Photosynthetic response to dynamic changes of light and air humidity in two moss species from the Tibetan Plateau

Abstract

Bryophytes are widely distributed in alpine meadow and wetlands on the Tibetan Plateau, where light intensity and air moisture are highly variable in time. To address how bryophytes respond to their light and moisture environments, we examined dynamic photosynthesis in two moss species, Distichium inclinatum common in meadow, and Encalypta alpine frequently found in wetland. Photosynthetic induction response was faster in the two moss species than in most vascular species. In both species the 90% induction time after a sudden light increase from 50 to 600 lmol m À2 s À1 was within 3 min. The induction was faster in mosses experiencing a period of weak light than in those in total darkness. E. alpina, the wetland species, showed more rapid induction response and shorter post-illumination CO 2 fixation to sunflecks than D. inclinatum, the meadow species. Photosynthetic rate (A max ) under saturated light in the two species increased linearly with increasing air relative humidity (RH). The meadow species D. inclinatum showed higher A max under low RHs, but exhibited lower A max under high RHs in comparison with the wetland moss E. alpina. Moreover, the quantum efficiency increased linearly with increasing RH, indicating that air humidity plays a critical role in photochemical activities in the alpine mosses. The study suggests that there are acclimations in dynamic photosynthesis in response to light and humidity, and the acclimations would benefit a high leaf carbon gain in the two alpine moss species in their common habitats.

Bryophyte photosynthesis in sunflecks: greater relative induction rate than in tracheophytes

“…Our experiments confirmed and extended the findings of Cui et al (2009), that induction times of bryophyte photosynthesis are considerably shorter compared to the published values measured in tracheophytes ( Figure 4). Photosynthetic induction time IT50 (50% of maximum photosynthesis) in tracheophytes strongly correlates with the initial stomatal conductance (Gsi) before the induction (Allen & Pearcy, 2000).…”

“…Although there is a discussion about photosynthetic performance of bryophytes in sunflecks (Glime, 2007), measurements are almost lacking. The only paper dealing with photosynthetic induction dynamics published so far revealed that two alpine mosses reached 90% of net photosynthetic capacity (Amax) within 3 min (Cui et al, 2009), whereas tracheophytes need usually 7-40 min (Naumburg & Elsworth, 2000).…”

Higher photosynthetic capacity and different functional trait scaling relationships in erect bryophytes compared with prostrate species

“…1; Table 2, Table S4 in the ESM). The reason for the similar LSPs of the two groups of bryophytes in our study is that they grow in similar environments and become acclimated to the shaded understory environment (Cui et al 2008;Rascher et al 2011). The higher photosynthetic capacity of erect bryophytes is due to their higher chloroplast pigment concentrations (Chl mass , Chl area , Carmass and Car area ), which enhance their ability to harvest the Table 2 Comparisons of functional trait levels [mean ± SE, range and variance (fold) of species means] between the two groups of bryophytes (p values for comparisons are shown) collected from the old-growth fir forest of Dagu Glacier Park There were 16 prostrate (P) and 12 erect (E) bryophytes, and n = 4 for each bryophyte…”

Potential for fast chlorophyllafluorescence measurement in bryophyte ecophysiology

“…Very often only maximum quantum efficiency of PSII (F^/F^) has been used to characterize the photochemical performance of PSII in bryophyte tissues (Robinson et al, 2000;Proctor, 2003;Cui et al, 2009;Granath et al, 2009;Laine et al, 2011). However, the present study showed that other fluorescence parameters might be also useful in characterizing various aspects of photochemistry in bryophytes in field conditions, as there was no general linear relationship between them and FjF^.…”

“…Recently chlorophyll fluorescence analysis has been used to study photosynthetic response to variability of light and moisture (Cui et al, 2009;Hájek et al, 2009), nitrogen deposition (Granath et al, 2009), growth rate (Laine et al, 2011), as well as salinity tolerance (Garbary et al, 2008;Bates et al, 2009). So far, fluorescence measurements have not been performed in natural habitats with several bryophyte species differing in putative adaptation strategies.…”