Mean Annual Net Primary Productivity Research Articles

Spatial-temporal analysis of net primary production (NPP) and its relationship with climatic factors in Iran.

Fluctuations of the climate variables have increased in the recent years. These fluctuations are different in each climatic region. Net primary production (NPP) indicating the plant growth and carbon stabilization over period of time is influenced by these fluctuations. Investigation of the variations in the NPP and analysis of its relationship with the climatic and environmental variables can play a key role in determining the effects of fluctuations of climatic variables on the NPP. Therefore, the present study was conducted to investigate the spatiotemporal changes in the NPP and its correlation with precipitation rate and temperature during 2000-2014 based on the annual NPP estimates determined by the moderate resolution imaging spectroradiometer (MODIS) sensor and precipitation and temperature data of the synoptic stations in eight climate regions in Iran. The slope of variations in the NPP was calculated in these climatic regions, and then, the changes in the NPP trend at two confidence levels of 95 and 99% were investigated based on the pixel-based method using the Mann-Kendall test. The sensitivity of NPP to climatic variables of temperature and precipitation was also estimated by calculating the correlation. The results showed the significant spatial distribution of NPP in the whole region under study indicating a declining trend from north to south and from west to east directions. The results also indicated the nonlinear variations in the temporal distribution of NPP. The annual mean NPP was found to follow the climatic boundaries in the climatic regions except for climate region 2, and region with the higher annual mean precipitation had higher annual mean NPP. Analysis of the trend by the Mann-Kendall method revealed that 3.2% of the pixels in the whole region followed a certain trend. Among the pixels, 70% of them followed a negative trend and the remaining 30% followed a positive trend. The greatest number of pixels with a certain trend was found in the Gulf of Oman coast climate region so that 93% of the pixels had a positive trend. The lowest number of pixels with a certain trend was observed in eastern Alborz foothills so that 87% of the pixels showed a negative trend. Slope variations of the NPP in the whole region varied from - 35 to 46 gC m2 year-1. The eastern plateau had the highest negative slope variations among the climate regions, and the highest positive slope variation of 42% was observed in the highlands climate region. In general, the precipitation rate and temperature showed a mean partial coefficient of 0.22 and 0.02, respectively, and the correlation between the NPP and temperature and precipitation was different in each climatic region. The temperature was negatively correlated with the NPP in four climatic regions with higher annual mean temperatures and in other climatic regions; it had a weak positive correlation. Therefore, the sensitivity of NPP to precipitation and temperature was different in each climatic region.

Exports and inputs of organic carbon on agricultural soils in Germany

The quantity and quality of organic carbon (Corg) input drive soil Corg stocks and thus fertility and climate mitigation potential of soils. To estimate fluxes of Corg as net primary production (NPP), exports, and inputs on German arable and grassland soils, we used field management data surveyed within the Agricultural Soil Inventory (n = 27.404 cases of sites multiplied by years). Further, we refined the concept of yield-based Corg allocation coefficients and delivered a new regionalized method applicable for agricultural soils in Central Europe. Mean total NPP calculated for arable and grassland soils was 6.9 ± 2.3 and 5.9 ± 2.9 Mg Corg ha−1 yr−1, respectively, of which approximately half was exported. On average, total Corg input calculated did not differ between arable (3.7 ± 1.8 Mg ha−1 yr−1) and grassland soils (3.7 ± 1.3 Mg ha−1 yr−1) but Corg sources were different: Grasslands received 1.4 times more Corg from root material than arable soils and we suggest that this difference in quality rather than quantity drives differences in soil Corg stocks between land use systems. On arable soils, side products were exported in 43% of the site * years. Cover crops were cultivated in 11% of site * years and contributed on average 3% of the mean annual total NPP. Across arable crops, total NPP drove Corg input (R2 = 0.47) stronger than organic fertilization (R2 = 0.11). Thus, maximizing plant growth enhances Corg input to soil. Our results are reliable estimates of management related Corg fluxes on agricultural soils in Germany.

