Editorial

3 pages, 643 KiB

Open AccessEditorial

Responses of Forest Ecosystems to Nitrogen Deposition

by Frank S. Gilliam

Forests 2021, 12(9), 1190; https://doi.org/10.3390/f12091190 - 02 Sep 2021

Cited by 2 | Viewed by 1657

Environmental legislation in countries around the world has led to notable recent declines in the atmospheric deposition of nitrogen (N), although most decreases relate to oxidized N, with reduced N increasing in many areas [...] Full article

(This article belongs to the Special Issue Responses of Forest Ecosystems to Nitrogen Deposition)

Research

Jump to: Editorial, Review

13 pages, 1943 KiB

Open AccessArticle

Assessing the Linkages between Tree Species Composition and Stream Water Nitrate in a Reference Watershed in Central Appalachia

by Mark B. Burnham, Martin J. Christ, Mary Beth Adams and William T. Peterjohn

Forests 2021, 12(8), 1116; https://doi.org/10.3390/f12081116 - 20 Aug 2021

Cited by 1 | Viewed by 1500

Abstract

Many factors govern the flow of deposited nitrogen (N) through forest ecosystems and into stream water. At the Fernow Experimental Forest in WV, stream water nitrate (NO₃⁻) export from a long-term reference watershed (WS 4) increased in approximately 1980 and [...] Read more.

Many factors govern the flow of deposited nitrogen (N) through forest ecosystems and into stream water. At the Fernow Experimental Forest in WV, stream water nitrate (NO₃⁻) export from a long-term reference watershed (WS 4) increased in approximately 1980 and has remained elevated despite more recent reductions in chronic N deposition. Long-term changes in species composition may have altered forest N demand and the retention of deposited N. In particular, the abundance and importance value of Acer saccharum have increased since the 1950s, and this species is thought to have a low affinity for NO₃⁻. We measured the relative uptake of NO₃⁻ and ammonium (NH₄⁺) by six important temperate broadleaf tree species and estimated stand uptake of total N, NO₃⁻, and NH₄⁺. We then used records of stream water NO₃⁻ and stand composition to evaluate the potential impact of changes in species composition on NO₃⁻ export. Surprisingly, the tree species we examined all used both mineral N forms approximately equally. Overall, the total N taken up by the stand into aboveground tissues increased from 1959 through 2001 (30.9 to 35.2 kg N ha⁻¹ yr⁻¹). However, changes in species composition may have altered the net supply of NO₃⁻ in the soil since A. saccharum is associated with high nitrification rates. Increases in A. saccharum importance value could result in an increase of 3.9 kg NO₃⁻-N ha⁻¹ yr⁻¹ produced via nitrification. Thus, shifting forest species composition resulted in partially offsetting changes in NO₃⁻ supply and demand, with a small net increase of 1.2 kg N ha⁻¹ yr⁻¹ in NO₃⁻ available for leaching. Given the persistence of high stream water NO₃⁻ export and relatively abrupt (~9 year) change in stream water NO₃⁻ concentration circa 1980, patterns of NO₃⁻ export appear to be driven by long-term deposition with a lag in the recovery of stream water NO₃⁻ after more recent declines in atmospheric N input. Full article

(This article belongs to the Special Issue Responses of Forest Ecosystems to Nitrogen Deposition)

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17 pages, 1456 KiB

Open AccessArticle

Long-Term Projection of Species-Specific Responses to Chronic Additions of Nitrogen, Sulfur, and Lime

by Alexander Storm, Mary Beth Adams and Jamie Schuler

Forests 2021, 12(8), 1069; https://doi.org/10.3390/f12081069 - 11 Aug 2021

Cited by 2 | Viewed by 1670

Abstract

Elevated acid deposition has been a concern in the central Appalachian region for decades. A long-term acidification experiment on the Fernow Experimental Forest in central West Virginia was initiated in 1996 and continues to this day. Ammonium sulfate was used to simulate elevated [...] Read more.

