Lower Net Primary Productivity Research Articles

Ecological processes and biogeochemical cycling in salt marshes: synthesis of studies in the Bahía Blanca estuary (Argentina)

Here we offer an integrative review of biogeochemical cycling of carbon, nitrogen, phosphorus, and several metals in salt marshes of the Bahia Blanca Estuary, located in South America, which is a region underrepresented in the literature. The dominant species, Spartina alterniflora and Sarcocornia perennis, have low net aboveground primary productivity but play substantial and contrasting roles in the biogeochemical cycling of elements. S. perennis was more efficient at metal sequestration, whereas S. alterniflora was important in the immobilization of phosphorus. Because of the differences in net aboveground primary productivity between high and low marsh, plant position should be considered to evaluate the role of S. alterniflora on biogeochemical cycles. Some elements were also in high concentrations in belowground tissues but, based on our data, we could not accurately estimate net belowground primary productivity, a key process to evaluate elemental cycling in salt marshes. In spite of uncertainties in the estimations, the slower decomposition rates in S. alterniflora would be indicative of a higher contribution to the long-term storage of nutrients and metals within the marsh. Regardless shortcomings, our work represents a valuable tool for comparisons with salt marshes worldwide.

Power in numbers. Drivers of high population density in insular lizards

AbstractAimIslands organisms usually have fewer predator and competitor species than mainland ones. This is thought to result in high population densities on islands. We hypothesize that insular lizards have denser populations than mainland species and that density, in general, is negatively correlated with competitor and predator richness.LocationGlobal.MethodsWe compared densities of 346 lizard species on islands and the mainland while examining the relationship between density and, predator and competitor richness, primary productivity, seasonality and island area. We controlled for phylogenetic non‐independence, body mass and study area, which are known to strongly affect population density.ResultsInsular populations (especially on snake‐free islands) are denser than mainland ones. Mainland populations of lizard species that also inhabit islands were denser than those of species that do not inhabit islands. Population density was the highest on islands with low net primary productivity and was not significantly affected by competitor or predator richness. Moreover, insular populations show high density regardless of island area.Main conclusionsWe conclude that the ability of mainland species to reach high population densities may increase their chances in reaching and successfully colonizing islands. We postulate that population density may be affected by predator and competitor density rather than by their richness. Density increase on islands may result not from the environmental simplicity of island faunas but through propagule sorting or pressure.

Photosynthetic production in the central Arctic Ocean during the record sea-ice minimum in 2012

Abstract. The ice-covered central Arctic Ocean is characterized by low primary productivity due to light and nutrient limitations. The recent reduction in ice cover has the potential to substantially increase phytoplankton primary production, but little is yet known about the fate of the ice-associated primary production and of the nutrient supply with increasing warming. This study presents results from the central Arctic Ocean collected during summer 2012, when sea-ice extent reached its lowest ever recorded since the onset of satellite observations. Net primary productivity (NPP) was measured in the water column, sea ice and melt ponds by 14CO2 uptake at different irradiances. Photosynthesis vs. irradiance (PI) curves were established in laboratory experiments and used to upscale measured NPP to the deep Eurasian Basin (north of 78° N) using the irradiance-based Central Arctic Ocean Primary Productivity (CAOPP) model. In addition, new annual production has been calculated from the seasonal nutrient drawdown in the mixed layer since last winter. Results show that ice algae can contribute up to 60% to primary production in the central Arctic Ocean at the end of the productive season (August–September). The ice-covered water column has lower NPP rates than open water due to light limitation in late summer. As indicated by the nutrient ratios in the euphotic zone, nitrate was limiting primary production in the deep Eurasian Basin close to the Laptev Sea area, while silicate was the main limiting nutrient at the ice margin near the Atlantic inflow. Although sea-ice cover was substantially reduced in 2012, total annual new production in the Eurasian Basin was 17 ± 7 Tg C yr−1, which is within the range of estimates of previous years. However, when adding the contribution by sub-ice algae, the annual production for the deep Eurasian Basin (north of 78° N) could double previous estimates for that area with a surplus of 16 Tg C yr−1. Our data suggest that sub-ice algae are an important component of the productivity in the ice-covered Eurasian Basin of the central Arctic Ocean. It remains an important question whether their contribution to productivity is on the rise with thinning ice, or whether it will decline due to overall sea-ice retreat and be replaced by phytoplankton.