Monitoring and driving force analysis of net primary productivity in native grassland: A case study in Xilingol steppe, China

Grassland is an important type of terrestrial ecosystem. Using remote sensing technology to study the change and driving force of native grassland productivity at large scale is an important way to understand the ecological status of grassland. In this study, potential and actual net primary productivity (NPP) of Xilingol steppe from 2000 to 2018 were examined based on climatic model and light-use efficiency model, respectively. NPP damage value driven by human activities was calculated from the difference between potential and actual NPP. The least square method was used to analyze the temporal and spatial variation of NPP in Xilingol and the driving role of climate and human activities on NPP. The results showed that NPP in Xilingol increased from west to east, with mean annual NPP being 271.54 g C·m-2·a-1, the area with increased NPP (grassland restoration) being 36500 km2, and the area with decreased NPP (grassland degradation) being 59900 km2. The potential NPP tended to rise under the driving force of temperature and precipitation, with an average annual increase of 6.5 g C·m-2·a-1, which indicated that regional climate played a positive role in the improvement of NPP in Xilingol steppe, and that human activities were the main driving force for grassland degradation. The value of NPP damage driven by human activities decreased from east to west and from south to north, with the highest value in Wuzhumuqin meadow and southern steppe. Human activities, such as mining and reclamation, had the most obvious negative impact on grassland NPP.

Ambient temperature correlates with geographic variation in body size of least horseshoe bats.

Geographic variation in body size is common within many animal species. The causes of this pattern, however, remain largely unexplored in most vertebrate groups. Bats are widely distributed globally owing to their ability of powered flight. Most bat species encounter a variety of climatic conditions across their distribution range, making them an ideal taxon for the study of ecogeographic patterns in body size. Here, we used adult least horseshoe bats, Rhinolophus pusillus, to test whether geographic variation in body size was determined by heat conservation, heat dissipation, climatic seasonality, or primary productivity. We measured body mass and head-body length for 246 adult bats from 12 allopatric colonies in China. We quantified the ecological conditions inhabited by each colony, including mean maximum temperature of the warmest month, mean minimum temperature of the coldest month, temperature seasonality, precipitation seasonality, and annual net primary productivity (ANPP). Body mass and head-body length, 2 of the most reliable indicators of body size, exhibited marked differences between colonies. After controlling for spatial autocorrelation, the mean minimum temperature of the coldest month explained most of the variation in body size among colonies, regardless of sex. The mean maximum temperature, climatic seasonality, and ANPP had limited power in predicting body size of males or females in comparison with mean minimum temperature. These results support the heat conservation hypothesis and suggest adaptive responses of body size to cold climates in cave-dwelling bats.

Comprehensive assessments of carbon dynamics in an intermittently-irrigated rice paddy

Rice is a major crop that feeds more than half of the global population. Rice paddies play a complex role in the carbon cycle by emitting CH4 to the atmosphere while either sequestering or releasing CO2 to the atmosphere. Here, we present 3.5 years of eddy covariance measurements of CO2 and CH4 fluxes over an intermittently irrigated, single crop rice paddy in South Korea in tandem with carbon stock measurements for leaves, stems, grains, and roots. The rice paddy acted as a slight sink or neutral in CO2 (−47 ± 51 g C m−2y−1; mean ± 95% confidence interval) with 941 ± 130 g C m−2y−1 and 894 ± 108 g C m−2y−1 as the gross primary production (GPP) and ecosystem respiration (Reco), respectively. The mean annual net primary productivity (NPP) was 666 ± 31 g C m−2y−1, which was partitioned to leaves (9%), stems (30%), grains (51%), and roots (10%), for a harvest index of 57%. The paddy emitted 20.6 ± 1.5 g C m−2y−1 in the form of CH4, of which between 82 and 96% was emitted during the cultivation period (~132 days) . The CH4 flux showed a mid-season decline caused by mid-season drainage, which produced aerobic soil conditions that inhibited CH4 emissions. The proportion of estimated ebullitive flux to total CH4 flux ranged from 10 to 17% during the cultivation period. GPP, Reco, and CH4 fluxes varied by 12%, 11%, and 7%, respectively, over the 3-year period. When considering the harvest and the global warming potential of CH4, the paddy shifted from a greenhouse gas sink to a strong source (2,741 ± 468 g CO2 eq m−2y−1). These findings will improve our understanding of carbon budgets and cycles, and help develop greenhouse gas and water management strategies for rice paddies.

