Effects of mixing two legume species at seedling stage under different environmental conditions

Abstract

While intercropping is known to have positive effects on crop productivity, it is unclear whether the effects of mixing species start at the early plant stage, that is, during germination. We tested whether the germination of two legume species, alsike clover and black medic, characterized by a contrasting response to water availability and temperature is affected by mixing. We set up four experiments in each of which we compared a 1:1 mixture against the two monocultures, and combined this with various other experimental factors. These additional factors were (i) varied seed densities (50%, 100% and 150% of a reference density) in two field trials in 2016 and 2017, (ii) varied seed densities (high and low) and water availability (six levels, between 25% and 100% of water holding capacity (WHC)) in a greenhouse pot trial, (iii) varied seed spacing in a climate chamber, and (iv) varied temperatures (12 °C, 20 °C and 28 °C) and water availability (four levels between 25% and 100% of WHC) in a climate chamber. Across all experiments, the absolute mixture effects (AME) on germination ranged between −9% and +11%, with a median of +1.3%. Within experiments, significant mixture effects were observed, but the direction of these effects was inconsistent. In the field, AME on germination was significantly negative at some of the tested seed densities. A positive AME was observed in the climate chamber at 12 °C, and the mean AME decreased with increasing temperature. Higher density was associated with decreased germination in the field, indicating negative interaction through competition or allelopathy, among seedlings. Our findings indicate that interaction among seeds in species mixtures may be ongoing during germination, but that the direction of the mixture effect is affected by complex interactions with abiotic and biotic factors.

Effects of spring wheat / faba bean mixtures on early crop development

“…higher relative SW emergence in mixtures compared to monocultures. It may be assumed that the higher SW emergence in mixtures was due to the temporal complementarity effect in resource use between SW and FB (Li et al, 2016;Xiao et al, 2018) in the very early stage of plant development (Elsalahy et al, 2021). In our eld experiment, we observed that FB was slower to germinate than SW, potentially because of the (necessarily) deeper seed depth of FB (6 cm) than of SW (3 cm).…”

“…The relative emergence of SW was 16.4% higher than FB (Table 6) at that stage, indicating dominance, but the PEER value of FB (0.51 at LD and 0.50 at HD; Table 6) showed no reduction of FB emergence in the mixture compared to FB monoculture. The higher emergence of SW in the mixture than in the SW monoculture was observed presumably due to the complementarity effect (Xiao et al, 2018), and could be linked to asynchronous germination between the two species (Elsalahy et al, 2021). At the same time, the observed dominance of SW did not lead to the suppression of FB emergence in the mixture possibly due to the small size of the cereal, and the short time of co-growth between the two species.…”

“…In our eld experiment, we observed that FB was slower to germinate than SW, potentially because of the (necessarily) deeper seed depth of FB (6 cm) than of SW (3 cm). In the mixture, this asynchronous germination between SW and FB may allow SW to temporarily access more resources and induce higher germination than in monoculture (Elsalahy et al, 2021).…”

“…Most studies on mixtures have concentrated on nal (grain) yield which integrates growth dynamics between species over the whole growing period. In contrast, only a few studies have investigated the degree of interaction between intercrops that may already be detected at a very early growing stage (Bellostas et al, 2003;Benincasa et al, 2012;Elsalahy et al, 2021), such as at crop emergence and the carry-on effects of mixing from early to later growth stages.…”

Environment Modification Mediates Seed-to-seed Interactions between Dominant Species in the Yangtze River Estuary

“…However, as plant traits differ in different life history stages, the form, intensity and mechanism of interspecific interactions may change with the ontogenetic process of plants [10][11][12]. Researchers have recognized the importance of regeneration on community assembly and investigated some adult-to-seed and seed-toseed interactions in recent years [13][14][15], but our understanding of interspecific interaction mechanisms during early life history stage of plants (i.e., germination) is still limited.…”