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Although there is mounting concern about how high vapor pressure deficit (VPD) and low soil moisture (SM) affect ecosystem productivity, their relative importance is still under debate. Here, we comprehensively quantified the relative impacts of these two factors on ecosystem gross primary production (GPP) using observations from a global network of eddy‐covariance towers and two approaches (sensitivity analysis and linear regression model). Both approaches agree that a higher percentage of sites experience GPP reduction from high VPD than from low SM over the growing season. However, the constraint of high VPD and low SM on GPP reduction is tightly linked with climates and plant functional types. Humid and mesic ecosystems including forests and grasslands are dominated by VPD, while the semi‐arid and arid ecosystems including shrublands and savannas are dominated by SM. The varying dominant role of these two factors on GPP is closely related to plant stomatal behavior, as predicted by a stomatal conductance model. Additionally, we highlight the non‐linear impact of SM on GPP during droughts and the possible underestimation of the SM effects for deep‐rooted plants when only using surface‐layer SM. Our results shed light on a better understanding of the impacts of VPD and SM on vegetation productivity, with important implications for modeling the response and feedback of ecosystem dynamics to current and future climates. Plain Language Summary: Vapor pressure deficit (VPD) has increased over recent decades and is expected to continue to rise in the future with climate change. Projected changes in precipitation and soil moisture (SM) are more uncertain with higher spatial variability and larger projected intermodel spread. Given the global environmental changes underway, it is of paramount importance to independently assess the effects of high VPD and low SM on ecosystem productivity. Here, we assessed the relative impacts of these two factors on ecosystem gross primary production (GPP) using observations from a global network of eddy‐covariance towers. We find that reductions in GPP are more attributable to high VPD rather than low SM, on average. The constraint of these two factors on GPP reduction is tightly linked with climates and plant functional types. We further emphasize the amplified impact of SM on GPP during droughts and the need to consider using deep SM. Overall, our findings provide a more comprehensive and quantitative attribution of the impact of increasing atmospheric dryness and changes in soil water deficit on ecosystem productivity in a changing climate. Key Points: Reductions in gross primary production (GPP) are more attributable to high vapor pressure deficit (VPD) rather than low soil moisture (SM) across all sitesThe constraint of high VPD and low SM on GPP reduction is tightly linked with climates and plant functional typesOur results highlight that the relative and non‐linear impacts of VPD and SM on GPP should be adequately considered [ABSTRACT FROM AUTHOR]

Introduction: Understanding the seasonality of vegetation growth is important for maintaining sustainable development of grassland livestock systems over the Tibetan Plateau (TP). Current knowledge of changes in the seasonality of TP grasslands is restricted to spring and autumn phenology, with little known about the date of peak vegetation growth, the most relevant quantity for grassland productivity. Methods: We investigate the shifts of the date of peak vegetation growth and its climatic controls for the alpine grasslands over the TP during 2001-2020 using a framework based on the law of minimum, which is based on the assumption that peak vegetation growth would be consistent with the peak timing of the most limiting climatic resource. Results: The date of peak vegetation growth over the TP advanced by 0.81 days decade-1 during 2001-2020. This spring-ward shift mainly occurs in the semihumid eastern TP, where the peak growth date tracks the advancing peak precipitation, and shifted towards the timing of peak temperature. The advancing peak growth over the eastern TP significantly stimulated the ecosystem production by 1.99 gCm-2 year-1 day-1 during 2001-2020, while this positive effect weakened from 3.02 gCm-2 year-1 day-1 during 2000s to 1.25 gCm-2 year-1 day-1 during 2010s. Discussion: Our results highlighted the importance of water availability in vegetation growth over the TP, and indicated that the TP grassland is moving towards a tipping point of transition from thermal-constrained to water-constrained ecosystem under the rapid warming climate. [ABSTRACT FROM AUTHOR]

Abstract Although there is mounting concern about how high vapor pressure deficit (VPD) and low soil moisture (SM) affect ecosystem productivity, their relative importance is still under debate. Here, we comprehensively quantified the relative impacts of these two factors on ecosystem gross primary production (GPP) using observations from a global network of eddy‐covariance towers and two approaches (sensitivity analysis and linear regression model). Both approaches agree that a higher percentage of sites experience GPP reduction from high VPD than from low SM over the growing season. However, the constraint of high VPD and low SM on GPP reduction is tightly linked with climates and plant functional types. Humid and mesic ecosystems including forests and grasslands are dominated by VPD, while the semi‐arid and arid ecosystems including shrublands and savannas are dominated by SM. The varying dominant role of these two factors on GPP is closely related to plant stomatal behavior, as predicted by a stomatal conductance model. Additionally, we highlight the non‐linear impact of SM on GPP during droughts and the possible underestimation of the SM effects for deep‐rooted plants when only using surface‐layer SM. Our results shed light on a better understanding of the impacts of VPD and SM on vegetation productivity, with important implications for modeling the response and feedback of ecosystem dynamics to current and future climates.

The amount of and changes in a country’s natural assets are crucial for developing national strategic plans and policies due to their foundational role in determining the resilience of social-environmental systems (SES), especially under a changing climate. Many integrated metrics on natural assets have been proposed based on individual measures to provide insights into the state of national natural resources. This is particularly true for countries experiencing extreme environmental stresses. Drawing on longitudinal data spanning from 1980 to 2020, the objective of this study is to analyze nuanced distinctions across 23 political entities (PEs) in the dryland regions of mid-latitudinal Asia, investigating their interannual variabilities over the four-decade study period and discerning potential driving forces. We examined three key integrated measures of the SES: ecosystem water use efficiency, human appropriation of net primary production, and human appropriation of water resources. We found increased variability as well as spikes in extreme values in each of these three measures of SES function among the 23 PEs over the study period. Water stress played an increasing and more important role than temperature in influencing the magnitude and variations of the three measures. Our results also indicate that human interventions may help increase the efficiency of water use in this dryland region of the world.