Elevation, moisture and shade drive the functional and phylogenetic meadow communities’ assembly in the northeastern Tibetan Plateau

Despite a long history of alpine meadows studies, uncertainty remains about the importance of environmental factors in structuring their assembly. We examined the functional and phylogenetic structure of 170 alpine Tibetan meadow communities in relation to elevation, soil moisture and shade. Functional community structure was estimated with both communityweighted mean (CWM) trait values for specific leaf area (SLA), plant height and seed mass and functional diversity (Rao’s quadratic index) for their traits individually and in combination (multivariate functional diversity). We found that shade induced by woody plants significantly increased the phylogenetic diversity and functional diversity of SLA of co-occurring species, suggesting that woody plants behave as “ecosystem engineers” creating a different environment that allows the existence of shade tolerant species and thereby facilitates the coexistence of plant species with different light resource acquisition strategies. We also found evidence for a clear decrease in phylogenetic diversity, CWM and functional diversity related to plant height in the two extreme, both the dry and wet, soil moisture conditions. This indicates that both drought and excess moisture may act as environmental filters selecting species with close phylogenetic relationships and similar height. Moreover, we detected significant decreases in both CWM and functional diversity for seed mass along elevational gradients, suggesting that low net primary productivity (NPP) limits seed size. Finally, because of different individual trait responses to environmental factors, the multivariate functional diversity did not change across environmental gradients. This lack of multivariate response supports the hypothesis that multiple processes, such as environmental filtering, competition and facilitation, may operate simultaneously and exert opposing effects on community assembly along different niche (e.g., water use, light acquisition) axes, resulting in no overall functional community structure change. This contrast between individual and multivariate trait patterns highlights the importance of examining individual traits linked with different ecological processes to better understand the mechanisms of community assembly.

Soil Carbon Dynamics of Transition to Pacific Northwest Cellulosic Ethanol Feedstock Production

Cellulosic ethanol commercialization promises to produce energy from agricultural biomass. Available biomass depends on plant net primary productivity (NPP) and crop type, which maintain total soil organic carbon (TOC). Effect of crop-type, residue removal, and NPP on ethanol yield and TOC levels were assessed by means of a three-pool C model derived from long-term soil incubation, acid hydrolysis, and curve fitting of a nonlinear regression model. A 2-yr field study consisting of three input regimes (Low, Medium, or High NPP), three crops [corn (Zea mays L.), wheat (Triticum aestivum, L.), and switchgrass (SG, Panicum virgatum L., cv. Blackwell)], and two harvest levels [residue removed (R) or residue not removed (NR)] was conducted near Prosser, WA, USA. After 2 yr, ethanol yield of all crops were similar under Low NPP while ethanol yield of SG under Medium and High NPP was significantly greater than that of corn or wheat under the same NPP. Switchgrass significantly contributed to active [mean residence time (MRT) 500 yr) soil C pools. Other crops had net zero or significantly reduced C pools. During a transition to cellulosic energy production, SG will contribute to soil C maintenance across a range of potential net productivity.

