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

Abstract

Increasing atmospheric nitrogen (N) deposition could profoundly impact community structure and ecosystem functions in forests. However, conventional experiments with understory addition of N (UAN) largely neglect canopy-associated biota and processes and therefore may not realistically simulate atmospheric N deposition to generate reliable impacts on forest ecosystems. Here we, for the first time, designed a novel experiment with canopy addition of N (CAN) vs. UAN and reviewed the merits and pitfalls of the two approaches. The following hypotheses will be tested: i) UAN overestimates the N addition effects on understory and soil processes but underestimates those on canopy-associated biota and processes, ii) with low-level N addition, CAN favors canopy tree species and canopy-dwelling biota and promotes the detritus food web, and iii) with high-level N addition, CAN suppresses canopy tree species and other biota and favors rhizosphere food web. As a long-term comprehensive program, this experiment will provide opportunities for multidisciplinary collaborations, including biogeochemistry, microbiology, zoology, and plant science to examine forest ecosystem responses to atmospheric N deposition.

Substrate stoichiometry determines nitrogen fixation throughout succession in southern Chinese forests

“…At the SMT site, we selected a 50‐year‐old evergreen broadleaved forest that was originally a limestone site in 1965 (Zhang et al . ). At the DHS site, we selected an 80‐year‐old coniferous forest and an 80‐year‐old coniferous/broadleaved forest, which were established on degraded lands in 1930, and we selected a > 400‐year‐old broadleaved forest that has been protected since 1633 (Brown et al .…”

“…At the SMT site, NH 4 NO 3 solutions equivalent to 3 mm of precipitation were applied below the canopy monthly during the growing season (April‒October) from April 2013 to July 2016 in the N‐addition plots (Zhang et al . ; Zheng et al . ).…”

“…At the HS site, we selected a 30year-old eucalyptus (Eucalyptus urophylla) plantation and a 30-year-old acacia (Acacia auriculiformis) plantation, which were established on degraded grasslands in 1984 (Zheng et al 2016). At the SMT site, we selected a 50-year-old evergreen broadleaved forest that was originally a limestone site in 1965 (Zhang et al 2015). At the DHS site, we selected an 80-yearold coniferous forest and an 80-year-old coniferous/broadleaved forest, which were established on degraded lands in 1930, and we selected a > 400-year-old broadleaved forest that has been protected since 1633 (Brown et al 1995) (the DHS forest sites selected for this experiment were near those for Experiment 1).…”

Fire rather than nitrogen addition affects understory plant communities in the short term in a coniferous‐broadleaf mixed forest

“…Nitrogen was applied once on 23 July 2014 and three times (16.67 kg N ha −1 ) in May, July, and September in both 2015 and 2016. The N addition level was chosen according to the background rate of N deposition in this region and a N-fertilization experiment in the same region (Zhang et al, 2015b). visually using a square grid method (Yang et al, 2012).…”

Difference in response of water use to evaporative demand for codominant diffuse‐porous versus ring‐porous tree species under N addition in a temperate forest

“…According to the report of Zhang et al (2015), the N deposition in precipitation is about 19.6 kg N ha −1 year −1 in JGS, which has greatly exceeded the critical load of temperate region (10 kgN ha −1 year −1 ; Ochoa-Hueso et al, 2011). According to the report of Zhang et al (2015), the N deposition in precipitation is about 19.6 kg N ha −1 year −1 in JGS, which has greatly exceeded the critical load of temperate region (10 kgN ha −1 year −1 ; Ochoa-Hueso et al, 2011).…”