IntroductionUnderstanding the seasonality of vegetation growth is important for maintaining sustainable development of grassland livestock systems over the Tibetan Plateau (TP). Current knowledge of changes in the seasonality of TP grasslands is restricted to spring and autumn phenology, with little known about the date of peak vegetation growth, the most relevant quantity for grassland productivity.MethodsWe investigate the shifts of the date of peak vegetation growth and its climatic controls for the alpine grasslands over the TP during 2001–2020 using a framework based on the law of minimum, which is based on the assumption that peak vegetation growth would be consistent with the peak timing of the most limiting climatic resource.ResultsThe date of peak vegetation growth over the TP advanced by 0.81 days decade-1 during 2001–2020. This spring-ward shift mainly occurs in the semi-humid eastern TP, where the peak growth date tracks the advancing peak precipitation, and shifted towards the timing of peak temperature. The advancing peak growth over the eastern TP significantly stimulated the ecosystem production by 1.99 gCm-2 year-1 day-1 during 2001–2020, while this positive effect weakened from 3.02 gCm-2 year-1 day-1 during 2000s to 1.25 gCm-2 year-1 day-1 during 2010s.DiscussionOur results highlighted the importance of water availability in vegetation growth over the TP, and indicated that the TP grassland is moving towards a tipping point of transition from thermal-constrained to water-constrained ecosystem under the rapid warming climate.

Bangladesh has the single largest mangrove forest in the world, which is under threat from catastrophic disturbance and anthropogenic pressure. The study investigated monthly reproductive litterfall and correlated with climatic factors from March 2016 to February 2018. We applied circular statistics to detect seasonal trends of reproductive litterfall of Heritiera fomes, Xylocarpus mekongensis and Bruguiera sexangula in the Sundarbans. Although flower and fruit fall of H. fomes and X. mekongensis occurred for a specific period. But B. sexangula continued throughout the year. Flower fall of all three species peaked during March. Fruit fall of H. fomes, and X. mekongensis peaked during July and August respectively and the propagule fall of B. sexangula peaked during July. The highest proportion of flower fall was recorded in B. sexangula (2.13 ± 0.29 Mg ha−1year−1) followed by X. mekongensis (1.23 ± 0.07 Mg ha−1year−1) and H. fomes (1.06 ± 0.09 Mg ha−1year−1). But the highest fruit fall was recorded in H. fomes followed by X. mekongensis and B. sexangula. Annual flower and fruit fall were significantly different (p

Understanding how to scale up effects of biological diversity on ecosystem functioning and services remains challenging. There is a general consensus that biodiversity loss alters ecosystem processes underpinning the goods and services upon which humanity depends. Yet most of that consensus stems from experiments performed at small spatial scales for short time frames, which limits transferability of conclusions to longer‐term, landscape‐scale conservation policies and management. Here we develop quantitative scaling relationships linking 374 experiments that tested plant diversity effects on biomass production across a range of scales. We show that biodiversity effects increase by factors of 1.68 and 1.10 for each 10‐fold increase in experiment temporal and spatial scales, respectively. Contrary to prior studies, our analyses suggest that the time scale of experiments, rather than their spatial scale, is the primary source of variation in biodiversity effects. But consistent with earlier research, our analyses reveal that complementarity effects, rather than selection effects, drive the positive space–time interactions for plant diversity effects. Importantly, we also demonstrate complex space–time interactions and nonlinear responses that emphasize how simple extrapolations from small‐scale experiments are likely to underestimate biodiversity effects in real‐world ecosystems. Quantitative scaling relationships from this research are a crucial step towards bridging controlled experiments that identify biological mechanisms across a range of scales. Predictions from scaling relationships like these could then be compared with observations for fine‐tuning the relationships and ultimately improving their capacities to predict consequences of biodiversity loss for ecosystem functioning and services over longer time frames across real‐world landscapes. [ABSTRACT FROM AUTHOR]

Climate warming has yielded earlier ice break‐up dates in recent decades for lakes leading to water temperature increases, altered habitat, and both increases and decreases to ecosystem productivity. Within lakes, the effect of climate warming on secondary production in littoral and pelagic habitats remains unclear. The intersection of changing habitat productivity and warming water temperatures on salmonids is important for understanding how climate warming will impact mountain ecosystems. We develop and test a conceptual model that expresses how earlier ice break‐up dates influence within lake habitat production, water temperatures and the habitat utilized by, resources obtained and behavior of salmonids in a mountain lake. We measured zoobenthic and zooplankton production from the littoral and pelagic habitats, thermal conditions, and the habitat use, resource use, and fitness of Brook Trout (Salvelinus fontinalis). We show that earlier ice break‐up conditions created a "resource‐rich" littoral–benthic habitat with increases in zoobenthic production compared to the pelagic habitat which decreased in zooplankton production. Despite the increases in littoral–benthic food resources, trout did not utilize littoral habitat or zoobenthic resources due to longer durations of warm water temperatures in the littoral zone. In addition, 87% of their resources were supported by the pelagic habitat during periods with earlier ice break‐up when pelagic resources were least abundant. The decreased reliance on littoral–benthic resources during earlier ice break‐up caused reduced fitness (mean reduction of 12 g) to trout. Our data show that changes to ice break‐up drive multi‐directional results for resource production within lake habitats and increase the duration of warmer water temperatures in food‐rich littoral habitats. The increased duration of warmer littoral water temperatures reduces the use of energetically efficient habitats culminating in decreased trout fitness. [ABSTRACT FROM AUTHOR]

