Showing papers on "Productivity (ecology) published in 2021"

Increasing effects of chronic nutrient enrichment on plant diversity loss and ecosystem productivity over time.

Abstract: Human activities are enriching many of Earth’s ecosystems with biologically limiting mineral nutrients such as nitrogen (N) and phosphorus (P). In grasslands, this enrichment generally reduces plant diversity and increases productivity. The widely demonstrated positive effect of diversity on productivity suggests a potential negative feedback, whereby nutrient-induced declines in diversity reduce the initial gains in productivity arising from nutrient enrichment. In addition, plant productivity and diversity can be inhibited by accumulations of dead biomass, which may be altered by nutrient enrichment. Over longer time frames, nutrient addition may increase soil fertility by increasing soil organic matter and nutrient pools. We examined the effects of 5–11 yr of nutrient addition at 47 grasslands in 12 countries. Nutrient enrichment increased aboveground live biomass and reduced plant diversity at nearly all sites, and these effects became stronger over time. We did not find evidence that nutrient-induced losses of diversity reduced the positive effects of nutrients on biomass; however, nutrient effects on live biomass increased more slowly at sites where litter was also increasing, regardless of plant diversity. This work suggests that short-term experiments may underestimate the long-term nutrient enrichment effects on global grassland ecosystems.

Patterns and mechanisms of spatial variation in tropical forest productivity, woody residence time, and biomass

Abstract: Tropical forests vary widely in biomass carbon (C) stocks and fluxes even after controlling for forest age. A mechanistic understanding of this variation is critical to accurately predicting responses to global change. We review empirical studies of spatial variation in tropical forest biomass, productivity and woody residence time, focusing on mature forests. Woody productivity and biomass decrease from wet to dry forests and with elevation. Within lowland forests, productivity and biomass increase with temperature in wet forests, but decrease with temperature where water becomes limiting. Woody productivity increases with soil fertility, whereas residence time decreases, and biomass responses are variable, consistent with an overall unimodal relationship. Areas with higher disturbance rates and intensities have lower woody residence time and biomass. These environmental gradients all involve both direct effects of changing environments on forest C fluxes and shifts in functional composition - including changing abundances of lianas - that substantially mitigate or exacerbate direct effects. Biogeographic realms differ significantly and importantly in productivity and biomass, even after controlling for climate and biogeochemistry, further demonstrating the importance of plant species composition. Capturing these patterns in global vegetation models requires better mechanistic representation of water and nutrient limitation, plant compositional shifts and tree mortality.

Carbon cycling in mature and regrowth forests globally

Abstract: Forests are major components of the global carbon (C) cycle and thereby strongly influence atmospheric carbon dioxide (CO2) and climate. However, efforts to incorporate forests into climate models and CO2 accounting frameworks have been constrained by a lack of accessible, global-scale synthesis on how C cycling varies across forest types and stand ages. Here, we draw from the Global Forest Carbon Database, ForC, to provide a macroscopic overview of C cycling in the world’s forests, giving special attention to stand age-related variation. Specifically, we use 11 923 ForC records for 34 C cycle variables from 865 geographic locations to characterize ensemble C budgets for four broad forest types—tropical broadleaf evergreen, temperate broadleaf, temperate conifer, and boreal. We calculate means and standard deviations for both mature and regrowth (age < 100 years) forests and quantify trends with stand age in regrowth forests for all variables with sufficient data. C cycling rates generally decreased from tropical to temperate to boreal in both mature and regrowth forests, whereas C stocks showed less directional variation. Mature forest net ecosystem production did not differ significantly among biomes. The majority of flux variables, together with most live biomass pools, increased significantly with the logarithm of stand age. As climate change accelerates, understanding and managing the carbon dynamics of forests is critical to forecasting, mitigation, and adaptation. This comprehensive and synthetic global overview of C stocks and fluxes across biomes and stand ages contributes to these efforts.

Revisiting global vegetation controls using multi-layer soil moisture

Abstract: The productivity of terrestrial vegetation is determined by a multitude of drivers between the land surface and atmosphere. Water availability is critical for vegetation productivity, but the verti...

