Interannual Variability In Productivity Research Articles

The roles of non-structural carbohydrates in fruiting: a review focusing on mango (Mangifera indica).

Reproductive development of fruiting trees, including mango (Mangifera indica L.), is limited by non-structural carbohydrates. Competition for sugars increases with cropping, and consequently, vegetative growth and replenishment of starch reserves may reduce with high yields, resulting in interannual production variability. While the effect of crop load on photosynthesis and the distribution of starch within the mango tree has been studied, the contribution of starch and sugars to different phases of reproductive development requires attention. This review focuses on mango and examines the roles of non-structural carbohydrates in fruiting trees to clarify the repercussions of crop load on reproductive development. Starch buffers the plant's carbon availability to regulate supply with demand, while sugars provide a direct resource for carbon translocation. Sugar signalling and interactions with phytohormones play a crucial role in flowering, fruit set, growth, ripening and retention, as well as regulating starch, sugar and secondary metabolites in fruit. The balance between the leaf and fruit biomass affects the availability and contributions of starch and sugars to fruiting. Crop load impacts photosynthesis and interactions between sources and sinks. As a result, the onset and rate of reproductive processes are affected, with repercussions for fruit size, composition, and the inter-annual bearing pattern.

Stronger increases but greater variability in global mangrove productivity compared to that of adjacent terrestrial forests.

Mangrove forests are a highly productive ecosystem with important potential to offset anthropogenic greenhouse gas emissions. Mangroves are expected to respond differently to climate change compared to terrestrial forests owing to their location in the tidal environment and unique ecophysiological characteristics, but the magnitude of difference remains uncertain at the global scale. Here we use satellite observations to examine mean trends and interannual variability in the productivity of global mangrove forests and nearby terrestrial evergreen broadleaf forests from 2001 to 2020. Although both types of ecosystem experienced significant recent increases in productivity, mangroves exhibited a stronger increasing trend and greater interannual variability in productivity than evergreen broadleaf forests on three-quarters of their co-occurring coasts. The difference in productivity trends is attributed to the stronger CO2 fertilization effect on mangrove photosynthesis, while the discrepancy in interannual variability is attributed to the higher sensitivities to variations in precipitation and sea level. Our results indicate that mangroves will have a faster increase in productivity than terrestrial forests in a CO2-rich future but may suffer more from deficits in water availability, highlighting a key difference between terrestrial and tidal ecosystems in their responses to climate change.

Drivers of productivity on the Agulhas Bank and the importance for marine ecosystems

The Agulhas Bank, an area of broad continental shelf extending 250 km offshore of South Africa, sustains rich and productive fisheries. However, its primary production is driven by a complex mosaic of biophysical mechanisms, highly variable in time and space. The key drivers include a system of multiple costal upwellings, complex shelf currents and an interaction with the powerful Agulhas current. The patterns of spatial and temporal variability of primary production on the Agulhas Bank are critical for the spawning and survival of early life stages of many commercially important species exploited along the coastline of South Africa. In particular, the ‘chokka’ squid fishery is an important source of revenue for the Eastern Cape coastal region in South Africa, with low catch years causing socioeconomic hardship. After spawning on the Eastern Agulhas Bank, the squid paralarvae are thought to be transported west to the Central Agulhas Bank (CAB). This region is associated with a cool, productive, but rather intermittent, oceanic feature known as the ‘cold ridge’ (CR). If and when it occurs, this feature could provide a sufficient amount of concentrated (relative to the background values) food for the paralarvae to survive during its passive or near-passive stage. To date, a long-term analysis of CR variability and the mechanisms associated with this has not been conducted. Here, we used a high-resolution biogeochemical ocean model (NEMO-MEDUSA) to investigate the drivers of the productivity on the Agulhas Bank, specifically in the vicinity of the CR. Evidence of the CR is found from November to April and variability in its strength and spatial extent is comparable to that observed in remote sensing data. Interannual variability in productivity on the CAB is correlated to wind stress and zonal currents with the most productive events associated with anomalous easterly winds and enhanced westward flow on the Bank. These events coincide with the existence of an intense CR, important for overall productivity on the Bank, which may impact the recruitment of chokka squid and other fish species. From this simulation, we observe a season of low productivity in 2012 which may potentially relate to the infamous low catch in 2013 which caused economic hardship in the area.

