Aims From the light-competition hypothesis,competition for light is asymmetric and the observed increases in plant-size variability with increasingly denser canopies are primarily due to competition for light.Greater ...Aims From the light-competition hypothesis,competition for light is asymmetric and the observed increases in plant-size variability with increasingly denser canopies are primarily due to competition for light.Greater plant height provides pre-emptive access to light and produces increased height differences among species.The question is what produces these differences in plant height or height growth response among species in response to fertilization.Methods In 2009,a field experiment of N,P and N+P enrichments at three levels each was initiated in an alpine meadow on the northeast Qinghai-Tibet Plateau.Effects of fertilization on species richness,aboveground net primary production(ANPP),relative light intensity and plant height of different plant functional groups were determined.Festuca ovina(grass),Kobresia humilis(sedge),Oxytropis ochrocephala(legume),Taraxacum lugubre(rosette forb)and Geranium pylzowianum(upright forb)were selected as exemplars of each of the indicated functional groups.The N:C ratios in aboveground biomass,gibberellic acid(GA_(3))concentrations in leaves,plant heights and height relative growth rate(RGR)of these exemplar species were analyzed in detail.Important Findings Species richness of grasses significantly increased with increasing N+P levels.Species richness of legumes and upright forbs decreased after N and N+P additions.P addition had no significant effect on species richness.The effects of N+P addition on species richness and ANPP were consistently stronger than those of the single N or P fertilization.Reductions in species richness caused by nutrient addition paralleled the increases in ANPP and decreases in light intensity under the canopies,indicating indirect effect of nutrient addition on species richness via ANPP-induced light competition.The exemplar species that responded most positively to fertilization in height and RGR also displayed stronger increases in their GA_(3) content and N:C ratios.GA_(3) concentrations and N:C ratios were positively correlated with height RGR when the data were pooled for all species.The tallest and the fastest-growing grass,F.ovina,had the largest increase in N:C ratios and the highest leaf GA_(3) concentrations after nutrient addition.These results indicated that differential responses of GA_(3) concentrations and N:C ratios to fertilization were related to the inequality in plant heights among species.展开更多
Single C3N4 crystals with 1-3μm in length and 300 nm in cross area was obtained on nickel substrate.The results rule out the uncertainty of the experimental lattice parameters caused by C-Si-N phase when the growth w...Single C3N4 crystals with 1-3μm in length and 300 nm in cross area was obtained on nickel substrate.The results rule out the uncertainty of the experimental lattice parameters caused by C-Si-N phase when the growth was on silicon.The X-ray diffraction and transmission electron microscopy with selective-area electron diffraction give the lattice constants a=0.624 nm and c=0.236 nm for β-C3N4,and a=0.638 nm and c=0.464 8 nm for αC3N4,which are respectively 2.5% and 1.3% lower than those of the latest first-principle calculations.An N:C ratio of 1.30-1.40 was determined by energy dispersive X-ray.Based on the experimental lattice constants,the bulk modulus of the obtained β-C3N4 are in the region of 425-445 GPa.展开更多
基金National Natural Science Foundation of China(31270472)Specific Fund for Agro-scientific Research in the Public Interest(201203006).
文摘Aims From the light-competition hypothesis,competition for light is asymmetric and the observed increases in plant-size variability with increasingly denser canopies are primarily due to competition for light.Greater plant height provides pre-emptive access to light and produces increased height differences among species.The question is what produces these differences in plant height or height growth response among species in response to fertilization.Methods In 2009,a field experiment of N,P and N+P enrichments at three levels each was initiated in an alpine meadow on the northeast Qinghai-Tibet Plateau.Effects of fertilization on species richness,aboveground net primary production(ANPP),relative light intensity and plant height of different plant functional groups were determined.Festuca ovina(grass),Kobresia humilis(sedge),Oxytropis ochrocephala(legume),Taraxacum lugubre(rosette forb)and Geranium pylzowianum(upright forb)were selected as exemplars of each of the indicated functional groups.The N:C ratios in aboveground biomass,gibberellic acid(GA_(3))concentrations in leaves,plant heights and height relative growth rate(RGR)of these exemplar species were analyzed in detail.Important Findings Species richness of grasses significantly increased with increasing N+P levels.Species richness of legumes and upright forbs decreased after N and N+P additions.P addition had no significant effect on species richness.The effects of N+P addition on species richness and ANPP were consistently stronger than those of the single N or P fertilization.Reductions in species richness caused by nutrient addition paralleled the increases in ANPP and decreases in light intensity under the canopies,indicating indirect effect of nutrient addition on species richness via ANPP-induced light competition.The exemplar species that responded most positively to fertilization in height and RGR also displayed stronger increases in their GA_(3) content and N:C ratios.GA_(3) concentrations and N:C ratios were positively correlated with height RGR when the data were pooled for all species.The tallest and the fastest-growing grass,F.ovina,had the largest increase in N:C ratios and the highest leaf GA_(3) concentrations after nutrient addition.These results indicated that differential responses of GA_(3) concentrations and N:C ratios to fertilization were related to the inequality in plant heights among species.
文摘Single C3N4 crystals with 1-3μm in length and 300 nm in cross area was obtained on nickel substrate.The results rule out the uncertainty of the experimental lattice parameters caused by C-Si-N phase when the growth was on silicon.The X-ray diffraction and transmission electron microscopy with selective-area electron diffraction give the lattice constants a=0.624 nm and c=0.236 nm for β-C3N4,and a=0.638 nm and c=0.464 8 nm for αC3N4,which are respectively 2.5% and 1.3% lower than those of the latest first-principle calculations.An N:C ratio of 1.30-1.40 was determined by energy dispersive X-ray.Based on the experimental lattice constants,the bulk modulus of the obtained β-C3N4 are in the region of 425-445 GPa.
