Abstract
Seedlings in regenerating layer are frequently attacked by herbivorous insects, while the combined effects of defoliation and shading are not fully understood. In the present study, two Leguminosae species (Robinia pseudoacacia and Amorpha fruticosa) were selected to study their responses to combined light and defoliation treatments. In a greenhouse experiment, light treatments (L+, 88% vs L−, 8% full sunlight) and defoliation treatments (CK, without defoliation vs DE, defoliation 50% of the upper crown) were applied at the same time. The seedlings’ physiological and growth traits were determined at 1, 10, 30, and 70 days after the combined treatment. Our results showed that the effects of defoliation on growth and carbon allocation under high light treatments in both species were mainly concentrated in the early stage (days 1–10). R. pseudoacacia can achieve growth recovery within 10 days after defoliation, while A. fruticosa needs 30 days. Seedlings increased SLA and total chlorophyll concentration to improve light capture efficiency under low light treatments in both species, at the expense of reduced leaf thickness and leaf lignin concentration. The negative effects of defoliation treatment on plant growth and non-structural carbohydrates (NSCs) concentration in low light treatment were significantly higher than that in high light treatment after recovery for 70 days in R. pseudoacacia, suggesting sufficient production of carbohydrate would be crucial for seedling growth after defoliation. Plant growth was more sensitive to defoliation and low light stress than photosynthesis, resulting in NSCs accumulating during the early period of treatment. These results illustrated that although seedlings could adjust their resource allocation strategy and carbon dynamics in response to combined defoliation and light treatments, individuals grown in low light conditions will be more suppressed by defoliation. Our results indicate that we should pay more attention to understory seedlings’ regeneration under the pressure of herbivorous insects.
Highlights
The regeneration of woody plant seedlings is an important component of maintaining the vegetation diversity of forest ecosystem (Fukushima et al, 2008)
We explored the effects of artificial defoliation in different light availability on plant growth, leaf traits and carbon allocation of Robinia pseudoacacia and Amorpha fruticosa
Basal diameter and total biomass were affected by time and light treatments, but the interaction of light and Combined Treatment Effects on Carbon Allocation
Summary
The regeneration of woody plant seedlings is an important component of maintaining the vegetation diversity of forest ecosystem (Fukushima et al, 2008). In the process of vegetation regeneration, woody plant seedlings often suffer from leaf damage due to herbivores, especially in the context of changing climate conditions (Cannon, 2004; BallinaGómez et al, 2010). Among the numerous ecological factors, light conditions and defoliation have an important impact on the survival and regeneration of seedlings (Ballina-Gómez et al, 2010; Chen et al, 2011; Kuehne et al, 2014). In forest ecosystems, plants usually distribute in various light environments, among which gaps and understory are the most important living environments for regenerating layer seedlings (Wang and Zhou, 2000). Gaps create heterogeneity in understory conditions, which is important for plant regeneration by modifying microclimate and resource availability (Kern et al, 2013). Revealing the physiological and ecological adaptability of the plant seedling stage to light intensity has important practical significance
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