Net Primary Production In Response Research Articles

The functional diversity-productivity relationship of woody plants is climatically sensitive.

Plot-scale experiments indicate that functional diversity (FD) plays a pivotal role in sustaining ecosystem functions such as net primary productivity (NPP). However, the relationships between functional diversity and NPP across larger scale under varying climatic conditions are sparsely studied, despite its significance for understanding forest-atmosphere interactions and informing policy development. Hence, we examine the relationships of community-weighted mean (CWM) and functional dispersion (FDis) of woody plant traits on NPP across China and if such relationships are modulated by climatic conditions at the national scale. Using comprehensive datasets of distribution, functional traits, and productivity for 9120 Chinese woody plant species, we evaluated the distribution pattern of community-weighted mean and functional dispersion (including three orthogonal trait indicators: plant size, leaf morphology, and flower duration) and its relationships with NPP. Finally, we tested the effects of climatic conditions on community-weighted mean/functional dispersion-NPP relationships. We first found overall functional diversity-NPP relationships, but also that the magnitude of these relationships was sensitive to climate, with plant size community-weighted mean promoting NPP in warm regions and plant size functional dispersion promoting NPP in wet regions. Second, warm and wet conditions indirectly increased NPP by its positive effects on community-weighted mean or functional dispersion, particularly through mean plant size and leaf morphology. Our study provides comprehensive evidence for the relationships between functional diversity and NPP under varying climates at a large scale. Importantly, our results indicate a broadening significance of multidimensional plant functional traits for woody vegetation NPP in response to rising temperatures and wetter climates. Restoration, reforestation actions and natural capital accounting need to carefully consider not only community-weighted mean and functional dispersion but also their interactions with climate, to predict how functional diversity may promote ecosystem functioning under future climatic conditions.

Spatiotemporal pattern of NPP and its response to climatic factors in the Yangtze River Economic Belt

Net primary productivity (NPP) of terrestrial ecosystems serves as a crucial carbon sink, playing a significant role in mitigating climate change. This study, focusing on the Yangtze River Economic Belt (YREB), a key area for both economic development and ecological conservation in China, evaluates the temporal and spatial changes in regional NPP and its responses to climatic factors against the backdrop of global change. Utilizing long-term NPP and meteorological grid data from 1981 to 2017, we analyzed the annual change patterns of NPP and its linear and nonlinear responses to climatic factors using copula functions. Our findings indicate that 57.00 % of the YREB has experienced a significant increase in NPP, with the most substantial decreases observed in Shanghai and its surrounding areas (P < 0.05). Temperature emerged as the primary climatic driver, positively correlating with NPP changes in over half of the study area (P < 0.05). Moreover, the nonlinear response of NPP to temperature and precipitation underscores the complex interactions between these factors, revealing a sensitivity to temperature variations that surpasses that to precipitation. The study also highlights the influence of solar radiation and topographic factors, with a significant positive correlation between NPP and solar radiation observed in 15.85 % of the area (P < 0.05). The practical significance of these findings lies in their implications for regional ecological management and climate resilience strategies. The positive correlation between temperature and NPP underscores the potential for targeted temperature management to optimize carbon sequestration across the YREB. Furthermore, the identified nonlinear responses and the role of solar radiation and topography in influencing NPP offer valuable insights for the formulation of adaptive strategies that enhance ecosystem productivity and contribute to achieving carbon neutrality goals. By elucidating the dynamics of NPP in response to a range of environmental factors, this study provides a foundation for informed decision-making in ecological conservation and climate change mitigation efforts within the YREB and similar regions globally.

Diazotrophy as a key driver of the response of marine net primary productivity to climate change

