Solidago Gigantea

As reported in Dassonville et al. (2008), the main impact of Solidago gigantea was on soil P. In most studied sites, P availability increased consecutively to invasion. Nutrient uplift is not the mechanism responsible for this increased as the rooting depth is comparable in both invasive and resident vegetation (Herr et al., 2007). In order to understand the mechanisms affecting P availability, we examined seasonal variation of labile inorganic and organic P fractions, microbial P, and phosphomonoesterase activity in soil as well as P in standing biomasses (above- and belowground) (Herr et al, 2007). Higher concentrations of several labile fractions of P were observed in invaded soils compared to uninvaded soils (figures 2 and 3). Soil pH was also lower in invaded stands than under the resident vegetation. Soil pH is one of the most important parameters determining adsorption/desorption equilibrium of phosphates in soils (Hinsinger, 2001). The observed half-a-unit decrease of pH might favour solubility of mineral P compounds as suggested by Chapuis-Lardy et al. (2006). Decreased pH was also invoked as a possible mechanism for the increased P availability under the exotic invasive Lepidium latifolium (Blank and Young, 2002). The P stock in aboveground biomass of Solidago gigantea is higher than in the resident vegetation so that the quantity of P returning to the soil through litterfall is slightly higher in invaded plots. However, these amounts are not sufficient to explain a rapid increase in P availability in invaded plots compared to uninvaded ones. Fast nutrient leaching and mineralization were already reported for roots, suggesting that roots play a major role in the cycling of nutrients (Scheffer and Aerts, 2000). The increased P availability under Solidago gigantea probably comes mainly from the decomposition of belowground dead biomass. A massive P uptake takes place in autumn alimenting the production of fine roots. This P accumulation exceeds the P needs for aboveground biomass production in the subsequent year. Then, due to massive fine roots death in winter and spring, most of the P stored in belowground organs in autumn is lost in belowground litter. Phosphorus is easily released from dying roots (Eason and Newman, 1990) and quick release of P from decomposing roots was invoked as a possible mechanism of P enrichment in the soil (Campbell et al., 1993). Intense mobilization of P by Solidago roots in autumn and restitution of easily decomposable root debris in next spring may contribute to the higher availability of soil P observed in invaded plots in our study.

Figure 2. Seasonal variation of soil resin-Pi (0-10 cm) in plots invaded by early Goldenrod and adjacent, uninvaded plots. Means (n=6) and standard deviations. Figure from Herr C., Chapuis-Lardy L., Dassonville N., Vanderhoeven S. & Meerts P., 2007. Seasonal effect of the exotic invasive plant Solidago gigantea on soil phosphorus pools and fluxes. Journal of Plant Nutrition and Soil Science 170: 729-738. Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.

Figure 2. Seasonal variation of soil resin-Pi (0-10 cm) in plots invaded by early Goldenrod and adjacent, uninvaded plots. Means (n=6) and standard deviations. Figure from Herr C., Chapuis-Lardy L., Dassonville N., Vanderhoeven S. & Meerts P., 2007. Seasonal effect of the exotic invasive plant Solidago gigantea on soil phosphorus pools and fluxes. Journal of Plant Nutrition and Soil Science 170: 729-738. Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.

Phosphorus Fractions Different Soils

Figure 3. Seasonal variation of different soil P fractions (0-10 cm) in plots invaded by early Goldenrod and adjacent, uninvaded plots. (A) bicarb-Pi, (B) bicarb-Po, (C) NaOH-Pi, (D) NaOH-Po. Means (n=6) and standard deviations. Figure from Herr C., Chapuis-Lardy L., Dassonville N., Vanderhoeven S. & Meerts P., 2007. Seasonal effect of the exotic invasive plant Solidago gigantea on soil phosphorus pools and fluxes. Journal of Plant Nutrition and Soil Science 170: 729-738. Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.

Figure 3. Seasonal variation of different soil P fractions (0-10 cm) in plots invaded by early Goldenrod and adjacent, uninvaded plots. (A) bicarb-Pi, (B) bicarb-Po, (C) NaOH-Pi, (D) NaOH-Po. Means (n=6) and standard deviations. Figure from Herr C., Chapuis-Lardy L., Dassonville N., Vanderhoeven S. & Meerts P., 2007. Seasonal effect of the exotic invasive plant Solidago gigantea on soil phosphorus pools and fluxes. Journal of Plant Nutrition and Soil Science 170: 729-738. Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.

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