Satellite observations reveal seasonal redistribution of northern ecosystem productivity in response to interannual climate variability

Interannual variability (IAV) in ecosystem productivity may reveal vulnerabilities of vegetation to climate stressors. We analyzed IAV of northern hemisphere ecosystems using several remote sensing datasets, including longstanding observations of the normalized difference vegetation index (NDVI) and more novel metrics for productivity including solar-induced chlorophyll fluorescence (SIF) and the near-infrared reflectance of vegetation (NIRv). Although previous studies have suggested SIF better tracks variations in ecosystem productivity at seasonal timescales, we found that satellite datasets (including SIF) and eddy covariance flux tower observations were subject to significant uncertainty when assessing IAV at fine spatial scales. Even when observations were aggregated regionally, IAV in productivity estimated by the various satellite products were not always well correlated. In response to these inconsistencies, we applied a statistical method on regionally aggregated productivity data in four selected North American ecoregions and identified two dominant modes of IAV—seasonal redistribution and amplification—that were consistent across satellite datasets. The seasonal redistribution mode, which played a stronger role at lower latitudes, associated high (low) spring productivity with warm (cold) spring and summer temperatures, but also with lower (higher) productivity and water availability in summer and fall, indicating that enhanced growth in spring may contribute to an earlier depletion of water resources. The amplification mode associated an increase (decrease) in productivity across the growing season with above-average (below-average) summer moisture conditions. Even though our statistical analysis at large spatial scales revealed meaningful links between terrestrial productivity and climate drivers, our analysis does suggest that IAV and long-term trends in presently available novel and more established satellite observations must be interpreted cautiously, with careful attention to the spatial scales at which a robust signal emerges.

Productivity dynamics of oak forests of the Crimean Peninsula

The work proposes a methodology for studying the productivity dynamics of forest ecosystems based on remote sensing data. The possibility of using the NDVI vegetation index to study the interannual variability in productivity of regional ecosystems is shown. The long-term productivity dynamics of oak forests of the Crimean Peninsula is analyzed. On the basis of the data series obtained, the periods characterized by peculiarities of the productivity dynamics of forest ecosystems are identified.

Variability in primary productivity determines metapopulation dynamics.

Temporal variability in primary productivity can change habitat quality for consumer species by affecting the energy levels available as food resources. However, it remains unclear how habitat-quality fluctuations may determine the dynamics of spatially structured populations, where the effects of habitat size, quality and isolation have been customarily assessed assuming static habitats. We present the first empirical evaluation on the effects of stochastic fluctuations in primary productivity—a major outcome of ecosystem functions—on the metapopulation dynamics of a primary consumer. A unique 13-year dataset from an herbivore rodent was used to test the hypothesis that inter-annual variations in primary productivity determine spatiotemporal habitat occupancy patterns and colonization and extinction processes. Inter-annual variability in productivity and in the growing season phenology significantly influenced habitat colonization patterns and occupancy dynamics. These effects lead to changes in connectivity to other potentially occupied habitat patches, which then feed back into occupancy dynamics. According to the results, the dynamics of primary productivity accounted for more than 50% of the variation in occupancy probability, depending on patch size and landscape configuration. Evidence connecting primary productivity dynamics and spatiotemporal population processes has broad implications for metapopulation persistence in fluctuating and changing environments.

Negative impacts of high temperatures on growth of black spruce forests intensify with the anticipated climate warming.

