Development and plasticity of endangered shrubLindera melissifolia(Lauraceae) seedlings under contrasting light regimes

Abstract

Lindera melissifolia (Walt.) Blume seedlings were raised in a growth chamber to determine the effects of light availability on shoot growth pattern, and basic leaf and stem growth. Lindera melissifolia seedlings exhibited a sympodial shoot growth pattern for 3 months following emergence from the soil medium, but this pattern was characterized by a reduction in leaf blade area approximately 30 days after emergence, followed by increases in leaf blade area. Seedlings receiving low light were 76% taller than seedlings receiving high light. Seedlings receiving low light also had larger leaf blade dimensions, blade area, seedling leaf area, and greater mass. Seedlings raised in high light had a greater proportional distribution of biomass in the roots, suggesting possible water stress from greater vapor pressure deficits. Furthermore, these seedlings displayed sharp angles of blade inclination and blade folding -acclimation that reduces exposure to light and subsequent higher leaf temperatures in open environments. These differences in morphological response to light resulted in high phenotypic variability in L. melissifolia seedlings. Lindera melissifolia seedling development showed a brief period of phenotypic plasticity, followed by ontogenetic plasticity. The short period of phenotypic plasticity may, however, have profound ecological implications for the conservation and recovery of this federally endangered shrub. Further experimentation should take into account the development of ontogenetic standards for comparisons of plant traits in addition to temporal standards.

Environmental Controls of Reproduction and Early Growth ofLindera melissifolia(Lauraceae)

“…These results are consistent with other studies that have shown that L. melissifolia is highly plastic in response to shading (Wright 1990b, Aleric and Kirkman 2005, Lockhart et al 2012, Lockhart et al 2013. Consistent with Lockhart et al (2012), we found that L. melissifolia seedlings grown under higher light conditions allocate greater resources to roots. While L. melissifolia seedlings expressed clear morphological patterns in response to varied light and moisture, the role of interaction between these two factors remains unclear.…”

“…In our field observations, L. melissifolia adults occurred under a variety of overstory conditions at both sites ranging from 5.5-86.6% transmittance as measured with a quantum line sensor, and co-occurred with both full sun-and shade-tolerant species. Leaves of adults present in the areas of highest transmittance had a curled form, similar to those described by Aleric and Kirkman (2005) and Lockhart et al (2012) under high light and presumed stress. Other studies have observed that L. melissifolia has decreased photosynthetic efficiency under conditions of higher light (Aleric and Kirkman 2005, Wright 1990b) and concluded this could lead to decreased competitive ability in open canopy areas with low moisture (Wright 1990b).…”

“…Failure to detect interaction between light and moisture at the higher light levels may have been due to a lack of tightly controlled conditions such as those found in a growth chamber, and a temperature spike was recorded in the greenhouse where maximum temperatures reached 468C consistently for a week, possibly detrimentally impacting plants. It should also be noted that the highest level of light in our greenhouse study was considerably lower in solar transmittance (340 compared to 600 lmol/ m2/s photosynthetically active radiation) when compared to those used by Lockhart et al (2012), and this level may not have been high enough transmittance to detect the expected interaction with moisture.…”

“…Although it is known to occur in full sun conditions in North Carolina, South Carolina, and Georgia (Devall et al 2001), photosynthetic efficiency decreases in these conditions (Aleric and Kirkman 2005), and reduced biomass and height of seedlings grown in high levels of light have been observed (Lockhart et al 2012). Additionally, L. melissifolia may have low water use efficiency in high light environments, leading to lower drought tolerance under these conditions, which could adversely affect adults and also hinder seedling establishment (Wright 1990b).…”

“…Additionally, L. melissifolia may have low water use efficiency in high light environments, leading to lower drought tolerance under these conditions, which could adversely affect adults and also hinder seedling establishment (Wright 1990b). Seedlings grown under high levels of light exhibit disproportionate root growth, indicating drought stress, as well as increased leaf folding and inclination to reduce surface exposure to light (Lockhart et al 2012). Studies on photosynthetic ability of adults under differing light levels have shown that, while L. melissifolia is an effective competitor under flooded, low light conditions, it is likely outcompeted in open areas (Wright 1990b).…”