Networks of direct and indirect biotic interactions underpin the complex dynamics and stability of ecological systems, yet experimental and theoretical studies often yield conflicting evidence regarding the direction (positive or negative) or magnitude of these interactions. We revisited pioneering data sets collected at the deciduous forested Horonai Stream and conducted ecosystem‐level syntheses to demonstrate that the direction of direct and indirect interactions can change depending on the timescale of observation. Prior experimental studies showed that terrestrial prey that enter the stream from the adjacent forest caused positive indirect effects on aquatic invertebrates during summer by diverting fish consumption. Seasonal and annual estimates of secondary production and organic matter flows along food web pathways demonstrate that this seasonal input of terrestrial invertebrate prey increases production of certain fish species, reversing the indirect effect on aquatic invertebrates from positive at the seasonal timescale to negative at the annual timescale. Even though terrestrial invertebrate prey contributed 54% of the annual organic matter flux to fishes, primarily during summer, fish still consumed 98% of the aquatic invertebrate annual production, leading to top‐down control that is not revealed in short‐term experiments and demonstrating that aquatic prey may be a limiting resource for fishes. Changes in the direction or magnitude of interactions may be a key factor creating nonlinear or stabilizing feedbacks in complex systems, and these dynamics can be revealed by merging experimental and comparative approaches at different scales. [ABSTRACT FROM AUTHOR]

To create a comprehensive view of ecosystem resource use, we integrated parallel resource use efficiency observations into a multiple-resource use efficiency (mRUE) framework using a dynamic factor analysis model. Results from 56 site-years of eddy covariance data and mRUE factors for a site in the US Midwest show temporal dynamics and coherence (using Pearson's R) among resources are associated with interannual variation in precipitation. Loading factors are derived from mRUE observations and quantify how strongly data are connected to the underlying ecosystem state. Water and light resource use loading factors are coherent at annual timescales (Pearson's R of 0.86), whereas declining patterns of carbon use efficiency loading factors highlight the ecosystem's trade-off between carbon uptake and respiration during the growing season. At annual and monthly timescales, influence decreases from ~ 85 to ~ 65% for loading factors for carbon use, while influence of light use loading factors peaks to ~ 60% at growing season timescales. Quantifying variation in ecosystem function provides novel insights into the temporal dynamics of changing importance of multiple resources to ecosystem function. [ABSTRACT FROM AUTHOR]

Assessments of changes in landscape patterns and functions during urban development need to factor urban fringes (UPs) as part of the overall social-environmental system, especially in regions with poor transportation systems where urban functions depend heavily on surrounding suburbs. In this study, we use net primary production (NPP) as an integrative measure to delineate UPs and to measure the expansion in 15 urban areas in the remote Qinghai-Tibet Plateau. Using a logistic curve fitting model based on NPP to delineate differences between the UF and rural landscapes, we explore how NPP-inferred UF expansions may have changed with increase in urban population and the secondary and tertiary industrial production. The UF width (area) was 17.4 km (950.67 km ^2 ) in 2000 but increased to 27.0 km (2289.06 km ^2 ) in 2019 for Lhasa. For Xining, this was from 28.0 km (2461.76 km ^2 ) to 36.0 km (4069.44 km ^2 ) during 2000–2019. For the prefecture-level cities, the rate increased from 2–16 km (12.56–803.84 km ^2 ) to 7–17 km (153.86–907.46 km ^2 ). More importantly, the ratio between UF width and population during the five study periods showed a linear decreasing trend, but an exponential decrease with economic measures. The urban expansion due to population increase changed from 26 m in 2000 to 21 m in 2019 for every increase of 1000 residents, while the expansion due to economic changes was significantly reduced from 732 m per billion RMB (Ren Min Bi) in 2000 to 52 m per billion RMB in 2019. We confirm a hypothesis that the ratio of expansion of UFs was more dependent on economic growth in early stages of urbanization than in later stages, whereas urban population promoted expansions over the entire study period.

Peatlands play an important role in the global carbon cycle due to the high carbon storage in the substrate. Ecosystem production depends, for example, on the solar energy amount that reaches the vegetation, however the diffuse component of this flux can substantially increase ecosystem net productivity. This phenomenon is observed in different ecosystems, but the study of the atmosphere optical properties on peatland production is lacking. In this paper, the presented methodology allowed us to disentangle the diffuse radiation impact on the net ecosystem production (NEP) of Rzecin peatland, Poland. It allowed us to assess the impact of the atmospheric scattering process determined by the aerosol presence in the air mass. An application of atmospheric radiation transfer (ART) and ecosystem production (EP) models showed that the increase of aerosol optical thickness from 0.09 to 0.17 caused NEP to rise by 3.4–5.7%. An increase of the diffusion index (DI) by 0.1 resulted in an NEP increase of 6.1–42.3%, while a DI decrease of 0.1 determined an NEP reduction of −49.0 to −10.5%. These results show that low peatland vegetation responds to changes in light scattering. This phenomenon should be taken into account when calculating the global CO2 uptake estimation of such ecosystems.

Background Submerged plants composed of charophytes (green algae) and angiosperms develop dense vegetation in small, shallow lakes and in littoral zones of large lakes. Many small, oligotrophic plant species have declined due to drainage and fertilization of lakes, while some tall, eutrophic species have increased. Although plant distribution has been thoroughly studied, the physiochemical dynamics and biological challenges in plant-dominated lakes have been grossly understudied, even though they may offer the key to species persistence. Scope Small plant-dominated lakes function as natural field laboratories with eco-physiological processes in dense vegetation dictating extreme environmental variability, intensive photosynthesis and carbon cycling. Those processes can be quantified on a whole lake basis at high temporal resolution by continuously operating sensors for light, temperature, oxygen, etc. We explore this hitherto hidden world. Conclusions Dense plant canopies attenuate light and wind-driven turbulence and generate separation between warm surface water and colder bottom waters. Daytime vertical stratification becomes particularly strong in dense charophyte vegetation, but stratification is a common feature in small, shallow lakes also without plants. Surface cooling at night induces mixing of the water column. Daytime stratification in plant stands may induce hypoxia or anoxia in dark bottom waters by respiration, while surface waters develop oxygen supersaturation by photosynthesis. Intensive photosynthesis and calcification in shallow charophyte lakes depletes dissolved inorganic carbon (DIC) in surface waters, whereas DIC is replenished by respiration and carbonate dissolution in bottom waters and returned to surface waters before sunrise. Extreme diel changes in temperature, DIC and oxygen in dense vegetation can induce extensive rhythmicity of photosynthesis and respiration and become a severe challenge to the survival of organisms. Large phosphorus pools are bound in plant tissue and carbonate precipitates. Future studies should test the importance of this phosphorus sink for ecosystem processes and competition between phytoplankton and plants. [ABSTRACT FROM AUTHOR]

