A pH value is actually a measure of hydrogen ion concentration. Because hydrogen ion concentration varies over a wide range, a logarithmic scale pH is used: for a pH decrease of 1, the acidity increases by a factor of Therefore, at high alkaline pH values, the hydrogen ion concentration is low.
Most soils have pH values between 3. In higher rainfall areas the natural pH of soils typically ranges from 5 to 7, while in drier areas the range is 6. Acid sulfate soils can have extremely acidic pH values pH less than 4.
Natural soil pH depends on the rock from which the soil was formed parent material and the weathering processes that acted on it—for example climate, vegetation, topography and time. These processes tend to cause a lowering of pH increase in acidity over time. Soil pH affects the amount of nutrients and chemicals that are soluble in soil water , and therefore the amount of nutrients available to plants. Some nutrients are more available under acid conditions while others are more available under alkaline conditions.
The development of strongly acidic soils less than 5. Alkaline soils may have problems with deficiencies of nutrients such as zinc, copper, boron and manganese. Soils with an extremely alkaline pH greater than 9 are likely to have high levels of sodium. Many pin oaks in the Midwest suffer from iron chlorosis which is characterized by yellowish green foliage. The yellowing of the leaves is caused by a deficiency of iron within the plant. Most Iowa soils contain sufficient quantities of iron for good plant growth and leaf coloration.
Unfortunately, much of the iron is in an insoluble form and is unavailable to pin oaks when the soil pH is above 7. Iron is readily available to pin oaks at a pH range of 5 to 6. Since efforts to correct iron chlorosis are extremely difficult, gardeners should avoid planting pin oaks in alkaline soils.
This article originally appeared in the May 24, issue, p. Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach.
If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 24, Specifically, results confirm that A.
On the contrary, the total pollen allergenicity was lower at pH6 than pH5, the only two pH values at which plants produced flowers and then pollen.
Since, there is a number of important environmental factors that may control the distribution of common ragweed i.
Despite this, we would point out that: a soil pH is known to control the uptake of macro- and micronutrients N, Mg, and so on from soil so it is a quite important factor to be monitored, especially for invasive plants; b we used natural soil for growing plants and measuring the pH; this choice made experimental conditions more close to those of field conditions and then the subsequent results useful for future field experiments regarding the species' control; c we observed in a crop field as specified in the introduction that the amendment of soil using calcium hydroxide highly reduced the species growth.
The method we used in our test to modify the original reaction condition of soil, which implies the addition of calcium hydroxide to increase pH value, can have changed the original quantity of calcium. Thus, calcium could act as confounding factor in understanding the effect of pH on plants. Although calcium is not a major nutrient, it plays a key role in many physiological processes such as the stabilization of cell wall structures, the function of a major secondary-messenger molecule in plants under different developmental cues, the participation in mechanisms of water and nutrient uptake, etc.
White and Broadley, As a consequence, the addition of calcium hydroxide were intended to reproduce conditions similar to field ones in which calcium is generally the most representative cation in soil exchange complex and to simulate the actual system regulating pH values. The germination rate of A. These results are in accordance with those of Sang et al. In general, among the intermediate values of pH tested in this study for the subsequent analyses growth curve and reproductive investment , plants grown at pH5 and pH6 performed better than those grown at pH7.
With regard to vegetative traits, the shortest height as well as the slowest growth rate for all vegetative traits were recorded at pH7. This results are in disagreement with those of an old work of Turner reporting that A.
Tessmer et al. Nevertheless, in our results although A. Physiological mechanisms of adaptation of plants to non-optimal soil pH are well-known in literature. This behavior is consistent with observations we made in our study, since the pH of soil conspicuously decreased over time at all the pH values monitored data not shown. However, observing the whole dataset of vegetative plant traits, plants grown at pH7 exhibited the lowest absolute value of biomass even if not significantly different from pH5 and pH6 , in addition to the lowest values of plant height and velocity of growth in addition to the lack of male inflorescences.
