Photosynthesis

Results of the comparison reveal a decrease in photosynthetic capacity in leaves sampled during the second time period which is associated with decreasing ability of leaves to respond to light intensity and internal air space carbon dioxide concentration, increasing mesophyll resistance, and increasing stomatal resistance.

The responses of soybean to elevated [ CO₂ ] have been investigated extensively using enclosure studies. A meta-analysis of 111 of these studies showed that elevated [ CO₂ ] (from 450 to 1,250 μmol mol–1) increased the soybean leaf CO₂ assimilation rate by 39%, but decreased Rubisco activity by 11%. Leaf photosynthesis is sensitive to leaf water potential (indicator of leaf water status); leaf photosynthesis of crop plants usually begins to drops in response to the decline in leaf water potential through the decline in stomatal conductance (indicator of stomatal opening). Effects of temperature on canopy photosynthesis and CGR are characterized by an optimal temperature response range falling between minimal and maximal optimal temperatures, and suboptimal and supra optimal temperatures falling below and above the optimal range, respectively (Hollinger and Angel, 2009). The most sensitive part of the photosynthetic apparatus to heat stress is photosystem II. The effects of short-term cold temperature on soybean growth and development, biomass partitioning, photosynthesis, and carbohydrate metabolism showed that short-term cold temperature delays reproductive stages, by reducing photosynthesis and altering biomass allocation. However, higher aluminum concentrations (800 mg/kg) caused declining chlorophyll contents, depressed photosynthesis rates (PN), enhanced transpiration rates, and decreased PAR utilization efficiency (PUE) and water utilization efficiency. Plants grown in growth chamber under semi-aseptic conditions and inoculated at seed, seedling and plant stages, and compared to non-inoculated (control) plants. Light and epi-fluorescence microscopy analyses showed that leaves of inoculated plants had higher density of smaller stomata (297 vs. 247 n/mm²), thicker palisade parenchyma (95.0 vs. 85.8 mm), and larger intercellular spaces in the mesophyll (57.5% vs. 52.2%), compared to non-inoculated plants.