Effect of simulated litterfall and sapling growth of invasive Quercus rubra and native Q. robur on soil in a pot experiment

Abstract

Quercus rubra is an invasive species which can modify soil properties and change the structure and functions of the forest ecosystem. Its effect on soil physicochemical properties, including the content of nutrients (total and available) and phenolic compounds, was compared with that of native Quercus robur in a two-year pot experiment. Three treatments were applied to pots with soil: adding leaf litter (L), planting a sapling (S), and their combination (S + L). The litter was analyzed for its chemical composition before being added to the pots to determine whether it varied between species and whether this variation was reflected in the properties of L and S + L soils. The treatments were compared with the control, which consisted of soil-only pots, i.e., without litter and sapling. Both species increased the content of available nutrients (except N-NO3) and the content of phenolic compounds in the soil, with the former (namely N-NH4, P-PO4, and exchangeable K, Ca, and Mg) more affected by Q. robur and the latter (especially t-ferulic acid, myricetin, and quercetin) more affected by Q. rubra. Interestingly, this effect was pronounced for pots with saplings (S and S + L), while it was almost insignificant for pots with litter (L) only. When compared to the control, the treatments generally did not affect the total nutrient content in the soil. However, when comparing species, there was less total K and Mg under Q. rubra than under Q. robur saplings. The litter used in the experiment was significantly different between the two species. The Q. rubra leaves contained less N, P, K, Ca, total phenolics, and condensed tannins, and more organic C, (+)-catechin, ellagic acid, (–)-epicatechin, t-ferulic acid, kaempferol, and syringic acid than the leaves of Q. robur. However, since the effect of adding litter was negligible, these differences did not translate into differences in soil properties. Based on the obtained results, it is expected that the growth of invasive Q. rubra will result in worse soil conditions (less total and available nutrients and more phenolics) in the short term than the growth of native Q. robur in the same habitat. This means that planting Q. rubra outside its native range is associated with a risk of soil deterioration and, therefore, should be avoided, and the spontaneous dispersal of this species should be prevented.