磷添加对米槠和杉木及其混合细根分解的影响

Effects of phosphorus addition on fine root decomposition of Castanopsis carlesii,Cunninghamia lanceolata and mixed

为探讨磷(P)添加对中亚热带林木细根分解的影响,在P有效性较低的森林收集常见树种米槠、杉木细根及混合细根(米槠、杉木两树种的细根按质量比1∶1比例混合),同时设置P添加处理,进行室内无土培养分解试验。结果表明:在分解初期(0~7 d),对照(CK)下,混合细根的干质量残留率实际值显著大于预测值,抑制了分解,而分解后期(7 d后),两者没有显著差异,分解速率趋于一致;P添加处理总体上减少了3种细根的干质量残留率,但仅对单独分解的杉木细根具有显著作用;与CK相比,P添加处理对杉木细根、混合细根中氮(N)分解释放的影响较小,仅单独分解的米槠细根中N的释放显著变慢;P添加处理使3种细根在分解过程中P大量富集,且初始P含量最少的杉木细根富集最多,分解末期(112 d),杉木细根的P残留率比CK增加了474.69%;与CK相比,P添加处理显著降低了米槠、杉木细根的酸性磷酸酶(AP)活性,但增加了混合细根以及杉木细根的纤维素水解酶(CBH)、β-葡萄糖苷酶(βG)、酚氧化酶(PhOx)和过氧化物酶(PerOx)活性。相关分析发现,细根分解速率与初始N浓度、PerOx呈显著性正相关,与木质素、木质素/N呈显著负相关。112 d分解期内,混合细根未显著影响分解速率,P添加处理也没有促进混合细根和米槠细根的分解,但显著提高了低P含量杉木细根的分解速率,并使P在分解残留细根中大量富集。中亚热带林木细根分解受到底物的木质素含量以及N浓度影响,且在分解过程中的酶(如PerOx)活性变化能较好地反映分解速率变化。

This study aimed to explore the effect of phosphorus(P)addition on the decomposition of fine roots of trees in the middle subtropics.Experiments were conducted on the individual fine roots of Castanopsis carlesii and Cunninghamia lanceolate as well as the mixed fine roots of both species(combined to a mass ratio of 1∶1),sourced from the forest with low P availability.Experiments investigating by P addition processing and the decomposition of soilless culture were conducted in the laboratory.The results showed that:under the control treatment(CK),the observed value of residual dry mass for the mixed fine roots was significantly higher than the perdicted value during the initial stage of decomposition(0-7 d),which inhibited the decomposition,but there was no significant difference during the late stage(after 7 d),at which point the decomposition rate tended to be consistent.P addition treatment generally reduced the residual rates of all samples but had a significant effect only on the single decomposition of the fine roots of Cunninghamia lanceolata.Compared with CK,P addition non-significantly slowed down the release of nitrogen(N)in Cunninghamia lanceolata and in the mixed fine roots and exhibited a significant slower on the fine roots of Castanopsis carlesii;P addition promote the enrichment of P in all three fine root samples,and the fine roots of Cunninghamia lanceolata with the lowest initial P content were the most abundant.At the end of the decomposition(112 days),the residual rate of fine root P in Cunninghamia lanceolata increased by 474.69%compared with that in the control;P addition significantly decreased the activity of acid phosphatase(AP)in the fine roots of Castanopsis carlesii and Cunninghamia lanceolata but increased the activities of cellulose hydrolase(CBH),β-1,4-glucosidase(βG),phenol oxidase(PhOx),and peroxidase(PerOx)in the fine roots of Cunninghamia lanceolata and in the mixed fine roots.Correlation analysis showed that the rate of fine root decomposition was significantly and positively correlated with the initial N concentration and PerOx but significantly negatively correlated with lignin and lignin/N content.Overall,after 112 d of decomposition,the mixed fine roots did not significantly affect the decomposition rate,and P addition also did not affect the decomposition of the mixed and Castanopsis carlesii fine roots but did significantly increase the decomposition rate of Cunninghamia lanceolate,with the lowest initial root P content.P was substantially enriched in all the three fine roots during decomposition.Our findings demonstrated that fine root decomposition is dependent on the lignin content and N concentration of the root substrate,and the enzyme(such as PerOx)activity in the decomposition process is a good indicator of the decomposition rate.