Benthic invaders control the phosphorus cycle in the world's largest freshwater ecosystem.

Abstract: The productivity of aquatic ecosystems depends on the supply of limiting nutrients. The invasion of the Laurentian Great Lakes, the world's largest freshwater ecosystem, by dreissenid (zebra and quagga) mussels has dramatically altered the ecology of these lakes. A key open question is how dreissenids affect the cycling of phosphorus (P), the nutrient that limits productivity in the Great Lakes. We show that a single species, the quagga mussel, is now the primary regulator of P cycling in the lower four Great Lakes. By virtue of their enormous biomass, quagga mussels sequester large quantities of P in their tissues and dramatically intensify benthic P exchanges. Mass balance analysis reveals a previously unrecognized sensitivity of the Great Lakes ecosystem, where P availability is now regulated by the dynamics of mussel populations while the role of the external inputs of phosphorus is suppressed. Our results show that a single invasive species can have dramatic consequences for geochemical cycles even in the world's largest aquatic ecosystems. The ongoing spread of dreissenids across a multitude of lakes in North America and Europe is likely to affect carbon and nutrient cycling in these systems for many decades, with important implications for water quality management.

Risk and vulnerability of Mongolian grasslands under climate change

Abstract: Climate change is projected to increase the aridity of semi-arid ecosystems, including Mongolian grasslands (MG), which provide ecosystem services that support food supply and pastoralist lifestyle. Here, we conducted a grid-scale (0.5◦ × 0.5◦) probabilistic risk assessment of MG under climate change for 40 years (1976-2015) based on probability theory. We evaluated changes of risk (impacts) and vulnerability of MG to drought between the recent two decades R20 = 1996-2015 and the previous two decades P20 = 1976-1995. The risk is quantified as the product of the probability of hazardous drought and ecosystem vulnerability. The probability of hazardous drought is defined from the Standardized Precipitation-Evapotranspiration Index. Vulnerability is defined as the expected differences of key ecosystem variables between years with and without hazardous conditions. The ecosystem variables are productivity (peak aboveground biomass, net primary productivity, and leaf area index) and root-zone plant-available soil moisture, simulated with a process-based vegetation model Organizing Carbon and Hydrology in Dynamic Ecosystems-Grassland Management validated with field observations of biomass and soil moisture. Results reveal that MG experienced more frequent hazardous droughts with rapid warming and slight drying during R20 aggravated by ever-increasing grazing intensity (34% compared to P20), which resulted in a reduction in soil water availability and grassland productivity, particularly in northeastern areas (20%-65%). The risk of drought to productivity increased by 10% between P20 and R20 over extended areas, particularly in northcentral and northeast Mongolia. The increase in the risk to MG was mainly caused by climate change-induced increase in the probability of hazardous drought and, to a lesser extent, by the increasing vulnerability. Recent droughts modify the risk to grasslands, particularly in northcentral and northeast Mongolia, suggesting that these regions need strategic management for both adaptation and ecosystem conservation to cope with climate change impacts.

Potential microalgal strains for converting flue gas CO2 into biomass

Abstract: A screening method using 15% CO2 (v/v) as screening stress and a spotting plate method was developed to isolate microalgae with the potential to convert flue gas CO2 to biomass. A total of six microalgal strains, belonging to the genera Chlorella, Heynigia, Desmodesmus, and Scenedesmus, were isolated from ponds near metallurgical/cement/power plants. The growth of these isolated strains was dramatically promoted at 5 to 15% CO2 when they were cultivated in bubble column photobioreactors aerating with 0.03%, 5%, 10%, and 15% CO2. The growth of Heynigia riparia SX01 in particular showed substantial improvement with the increase of CO2 concentrations from 5 to 15%. Furthermore, the maximum biomass, overall biomass productivity, maximum biomass productivity, and maximum CO2 fixation rate of these microalgal strains greatly increased at 5 to 15% CO2 as well. Chlorella sorokiniana GS03 showed the highest values in maximum biomass productivity (0.36 g L−1 day−1) and maximum CO2 fixation rate (0.66 g L−1 day−1) at 5% CO2. Heynigia riparia SX01 exhibited the highest values of maximum biomass (3.28 g L−1), overall biomass productivity (0.27 g L−1 day−1), maximum biomass productivity (0.39 g L−1 day−1), and maximum CO2 fixation rate (0.71 g L−1 day−1) at 15% CO2. This study provides not only an efficient screening method obtaining microalgae with wide CO2 tolerance but also microalgal strains utilizing high levels of CO2 up to 15% to produce biomass, which contributes to further exploration in converting real flue gas CO2 into biomass feedstock.

