The photosynthetic response of American chestnut seedlings to differing light conditions

Abstract

Restoration attempts to reintroduce American chestnut trees to the eastern deciduous forest by means of a disease-resistant Chinese–American hybrid seed are in progress. Knowing the light conditions required for optimum seedling performance is necessary to maximize the success of reintroduction. American chestnut ( Castanea dentata (Marsh.) Borkh.) seedlings were planted in two replicate forests in Vinton County, Ohio, in areas that had been thinned (more available light) and in control areas (intact canopy, less available light). The photosynthetic capacity of 12 seedlings per treatment was assessed using an infrared gas-exchange analyzer. Seedlings in the thinned treatment reached light-saturating rates of photosynthesis at an irradiance level approximately 33% higher than did the seedlings in the control treatment. Seedlings grown in the thinned treatment had a significantly greater maximum rate of photosynthesis (Amax), dark respiration rate (Rd), and daily carbon gain per seedling than seedlings grown in the control treatment. The light compensation point (LCP), quantum efficiency (ϕ), leaf mass per area (LMA), and leaf nitrogen concentration per unit leaf area (Narea) were not significantly different between treatments. American chestnut seedlings in the thinned treatment clearly maximize leaf-level photosynthetic capacity. These results will aid land managers in planning reintroduction trials by providing information on the light conditions required for maximum seedling success.

American Chestnut Growth and Survival Five Years after Planting in Two Silvicultural Treatments in the Southern Appalachians, USA

“…These same trends are similar to those found in a two-year old field study [19] and in an outdoor shade-house study [17]. Despite the low levels of growth in the midstory-removal treatment, survival rates in this treatment indicate chestnuts will meet photosynthetic demands under an intact forest overstory canopy for at least five growing seasons, similar to previous studies [16,20]. Our results support the observations of Paillet [42], who hypothesized that chestnut efficiently uses limited light resources through recurrent root-collar sprouting and advantageous growth once released.…”

“…Pure American chestnut seedlings respond positively to increased light in the field and under controlled environmental conditions [15][16][17][18]. Chestnut seedlings had similar or better survival in shaded conditions compared to openings receiving full sunlight [15,[19][20][21].…”

“…Based on this limited amount of empirical research, chestnut likely has silvicultural requirements similar to oak (Quercus) species in that the seedlings can persist in the absence of disturbance, but growth is stimulated by increased light [12,22]. A commercial shelterwood harvest has been shown to be an acceptable regeneration method for chestnut due to the species' positive response to increased light levels [15,16] that will occur following canopy removal, cf. [23].…”

Disturbance History and Decline of American Chestnut

“…Although chestnut is classified as moderately shadetolerant (Joesting et al 2007, Joesting et al 2009), in its new position as an understory tree, shade has a major effect on chestnut's competitive ability. Studies have suggested that current chestnut growth and abundance are greater on sites with higher light availability (Paillet 1988, Griffin 1989, Griffin 1992.…”

Determining the shade tolerance of American chestnut using morphological and physiological leaf parameters

“…There is disagreement regarding the shade tolerance classification of American chestnut (McCament and McCarthy, 2005;Wang et al, 2006;Joesting et al, 2007). American chestnut seedlings and saplings are capable of surviving in the shade, much like the ''sit and wait'' strategy of shade tolerant species (Paillet, 1993).…”