estimating CO_2 fluxes from estuarial saline wetlands.In this study,the static chamber-gas chromatography(GC) method was used to quantify CO_2 budget of an estuarial saline reed(Phragmites australis) wetland in Jiaozhou Bay in Qingdao City of Shandong Province,China during the reed growing season(May to October) in 2014.The CO_2 budget study involved net ecosystem CO_2 exchange(NEE),ecosystem respiration(Reco) and gross primary production(GPP).Temporal variation in CO_2 budget and the impact of air/soil temperature,illumination intensity and aboveground biomass exerted on CO_2 budget were analyzed.Results indicated that the wetland was acting as a net sink of 1129.16 g/m^2 during the entire growing season.Moreover,the values of Reco and GPP were 1744.89 g/m^2 and 2874.05 g/m^2,respectively;the ratio of Reco and GPP was 0.61.Diurnal and monthly patterns of CO_2 budget varied significantly during the study period.Reco showed exponential relationships with air temperature and soil temperature at 5 cm,10 cm,20 cm depths,and soil temperature at 5 cm depth was the most crucial influence factor among them.Meanwhile,temperature sensitivity(Q10) of Reco was negatively correlated with soil temperature.Light and temperature exerted strong controls over NEE and GPP.Aboveground biomass over the whole growing season showed non-linear relationships with CO_2 budget,while those during the early and peak growing season showed significant linear relationships with CO_2 budget.This research provides valuable reference for CO_2 exchange in estuarial saline wetland ecosystem.

Evaluating and quantifying the effect of various spruce budworm intervention strategies on forest carbon dynamics in Atlantic Canada

Spruce budworm (SBW) outbreaks are one of the most devastating natural disturbances in spruce-balsam fir forests of eastern North America. Both early intervention strategy (EIS) and foliage protection strategy (FP) are being tested to limit forest losses, but the quantitative impact on forest carbon (C) dynamics is still unclear. In this study, we designed 19 separate scenarios of no intervention or varying success of EIS, FP, and their combination on SBW caused defoliation and mortality. We then used the TRIPLEX-Insect model to quantify their effects on forest C dynamics in the forests of the four provinces of Atlantic Canada. A scenario applying FP to 10%of the area with the greatest potential C losses of living biomass, protecting foliage in 10%of the forests is more realistic than higher proportion of FP given the high cost and large areas involved, resulted in reducing average cumulative net ecosystem productivity (NEP) from 2020 to 2039 by 56%–127%compared to a no outbreak scenario.Our results showed that FP would have to be applied everywhere to reduce tree mortality and increase NEP more than 8 years of successful EIS applied. However, if EIS can be successfully implemented for 12 years, it will maintain more forest C than FP applied everywhere during a moderate outbreak. We also found that the combination of EIS followed by FP in 10%of the areas disturbed by the SBW could maintain average cumulative NEP at similar levels to no defoliation in every province of Atlantic Canada. Black/red spruce forests younger than 60years old underwent the smallest changes in C dynamics whether using EIS, FP, or both. This highlights the importance of forest species, forest age, and their interactions on the effectiveness of a treatment during SBW outbreak. Overall, 31%–76%of the study area in Atlantic Canada could convert from a C sink to a source by 2039,if no protective measures are used under the worst-case scenarios, thus contributing to future climate warming.

Carbon dioxide fluxes of tundra vegetation communities on an esker top in the low-Arctic

