Photosynthetic Induction in Two Fern Species with Different Eco-types in Xishuangbanna Tropical Rainforest
西双版纳热带雨林中两种生态型蕨类植物的光合特性比较研究

We compared the characteristics of photosynthesis and photosynthetic induction in an epiphytic fern (Neottopteris nidus) and a terrestrial fern (Asplenium finlaysonianum) in the understory of the Xishuangbanna tropical rainforest to study the light-fleck utilization strategy in the two eco-type ferns. Maximum photosynthetic rate, dark respiration, apparent quantum yield,light saturation point and light compensation point did not differ between the two fern species. However, maximum stomatal conductance was higher in A. finlaysonianum than in N. nidus, which indicates better photosynthetic water-use efficiency in the latter species. Compared to N. nidus, A. finlaysonianum had a higher initial stomatal conductance on exposure to low light (20 mmol.m-2.s-1) for 30 min after 3 h dark adaptation. The time required to reach 50% (T50%) and 90% (T90%) maximal net photosynthetic rate in A. finlaysonianum was shorter than that in N. nidus (T50% 0.57 and 5.31 min, T90% 5.85 and 26.33 min in A. finlaysonianum and N. nidus, respectively).Attaining maximal stomatal conductance significantly lagged behind the increase in net photosynthetic rate during the induction course. The time required to reach maximum stomatal conductance was longer in N. nidus than in A.finlaysonianum, but the ferns did not differ in maintaining capacity of photosynthetic induction during induction loss. Thus, water conservation takes priority over carbon gain in N. nidus, which limits the use of light flecks for CO2 fixation in this epiphytic fern as compared to most terres trial understory plants such as A. finlaysonianum.