Elevated acid deposition has been a concern in the central Appalachian region for decades. A long-term acidification experiment on the Fernow Experimental Forest in central West Virginia was initiated in 1996 and continues to this day. Ammonium sulfate was used to simulate elevated acid deposition. A concurrent lime treatment with an ammonium sulfate treatment was also implemented to assess the ameliorative effects of base cations to offset acidification. We show that the forest vegetation simulator growth model can be locally calibrated and used to project stand growth and development over 40 years to assess the impacts of acid deposition and liming. Modeled projections showed that pin cherry (initially) and sweet birch responded positively to nitrogen and sulfur additions, while black cherry, red maple, and cucumbertree responded positively to nitrogen, sulfur, and lime. Yellow-poplar negatively responded to both treatments. Despite these differences, our projections show a maximum of 5% difference in total stand volume among treatments after 40 years. Full article

(This article belongs to the Special Issue Responses of Forest Ecosystems to Nitrogen Deposition)

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23 pages, 2392 KiB

Open AccessArticle

Nitrogen Fertilization, Stand Age, and Overstory Tree Species Impact the Herbaceous Layer in a Central Appalachian Hardwood Forest

by Lacey J. Smith and Kirsten Stephan

Forests 2021, 12(7), 829; https://doi.org/10.3390/f12070829 - 24 Jun 2021

Cited by 5 | Viewed by 2021

Abstract

Research Highlights: Herb-layer community composition, abundance, species richness, and Shannon–Wiener diversity index are shaped by nitrogen fertilization, disturbance history, and the overstory tree species in its immediate vicinity. Background and Objectives: While the herbaceous layer in deciduous forests is increasingly recognized for its [...] Read more.

Research Highlights: Herb-layer community composition, abundance, species richness, and Shannon–Wiener diversity index are shaped by nitrogen fertilization, disturbance history, and the overstory tree species in its immediate vicinity. Background and Objectives: While the herbaceous layer in deciduous forests is increasingly recognized for its importance in various aspects of forest ecosystem function, this study sought to describe the factors impacting the herbaceous layer. Specifically, this study’s objective was to quantify and compare herb-layer species composition, cover, and other community indices in watersheds with (a) different levels of N deposition, (b) different stand ages due to differing disturbance histories, and (c) different watershed aspects. This study also tested the hypothesis that herb-layer characteristics vary beneath tree species with contrasting nutrient dynamics (i.e., red and sugar maple). Materials and Methods: At the Fernow Experimental Forest in West Virginia (USA), the cover of all herb-layer species was recorded directly under nine red maple and nine sugar maple trees in each of four watersheds (WS): long-term fertilized WS3 and unfertilized WS7, both with a stand age of about 50 years, and two unmanaged watersheds with 110-year-old stands and opposite watershed aspects (south-facing WS10, north-facing WS13). Community composition and plot-level indices of diversity were evaluated with multivariate analysis and ANOVA for watershed-level differences, effects of the maple species, and other environmental factors. Results: In the fertilized watershed (WS3), herb-layer diversity indices were lower than in the unfertilized watershed of the same stand age (WS7). In the unfertilized watershed with the 50-year-old stand (WS7), herb-layer diversity indices were higher than in the watershed with the 110-year-old stand of the same watershed aspect (WS13). WS10 and WS13 had similar herb-layer characteristics despite opposite watershed aspects. The presence of sugar maple corresponded to higher cover and diversity indices of the herb-layer in some of the watersheds. Conclusions: Despite the limitations of a case study, these findings bear relevance to future forest management since the forest herb layer plays important roles in deciduous forests through its influence on nutrient cycling, productivity, and overstory regeneration. Full article

(This article belongs to the Special Issue Responses of Forest Ecosystems to Nitrogen Deposition)

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11 pages, 1713 KiB

Open AccessArticle

Effect of Long-Term Nitrogen and Phosphorus Additions on Understory Plant Nutrients in a Primary Tropical Forest

by Qinggong Mao, Hao Chen, Cong Wang, Zongqing Pang, Jiangming Mo and Xiankai Lu

Forests 2021, 12(6), 803; https://doi.org/10.3390/f12060803 - 18 Jun 2021

Cited by 5 | Viewed by 2002

Abstract

Humid tropical forests are commonly characterized as N-rich but P-deficient. Increased N deposition may drive N saturation and aggravate P limitation in tropical forests. Thus, P addition is proposed to mitigate the negative effects of N deposition by stimulating N cycling. However, little [...] Read more.

