Shade Delayed Flowering Phenology and Decreased Reproductive Growth of Medicago sativa L.

Abstract

Alfalfa (Medicago sativa L.) is an important forage in intercropping or rotation ecosystem, and shading is the principal limiting factor for its growth under the crop or forest. Agronomic studies showed that shading would systematically reduce the biomass of alfalfa. However, little is known about the reproduction of alfalfa under shading conditions. In order to study the effect of shading on the reproductive characteristics of alfalfa, two alfalfa cultivars (“Victoria” and “Eureka”) were used to study the effect of shading levels (full light, 56.4% shade, and 78.7% shade) on alfalfa flowering phenology, pollen viability, stigma receptivity, and seed quality. Results showed that shading delayed flowering phenology, shortened the flowering stage, faded the flower colors, and significantly reduced pollen viability, stigma receptivity, the number of flowers, quantity, and quality of seeds. Under shading conditions, seed yield per plant was obviously positively correlated with germination potential, germination rate, pollen viability, and 1,000-seed weight. The number of flower buds, pollen viability, 1,000-seed weight, and germination rate had the greatest positive direct impact on seed yield per plant. Our findings suggested that delayed flowering and reducing reproduction growth were important strategies for alfalfa to cope with shading and pollen viability was the key bottleneck for the success of alfalfa reproduction under shading. However, given that alfalfa is a perennial vegetative-harvest forage, delaying flowering in a weak light environment was beneficial to maintain the high aboveground biomass of alfalfa. Therefore, this should be taken into account when breeding alfalfa cultivars suitable for intercropping. Future research should further reveal the genetic and molecular mechanism of delayed flowering regulating the accumulation and distribution of assimilates between vegetative and reproductive organs of alfalfa under shading, so as to provide a theoretical basis for breeding of shade-tolerant alfalfa cultivars.

Forage quality and physiological performance of mowed alfalfa (Medicago sativa L.) subjected to combined light quality and drought

“…As a perennial forage, alfalfa dwells in meadowlands ( Wang et al., 2009 ; Guo et al., 2016a ), where populations grow in full sunlight. However, alfalfa can also be distributed under canopies of forest trees ( Qin et al., 2022 ). Light is a fatal factor that may limit the growth and development of undergrowth ( Zhao et al., 2020 ; Chu et al., 2021 ; Song et al., 2022 ).…”

“…Shade can systematically reduce biomass production in alfalfa, but the light deficit would not threaten survival in shading up to 50% ( Lin et al., 1998 ; Varella et al., 2001 ). It has also been found that shade limits the reproduction of alfalfa through the delay of flowering ( Lorenzo et al., 2019 ; Qin et al., 2022 ). Given that populations at the understory layer are subjected to the sunlight spectrum of transmittance ( Wei et al., 2019 ; Wei et al., 2020 ), the light spectrum is a determinative factor of illumination condition for plant growth and development ( Chu et al., 2021 ; Zhou et al., 2021a ).…”

Enhancing growth, quality, and metabolism of nitrogen of alfalfa (Medicago sativa L.) by high red–blue light intensity

“…Qin et al. (2022) discovered that high‐light intensity had the capacity to induce alfalfa to bloom. Our data corroborated these findings, as alfalfa subjected to light intensity treatments of 500 and 600 µmol m −2 s −1 entered the initial flowering stage on the 35th day.…”

“…The accumulation of photosynthetic yield was found to be regulated by light intensity, thereby exerting a subsequent influence on the differentiation of flower buds (Wen et al, 2021). Qin et al (2022) discovered that high-light intensity had the capacity to induce alfalfa to bloom. Our data corroborated these findings, as alfalfa subjected to light intensity treatments of 500 and 600 µmol m −2 s −1 entered the initial flowering stage on the 35th day.…”

“…Lin et al (1998) reported that alfalfa yield decreased 37% and 71% when the 50% and 80% were shaded. In addition, reduced light intensity resulted in a delay in the flowering of alfalfa, accompanied by a reduction in flowering rates (Qin et al, 2022). Taking into comprehensive consideration the growth performance, nutritional quality, and production energy consumption of lettuce, it was determined that commercial lettuce could achieve maximal growth under the conditions of a light intensity of 250 µmol m −2 s −1 and a photoperiod of 16/8 h (Zhang et al, 2018).…”