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

doi:10.1016/j.scitotenv.2018.08.158

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

Sci Total Environ. 2019 Jan 15:648:325-336. doi: 10.1016/j.scitotenv.2018.08.158. Epub 2018 Aug 14.

Authors

Yanting Hu¹, Ping Zhao², Liwei Zhu¹, Xiuhua Zhao¹, Guangyan Ni¹, Lei Ouyang¹, Karina V R Schäfer³, Weijun Shen⁴

Affiliations

¹ Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Road Xingke 723, District Tianhe, Guangzhou 510650, China.
² Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Road Xingke 723, District Tianhe, Guangzhou 510650, China; Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Road Xingke 723, District Tianhe, Guangzhou 510650, China. Electronic address: zhaoping@scib.ac.cn.
³ Department of Biological Sciences, Rutgers University, 195 University Avenue, Newark 07102, NJ, USA; Department of Earth and Environmental Sciences, Rutgers University, 195 University Avenue, Newark 07102, NJ, USA.
⁴ Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Road Xingke 723, District Tianhe, Guangzhou 510650, China; Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Road Xingke 723, District Tianhe, Guangzhou 510650, China.

PMID: 30121032
DOI: 10.1016/j.scitotenv.2018.08.158

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 (J_s) and intrinsic water use efficiency (WUE_i) 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 J_s and WUE_i of the dominant tree species. Canopy N addition increased WUE_i of Q. variabilis, whereas understory addition treatment had a minimal impact on WUE_i. Both N additions did not exert impacts on WUE_i of L. formosana and Q. acutissima. Canopy N addition exerted negative impacts on J_s 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 J_s of L. formosana in 2014. Probably owing to the increased soil acidification as the experiment proceeded, J_s 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 J_s and WUE_i to canopy and understory N addition, and exaggerated its influences induced by the variation of soil chemical properties.

Keywords: C:N ratio; Canopy nitrogen addition; Nitrogen content; Sap flux; Understory nitrogen addition; Water use efficiency.