Investigating the contribution of climate variables to estimates of net primary productivity in a tropical deciduous forest in India.

Investigating the impact of climate variables on net primary productivity is crucial to evaluate the ecosystem health and the status of forest type response to climate change. The objective of this paper is (1) to estimate spatio-temporal patterns of net primary productivity (NPP) during 2001 to 2010 in a tropical deciduous forest based on the input variable dataset (i.e.meteorological and biophysical) derived from the remote sensing and other sources and (2) to investigate the effects of climate variables on NPP during 2001 to 2010. The study was carried out in Katerniaghat Wildlife Sanctuary that forms a part of a tropical forest and is situated in Uttar Pradesh, India, along the Indo-Nepal border. Mean annual NPP was observed to be highest during 2007 with a value of 878gCm-2year-1 and 781.25gCm-2year-1 for sal and teak respectively. A decline in mean NPP during 2002-2003, 2005 and 2008-2010 could be attributed to drought, increased temperature and vapour pressure deficit (VPD). The time lag correlation analysis revealed precipitation as the major variables affecting NPP, whereas combination of temperature and VPD showed dominant effect on NPP as revealed by generalized linear modelling. The carbon gain in NPP in sal forest was observed to be marginal higher than that of teak plantation throughout the study period. The decrease in NPP was observed during 2010, pertaining to increased VPD. Contribution of different climatic variables through some link process was revealed in statistical analysis and clearly indicated the co-dominance of all the variables in explaining NPP.

Spatiotemporal Changes in Vegetation Net Primary Productivity and Its Responses to Climatic Factors in Jiangsu Province, Eastern China

Vegetation net primary productivity (NPP) is an important indicator in determining the ecological functions and carbon cycle of terrestrial ecosystems. As an important part of Chinese Yangtze River Delta region, Jiangsu is one of main grain producing areas in China. Therefore, understanding of spatio-temporal changes in NPP has a practical significance to ensure ecological sustainability in this region. In this study, we used satellite-based vegetation productivity model, the Carnegie-Ames-Stanford Approach (CASA) to assess spatio-temporal variations in NPP and analyzed the relationships between NPP and climatic factors over Jiangsu. The results showed that annual mean NPP reached up to 745.26 ± 69.21 g C m-2 year-1, with high NPP values mainly in the central and southwestern regions. Besides that, annual mean NPP increased from 2000 to 2015, with a rate of 6.54 g C m-2 year-1. The increasing trends with higher changing rate were mainly found in the northern regions of Jiangsu, whereas the decreasing trends were mainly found in central and southern Jiangsu. Moreover, the correlation analysis indicated that the mean temperature and total precipitation in spring had a significant relationship with the corresponding NPP in most part of Jiangsu. The findings will have an important significance for improving the ecosystem management in Jiangsu.

Grassland Productivity Response to Climate Change in the Hulunbuir Steppes of China

As global climate change deeply affects terrestrial ecosystem carbon cycle, it is necessary to understand how grasslands respond to climate change. In this study, we examined the role of climate change on net primary productivity (NPP) from 1961 to 2010 in the Hulunbuir grasslands of China, using a calibrated process-based biogeochemistry model. The results indicated that: Temperature experienced a rise trend from 1961; summer and autumn precipitation showed a rise trend before the 1990s and decline trend after the 1990s. Winter and spring precipitation showed an ascending trend. Simulated NPP had a high inter-annual variability during the study period, ranging from 139 g Cm−2 to 348 g Cm−2. The annual mean NPP was significant and positive in correlation with the annual variation of precipitation, and the trend was first raised then fell with the turn point at the 1990s. Temperature had a 20–30 d lag in summer, but none in spring and autumn; precipitation had a 10–20 d lag in summer. The climate lag effect analysis confirmed that temperature had a positive effect on NPP in spring and a negative effect in summer.