Previous studies have shown that carbon dioxide fluxes vary considerably among Arctic environments and it is important to assess these differences in order to develop our understanding of the role of Arctic tundra in the global carbon cycle. Although many previous studies have examined tundra carbon dioxide fluxes, few have concentrated on elevated terrain(hills and ridge tops) that is exposed to harsh environmental conditions resulting in sparse vegetation cover and seemingly low productivity. In this study we measured carbon dioxide(CO2) exchange of four common tundra communities on the crest of an esker located in the central Canadian low-Arctic. The objectives were to quantify and compare CO2 fluxes from these communities, investigate responses to environmental variables and qualitatively compare fluxes with those from similar communities growing in less harsh lowland tundra environments. Measurements made during July and August 2010 show there was little difference in net ecosystem exchange(NEE) and gross ecosystem production(GEP) among the three deciduous shrub communities, Arctous alpina, Betula glandulosa and Vaccinium uliginosum, with means ranging from -4.09 to -6.57 μmol·m^-2·s^-1 and -7.92 to -9.24 μmol·m^-2·s^-1, respectively. Empetrum nigrum communities had significantly smaller mean NEE and GEP(-1.74 and -4.08 μmol·m^-2·s^-1, respectively). Ecosystem respiration(ER) was similar for all communities(2.56 to 3.03 μmol·m^-2·s^-1), except the B. glandulosa community which had a larger mean flux(4.66 μmol·m^-2·s^-1). Overall, fluxes for these esker-top communities were near the upper range of fluxes reported for other tundra communities. ER was related to soil temperature in all of the communities. Only B. glandulosa GEP and ER showed sensitivity to a persistent decline in soil moisture throughout the study. These findings may have important implications for how esker tops would be treated in construction of regional carbon budgets and for predicting the impacts of climate change on Arctic tundra future carbon budgets.

Spatial and Temporal Analysis of Carbon Sequestrations in the Conterminous United States

This study develops geospatial analysis of terrestrial carbon exchange for the conterminous United State and estimates large-scale NEP （net ecosystem production） dynamic from 2008 to 2013. We apply land-use and land-cover data in order to coherently include cropland, forest, wetland and other ecologically active landscapes in the mapping. Our results show a distribution of high harvest carbon release in the Corn Belt states, in addition to hot spots around the US in areas like Southern California and Arizona. Harvest carbon is low in areas in the southern United States, and central/southern Appalachian Mountains. We identify NEP changes for coupled agricultural, forest and other high-carbon-uptake ecosystems systems, conversions to and from crop, and land in frequent conversion among forest, wetland, pasture and rangeland. Findings from this study will provide important information to support and promote the co-production of science and decision-making.

Effect of water stress on ecosystem photosynthesis and respiration of a Leymus chinensis steppe in Inner Mongolia

Many studies on global climate have forecast major changes in the amounts and spatial patterns of precipitation that may significantly affect temperate grasslands in arid and semi-arid regions. As a part of ChinaFLUX, eddy covariance flux measurements were made at a semi-arid Leymus chinensis steppe in Inner Mongolia, China during 2003-2004 to quantify the response of carbon exchange to environmental changes. Results showed that gross ecosystem production (FGEP) and ecosystem respiration (Reco) of the steppe were significantly depressed by water stress due to lack of precipitation during the growing season. Temperature was the dominant factor affecting FGEP and Reco in 2003, whereas soil moisture imposed a significant influence on both Reco and FGEP in 2004. Under wet conditions, Reco showed an exponentially increasing trend with temperature (Q10 = 2.0), but an apparent reduction in the value of Reco and its temperature sensitivity were observed during the periods of water stress (Q10=1.6). Both heat and water stress can cause decrease in FGEP. The sea-sonality of ecosystem carbon exchange was strongly correlated with the variation of precipitation. With less precipitation in 2003, the steppe sequestrated carbon in June and July, and went into a senescence in early August due to water stress. As compared to 2003, the severe drought during the spring of 2004 delayed the growth of the steppe until late June, and the steppe became a CO2 sink from early July until mid-September, with ample precipitation in August. The semi-arid steppe released a total of 9.7 g C·m-2 from May 16 to the end of September 2003, whereas the net carbon budget during the same period in 2004 was close to zero. Long-term measurements over various grasslands are needed to quantify carbon balance in temperate grasslands.

