Photosynthesis and Stomatal Conductance Patterns of Two Fern Species From Different Forest Understoreys

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Abstract
(1) Photosynthesis and water use in Pteridium aquilinum (bracken) and Blechnum discolor (crown fern) were investigated in the field. The bracken formed an understorey in a Pinus radiata plantation, and the crown fern grew under New Zealand beech forest. (2) A higher percentage of the above-canopy photosynthetically active photon flux reached the Pteridium understorey than the Blechnum understorey. Sunflecks is contributed a large fraction of the photon flux in both understoreys. (3) Mean maximum rates of photosynthesis for Pteridium aquilinum and Blechnum discolor were 9.8 and 3.7 .mu.mol m-2 s-1, respectively (projected area). (4) In both species, stomatal conductances were high relative to photosynthetic capacity under normal environmental conditions. Stomata in both fern species responded proportionally less than stomata in the overestorey tree species to changes in photosynthetically active photon flux density and leaf air vapour concentration gradient (.DELTA.W).