The dynamics of soil moisture balance components and their relations with the productivity of natural vegetation in an arid region of northwestern China

Precipitation and groundwater are important water source in soil and are vital for the survival and growth of natural vegetation in arid regions. Analyses on the dynamics of soil water balance components and their relations with plant growth are usually restricted by the lack of continuous measurement of deep soil moisture at a local or regional scale. By monitoring monthly soil water contents in the 0–3 m soil profiles, we analyzed the contributions of precipitation and groundwater to the growth of natural vegetation in an arid region of northwestern China from 2011 to 2013. The results showed that the 0–3 m desert soil and the 0–1.8 m grassland soil exhibited moderate spatial variability in the soil water contents (θ). Temporal variability of spatial mean θ decreased with depth in the soils of the desert and grassland. The profile-average of spatial mean θ maintained 0.11 cm3 cm−3 in the desert and varied from 0.37 to 0.44 cm3 cm−3 in the grassland over time. The evapotranspiration after calibration gave accurate estimation of water available for plants (402.0 and 532.4 mm year−1 in the desert and grassland, respectively). Annual mean net primary productivity of the grassland (233.4 g C m−2) was 3.8 times that of the desert. Water exchange in the desert soils was dominated by recharge into the 0–1 m soil from layers deeper than 3 m, with annual mean value of 303.4 mm. Recharge alternated with discharge events in grassland soils. Annual mean recharge and discharge amounts were 494.2 and 50.1 mm for the 0–1 m layer and 641.1 and 228.9 mm for the 0–3 m soil profile, respectively. Water supply into soil was totally consumed by evapotranspiration. Precipitation use efficiency increased when groundwater level became shallow (0.04 and 0.11 g C m−2 mm−1 in the desert and grassland, respectively). Groundwater supplied about 75% of water requirement for natural vegetation, and its use efficiencies were 0.12 and 0.33 g C m−2 mm−1 in the desert and grassland, respectively. Seedling of herbaceous species with trichomes at the interspace and under the canopy of shrubs can guarantee great utilization of precipitation in the desert. Transplanting of shrubs with large amounts of shallow lateral roots and shrubs with deep rooting systems can effectively utilize the shallow and deep soil water or groundwater. Reducing the irrigation consumption of groundwater and controlling the expansion of oasis cropland are foremost to guarantee the ecological water requirement and maintain the sustainability of natural ecosystems. Keep or increase current area and layout of the grassland may benefit the water cycle and carbon sequestration in the arid regions.

Spatiotemporal variations in productivity and water use efficiency across a temperate forest landscape of Northeast China