Altitudinal variation of ecosystem CO_(2) fluxes in an alpine grassland from 3600 to 4200 m

Aims Recent studies have recognized the alpine grasslands on the Qinghai-Tibetan plateau as a significant sink for atmospheric CO_(2).The carbon-sink strength may differ among grassland ecosystems at various altitudes because of contrasting biotic and physical environments.This study aims(i)to clarify the altitudinal pattern of ecosystem CO_(2) fluxes,including gross primary production(GPP),daytime ecosystem respiration(Redaytime)and net ecosystem production(NEP),during the period with peak above-ground biomass;and(ii)to elucidate the effects of biotic and abiotic factors on the altitudinal variation of ecosystem CO_(2) fluxes.Methods Ecosystem CO_(2) fluxes and abiotic and biotic environmental factors were measured in an alpine grassland at four altitudes from 3600 to 4200 m along a slope of the Qilian Mountains on the northwestern Qinghai-Tibetan Plateau during the growing season of 2007.We used a closed-chamber method combined with shade screens and an opaque cloth to measure several carbon fluxes,GPP,Redaytime and NEP,and factors,light-response curve for GPP and temperature sensitivity of Redaytime.Above-and below-ground biomasses and soil C and N contents at each measurement point were also measured.Important Findings(i)Altitudinal pattern of ecosystem CO_(2) fluxes:The maximum net ecosystem CO_(2) flux(NEPmax),i.e.the potential ecosystem CO_(2) sink strength,was markedly different among the four altitudes.NEPmax was higher at the highest and lowest sites,ap proximately
7.460.9 and
6.760.6 lmol CO_(2) m^(-2)s^(-1)(mean 6 standard error),respectively,but smaller at the intermediate altitude sites(3800 and 4000 m).The altitudinal pattern of maximum gross primary production was similar to that of NEPmax.The Redaytime,however,was significantly higher at the lowest altitude(3.460.3 lmol CO_(2) m^(-2)s^(-1))than at the other three altitudes.(ii)Altitudinal variation of vegetation biomass:The aboveground biomass was higher at the highest altitude(154627 g DW m
2)than at the other altitudes,which we attribute mainly to the large biomass in cushion plants at the highest altitude.The small above-ground biomass at the lower altitudes was probably due to heavy grazing during the growing season.(iii)Features of ecosystem CO_(2) fluxes:Redaytime and GPP were positively correlated with above-ground biomass.The low ratio of Redaytime to GPP at either the measurement point or the site level suggests that CO_(2) uptake efficiency tends to be higher at higher altitudes,which indicates a high potential sink strength for atmospheric CO_(2) despite the low temperature at high altitudes.The results suggest that the effect of grazing intensity on ecosystem carbon dynamics,partly by decreasing vegetation biomass,should be clarified further.

Basic Principles of Gross Ecosystem Product(GEP)Accounting

Gross ecosystem product(GEP) is the gross value of all ecosystem products and services provided by ecosystems for human society. In practice, GEP measures the ecosystems’ contributions to human well-being and constitutes one of the core issues in the construction of ecological civilization systems. Currently, GEP accounting faces a series of problems, such as the inconsistency of accounting subjects and a lack of accounting standards,the result of which is the non-reproducibility and weak applicability of accounting results. In this paper, mainstream models for ecosystem service valuation are summarized in a systematic manner. On this basis, eight basic principles are established for screening accounting indicators: biological productivity, human benefits, production territoriality, current increment, actual effectiveness, physical metrizability, data availability, and harmlessness. Next, a series of ecosystem service subjects are identified that need to be excluded from accounting, and the detailed reasons for their exclusion are presented. Finally, three ideas for improving GEP accounting are offered from the perspectives of the relationship between biological production and human production, the circulation-transport relationship and spatial differences, and harms to the ecosystem carrying capacity. The purpose is to provide positive considerations aimed at promoting the socio-economic applications of accounting and to contribute to the scientific quantification of the values of ecological products.