High Arctic Vegetation Change Mediated by Hydrological Conditions

Abstract: Increasing air temperatures are driving widespread changes to Arctic vegetation. In the high Arctic, these changes are patchy and the causes of heterogeneity are not well understood. In this study, we explore the determinants of high Arctic vegetation change over the last three decades on Banks Island, Northwest Territories. We used Landsat imagery (1984–2014) to map long-term trends in vegetation productivity and regional spatial data to investigate the relationships between trends in productivity and terrain position. Field sampling investigated vegetation community composition in different habitat types. Our analysis shows that vegetation productivity changes are substantial on Banks Island, where productivity has increased across about 80% of the study area. Rising productivity levels can be attributed to increasing biomass of the plant communities in both upland and lowland habitats. Our analysis also shows that the magnitude of greening is mediated by terrain characteristics related to soil moisture. Shifts in tundra vegetation will impact wildlife habitat quality, surface energy balance, permafrost dynamics, and the carbon cycle; additional research is needed to explore the effects of more productive vegetation communities on these processes in the high Arctic.

A comprehensive framework for seasonal controls of leaf abscission and productivity in evergreen broadleaved tropical and subtropical forests

Abstract: Summary Relationships among productivity, leaf phenology, and seasonal variation in moisture and light availability are poorly understood for evergreen broadleaved tropical/subtropical forests, which contribute 25% of terrestrial productivity. On the one hand, as moisture availability declines, trees shed leaves to reduce transpiration and the risk of hydraulic failure. On the other hand, increases in light availability promote the replacement of senescent leaves to increase productivity. Here, we provide a comprehensive framework that relates the seasonality of climate, leaf abscission, and leaf productivity across the evergreen broadleaved tropical/subtropical forest biome. The seasonal correlation between rainfall and light availability varies from strongly negative to strongly positive across the tropics and maps onto the seasonal correlation between litterfall mass and productivity for 68 forests. Where rainfall and light covary positively, litterfall and productivity also covary positively and are always greater in the wetter sunnier season. Where rainfall and light covary negatively, litterfall and productivity are always greater in the drier and sunnier season if moisture supplies remain adequate; otherwise productivity is smaller in the drier sunnier season. This framework will improve the representation of tropical/subtropical forests in Earth system models and suggests how phenology and productivity will change as climate change alters the seasonality of cloud cover and rainfall across tropical/subtropical forests.

Deep maxima of phytoplankton biomass, primary production and bacterial production in the Mediterranean Sea