Humid tropical forests are commonly characterized as N-rich but P-deficient. Increased N deposition may drive N saturation and aggravate P limitation in tropical forests. Thus, P addition is proposed to mitigate the negative effects of N deposition by stimulating N cycling. However, little is known regarding the effect of altered N and P supply on the nutrient status of understory plants in tropical forests, which is critical for predicting the consequences of disturbed nutrient cycles. We assessed the responses of N concentration, P concentration, and N:P ratios of seven understory species to N and P addition in an 8-year fertilization experiment in a primary forest in south China. The results showed that N addition had no effect on plant N concentration, P concentration, and N:P ratios for most species. In contrast, P addition significantly increased P concentration, and decreased N:P ratios but had no effect on plant N concentration. The magnitude of P concentration responses to P addition largely depended on the types of organs and species. The increased P was more concentrated in the fine roots and branches than in the leaves. The gymnospermous liana Gnetum montanum Markgr. had particularly lower foliar N: P (~9.8) and was much more responsive to P addition than the other species studied. These results indicate that most plants are saturated in N but have great potential to restore P in primary tropical forests. N deposition does not necessarily aggravate plant P deficiency, and P addition does not increase the retention of deposited N by increasing the N concentration. In the long term, P inputs may alter the community composition in tropical forests owing to species-specific responses. Full article

(This article belongs to the Special Issue Responses of Forest Ecosystems to Nitrogen Deposition)

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9 pages, 1023 KiB

Open AccessArticle

Long-Term Nitrogen Addition Decreases Soil Carbon Mineralization in an N-Rich Primary Tropical Forest

by Xiankai Lu, Qinggong Mao, Zhuohang Wang, Taiki Mori, Jiangming Mo, Fanglong Su and Zongqing Pang

Forests 2021, 12(6), 734; https://doi.org/10.3390/f12060734 - 04 Jun 2021

Cited by 9 | Viewed by 2886

Abstract

Anthropogenic elevated nitrogen (N) deposition has an accelerated terrestrial N cycle, shaping soil carbon dynamics and storage through altering soil organic carbon mineralization processes. However, it remains unclear how long-term high N deposition affects soil carbon mineralization in tropical forests. To address this [...] Read more.

Anthropogenic elevated nitrogen (N) deposition has an accelerated terrestrial N cycle, shaping soil carbon dynamics and storage through altering soil organic carbon mineralization processes. However, it remains unclear how long-term high N deposition affects soil carbon mineralization in tropical forests. To address this question, we established a long-term N deposition experiment in an N-rich lowland tropical forest of Southern China with N additions such as NH₄NO₃ of 0 (Control), 50 (Low-N), 100 (Medium-N) and 150 (High-N) kg N ha⁻¹ yr⁻¹, and laboratory incubation experiment, used to explore the response of soil carbon mineralization to the N additions therein. The results showed that 15 years of N additions significantly decreased soil carbon mineralization rates. During the incubation period from the 14th day to 56th day, the average decreases in soil CO₂ emission rates were 18%, 33% and 47% in the low-N, medium-N and high-N treatments, respectively, compared with the Control. These negative effects were primarily aroused by the reduced soil microbial biomass and modified microbial functions (e.g., a decrease in bacteria relative abundance), which could be attributed to N-addition-induced soil acidification and potential phosphorus limitation in this forest. We further found that N additions greatly increased soil-dissolved organic carbon (DOC), and there were significantly negative relationships between microbial biomass and soil DOC, indicating that microbial consumption on soil-soluble carbon pool may decrease. These results suggests that long-term N deposition can increase soil carbon stability and benefit carbon sequestration through decreased carbon mineralization in N-rich tropical forests. This study can help us understand how microbes control soil carbon cycling and carbon sink in the tropics under both elevated N deposition and carbon dioxide in the future. Full article