The role of shrub(Potentilla fruticosa)on ecosystem CO_(2) fluxes in an alpine shrub meadow

Aims Recent studies have shown that alpine meadows on the Qinghai-Tibetan plateau act as significant CO_(2)sinks.On the plateau,alpine shrub meadow is one of typical grassland ecosystems.The major alpine shrub on the plateau is Potentilla fruticosa L.(Rosaceae),which is distributed widely from 3200 to 4000 m.Shrub species play an important role on carbon sequestration in grassland ecosystems.In addition,alpine shrubs are sensitive to climate change such as global warming.Considering global warming,the biomass and productivity of P.fruticosa will increase on Qinghai-Tibetan Plateau.Thus,understanding the carbon dynamics in alpine shrub meadow and the role of shrubs around the upper distribution limit at present is essential to predict the change in carbon sequestration on the plateau.However,the role of shrubs on the carbon dynamics in alpine shrub meadow remains unclear.The objectives of the present study were to evaluate the magnitude of CO_(2)exchange of P.fruticosa shrub patches around the upper distribution limit and to elucidate the role of P.fruticosa on ecosystem CO_(2)fluxes in an alpine meadow.Methods We used the static acrylic chamber technique to measure and estimate the net ecosystem productivity(NEP),ecosystem respiration(Re),and gross primary productivity(GPP)of P.fruticosa shrub patches at three elevations around the species’upper distribution limit.Ecosystem CO_(2)fluxes and environmental factors were measured from 17 to 20 July 2008 at 3400,3600,and 3800 m a.s.l.We examined the maximum GPP at infinite light(GPPmax)and maximum Re(Remax)during the experimental time at each elevation in relation to aboveground biomass and environmental factors,including air and soil temperature,and soil water content.Important Findings Patches of P.fruticosa around the species’upper distribution limit absorbed CO_(2),at least during the daytime.Maximum NEP at infinite light(NEPmax)and GPPmax of shrub patches in the alpine meadow varied among the three elevations,with the highest values at 3400 m and the lowest at 3800 m.GPPmax was positively correlated with the green biomass of P.fruticosa more strongly than with total green biomass,suggesting that P.fruticosa is the major contributor to CO_(2)uptake in the alpine shrub meadow.Air temperature influenced the potential GPPat the shrub-patch scale.Remax was correlated with aboveground biomass and Remax normalized by aboveground biomass was influenced by soil water content.Potentilla fruticosa height(biomass)and frequency increased clearly as elevation decreased,which promotes the large-scale spatial variation of carbon uptake and the strength of the carbon sink at lower elevations.

Ecosystem Carbon Allocation of a Temperate Mixed Forest and a Subtropical Evergreen Forest in China

Ecosystem carbon allocation can indicate ecosystem carbon cycling visually through its quantification within different carbon pools and carbon exchange.Using the ecological inventory and eddy covariance measurement applied to both a mature temperate mixed forest in Changbai Mountain (CBM)and a mature subtropical evergreen forest in Dinghu Mountain (DHM),we partitioned the ecosystem carbon pool and carbon exchange into different components,determined the allocation and analyzed relationships within those components.Generally, the total carbon stock of CBM was slightly higher than that of DHM due to a higher carbon stock in the arbor layer at CBM.It was interesting that the proportions of carbon stock in vegetation,soil and litter were similar for the two mature forests.The ratio of vegetation carbon pool to soil carbon stock was 1.5 at CBM and 1.3 at DHM.However, more carbon was allocated to the trunk and root from the vegetation carbon pool at CBM,while more carbon was allocated to foliage and branches at DHM.Moreover,77% of soil carbon storage was limited to the surface soil layer (0-20cm),while there was still plentiful carbon stored in the deeper soil layers at DHM.The root/shoot ratios were 0.30 and 0.25 for CBM and DHM,respectively.The rates of net ecosystem productivity (NPP)to gross ecosystem productivity (GPP)were 0.76 and 0.58,and the ratios of ecosystem respiration (Re)to GPP were 0.98and 0.87for CBM and DHM,respectively.The net ecosystem carbon exchange/productivity (NEP)was 0.24t C ha^-1 yr^-1 for CBM and 3.38t C ha^-1 yr^-1 for DHM.Due to the common seasonal and inter-annual variations of ecosystem carbon exchange resulting from the influence of environmental factors,it was necessary to use the long record dataset to evaluate the ecosystem sink capacity.