Various climatic and hydrological variables such as precipitation, soil moisture, stream flow, and water level can be used to assess drought conditions, however, the response of ecosystem productivity to such metrics is not very clear. In this study, we examined the sensitivity of GPP anomalies to five drought indicators: the Standardized Precipitation Index (SPI), the Standardized Precipitation–Evapotranspiration Index (SPEI), Palmer Drought Severity Index (PDSI), deficit of soil moisture (DSM), and the difference between precipitation (P) and evapotranspiration (ET) (D(P-ET)). The global spatial distributions of drying and wetting trends from 2000 to 2014 determined by these five indices were similar. Additionally, the percent of drought-impacted areas decreased over the study period, indicating a reduction in drought conditions. GPP increased over the study period in the Northern Hemisphere (NH) but decreased in the Southern Hemisphere (SH), resulting in a net increase in global GPP. GPP anomalies were more sensitive to drought indices in the SH than in the NH. Among the five indices, GPP anomalies were most closely correlated with SPI in the NH (R = 0.60, P < 0.05) and SPEI in the SH (R = 0.93, P < 0.01). Regionally speaking, annual and seasonal GPP anomalies were most sensitive to DSM and PDSI, highlighting the importance of soil moisture observations to regional drought monitoring and assessment. The results of this study are important for evaluating the impacts of drought on ecosystem production and the global carbon cycle. [ABSTRACT FROM AUTHOR]

• 8-years of continuous CO 2 fluxes from a pristine East-Central European peatland. • A temperate peatland with an overall robust sink of CO 2. • CO 2 source under dry and hot conditions. • High summertime TA and VPD limiting net ecosystem production. • Net ecosystem production increases during warmer spring and decreases in a hot summer. Peatlands are among the largest stocks of soil carbon, which can be stored for thousands of years under well-wetted conditions. The main goals of the study were to assess annual and seasonal CO 2 balances of a temperate peatland and the main biophysical factors affecting these CO 2 fluxes. The studied peatland was usually a CO 2 sink with a mean annual net ecosystem production (NEP) of 110±83 gCO 2 -C·m−2·yr−1 and extreme balances in 2006 (-17 gCO 2 -C·m−2·yr−1) and 2011 (194 gCO 2 -C·m−2·yr−1). Annual fluxes were not significantly correlated with biophysical variables, unlike seasonal data. Furthermore, the average air temperature in spring and summer was related to NEP at r2=0.65 and r2=0.61, respectively (warmer spring increased NEP while hot summer decreased NEP in these seasons). A decrease in daytime measured NEP during the summer period (June-August) was observed when TA exceeded 25 °C or VPD was above 15 hPa, respectively, due to the growing R eco and possibly plant photorespiration. These findings suggest a negative impact of ongoing global warming on temperate peatland CO 2 balances. [ABSTRACT FROM AUTHOR]

The purpose of the paper is to justify special natural discount rates in the efficiency assessment of conservation activities. Nowadays, the social rate of discounting suggested by D. Pearce is often used. However, many ecosystem values differ in such aspects as absence of high-grade anthropogenic substitutes and conservative character of natural “technologies”, and consequently simple, not expanded, reproduction. As a result, there exists the need for special discounting rate for non-replaceable production and services restricted in their reprocessing and consumption. This follows from the analysis of a consumer choice trajectory in the course of budget growth over a level at which the maximum of consumption of the limited good is reached. The paper estimates the reduction value for discounting rates for renewable natural resources restricted in regeneration in the special case of individual utility functions of the Cobb-Douglas type and, for a collective consumption, using equal-parts resource sharing among consuming community members. The idea of special discount rates for the production and non-material services of ecosystems is useful both for economic efficiency assessment of nature conservation activities and for calculation of compensations from the activities that adversely affect environment quality.

Peatland net ecosystem production is a key variable to assess changes in the functional role of peatlands in the global carbon cycle. Light use efficiency (LUE) models in combination with satellite data have been used to estimate production for most major ecosystems, but peatlands have been largely ignored. The objectives of this study were: 1) to examine how the LUE parameter epsilon, ε (the amount of carbon fixed or converted to biomass per unit absorbed photosynthetically active radiation), varies between and within four different peatlands; 2) to examine how the variations in ε relate to variations in environmental conditions; and 3) to evaluate a LUE-based model for estimation of ε in peatlands. We achieve these objectives using a combination of eddy covariance flux measurements, climate data and satellite data and estimate ε using the LUE-based vegetation photosynthesis model (VPM). The results show that: 1) mean site-specific flux-derived ε values (± standard deviation) were split into three statistically different groups: lowest values at the two colder fens, Kaamanen and Sandhill (0.22 ± 0.18 and 0.23 ± 0.20 g C MJ − 1 , respectively), highest values at the treed fen La Biche (0.47 ± 0.27 g C MJ − 1 ) and intermediate values at the bog, Mer Bleue (0.34 ± 0.18 g C MJ − 1 ); 2) Variations in monthly ε within sites related mainly to air temperature, while variations in annual ε within sites related mainly to wetness variables; 3) relative mean absolute errors of estimates of ε for the four sites ranged between 19% and 35%, with r 2 values ranging between 72% and 93%. LUE models are appealing as they are relatively simple formulations of variables that are easily obtained from satellite data. Challenges associated with the use of satellite data derived input variables are further discussed in the paper. [ABSTRACT FROM AUTHOR]