Abstract. The impact of anthropogenic climate change on marine net primary production (NPP) is a reason for concern because changing NPP will have widespread consequences for marine ecosystems and their associated services. Projections by the current generation of Earth system models have suggested decreases in global NPP in response to future climate change, albeit with very large uncertainties. Here, we make use of two versions of the Institut Pierre-Simon Laplace Climate Model (IPSL-CM) that simulate divergent NPP responses to similar high-emission scenarios in the 21st century and identify nitrogen fixation as the main driver of these divergent NPP responses. Differences in the way N fixation is parameterised in the marine biogeochemical component PISCES (Pelagic Interactions Scheme for Carbon and Ecosystem Studies) of the IPSL-CM versions lead to N-fixation rates that are either stable or double over the course of the 21st century, resulting in decreasing or increasing global NPP, respectively. An evaluation of these two model versions does not help constrain future NPP projection uncertainties. However, the use of a more comprehensive version of PISCES, with variable nitrogen-to-phosphorus ratios as well as a revised parameterisation of the temperature sensitivity of N fixation, suggests only moderate changes in globally averaged N fixation in the 21st century. This leads to decreasing global NPP, in line with the model-mean changes of a recent multi-model intercomparison. Lastly, despite contrasting trends in NPP, all our model versions simulate similar and significant reductions in planktonic biomass. This suggests that projected plankton biomass may be a more robust indicator than NPP of the potential impact of anthropogenic climate change on marine ecosystems across models.

Seasonal Dynamics of Algal Net Primary Production in Response to Phosphorus Input in a Mesotrophic Subtropical Plateau Lake, Southwestern China

A comprehensive 3-dimensional hydrodynamic and eutrophication model, the environmental fluid dynamics code model (EFDC) with three functional phytoplankton groups, was applied to simulate the algal dynamics in a mesotrophic P-limited subtropical plateau lake, Lake Erhai, Southwestern China. Field investigations revealed the seasonal patterns in external total phosphorus (TP) input and TP concentration, as well as the composition of the phytoplankton community. The model was calibrated to reproduce qualitative features and the succession of phytoplankton communities, and the net primary production was calculated. The modeled daily net primary production (NPP) ranged between −16.89 and 15.12 mg C/m2/d and exhibited significant seasonal variation. The competition for phosphorus and temperature was identified as the primary governing factor of NPP by analyzing the parameter sensitivity and limitation factors of the lake. The simulation of four nutrient loading reduction scenarios suggested high phytoplankton biomass and NPP sensitivity to the external TP reduction. A significant positive correlation was found among NPP, total phytoplankton biomass and TP concentration. Overall, this work offers an alternative approach to estimating lake NPP, which has the potential to improve sustainable lake management.

Persistent Uncertainties in Ocean Net Primary Production Climate Change Projections at Regional Scales Raise Challenges for Assessing Impacts on Ecosystem Services

Ocean net primary production (NPP) results from CO2 fixation by marine phytoplankton, catalysing the transfer of organic matter and energy to marine ecosystems, supporting most marine food webs, and fisheries production as well as stimulating ocean carbon sequestration. Thus, alterations to ocean NPP in response to climate change, as quantified by Earth system model experiments conducted as part of the 5th and 6th Coupled Model Intercomparison Project (CMIP5 and CMIP6) efforts, are expected to alter key ecosystem services. Despite reductions in inter-model variability since CMIP5, the ocean components of CMIP6 models disagree roughly 2-fold in the magnitude and spatial distribution of NPP in the contemporary era, due to incomplete understanding and insufficient observational constraints. Projections of NPP change in absolute terms show large uncertainty in CMIP6, most notably in the North Atlantic and the Indo-Pacific regions, with the latter explaining over two-thirds of the total inter-model uncertainty. While the Indo-Pacific has previously been identified as a hotspot for climate impacts on biodiversity and fisheries, the increased inter-model variability of NPP projections further exacerbates the uncertainties of climate risks on ocean-dependent human communities. Drivers of uncertainty in NPP changes at regional scales integrate different physical and biogeochemical factors that require more targeted mechanistic assessment in future studies. Globally, inter-model uncertainty in the projected changes in NPP has increased since CMIP5, which amplifies the challenges associated with the management of associated ecosystem services. Notably, this increased regional uncertainty in the projected NPP change in CMIP6 has occurred despite reduced uncertainty in the regional rates of NPP for historical period. Improved constraints on the magnitude of ocean NPP and the mechanistic drivers of its spatial variability would improve confidence in future changes. It is unlikely that the CMIP6 model ensemble samples the complete uncertainty in NPP, with the inclusion of additional mechanistic realism likely to widen projections further in the future, especially at regional scales. This has important consequences for assessing ecosystem impacts. Ultimately, we need an integrated mechanistic framework that considers how NPP and marine ecosystems respond to impacts of not only climate change, but also the additional non-climate drivers.