Carbon and nitrogen dynamics in a Pinus densiflora forest with low and high stand densities

Aims Understanding carbon(C)and nitrogen(N)dynamics and their dependence on the stand density of an even-aged,mature forest provides knowledge that is important for forest management.This study investigated the differences in ecosystem total C and N storage and flux between a low-density stand(LD)and a high-density stand(HD)and examined the effects of stand density on aboveground net primary productivity(ANPP),total belowground C allocation(TBCA)and net ecosystem production(NEP)in a naturally regenerated,65-to 75-year-old Pinus densiflora S.et Z.forest.Methods LD(450 trees ha^(−1))and HD(842 trees ha^(−1))were established in an even-aged,mature P.densiflora forest in September 2006.The forest had been naturally regenerated following harvesting,and the stand density was naturally maintained without any artificial management such as thinning.The diameter at breast height(DBH≥5.0cm)of all live stems within the stands was measured yearly from 2007 to 2011.To compare C and N storage and fluxes in LD and HD,C and N pools in aboveground and belowground biomass,the forest floor,coarse woody debris(CWD)and soil;soil CO_(2) efflux(R_(S));autotrophic respiration(R_(A));litter production;and soil N availability were measured.Further,ANPP,TBCA and NEP were estimated from plot-based measurement data.Important Findings Ecosystem C(Mg C ha^(−1))and N(Mg N ha^(−1))storage was,respectively,173.0±7.3(mean±SE)and 4.69±0.30 for LD and 162±11.8 and 4.08±0.18 for HD.There were no significant differences in C and N storage in the ecosystem components,except for soils,between the two stands.In contrast,there were significant differences in aboveground ANPP and TBCA between the two stands(P<0.05).Litterfall,biomass increment and R_(S) were major C flux components with values of,respectively,3.89,3.74 and 9.07 Mg C ha^(−1) year^(−1) in LD and 3.15,2.94 and 7.06 Mg C ha^(−1) year^(−1) in HD.Biometric-based NEP(Mg C ha^(−1) year^(−1))was 4.18 in LD and 5.50 in HD.Although the even-aged,mature P.densiflora forest had similar C and N allocation patterns,it showed different C and N dynamics depending on stand density.The results of the current study will be useful for elucidating the effects of stand density on C and N storage and fluxes,which are important issues in managing natural mature forest ecosystems.

Seasonal drought effects on carbon sequestration of a mid-subtropical planted forest of southeastern China

Continuous measurement of carbon dioxide exchange using the eddy covariance (EC) technique is made at the Qianyanzhou mid-subtropical planted forest as part of the ChinaFLUX network. Qianyanzhou planted forest is affected by typical subtropical continental monsoon climate. It has plentiful water and heat resource but is in inconsistency of its seasonal distribution in the mid-subtropical region, thus seasonal drought frequently occurs in this planted forest. In this study, seasonal drought effect on ecosystem carbon sequestration was analyzed based on net ecosystem productivity (NEP), ecosystem respiration (RE) and gross ecosystem productivity (GEP) at the month scale in 2003 and 2004. In this drought-stressed planted forest, ecosystem carbon sequestration showed a clear seasonality, with low rates during seasonal drought and in winter. The declining degree of ecosystem carbon sequestration under the seasonal drought condition was determined by the accumulation of soil moisture deficits and a co-occurrence of high temperatures. Different drought effects are expected for RE and GEP. The net effect of ecosystem carbon balance depends on how these two quantities are affected relatively to each other. Summer drought and heat wave are two aspects of weather that likely play an important part in the annual NEP of forest in this region.

Patterns and ecological determinants of woody plant height in eastern Eurasia and its relation to primary productivity

