Relations Between Sunfleck Sequences and Photoinhibition of Photosynthesis in a Tropical Rain Forest Understory Herb

Abstract

We report the photosynthetic characteristics of a C3 shade plant native to the tropical rain forest understory. It was shown that Elatostema repens Lour. (Hall) f. (Urticaceae) presents a large light adjustment capacity. The effects of several lightfleck sequences on photoinhibition of photosynthesis and carbon gain are analyzed. Photoinhibition is measured both as a decrease in leaf net CO2 uptake in limiting light (shown to be linearly correlated to quantum yield of O2 evolution measured at saturating CO2) and as a decrease of the ratio of variable fluorescence (Fv) to maximum fluorescence (Fmax) measured in liquid nitrogen. It is shown that lightflecks (from 10 to 30 min in duration) of 700 μmol m–2 s–1 (high light) induce photoinhibition, and that the effects of those successive high light periods are additive; there is apparently no recovery from photoinhibition during the low light periods (from 10 to 45 min in duration). In contrast, the Fv/Fmax ratio, though decreasing similarly to quantum yield of net CO2 uptake on leaves submitted to a continuous illumination of 700 μmol m–2 s–1, is only decreased a little on leaves submitted to lightfleck sequences of the same photon flux density. Lightflecks of 250 μmol m–2 s–1 are not photoinhibitory. Compared to the control maintained under light growth condition (40 μmol m–2 s–1) carbon gain is increased on leaves submitted to lightflecks; this gain remains high throughout the light cycles on leaves submitted to nonphotoinhibitory lightflecks and to the photoinhibitory lightflecks followed by the shortest low light period. In the other cases, carbon gain, higher than that of the control at the beginning of the treatments, decreases and becomes lower than the control carbon gain. Finally, the relevance of photoinhibition in the tropical rain forest understory environment is discussed.

Interactions between plant size and canopy openness influence vital rates and life‐history tradeoffs in two neotropical understory herbs

“…In particular, Calathea may be more shade‐adapted than Heliconia . A possible explanation for slightly lower survival in high light is photoinhibition; other understory herbs that were suddenly exposed to large quantities of light have been seen to experience photoinhibition (Gouallec et al, 1990; Lovelock et al, 1994). Photoinhibition is a reduction in the efficiency of photosynthesis resulting from damage to proteins in the photosystems or from the dissipation of excess energy (Krause, 1988), and is often associated with rapid leaf senescence (Lovelock et al, 1994).…”

Seedling growth responses to soil resources in the understory of a wet tropical forest

“…In addition, the growth of six shade-tolerant species was negatively correlated to irradiance. Shadetolerant species may experience photo-inhibition and poor growth in sunflecks lasting 10 minutes or longer (Le Gouallec et al 1990, Krause et al 2007, which can contribute 10-85% of daily light levels (Pearcy 2007). The inverse relationship between low-light survival and magnitude of growth responses to nutrients conflicts with other studies (Denslow et al 1987, Lawrence 2001) that examined only P and inorganic N. Our results suggest that shade-tolerant species have a lower nutrient demand.…”

Photoinhibition of Photosynthesis in Plants Growing in Natural Tropical Forest Gaps. A Chlorophyll Fluorescence Study

“…Leitsch et aI., 1994). On the other hand, photoinhibition caused by sequences of lightflecks in shade-grown plants of the tropical understory herb Elatostema repens was not reversible in low light during periods up to 45 min (Le Gouallec et al, 1990). Mulkey and Pearcy (1992) demonstrated that long-term (13d) acclimation to gap conditions with daily high light periods increased the ability of leaves to recover from photoinhibition.…”