Oceanic primary production decline halved in eddy-resolving simulations of global warming

Abstract. The decline in ocean primary production is one of the most alarming consequences of anthropogenic climate change. This decline could indeed lead to a decrease in marine biomass and fish catch, as highlighted by recent policy-relevant reports. Because of computational constraints, current Earth system models used to project ocean primary production under global warming scenarios have to parameterize flows occurring below the resolution of their computational grid (typically 1∘). To overcome these computational constraints, we use an ocean biogeochemical model in an idealized configuration representing a mid-latitude double-gyre circulation and perform global warming simulations under an increasing horizontal resolution (from 1 to 1/27∘) and under a large range of parameter values for the eddy parameterization employed in the coarse-resolution configuration. In line with projections from Earth system models, all our simulations project a marked decline in net primary production in response to the global warming forcing. Whereas this decline is only weakly sensitive to the eddy parameters in the eddy-parameterized coarse 1∘ resolution simulations, the simulated decline in primary production in the subpolar gyre is halved at the finest eddy-resolving resolution (−12 % at 1/27∘ vs. −26 % at 1∘) at the end of the 70-year-long global warming simulations. This difference stems from the high sensitivity of the sub-surface nutrient transport to model resolution. Although being only one piece of a much broader and more complicated response of the ocean to climate change, our results call for improved representation of the role of eddies in nutrient transport below the seasonal mixed layer to better constrain the future evolution of marine biomass and fish catch potential.

Evaluating the dynamics of grassland net primary productivity in response to climate change in China

Net primary productivity (NPP) has been considered as a direct indicator to access the terrestrial primary production. However, considerable uncertainties remain toward the response mechanism of NPP to climate change across annual and seasonal scales, especially for grassland ecosystems. In this study, the spatiotemporal dynamics of grassland NPP and its prominent climate-controlling factor were evaluated based on the CASA model and ground-based meteorological data across annual and seasonal scales in China from 1982 to 2016. Results showed that the annual mean grassland NPP was 294.58 gC·m−2·a−1 over the 35 years; the largest annual mean NPP was observed in Alpine sub-alpine meadow (235.72 ± 13.21 gC·m−2·a−1), while the smallest annual mean NPP value occurred in Desert grassland (97.27 ± 9.64 gC·m−2·a−1). Moreover, the multiyear mean grassland NPP showed a decreasing trend from the southeast to the northwest spatially. Temporally, grassland NPP exhibited a significant increasing trend (slope = 2.4 gC·m−2·a−1; p < 0.0001) over the whole study period; an abrupt change point across the grassland NPP time series was observed in 1999. Specially, 66.34% of the grassland area showed an increasing trend in NPP, and the areas with a significant increasing trend were concentrated in Qinghai-Tibet Plateau and the northern area of Xinjiang. Further climate factor analysis with NPP indicated that NPP positively correlated with precipitation and negatively correlated with temperature for the whole grassland area. In particular, the temperature was a dominant driver in NPP variations for Alpine sub-alpine meadow, Slope grassland and Alpine sub-alpine grassland, while precipitation controlled the most in NPP variations for Plain grassland and Desert grassland. The accumulation of grassland NPP in spring and autumn benefits from the increase in temperature, and precipitation promoted the accumulated NPP in summer and winter.

Changes and controls of aboveground net primary production in response to grassland policy in Inner Mongolian grasslands of China

Over-reclamation of grassland resources has increasingly contributed to environmental degradation in China. With grassland degradation, actions have been taken to maintain or restore natural grasslands through efforts such as ecological engineering. Inner Mongolia is considered being one of the most severely degraded areas in China and consequently almost all of the national land restoration projects for environmental protection were implemented there, making it the province with the highest investment in environmental restoration programs in China. In this study, we use the estimation model relationship established between the vegetation index extracted from remote sensing images and the measured biomass in the field to inversely calculate the biomass in the study area. And then we focused on the changes in the aboveground net primary productivity (ANPP) of these grassland ecosystems, which is crucial for gaining a better understanding of grassland changes in the light of rapidly changing environmental policies and governance regimes in China. The interannual variation of ANPP fluctuated greatly (fluctuated from 87.81 g/m2 to 88.5234 g/m2 between 2000 and 2017). The grassland changes in the whole region are basically stable, but the changes in individual areas are more serious. The ANPP was negatively correlated with the mean annual temperature and positively correlated with the annual precipitation. The hydrothermal conditions directly affected the distribution and accumulation of ANPP along meadow, typical and desert grasslands. Different stages of grassland policy have different target orientations and have positive and negative impacts on ANPP.

