The effect of ozone on the yellowing process of magnesium-deficient clonal Norway spruce grown under defined conditions

Effects of elevated ozone on the uptake and allocation of macronutrients in poplar saplings above- and belowground

Ground-level ozone (O₃) is a secondary air pollutant and affects the roots and soil processes of trees. Therefore, O₃ can affect the uptake and allocation of nutrients in trees, which merits further clarification. A fumigation experiment with five O₃ levels was conducted in 15 open top chambers for two poplar clones, and the concentrations of six macronutrients (N, P, K, S, Ca, Mg) in different organs and leaf positions were determined. Under all O₃ levels, the concentration of mobile nutrients (N and P) was higher in upper leaves than in lower leaves, while the non-mobile nutrients (Ca and S) concentration was the opposite. Relative to charcoal filtered ambient air (CF), high O₃ treatment (NF60) significantly increased the concentration of mobile nutrients K and Mg in upper leaves by 38 % and 33 %, in lower leaves by 142 % and 65 %, respectively, which suggested the effect of O₃ on their concentrations was greater at the lower leaf position than at the upper leaf position. Elevated O₃ significantly increased the macronutrient concentrations in most organs. The effects of O₃ on nutrient concentrations were attributed using graphical vector analysis, suggested that the increase of nutrient concentration in the shoots was attributed to excessive nutrient stocks, while their increase in root was attributed to the "concentration" effect. Compared to CF, NF60 also reduced the root-to-shoot ratio of N, P, S, K, Ca and Mg stocks by 34 %, 39 %, 37 %, 64 %, 46 % and 42 %, respectively, indicating the allocation of increased nutrients to shoots in response to O₃ stress. Changes in the allocation pattern of nutrients in different leaf positions and organs of poplar were primarily in response to O₃ stress since these nutrients play important roles in some physiological processes. These results will help improve the plantation nutrient utilization by optimizing fertilizer management regimes under O₃ pollution.

Elevated tropospheric ozone affects the concentration and allocation of mineral nutrients of two bamboo species

The increase in tropospheric ozone (O₃) affects plant physiology and ecosystem processes, and consequently the cycle of nutrients. While mineral nutrients are critical for plant growth, the effect of elevated tropospheric O₃ concentration on the uptake and allocation of mineral nutrients by plants is not well understood. Using open top chambers (OTCs), we investigated the effect of elevated O₃ on calcium (Ca), magnesium (Mg) and iron (Fe) in mature bamboo species Phyllostachys edulis and Oligostachyum lubricum. Our results showed that elevated O₃ decreased the leaf biomass of P. edulis and O. lubricum by 35.1% and 26.7%, respectively, but had no significant effect on the biomass of branches, stem or root. For P. edulis, elevated O₃ increased the nutrient (Ca, Mg and Fe) concentration and allocation in leaf but reduced the concentration in other organs. In contrast, elevated O₃ increased the nutrient concentration and allocation in the branch of O. lubricum but decreased that of other organs. We also found that that P. edulis and O. lubricum responded differently to elevated O₃ in terms of nutrient (Ca, Mg and Fe) uptake and allocation. This information is critical for nutrient management and adaptation strategies for sustainable growth of P. edulis and O. lubricum under global climate change.

Structural changes in the vascular bundles of light-exposed and shaded spruce needles suffering from Mg deficiency and ozone pollution

The correlation between structural changes of the vascular bundles and needle yellowing was examined for needles of damaged spruce (Picea abies (L.) Karst.) growing at a Mg-deficient and ozone polluted mountain site in the Central Black Forest (840m a.s.l.). In the previous year's sun-exposed needles, the following sequence of events was observed: (1) rapid needle yellowing, (2) hypertrophy and anomalous divisions of cambium cells, (3) phloem collapse, and, (4) production of atypical xylem tracheids. Under defined shade (reduction of the photosynthetically active photon flux density of the ambient light by 85-90%), the needles remained green, while the phloem collapsed completely within the first 6 weeks of shading; subsequently, a reversal of the collapse was observed. Under both light conditions, the content of Mg not bound to chlorophyll (Mg(free)) was in the range of 0.1 mg g(-1) needle dry matter, and hardly changed throughout the investigation period. After Mg fertilization, the Mg(free) level of the previous year's needles increased to 0.2 mg g(-1) dry matter, the light-exposed needles remained green, and the vascular bundles developed no anomalies. The data show that the rapid needle yellowing of ozone-exposed Mg-deficient needles did not depend on the collapse of the phloem. Mg deficiency played a key role in the development of anomalous vascular bundles under light, and also appears to explain the transient changes in sieve cell structure under shade. The role of Mg deficiency, rather than ozone pollution, in the damage of the sieve cells was confirmed in a long-term ozone exposure experiment with young clonal spruce growing under defined conditions.