Effects of Nitrogen on Temporal and Spatial Patterns of Nitrate in Streams and Soil Solution of a Central Hardwood Forest

Abstract

This study examined changes in stream and soil water NO − may be influenced by spatial heterogeneity of watershed processes which vary over time in response to N availability.

CAN Canopy Addition of Nitrogen Better Illustrate the Effect of Atmospheric Nitrogen Deposition on Forest Ecosystem?

“…In N-limited or young forests, enhanced N availability can stimulate plant growth and cause a substantial CO 2 sequestration 20 22 . By contrast, excessive N deposition can impose negative impacts on forest structure and functions, including loss of biodiversity 10 14 , invasion of exotic species 23 , soil acidification 12 19 , eutrophication and N saturation 11 16 24 , and declines in forest growth 25 . Based the conventional N manipulative experiments, three major consensus have been reached: i) the responses of forest ecosystems to N enrichment vary with the duration of N additions, forest history, and soil characteristics, ii) low N deposition facilitates plant growth and gross primary productivity (GPP), but excess N input reduces forest productivity, and iii) a tipping point (threshold load) may exist where forest ecosystems do not respond to extra N addition, and this status refers to “N saturation” 24 .…”

“…Using a helicopter to spray a fine mist of liquid NH 4 NO 3 onto the canopy of a 21-ha area on five different dates during the growing season (from May to August) in low-elevation transition spruce-fir forests in east-central Maine, USA, Gaige et al (2007) and Dail et al (2009) examined the response of a mature coniferous forest to N deposition 32 37 , but this program was terminated after four years possibly due to expensive cost. Another excellent whole-watershed study on evaluating acidic deposition effects on temperate forests, with three aerial applications of (NH 4 ) 2 SO 4 annually by a low flying fixed-wing aircraft, has been carrying out in the Fernow Experimental Forest (FEF), West Virginia, USA since 1989 11 15 21 25 42 43 44 45 46 . A paired experiment using the same approach has also been conducting in a temperate forest in the Bear Brook Watershed of Maine, USA since 1989 47 .…”

“…Reactive N deposited from the atmosphere to the land and water body can cause cascading environmental problems, including environmental pollution, biodiversity loss, greenhouse gas emissions, soil acidification, and degradation of terrestrial and aquatic ecosystems 9 10 11 12 13 14 . As one of the global change drivers, increasing atmospheric N deposition has the potential to shift the structure and functions of forest ecosystems 3 9 15 .…”

Long-term nitrogen addition decreases carbon leaching in a nitrogen-rich forest ecosystem

“…Because soil solution chemistry can be considered as a sensitive indicator of biogeochemical processes within forest stands, responding quickly to disturbances or stresses such as excess N (e.g. McDowell et al, 2004;Pregitzer et al, 2004;Michel et al, 2006;Gilliam and Adams, 2011), we mainly focused our study on the response of soil solution chemistry to N addition. Earlier measurements in these forests have indicated no changes in DOC dynamics in response to short-term (1 to 2 yr) N deposition treatment (Fang et al, 2009).…”

Tree Growth and Water-Use Efficiency Do Not React in the Short Term to Artificially Increased Nitrogen Deposition

“…The aim of this study was to evaluate the short-term effects of N addition by using two different N fertilization systems, above and below the canopy, on tree growth, intrinsic water-use efficiency at leaf level and on several leaves functional traits. To our knowledge, very few experimental studies explored the effects of N depositions on forest ecosystems through canopy fertilization [24,28,29]. Even less did it by comparing N fertilizer addition on the ground and above the canopy [22], or by investigating the iWUE changes after N fertilizations through stable isotope analyses [30].…”