Effects of landscape disturbance on seed germination of Enterolobium contortisiliquum (Fabaceae) in Brazilian seasonally tropical dry forest : are seeds a sensitive biomarker of environmental stress?

Abstract

Habitat disturbance of native forests is currently the major threat to biodiversity conservation. Plant species can be negatively affected as a result of landscape conversion; thus, it is essential to detect the potential effects of environmental stress on plant performance using reliable bioindicators of quick, cheap diagnosis. Fluctuating asymmetry (FA) describes the degree of the random differences in shape and size among two sides of a bilateral trait of the organisms and reflects the developmental instability of an organism, so we can use it to predict the effects on plant fitness. We evaluated the land-use change stress on seed FA levels, seed germination, and the subsequent seedling development of seed produced by trees that occur in an anthropized and a preserved area of seasonally tropical dry forests (STDF) in Brazil. We sampled 10 ten reproductive trees of Enterolobium contortisiliquum of each landscape condition, and then, 100 seeds per each tree were collected. Additionally, 50 seeds were randomly selected for each tree to determine plant fitness. Despite, we found no true FA in the community, the anthropized area had a lower seed nutritional quality and percentage of germination, and higher germination time of seeds produced than in preserved areas. The dry weight of the aerial part of seedlings did not differ between areas. However, root dry weight and total dry weight were higher in seedlings developed from seeds of anthropized than in preserved areas. Our findings show that seeds of E. contortisiliquum are not a sensitive biomarker to detect full stress conditions of habitat disturbance. However, we demonstrate that habitat disturbance negatively affects plant fitness, decreasing germination percentage, and nutritional quality, and increasing germination time. This fact has potential consequences on recruitment, establishment and survival of E. contortisiliquum in regenerating areas of STDF’s in Brazil.