Complex effects of different types of acid rain on root growth of Quercus acutissima and Cunninghamia lanceolata saplings

Background:Soil acidification caused by acid rain(AR)can damage plant roots,which in turn negatively impacts plant health.In response to changing AR types,research efforts to elucidate their specific impacts on plants have become intense.Methods:For this study,we investigated the effects of simulated sulfuric,nitric,and mixed AR on the root systems of Quercus acutissima Carr.and Cunninghamia lanceolata(Lamb.)Hook.under different acidity levels.Results:As the AR S/N ratio and pH decreased,the height growth rate(HGR),basal diameter growth rate(DGR),total root length(TRL)and total root surface area(TRS)of C.lanceolata decreased,whereas the TRL and TRS of Q.acutissima remained the same.When the NO_(3)^(−)concentration in AR was increased,the root activity,superoxide dismutase(SOD)and catalase(CAT)activities of C.lanceolata roots revealed a downward trend;however,the root activity of Q.acutissima and the peroxidase(POD)activity of C.lanceolata roots revealed an upward trend.Further,redundant analysis and structural equation models indicated that AR pH had a greater impact on the HGR of Q.acutissima than that of C.lanceolata,while the impact of the AR S/N ratio on C.lanceolata growth rates was greater than that of Q.acutissima.Conclusions:Our results suggested that the root systems of different tree species had variable responses to AR,and the AR S/N ratio was an important factor affecting plant root growth.This might facilitate new strategies for the culti‑vation and protection of plantations in the future.

Efects of sulfuric,nitric,and mixed acid rain on the decomposition of fne root litter in Southern China

Background:China has been increasingly subject to signifcant acid rain,which has negative impacts on forest ecosystems.Recently,the concentrations of NO_(3)^(−)in acid rain have increased in conjunction with the rapid rise of nitrogen deposition,which makes it difcult to precisely quantify the impacts of acid rain on forest ecosystems.Methods:For this study,mesocosm experiments employed a random block design,comprised of ten treatments involving 120 discrete plots(0.6 m×2.0 m).The decomposition of fne roots and dynamics of nutrient loss were evaluated under the stress of three acid rain analogues(e.g.,sulfuric(SO_(4)^(2−)/NO_(3)^(−)5:1),nitric(1:5),and mixed(1:1)).Furthermore,the infuences of soil properties(e.g.,soil pH,soil total carbon,nitrogen,C/N ratio,available phosphorus,available potassium,and enzyme activity)on the decomposition of fne roots were analyzed.Results:The soil pH and decomposition rate of fne root litter decreased when exposed to simulated acid rain with lower pH levels and higher NO_(3)^(−)concentrations.The activities of soil enzymes were signifcantly reduced when subjected to acid rain with higher acidity.The activities of soil urease were more sensitive to the efects of the SO_(4)^(2−)/NO_(3)^(−)(S/N)ratio of acid rain than other soil enzyme activities over four decomposition time periods.Furthermore,the acid rain pH signifcantly infuenced the total carbon(TC)of fne roots during decomposition.However,the S/N ratio of acid rain had signifcant impacts on the total nitrogen(TN).In addition,the pH and S/N ratio of the acid rain had greater impacts on the metal elements(K,Ca,and Al)of fne roots than did TC,TN,and total phosphorus.Structural equation modeling results revealed that the acid rain pH had a stronger indirect impact(0.757)on the decomposition rate of fne roots(via altered soil pH and enzyme activities)than direct efects.However,the indirect efects of the acid rain S/N ratio(0.265)on the fne root decomposition rate through changes in soil urease activities and the content of litter elements were lower than the pH of acid rain.Conclusions:Our results suggested that the acid rain S/N ratio exacerbates the inhibitory efects of acid rain pH on the decomposition of fne root litter.