Combined Effects of Elevated O3 Concentrations and Enhanced UV-B Radiation of the Biometric and Biochemical Properties of Soybean Roots.

Enhanced ultraviolet-B (UV-B) radiation and elevated tropospheric ozone alone may inhibit the growth of agricultural crops. However, research regarding their combined effects on growth and biochemical properties of roots is still scarce. Using open top chambers, we monitored the response of growth, secondary metabolites, endogenous hormones and enzyme activities of soybean roots to elevated O3 and enhanced UV-B individually and in combination at stages of branching, flowering and podding. Our results indicated that the root biomass decreased by 23.6, 25.2, and 27.7%, and root oxidative capacity declined by11.2, 39.9, and 55.7% exposed to elevated O3, enhanced UV-B, and O3 + UV-B, respectively, compared to the control treatment. Concentrations of quercetin and ABA were significantly increased, while concentrations of total polyphenol and P-coumaric acid responded insignificantly to elevated O3, enhanced UV-B, and O3 + UV-B during the whole period of soybean growth. Elevated O3, enhanced UV-B and O3 + UV-B showed significant negative effects on superoxide dismutase (EC 1.15.1.1) activity at flowering stage, on activities of peroxidase (EC 1.11.1.7) and catalase (EC 1.11.1.6) at podding stage, on ascorbate peroxidase activity during the whole period of soybean growth. Moreover, compared to hormones and enzyme activity, secondary metabolisms showed stronger correlation with root growth exposed to elevated O3 and enhanced UV-B individually and in combination. Our study concluded that combined effects of O3 and UV-B radiation significantly exacerbated the decline of soybean root growth, and for annual legumes, the inhibited root growth exposed to O3 and/or UV-B radiation was mostly associated with secondary metabolisms (especially flavonoids).

Combined effects of O3 and UV radiation on secondary metabolites and endogenous hormones of soybean leaves.

Enhanced ultraviolet radiation (UV) and elevated tropospheric ozone (O3) may individually cause reductions in the growth and productivity of important agricultural crops. However, research regarding their combined effects on important agricultural crops is still scarce, especially on changes in secondary metabolites and endogenous hormones, which are important protective substances and signal components that control plant responses to environment stresses. In this study, using an experimental setup of open top chambers, we monitored the responses of seed yield per plant, leaf secondary metabolites and leaf endogenous hormones under the stress of elevated O3 and enhanced UV radiation individually, as well as their combined stress. The results indicated that elevated O3 (110 ± 10 nmol mol-1 for 8 hours per day) and enhanced UV radiation (1.73 kJ h-1 m-2) significantly decreased seed yield per plant. Concentrations of rutin, queretin and total flavonoids were significantly increased under the elevated O3 treatment or the enhanced UV radiation treatment or the combination treatment at flowering and podding stages, and concentrations of rutin, queretin and total flavonoids showed significant correlations with seed yield per plant. Concentrations of ABA and IAA decreased under the three treatments. There was a significant positive correlation between the ABA concentration and seed yield and a negative correlation between the IAA concentration and seed yield. We concluded that the combined stress of elevated O3 and UV radiation significantly decreased seed yield per plant. Yield reduction was associated with changes in the concentrations of flavonoids, ABA and IAA in soybean leaves. The effects of the combined O3 and UV stress were always greater than those of the individual stresses alone.

[C:N:P stoichiometry characteristics of litter and soil of forests in Great Xing'an Mountains with different fire years.] / å¤§å ´å®‰å²­ä¸åŒç«çƒ§å¹´é™æ£®æž—å‡‹è½ç‰©å’ŒåœŸå£¤C、N、P化学计量特征.

We investigated the fire impacts on nutrients in litter and soil, and their C:N:P stoichio-metry in forests of Great Xing'an Mountains. The studied sites differed in their burning year (post-fire 4, 14, 40, 70 years and unburned within 120 years) and had different topographic locations (sloped land and flat land). The results showed that there were significant differences in stoichio-metry characteristics of C, N, P for both litter and soil with different burning years. No significant fluctuation was observed for the litter C content, while the contents of litter N and P increased with the increasing post-fire recovery years. In specific, we found the contents of litter N and P decreased at post-fire 4 and 14 years and nearly recovered to the control level at 40 years after fire. Additionally, C:N and C:P ratios of litter decreased, but N:P ratio of litter increased following post-fire recovery time. The contents of C, N, P and their ratios (C:N, C:P and N:P) in soil decreased with soil depth. Soil C content exhibited an increasing trend following post-fire recovery time and was significantly higher than the control at post-fire 70 years in sloped land, but no significant difference in the flat land. Significant interactive effects between fire history and slope were observed in soil P content and C:P ratio. Soil P content was higher than the control at post-fire 4 years in sloped land, but was higher than the control at post-fire 40 years in flat land. The C:P ratio recovered to the control level at post-fire 14 years in sloped land, and there was no significant diffe-rence in flat land. Redundancy analysis showed that slope effect played a more vital role than fire history effect in soil organic layer, while fire history effect was the most important factor for the varia-tion of soil nutrients in soil mineral layer. In our study, nutrients of litter and soil were lower than the control level at post-fire 4 and 14 years. The quality of litter and soil was improved with accele-rated plant growth and litter decomposition following post-fire recovery time and recovered to the pre-fire level at post-fire 40 years, reaching a steady status.