There is an ongoing world-wide decline of seagrass ecosystems, one of the world's most efficient carbon sink habitats. In spite of this, there is a clear lack of studies experimentally testing the effects of anthropogenic disturbances on carbon sequestration of seagrass systems., We assessed the effects of two disturbances of global concern on the carbon sink function in a five-month in situ experiment within a tropical seagrass ( Thalassia hemprichii) meadow by testing the impacts of shading and simulated grazing at two levels of intensity using shading cloths and clipping of shoot tissue. We measured the effects of these disturbances on the carbon sequestration process by assessing the net community production ( NCP), carbon and nitrogen content in tissue biomass, and organic matter and THAA (total hydrolysable amino acids) in the sediment down to 40 cm depth., Treatments of high-intensity shading and high-intensity clipping were similarly impacted and showed a significantly lower NCP and carbon content in the below-ground biomass compared to the seagrass control. No significant effects were seen in organic carbon, total nitrogen, C:N ratio and THAA in the sediment for the seagrass treatments. However, both clipping treatments showed different depth profiles of carbon and THAA compared to the seagrass control, with lower organic carbon and THAA content in the surface sediment. This can be explained by the clipping of shoot tissue causing a less efficient trapping of allochthonous carbon and reduced input of shredded seagrass leaves to the detritus sediment layer. In the clipping plots, erosion of the surface sediment occurred, which was also most likely caused by the removal of above-ground plant biomass., Synthesis. Our findings show that during the course of this experiment, there were no impacts on the sedimentary carbon while the high-intensity disturbances caused a clear depletion of carbon biomass and reduced the seagrass meadow's capacity to sequester carbon. From a long-term perspective, the observed effect on the carbon biomass pool in the high-intensity treatments and the sediment erosion in the clipping plots may lead to loss in sedimentary carbon. [ABSTRACT FROM AUTHOR]

Introduction: Understanding the seasonality of vegetation growth is important for maintaining sustainable development of grassland livestock systems over the Tibetan Plateau (TP). Current knowledge of changes in the seasonality of TP grasslands is restricted to spring and autumn phenology, with little known about the date of peak vegetation growth, the most relevant quantity for grassland productivity., Methods: We investigate the shifts of the date of peak vegetation growth and its climatic controls for the alpine grasslands over the TP during 2001-2020 using a framework based on the law of minimum, which is based on the assumption that peak vegetation growth would be consistent with the peak timing of the most limiting climatic resource., Results: The date of peak vegetation growth over the TP advanced by 0.81 days decade-1 during 2001-2020. This spring-ward shift mainly occurs in the semi-humid eastern TP, where the peak growth date tracks the advancing peak precipitation, and shifted towards the timing of peak temperature. The advancing peak growth over the eastern TP significantly stimulated the ecosystem production by 1.99 gCm-2 year-1 day-1 during 2001-2020, while this positive effect weakened from 3.02 gCm-2 year-1 day-1 during 2000s to 1.25 gCm-2 year-1 day-1 during 2010s., Discussion: Our results highlighted the importance of water availability in vegetation growth over the TP, and indicated that the TP grassland is moving towards a tipping point of transition from thermal-constrained to water-constrained ecosystem under the rapid warming climate., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Xu, Liu, Wang and Wang.)

Soil respiration is recognized to be influenced by temperature, moisture, and ecosystem production. However, little is known about how plant community structure regulates responses of soil respiration to climate change. Here, we used a 13-year field warming experiment to explore the mechanisms underlying plant community regulation on feedbacks of soil respiration to climate change in a tallgrass prairie in Oklahoma, USA. Infrared heaters were used to elevate temperature about 2 °C since November 1999. Annual clipping was used to mimic hay harvest. Our results showed that experimental warming significantly increased soil respiration approximately from 10% in the first 7 years (2000-2006) to 30% in the next 6 years (2007-2012). The two-stage warming stimulation of soil respiration was closely related to warming-induced increases in ecosystem production over the years. Moreover, we found that across the 13 years, warming-induced increases in soil respiration were positively affected by the proportion of aboveground net primary production ( ANPP) contributed by C3 forbs. Functional composition of the plant community regulated warming-induced increases in soil respiration through the quantity and quality of organic matter inputs to soil and the amount of photosynthetic carbon (C) allocated belowground. Clipping, the interaction of clipping with warming, and warming-induced changes in soil temperature and moisture all had little effect on soil respiration over the years (all P > 0.05). Our results suggest that climate warming may drive an increase in soil respiration through altering composition of plant communities in grassland ecosystems. [ABSTRACT FROM AUTHOR]

Studies on carbon flux in the oceans have been highlighted in recent years due to increasing awareness about climate change, but the coastal ecosystem remains one of the unexplored fields in this regard. In this study, the dynamics of carbon flux in a vegetative coastal ecosystem were examined by an evaluation of net and gross ecosystem production (NEP and GEP) and CO2 exchange rates (net ecosystem exchange, NEE). To estimate NEP and GEP, community production and respiration were measured along different habitat types (eelgrass and macroalgal beds, shallow and deep sedimentary, and deep rocky shore) at Gwangyang Bay, Korea from 20 June to 20 July 2007. Vegetative areas showed significantly higher ecosystem production than the other habitat types. Specifically, eelgrass beds had the highest daily GEP (6.97 ± 0.02 g C m-2 d-1), with a large amount of biomass and high productivity of eelgrass, whereas the outer macroalgal vegetation had the lowest GEP (0.97 ± 0.04 g C m-2 d-1). In addition, macroalgal vegetation showed the highest daily NEP (3.31 ± 0.45 g C m-2 d-1) due to its highest P : R ratio (2.33). Furthermore, the eelgrass beds acted as a CO2 sink through the air-seawater interface according to NEE data, with a carbon sink rate of 0.63 mg C m-2 d-1. Overall, ecosystem production was found to be extremely high in the vegetated systems (eelgrass and macroalgal beds), which occupy a relatively small area compared to the unvegetated systems according to our conceptual diagram of a carbon-flux box model. These results indicate that the vegetative ecosystems showed significantly high capturing efficiency of inorganic carbon through coastal primary production. [ABSTRACT FROM AUTHOR]

