Intra- and inter-specific variation in canopy photosynthesis in a mixed deciduous forest

Abstract

Within the same forest, photosynthesis can vary greatly among species and within an individual tree. Quantifying the magnitude of variation in leaf-level photosynthesis in a forest canopy will improve our understanding of and ability to model forest carbon cycling. This information requires extensive sampling of photosynthesis in the canopy. We used a 22-m-tall, four-wheel-drive aerial lift to reach five to ten leaves from the tops of numerous individuals of several species of temperate deciduous trees in central Massachusetts. The goals of this study were to measure light-saturated photosynthesis in co-occurring canopy tree species under field conditions, and to identify sampling schemes appropriate for canopy tree studies with challenging logistics. Photosynthesis differed significantly among species. Even though all leaves measured were canopy-top, sun-acclimated foliage, the more shade-tolerant species tended to have lower light-saturated photosynthetic rates (P ) than the shade-intolerant species. Likewise, leaf mass per area (LMA) and nitrogen content (N) varied significantly between species. With only one exception, the shade-tolerant species tended to have lower nitrogen content on an area basis than the intolerant species, although the LMA did not differ systematically between these ecological types. Light-saturated P rates and nitrogen content, both calculated on either an area or a mass basis, and the leaf mass to area ratio, significantly differed not only among species, but also among individuals within species (P<0.0001 for both). Differences among species accounted for a greater proportion of variance in the P rates and the nitrogen content than the differences among individuals within a species (58.5-78.8% of the total variance for the measured parameters was attributed to species-level differences versus 5.5-17.4% of the variance was attributed to differences between individual trees of a given species). Furthermore, more variation is accounted for by differences among leaves in a single individual tree, than by differences among individual trees of a given species (10.7-30.4% versus 5.5-17.4%). This result allows us to compare species-level photosynthesis, even if the sample size of the number of trees is low. This is important because studies of canopy-level photosynthesis are often limited by the difficulty of canopy access. As an alternative to direct canopy access measurements of photosynthesis, it would be useful to find an "easy-to-measure" proxy for light-saturated photosynthetic rates to facilitate modeling forest carbon cycling. Across all species in this study, the strongest correlation was between nitrogen content expressed on an area basis (mmol m, N ) and light-saturated P rate (μmol m s, P ) (r=0.511). However, within a given species, leaf nitrogen was not tightly correlated with photosynthesis. Our sampling design minimized intra-specific leaf-level variation (i.e., leaves were taken only from the top of the canopy and at only one point in the season). This implies that easy-to-me...

Seasonal shift of dominance in a submerged rooted macrophyte community of Lake Balaton

“…When the size of plant exceeds the boundary of an environmental factor the overall phenotypic integrity is disrupted and significant intraspecific variability occurs (Bassow and Bazzaz, 1997;Gutschick, 1999;Torres Boeger and Poulson, 2003). Despite the well established assumption that both P. perfoliatus and M. spicatum are shade-tolerant plants, our results show that only by the end of summer and only the basal part of these macrophytes were located at depth with minimal, i.e.…”

Functional ecology of advance regeneration in relation to light in boreal forests

“…Leverenz (1996) reported that P max of sun leaves increased from shade tolerant Abies (approximately 7.0 µmol·m -2 ·s -1 ) to shade intolerant Pinus (approximately 16.0 µmol·m -2 ·s -1 ) species. Bassow and Bazzaz (1997) also found that P max decreased with increasing shade tolerance in temperate deciduous trees. Apparently the cost of maintaining high photosynthetic capacity is not justified in shade.…”

Effect of Tree Spacing on Tree Level Volume Growth, Morphology, and Wood Properties in a 25-Year-Old Pinus banksiana Plantation in the Boreal Forest of Quebec

“…Diameter growth has been positively related to photosynthetic biomass and its efficiency [26,27,47], as well as to the relationships between crown ratio and stem taper [28,[49][50][51]. Shade intolerant tree species, such as jack pine [52], exhibit a more open crown and a high photosynthetic capacity [53] and the dominant trees of this species seems to benefit from the sunlight access during the first years after plantation establishment. A reduction of photosynthesis and carbon production is normally observed when intra-and inter-specific competition occurs (crown closure).…”