Abstract
Plant size influences plant responses to combined environmental factors under climate change. However, their roles in plant ecophysiological responses are not fully understood. Two rapidly growing Leguminosae species (Robinia pseudoacacia and Amorpha fruticosa) were used to examine plant responses to combined drought and defoliation treatments (two levels of both treatments). Both 1.5 month-old seedlings and 3 month-old seedlings were grown in a greenhouse, and seedling growth, leaf gas exchanges, stem hydraulics, and concentrations of non-structural carbohydrates were determined after 60 days of treatment. Our results indicated defoliation had no significant effect on plant height, basal diameter, and total biomass whatever plant sizes and species. Under the low water availability treatment, the defoliated seedlings significantly increased by 24% in stem water potential compared with non-defoliated seedlings in large R. pseudoacacia. Compared with the high water availability in large non-defoliated R. pseudoacacia seedlings, the low water availability significantly reduced by 26% in stem starch concentration to maintain the stem soluble sugar concentration stable, but not in small R. pseudoacacia seedlings. We also found a negative correlation between leaf and root soluble sugar concentration under low water availability in A. fruticosa. The results demonstrate defoliation could relieve the effect of low water availability in large seedlings. Large seedlings had more compensatory mechanisms in response to defoliation and drought treatments than small seedlings, thus species with large carbon reserves are more recommended for vegetation restoration under combined drought and defoliation conditions. Future studies with more species are crucial for obtaining more rigorous conclusions.
Highlights
Global climate change is expected to increase both the level of insect damage and the occurrence of severe drought (Jacquet et al, 2014; Nahar et al, 2017; Gely et al, 2020)
We investigated the effects of low water availability, artificial defoliation, and plant size on the growth and carbon allocation of two Leguminosae woody species (R. pseudoacacia and A. fruticosa) in order to investigate how they responded to defoliation and low water availability with different plant sizes
During harvest in September, in R. pseudoacacia, the defoliation treatment had no significant effect on seedling growth (Table 1), whereas plant size had a significant impact on seedling growth (Table 1)
Summary
Global climate change is expected to increase both the level of insect damage and the occurrence of severe drought (Jacquet et al, 2014; Nahar et al, 2017; Gely et al, 2020). There are few studies focused on the combined effects of defoliation, drought, and plant size on plant growth (Quentin et al, 2012; Jacquet et al, 2014), especially in terms of their response mechanisms at the individual level. Studying the effects of plant size on the response and intrinsic mechanisms of tree species to combined insect disturbances and varying water availability is extremely important for predicting tree species’ growth and dynamics in the context of climate change, and it could provide more comprehensive information on current changes in forest ecosystem productivity (Jacquet et al, 2014; Assal et al, 2016; Wagg et al, 2017). If the assimilation is reduced, the deficiency of NSCs will affect plant growth, respiration and other metabolic processes (Dietze et al, 2014)
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