(This article belongs to the Special Issue Responses of Forest Ecosystems to Nitrogen Deposition)

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25 pages, 2654 KiB

Open AccessArticle

Effects of Moderate Nitrate and Low Sulphate Depositions on the Status of Soil Base Cation Pools and Recent Mineral Soil Acidification at Forest Conversion Sites with European Beech (“Green Eyes”) Embedded in Norway Spruce and Scots Pine Stands

by Florian Achilles, Alexander Tischer, Markus Bernhardt-Römermann, Ines Chmara, Mareike Achilles and Beate Michalzik

Forests 2021, 12(5), 573; https://doi.org/10.3390/f12050573 - 02 May 2021

Cited by 6 | Viewed by 2936

Abstract

High N depositions of past decades brought changes to European forests including impacts on forest soil nutrition status. However, the ecosystem responses to declining atmospheric N inputs or moderate N depositions attracted only less attention so far. Our study investigated macronutrient (N, S, [...] Read more.

High N depositions of past decades brought changes to European forests including impacts on forest soil nutrition status. However, the ecosystem responses to declining atmospheric N inputs or moderate N depositions attracted only less attention so far. Our study investigated macronutrient (N, S, Ca²⁺, Mg²⁺, K⁺) pools and fluxes at forest conversion sites over 80 years old in Central Germany with European beech (so-called “Green Eyes” (GE)). The GE are embedded in large spruce and pine stands (coniferous stands: CS) and all investigated forest stands were exposed to moderate N deposition rates (6.8 ± 0.9 kg ha⁻¹ yr⁻¹) and acidic soil conditions (pH_H2O < 4.7). Since the understanding of forest soil chemical and macronutrient status is essential for the evaluation of forest conversion approaches, we linked patterns in water-bound nutrient fluxes (2001–2018) and in predicted macronutrient storage in the herbaceous and tree layer to patterns in litter fall (2016–2017) and in forest floor and mineral soil macronutrient stocks at GE and CS assessed in 2018. Our results exhibited 43% (N_t) and 21% (S) higher annual throughfall fluxes at CS than at GE. Seepage water at 100 cm mineral soil depth (2001–2018) of CS is characterized by up to fivefold higher NO₃⁻ (GE: 2 ± 0.7 µmol_c L⁻¹; CS: 9 ± 1.4 µmol_c L⁻¹) and sevenfold higher SO₄²⁻ (GE: 492 ± 220 µmol_c L⁻¹; CS: 3672 ± 2613 µmol_c L⁻¹) concentrations. High base cation (∑ Ca²⁺, Mg²⁺, K⁺) concentrations in CS mineral soil seepage water (100 cm depth: 2224 ± 1297 µmol_c L⁻¹) show significant positive correlations with SO₄²⁻. Tree uptake of base cations at GE is associated especially with a Ca²⁺ depletion from deeper mineral soil. Foliar litter fall turns out to be the main pathway for litter base cation return to the topsoil at GE (>59%) and CS (>66%). The litter fall base cation return at GE (59 ± 6 kg ha⁻¹ yr⁻¹) is almost twice as large as the base cation deposition (30 ± 5 kg ha⁻¹ yr⁻¹) via throughfall and stemflow. At CS, base cation inputs to the topsoil via litter fall and depositions are at the same magnitude (24 ± 4 kg ha⁻¹ yr⁻¹). Macronutrient turnover is higher at GE and decomposition processes are hampered at CS maybe through higher N inputs. Due to its little biomass and only small coverage, the herbaceous layer at GE and CS do not exert a strong influence on macronutrient storage. Changes in soil base cation pools are tree species-, depth- and might be time-dependent, with recently growing forest floor stocks. An ongoing mineral soil acidification seems to be related to decreasing mineral soil base cation stocks (through NO₃⁻ and especially SO₄²⁻ leaching as well as through tree uptake). Full article

(This article belongs to the Special Issue Responses of Forest Ecosystems to Nitrogen Deposition)