Assessing the Dynamics of Grassland Net Primary Productivity in Response to Climate Change at the Global Scale

Understanding the net primary productivity (NPP) of grassland is crucial to evaluate the terrestrial carbon cycle. In this study, we investigated the spatial distribution and the area of global grassland across the globe. Then, we used the Carnegie-Ames-Stanford Approach (CASA) model to estimate global grassland NPP and explore the spatio-temporal variations of grassland NPP in response to climate change from 1982 to 2008. Results showed that the largest area of grassland distribution during the study period was in Asia (1737.23 × 104 km2), while the grassland area in Europe was relatively small (202.83 × 104 km2). Temporally, the total NPP increased with fluctuations from 1982 to 2008, with an annual increase rate of 0.03 Pg C/yr. The total NPP experienced a significant increasing trend from 1982 to 1995, while a decreasing trend was observed from 1996 to 2008. Spatially, the grassland NPP in South America and Africa were higher than the other regions, largely as a result of these regions are under warm and wet climatic conditions. The highest mean NPP was recorded for savannas (560.10 g C/(m2·yr)), whereas the lowest was observed in open shrublands with an average NPP of 162.53 g C/(m2·yr). The relationship between grassland NPP and annual mean temperature and annual precipitation (AMT, AP, respectively) varies with changes in AP, which indicates that, grassland NPP is more sensitive to precipitation than temperature.

Influence of precipitation on CO2 soil emission in pine forests of the Central Siberia boreal zone

Boreal forests in Siberia cover more than 70% of the area of this region. Due to climate change these ecosystems represent a very sensitive and significant source of carbon. In the forests, the total ecosystem respiration tends to be dominated by the soil respiration, which accounts for approximately 70% of this large flux. Global models predict that the soil respiration will increase more than the total net primary productivity in response to climate warming and increasing precipitation. In consequence, the terrestrial carbon sink is expected to decline. However, for the Siberian boreal forest there is still a gap in understanding of the future response of soil emission to drought or overprecipitation conditions. In our study we estimate how various moisture conditions could change soil emission in the boreal zone. From field observation data we find optimal soil moisture conditions. The highest dependence between the soil temperature and soil emission rates has been obtained under the optimal soil moisture conditions.

Effects of species replacement on the relationship between net primary production and soil nitrogen availability along a topographical gradient: Comparison of belowground allocation and nitrogen use efficiency between natural forests and plantations

Changes in dominant plant species can influence the net primary production (NPP) via changes in species traits, including nitrogen use efficiency (NUE) and belowground allocation enhancing N uptake, as well as soil N availability. We investigated changes in above- and belowground NPP, N uptake, and NUE in response to changes in soil N in natural forests and plantations, with and without changes in species compositions among the environmental gradient, respectively. In plantations, NPP increased with increasing availability of soil N in the presence of constant NUE and the proportion of belowground NPP to total NPP. However, in natural forests, aboveground, belowground, and total NPP were high for the available middle range soil N. Belowground NPP and the proportion of belowground NPP to total NPP in natural forests was positively related to aboveground NPP. Both belowground NPP and soil N mineralization rates explained stand N uptake rates. These results indicated that belowground allocation might facilitate aboveground NPP with enhancement of N uptake by root allocation. Stand NUE decreased with soil N availability in natural forests and was stable in plantations, and resulted in lower production in natural forests and higher production in plantations under high soil N availability. The community weighted mean (CWM) of N resorption efficiency was positively related to NUE. The CWM of juvenile root growth, as reported previously for planted juveniles, was positively related to belowground NPP allocation. In addition, the ranges of CWMs were broader in natural forests than in plantations. This suggested that the different changes in NPP in response to changes in soil N between natural forests and plantations was due to the changes in leaf and root species traits via changing in species composition among sites. In conclusion, the present study showed that the changes in species specific traits in root growth and leaf N strongly affected the relationship between soil N availability and stand carbon and N dynamics.

