• Energy Research

Anthropogenically derived nitrogen (N) has a central role in global environmental changes, including climate change, biodiversity loss, air pollution, greenhouse gas emission, water pollution, as well as food production and human health. Current understanding of the biogeochemical processes that govern the N cycle in coupled human-ecological systems around the globe is drawn largely from the long-term ecological monitoring and experimental studies. Here, we review spatial and temporal patterns and trends in reactive N emissions, and the interactions between N and other important elements that dictate their delivery from terrestrial to aquatic ecosystems, and the impacts of N on biodiversity and human society. Integrated international and long-term collaborative studies covering research gaps will reduce uncertainties and promote further understanding of the nitrogen cycle in various ecosystems.

Anthropogenically derived nitrogen (N) has a central role in global environmental changes, including climate change, biodiversity loss, air pollution, greenhouse gas emission, water pollution, as well as food production and human health. Current understanding of the biogeochemical processes that govern the N cycle in coupled human-ecological systems around the globe is drawn largely from the long-term ecological monitoring and experimental studies. Here, we review spatial and temporal patterns and trends in reactive N emissions, and the interactions between N and other important elements that dictate their delivery from terrestrial to aquatic ecosystems, and the impacts of N on biodiversity and human society. Integrated international and long-term collaborative studies covering research gaps will reduce uncertainties and promote further understanding of the nitrogen cycle in various ecosystems.

AbstractTropical ecosystems face escalating global change. These shifts can disrupt tropical forests' carbon (C) balance and impact root dynamics. Since roots perform essential functions such as resource acquisition and tissue protection, root responses can inform about the strategies and vulnerabilities of ecosystems facing present and future global changes. However, root trait dynamics are poorly understood, especially in tropical ecosystems. We analyzed existing research on tropical root responses to key global change drivers: warming, drought, flooding, cyclones, nitrogen (N) deposition, elevated (e) CO2, and fires. Based on tree species‐ and community‐level literature, we obtained 266 root trait observations from 93 studies across 24 tropical countries. We found differences in the proportion of root responsiveness to global change among different global change drivers but not among root categories. In particular, we observed that tropical root systems responded to warming and eCO2 by increasing root biomass in species‐scale studies. Drought increased the root: shoot ratio with no change in root biomass, indicating a decline in aboveground biomass. Despite N deposition being the most studied global change driver, it had some of the most variable effects on root characteristics, with few predictable responses. Episodic disturbances such as cyclones, fires, and flooding consistently resulted in a change in root trait expressions, with cyclones and fires increasing root production, potentially due to shifts in plant community and nutrient inputs, while flooding changed plant regulatory metabolisms due to low oxygen conditions. The data available to date clearly show that tropical forest root characteristics and dynamics are responding to global change, although in ways that are not always predictable. This synthesis indicates the need for replicated studies across root characteristics at species and community scales under different global change factors.

AbstractTropical ecosystems face escalating global change. These shifts can disrupt tropical forests' carbon (C) balance and impact root dynamics. Since roots perform essential functions such as resource acquisition and tissue protection, root responses can inform about the strategies and vulnerabilities of ecosystems facing present and future global changes. However, root trait dynamics are poorly understood, especially in tropical ecosystems. We analyzed existing research on tropical root responses to key global change drivers: warming, drought, flooding, cyclones, nitrogen (N) deposition, elevated (e) CO2, and fires. Based on tree species‐ and community‐level literature, we obtained 266 root trait observations from 93 studies across 24 tropical countries. We found differences in the proportion of root responsiveness to global change among different global change drivers but not among root categories. In particular, we observed that tropical root systems responded to warming and eCO2 by increasing root biomass in species‐scale studies. Drought increased the root: shoot ratio with no change in root biomass, indicating a decline in aboveground biomass. Despite N deposition being the most studied global change driver, it had some of the most variable effects on root characteristics, with few predictable responses. Episodic disturbances such as cyclones, fires, and flooding consistently resulted in a change in root trait expressions, with cyclones and fires increasing root production, potentially due to shifts in plant community and nutrient inputs, while flooding changed plant regulatory metabolisms due to low oxygen conditions. The data available to date clearly show that tropical forest root characteristics and dynamics are responding to global change, although in ways that are not always predictable. This synthesis indicates the need for replicated studies across root characteristics at species and community scales under different global change factors.

AbstractGovernment and international agencies have highlighted the need to focus global change research efforts on tropical ecosystems. However, no recent comprehensive review exists synthesizing humid tropical forest responses across global change factors, including warming, decreased precipitation, carbon dioxide fertilization, nitrogen deposition, and land use/land cover changes. This paper assesses research across spatial and temporal scales for the tropics, including modeling, field, and controlled laboratory studies. The review aims to (1) provide a broad understanding of how a suite of global change factors are altering humid tropical forest ecosystem properties and biogeochemical processes; (2) assess spatial variability in responses to global change factors among humid tropical regions; (3) synthesize results from across humid tropical regions to identify emergent trends in ecosystem responses; (4) identify research and management priorities for the humid tropics in the context of global change. Ecosystem responses covered here include plant growth, carbon storage, nutrient cycling, biodiversity, and disturbance regime shifts. The review demonstrates overall negative effects of global change on all ecosystem properties, with the greatest uncertainty and variability in nutrient cycling responses. Generally, all global change factors reviewed, except for carbon dioxide fertilization, demonstrate great potential to trigger positive feedbacks to global warming via greenhouse gas emissions and biogeophysical changes that cause regional warming. This assessment demonstrates that effects of decreased rainfall and deforestation on tropical forests are relatively well understood, whereas the potential effects of warming, carbon dioxide fertilization, nitrogen deposition, and plant species invasions require more cross‐site, mechanistic research to predict tropical forest responses at regional and global scales.

AbstractGovernment and international agencies have highlighted the need to focus global change research efforts on tropical ecosystems. However, no recent comprehensive review exists synthesizing humid tropical forest responses across global change factors, including warming, decreased precipitation, carbon dioxide fertilization, nitrogen deposition, and land use/land cover changes. This paper assesses research across spatial and temporal scales for the tropics, including modeling, field, and controlled laboratory studies. The review aims to (1) provide a broad understanding of how a suite of global change factors are altering humid tropical forest ecosystem properties and biogeochemical processes; (2) assess spatial variability in responses to global change factors among humid tropical regions; (3) synthesize results from across humid tropical regions to identify emergent trends in ecosystem responses; (4) identify research and management priorities for the humid tropics in the context of global change. Ecosystem responses covered here include plant growth, carbon storage, nutrient cycling, biodiversity, and disturbance regime shifts. The review demonstrates overall negative effects of global change on all ecosystem properties, with the greatest uncertainty and variability in nutrient cycling responses. Generally, all global change factors reviewed, except for carbon dioxide fertilization, demonstrate great potential to trigger positive feedbacks to global warming via greenhouse gas emissions and biogeophysical changes that cause regional warming. This assessment demonstrates that effects of decreased rainfall and deforestation on tropical forests are relatively well understood, whereas the potential effects of warming, carbon dioxide fertilization, nitrogen deposition, and plant species invasions require more cross‐site, mechanistic research to predict tropical forest responses at regional and global scales.