BackgroundForests are increasingly valued for non-timber ecosystem services in place of conventional wood fiber production. Biomass carbon sequestration is one of the key ecosystem services forests are relied upon for mitigating global climate change. However, planning for large-scale tree planting and managing established forest stands for carbon sequestration require careful consideration of the gain in biomass production and tradeoff for other regulatory services. How a tradeoff between forest production and conservation of water resources is shaped by the condition of forest stand and environmental factors remains a question of broad interest in sustainable forest ecosystem management.MethodsWe studied the spatiotemporal patterns of net primary productivity (NPP), evapotranspiration (ET), and water use efficiency (WUE), and their relationships with local climatic and forest stand factors over a temperate forest landscape in Changbai Mountain, Northeast China. The time series of spatial data on NPP and ET were extracted from the global remote sensing datasets for the MOD16A3 and MOD17A3 products for the period 2000–2014. The time series of spatial patterns of annual precipitation and annual mean temperature were obtained as grid maps for regional meteorological variables. Stand patches were categorized into the types of conifers, broadleaves, and mixed-wood, as well as age-classes of young, mid-age, near mature, mature, and old-growth stands, and by establishment into natural and planted. Information on stands and selective site variables were compiled from the Forest Inventory Datasets of China. Analyses were performed with Arc-GIS.ResultsOver the study period of 2000–2014, the landscape-level annual NPP varied between 311.7 and 573.6 gC∙m− 2∙a− 1, ET between 559.9 and 603.0 mm∙a− 1, and WUE between 0.54 and 1.01 gC∙m− 2∙mm− 1. Across the forest landscape, the mean annual NPP varied between 205.0 and 639.4 gC∙m− 2∙a− 1, ET between 441.5 and 784.0 mm∙a− 1, and WUE in the range of 0.46–1.10 gC∙m− 2∙mm− 1. The spatial variations in NPP, ET, and WUE were commonly attributable to forest type, stand age class and density, establishment mode, and temperature variables, with some effects of other selective factors on ET and WUE. The three forest types were significantly (p < 0.05) differentiated in the mean annual NPP, ET, and WUE: the coniferous forests were highest in NPP (505.3 ± 1.4 gC∙m− 2∙a− 1; n = 1041) and WUE (0.872 ± 0.004 gC∙m− 2∙mm− 1; n = 1041), and lowest in ET (584.1 ± 1.6 mm∙a− 1; n = 1041), followed by the mixed-wood forests (NPP: 500.5 ± 0.8 gC∙m− 2∙a− 1; WUE: 0.856 ± 0.02 gC∙m− 2∙mm− 1; ET: 589.3 ± 0.9 mm∙a− 1; n = 2156); whereas the broadleaved forests were lowest in NPP (491.6 ± 0.6 gC∙m− 2∙a− 1; n = 4428) and WUE (0.832 ± 0.02 gC∙m− 2∙mm− 1; n = 4428), and highest in ET (594.7 ± 0.6 mm∙a− 1; n = 4428). The mean annual NPP, ET and WUE increased with stand age typically in coniferous forests, and weakly in mixed-wood forests. The natural stands had significantly (p < 0.001) greater NPP and WUE than planted stands in conifers and mixed-woods.ConclusionsForest type and stand-age class are factors of key consideration in planning and managing forest landscape for achieving the compromise between regional carbon balance and water usage. Facilitating the establishment of coniferous trees and conservation of mature forest stands, and near-natural management of planted forests, can be favorable options for delivering ecosystem services of carbon sequestration and water conservation in temperate regions.

Modelling and analysis of net primary productivity and its response mechanism to climate factors in temperate grassland, northern China

ABSTRACTGrassland productivity is the most direct indicator of grassland’s ecological status; thus, precise and rapid estimation of grassland productivity has an important significance for evaluating regional ecological carrying capacity, utilizing and developing natural resources reasonably. In this study, based on Moderate Resolution Imaging Spectroradiometer remote-sensing data, meteorological data, and ground measured data, the light utilization efficiency parameter of Carnegie–Ames–Stanford Approach model was optimized, and the optimized model was used to estimate net primary productivity (NPP) and analyse its spatio-temporal distribution of Xilingol grassland between 2005 and 2014. In addition, we investigated the NPP response mechanism to climate factors from two aspects, i.e. the accumulation amount and time of NPP. The results indicated that (i) Maximum light utilization efficiency was calculated to be 0.539 g C MJ−1 for Xilingol grassland according to the least error criterion. (ii) Validation against NPP observations from 30 sites showed good performance of the optimized model in the research area, with an overall coefficient of determination (R2) of 0.72 and mean relative estimation error of 0.29. (iii) The annual mean NPP of Xilingol grassland was 161.23 g C m–2 year–1, with a decreasing trend from the northeast to the southwest. (iv) NPP presented increasing trend with a rate of 3.89 g C m–2 year–1 overall during 20052014, and the largest increase in NPP was found in temperate meadow-steppe. However, desert ecosystems showed the largest increasing rate after NPP standardization. (v) Precipitation was the main factor for driving carbon accumulation at the inter-annual scale, and the time to maximum NPP was significantly correlated with spring precipitation (R2 = 0.637), NPP peaked early as the spring precipitation increasing.

