Responses of sap flux and intrinsic water use efficiency to canopy and understory nitrogen addition in a temperate broadleaved deciduous forest

Yanting Hu, Ping Zhao, Liwei Zhu, Xiuhua Zhao, Guangyan Ni, Lei Ouyang, Karina V.R. Schäfer, Weijun Shen

Research output: Contribution to journalArticle

4 Scopus citations

Abstract

Increasing atmospheric nitrogen (N) deposition could profoundly impact structure and functioning of forest ecosystems. Therefore, we conducted a two-year (2014–2015) experiment to assess the responses of tree sap flux density (Js) and intrinsic water use efficiency (WUEi) of dominant tree species (Liquidambar formosana, Quercus acutissima and Quercus variabilis) to increased N deposition at a manipulative experiment with canopy and understory N addition in a deciduous broadleaved forest. Five treatments were administered including N addition of 25 kg ha−1 year−1 and 50 kg ha−1 year−1 onto canopy (C25 and C50) and understory (U25 and U50), and control treatment (CK, without N addition). Our results showed neither canopy nor understory N addition had an impact on leaf N content and C:N ratio (P > 0.05). Due to the distinct influencing ways, canopy and understory N addition generated different impacts on Js and WUEi of the dominant tree species. Canopy N addition increased WUEi of Q. variabilis, whereas understory addition treatment had a minimal impact on WUEi. Both N additions did not exert impacts on WUEi of L. formosana and Q. acutissima. Canopy N addition exerted negative impacts on Js and its sensitivity to micrometeorological factors of Q. acutissima and Q. variabilis in 2014, while understory addition showed no effect. Neither canopy nor understory N addition had an influence on Js of L. formosana in 2014. Probably owing to the increased soil acidification as the experiment proceeded, Js of L. formosana and Q. variabilis was decreased by understory N addition while canopy addition had a minimal effect in 2015. Thus, the traditional understory addition approach could not fully reflect the effects of increased N deposition on the canopy-associated transpiration process indicated by the different responses of Js and WUEi to canopy and understory N addition, and exaggerated its influences induced by the variation of soil chemical properties.

Original languageEnglish (US)
Pages (from-to)325-336
Number of pages12
JournalScience of the Total Environment
Volume648
DOIs
StatePublished - Jan 15 2019

All Science Journal Classification (ASJC) codes

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution

Keywords

  • C:N ratio
  • Canopy nitrogen addition
  • Nitrogen content
  • Sap flux
  • Understory nitrogen addition
  • Water use efficiency

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