地形对草甸草原植被生产力分布格局的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 地形对草甸草原植被生产力分布格局的影响 DOI: 10.5846/stxb201306201748 作者: 作者单位: 鲁东大学地理与规划学院,中国环境科学研究院生态研究所,中国环境科学研究院生态研究所,中国环境科学研究院生态研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金(41271193);国家环境保护公益性行业科研专项(200909021) Impact of topography on the spatial distribution pattern of net primary productivity in a meadow Author: Affiliation: Ludong University,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:草原植被生产力在陆地生态系统碳平衡分析中扮演重要角色,而地形作为影响植被生产力(NPP)分布格局的重要环境因子在已有的草原遥感监测研究中没有被充分重视。以USGS和GLCF共享MODIS和DEM数据为数据源,选取呼伦贝尔辉河湿地保护区草甸草原核心区为研究对象,在地面光谱生物量模型构建的基础上,采用ARCGIS的空间分析功能对呼伦贝尔草甸草原2000-2012年的NPP分布格局进行了分析。研究结果表明,地形对草甸草原植被生产力分布格局有显著的影响。在海拔高度、坡度和坡向等3个地形因子中,海拔高度引起的NPP变化幅度最大,坡度次之,坡向最小。在总体特征上,海拔高度每升高10m,生产力增加4.78 g/m2;坡度每增加1°生产力增加-1.42 g/m2;N坡向植被生产力水平最高(184.8 g/m2),西南(SW)坡向最低(173.3 g/m2)。从不同地形因子的分布面积特点判断,地形对草甸草原NPP的影响尺度介于土壤环境异质性和草场类型异质性之间。不同生产力水平年份对生产力分布格局的影响趋势一致,但变化幅度不同,在中等生产力水平年份NPP变幅最大。 Abstract:Net primary productivity (NPP) of grassland plays an important role in terrestrial ecosystems, and its spatial heterogeneous traits have significant influence upon regional carbon cycle, grazing capacity, soil erosion, and ecosystem safety assessment. How topography, one of significant environmental factors, affects grassland productivity is not well addressed in the remote sensing of grassland ecosystems. This paper selected a protected meadow of the National Natural Reserve of Huihe wetland, used USGS EOS-MODIS/Terra NDVI data and GLCF DEM data, and adopted spatial analysis function of ARCGIS to analyze the NPP distribution pattern form 2000 to 2012 in Hulunbuir meadow based on the ground spectrum biomass model, topographical controlling factors, and yearly precipitation classification. The results showed that the ground spectrum biomass model can be used to assess meadow productivity, and the most suitable model is y =15.968e3.5434x (Sig=0.000) for predicting Hulunbuir meadow productivity in regional scale (where y and x represent productivity and NDVI, respectively). Simulated results confirmed that topography had a remarkable impact on meadow productivity distribution pattern. Consequently, among three topographical factors of altitude, slope and aspect, altitude gave rise to the most significant changes, the effect of the slope was intermediate, and the aspect played a minimal effect. Firstly, under the conditions of the slope of 0-2 degrees and aspect of NE, NPP increased 0.478 g/m2 per meter rising of elevation in normal yearly precipitation level; 0.414 g/m2 in lower yearly precipitation level; 0.482 g/m2 in moderate yearly precipitation level; and 0.525 g/m2 in higher yearly precipitation level, respectively. Secondly, under the conditions of altitude of 760-780 m and aspect of NE, the meadow productivity decreased 0.142 g/m2 per degree increase of slope in the normal yearly precipitation level, and decreased 0.161 g/m2 in the lower yearly precipitation level, 0.135 g/m2 in the moderate yearly precipitation level, 0.133 g/m2 in the higher yearly precipitation level, respectively. Thirdly, under the conditions of the altitude of 760-780 m and the slope of 0-2 degrees, the highest NPP (184.6 g/m2) occurred on the N aspect and the lowest NPP (173.3 g/m2) on the W aspect, respectively. The NPP was lower on the SW aspect in the lower yearly precipitation level and on the W aspect in the moderate yearly precipitation level. By contrast, lower NPP occupied on the SE aspect in the higher yearly precipitation level. According to NPP distribution area, the topographical factors had higher (lower) effect on NPP of the meadow than soil heterogeneity (grassland type) on spatial scale. The trend of this effect did not vary across years with various NPP but differed in effect degree, being higher in the years with intermediate NPP. 参考文献 相似文献 引证文献

Causal relationships versus emergent patterns in the global controls of fire frequency

Abstract. Global controls on month-by-month fractional burnt area (2000–2005) were investigated by fitting a generalised linear model (GLM) to Global Fire Emissions Database (GFED) data, with 11 predictor variables representing vegetation, climate, land use and potential ignition sources. Burnt area is shown to increase with annual net primary production (NPP), number of dry days, maximum temperature, grazing-land area, grass/shrub cover and diurnal temperature range, and to decrease with soil moisture, cropland area and population density. Lightning showed an apparent (weak) negative influence, but this disappeared when pure seasonal-cycle effects were taken into account. The model predicts observed geographic and seasonal patterns, as well as the emergent relationships seen when burnt area is plotted against each variable separately. Unimodal relationships with mean annual temperature and precipitation, population density and gross domestic product (GDP) are reproduced too, and are thus shown to be secondary consequences of correlations between different controls (e.g. high NPP with high precipitation; low NPP with low population density and GDP). These findings have major implications for the design of global fire models, as several assumptions in current models – most notably, the widely assumed dependence of fire frequency on ignition rates – are evidently incorrect.

