Evidence and causes of recent decreases in nitrogen deposition in temperate forests in Northeast China.

High reactive nitrogen (N) emissions due to anthropogenic activities in China have led to an increase in N deposition and ecosystem degradation. The Chinese government has strictly regulated reactive N emissions since 2010, however, determining whether N deposition has reduced requires long-term monitoring. Here, we report the patterns of N deposition at a rural forest site (Qingyuan) in northeastern China over the last decade.

Transformation mechanisms of ammonium and nitrate in subsurface wastewater infiltration system: Implication for reducing greenhouse gas emissions.

Subsurface wastewater infiltration system (SWIS) has been recognized as a cost-effective and environmentally friendly tool for wastewater treatment. However, there is a lack of knowledge on the transformation processes of nitrogen (N), hindering the improvement of the N removal efficiency in SWIS. Here, the migration and transformation mechanisms of ammonium (NH-N) and nitrate (NO-N) over 10 days were explored by N labeling technique.

Patterns and drivers of atmospheric inorganic nitrogen deposition in Northeast Asia.

Elevated nitrogen (N) deposition due to intensified emissions of NH and NO is a global problem with profound consequences on living organisms and the environment. Although N emission rates are currently considered to be high in East Asia, reports on the current N deposition level and composition are still limited, especially in northeastern China, where official N deposition monitoring sites are unavailable. This limits our understanding of the spatio-temporal N deposition patterns and their influencing factors at regional to continental scales.

Effect of increased carbon load on denitrification efficiency and nitrate isotope enrichment factors in subsurface wastewater infiltration system.

Denitrification plays a dominant role in nitrate removal in subsurface wastewater infiltration system (SWIS). However, the effect of increased carbon (C) load on denitrification efficiency in the SWIS remain unclear. In this study, we used analyses of stable isotopes of nitrogen (N) and oxygen (O) in nitrate to investigate the N and O isotope enrichment factors ( ε and ε) and quantified N losses via denitrification in SWIS.

Isotopic imprints of aerosol ammonium over the north China plain.

Atmospheric PM poses a variety of health and environmental risks to urban environments. Ammonium is one of the main components of PM, and its role in PM pollution will likely increase in the coming years as NH emissions are still unregulated and rising in many cities worldwide. However, partitioning urban NH sources remains challenging.

Soil enzyme activity and stoichiometry in secondary grasslands along a climatic gradient of subtropical China.

Soil extracellular enzymes plays key roles in ecosystem carbon (C), nitrogen (N), and phosphorus (P) cycling, and are very sensitive to climatic, plant, and edaphic factors. However, the interactive effects of these factors on soil enzyme activities at large spatial scales remain unclear. Here, we investigated the spatial pattern of the activities of five soil hydrolyzing enzymes [β-D-cellobiohydrolase (CB), β-1,4-glucosidase (BG), β-1,4-N-acetyl-glucosaminidase (NAG), L-leucine aminopeptidase (LAP), and acid phosphatase (AP)], and their C:N:P acquisition ratios in relation to plant inputs and edaphic properties across a 600-km climatic gradient in secondary grasslands of subtropical China.

Retention of deposited ammonium and nitrate and its impact on the global forest carbon sink.

The impacts of enhanced nitrogen (N) deposition on the global forest carbon (C) sink and other ecosystem services may depend on whether N is deposited in reduced (mainly as ammonium) or oxidized forms (mainly as nitrate) and the subsequent fate of each. However, the fates of the two key reactive N forms and their contributions to forest C sinks are unclear. Here, we analyze results from 13 ecosystem-scale paired N-labelling experiments in temperate, subtropical, and tropical forests.

Unexpected high retention of N-labeled nitrogen in a tropical legume forest under long-term nitrogen enrichment.

The responses of forests to nitrogen (N) deposition largely depend on the fates of deposited N within the ecosystem. Nitrogen-fixing legume trees widely occur in terrestrial forests, but the fates of deposited N in legume-dominated forests remain unclear, which limit a global evaluation of N deposition impacts and feedbacks on carbon sequestration. Here, we performed the first ecosystem-scale N labeling experiment in a typical legume-dominated forest as well as in a nearby non-legume forest to determine the fates of N deposition between two different forest types and to explore their underlying mechanisms.

Quantifying nitrogen uptake and translocation for mature trees: an in situ whole-tree paired 15N labeling method.

Nitrogen (N) is one of the major nutrients limiting plant growth in terrestrial ecosystems. To avoid plant-microbe competition, previous studies on plant N uptake preference often used hydroponic experiments on fine roots of seedlings and demonstrated ammonium preference for conifer species; however, we lack information about N uptake and translocation in the field. In this paper, we described a method of in situ paired 15N labeling and reported the rates and time course of N uptake and translocation by mature trees in situ.

Dynamics and multi-annual fate of atmospherically deposited nitrogen in montane tropical forests.

The effects of nitrogen (N) deposition on forests largely depend on its fate after entering the ecosystem. While several studies have addressed the forest fate of N deposition using N tracers, the long-term fate and redistribution of deposited N in tropical forests remains unknown. Here, we applied N tracers to examine the fates of deposited ammonium ( ) and nitrate ( ) separately over 3 years in a primary and a secondary tropical montane forest in southern China.

Fate of atmospherically deposited NH and NO in two temperate forests in China: temporal pattern and redistribution.

The impacts of anthropogenic nitrogen (N) deposition on forest ecosystems depend in large part on its fate. However, our understanding of the fates of different forms of deposited N as well as the redistribution over time within different ecosystems is limited. In this study, we used the N-tracer method to investigate both the short-term (1 week to 3 months) and long-term (1-3 yr) fates of deposited NH or NO by following the recovery of the N in different ecosystem compartments in a larch plantation forest and a mixed forest located in northeastern China.

High retention of N-labeled nitrogen deposition in a nitrogen saturated old-growth tropical forest.

The effects of increased reactive nitrogen (N) deposition in forests depend largely on its fate in the ecosystems. However, our knowledge on the fates of deposited N in tropical forest ecosystems and its retention mechanisms is limited. Here, we report the results from the first whole ecosystem N labeling experiment performed in a N-rich old-growth tropical forest in southern China.

Effects of nitrogen deposition on carbon cycle in terrestrial ecosystems of China: A meta-analysis.

Nitrogen (N) deposition in China has increased greatly, but the general impact of elevated N deposition on carbon (C) dynamics in Chinese terrestrial ecosystems is not well documented. In this study we used a meta-analysis method to compile 88 studies on the effects of N deposition C cycling on Chinese terrestrial ecosystems. Our results showed that N addition did not change soil C pools but increased above-ground plant C pool.

Effects of litter manipulation on litter decomposition in a successional gradients of tropical forests in southern China.

Global changes such as increasing CO2, rising temperature, and land-use change are likely to drive shifts in litter inputs to forest floors, but the effects of such changes on litter decomposition remain largely unknown. We initiated a litter manipulation experiment to test the response of litter decomposition to litter removal/addition in three successional forests in southern China, namely masson pine forest (MPF), mixed coniferous and broadleaved forest (MF) and monsoon evergreen broadleaved forest (MEBF). Results showed that litter removal decreased litter decomposition rates by 27%, 10% and 8% and litter addition increased litter decomposition rates by 55%, 36% and 14% in MEBF, MF and MPF, respectively.