Shade tolerance response of legumes in terms of biomass accumulation, leaf photosynthesis, and chlorophyll pigment under reduced sunlight

Abstract

Legumes have a distinct morpho-physiological response to reduced sunlight, but their capacity to adapt to the levels of shading due to intercropping systems is not sufficiently understood. Such adaptation to shade-60% of full sun in terms of physiological attributes-was examined in cowpea (Vigna unguiculata Savi), lablab (Lablab purpureus Adans.), lima bean (Phaseolus lunatus), pigeonpea [Cajanus cajan (L.) Millsp.], and pole bean (Phaseolus vulgaris). Although the capacity of photosynthetic machinery decreased under shade, the capacity continued to exceed the actual rate of photosynthesis. Compared with those under full sun, leaves under shade were thinner (specific weight only 56% of that under full sun), larger (surface area greater by 54.7%), and recorded a 15% higher leaves/stem ratio (by weight) and a 25.6% higher leaves/total dry weight ratio. However, the concentration of chlorophyll pigments per unit weight and per unit surface area was significantly higher in leaves under shade. Water stress was probably higher for leaves under full sun given the higher canopy temperatures and lower relative water content. At final biomass harvest, across the species shading has reduced the biomass 32% in 2009 and 34.6% in 2010 over unshade. Biomass was greater in lima bean (413 g m −2 ), and pigeonpea (408 g m −2 ) then lowest in lablab (180 g m −2 ) and cowpea (216 g m −2 ). Of the five legumes tested, lablab and cowpea showed the greatest tolerance to shade and therefore are better suited to the low-light environment of intercropping.

Seedling growth and photosynthetic response of Pterocarpus indicus L. to shading stress

“…Such an effect in the pigments, i.e., total Chl (a+b), occurred in the moderate shade treatment, indicating that P. indicus could increase chlorophyll pigments at low irradiance, leading to maximizing light-harvesting capacity. 5 , 42 , 43 The shade leaves of P. indicus seedlings have different chlorophyll concentrations depending on the light intensity; the thinner shade leaves contain more significant amounts of chlorophyll. 44 Carotenoid and Chl a/b ratio, which are indicators of the photosynthetic activity of the plant leaves, 45 have several physiological functions associated with abiotic stress.…”

“…Light governs the rate of photosynthesis in leaves and also regulates the structure and function of the photosynthetic apparatus. 5 Light deficiency caused by shade restricts the capacity of plants to capture sunlight and in turn reduces the photosynthetic capacity, thereby degrading the whole plant growth processes from germination and seedling development to florescence. 6 A decrease in PSII quantum efficiency and reaction center, electron transport, and ATPase and Rubisco activities etc.…”

“… 14 So far, to determine such plant performance in low light environment, various parameters of morphology, anatomy, physiology, phenology, and genetics have been assessed in many studies to improve understanding of shade-tolerant mechanism in plants. 5 , 9 , 14 However, most of these previous studies had been conducted for short-term or under field conditions primarily affected by diverse environmental factors. Hence, for a more precise understanding of each tree species, a long-term study on how plant seedlings acclimate to shade stress in the environment where edaphic and biotic factors are controlled is required.…”