Abstract: . The deep chlorophyll maximum (DCM) is a ubiquitous feature of phytoplankton vertical distribution in stratified waters that is relevant to our understanding of the mechanisms that underpin the variability in photoautotroph ecophysiology across environmental gradients and has implications for remote sensing of aquatic productivity. During the PEACETIME (Process studies at the air-sea interface after dust deposition in the Mediterranean Sea) cruise, carried out from 10 May to 11 June 2017, we obtained 23 concurrent vertical profiles of phytoplankton chlorophyll a , carbon biomass and primary production, as well as heterotrophic prokaryotic production, in the western and central Mediterranean basins. Our main aims were to quantify the relative role of photoacclimation and enhanced growth as underlying mechanisms of the DCM and to assess the trophic coupling between phytoplankton and heterotrophic prokaryotic production. We found that the DCM coincided with a maximum in both the biomass and primary production but not in the growth rate of phytoplankton, which averaged 0.3 d−1 and was relatively constant across the euphotic layer. Photoacclimation explained most of the increased chlorophyll a at the DCM, as the ratio of carbon to chlorophyll a ( C:Chl a ) decreased from ca. 90–100 ( g:g ) at the surface to 20–30 at the base of the euphotic layer, while phytoplankton carbon biomass increased from ca. 6 mg C m−3 at the surface to 10–15 mg C m−3 at the DCM. As a result of photoacclimation, there was an uncoupling between chlorophyll a -specific and carbon-specific productivity across the euphotic layer. The ratio of fucoxanthin to total chlorophyll a increased markedly with depth, suggesting an increased contribution of diatoms at the DCM. The increased biomass and carbon fixation at the base of the euphotic zone was associated with enhanced rates of heterotrophic prokaryotic activity, which also showed a surface peak linked with warmer temperatures. Considering the phytoplankton biomass and turnover rates measured at the DCM, nutrient diffusive fluxes across the nutricline were able to supply only a minor fraction of the photoautotroph nitrogen and phosphorus requirements. Thus the deep maxima in biomass and primary production were not fuelled by new nutrients but likely resulted from cell sinking from the upper layers in combination with the high photosynthetic efficiency of a diatom-rich, low-light acclimated community largely sustained by regenerated nutrients. Further studies with increased temporal and spatial resolution will be required to ascertain if the peaks of deep primary production associated with the DCM persist across the western and central Mediterranean Sea throughout the stratification season.

Repetitive seasonal drought causes substantial species-specific shifts in fine-root longevity and spatio-temporal production patterns in mature temperate forest trees.

Abstract: Temperate forest ecosystems are exposed to a higher frequency, duration and severity of drought. To promote forest longevity in a changing climate, we require a better understanding of the long-term impacts of repetitive drought events on fine-root dynamics in mature forests. Using minirhizotron methods, we investigated the effect of seasonal drought on fine-root dynamics in single-species and mixed-species arrangements of Fagus sylvatica (European beech) and Picea abies (Norway spruce) by means of a 4-yr-long throughfall-exclusion experiment. Fine-root production of both species decreased under drought. However, this reduction was not evident for P. abies when grown intermixed with F. sylvatica. Throughfall-exclusion prolonged the lifespan of P. abies roots but did not change the lifespan of F. sylvatica roots, except in 2016. Fagus sylvatica responded to drought by reducing fine-root production at specific depths and during roof closure. This is the first study to examine long-term trends in mature forest fine-root dynamics under repetitive drought events. Species-specific fine-root responses to drought have implications for the rate and depth of root-derived organic matter supply to soil. From a root dynamics perspective, intermixing tree species is not beneficial to all species but dampens drought impacts on the belowground productivity of P. abies.

Timing of drought in the growing season and strong legacy effects determine the annual productivity of temperate grasses in a changing climate

Abstract: . The frequency of extreme weather events, such as droughts, is assumed to increase and lead to alterations in ecosystem productivity and thus the terrestrial carbon cycle. Although grasslands typically show reduced productivity in response to drought, the effects of drought on grassland productivity have been shown to vary strongly. Here we tested, in a 2-year field experiment, if the resistance and the recovery of grasses to drought varies throughout a growing season and if the timing of the drought influences drought-induced reductions in annual aboveground net primary production (ANPP) of grasses. For the experiment we grew six temperate and perennial C 3 grass species and cultivars in a field as pure stands. The grasses were cut six times during the growing season and subject to 10 week drought treatments that occurred either in the spring, the summer or the fall. Averaged across all grasses, drought-induced losses in productivity in spring were smaller ( − 20 % to − 51 %) than in summer and fall ( − 77 % to − 87 %). This suggests a higher resistance to drought in spring when plants are in their reproductive stage and their productivity is the highest. After the release from drought, we found no prolonged suppression in growth. In contrast, post-drought growth rates of formerly drought-stressed swards outperformed the growth rates of the control swards. The strong overcompensation in growth after the drought release resulted in relatively small overall drought-induced losses in annual ANPP that ranged from − 4 % to − 14 % and were not affected by the timing of the drought event. In summary, our results show that (i) the resistance in growth rates of grasses to drought varies across the season and is increased during the reproductive phenological stage when growth rates are highest; (ii) that the positive legacy effects of drought indicate a high recovery potential of temperate grasses to drought; and (iii) that the high recovery can compensate for immediate drought effects on total annual biomass production to a significant extent.

