Ecological risks in anthropogenic disturbance of nitrogen cycles in natural terrestrial ecosystems

Abstract

Anthropogenic addition of reactive nitrogen (Nr) to the biosphere is increasing globally and some terrestrial ecosystems are suffering from a state of excess Nr for biological nitrogen (N) demand, termed N saturation. Here, we review the ecological risks in relation to N saturation and prospective responses to N saturation. Excess Nr increases the risks of local extinction of rare plant species, encouragement of exotic plant species, disturbance of nutrient balance in plant organs, and increase of herbivory in plant communities. On the ecosystem scale, excess bioavailable N induces forest decline, disturbance of nutrient cycling within ecosystems, depending on vegetation, soil, land-use, and N-loading history. These Nr risks will increase in the Asian region, where impacts of Nr in natural terrestrial ecosystems have been scarcely studied. Whether much of the terrestrial ecosystems on a global level are in the sate of N saturation or not is still controversial, but the potential risks of excess Nr seem to be increasing. The fundamental ways to mitigate Nr risks are to reduce Nr production, prevent Nr translocation, and promote conversion of Nr to N 2 . Temporal, but promising actions against ecological N risks may include management of forests and riparian zones, and carbon addition in grassland.

Centennial-scale analysis of the creation and fate of reactive nitrogen in China (1910–2010)

“…The rapid growth since 1970 was largely driven by the emergence of a domestic N fertilizer industry and the intensive agriculture during the 1970s, and as a result, chemical fertilizer of 29 Tg N accounted for over one-half of Nr use in 2010. To a large extent, the impact of humans on the N cycle stems from their attempt to alleviate N deficiencies in agriculture by the application of fertilizer (7). Recently, the average N fertilizer application rate on Chinese cropland has reached 240 kg/ha per year.…”

“…Nr accumulation in different reservoirs has a wide variety of consequences, magnified with time as Nr moves along its biogeochemical pathways (6). These consequences result in a cascade of environmental changes, including smog, acid rain, forest dieback, coastal dead zones, biodiversity loss, stratospheric ozone depletion, and an enhanced greenhouse effect as well as health problems (5)(6)(7)(8). Currently, there is great interest in improving the efficiency of Nr use and balancing food production, energy consumption, and industrial needs with the aim of minimizing damages to environmental systems (9).…”

Impacts of enhanced nitrogen deposition and soil acidification on biomass production and nitrogen leaching in Chinese fir plantations

“…It has been reported that increasing N availability by N deposition has outweighed soil acidification caused by acid rain in some European (Emmett et al 1998) and North American forests, but little is known about Asian forests (Fujimaki et al 2009). Also, acidification impacts are not immediate, and it may be possible that increased N availability may not necessarily offset acidification impacts in the long term.…”

Rapid loss of phosphorus during early pedogenesis along a glacier retreat choronosequence, Gongga Mountain (SW China)

“…Nevertheless, the rapid loss of the original mineral P should cause a shortage of bioavailable P for montane ecosystems in the short-term, compared with the relatively flat region Syers 1976, Vitousek et al, 2010;Eger et al, 2011;Vincent et al, 2013). On the other hand, N deposition has dramatically increased in terrestrial ecosystems (Pardo et al, 2011;Fujimaki et al, 2009), which might decrease microbial biomass (Treseder, 2008) and change litter decomposition (Knorr et al, 2005). The P in microbial biomass was regarded as the major P pool (Turner et al, 2013), while the litter decomposition was an important avenue for P return (Fillippelli, 2008).…”