To study the effects of low nutrition on pho tosynthetic capacity and accumulation of total nitrogen(N) and phosphorus(P) in three climber plant species Pharbitis nil(Linn.) Choisy, Lonicera japonica Thunb. and Parthenocissus tricuspidata(Sieb.et Zucc.) Planch, al climber plants were exposed to low nutrition at 6 levels(Hoagland solution as control, 1/2, 1/4, 1/8, 1/16 and 1/32 strength Hoagland solution) for 30 days. Photosynthetic capacity was determined by measuring leaf chlorophyl fluorescence, chlorophyll content, carbonic anhydrases activity and growth. Accumulation of total N and P was studied by measuring N and P content in plant tissues. Low nutrition decreased the photosynthetic capacity of P. nil while L. japonica maintained high photosynthetic capacity under low nutrition. Photosynthetic apparatus of P. tricu spidata suffered no damage when exposed to low nutrition L. japonica and P. tricuspidata had better adaptability to low nutrition than P. nil. With a faster growth rate, P. ni consumed more nutrition(N and P), and its growth was mainly affected by P deficiency under low nutrition Although L. japonica suffered damage from N and P deficiency simultaneously, but the nutrient deficiency was not serious except for 1/32-strength Hoagland solution P. tricuspidata grew slowly, so its requirement of N and Pwere the least, even if it was mainly affected by the P deficiency, it could still grow well under low nutrition.With the consideration of fertilizing N and P fertilizers in karst areas which were with lower N and P contents, plant species, N/P ratio threshold and low nutrition level should be taken into account synchronously. This study could provide a general consideration for the planning and developing low nutrition resistant plants and fertilizing the three climber plant species in the low nutrition environment.
The effect of extracellular carbonic anhydrase (CAex) on stable carbon isotope fractionation in algae is still unclear. The stable carbon isotope composition and algal growth in the presence and absence of the membrane-impermeable CA inhibitor acetazolamide were compared in Chlamydomonas reinhardtii and Chlorella vulgaris. The CAex of both algal species contributed about 9‰ of the stable carbon isotope fractionation and exhibited a dosage effect. Therefore, evidence in vivo that CAex leads to a larger carbon isotope fractionation of algae is presented.
The amount of bicarbonate utilised by plants is usually ignored because of limited measurement methods.Accordingly, this study quantified the photosynthetic assimilation of inorganic carbon(CO_2and HCO_3^-) by plants. The net photosynthetic CO_2assimilation(PN), the photosynthetic assimilation of CO_2 and bicarbonate(PN'),the proportion of increased leaf area(fLA) and the stable carbon isotope composition(δ^(13)C) of Orychophragmus violaceus(Ov) and Brassica juncea(Bj)under three bicarbonate levels(5, 10 and 15 mm NaHCO_3)were examined to determine the relationship among PN,PN' and fLA. PN', not PN,changed synchronously with fLA.Moreover, the proportions of exogenous bicarbonate and total bicarbonate(including exogenous bicarbonate and dissolved CO_2-generated bicarbonate) utilised by Ov were 2.27 % and 5.28 % at 5 mm bicarbonate, 7.06 % and13.28 % at 10 mm bicarbonate, and 8.55 % and 17.31 % at15 mm bicarbonate, respectively. Meanwhile, the proportions of exogenous bicarbonate and total bicarbonate utilised by Bj were 1.77 % and 3.28 % at 5 mm bicarbonate,2.11 % and 3.10 % at 10 mm bicarbonate, and 2.36 % and3.09 % at 15 mm bicarbonate, respectively. Therefore, the dissolved CO_2-generated bicarbonate and exogenous bicarbonate are important sources of inorganic carbon for plants.
