# Long Term Effects of Forest Liming on the Acid-Base Budget
## 4 Discussion
The loss of more than 5 kg NO3\({}^{-}\) ha\({}^{-1}\) a\({}^{-1}\)[22] indicates N saturation on a low level (cf. [55]). Liming increases the leaching of NO3\({}^{-}\) and therefore the acid load. This is an example of the risks which are associated with liming of N saturated forest areas. However, on the control plot, NO3\({}^{-}\) is for the most part accompanied by Al which could be a risk for biota living in adjacent freshwater ecosystems and can cause higher costs and increased technical effort to remove aluminum from drinking water [56]. After liming the absolute portion and relative proportion of Al is reduced and instead of Al more Mb cations (especially Mg) are transported together with NO3\({}^{-}\) to the outside of the ecosystem. To improve the accuracy of the acid load by biomass increment it is important to know in which form N is taken up by the forest stand. The sample calculations for the three study areas show that uptake of N only in the form of NO3\({}^{-}\) reduces the acid load considerably, in the case of IO even below zero, which means net proton consumption. On the other hand, a high proportion of NH4\({}^{+}\) could almost double the acid load. Experiments indicate for _Pica abies_ that a large proportion of its N uptake from the soil is NH4\({}^{+}\)[57; 58; 59]. Based on the literature, it is more likely that there is an underestimate in the acid load by biomass increment when the influence of the utilized N form is not taken into account. For the long-term, it is unknown if liming leads to a loss of a greater amount of N if a reduction of N deposition occurs. It could be hypothesized, that the amount of N lost with seepage water is the same. Under current deposition, limed ecosystems could show a more rapid increase of N in seepage waters. However, with reduced N deposition the limed areas may begin to store N and evade N saturation at an earlier point in time. Liming increases tree growth and additional N can be retained by the vegetation or removed by harvesting. In IO and HS, liming leads also to a slight increase of the acid load from the N budget but is less important to the other proton sources. Most of the N input is retained in the ecosystem of these two study areas even on the high-dose treatment 8 with 15 t/ha. In the case of IO liming could prevent the ecosystem to reach N saturation as there was significantly more N taken up and stored in the stem wood of the trees on the liming trials [22]. Possible reasons for this could be a higher number of living cells (cf. [60]) or that N is taken up to a greater extent as NO3\({}^{-}\) instead of NH4\({}^{+}\), which is stored in the wood (cf. [61]). Why this effect could not be observed for the spruce forest stand in AD is not clear. This study clearly shows the importance of minimizing the input of N into forest ecosystems as long as most of the N is still retained and not lost as nitrate by seepage water flux. Otherwise, nitrate loss would likely continue over decades similar to the sulfate outputs (cf. [3; 62]). The lower amount of anions in the seepage water in HS compared to AD and IO leads to stronger retention of the applied Mb cations (Mg and Ca). Therefore, sandy soils should not be excluded automatically from liming treatments. Instead, the period between liming treatments can be longer for sandy soils with similar conditions to HS. The lower cation exchange capacity in HS [22] does not cause higher outputs of Mg and Ca by the seepage water. Conceptualization, M.G., J.B., G.S. and W.W.; methodology, M.G., J.B., G.S. and W.W.; validation, M.G., J.B. and W.W.; formal analysis, M.G. ; investigation, M.G. ; resources, M.G. and W.W.; data curation, M.G. ; writing--original draft preparation, M.G. ; visualization, M.G. ; supervision, M.G., J.B., G.S. and W.W.; project administration, M.G. and G.S. All authors have read and agreed to the published version of the manuscript.