Increased litter in subtropical forests boosts soil respiration in natural forests but not plantations of Castanopsis carlesii

Changes in net primary productivity in response to climate change are likely to affect litter inputs to forest soil. However, feedbacks between changes in litter input and soil carbon dynamics remain poorly understood in tropical and subtropical forests. This study aims to test whether the effects of litter manipulation on soil respiration differ between natural and plantation forests. Soil respiration, soil properties, fine root biomass and enzyme activity were measured in adjacent plots with doubling vs. eliminating litter input in both natural and plantation forests of Castanopsis carlesii in southern China. After only 3 years of litter manipulation, the magnitude of change in soil respiration was greater in response to a doubling of the litter input (+24%) than to the elimination of litter input (−15%) in the natural forest, possibly due to a positive priming effect on decomposition of soil organic carbon (SOC). The quick and intense priming effect was corroborated by elevated enzyme activities for five of the six enzymes analyzed. In contrast, the response to litter removal (−31%) was greater than the response to litter addition (1%; not significant) in the plantation forest. The lack of positive priming in the plantation forest may be related to its lower soil fertility, which could not meet the demand of soil microbes, and to its high clay content, which protected SOC from microbial attack. The positive priming effect in the natural forest but not plantation forest of C. carlesii is also consistent with the significant declines in total soil carbon observed following litter addition in the natural forest but not the plantation forest. Increases in aboveground litter production may trigger priming effects and subsequently transfer more soil carbon to atmospheric CO2 in the natural forest but not in the plantation forest with low fertility. Changes in litter inputs resulting from global change drivers may have different impacts on natural and plantation forests.

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.

Projecting the dynamics of terrestrial net primary productivity in response to future climate change under the RCP2.6 scenario

This paper aims to reveal the responses of global natural vegetation to future climate change in the twenty-first century. Thus, the dynamics of terrestrial net primary productivity (NPP) in three time slices, namely, 2030s, 2050s and 2070s are projected using a segmentation model that utilized 25 global climate models under the Representative Concentration Pathway 2.6 (RCP2.6) scenario. The results showed that forests would expand at the expense of grasslands and deserts in the current century. Terrestrial NPP is projected to increase globally from 127.04 ± 1.74 Pg DW·a−1 in 2030s to 127.62 ± 2.57 Pg DW·a−1 in 2070s. Temperate forest, the largest distributed vegetation, would contribute the most to the overall increase (548.50 Tg DW·a−1). The NPP of warm desert, savanna, and tropical forest is projected to increase by 31.03, 248.45 and 111.25 Tg DW·a−1, respectively. By contrast, the NPP of all the other vegetations would decline at the end of this century. In the tropical and the south temperate zones, terrestrial NPP is projected to decrease by 99.32 and 25.56 Tg DW·a−1, respectively, with the difference lying in the increasing–decreasing trend in the former and the continually decreasing trend in the latter. However, terrestrial NPP in the north temperate and north frigid zones is projected to increase consistently by 639.43 and 57.73 Tg DW·a−1, respectively. The “increase-peak-decline” trend of greenhouses gases described in the RCP2.6 would lead to the warming and cooling periods during this century. The vegetation NPP of various ecosystems or climate zones would respond differently to the future climate change. In general, ecosystems in northern high latitudes would become more vulnerable to future climate change compared to other vegetations.

Impacts of climate change on net primary productivity of grasslands in Inner Mongolia

Net primary productivity (NPP) of grasslands is a key variable for characterising carbon cycles in grassland ecosystems. The prediction of NPP in Inner Mongolia is important for adaptation to future climate change, food security and sustainable use of the grassland resources. The output from two models, potentially suitable for simulating NPP in response to climate change, was tested against observed aboveground forage mass of dry matter at eight sites in Inner Mongolia from 1995 to 2005. The Classification Indices-Based Model (CIBM) showed an acceptable agreement with field measurements. The impact of climate change on the NPP of grasslands was subsequently analysed by CIBM using future climate projections from a Global Circulation Model based on three greenhouse gas emission scenarios: A2 (medium-high emission), A1B (medium emission) and B2 (medium-low emission) differing in assumptions about patterns of global social and economic development. Generally, significant increases in NPP, compared with the baseline NPP of 3.6 tonnes ha–1 for 1961–90, were predicted. The magnitude of the increase in NPP depended on the emission scenario, as well as on the time frame and region considered. Overall the predicted NPP stimulation increased with the level of emissions assumed, being 4.8 tonnes ha–1 in the A2 scenario, 4.3 tonnes ha–1 in the B2 scenario and 4.5 tonnes ha–1 in the A1B scenario in the 2080s (2071–2100). The increase in NPP in response to climate change differed between regions and there was an interaction with emission scenario. For the A2 and the B2 emission scenarios, the western region of Inner Mongolia was predicted to exhibit the strongest NPP increases, but, under the A1B scenario for the 2050s, the south-eastern region exhibited the greatest increase in NPP. It is concluded that the productivity of grassland in Inner Mongolia is likely to increase in response to climate change but these predicted effects are sensitive to emission scenarios and differ regionally. This will provide opportunities but also challenges for herders and policy makers in adapting to this change.