Hydrologic Regimes Revealed Bundles and Tradeoffs Among Six Wetland Services

Ecosystem services are often described as occurring together in bundles, or tending not to occur together, representing tradeoffs. We investigated patterns and potential linkages in the provision of six wetland services in three experimental wetlands by measuring: flow attenuation, as peak flow reduction; stormwater retention, as outflow volume reduction; net primary productivity (NPP), as plant biomass; diversity support, as plant species richness; erosion resistance, as stability of surface soils in a flow path; and water quality improvement, as nutrient and sediment removal. Levels of ecosystem services differed in our system because of differences in hydrologic regime brought on by natural variation in clay-rich subsoils. The fastest-draining wetland (with thin clay layer) provided five of six services at their highest level, but had lowest NPP. In contrast, a ponded wetland (with thick clay layer) that was dominated by cattail (Typha spp.) provided the highest level of NPP, but lowest levels of all other services. Hence, in our site, drainage supported several bundled services, whereas ponding supported such high levels of NPP that other services appeared to be limited (suggesting tradeoffs). These outcomes show that high NPP has the potential to be a misleading indicator of overall ecosystem services. Rather than focusing on NPP, we suggest identifying and establishing hydrologic regimes that can support the services targeted for restoration in future projects. Further direct assessments of multiple services are needed to identify bundles and tradeoffs and provide guidance at the scale of local restoration projects.

Impacts of sea ice retreat, thinning, and melt-pond proliferation on the summer phytoplankton bloom in the Chukchi Sea, Arctic Ocean

Abstract In 2011, a massive phytoplankton bloom was observed in the Chukchi Sea under first-year sea ice (FYI), an environment in which primary productivity (PP) has historically been low. In this paper, we use a 1-D biological model of the Chukchi shelf ecosystem, in conjunction with in situ chemical and physiological data, to better understand the conditions that facilitated the development of such an unprecedented bloom. In addition, to assess the effects of changing Arctic environmental conditions on net PP (NPP), we perform model runs with varying sea ice and snow thickness, timing of melt, melt ponds, and biological parameters. Results from model runs with conditions similar to 2011 indicate that first-year ice (FYI) with at least 10% melt pond coverage transmits sufficient light to support the growth of shade-adapted Arctic phytoplankton. Increasing pond fraction by 20% enhanced peak under-ice NPP by 26% and produced rates more comparable to those measured during the 2011 bloom, but there was no effect of further increasing pond fraction. One of the important consequences of large under-ice blooms is that they consume a substantial fraction of surface nutrients such that NPP is greatly diminished in the marginal ice zone (MIZ) following ice retreat, where NPP has historically been the highest. In contrast, in model runs with

Satellite-measured net primary production in the Chesapeake Bay

The regional daily-integrated net primary production (NPP) model for the Chesapeake Bay, Chesapeake Bay Production Model (CBPM), has been improved for use with ocean color products from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the satellite Aqua. A polynomial regression formula for the photosynthetic parameter (i.e., optimal carbon fixation rate, PoptB) as a function of sea surface temperature (SST) was derived for the Chesapeake Bay. Results show that the CBPM-derived NPP using the new model for PoptB are improved for the Chesapeake Bay. Comparisons of MODIS-Aqua-derived and in situ-measured NPP show that the satellite-derived data correspond reasonably well to in situ measurements, although MODIS-Aqua-derived NPP values may be slightly overestimated for the upper Bay, primarily due to uncertainties in the bio-optical algorithm for satellite ocean color products for that region. We also generated MODIS-Aqua-derived NPP maps using the improved CBPM for the period of 2002 to 2011 to characterize NPP in the Chesapeake Bay. Spatial distributions of MODIS-Aqua-derived NPP products show that higher NPP values are generally found in the southern upper Bay and northern middle Bay (regions around 38.3°N–39.0°N), including the Potomac River, while relatively low NPP values were found in the northern upper Bay, the eastern area of middle Bay, and lower Bay. The temporal pattern of MODIS-Aqua-derived NPP showed lowest values in winter (December to February) over the entire Bay, while high NPP values were in late spring to summer (May to August), depending on location. Furthermore, there is a strong interannual variability in NPP for the Chesapeake Bay, and an apparent increasing trend from 2003 to 2011.

