Limitations to net photosynthesis as affected by nitrogen status in jack pine (Pinus banksiana Lamb.) seedlings |
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Authors: | Tan, Weixing Hogan, Gary D. |
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Abstract: | Relative limitations of nitrogen (N) status on the processescontributing to photosynthetic rate (A) were investigated. Jackpine {Pinus banksiana Lamb.) seedlings from seeds grown in sandculture were supplied with four different N treatments for 6weeks, which resulted in a needle N content ranging from 5085mmol m2 (1432 mg g1 dry weight). Leaf gasexchange at varying CO2 levels was measured and limitationson A350 (A at ambient CO2 level) caused by finite, limitingcarboxylation efficiency (c.e.), maximum A (Amax)and stomatalconductance were estimated from an analysis of the responseof A to internal CO2 concentration. Although c.e. and Amax decreasedlinearly with the decline in needle N, the magnitudes of theirchanges relative to A350 differed. Amax varied with A350 andalways exceeded A350 by 3738% c.e., however, declinedfaster than A350, as needle N level decreased. Consequently,relative limitation on A350 caused by inefficient Amax remainedconstant, but limitations caused by c.e. increased by 1015%at low N levels. In contrast, the limitation by stomatal conductancedeclined initially, but remained stable when N content droppedbelow 75 mmol m2. The results suggest: (1) a decreasein biochemical capacity, but not stomatal conductance, contributedto the reduction of A350 induced by N-deficiency in jack pineseedlings; and (2) the capacity of carboxylation appeared tobe impaired more than that of electron transport and/or photophosphorylationand its reduction may be the major reason for the reductionin A350. Key words: ACi analysis, carboxylation efficiency, electron transport, nitrogen deficiency, stomatal conductance |
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