Global patterns of nitrogen limitation: confronting two global biogeochemical models with observations

Projections of future changes in land carbon (C) storage using biogeochemical models depend on accurately modeling the interactions between the C and nitrogen (N) cycles. Here, we present a framework for analyzing N limitation in global biogeochemical models to explore how C-N interactions of current models compare to field observations, identify the processes causing model divergence, and identify future observation and experiment needs. We used a set of N-fertilization simulations from two global biogeochemical models (CLM-CN and O-CN) that use different approaches to modeling C-N interactions. On the global scale, net primary productivity (NPP) in the CLM-CN model was substantially more responsive to N fertilization than in the O-CN model. The most striking difference between the two models occurred for humid tropical forests, where the CLM-CN simulated a 62% increase in NPP at high N addition levels (30 g N m(-2) yr(-1)), while the O-CN predicted a 2% decrease in NPP due to N fertilization increasing plant respiration more than photosynthesis. Across 35 temperate and boreal forest sites with field N-fertilization experiments, we show that the CLM-CN simulated a 46% increase in aboveground NPP in response to N, which exceeded the observed increase of 25%. In contrast, the O-CN only simulated a 6% increase in aboveground NPP at the N-fertilization sites. Despite the small response of NPP to N fertilization, the O-CN model accurately simulated ecosystem retention of N and the fate of added N to vegetation when compared to empirical (15) N tracer application studies. In contrast, the CLM-CN predicted lower total ecosystem N retention and partitioned more losses to volatilization than estimated from observed N budgets of small catchments. These results point to the need for model improvements in both models in order to enhance the accuracy with which global C-N cycle feedbacks are simulated.

Incorporating temperature‐sensitive Q10 and foliar respiration acclimation algorithms modifies modeled ecosystem responses to global change

Evidence suggests that respiration acclimation (RA) to temperature in plants can have a substantial influence on ecosystem carbon balance. To assess the influence of RA on ecosystem response variables in the presence of global change drivers, we incorporated a temperature‐sensitive Q10 of respiration and foliar basal RA into the ecosystem model PnET‐CN. We examined the new algorithms' effects on modeled net primary production (NPP), total canopy foliage mass, foliar nitrogen concentration, net ecosystem exchange (NEE), and ecosystem respiration/gross primary production ratios. This latter ratio more closely matched eddy covariance long‐term data when RA was incorporated in the model than when not. Averaged across four boreal ecotone sites and three forest types at year 2100, the enhancement of NPP in response to the combination of rising [CO2] and warming was 9% greater when RA algorithms were used, relative to responses using fixed respiration parameters. The enhancement of NPP response to global change was associated with concomitant changes in foliar nitrogen and foliage mass. In addition, impacts of RA algorithms on modeled responses of NEE closely paralleled impacts on NPP. These results underscore the importance of incorporating temperature‐sensitive Q10 and basal RA algorithms into ecosystem models. Given the current evidence that atmospheric [CO2] and surface temperature will continue to rise, and that ecosystem responses to those changes appear to be modified by RA, which is a common phenotypic adjustment, the potential for misleading results increases if models fail to incorporate RA into their carbon balance calculations.