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12 pages, 1081 KiB

Open AccessArticle

Nitrogen Fertilization Increases Windstorm Damage in an Aggrading Forest

by Christopher A. Walter, Zachariah K. Fowler, Mary Beth Adams, Mark B. Burnham, Brenden E. McNeil and William T. Peterjohn

Forests 2021, 12(4), 443; https://doi.org/10.3390/f12040443 - 06 Apr 2021

Cited by 2 | Viewed by 1952

Abstract

Storms are the most significant disturbance events in temperate forests. Forests impacted by nitrogen deposition may face more severe storm damage as changes in soil and wood chemistry impact tree growth allocation, wood strength, and species composition. To examine these potential effects of [...] Read more.

Storms are the most significant disturbance events in temperate forests. Forests impacted by nitrogen deposition may face more severe storm damage as changes in soil and wood chemistry impact tree growth allocation, wood strength, and species composition. To examine these potential effects of nitrogen deposition, we measured tree damage from a windstorm in an aggrading forest that is part of a nitrogen fertilization experiment. We discovered that within the nitrogen fertilization treatment area there was significantly more basal area and stems damaged when compared to the reference treatment, and the nitrogen fertilization treatment had more snapped and severely damaged trees. Additionally, the effect of treatment and amount of damage to trees was different depending on tree species. If our results are indicative of the large and globally-distributed regions of temperate forests impacted by nitrogen deposition, then the increased windstorm disturbance risk posed by climate change could be more significant due to the effects of nitrogen deposition. Full article

(This article belongs to the Special Issue Responses of Forest Ecosystems to Nitrogen Deposition)

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10 pages, 1933 KiB

Open AccessArticle

Effects of Large-Scale Nitrogen Fertilization on Insect–Plant Interactions in the Canopy of Tall Alder Trees with N₂-Fixing Traits in a Cool Temperate Forest

by Jin Lee, Masahiro Nakamura and Tsutom Hiura

Forests 2021, 12(2), 210; https://doi.org/10.3390/f12020210 - 10 Feb 2021

Cited by 3 | Viewed by 1683

Abstract

Nitrogen (N) deposition is expected to influence forests. The effects of large-scale N fertilization on canopy layer insect–plant interactions in stands of tall, atmospheric nitrogen (N₂)-fixing tree species have never been assessed. We conducted a large-scale fertilization experiment (100 kg N [...] Read more.

Nitrogen (N) deposition is expected to influence forests. The effects of large-scale N fertilization on canopy layer insect–plant interactions in stands of tall, atmospheric nitrogen (N₂)-fixing tree species have never been assessed. We conducted a large-scale fertilization experiment (100 kg N ha⁻¹ year⁻¹ applied to approximately 9 ha) over three years (2012–2014) in a cool temperate forest in northern Japan. Our goal was to evaluate relational responses between alder (Alnus hirsuta [Turcz.]) and their insect herbivores to N deposition. Specifically, we assessed leaf traits (N concentration, C:N ratio, condensed tannin concentration, and leaf mass per unit area (LMA)) and herbivory by three feeding guilds (leaf damage by chewers and the densities of gallers and miners) between the fertilized site and an unfertilized control. Fertilization led to increased galler density in spring 2013 and increased leaf damage by chewers in late summer 2014. For leaf traits, the LMA decreased in spring 2013 and late summer 2014, and the C:N ratio decreased in late summer 2013. The N and condensed tannin concentrations remained unchanged throughout the study period. There was a negative correlation between LMA and leaf damage by chewers, but LMA was not correlated with galler density. These results show that large-scale N fertilization had a positive plant-mediated (i.e., indirect) effect on leaf damage by chewers via a decrease in LMA in the canopy layer. Changes in physical defenses in canopy leaves may be a mechanism by which N fertilization affects the herbivory in tall N₂-fixing trees. Full article

(This article belongs to the Special Issue Responses of Forest Ecosystems to Nitrogen Deposition)