An increasing number of studies conclude that water limitations and heat stress may hinder the capacity of black spruce (Picea mariana (Mill.) B.S.P.) trees, a dominant species of Canada's boreal forests, to grow and assimilate atmospheric carbon. However, there is currently no scientific consensus on the future of these forests over the next century in the context of widespread climate warming. The large spatial extent of black spruce forests across the Canadian boreal forest and associated variability in climate, demography, and site conditions pose challenges for projecting future climate change responses. Here we provide an evaluation of the impacts of climate warming and drying, as well as increasing [CO2 ], on the aboveground productivity of black spruce forests across Canada south of 60°N for the period 1971 to 2100. We use a new extensive network of tree-ring data obtained from Canada's National Forest Inventory, spatially explicit simulations of net primary productivity (NPP) and its drivers, and multivariate statistical modeling. We found that soil water availability is a significant driver of black spruce interannual variability in productivity across broad areas of the western to eastern Canadian boreal forest. Interannual variability in productivity was also found to be driven by autotrophic respiration in the warmest regions. In most regions, the impacts of soil water availability and respiration on interannual variability in productivity occurred during the phase of carbohydrate accumulation the year preceding tree-ring formation. Results from projections suggest an increase in the importance of soil water availability and respiration as limiting factors on NPP over the next century due to warming, but this response may vary to the extent that other factors such as carbon dioxide fertilization, and respiration acclimation to high temperature, contribute to dampening these limitations.

Environmental, biological and anthropogenic effects on grizzly bear body size: temporal and spatial considerations.

BackgroundIndividual body growth is controlled in large part by the spatial and temporal heterogeneity of, and competition for, resources. Grizzly bears (Ursus arctos L.) are an excellent species for studying the effects of resource heterogeneity and maternal effects (i.e. silver spoon) on life history traits such as body size because their habitats are highly variable in space and time. Here, we evaluated influences on body size of grizzly bears in Alberta, Canada by testing six factors that accounted for spatial and temporal heterogeneity in environments during maternal, natal and ‘capture’ (recent) environments. After accounting for intrinsic biological factors (age, sex), we examined how body size, measured in mass, length and body condition, was influenced by: (a) population density; (b) regional habitat productivity; (c) inter-annual variability in productivity (including silver spoon effects); (d) local habitat quality; (e) human footprint (disturbances); and (f) landscape change.ResultsWe found sex and age explained the most variance in body mass, condition and length (R2 from 0.48–0.64). Inter-annual variability in climate the year before and of birth (silver spoon effects) had detectable effects on the three-body size metrics (R2 from 0.04–0.07); both maternal (year before birth) and natal (year of birth) effects of precipitation and temperature were related with body size. Local heterogeneity in habitat quality also explained variance in body mass and condition (R2 from 0.01–0.08), while annual rate of landscape change explained additional variance in body length (R2 of 0.03). Human footprint and population density had no observed effect on body size.ConclusionsThese results illustrated that body size patterns of grizzly bears, while largely affected by basic biological characteristics (age and sex), were also influenced by regional environmental gradients the year before, and of, the individual’s birth thus illustrating silver spoon effects. The magnitude of the silver spoon effects was on par with the influence of contemporary regional habitat productivity, which showed that both temporal and spatial influences explain in part body size patterns in grizzly bears. Because smaller bears were found in colder and less-productive environments, we hypothesize that warming global temperatures may positively affect body mass of interior bears.

Comparison of carbon fluxes, growth and productivity of a winter wheat crop in three contrasting growing seasons