An improved phenology-based CASA model for estimating net primary production of forest in central China based on Landsat images

ABSTRACTThe optimum temperature () in the current Carnegie–Ames–Stanford Approach (CASA) model was defined as the mean temperature of the month when normalized difference vegetation index (NDVI) reaches its maximum. However, it requires improvements from a comprehensive perspective due to that the stability of the maximum NDVI acquisition is subjected to a variety of factors. The article proposed an improved CASA model by redefining the optimum temperature based on phenology () to model the net primary production (NPP) of forest in Shennongjia, central China, and analysed the relationship between annual mean NPP and topography. Logistic function was used to model the phenological phases of forest and was redefined as the mean temperature during the period of maturity stability. The improved was lower than the for five forest types. Specifically, the average of evergreen broadleaf forest, deciduous broadleaf forest, evergreen needleleaf forest, deciduous needleleaf forest, and mixed forest were 22.72°C, 23.31°C, 24.05°C, 23.41°C, and 23.18°C, respectively, whereas the corresponding average were 24.42°C, 24.90°C, 24.54°C, 24.57°C, and 24.43°C, respectively. The NPP observations transformed from field measured biomass were used to evaluate the accuracy of NPP estimated from the -based CASA model and the -based CASA model. The result indicated that the accuracy of the -based CASA model was higher than that of the -based CASA model, with the coefficients of determination of 0.837 (root mean square error (RMSE) = 75 g C m–2 year–1) and 0.632 (RMSE = 122 g C m–2 year–1), respectively. The total NPP of forest in Shennongjia modelled by the -based CASA model and the -based CASA model were 1.40 and 1.35 Tg C year–1, respectively. The relationship between the annual mean NPP and altitude showed a quadratic polynomial function at the altitude from 500 to 3000 m, while the relationship between the annual mean NPP and aspect showed a sine function when aspect in the range of 4.5–360.0°. The results demonstrate that the improvement of CASA model (-based CASA model) is of great significance in phenology and plays as a promising alternative method to model NPP for forest.

Temporal Variability in Net Primary Production in an Upwelling Area off Central Chile (36°S)

The temporal variability of Net Primary Production (NPP) off central Chile (36oS, 73oW), an area subjected to seasonal coastal upwelling, was analyzed using monthly in situ 13C incubations within the photic zone, along with bio-oceanographic variables from a fixed time series station, and satellite NPP estimations (NPPE) from the Vertically Generalized Production Model between 2006 and 2015. NPP and NPPE rates varied from 0.03 to 18.29 and from 0.45 to 9.07 g C m-2 d-1, respectively. Both rates were fairly well correlated with each other (r2 = 0.61), but when these data were separated into two periods, higher r2 value was found during winter (r2 = 0.70) with respect to the rest of the year (r2 = 0.24); the latter correlation was partially due to increased weekly NPPE variability during active and relaxed upwelling events. NPP rates along with other biophysical variables allowed for a division of the annual cycle into three distinct periods: September to January (high productivity, mean integrated NPP rates of 4.0 g C m-2 d-1), February to March (intermediate productivity, mean integrated NPP rates of 1.4 g C m-2 d-1), and May to August (basal level, mean integrated NPP rates of 0.5 g C m-2 d-1). NPP appeared to be partially controlled by nutrient inputs, either from upwelling (September-April) and river discharge (May-August), maintaining high NPP rates throughout the entire year, with an annual mean NPP rate of 1.1 kg C m-2 yr-1. In this region, El Nino Southern Oscillation events do not appear to impact the NPP interannual variability.

Carbon accumulation in loblolly pine plantations is increased by fertilization across a soil moisture availability gradient

