Date Published: May 31, 2018
Publisher: Public Library of Science
Author(s): Yuanfang Fan, Junxu Chen, Yajiao Cheng, Muhammad Ali Raza, Xiaoling Wu, Zhonglin Wang, Qinlin Liu, Rui Wang, Xiaochun Wang, Taiwen Yong, Weiguo Liu, Jiang Liu, Junbo Du, Kai Shu, Wenyu Yang, Feng Yang, Ricardo Aroca.
Intercropping is an important agronomic practice adopted to increase crop production and resource efficiency in areas with intensive agricultural production. Two sequential field trials were conducted in 2015–2016 to investigate the effect of shading on the morphological features, leaf structure, and photosynthetic characteristics of soybean in a maize-soybean relay-strip intercropping system. Three treatments were designed on the basis of different row configurations A1 (“50 cm + 50 cm” one row of maize and one row of soybean with a 50 cm spacing between the rows), A2 (“160 cm + 40 cm” two rows of maize by wide-narrow row planting, where two rows of soybean were planted in the wide rows with a width of 40 cm, and with 60 cm row spacing was used between the maize and soybean rows), and CK (sole cropping of soybean, with 70 cm rows spacing). Results showed that the photosynthetically active radiation transmittances of soybean canopy at V5 stage under A2 treatment (31.1%) were considerably higher than those under A1 (8.7%) treatment, and the red-to-far-red ratio was reduced significantly under A1 (0.7) and A2 (1.0) treatments compared with those under CK (1.2). By contrast with CK, stem diameter, total aboveground biomass, chlorophyll content and net photosynthetic rate decreased significantly except plant height under A1 and A2. The thickness of palisade tissue and spongy tissue of soybean leaf under A1 and A2 were significantly reduced at V5 stage compared with CK. The leaf thicknesses under A1 and A2 were lower than those in CK by 39.5% and 18.2%, respectively. At the R1 stage of soybean (after maize harvest), the soybean plant height, stem biomass, leaf biomass and petiole biomass under A1 and A2 treatments were still significantly lower than those under CK, but no significant differences were observed in Chl a/b, Pn, epidermis thickness and spongy tissue thickness of soybean leaves in A2 compared with CK. In addition, the soybean yields (g plant-1) under A1 and A2 were 54.69% and 16.83% lower than those in CK, respectively. These findings suggested that soybean plants can regulate its morphological characteristics and leaf anatomical structures under different light environments.
Intercropping is an important cropping system extensively used worldwide for food and dietary fiber purposes. In intercropping system, at least two crops are grown on the same land for a specific period of time with alternating strips, which partially overlap in the growth period. For instance, maize-soybean relay-strip intercropping is widely adopted in southwestern parts of China, where maize is sown in April and harvested in August, while soybean is sown in June and harvested in October. The advantages of this system include the effective and efficient utilization of farmland resources and low incidences of diseases, pests, and weed damage[4,5]. This system also increases the economic benefits compared with that of sole cropping of soybean[6,7]. The success of this approach is attributed to the efficient utilization of water and light, thereby increasing crop yield and improving the biodiversity and ecological services[8,9].
The shading of maize affected the morphological features, leaf anatomical structure, and photosynthetic characteristics of soybean, thereby increasing soybean plant height and decreasing the stem diameter, biomass of aboveground parts, chlorophyll content, and leaf thickness in the maize-soybean relay-strip intercropping system. The stem diameter, biomass of aboveground parts, Chla content, net photosynthetic rate, and leaf thickness of soybean increased rapidly because of the restoration of the illumination environment of soybean canopy after the maize was harvested, thereby providing the material and energy base for the photosynthetic compensatory growth of soybean in later periods. The morphological and photosynthetic characteristics of soybean under A1 and A2 were also different during shading and light recovery. The soybean leaf anatomical structure under A2 treatment has a good adaptability, and the palisade tissue and spongy parenchyma were further developed. Therefore, optimizing population allocation is conducive to the plasticity of soybean growth regulation and the coordinated high yield of maize and soybean in the maize-soybean relay-strip intercropping system.