Three winter wheat growing seasons were compared in order to analyse crop development, CO 2 fluxes and inter-annual variability in productivity. Crop development monitoring, leaf scale measurements and continuous eddy-covariance measurements were conducted in a production crop at the Lonzée experimental site in Belgium. The 3 years were characterised by similar soil proprieties (same site), similar management (sowing, harvesting, plant protection and nitrogen application, adhering to regional standards), and the use of recommended cultivars (the most productive ones for this region). The comparison of carbon fluxes, growth and productivity in the three growing seasons highlighted mechanisms affected by meteorological conditions and, in some cases, modulated by a cultivar effect. In particular, it was shown that (a) precociousness or lateness in stage development was triggered mainly by cumulated temperature during winter and early spring; (b) early development in one season could explain the larger ecosystem net carbon sequestration that year, but had no impact on grain yield; (c) low grain yield in one season was the result of a complex mechanism including drought in early spring, which hindered flag leaf development, and moist conditions in late spring, which restrained radiation and favoured the development of fungal diseases. In all cases, it was found that grain yield could not be related to gross primary productivity or net ecosystem exchange, suggesting that reallocation and translocation processes play a substantial role in grain filling.

Productivity and modifications of ecosystem processes in gaps of a low Macchia in southern Italy

Abstract. Disturbance in Mediterranean shrub lands creates gaps that break up the shrub cover and potentially restrict productivity and other ecosystem processes. Gaps make up to about 20% of the low Macchia area at the Castel Volturno nature reserve (southern Italy). The plant community consists mainly of small annual species (legumes, grasses and forbs) that germinate in November and die out before the onset of summer drought. The inter-annual variability in productivity and the relative abundance of legumes, grasses and forbs were assessed over 4 yr (2004–2007) to evaluate main potential modifications of ecosystem processes determined by the occurrence of gaps in the shrub cover. In the study years, at the peak production, plant mass varied from about 250 to 700 g m−2; biomass belowground allocation varied from 23% in the wettest to 44% in the driest year. Belowground/aboveground biomass ratios were negatively related to rainfall and positively related to the length of the dry period, showing that water availability controls biomass allocation patterns. Legumes were the most abundant fraction (about 60%) of the aboveground mass in the wettest year. In the drier years legumes exhibited a shorter life cycle and senesced by mid-spring. Among the three functional groups monitored, legumes were the most sensitive to water shortage and their biomass was positively related to the amount of rainfall and negatively related to the length of the dry period. The higher fraction of legume mass was associated with higher nitrogen content in plant tissues and in the soil. Senesced annual species decomposed more than senescent Phillyrea sp. leaves. The stability of organic carbon pool, evaluated through the endogenous mineralization coefficient (CEM), was lower in gaps than in understorey soils.

Influence of sea ice on primary production in the Southern Ocean: A satellite perspective

Sea ice in the Southern Ocean is a major controlling factor on phytoplankton productivity, but the relationship is modified by regional differences in atmospheric and oceanographic conditions. We used the phytoplankton biomass, photosynthetically active radiation (PAR), and cloud cover data from Sea‐viewing Wide Field of View Sensor (SeaWiFS), ice concentrations data from Special Sensor Microwave Imager (SSM/I) and Advanced Microwave Scanning Radiometer‐EOS (AMSR‐E), sea‐surface temperature data from advanced very high resolution radiometer (AVHRR), and a vertically integrated model to estimate primary productivity south of 60°S. We also selected six areas within the Southern Ocean and analyzed the variability of the primary productivity and trends through time. We found substantial interannual variability in productivity from 1997 to 2005 in all regions of the Southern Ocean, and this variability appeared to be driven in large part by ice dynamics. The most productive regions of Antarctic waters were the continental shelves, and no sustained blooms occurred in waters of greater depth (>1000 m). We suggest that this is due to the slightly greater mixed layer depths found in waters off the continental shelf, and that the interactive effects of iron and irradiance result in the limitation of phytoplankton biomass over large regions of the Southern Ocean. Annual productivity of the Southern Ocean averaged 23.65 g C m−2 a−1, but yearly means for the years between 1998 and 2004 ranged from 22.10 to 25.49 g C m−2 d−1, respectively. Annual primary productivity over the entire Southern Ocean appears to have increased significantly since 1998, and much of this increase was confined to the months of January and February. Causes for this trend are presently unclear.

