Ecosystems最新文献

Trees affect the biotic and abiotic properties of the soil in which they grow. Tree species-specific effects can persist for a long time, even after the trees have been removed. We investigated to what extent such soil legacies of different tree species may impact tree seedlings in their emergence and growth. We performed a plant–soil feedback experiment, using soil that was conditioned in plots that vary in tree species composition in Białowieża Forest, Poland. Soil was taken from plots varying in proportion of birch, hornbeam, pine, and oak. In each soil, seeds of the same four target species were sown in pots. Seedling emergence and growth were monitored for one growing season. To further explore biotic implications of soil legacies, ectomycorrhizal root tip colonization of oak, a keystone forest species, was determined. We found no effect of soil legacies of tree species on the emergence measures. We, however, found a clear negative effect of pine legacies on the total biomass of all four seedling species. In addition, we found relationships between the presence of pine and soil fertility and between soil fertility and root tip colonization. Root tip colonization was positively correlated with the biomass of oak seedlings. We conclude that tree species can leave legacies that persist after that species has been removed. These legacies influence the growth of the next generation of trees likely via abiotic and biotic pathways. Thus, the choice of species in today’s forest may also matter for the structure and composition of future forests.

Composting organic matter can lower the global warming potential of food and agricultural waste and provide a nutrient-rich soil amendment. Compost applications generally increase net primary production (NPP) and soil water-holding capacity and may stimulate soil carbon (C) sequestration. Questions remain regarding the effects of compost nitrogen (N) concentrations and application rates on soil C and greenhouse gas dynamics. In this study, we explored the effects of compost with different initial N quality (food waste versus green waste compost) on soil greenhouse gas fluxes, aboveground biomass, and soil C and N pools in a fire-impacted annual grassland ecosystem. Composts were applied annually once, twice, or three times prior to the onset of the winter rainy season. A low-intensity fire event after the first growing season also allowed us to explore how compost-amended grasslands respond to burning events, which are expected to increase with climate change. After four growing seasons, all compost treatments significantly increased soil C pools from 9.5 ± 0.9 to 30.2 ± 0.7 Mg C ha⁻¹ (0–40 cm) and 19.5 ± 0.9 to 40.1 ± 0.7 Mg C ha⁻¹ (0–40 cm) relative to burned and unburned controls, respectively. Gains exceeded the compost-C applied, representing newly fixed C. The higher N food waste compost treatments yielded more cumulative soil C (5.2–10.9 Mg C ha⁻¹) and aboveground biomass (0.19–0.66 Mg C ha⁻¹) than the lower N green waste compost treatments, suggesting greater N inputs further increased soil stocks. The three-time green waste application increased soil C and N stocks relative to a single application of either compost. There was minimal impact on net ecosystem greenhouse gas emissions. Aboveground biomass accumulation was higher in all compost treatments relative to controls, likely due to increased water-holding capacity and N availability. Results show that higher N compost resulted in larger C gains with little offset from greenhouse gas emissions and that compost amendments may help mediate effects of low-intensity fire by increasing fertility and water-holding capacity.

While the influence of canopy trees on soils in natural and restored forest environments is well studied, the influence of understory species is not. Here, we evaluate the effects of outplanted native woody understory on invasive grass biomass and soil nutrient properties in heavily grass-invaded 30 + year-old plantations of a native N-fixing tree Acacia koa in Hawai‘i. We analyze soils from under A. koa trees with versus without planted woody understory and compare these to soils from under remnant pasture trees of the pre-deforestation dominant, Metrosideros polymorpha where passive recruitment of native woody understory has occurred since the cessation of grazing. Simultaneously, we experimentally planted understory species at three times the density used by managers to see if this could quickly decrease grass biomass and change soil nutrient dynamics. We found that invasive grass biomass declined with understory planting in surveyed and experimental sites. Yet, woody understory abundance had no effect on N cycling. Short-term N availability and nitrification potential were higher under A. koa than M. polymorpha trees regardless of understory. Net N mineralization either did not differ (~ 1 mo) between canopy species or was higher (171 day incubations) under remnant M. polymorpha where organic matter was also higher. The only influence of understory on soil was a positive correlation with loss-on-ignition (organic matter) under M. polymorpha. We also demonstrate differential controls over N cycling under the two canopy tree species. Overall, understory restoration has not changed soil characteristics even as invasive grass biomass declines.