Evaluating the monthly and interannual variation of net primary production in response to climate in Wuhan during 2001 to 2010

As the difference between photosynthesis, or gross primary productivity (GPP), and autotrophic respiration (RA), net primary productivity (NPP) is a key component of the terrestrial carbon cycle. The temporal and spatial response of NPP to climate change is thus one of the most important aspects in the study of climate-vegetation relationship. In this study, we developed a new method to estimate NPP accurately by finding a linear relationship between solar radiation and photosynthetically active radiation (PAR) and improving maximum light use efficiency (LUE) of vegetation, which could be adopted and used in other regions of the world. We utilize normalized difference vegetation index (NDVI) datasets of Moderate Resolution Imaging Spectroradiometer (MODIS) from 2001 to 2010 and geographic information system (GIS) techniques to reveal the monthly and interannual change of NPP in Wuhan, China. We also applied the lagged cross-correlation analysis method to study the delayed and continuous effects on monthly and interannual variations of NPP to climatic factors (air temperature, precipitation, total radiation and sunshine percentage). The result showed that precipitation and total radiation were the major climatic factors influencing monthly variation of NPP, and sunshine percentage mostly determined the interannual variation of NPP for different vegetation. Monthly NPP showed significant positive correlation with total radiation of that month, and the effect could persist for one month; significant positive one month lagged correlation was also observed between monthly variation of NPP and precipitation, and the influences of changing climate on NPP would last for two months.

Above- and belowground responses to nitrogen addition in a Chihuahuan Desert grassland

Increased available soil nitrogen can increase biomass, lower species richness, alter soil chemistry and modify community structure in herbaceous ecosystems worldwide. Although increased nitrogen availability typically increases aboveground production and decreases species richness in mesic systems, the impacts of nitrogen additions on semiarid ecosystems remain unclear. To determine how a semiarid grassland responds to increased nitrogen availability, we examined plant community structure and above- and belowground net primary production in response to long-term nitrogen addition in a desert grassland in central New Mexico, USA. Plots were fertilized annually (10 g N m(-2)) since 1995 and NPP measured from 2004 to 2009. Differences in aboveground NPP between fertilized and control treatments occurred in 2004 following a prescribed fire and in 2006 when precipitation was double the long-term average during the summer monsoon. Presumably, nitrogen only became limiting once drought stress was alleviated. Belowground NPP was also related to precipitation, and greatest root growth occurred the year following the wettest summer, decreasing gradually thereafter. Belowground production was unrelated to aboveground production within years and unrelated to nitrogen enrichment. Species richness changed between years in response to seasonal precipitation variability, but was not altered by nitrogen addition. Community structure did respond to nitrogen fertilization primarily through increased abundance of two dominant perennial grasses. These results were contrary to most nitrogen addition studies that find increased biomass and decreased species richness with nitrogen fertilization. Therefore, factors other than nitrogen deposition, such as fire or drought, may play a stronger role in shaping semiarid grassland communities than soil fertility.

The response of marine carbon and nutrient cycles to ocean acidification: Large uncertainties related to phytoplankton physiological assumptions

[1] Alongside climate change, anthropogenic emissions of CO2 will cause ocean acidification (OA), which will impact upon key biogeochemical processes in the ocean such as net primary production (NPP), carbon export (CEX), N2 fixation (NFIX), denitrification (DENIT), and ocean suboxia (SOX). However, appraising the impact of OA on marine biogeochemical cycles requires ocean general circulation and biogeochemistry models (OGCBMs) that necessitate a number of assumptions regarding the response of phytoplankton physiological processes to OA. Of particular importance are changes in C:N:P stoichiometry, which cannot be accounted for in current generation OGCBMs that rely on fixed Redfield C:N:P ratios. We developed a new version of the PISCES OGCBM that resolves the cycles of C, N, and P independently to investigate the impact of assumptions that OA (1) enhances NPP, (2) enhances losses of fixed carbon in dissolved organic forms, and (3) modifies the uptake of nutrients by phytoplankton. In total, six simulations were performed over the period 1860–2100. We find that while the prescribed “CO2 sensitivity” of rate processes explains the NPP response, there are large uncertainties in the response of CEX, NFIX, DENIT, and SOX related to assumptions regarding the fate of fixed carbon and nutrient uptake. The overall responses of NPP and CEX are opposite and of similar magnitude to those predicted to occur from climate change alone, suggesting that changes in stoichiometry and NPP in response to OA (and probably also climate change) need to be evaluated in non-Redfield coupled-climate OGCBMs. Using a recent synthesis of OA experiments, it was not possible to evaluate whether one or more of our scenarios was most likely. Future coupled experimental modeling approaches are necessary to better understand the impact of OA on ocean biogeochemistry.