Cuttings of Populus cathayana were exposed to three different alkaline regimes (0, 75, and 150 mM Na 2 CO 3 ) in a semicontrolled environment. The net photosynthesis rate (P N ), mesophyll conductance (g m ), the relative limitations posed by stomatal conductance (L s ) and by mesophyll conductance (L m ), photosynthetic nitrogen-use efficiency (PNUE), carbon isotope composition (δ 13 C), as well as specific leaf area (SLA) were measured. P N decreased due to alkaline stress by an average of 25% and g m decreased by an average of 57%. Alkaline stress caused an increase of L m but not L s , with average L s of 26%, and L m average of 38% under stress conditions. Our results suggested reduced assimilation rate under alkaline stress through decreased mesophyll conductance in P. cathayana. Moreover, alkaline stress increased significantly δ 13 C and it drew down CO 2 concentration from the substomatal cavities to the sites of carboxylation (C i -C c ), but decreased PNUE. Furthermore, a relationship was found between PNUE and C i -C c . Meanwhile, no correlation was found between δ 13 C and C i /C a , but a strong correlation was proved between δ 13 C and C c /C a , indicating that mesophyll conductance was also influencing the 13 C/ 12 C ratio of leaf under alkaline stress.

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To lay the scientific basis for super rice production in light-poor areas, an experiment was conducted under real field conditions. The experiment used a super-hybrid rice combination "II Youhang 2" to study the effects of pre-flowering light deficiency on rice biomass production and physiology. In the experiment, shading rates were set at 55% and 85% from jointing through initial heading stage. Natural light condition was set as the control of the experiment. The results showed that yield of light deficient treatments (shading rates of 55% and 85%) dropped significantly by 48.25% and 70.54% compared with the control. The drop was mainly due to fewer numbers of spikes per plant and grains per panicle. There was no significant difference in seed setting rate between the control and shading treatments. Compared with the control, biomass and harvest index of light deficient treatments also significantly dropped. This was attributed to restrained net assimilation rate (NAR) and leaf area index (LAI), which significantly retarded crop growth rate. There were inhibited pre-flowering dry matter accumulation, translocation and contribution to grain and vegetative organ under light deficiency. The inhibition was enhanced with increased intensity of light deficiency. Moreover, net photosynthetic rate, nitrate reductase activity and bleeding rate decreased and MDA content increased under pre-flowering light deficit, and the change was becoming more obvious under high shading intensity. Pre-flowering light deficit weakened photosynthesis, membrane system and root activity. It also blocked photosynthate transport, and restrained leaf growth and NAR. These factors limited photosynthetic produce capability, decreased biomass production and significantly dropped crop yield.