title: Thinning effect on photosynthesis depends on needle ages in a Chinese fir (Cunninghamia lanceolata) plantation.
abstract: Canopies in evergreen coniferous plantations often consist of various-aged needles. However, the effect of needle age on the photosynthetic responses to thinning remains ambiguous. Photosynthetic responses of different-aged needles to thinning were investigated in a Chinese fir (Cunninghamia lanceolata) plantation. A dual isotope approach [simultaneous measurements of stable carbon (δ13C) and oxygen (δ18O) isotopes] was employed to distinguish between biochemical and stomatal limitations to photosynthesis. Our results showed that increases in net photosynthesis rates upon thinning only occurred in the current-year and one-year-old needles, and not in the two- to four-year-old needles. The increased δ13C and declined δ18O in current year needles of trees from thinned stands indicated that both the photosynthetic capacity and stomatal conductance resulted in increasing photosynthesis. In one-year-old needles of trees from thinned stands, an increased needle δ13C and a constant needle δ18O were observed, indicating the photosynthetic capacity rather than stomatal conductance contributed to the increasing photosynthesis. The higher water-soluble nitrogen content in current-year and one-year-old needles in thinned trees also supported that the photosynthetic capacity plays an important role in the enhancement of photosynthesis. In contrast, the δ13C, δ18O and water-soluble nitrogen in the two- to four-year-old needles were not significantly different between the control and thinned trees. Thus, the thinning effect on photosynthesis depends on needle age in a Chinese fir plantation. Our results highlight that the different responses of different-aged needles to thinning have to be taken into account for understanding and modelling ecosystem responses to management, especially under the expected environmental changes in future.
authors.affiliation: Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Ren-Shan
authors.initials: RS
authors.lastname: Li
authors.affiliation: Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China; Huitong National Research Station of Forest Ecosystem, Huitong 418307, China. Electronic address: yqp226@gmail.com.
authors.forename: Qing-Peng
authors.initials: QP
authors.lastname: Yang
authors.affiliation: Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China; Huitong National Research Station of Forest Ecosystem, Huitong 418307, China.
authors.forename: Wei-Dong
authors.initials: WD
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Wen-Hui
authors.initials: WH
authors.lastname: Zheng
authors.affiliation: State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
authors.forename: Yong-Gang
authors.initials: YG
authors.lastname: Chi
authors.affiliation: Center for Remote Sensing and Spatial Analysis, Department of Ecology, Evolution and Natural Resources, Rutgers University, New Brunswick, NJ 08901, USA.
authors.forename: Ming
authors.initials: M
authors.lastname: Xu
authors.affiliation: Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China.
authors.forename: Yun-Ting
authors.initials: YT
authors.lastname: Fang
authors.affiliation: Forest Dynamics, Swiss Federal Research Institute WSL, Zuercherstrasse 111, 8903 Birmensdorf, Switzerland.
authors.forename: Arthur
authors.initials: A
authors.lastname: Gessler
authors.affiliation: Forest Dynamics, Swiss Federal Research Institute WSL, Zuercherstrasse 111, 8903 Birmensdorf, Switzerland; Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China.
authors.forename: Mai-He
authors.initials: MH
authors.lastname: Li
authors.affiliation: Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China; Huitong National Research Station of Forest Ecosystem, Huitong 418307, China. Electronic address: slwang@iae.ac.cn.
authors.forename: Si-Long
authors.initials: SL
authors.lastname: Wang
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis; D032486:Cunninghamia / Q000502:physiology*; D016468:Forestry; D009584:Nitrogen / Q000032:analysis; D010103:Oxygen Isotopes / Q000032:analysis; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology*; D014197:Trees
chemical_list: D002247:Carbon Isotopes; D010103:Oxygen Isotopes; D009584:Nitrogen
keywords: Dual isotope approach; Needle age; Thinning; Water-soluble nitrogen; δ(13)C; δ(18)O