Physiological responses to nitrogen and sulphur addition and raised temperature in Sphagnum balticum.
Sphagnum, the main genus which forms boreal peat, is strongly affected by N and S deposition and raised temperature, but the physiological mechanisms behind the responses are largely unknown. We measured maximum photosynthetic rate (NP(max)), maximum efficiency of photosystem II [variable fluorescence (F (v))/maximum fluorescence yield (F (m))] and concentrations of N, C, chlorophyll and carotenoids as responses to N and S addition and increased temperature in Sphagnum balticum (a widespread species in the northern peatlands) in a 12-year factorial experiment. NP(max) did not differ between control (0.2 g N m(-2) year(-1)) and high N (3.0 g N m(-2) year(-1)), but was higher in the mid N treatment (1.5 g N m(-2) year(-1)). N, C, carotenoids and chlorophyll concentration increased in shoot apices after N addition. F (v)/F (m) did not differ between N treatments. Increased temperature (+3.6 degrees C) had a small negative effect on N concentration, but had no significant effect on NP(max) or F (v)/F (m). Addition of 2 g S m(-2) year(-1) showed a weak negative effect on NP(max) and F (v)/F (m). Our results suggest a unimodal response of NP(max) to N addition and tissue N concentration in S. balticum, with an optimum N concentration for photosynthetic rate of ~13 mg N g(-1). In conclusion, high S deposition may reduce photosynthetic capacity in Sphagnum, but the negative effects may be relaxed under high N availability. We suggest that previously reported negative effects on Sphagnum productivity under high N deposition are not related to negative effects on the photosynthetic apparatus, but differences in optimum N concentration among Sphagnum species may affect their competitive ability under different N deposition regimes.
Granath
Gustaf
G
Department of Plant Ecology, Evolutionary Biology Centre, Uppsala University, 75236 Uppsala, Sweden. Gustaf.Granath@ebc.uu.se
Wiedermann
Magdalena M
MM
Strengbom
Joachim
J
D000704:Analysis of Variance; D002338:Carotenoids / Q000032:analysis; D002734:Chlorophyll / Q000032:analysis; D005453:Fluorescence; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D044003:Sphagnopsida / Q000502:physiology*; D013455:Sulfur / Q000032:analysis / Q000378:metabolism*; D013548:Sweden; D013696:Temperature
D002734:Chlorophyll; D002338:Carotenoids; D013455:Sulfur; D009584:Nitrogen