Effects of abscisic acid and brassinolide on photosynthetic characteristics of Leymus chinensis from Songnen Plain grassland in Northeast China.

BACKGROUND: It has been well demonstrated that plant growth regulators have important functions in multiple physiological processes. ABA and BR play crucial roles in response of crops to stresses. Photosynthetic capacity of Leymus. chinensis treated by various concentrations of ABA and BR in combination was determined. Further more, the mechanisms of ABA and BR treatments and potential for recovery of saline-alkali grasslands were discussed. RESULTS: Abscisic acid (ABA) and brassinolide (BR) affected leaf gas exchange, growth and biomass of L. chinensis. The application of ABA and BR mixtures, especially that of 0.01 mM ABA and 2 × 10-4 mM BR, increased the net photosynthetic rate, stomatal conductance, water use efficiency, the maximum net photosynthetic rate, light-saturated rate, leaf respiration rate, the maximum RUBP carboxylation rate, the maximum electron transport rate, the maximum triose-phosphate utilization, carboxylation efficiency and the quantum efficiency of PSII and subsequently enhanced density, height and biomass in L. chinensis. We also observed reduction in the light compensation and saturation points following the application of ABA and BR treatments. CONCLUSIONS: We concluded that proper use of plant growth regulators can enhance the plant growth and productivity on the Songnen grassland, which is particularly important for the improvement of saline - alkaline grassland and the yield of grazing lands.

The effects of warming and nitrogen addition on soil nitrogen cycling in a temperate grassland, northeastern China.

BACKGROUND: Both climate warming and atmospheric nitrogen (N) deposition are predicted to affect soil N cycling in terrestrial biomes over the next century. However, the interactive effects of warming and N deposition on soil N mineralization in temperate grasslands are poorly understood. METHODOLOGY/PRINCIPAL FINDINGS: A field manipulation experiment was conducted to examine the effects of warming and N addition on soil N cycling in a temperate grassland of northeastern China from 2007 to 2009. Soil samples were incubated at a constant temperature and moisture, from samples collected in the field. The results showed that both warming and N addition significantly stimulated soil net N mineralization rate and net nitrification rate. Combined warming and N addition caused an interactive effect on N mineralization, which could be explained by the relative shift of soil microbial community structure because of fungal biomass increase and strong plant uptake of added N due to warming. Irrespective of strong intra- and inter-annual variations in soil N mineralization, the responses of N mineralization to warming and N addition did not change during the three growing seasons, suggesting independence of warming and N responses of N mineralization from precipitation variations in the temperate grassland. CONCLUSIONS/SIGNIFICANCE: Interactions between climate warming and N deposition on soil N cycling were significant. These findings will improve our understanding on the response of soil N cycling to the simultaneous climate change drivers in temperate grassland ecosystem.

[Response of phytolith in Leymus chinensis to the simulation of global warming and nitrogen deposition on Songnen grassland, China].

Using infrared radiator and applying nitrogen on Leymus chinensis community on Songnen grassland to simulate global warming and nitrogen deposition, phytolith was extracted from L. chinensis, the morphology and content of phytolith were analyzed. Phytolith in L. chinensis were classified into 4 main classes and 12 subclasses, as well as some small phytolith fragments. Of all the phytolith types, the hat-shaped take as much as 70%. The hat-shaped with spire and hat-shaped with flat peak may have different growth mechanisms from the echinate hat-shaped, and the point-shaped phytolith is more sensitive to N deposition. Compared with control check (CK), the warming treatment seemed to promote the growth of phytolith (increased the length and width 0.1-2.6 microm), while the N deposition treatment had an effect of inhibition on the growth of phytolith (decreased the length and width 0.1-1.4 microm), and when warming and N deposition mixed, in this treatment the effect of inhibition caused by N deposition declined. Hollow elongate (46% of elongate) was observed only in N deposition treatment, and the content of other types (elongate, point-shaped, hat-shaped excluded) increased to 10%, it was supposed, as L. chinensis is the dominant species in Songnen grassland, the effect of N deposition might be more significant than warming on such grassland, and warming could mitigate the affection of N deposition. Phytolith was sensitive to the change of environmental factors, this study provided an experimental evidence for phytolith as a reliable proxy indicator for paleo-environment.

[Monthly dynamics and distribution of major cations in Iris lactea].

The study on the monthly absorption, transportation, and distribution of Na+, K+, Ca2+ and Mg2+ in Iris lactea under saline-alkali field conditions showed that the contents of test cations in I. lactea varied with months. After June, the cations contents in plant increased with growth. Root Ca2+ and Na+ contents were the highest in July, being 2.30% and 0.51%, respectively, while root K+ and Mg2+ contents were the highest in September (0.27%) and October (0.28%), respectively. Leaf Na+ content was the highest in July (0.57%), while leaf K+, Ca2+ and Mg2+ contents were the highest in August, being 1.30%, 2.69% and 0.47%, respectively. In July and August, the selective absorption (SA) of K+ was higher than that of Na+, while the selective transport (ST) was in adverse. The cations contents in I. lactea were significantly higher than those in soil, suggesting that I. lactea had high accumulation capacity to these cations. The cations were mainly accumulated in the 0-30 cm aboveground part and 0-40 cm underground part of I. lactea, and the average contents of Na+, K+, Ca2+ and Mg2+ in aboveground part were 9.11, 4.07, 0.98 and 2.27 times of those in underground part, respectively.

[Ecohydrological functions of litter in three main plant communities on Songnen grassland].

With the litter layers of Leymus chinensis, Chloria virgata and Puccinellia tenuiflora communities on Songnen grassland as test objects, this paper studied their litter storage, water holding capacity, rainfall interception, and restraining effect on soil evaporation. The results showed that in the litter layers of L. chinensis, C. virgata and P. tenuiflora communities, the litter storage was 4.7, 3.0 and 2.6 t x hm(-2), maximum water holding capacity was 9.6, 7.4 and 5.0 t x hm(-2), maximum water holding rate was 208.4%, 262.8% and 202.2%, rainfall interception was 6.57, 5.79 and 5.26 t x hm(-2), and interception rate was 6.22%, 5.52% and 5.23%, respectively. The interception capacity was increased, while the interception rate was decreased with increasing rainfall. Under the cover of litter with a thickness of 0.5-2 cm, soil evaporation was decreased by 7.95%-56.79%, compared with that without litter cover. The restraining effect on soil evaporation increased with increasing litter thickness and soil water content.