Abstract: Efforts to increase our understanding of the terrestrial carbon balance have resulted in a dense global network of eddy covariance towers, which are able to measure the net ecosystem exchange of CO2, H2O and energy between ecosystems and the atmosphere. However, the typical set-up on an eddy covariance tower does not monitor lateral CO2- and carbon fluxes such as dissolved organic carbon (DOC). By ignoring DOC fluxes eddy covariance-based CO2 balances overestimate the carbon sink of ecosystems as part of the DOC drains into the inland waters and get respired outside the footprint of the eddy covariance tower. In this study we quantify 7 years (2000–2006) of DOC fluxes from a temperate Scots pine forest in Belgium and analyse its inter-annual variability. On average, 10gCm−2 year−1 is leached from the pine forest as DOC. If the DOC fluxes are considered relative to the gross ecosystem carbon fluxes we see that DOC fluxes are small: 0.8±0.2% relative to gross primary productivity, 1.0±0.3% relative to ecosystem respiration, and (2.4±0.4%) relative to soil respiration. However, when compared to net fluxes such as net ecosystem productivity and net biome productivity the DOC flux is no longer negligible (11±7% and 17%, respectively), especially because the DOC losses constitute a systematic bias and not a random error. The inter-annual variability of the DOC fluxes followed that of annual water drainage. Hence, drainage drives DOC leaching at both short and long time scales. Finally, it is noted that part of the carbon that is leached from the ecosystem as DOC is respired or sequestered elsewhere, so the physical boundaries of accounting should always be reported together with the carbon budget. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we present estimated ranges in carbon (C) sequestration per kg nitrogen (N) addition in above-ground biomass and in soil organic matter for forests and heathlands, based on: (i) empirical relations between spatial patterns of carbon uptake and influencing environmental factors including nitrogen deposition (forests only), (ii) 15N field experiments, (iii) long-term low-dose N fertilizer experiments and (iv) results from ecosystem models. The results of the various studies are in close agreement and show that above-ground accumulation of carbon in forests is generally within the range 15–40kgC/kgN. For heathlands, a range of 5–15kgC/kgN has been observed based on low-dose N fertilizer experiments. The uncertainty in C sequestration per kgN addition in soils is larger than for above-ground biomass and varies on average between 5 and 35kgC/kgN for both forests and heathlands. All together these data indicate a total carbon sequestration range of 5–75kgC/kgN deposition for forest and heathlands, with a most common range of 20–40kgC/kgN. Results cannot be extrapolated to systems with very high N inputs, nor to other ecosystems, such as peatlands, where the impact of N is much more variable, and may range from C sequestration to C losses. [Copyright &y& Elsevier]

This study presents a basin-scale integrative hydrological, ecological, and economic (HEE) modeling system, aimed at evaluating the impact of resources management, especially agricultural water resources management, on the sustainability of regional water resources. The hydrological model in the modeling system was adapted from SWAT, the Soil and Water Assessment Tool, to simulate the water balance in terms of soil moisture, evapotranspiration, and streamflow. An ecological model was integrated into the hydrological model to compute the ecosystem production of biomass production and yield for different land use types. The economic model estimated the monetary values of crop production and water productivity over irrigated areas. The modeling system was primarily integrated and run on a Windows platform and was able to produce simulation results at daily time steps with a spatial resolution of hydrological response unit (HRU). The modeling system was then calibrated over the period from 1983 to 1991 for the upper and middle parts of the Yellow River basin, China. Calibration results showed that the efficiencies of the modeling system in simulating monthly streamflow over 5 hydrological stations were from 0.54 to 0.68 with an average of 0.64, indicating an acceptable calibration. Preliminary simulation results from 1986 to 1995 revealed that water use in the study region has largely reduced the streamflow in many parts of the area except for that in the riverhead. Spatial distribution of biomass production, and crop yield showed a strong impact of irrigation on agricultural production. Water productivity over irrigated cropland ranged from 1 to 1640 USD/(ha·mm−1), indicating a wide variation of the production conditions within the study region and a great potential in promoting water use efficiency in low water productivity areas. Generally, simulation results from this study indicated that the modeling system was capable of tracking the temporal and spatial variability of pertinent water balance variables, ecosystem dynamics, and regional economy, and provided a useful simulation tool in evaluating long-term water resources management strategies in a basin scale. [ABSTRACT FROM AUTHOR]

We present an approach that sets limits on annual carbon fluxes for different aged forests by using a simple process-based model (3-PG) and information derived from yield tables and local weather stations. Given a measure of height-growth potential, model predictions are constrained to match stand dynamics described in yield tables. Thus constrained, the model can provide reasonable annual estimates of gross photosynthesis under a specified climate, even with inexact knowledge of soil properties. If we assume that leaf litterfall and fineroot turnover approach equilibrium at canopy closure, maximum net annual ecosystem exchange can also be predicted from modeled estimates of these two detrital components and estimates of foliage, branch, stem and coarse-root production. The latter four components of production are predicted from allometric relationships with mean stem diameter. The approach is demonstrated for Douglas-fir (Pseudotsuga menzie-sii (Mirb.) Franco) stands between Ages 20 and 150 years growing under conditions typical of those at Wind River, Washington, USA. Gross photosynthesis (Pg) by Douglas-fir at Ages 20, 70 and 150 years with leaf area indices (L) of 8.1, 6.9 and 4.0 was predicted at 1630, 1580 and 1160 g C m−2year−1, respectively. Maximum net ecosystem production (Pe) for thesame range in age classes was predicted to average 275, 294 and 207 g C m−2year−1, respectively. The predicted reductions in L for older stands do not occur because other species fill the canopy gaps created by natural mortality of Douglas-fir. As a result of the development of an understory, total Pg is predicted to decrease only slightly with the aging of the overstory. Estimates of Pe exclude respiration from coarse woody debris, although additions of this component are provided annually by the model. The process-based modeling approach, constrained by yield table estimates of stand properties, sets reasonable limits on annual carbon exchange and suggests which environmental variables deserve careful monitoring to refine estimates of carbon fluxes. [ABSTRACT FROM AUTHOR]