Aims Plant height is a key functional trait related to aboveground bio-mass,leaf photosynthesis and plant fitness.However,large-scale geographical patterns in community-average plant height(cAPH)of woody species and drivers of these patterns across different life forms remain hotly debated.Moreover,whether cAPH could be used as a predictor of ecosystem primary productivity is unknown.Methods We compiled mature height and distributions of 11422 woody spe-cies in eastern Eurasia,and estimated geographic patterns in cAPH for different taxonomic groups and life forms.then we evaluated the effects of environmental(including current climate and historical climate change since the Last Glacial Maximum(LGM))and evolutionary factors on cAPH.Lastly,we compared the predictive power of cAPH on primary productivity with that of LiDAR-derived canopy-height data from a global survey.Important Findings Geographic patterns of cAPH and their drivers differed among taxonomic groups and life forms.the strongest predictor for cAPH of all woody species combined,angiosperms,all dicots and deciduous dicots was actual evapotranspiration,while temperature was the strongest pre-dictor for cAPH of monocots and tree,shrub and evergreen dicots,and water availability for gymnosperms.Historical climate change since the LGM had only weak effects on cAPH.No phylogenetic signal was detected in family-wise average height,which was also unrelated to the tested environmental factors.Finally,we found a strong correlation between cAPH and ecosystem primary productivity.Primary productivity showed a weaker relationship with cAPH of the tallest species within a grid cell and no relationship with LiDAR-derived canopy height reported in the global survey.Our findings suggest that current climate rather than historical climate change and evolutionary history determine the geographical patterns in cAPH.However,the relative effects of climatic factors representing environmental energy and water availability on spatial variations of cAPH vary among plant life forms.Moreover,our results also suggest that cAPH can be used as a good predictor of ecosystem primary productivity.

Evaluation of the carbon sequestration of Zhalong Wetland under climate change

Wetland ecosystems are crucial to the global carbon cycle.In this study,the Zhalong Wetland was investigated.Based on remote sensing and meteorological observation data from 1975-2018 and the downscaled fifth phase of the coupled model intercomparison project(CMIP5)climate projection dataset from 1961-2100,the parameters of a net primary productivity(NPP)climatic potential productivity model were adjusted,and the simulation ability of the CMIP5 coupled models was evaluated.On this basis,we analysed the spatial and temporal variations of land cover types and landscape transformation processes in the Zhalong Nature Reserve over the past 44 years.We also evaluated the influence of climate change on the NPP of the vegetation,microbial heterotrophic respiration(Rh),and net ecosystem productivity(NEP)of the Zhalong Wetland and predicted the carbon sequestration potential of the Zhalong Wetland from 2019-2029 under the representative concentration pathways(RCP)4.5 and RCP 8.5 scenarios.Our results indicate the following:(1)Herbaceous bog was the primary land cover type of the Zhalong Nature Reserve,occupying an average area of 1168.02±224.05 km^(2),equivalent to 51.84% of the total reserve area.(2)Since 1975,the Zhalong Nature Reserve has undergone a dry-wet-dry transformation process.Excluding several wet periods during the mid-1980s to early 1990s,the reserve has remained a dry habitat,with particularly severe conditions from 2000 onwards.(3)The 1975-2018 mean NPP,Rh,and NEP values of the Zhalong Wetland were 500.21±52.76,337.59±10.80,and 162.62±45.56 gC·m^(2)·a^(-1),respectively,and an evaluation of the carbon balance indicated that the reserve served as a carbon sink.(4)From 1975-2018,NPP showed a significant linear increase,Rh showed a highly significant linear increase,while the increase in the carbon absorption rate was smaller than the increase in the carbon release rate.(5)Variations in NPP and NEP were precipitation-driven,with the correlations of NPP and NEP with annual precipitation and summer precipitation being highly significantly positive(P<0.001);variations in Rh were temperature-driven,with the correlations of Rh with the average annual,summer,and autumn temperatures being highly significantly positive(P<0.001).The interaction of precipitation and temperature enhances the impact on NPP,Rh and NEP.(6)Under the RCP 4.5 and RCP 8.5 scenarios,the predicted carbon sequestration by the Zhalong Wetland from 2019-2029 was 2.421(±0.225)× 10^(11) gC·a^(-1) and 2.407(±0.382)× 10^(11)gC·a^(-1),respectively,which were both lower than the mean carbon sequestration during the last 44 years(2.467(±0.950)× 10^(11) gC·a^(-1)).Future climate change may negatively contribute to the carbon sequestration potential of the Zhalong Wetland.The results of the present study are significant for enhancing the abilities of integrated eco-meteorological moni-toring,evaluation,and early warning systems for wetlands.