Silvicultural practices, particularly fertilization, may counteract or accentuate the effects of climate change on carbon cycling in planted pine ecosystems, but few studies have empirically assessed the potential effects. In the southeastern United States, we established a factorial throughfall reduction (D) × fertilization (F) experiment in 2012 in four loblolly pine (Pinus taeda L.) plantations encompassing the climatic range of the species in Florida (FL), Georgia (GA), Oklahoma (OK), and Virginia (VA). Net primary productivity (NPP) was estimated from tree inventories for four consecutive years, and net ecosystem productivity (NEP) as NPP minus heterotrophic respiration (RH). Soil respiration (RS) was measured biweekly-monthly for at least one year at each site and simultaneous measurements of RS & RH were taken five to eight times through the year for at least one year during the experiment. Reducing throughfall by 30% decreased available soil water at the surface and for the 0–90 cm soil profile. Fertilization increased NPP at all sites and D decreased NPP (to a lesser extent) at the GA and OK sites. The F + D treatment did not affect NPP. Mean annual NPP under F ranged from 10.01 ± 0.21 MgC·ha−1·yr−1 at VA (mean ± SE) to 17.20 ± 0.50 MgC·ha−1·yr−1 at FL, while the lowest levels were under the D treatment, ranging from 8.63 ± 0.21 MgC·ha−1·yr−1 at VA to 14.97 ± 0.50 MgC·ha−1·yr−1 at FL. RS and RH were, in general, decreased by F and D with differential responses among sites, leading to NEP increases under F. Throughfall reduction increased NEP at FL and VA due to a negative effect on RH and no effect on NPP. Mean annual NEP ranged from 1.63 ± 0.59 MgC·ha−1·yr−1 in the control at OK to 8.18 ± 0.82 MgC·ha−1·yr−1 under F + D at GA. These results suggest that fertilization will increase NEP under a wide range of climatic conditions including reduced precipitation, but either NPP or RH could be the primary driver because F can increase stand growth, as well as suppress RS and RH. Moreover, D and F never significantly interacted for an annual C flux, potentially simplifying estimates of how fertilization and drought will affect C cycling in these ecosystems.

Estimating Net Primary Productivity and Carbon Inputs by Soybean Crops in Argentina

ABSTRACTMonitoring crop net primary productivity (NPP) and its proportion returned to soil in the form of carbon (C) input is vital to better understand the ecological responses to environmental and anthropogenic changes. However, quantification of NPP and C inputs from cropping systems at a regional scale is challenging due to the temporal and spatial variability of soils, climate, and management practices. The aim of this study was to estimate (i) the NPP from soybean crop [Glycine max (L.) Merr.] and (ii) the C inputs from soybean residues into soils of the Pampas and Extra-Pampas regions of Argentina between 1993 and 2005 using a simple approach based on the crop yield census records, a C budget equation, and crop-specific conversion factors at regional scale. Soybean NPP (t ha−1 year−1) at a regional scale was estimated by grain yields and harvested areas reported in the long-term (1993–2005) National database for several districts within each province. The mean annual soybean NPP in the Pampas was 0.3 t ha−1 higher (P < 0.05) than in the Extra-Pampas, resulting in a higher C input from soybean residues of 0.4 t ha−1 year−1 in the Pampas region. Due to improved cultivars and higher nutrient inputs in the Pampas region, the mean NPP and C inputs increased by about 25% from 1999 to 2005. Crop NPP and C inputs from residues into soils play a major role in C dynamics and should be considered for further studies at different scales to understand soil organic C modifications through agricultural changes.

Application of a new model using productivity coupled with hydrothermal factors (PCH) for evaluating net primary productivity of grassland in southern China

Abstract. Grassland ecosystems play important roles in the global carbon cycle. The net primary productivity (NPP) of grassland ecosystems has become the hot spot of terrestrial ecosystems. To simulate grassland NPP in southern China, a new model using productivity coupled with hydrothermal factors (PCH) was built and validated based on data recorded from 2003 to 2014. The results show a logarithmic correlation between grassland NPP and mean annual temperature and a linear positive correlation between grassland NPP and mean annual precipitation in southern China, both highly significant relationships. There was a highly significant correlation between simulated and measured NPP (R2 = 0. 8027). Both RMSE and relative root mean square error (RRMSE) were relatively low, showing that the simulation results of the model were reliable. The NPP values in the study area had a decreasing trend from east to west and south to north. Mean NPP was 471.62 g C m−2 from 2003 to 2014. Additionally, the mean annual NPP of southern grassland presented a rising trend, increasing 3.49 g C m−2 yr−1 during the past 12 years. These results document performance and use of a new method to estimate the grassland NPP in southern China.