Forest growth is important both economically (yielding billions of dollars of annual revenues) and ecologically (with respect to ecosystem health and global carbon budgets). The growth of all forests follows a predictable general trend with age. In young forests, it accelerates as canopies develop; it then declines substantially soon after full canopy leaf area is reached. The classic explanation for the decline in growth invoked the increasing respiration costs required to sustain the larger masses of wood characteristic of older forests. Direct measurements of respiration have largely refuted this hypothesis, and recent work has focused on stand-level rates of resource supply, resource use, and growth. We developed and tested a hypothesis at the scale of individual trees (in relation to stand structure) to explain this declining stand-level rate of stem growth. According to our hypothesis, changes in stand structure allow dominant trees to sustain high rates of growth by increasing their acquisition of resources and using these resources efficiently (defined as stem growth per unit of resource used); smaller, nondominant trees grow more slowly as a result of their more limited acquisition of resources and a reduced rate of growth per unit of resource acquired. In combination, these two trends reduce overall stand growth. We tested this hypothesis by comparing growth, growth per unit of leaf area, and variation among trees within plots in two series of plantations of Eucalyptus in Brazil and by estimating individual-tree rates of growth and use of light, water, and nutrients in a plantation of Eucalyptus saligna in Hawaii. Our results supported the individual-tree hypothesis. We conclude that part of the universal age-related decline in forest growth derives from competition-related changes in stand structure and the resource-use efficiencies of individual trees. [ABSTRACT FROM AUTHOR]

This study uses a 12-year time series (2001–2012) of eddy covariance measurements to investigate the long-term net ecosystem exchange (NEE) of carbon dioxide (CO _2 ) and inter-annual variations in relation to abiotic drivers in a boreal fen in northern Sweden. The peatland was a sink for atmospheric CO _2 in each of the twelve study years with a 12-year average (± standard deviation) NEE of −58 ± 21 g C m ^−2 yr ^−1 . For ten out of twelve years, the cumulative annual NEE was within a range of −42 to −79 g C m ^−2 yr ^−1 suggesting a general state of resilience of NEE to moderate inter-annual climate variations. However, the annual NEE of −18 and −106 g C m ^−2 yr ^−1 in 2006 and 2008, respectively, diverged considerably from this common range. The lower annual CO _2 uptake in 2006 was mainly due to late summer emissions related to an exceptional drop in water table level (WTL). A positive relationship ( R ^2 = 0.65) between pre-growing season (January to April) air temperature (Ta) and summer (June to July) gross ecosystem production (GEP) was observed. We suggest that enhanced GEP due to mild pre-growing season air temperature in combination with air temperature constraints on ecosystem respiration (ER) during the following cooler summer explained most of the greater net CO _2 uptake in 2008. Differences in the annual and growing season means of other abiotic variables (e.g. radiation, vapor pressure deficit, precipitation) and growing season properties (i.e. start date, end date, length) were unable to explain the inter-annual variations of NEE. Overall, our findings suggest that this boreal fen acts as a persistent contemporary sink for atmospheric CO _2 that is, however, susceptible to severe anomalies in WTL and pre-growing season air temperature associated with predicted changes in climate patterns for the boreal region.

Two independent methods of estimating gross ecosystem production (GEP) were compared over a period of 2 years at monthly integrals for a mixed forest of conifers and deciduous hardwoods at Harvard Forest in central Massachusetts. Continuous eddy flux measurements of net ecosystem exchange (NEE) provided one estimate of GEP by taking day to night temperature differences into account to estimate autotrophic and heterotrophic respiration. GEP was also estimated with a quantum efficiency model based on measurements of maximum quantum efficiency (Qmax), seasonal variation in canopy phenology and chlorophyll content, incident PAR, and the constraints of freezing temperatures and vapour pressure deficits on stomatal conductance. Quantum efficiency model estimates of GEP and those derived from eddy flux measurements compared well at monthly integrals over two consecutive years (R2 = 098). Remotely sensed data were acquired seasonally with an ultralight aircraft to provide a means of scaling the leaf area and leaf pigmentation changes that affected the light absorption of photosynthetically active radiation to larger areas. A linear correlation between chlorophyll concentrations in the upper canopy leaves of four hardwood species and their quantum efficiencies (R2 = 0.99) suggested that seasonal changes in quantum efficiency for the entire canopy can be quantified with remotely sensed indices of chlorophyll. Analysis of video data collected from the ultralight aircraft indicated that the fraction of conifer cover varied from < 7% near the instrument tower to about 25% for a larger sized area. At 25% conifer cover, the quantum efficiency model predicted an increase in the estimate of annual GEP of < 5% because unfavourable environmental conditions limited conifer photosynthesis in much of the non-growing season when hardwoods lacked leaves. [ABSTRACT FROM AUTHOR]

Estimates of ammonium and nitrate availability in conifer and hardwood forests using an ion exchange resin (IER) bag method and with on-site incubations of soil cores in buried bags were compared. Correlations between the two methods were generally high. Correlation coefficients ( r) between IER nitrate and buried-bag mineralized nitrate ranged from 0.87 to 0.92. Both methods also correlated well with aboveground net primary production, litter fall N content, and fine root biomass. The major differences between the methods related to the relative importances of ammonium and nitrate forms of available N. The IER method indicated that both ammonium and nitrate were important on all sites, with nitrate predominating in most soils. The buried-bag results indicated that available N was primarily in the form of nitrate (all ammonium was oxidized), but that nitrate was insignificant on infertile sites. [ABSTRACT FROM AUTHOR]