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20 pages, 4101 KiB

Open AccessArticle

Long- and Short-Term Inorganic Nitrogen Runoff from a Karst Catchment in Austria

by Thomas Dirnböck, Heike Brielmann, Ika Djukic, Sarah Geiger, Andreas Hartmann, Franko Humer, Johannes Kobler, Martin Kralik, Yan Liu, Michael Mirtl and Gisela Pröll

Forests 2020, 11(10), 1112; https://doi.org/10.3390/f11101112 - 20 Oct 2020

Cited by 2 | Viewed by 2826

Abstract

Excess nitrogen (N) deposition and gaseous N emissions from industrial, domestic, and agricultural sources have led to increased nitrate leaching, the loss of biological diversity, and has affected carbon (C) sequestration in forest ecosystems. Nitrate leaching affects the purity of karst water resources, [...] Read more.

Excess nitrogen (N) deposition and gaseous N emissions from industrial, domestic, and agricultural sources have led to increased nitrate leaching, the loss of biological diversity, and has affected carbon (C) sequestration in forest ecosystems. Nitrate leaching affects the purity of karst water resources, which contribute around 50% to Austria’s drinking water supply. Here we present an evaluation of the drivers of dissolved inorganic N (DIN) concentrations and fluxes from a karst catchment in the Austrian Alps (LTER Zöbelboden) from 27 years of records. In addition, a hydrological model was used together with climatic scenario data to predict expected future runoff dynamics. The study area was exposed to increasing N deposition during the 20th century (up to 30 to 35 kg N ha⁻¹ y⁻¹), which are still at levels of 25.5 ± 3.6 and 19.9 ± 4.2 kg N ha⁻¹ y⁻¹ in the spruce and the mixed deciduous forests, respectively. Albeit N deposition was close to or exceeded critical loads for several decades, 70–83% of the inorganic N retained in the catchment from 2000 to 2018, and NO₃^- concentrations in the runoff stayed <10 mg L⁻¹ unless high-flow events occurred or forest stand-replacing disturbances. We identified tree growth as the main sink for inorganic N, which might together with lower runoff, increase retention of only weakly decreasing N deposition in the future. However, since recurring forest stand-replacement is predicted in the future as a result of a combination of climatically driven disturbance agents, pulses of elevated nitrate concentrations in the catchment runoff will likely add to groundwater pollution. Full article

(This article belongs to the Special Issue Responses of Forest Ecosystems to Nitrogen Deposition)

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Review

Jump to: Editorial, Research

12 pages, 3081 KiB

Open AccessReview

Response of Temperate Forest Ecosystems under Decreased Nitrogen Deposition: Research Challenges and Opportunities

by Frank S. Gilliam

Forests 2021, 12(4), 509; https://doi.org/10.3390/f12040509 - 19 Apr 2021

Cited by 6 | Viewed by 2294

Abstract

Although past increases in emissions and atmospheric deposition of reactive nitrogen (N_r) provided the impetus for extensive research investigating the effects of excess N in terrestrial and aquatic ecosystems, the Clean Air Act and associated rules have led to decreases in [...] Read more.

Although past increases in emissions and atmospheric deposition of reactive nitrogen (N_r) provided the impetus for extensive research investigating the effects of excess N in terrestrial and aquatic ecosystems, the Clean Air Act and associated rules have led to decreases in emissions and deposition of oxidized N, especially in the eastern U.S., but also in other regions of the world. Thus, research in the near future must address the mechanisms and processes of recovery for impacted forests as they experience chronically less N in atmospheric depositions. Recently, a hysteretic model was proposed to predict this recovery. By definition, hysteresis is any phenomenon in which the state of a property depends on its history and lags behind changes in the effect causing it. Long-term whole-watershed additions of N at the Fernow Experimental Forest allow for tests of the ascending limb of the hysteretic model and provide an opportunity to assess the projected changes following cessation of these additions. A review of 10 studies published in the peer-reviewed literature indicate there was a lag time of 3–6 years before responses to N treatments became apparent. Consistent with the model, I predict significant lag times for recovery of this temperate hardwood ecosystem following decreases in N deposition. Full article

(This article belongs to the Special Issue Responses of Forest Ecosystems to Nitrogen Deposition)

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