Comparative analysis of NPP changes in global tropical forests from 2001 to 2013

Net primary production (NPP) is the difference between total photosynthesis (gross primary production, GPP) and total plant respiration in an ecosystem. NPP is a key component of the terrestrial carbon cycle and is important in global climate research. Tropical forests, distributed mainly in Central Africa, Central and South America, and Southeast Asia, are among the most important ecosystems on earth. They are very important to analyses of the global carbon budget and to the projection of future climatic changes. In this study, we analyzed and compared the temporal and spatial changes of NPP within the three dominant areas of tropical forest from 2001 to 2013 by using data from the Moderate Resolution Imaging Spectroradiometer (MODIS). We found that Central and South America has the highest annual mean NPP, statistically, while the average NPP shows an increasing trend both in Central and South America and Central Africa but a decreasing trend in Southeast Asia.

Decreasing Net Primary Productivity in Response to Urbanization in Liaoning Province, China

Regional ecosystems have been greatly affected by the rapid expansion of urban areas. In order to explore the impact of land use change on net primary productivity (NPP) in rapidly developing cities during the current urbanization process, we quantified land use change in Liaoning province between 2000 and 2010 using net primary productivity as an indicator of ecosystem productivity and health. The Carnegie–Ames–Stanford Approach model was used to estimate NPP by region and land use. We used a unit circle-based evaluation model to quantify local urbanization effects on NPP around eight representative cities. The dominant land use types were farmland, woodland and urban, with urban rapidly replacing farmland. Mean annual NPP and total NPP decreased faster from 2005 to 2010 than from 2000 to 2005, reflecting increasing urbanization rates. The eastern, primarily woodland part of Liaoning province had the greatest reduction in NPP, while the western part, which was primarily farmland and grassland, had the lowest reduction.

Evaluating the grassland net primary productivity of southern China from 2000 to 2011 using a new climate productivity model

Grassland is the important component of the terrestrial ecosystems. Estimating net primary productivity (NPP) of grassland ecosystem has been a central focus in global climate change researches. To simulate the grassland NPP in southern China, we built a new climate productivity model, and validated the model with the measured data from different years in the past. The results showed that there was a logarithmic correlation between the grassland NPP and the mean annual temperature, and there was a linear positive correlation between the grassland NPP and the annual precipitation in southern China. All these results reached a very significant level (P<0.01). There was a good correlation between the simulated and the measured NPP, with R2 of 0.8027, reaching the very significant level. Meanwhile, both root mean square errors (RMSE) and relative root-mean-square errors (RRMSE) stayed at a relatively low level, showing that the simulation results of the model were reliable. The NPP values in the study area had a decreasing trend from east to west and from south to north, and the mean NPP was 471.62 g C m−2 from 2000 to 2011. Additionally, there was a rising trend year by year for the mean annual NPP of southern grassland and the tilt rate of the mean annual NPP was 3.49 g C m−2 yr−1 in recent 12 years. The above results provided a new method for grassland NPP estimation in southern China.

Estimation of net primary productivity in arid region based on coupling model.

Net primary productivity (NPP), as the base for the research of matter recycling and energy flow in terrestrial ecosystem, is sensitive to the changes of environment and climate in arid region, and also is an important indicator of eco-environmental characteristics. Based on remote sensing (RS) and geographic information system (GIS), using meteorological data, eddy cova-riance data, Landsat 8 and MODIS data, this study coupled SEBAL model and light utility efficiency model to estimate the NPP of vegetation in Manas River Watershed, and the spatial pattern of NPP and the relationships between NPP and terrain factors (elevation and slope) were analyzed. Results showed that the estimated result of NPP in Manas River Watershed by coupling model was reasonable and could actually reflect the NPP of vegetation. The total annual NPP of vegetation and the mean annual NPP in Manas River Watershed in 2013 were 7066.72 Tg C·a-1 and 278.06 g C·m-2·a-1 respectively. With the variation of geomorphic type and land cover, the NPP changed remarkably from south to north in a trend of increase-decrease-increase-decrease pattern. The temporal variations of NPP were also obvious, with the NPP in July and August accounting for 52.2% of total annual NPP. With the increase of the elevation and slope, the mean annual NPP decreased as a whole with fluctuations induced by different land covers and environmental factors.