Peatlands play an important role in the global carbon cycle due to the high carbon storage in the substrate. Ecosystem production depends, for example, on the solar energy amount that reaches the vegetation, however the diffuse component of this flux can substantially increase ecosystem net productivity. This phenomenon is observed in different ecosystems, but the study of the atmosphere optical properties on peatland production is lacking. In this paper, the presented methodology allowed us to disentangle the diffuse radiation impact on the net ecosystem production (NEP) of Rzecin peatland, Poland. It allowed us to assess the impact of the atmospheric scattering process determined by the aerosol presence in the air mass. An application of atmospheric radiation transfer (ART) and ecosystem production (EP) models showed that the increase of aerosol optical thickness from 0.09 to 0.17 caused NEP to rise by 3.4–5.7%. An increase of the diffusion index (DI) by 0.1 resulted in an NEP increase of 6.1–42.3%, while a DI decrease of 0.1 determined an NEP reduction of −49.0 to −10.5%. These results show that low peatland vegetation responds to changes in light scattering. This phenomenon should be taken into account when calculating the global CO2 uptake estimation of such ecosystems. [ABSTRACT FROM AUTHOR]

Conceptual model of climate change (ocean acidification [OA] and seawater warming) effects on coral reef mesocosms that either do (light blue) or do not (blue) feature seagrass beds. Solid lines denote abiotic effects (i.e., OA or OA + warming to 31C), whereas dotted lines depict effects of co-incubation with seagrass. CCM = carbon concentrating mechanism. ER=ecosystem respiration, GPP = gross primary production, NEP = net ecosystem metabolism, and P/R = photosynthesis/respiration ratio. • The combined effect of OA and rising temperatures stimulated the growth of macroalgae. • OA resulted in higher coral calcification rates when corals were co-incubated with seagrass. • Macroalgal growth was lower in seagrass-containing mesocosms. • Coral and macroalgal, but not seagrass, growth suffered at 31 °C under OA conditions. • Seagrass helped to stabilize the system's metabolism in response to projected climate change stressors. Ocean acidification (OA) and warming currently threaten coastal ecosystems across the globe. However, it is possible that the former process could actually benefit marine plants, such as seagrasses. The purpose of this study was to examine whether the effects of the seagrass Thalassia hemprichii can increase the resilience of OA-challenged coral reef mesocosms whose temperatures were gradually elevated. It was found that seagrass shoot density, photosynthetic efficiency, and leaf growth rate actually increased with rising temperatures under OA. Macroalgal growth rates were higher in the seagrass-free mesocosms, but the calcification rate of the model reef coral Pocillopora damicornis was higher in coral reef mesocosms featuring seagrasses under OA at 25 and 28 °C. Both the macroalgal growth rate and the coral calcification rate decreased in all mesocosms when the temperature was raised to 31 °C under OA. However, the variation in gross primary production, ecosystem respiration, and net ecosystem production in the seagrass mesocosms was lower than in seagrass-free controls, suggesting that the presence of seagrass in the mesocosms helped to stabilize the metabolism of the system in response to simulated climate change. [ABSTRACT FROM AUTHOR]

Restoring sites disturbed by industrial activity to a forested condition can ensure the continued provision of economic and ecosystem services from these areas. Impounded mine tailings are particularly challenging sites, and positive benefits of establishing trees must be balanced against risks associated with metal contamination, ongoing tailings stability, and the possibility of acid mine drainage. We used a hybrid biometric modelling approach based on dendrochronological reconstruction to retrospectively (1980–2015) quantify productivity and carbon dynamics of pine plantations growing on impounded mine tailings at the Vale waste management facility near Sudbury, Canada. Historical reclamation practices had remediated conditions sufficiently to allow conifer plantation establishment in the late 1970s. The revegetated sites were highly productive, when compared to reference conditions based on site index, wood volume growth, and ecosystem production, congruent with other studies showing that forests on revegetated post mining sites can be highly productive. However, metal concentrations in the forest floor were high, and further research is warranted to evaluate ecosystem impacts. Due to the requirement for energy-intensive inputs, we estimated that it took 12 years or more to recover the emissions associated with the revegetation process through C accumulated in biomass and soil at the revegetated sites. [ABSTRACT FROM AUTHOR]

Seagrasses are indicators of ecosystem state because they are sensitive to variations in water composition and clarity resulting from watershed-level impacts. A simulation model designed to study Zostera marina (eelgrass) habitat dynamics in a variable littoral zone environment was used to address the potential ecological responses to eutrophication in lower Chesapeake Bay. The adjacent channel boundary environment is a source of dissolved and particulate materials to the littoral zone. In the simulations, concentrations of key water quality variables in the adjacent estuarine channel boundary were either halved or doubled relative to the base case to investigate light versus nitrogen effects. The role of the seagrass meadow in littoral zone carbonand nitrogen dynamics was evaluated when meadow size was changed in the model. Particulate and dissolved organic carbon accounted for 83%of the submarine light attenuation in the seagrass meadow. In all model runs, the water column concentrations of chlorophyll a and dissolved inorganic nitrogen (DIN) were below the habitat criteria proposedas critical to seagrass survival. Eelgrass community production was carefully regulated by the interactive effects of light, nitrogen, and grazing on epiphyte growth. Increased eelgrass coverage in the littoral zone led to a simulated doubling of ecosystem primary productionbut reduced the fraction of production by planktonic and sediment microalgae. The simulation model presented here demonstrated the importance of material input from the channel in littoral zone biogeochemical dynamics. Submarine light regulated primary production more strongly than inorganic nitrogen concentrations in the model. External DIN concentrations influenced seagrass survival indirectly: enrichment stimulated growth of epiphytes and phytoplankton and promoted shading of the seagrass leaf. The model was based upon a unimpacted ecosystem and deteriorated water quality negatively influenced primary production g [ABSTRACT FROM AUTHOR]