Site quality and vegetation biomass in the tropical Sal mixed deciduous forest of Central India

Abstract: Tropical Sal forests are gaining wide recognitions due to its multifarious significance. An estimation of vegetational structure and biomass would be helpful for evaluating both productivity and sustainability of the forest ecosystems. Information regarding vegetational biomass, litter mass and fine root biomass, and overall dry matter dynamics are very limited. Therefore, the present work deals the vegetation biomass influenced by four different site quality of Sal dominating tropical deciduous forest of Chhattisgarh, India. The current study provides a framework under which all vegetational attributes can be quantified under varying site quality which is modified by different seasons. Our study revealed a significant increase in vegetational attributes and biomass as per increasing quality of sites. The density value (individuals/ha) and basal area (m2/ha) of tree, sapling and seedling in different sites were ranged from 710 to 1010, 2000 to 2500, 9750 to 14,500 and 33.5 to 46.8, 0.32 to 0.33, 17.96 to 21.43, respectively. The total biomass varied from 187.39 to 383.46 t ha−1. The fine root and forest floor biomass varied between 2.44 and 4.20 t ha−1, and 2.32 and 2.83 t ha−1, respectively among different sites and seasons. The total litter fall varied from 4.18 to 5.69 t ha−1 yr−1 across the site quality. It reflected that highest value of forest floor, litter floor and fine root biomass were seen in site quality (SQ) SQ-I followed by SQ-II, SQ-III and SQ-IV, respectively in different seasons. A great synergy exists among site quality, stand structure and biomass which surely affect ecosystem structure and its functions. Seasonal impacts are another factor that regulates vegetational statistics, forest floor, fine roots and pattern of litterfall in varying site qualities. Thus, a management implication is needed to understand site quality variation which entirely affects vegetational structure and biomass pattern that would help in strengthening sustainable forest management program.

Constraint on net primary productivity of the global ocean by Argo oxygen measurements

Abstract: The biological transformation of dissolved inorganic carbon to organic carbon during photosynthesis in the ocean, marine primary production, is a fundamental driver of biogeochemical cycling, ocean health and Earth’s climate system. The organic matter created supports oceanic food webs, including fisheries, and is an essential control on atmospheric carbon dioxide levels. Marine primary productivity is sensitive to changes due to climate forcing, but observing the response at the global scale remains a major challenge. Sparsely distributed productivity measurements are made using samples collected and analysed on research vessels. However, there are never enough ships and scientists to enable direct observations at the global scale with seasonal to annual resolution. Today, global ocean productivity is estimated using remote-sensing ocean-colour observations or general circulation models with coupled biological models that are calibrated with the sparse shipboard measurements. Here we demonstrate the measurement of gross oxygen production by photosynthesis using the diel cycle of oxygen concentration detected with the array of Biogeochemical-Argo profiling floats. The global ocean net primary productivity computed from this data is 53 Pg C y−1, which will be an important constraint on satellite and general circulation model-based estimates of the ocean productivity. Argo measurements provide a constrained estimate of net primary productivity of the global ocean of 53 Pg C y–1, according to a global analysis of diel oxygen variations.