Adaptive model of plankton dynamics for the North Atlantic

Plankton ecosystems in the North Atlantic display strong regional and interannual variability in productivity and trophic structure, which cannot be captured by simple plankton models. Additional compartments subdividing functional groups can increase predictive power, but the high number of parameters tends to compromise portability and robustness of model predictions. An alternative strategy is to use property state variables, such as cell size, normally considered constant parameters in ecosystem models, to define the structure of functional groups in terms of both behaviour and response to physical forcing. This strategy may allow us to simulate realistically regional and temporal differences among plankton communities while keeping model complexity at a minimum. We fit a model of plankton and DOM dynamics globally and individually to observed climatologies at three diverse locations in the North Atlantic. Introducing additional property state variables is shown to improve the model fit both locally and globally, make the model more portable, and help identify model deficiencies. The zooplankton formulation exerts strong control on model performance. Our results suggest that the current paradigm on zooplankton allometric functional relationships might be at odds with observed plankton dynamics. Our parameter estimation resulted in more realistic estimates of parameters important for primary production than previous data assimilation studies. Property state variables generate complex emergent functional relationships, and might be used like tracers to differentiate between locally produced and advected biomass. The model results suggest that the observed temperature dependence of heterotrophic growth efficiency [Rivkin, R.B., Legendre, L., 2001. Biogenic carbon cycling in the upper ocean: effects of microbial respiration. Science 291 (5512) 2398–2400] could be an emergent relation due to intercorrelations among temperature, nutrient concentration and growth efficiency. A major advantage of using property state variables is that no additional parameters are required, such that differences in model performance can be directly related to model structure rather than parameter tuning.

Identifying land cover variability distinct from land cover change: Cheatgrass in the Great Basin

An understanding of land use/land cover change at local, regional, and global scales is important in an increasingly human-dominated biosphere. Here, we report on an under-appreciated complexity in the analysis of land cover change important in arid and semi-arid environments. In these environments, some land cover types show a high degree of inter-annual variability in productivity. In this study, we show that ecosystems dominated by non-native cheatgrass ( Bromus tectorum) show an inter-annual amplified response to rainfall distinct from native shrub/bunch grass in the Great Basin, US. This response is apparent in time series of Landsat and Advanced Very High Resolution Radiometer (AVHRR) that encompass enough time to include years with high and low rainfall. Based on areas showing a similar amplified response elsewhere in the Great Basin, 20,000 km 2, or 7% of land cover, are currently dominated by cheatgrass. Inter-annual patterns, like the high variability seen in cheatgrass-dominated areas, should be considered for more accurate land cover classification. Land cover change science should be aware that high inter-annual variability is inherent in annual dominated ecosystems and does not necessarily correspond to active land cover change.

Productivity and complementarity in grassland microcosms of varying diversity

Several researchers have hypothesized that, through various mechanisms, loss of species and functional group richness from a plant community will affect the magnitude and interannual variability of productivity. To test this hypothesis, I conducted a microcosm study of California grassland communities that differed in species richness. I grew cohorts of microcosms that simulated undisturbed grassland (in one year) and gopher‐disturbed grassland (in two consecutive years). As the number of species per functional group decreased from 4 to 1, biomass production remained constant in all three cohorts. As species richness decreased from 16 to 1 (or 8 to 1, in either case including a drop in functional group richness), productivity declined in one of the cohorts. In this cohort, productivity of one polyculture marginally exceeded that of the most productive monoculture. Resource complementarity and a type of selection effect may have each contributed to the observed diversity‐productivity relationships. Results suggest the existence of a selection effect that involves species that are highly productive in mixtures, rather than in monoculture. Over two seasons, species and functional group richness did not affect the interannual variability of biomass production. Comparisons of interannual changes in the productivity of monocultures and polycultures suggested that, in some polycultures, increased water availability might have relieved interspecific competition more than intraspecific competition. Based on results from this experiment and other manipulative experiments, I develop a framework to explain the relationship between species richness and productivity in terrestrial plant communities. The framework highlights the importance of environmental variation in shaping the diversity/productivity relationship.