Legume productivity and photosynthetic responses anticipated with climate change—insights from lupins

摘要

Legume crops, including narrow-leafed lupin, symbiotically fix nitrogen and provide high-protein vegetables and grains.Soybean, pea and narrow-leafed lupin have shown both nitrogen fixation and grain yield responses to higher levels of CO_2.Cowpea has genetic variation for heat tolerance at the floral bud and pod set growth stages, with heat stress tolerant vegetable and grain types bred and released as cultivars; this might be expected in other legumes. The rate of net photosynthesis in narrow-leafed lupin is higher than in wheat, but lupin is more sensitive to water deficits and shade.Pre-anthesis growth of lupin is slow in low-nitrogen soils because substantial amounts of the dailyassimilated carbon are allocated to the nodulated roots to support nitrogen fixation.Nitrate supply to lupin does not improve pre-anthesis growth, but reduces nitrogen fixation.Elevated CO_2 increases biomass and the nitrogen fixed from the atmosphere in lupin under terminaldrought.The carbon 'cost' of fixing N_2 in nodules is high but varies significantly among symbioses. Both plant and bacterial traits determine the 'cost'.Lupin nitrogen fixation declines during post-anthesis because there is competition for photosynthate, which is directed to branch growth and grain-filling.In lupin, translocation of assimilates, and particularly nitrogenous solutes, may limit grain yield and depress harvest index.Conservation of translocated carbon by refixing respired CO_2 within developing legume pods could equate to as much as 20% of grain yield.