Soil Nutrient and Vegetation Diversity Patterns of Alpine Wetlands on the Qinghai-Tibetan Plateau

Abstract: To predict the consequences of environmental change on the biodiversity of alpine wetlands, it is necessary to understand the relationship between soil properties and vegetation biodiversity. In this study, we investigated spatial patterns of aboveground vegetation biomass, cover, species diversity, and their relationships with soil properties in the alpine wetlands of the Gannan Tibetan Autonomous Prefecture of on the Qinghai-Tibetan Plateau, China. Furthermore, the relative contribution of soil properties to vegetation biomass, cover, and species diversity were compared using principal component analysis and multiple regression analysis. Generally, the relationship between plant biomass, coverage, diversity, and soil nutrients was linear or unimodal. Soil pH, bulk density and organic carbon were also significantly correlated to plant diversity. The soil attributes differed in their relative contribution to changes in plant productivity and diversity. pH had the highest contribution to vegetation biomass and species richness, while total nitrogen was the highest contributor to vegetation cover and nitrogen–phosphorus ratio (N:P) was the highest contributor to diversity. Both vegetation productivity and diversity were closely related to soil properties, and soil pH and the N:P ratio play particularly important roles in wetland vegetation biomass, cover, and diversity.

Biodiversity response to forest management intensity, carbon stocks and net primary production in temperate montane forests.

Abstract: Managed forests are a key component of strategies aimed at tackling the climate and biodiversity crises Tapping this potential requires a better understanding of the complex, simultaneous effects of forest management on biodiversity, carbon stocks and productivity Here, we used data of 135 one-hectare plots from southwestern Germany to disentangle the relative influence of gradients of management intensity, carbon stocks and forest productivity on different components of forest biodiversity (birds, bats, insects, plants) and tree-related microhabitats We tested whether the composition of taxonomic groups varies gradually or abruptly along these gradients The richness of taxonomic groups was rather insensitive to management intensity, carbon stocks and forest productivity Despite the low explanatory power of the main predictor variables, forest management had the greatest relative influence on richness of insects and tree-related microhabitats, while carbon stocks influenced richness of bats, birds, vascular plants and pooled taxa Species composition changed relatively abruptly along the management intensity gradient, while changes along carbon and productivity gradients were more gradual We conclude that moderate increases in forest management intensity and carbon stocks, within the range of variation observed in our study system, might be compatible with biodiversity and climate mitigation objectives in managed forests

Biomass and Lipid Productivities of Cyanobacteria- Leptolyngbya foveolarum HNBGU001

Abstract: The initial biomass density had a significant effect on the growth behaviour of Leptolyngbya foveolarum HNBGU-001 in the batch culture. The test organism produced substantial amounts of biomass and lipids when allowed to grow at 40 °C and pH 8.0. The Placket-Burman design appropriately indicated the positive and negative influences of the tested nutrient factors on biomass and lipid productivities of L. foveolarum. Employing the Box-Behnken design of response surface methodology, the elevated concentrations of sulphate-S (300 mg/L) and carbonate-C (45.39 mg/L) but relatively low levels of phosphate-P (10 mg/L) and nitrate-N (375 mg/L) were identified as the optimal nutritional requirements of the test organism for the maximum lipid productivity (49.60 ± 0.70 mg/L/day) along with high lipid content (32.10 ± 0.40% dry cell weight) and biomass productivity (154.80 ± 3.60 mg/L/day). These maximized responses of biomass productivity, lipid content, and lipid productivity were respectively 2.8-, 2.4-, and 6.8-fold higher than their corresponding values under the unoptimized conditions. FAME analysis of lipids obtained from the test organism revealed some promising features for their use as algal biodiesel feedstock. Nonetheless, the test organism seems to have better potential than several other microalgae for use in biofuel production as it can give a high output of biomass as also lipids at elevated temperature prevalent in outdoor conditions of subtropical and tropical regions.

Low forest productivity associated with increasing drought‐tolerant species is compensated by an increase in drought‐tolerance richness