Freshwater ecosystems play a key role in the global carbon cycle by collecting, transporting, and processing a significant portion of global organic carbon. These processes can be disrupted in non-perennial rivers due to their changing hydrological patterns. We investigated how environmental factors influence organic matter dynamics in the Algars, a Mediterranean non-perennial river basin in the North-East Iberian Peninsula. We conducted seasonal sampling in 16 sites across the river network, collecting samples for (i) storage of benthic organic matter, (ii) transport of dissolved organic carbon and particulate organic matter, and (iii) organic matter processing via aerobic respiration in sediments (Raz–Rru method). We observed pronounced spatial and temporal fluctuations in organic matter processes, especially during distinct periods like summer and autumn. Consistent seasonal patterns of organic matter transport showed a remarkable longitudinal increase downstream, similar to observed aerobic respiration in sediments. Notably, high-flow events doubled observed seasonal transport (mean DOC load: 2344 ± 735 kg/day). Irregular spatial storage patterns between dry and wet channel sections were related to land use and flow intermittency. Notably, storage in dry channel sections was generally ten times higher than wet sections. Our study emphasizes the intricate influence of specific environmental variables on organic matter processes, within different organic matter fractions (for example, coarse and dissolved organic matter). Frequency of non-flow events, seasonal hydrological changes, and land use predominantly govern organic matter dynamics in the Algars basin. Understanding organic carbon dynamics in non-perennial systems will help estimate the impact of hydrological alterations associated with global change on river systems.

Quantifying nitrogen uptake rates across different forest types is critical for a range of ecological questions, including the parameterization of global climate change models. However, few measurements of forest nitrogen uptake rates are available due to the intensive labor required to collect in situ data. Here, we seek to optimize data collection efforts by identifying measurements that must be made in situ and those that can be omitted or approximated from databases. We estimated nitrogen uptake rates in 18 mature monodominant forest stands comprising 13 species of diverse taxonomy at the Morton Arboretum in Lisle, IL, USA. We measured all nitrogen concentrations, foliage allocation, and fine root biomass in situ. We estimated wood biomass increments by in situ stem diameter and stem core measurements combined with allometric equations. We estimated fine root turnover rates from database values. We analyzed similar published data from monodominant forest FACE sites. At least in monodominant forests, accurate estimates of forest nitrogen uptake rates appear to require in situ measurements of fine root productivity and are appreciably better paired with in situ measurements of foliage productivity. Generally, wood productivity and tissue nitrogen concentrations may be taken from trait databases at higher taxonomic levels. Careful sorting of foliage or fine roots to species is time consuming but has little effect on estimates of nitrogen uptake rate. By directing research efforts to critical in situ measurements only, future studies can maximize research effort to identify the drivers of varied nitrogen uptake patterns across gradients.

In a warming world, the input of glacier meltwater to inland water ecosystems is predicted to change, potentially affecting their productivity. Meta-ecosystem theory, which posits that the nutrient availability in the recipient ecosystem can determine the extent of cross-ecosystem boundary utilization, can be useful for studying landscape-scale influences of glacier meltwater on inland waters. Here, we investigate how the input of glacier meltwater in a river system in Southern Greenland influences the utilization of marine subsidies in freshwater fish. Our study system comprised four sites, with controls for glacial meltwater and marine subsidies, harboring a partially migrating population of arctic char, meaning that some individuals migrate to the ocean and others remain in freshwaters, and two fully resident populations as a freshwater reference. We assessed the incorporation of marine carbon in freshwater resident char using both bulk and amino acid stable isotope analysis of muscle tissue. In the population with partial migration, marine subsidies were a significant resource for resident char individuals, and estimates of trophic position suggest that egg cannibalism is an important mechanism underlying the assimilation of these marine subsidies. In proglacial streams, namely those with high glacial meltwater, the total dependence on marine subsidies increased and reached 83% because char become cannibals at smaller sizes. In the configuration of our focal meta-ecosystem, our results suggest that the importance of marine subsidies to freshwater fish strengthens within increasing meltwater flux from upstream glaciers.

With climate warming and drying, fire activity is increasing in Cajander larch (Larix cajanderi Mayr.) forests underlain by continuous permafrost in northeastern Siberia, and initial post-fire tree demographic processes could unfold to determine long-term forest carbon (C) dynamics through impacts on tree density. Here, we evaluated above- and belowground C pools across 25 even-aged larch stands of varying tree densities that established following a wildfire in ~ 1940 near Cherskiy, Russia. Total C pools increased with increased larch tree density, from ~ 9,000 g C m⁻² in low-density stands to ~ 11,000 g C m⁻² in high and very high-density stands, with increases most pronounced at tree densities < 1 stem m⁻² and driven by increased above- and belowground (that is, coarse roots) and live and dead (that is, woody debris and snags) larch biomass. Total understory vegetation and non-larch coarse root C pools declined with increased tree density due to decreased shrub C pools, but these pools were relatively small compared to larch biomass. Fine root, soil organic matter (OM), and near surface (0–30 cm) mineral soil (MS) C pools varied little with tree density, although soil C pools held most (18–28% in OM and 44–51% in MS) C stored in these stands. Thus, if changing fire regimes promote denser stands, C storage will likely increase, but whether this increase offsets C lost during fires remains unknown. Our findings highlight how post-fire tree demographic processes impact C pool distribution and stability in larch forests of Siberian permafrost regions.