Likely a trend, not captured by our data, indicating less vigor of the species at pH7 can be invoked and should be taken into account. In any case, these results should be carefully evaluated considering some confounding factors relating to the soil ecosystem: a soil pH is known to influence the availability and uptake of a micronutrient like Mg that is implicated in the plant's photosynthetic efficiency Dighton and Krumins, For instance, at high pH, Ca, and Mg tend to form less or not available compounds when reacting with P and many micronutrients Barber, ; b complex interactions between biotic i.
Key elements of soil useful for plants growth are nitrogen N , potassium K and phosphorous P that different plants species can preferentially absorb according to pH. Since A. However, Leskovsek et al. With regards to reproductive investments, at pH6 and pH5 A.
This behavior of the plants at pH7 could also be due to the effect of an excess of calcium hydroxide after the manipulation of the natural soil we used in our experiment. With regards to time to pollen emission it significantly decreased with plant dry weight shorter at pH5 than pH6 , as expected.
The influence of pH on the reproductive investment has been already observed for other species no literature information were found for A. For instance, in a work on the effect of different pH values from 4. Plants growing in too acid or too calcareous i. Consequently, a non-optimal soil pH condition for a plant can affect its growth and reproductive performances, as we have observed in this study for A. In any case, also reproductive investment in response to different pH ranges is species-specific as a result of evolutionary history and adaptation ability to environment of each species Ware, ; Zeng and Clark, ; Offord et al.
In this work, the soil pH at which a plant was grown affected common ragweed pollen allergenicity, which, in our experimental condition, was lowest at pH6. Unfortunately, no specific studies on the effects of soil pH on pollen allergenicity were performed to date.
For instance, Ghiani et al. Climate change was indicated to affect pollen allergenicity determined by a higher concentration of the Amb a 1 allergen in pollen of plants exposed to higher temperatures and drought El Kelish et al. Cloutier-Hurteau et al. They found positive relationships between the concentration of some trace elements Cd Ni and Pb in pollens and in soil or roots. Unfortunately, they did not measure the allergenicity of those pollen grains; moreover they did not find any relation of the trace elements concentration in pollen grain with soil pH probably due to the limited pH range of the investigated soils 7.
In our experiment, we can suppose that the addition of calcium hydroxide to soil in order to increase pH from 5 to 6 interfered with pollen allergenicity.
Indeed, we noticed a higher amount of flavonoids in pollen extracts from plant grown at pH6 probably produced to face the presence of calcium. This higher amount of secondary metabolites likely affected the IgE binding explaining the lower allergenicity detected for pH 6 pollen. Despite the fact that our results in controlled conditions indicate better performances of A.
In contrast, other authors found that the presence of A. However, it should be noted that in such studies the vegetative vigor and the reproductive performances of the plant in the growth sites were not reported. The inconsistency of field studies on pH preference of weeds has been related to the covariation of pH range with climatic gradients annual rainfall and temperature; Pinke et al. In our study, a neutral soil, obtained after the addition of calcium hydroxide to a natural acid soil, inhibited the emission of flowers besides the plant height during the observation period.
This result supports field observations by Italian farmers working on croplands highly invaded by A. In the management of IAPs, manipulating the soil attributes is one of the strategies to achieve a successful control, especially in agricultural environments. Particularly, nutrient and soil nitrogen management, highly dependent on soil pH values, or the addition of activate carbon have been used to achieve desired soil properties, and thus plant communities resistant to invasion Kulmatiski and Beard, ; Vasquez et al.
Although we acknowledge the limitations of only testing the effects of soil pH in controlled conditions, our study suggests that further in-field research on the effects of liming on the growth and performances of A.
Species-specific approaches, may be implemented by applying soil liming methods that may have management problems and high costs also tested in combination with other restoration methods such as N management, plowing, herbicide application, etc. In fact, it is surprising that the effect of invasive plants on soil pH has been investigated in numerous circumstances Ehrenfeld, , but not the opposite. Interesting findings of our experimental study are that: a in not optimal pH conditions pH7 in our study A.
These factors should be considered and may have possible implications during the evaluation of health risk linked to pollinosis. RG and SaCi conceived and designed the experiments. CM and SaCa conducted laboratory analyses. RG and RA analyzed the data and wrote results. RG and SaCi wrote the manuscript Introduction and Discussion ; all authors provided editorial advice and revised manuscript. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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