Abstract: Many temperate forests are changing in composition due to a combination of changes in land-use, management and climate-related disturbances. Previous research has shown that in some regions these changes frequently favour drought-tolerant tree species. However, the effects of these changes in composition on forest functioning (e.g. productivity) are unclear. We studied 25 years of change in individual tree biomass growth, ingrowth and mortality, and community composition and total plot biomass across 2663 permanent forest plots in Catalonia (NE Spain) comprising 85,220 trees of 59 species. We focused on the relationship between community-level forest productivity and drought tolerance (DT), which was estimated using hydraulic traits as well as biogeographic indicators. We found that there was a small increase (1.6%-3.2% on average) in community-mean DT (DTcwm) during the study period, concurrent with a strong increase (12.4%-19.4% on average) in DT richness (DTric; i.e. trait range). Most importantly, we found that the mean DT was negatively related to forest productivity, which was explained because drought-tolerant tree species have lower tree-level growth. In contrast, DT richness was strongly and positively related to forest productivity, probably because it allowed for a more stable production along wet and dry periods. These results suggest a negative impact of ongoing climate change on forest productivity mediated by functional composition shifts (i.e. selection of drought-tolerant species), and a positive effect of increased DT richness as a consequence of land-use legacies. Such a trend towards functional diversification, although temporary, would increase forests' capacity to resist drought and place them in a better position to face the expected change in climate.

Intraspecific variations in leaf traits, productivity and resource use efficiencies in the dominant species of subalpine evergreen coniferous and deciduous broad-leaved forests along the altitudinal gradient

Abstract: Many studies have reported intraspecific variations in leaf functional traits, but their contribution to plant performance and ecosystem function are poorly understood. We studied altitudinal gradients of intraspecific variations in leaf traits, productivity and resource use efficiency in the dominant species of subalpine evergreen coniferous and deciduous broad‐leaved forests in Japan. We addressed three hypotheses, which are exclusive to each other. (1) Leaf traits vary along the leaf economics spectrum (LES). Plants that grow at lower and higher altitudes have fast‐ and slow‐return strategies, respectively, which improve productivity or resource use efficiency in the respective habitat. (2) Leaf trait variations are not consistent with the LES, but they contribute to improving productivity or resource use efficiency in the respective habitat. (3) Leaf trait variations do not contribute to improving productivity or resource use efficiency at higher altitudes. On the studied mountain range, Fagus crenata, a deciduous broad‐leaved tree, and Abies mariesii, an evergreen conifer, are the dominant species at lower and higher altitudes respectively. In F. crenata, leaf mass per area (LMA) and nitrogen concentrations were higher at higher altitudes. The net assimilation rate and light use efficiency during the growing season were greater at higher altitudes, which compensated for the shorter growing season in terms of annual productivity. In A. mariesii, the LMA was lower and the leaf life span was unchanged at higher altitudes. Productivity and resource use efficiency decreased with altitude. Synthesis. We conclude that F. crenata improves its productivity and resource use efficiency at higher altitudes by altering its leaf functional traits (Hypothesis 2), whereas alterations to leaf traits in A. mariesii are not associated with any improvement at higher altitudes (Hypothesis 3), which may result from the negative impact of environmental stress. Hence, the ecological significance of altitudinal variations in leaf traits depends on species and environment.

Seasonal microbial food web dynamics in contrasting Southern Ocean productivity regimes

Abstract: Spatial and seasonal dynamics of microbial loop fluxes were investigated in contrasting productivity regimes in the Indian sector of the Southern Ocean. Observations carried out in late summer (February-March 2018; project MOBYDICK) revealed higher microbial biomasses and fluxes in the naturally iron-fertilized surface waters of Kerguelen island in comparison to surrounding off-plateau waters. Differences were most pronounced for bacterial heterotrophic production (2.3-fold), the abundance of heterotrophic nanoflagellates (HNF; 2.7-fold). Independent of site, grazing by HNF was the main loss process of bacterial production (80-100%), while virus-induced mortality was low (< 9%). Combining these results with observations from previous investigations during early spring and summer allowed us to describe seasonal patterns in microbial food web fluxes and to compare these to carbon export in the iron-fertilized and highnutrient, low-chlorophyll (HNLC) Southern Ocean. Our data suggest an overall less efficient microbial food web during spring and summer, when respiration and viral lysis, respectively, represent important loss terms of bacterially-mediated carbon. In late summer, primary production is more efficiently transferred to bacterial biomass and HNF and thus available for higher trophic levels. These results provide a new insight into the seasonal variability and the quantitative importance of microbial food web processes for the fate of primary production in the Southern Ocean.