Discerning ecosystem change and food web dynamics underlying anthropogenic eutrophication and the introduction of non-native species is necessary for ensuring the long-term sustainability of fisheries and lake biodiversity. Previous studies of eutrophication in Lake Victoria, eastern Africa, have focused on the loss of endemic fish biodiversity over the past several decades, but changes in the plankton communities over this same time remain unclear. To fill this gap, we examined sediment cores from a eutrophic embayment, Mwanza Gulf, to determine the timing and magnitude of changes in the phytoplankton and zooplankton assemblages over the past century. Biogeochemical proxies indicate nutrient enrichment began around ~ 1920 CE and led to rapid increases in primary production, and our analysis of photosynthetic pigments revealed three zones: pre-eutrophication (prior to 1920 CE), onset of eutrophication with increases in all pigments (1920–1990 CE), and sustained eutrophication with cyanobacterial dominance (1990 CE–present). Cladoceran remains indicate an abrupt decline in biomass in ~ 1960 CE, in response to the cumulative effects of eutrophication and lake-level rise, preceding the collapse of haplochromine cichlids in the 1980s. Alona and Chydorus, typically benthic littoral taxa, have remained at relatively low abundances since the 1960s, whereas the abundance of Bosmina, typically a planktonic taxon, increased in the 1990s concurrently with the biomass recovery of haplochromine cichlid fishes. Overall, our results demonstrate substantial changes over the past century in the biomass structure and taxonomic composition of Mwanza Gulf phytoplankton and zooplankton communities, providing a historical food web perspective that can help understand the recent changes and inform future resource management decisions in the Lake Victoria ecosystem.

Interactions such as mutualism and facilitation are common in ecosystems established by foundation species; however, their outcomes vary and show conditionality. In a Mexican Caribbean Bay, a seagrass-coralline algae (rhodoliths) mutualism protects the seagrass Thalassia testudinum from green turtle overgrazing. We postulate that the state of the seagrass meadow in this bay depends on the strengths of the interactions among seagrasses, green turtles, and coralline algae. Spatio-temporal changes through satellite imagery showed rhodolith bed developed rapidly from 2009 (undetected) to 2016 (bed of 6934 m²). Typically, such rapid expansion of the rhodoliths does not occur in seagrass meadows. An in situ growth experiment of coralline algae showed that a combination of reduction in light and wave movement (usual in dense seagrass meadows) significantly reduced their growth rates. In the rhodolith beds, the growth rates of the coralline algae Neogoniolithon sp. and Amphiroa sp. were high at 9.5 mm and 15.5 mm per growth tip y⁻¹, respectively. In a second experiment, we found lower mortality in coralline algae within a rhodolith bed compared to algae placed outside the bed, likely explained by the reduced resuspension that we found in a third experiment, and this positive feedback may explain the high population increase in the rhodoliths, once established when the turtles grazed down the seagrass canopy. Therefore, the grazing-protection mutualism between seagrasses and coralline algae is thus conditional and came into existence under a co-occurrence of intensive grazing pressure and rapid population growth of coralline algae facilitated by positive feedback from increased growth and reduced sediment resuspension by the dense rhodolith bed.

Interactions between tropical cyclones and wildfires occur widely and can tip closed forests into open-canopy structures that initiate a ‘grass–fire’ cycle. We examined cyclone–fire interactions in a monodominant tropical montane pine forest in the Dominican Republic using remotely-sensed imagery to quantify damage from fires between 1986 and 2004, a category 1 cyclone in 1998, and an extensive wildfire in 2005. We also measured forest structure and composition 14.7 years after the 2005 fire. The area inside the 2005 burn scars (fire perimeters) totaled 25,206 ha, of which 81% burned and 14% was cyclone damaged. Cyclone damage made the fire markedly more extensive and severe—high-severity fires were > 3 times more frequent with high-severity cyclone damage than no cyclone damage—but these markedly synergistic effects were restricted to areas that had not burned for at least 19 years before the 2005 fire. Though earlier fires from 1986 to 2004 were small and low-severity, they were sufficient, when present, to prevent high-severity fire in 2005 irrespective of cyclone severity. In areas with strong cyclone–fire interactions, there was a complete loss of pine canopies, yet these stands had abundant pine canopy recruitment by 2019 and showed no evidence of compositional shifts toward open-canopy structures with pyrogenic herbaceous understories, illustrating the resilience of this ecosystem to a range of cyclone–fire synergies. However, the future resilience of tropical montane pine forests to cyclone–fire synergies is uncertain as climate change increases the intensity of cyclones and frequency of drought-triggered fires in these ecosystems.