Net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), leaf water potential (ψleaf), leaf nitrogen content, and photosynthetic nitrogen use efficiency (PNUE) were compared between a typical C4 plant, Agriophyllum squarrosum and a C3 plant, Leymus chinensis, in Hunshandak Sandland, China. The plant species showed different diurnal gas exchange patterns on June 12-14 when photosynthetic photon flux density (PPFD), air temperature (Tair), and water potential were moderate. PN, E, and
gs of A. squarrosum showed distinct single peak while those of L. chinensis were depressed at noon and had two peaks in their diurnal courses. Gas exchange traits of both species showed midday depression under higher photosynthetic photon flux density (PPFD) and T air when Ψleaf was significantly low down on August 6-8. However, those of A. squarrosum were depressed less seriously. Moreover, A. squarrosum had higher PN, Ψleaf, water use efficiency (WUE), and PNUE than L. chinensis. Thus A. squarrosum was much more tolerant to heat and high irradiance and could utilise the resources on sand area more efficiently than L. chinensis. Hence species like A. squarrosum may be introduced and protected to reconstruct the degraded sand dunes because of their higher tolerance to stress and higher resource use efficiency. and S. L. Niu ... [et al.].
Stable carbon isotope composition (δ13C), net photosynthetic rate (PN), actual quantum yield of photosystem 2 (PS2) electron transport (ΦPS2), nitrogen content (Nc), and photosynthetic nitrogen use efficiency (PNUE) in the leaves of six broadleaf tree species were determined under field environmental conditions. The six tree species were Magnolia liliflora Desr., M. grandiflora Linn., M. denudata Desr., Prunus mume (Sieb.) Sieb. et Zucc. cv. Meiren Men, P. mume (Sieb.) Sieb. et Zucc. f. alphandii (Carr.) Rehd., and P. persica (L.) Batsch. var. rubro-plena. The relationships among δ13C, ΦPS2, P N, and PNUE, as well as their responses to Nc in the six species were also studied. Both P N and δ13C negatively correlated with Nc, but ΦPS2 positively correlated with Nc. This indicated that with Nc increase, PN and δ13C decreased, while ΦPS2 increased. There were weak negative correlations between δ13C and PNUE, and strong negative correlations (p<0.01) between ΦPS2 and PNUE. According to the variance analysis of parameters, there existed significant interspecific differences (p<0.001) of δ13C, PN, ΦPS2, PNUE, and Nc among the tree seedlings of the six tree species, which suggests that the potential photosynthetic capacities depend on plant species, irradiance, and water use capacity under field conditions. and S. X. Zheng, Z. P. Shangguan.
Clover seedlings were grown at different nitrogen concentrations (5, 10, 15, 20, 25 mM NO3 -, i.e. N5 to N25) and two irradiances, I (200 and 400 µmol m-2 s-1 of photon flux density, i.e. I 200 and I 400). Net photosynthetic rate (PN), photosynthetic nitrogen use efficiency (PNUE), leaf chlorophyll (Chl) content, maximum photochemical efficiency (Fv/Fm), and actual photochemical efficiency of photosystem 2 (PS2) (ΦPS2) increased from N5 to N15 and decreased with N15 to N25. P N, PNUE, and ΦPS2 were higher at I 400 than at I 200, but Fv/Fm and leaf Chl contents at I 400 were lower than at I 200. The effects of the N and I on specific leaf area (SLA) and N contents per unit dry mass (Nm) were similar, the SLA and Nm increased from N5 to N25 and they were higher at I 200 than at I 400. The nitrogen contents per unit area (Na) increased from N5 to N20, but decreased from N20 to N25. The Na was higher at I 200 than at I 400 when Trifolium repens grew at N5 and N10, but it was higher at I 400 than at I 200 at N15 to N25. and H. An, Z. P. Shangguan.
Annual plants transport a large portion of carbohydrates and nitrogenous compounds from leaves to seeds during the phase of reproductive growth. This study aimed to clarify how reproductive growth affects photosynthetic traits in leaves and matter transport within the plant in the annual herb Chenopodium album L. Plants were grown in pots and either reproductive tissues or axillary leaves were removed at anthesis. Matter transport was evaluated as temporal changes in dry mass (as a substitute of carbohydrates) and nitrogen content of aboveground organs: leaves, axillary leaves, stems and reproductive tissues. Photosynthetic capacity (light-saturated photosynthetic rate under ambient CO2 concentration), nitrogen, chlorophyll and soluble protein content were followed in the 20th leaf that was mature at the start of the experiment. Removal of reproductive tissues resulted in accumulation of dry mass in leaves and axillary leaves, and accumulation of nitrogen in stem as nitrogen resorption from leaves and axillary leaves proceeded with time. Removal of axillary leaves proportionally reduced dry mass and nitrogen allocation to reproductive tissues, thus affecting the quantity but not quality of seeds. Removal treatments did not alter the time course of photosynthetic capacity, nitrogen, chlorophyll or soluble protein content during senescence in the 20th leaf, but changed the photosynthetic capacity per unit of leaf nitrogen according to demand from reproductive tissues. Together, the results indicate that reproductive tissues affected carbon and nitrogen economy separately. The amount of carbon was adjusted in leaves through photosynthetic capacity and carbohydrate export from them, and the amount of nitrogen was adjusted by transport from stem to reproductive tissues. The plant's ability to independently regulate carbon and nitrogen economy should be important in natural habitats where the plant carbon-nitrogen balance can easily be disturbed by external factors.