Net primary productivity in Kazakhstan, its spatio-temporal patterns and relation to meteorological variables

Abstract Arid and semiarid environments are susceptible to environmental degradation and desertification. Modelling net primary productivity (NPP) and analysis of spatio-temporal patterns help to understand ecological functioning especially in these areas. In this study, we apply the Biosphere Energy Transfer Hydrology Model (BETHY/DLR) to derive NPP for Kazakhstan for 2003–2011. Results are analyzed regarding spatial, monthly, and inter-annual variations. Mean annual NPP for Kazakhstan is 143 g C m −2 and maximum productivity is reached in June. Most monthly NPP anomalies occur in semiarid North of Kazakhstan. These regions seem to be most strongly affected by changes in meteorology and are likely to be vulnerable to changing climate. Arid ecosystems show lower inter-annual NPP variability than semiarid lands. Correlations between NPP and meteorological parameters reveal variable influence of temperature, PAR, and precipitation on vegetation productivity during the year. Reaction of vegetation growth to precipitation is delayed 1–2 months. Temperature is most critical in spring and precipitation in summer affects NPP in August–October. The results presented in this study help to identify regions that are vulnerable to global change. They allow predictions on possible effects of expected future climate change on vegetation productivity in arid and semiarid Kazakhstan and support sustainable land management.

A global analysis of the impact of drought on net primary productivity

Abstract. We investigated the impact of drought on interannual variability of net primary productivity (NPP) from 1997 to 2009, using the standardized precipitation evapotranspiration index (SPEI) drought index and satellite-derived vegetation greenness converted to NPP. SPEI is positive for wet conditions and negative for dry conditions. We found that SPEI and NPP were coupled and showed in-phase behaviour on a global scale. We then used the Köppen climate classification to study the SPEI–NPP relations regionally and found that while NPP and SPEI were positively related (high SPEI, high NPP) in arid and in seasonal dry regions, the opposite occurs in most boreal regions (high SPEI, low NPP). High intensity drought events, such as the 2003 drought in Europe were picked up by our analysis. Our findings suggest that the strong positive relation between global average moisture availability and NPP consists of a composite of the positive relation across dry regions and the coherent NPP decline during and after intensive drought events in humid regions. Importantly, we also found that there are many areas on the globe that show no strong correlation between drought and NPP.

Estimations of net primary productivity and evapotranspiration based on HJ-1A/B data in Jinggangshan city, China

Net primary productivity (NPP) and evapotranspiration (ET) are two key variables in the carbon and water cycles of terrestrial ecosystems. In this study, to test a newly developed NPP algorithm designed for HJ-1 A/B data and to evaluate the usage of HJ-1 A/B data in the quantitative assessment of environments, NPP and ET in Jinggangshan city, Jiangxi province, are calculated using HJ-1 A/B data. The results illustrate the following: (1) The NPP and ET in Jinggangshan city in 2010 both show obvious seasonal variation, with the highest values in summer and the lowest values in winter, and relatively higher values were observed in autumn than in spring. (2) The spatial pattern indicates that the annual NPP is high in the southern area in Jinggangshan city and low in the northern area. Additionally, high NPP is distributed in forests located in areas with high elevation, and low NPP is found in croplands at low elevations. ET has no significant north-south difference, with high values in the southeast and northwest and low values in the southwest, and high ET is distributed in forests at low elevations in contrast to low ET in forests in high-elevation areas and in cropland and shrub grassland in low-elevation areas. (3) Compared to the MODIS product, the range of HJ-1 NPP is larger, and the spatial pattern is more coincident with the topography. The range of HJ-1 ET is smaller than that of the MODIS product, and ET is underestimated to some extent but can reflect the effect of topography. This study suggests that the algorithm can be used to estimate NPP and ET in a subtropical monsoon climate if remotely sensed images with high spatial resolution are available.

Impacts of temperature on primary productivity and respiration in naturally structured macroalgal assemblages.

