tailieunhanh - Báo cáo lâm nghiệp: "Yellow-cedar and western redcedar ecophysiological response to fall, winter and early spring temperature conditions"

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: "Yellow-cedar and western redcedar ecophysiological response to fall, winter and early spring temperature conditions" | 1 Ann. For. Sci. 63 2006 1-8 INRA EDP Sciences 2006 DOI forest 2005092 Original article Yellow-cedar and western redcedar ecophysiological response to fall winter and early spring temperature conditions Steven C. Grossnicklea John H. Russellb a CellFor Inc. PO Box 133 Brentwood Bay . Canada V8M 1R3 b British Columbia Ministry of Forests Cowichan Lake Research Station Box 335 Mesachie Lake . Canada V0R 2N0 Received 17 January 2005 accepted 23 September 2005 Abstract - Western redcedar Thuja plicata Donn and yellow-cedar Chamaecyparis nootkatensis D. Don Spach populations originating from an elevation zone where these two species naturally coexist were monitored to define their performance patterns in response to seasonal temperature conditions within the fall winter and early spring field conditions of the Pacific Northwest coastal forest region. Western redcedar and yellow-cedar populations were measured for changes in growth rhythms photosynthetic patterns and freezing tolerance. Net photosynthesis Pn for both species was directly related to minimum air temperature that occurred during the prior evening though no population differences were detected within each species. Photosynthesis was greater in western redcedar than yellow-cedar when minimum air temperature was above freezing. Freezing temperatures from 0 to -5 C caused a greater reduction in photosynthesis for western redcedar though not a complete cessation of photosynthetic capability in either species. Freezing tolerance increased at a moderate rate in the fall as mean air temperature declined for both species when their shoot systems were still active with freezing tolerance increasing at a rapid rate when shoot systems showed no mitotic activity. No shoot growth or mitotic activity was detected in shoot tips of both western redcedar and yellow-cedar when mean air temperature decreased to 4 C for the previous week. No population differences within each species were detected in the .