Rising global temperatures caused by human-mediated change has already triggered significant responses in organismal physiology, distribution and ecosystem functioning. Although the effects of rising temperature on the physiology of individual organisms are well understood, the effect on community-wide processes has remained elusive. The fixation of carbon via primary productivity is an essential ecosystem function and any shifts in the balance of primary productivity and respiration could alter the carbon balance of ecosystems. Here we show through a series of tests that respiration of naturally structured algal assemblages in southern New Zealand greatly increases with rising temperature, with implications for net primary productivity (NPP). The NPP of in situ macroalgal assemblages was minimally affected by natural temperature variation, possibly through photo-acclimation or temperature acclimation responses, but respiration rates and compensating irradiance were negatively affected. However, laboratory experiments testing the impacts of rising temperature on several photosynthetic parameters showed a decline in NPP, increasing respiration rates and increasing compensating irradiance. The respiration Q10 of laboratory assemblages (the difference in metabolic rates over 10°C) averaged 2.9 compared to a Q10 of 2 often seen in other autotrophs. However, gross primary productivity (GPP) Q10 averaged 2, indicating that respiration was more severely affected by rising temperature. Furthermore, combined high irradiance and high temperature caused photoinhibition in the laboratory, and resulted in 50% lower NPP at high irradiance. Our study shows that communities may be more severely affected by rising global temperatures than would be expected by responses of individual species. In particular, enhanced respiration rates and rising compensation points have the potential to greatly affect the carbon balance of macroalgal assemblages through declines in sub-canopy NPP, the impacts of which may be exacerbated over longer time-scales and could result in declines in sub-canopy species richness and abundance.

Switchgrass Influences on Soil Biogeochemical Processes in the Dryland Region of the Pacific Northwest

Switchgrass and other perennial grasses have been promoted as biomass crops for production of renewable fuels. The objective of this study was to evaluate the effect of biomass removal on soil biogeochemical processes. A 3-year field study consisting of three levels of net primary productivity (NPP; low, medium, and high growing season precipitation) and two biomass crops (winter wheat and switchgrass) was conducted near Pendleton, Oregon. Switchgrass increased soil carbon (C)–nitrogen (N) ratio, but the effect varied with net primary productivity (NPP) and soil depth. In situ soil respiration (carbon dioxide; CO2) rate from switchgrass increased with NPP level but switchgrass had greater cumulative flux than wheat in medium and low NPP. Nitrogen mineralization and microbial biomass carbon were significantly greater under switchgrass than under wheat at high and medium NPP. Introduction of switchgrass initiates major changes in soil nutrient dynamics through organic-matter input.

Disentangling the Relationships between Net Primary Production and Precipitation in Southern Africa Savannas Using Satellite Observations from 1982 to 2010

To obtain a better understanding of the variability in net primary production (NPP) in savannas is important for the study of the global carbon cycle and the management of this particular ecosystem. Using satellite and precipitation data sets, we investigated the variations in NPP in southern African savannas from 1982 to 2010, and disentangled the relationships between NPP and precipitation by land cover classes and mean annual precipitation (MAP) gradients. Specifically, we evaluate the utility of the third generation Global Inventory Monitoring and Modeling System (GIMMS3g) normalized difference vegetation index (NDVI) dataset, in comparison with Moderate-resolution Imaging Spectroradiometer (MODIS) derived NPP products, and find strong relationships between the overlapping data periods (2000–2010), such that we can apply our model to derive NPP estimates to the full 29-year NDVI time-series. Generally, the northern portion of the study area is characterized by high NPP and low variability, whereas the southern portion is characteristic of low NPP and high variability. During the period 1982 through 2010, NPP has reduced at a rate of −2.13 g∙C∙m−2∙yr−1 (p < 0.1), corresponding to a decrease of 6.7% over 29 years, and about half of bush and grassland savanna has experienced a decrease in NPP. There is a significant positive relationship between mean annual NPP and MAP in bush and grassland savannas, but no significant relationship is observed in tree savannas. The relationship between mean annual NPP and MAP varies with increases in MAP, characterized as a linear relationship that breaks down when MAP exceeding around 850–900 mm.

Ecosystem respiration and net primary productivity after 8–10 years of experimental through-fall reduction in an eastern Amazon forest

Background: There is much interest in how the Amazon rainforest may respond to future rainfall reduction. However, there are relatively few ecosystem-scale studies to inform this debate. Aims: We described the carbon cycle in a 1 ha rainforest plot subjected to 8–10 consecutive years of ca. 50% through-fall reduction (TFR) and compare these results with those from a nearby, unmodified control plot in eastern Amazonia. Methods: We quantified the components of net primary productivity (NPP), autotrophic (R a) and heterotrophic respiration, and estimate gross primary productivity (GPP, the sum of NPP and R a) and carbon-use efficiency (CUE, the ratio of NPP/GPP). Results: The TFR forest exhibited slightly lower NPP but slightly higher R a, such that forest CUE was 0.29 ± 0.04 on the control plot but 0.25 ± 0.03 on the TFR plot. Compared with four years earlier, TFR plot leaf area index and small tree growth recovered and soil heterotrophic respiration had risen. Conclusions: This analysis tested and extended the key findings of a similar analysis 4 years earlier in the TFR treatment. The results indicated that, while the forest recovered from extended drought in some respects, it maintained higher overall R a relative to the undroughted control, potentially causing the droughted forest to act as a net source of CO2.

Carbon dynamics in the Amazonian Basin: Integration of eddy covariance and ecophysiological data with a land surface model

a b s t r a c t Information contained in eddy covariance flux tower data has multiple uses for the development and application of global land surface models, such as evaluation/validation, calibration and process parameterization for carbon stocks and fluxes. In this study, we combine Large Scale Biosphere–Atmosphere Experiment in Amazonia (LBA) project data collected from a network of eddy covariance flux towers deployed across the Amazonian basin to improve the carbon stocks and flux estimated by a land surface model, the Integrated Science Assessment Model (ISAM). We evaluate the key model parameters for carbon allocation factors, maintenance respiration as well as the autotrophic respiration using the LBA site measurements. Our model results show that the total biomass ranges from 0.7 kg C m −2 yr −1 for the

Traceable components of terrestrial carbon storage capacity in biogeochemical models

Biogeochemical models have been developed to account for more and more processes, making their complex structures difficult to be understood and evaluated. Here, we introduce a framework to decompose a complex land model into traceable components based on mutually independent properties of modeled biogeochemical processes. The framework traces modeled ecosystem carbon storage capacity (Xss ) to (i) a product of net primary productivity (NPP) and ecosystem residence time (τE ). The latter τE can be further traced to (ii) baseline carbon residence times (τ'E ), which are usually preset in a model according to vegetation characteristics and soil types, (iii) environmental scalars (ξ), including temperature and water scalars, and (iv) environmental forcings. We applied the framework to the Australian Community Atmosphere Biosphere Land Exchange (CABLE) model to help understand differences in modeled carbon processes among biomes and as influenced by nitrogen processes. With the climate forcings of 1990, modeled evergreen broadleaf forest had the highest NPP among the nine biomes and moderate residence times, leading to a relatively high carbon storage capacity (31.5 kg cm(-2) ). Deciduous needle leaf forest had the longest residence time (163.3 years) and low NPP, leading to moderate carbon storage (18.3 kg cm(-2) ). The longest τE in deciduous needle leaf forest was ascribed to its longest τ'E (43.6 years) and small ξ (0.14 on litter/soil carbon decay rates). Incorporation of nitrogen processes into the CABLE model decreased Xss in all biomes via reduced NPP (e.g., -12.1% in shrub land) or decreased τE or both. The decreases in τE resulted from nitrogen-induced changes in τ'E (e.g., -26.7% in C3 grassland) through carbon allocation among plant pools and transfers from plant to litter and soil pools. Our framework can be used to facilitate data model comparisons and model intercomparisons via tracking a few traceable components for all terrestrial carbon cycle models. Nevertheless, more research is needed to develop tools to decompose NPP and transient dynamics of the modeled carbon cycle into traceable components for structural analysis of land models.

Evaluation of net primary productivity and its spatial and temporal patterns in southern China’s grasslands

The net primary productivity (NPP) of grassland ecosystems is an important indicator of the capacity for carbon (C) absorption. The Global Production Efficiency Model was adopted to simulate NPP in southern China’s grasslands and to analyse the temporal and spatial dynamics from 1981 to 2000. There was a high correlation between measured and simulated values (R2 = 0.84). Based on the data from 1981 to 2000, the mean annual NPP was 1082 g C m–2 year–1, and the highest value (1798 g C m–2 year–1) was in Hainan province, and the lowest value (500 g C m–2 year–1) was in south-western Tibet. The highest mean NPP values were in the permanent wetlands (1193 g C m–2 year–1) and savannas (1137 g C m–2 year–1); woody savannas had an intermediate value (1087 g C m–2 year–1), and the lowest NPP occurred in typical grasslands and open shrubs, the mean values were 709 and 689 g C m–2 year–1, respectively. Temporally, the total NPP in southern China’s grasslands slightly increased in the 20-year period, especially from 1981 to 1990. The mean annual total of NPP in the 20 years was 0.758 Pg C. Inter-annual variation in total NPP was driven mainly by mean annual temperature rather than mean annual precipitation. The results suggest that grassland ecosystems in southern China have a large C sink.