Abstract:

Based on a long-term experimental platform of simulated acid rain (SAR) in Dinghu Mountain, this study aimed to explore the response and adaptation mechanisms of litter decomposition and soil respiration to acid rain stress in a mixed coniferous and broad-leaved forest. Three treatment levels of SAR were considered including a control (CK, natural lake water with pH=4.5), T1 (pH=3.5), and T2 (pH=3.0). The leaf litter mass of two dominant species Schima superba and Castanopsis chinensis were quantified with PVC decomposition rings using in-situ decomposition approach over 15 months (from September 2019 to January 2021), and soil respiration rates in the decomposition rings were measured monthly. The results showed that the litter residual percentages of S. superba and C. chinensis under the CK, T1 and T2 treatments were 37.94%, 40.63%, 44.14%, and 21.92%, 40.27%, 48.72%, respectively, after 15 months of decomposition. There were no significant differences among different acid treatment levels in the early decomposition period (September 2019 to April 2020) (P>0.05), but a significant difference was found between the CK and T2 treatments in the later decomposition period (May 2020 to January 2021) (P<0.05). The SAR significantly decreased the annual soil respiration rate (P<0.05), but there was no significant difference between the T1 and T2 treatments measured without litter or with S. superba litter (P>0.05) in the decomposition rings. With C. chinensis litter, the annual soil respiration rate under the T2 treatment was significantly lower than that under the CK treatment (P<0.05), but there were no significant differences between the CK and T1, or between the T1 and T2 (P>0.05). Our study revealed that high intensity SAR (pH=3.0) inhibited the leaf litter decomposition of S. superba and C. chinensis, but this inhibition effect only appeared at the later stage of litter decomposition. SAR inhibited soil respiration, but litter mulching mitigated the inhibition to some extent, and the alleviating effect was related to the type of litter and the intensity of acid rain.

Key words: simulated acid rain, low subtropics, coniferous and broad-leaved mixed forest, litter decomposition, soil respiration rate, cumulative soil respiration

摘要：

基于鼎湖山野外模拟酸雨长期实验平台,以原位分解实验探讨凋落物分解和土壤呼吸过程对酸雨胁迫的响应与适应机制。设置3个不同处理水平的模拟酸雨,即CK（pH=4.5的天然湖水）、T1（pH=3.5）和T2（pH=3.0）。选取鼎湖山针阔叶混交林试验地优势树种木荷（Schima superba）和锥（Castanopsis chinensis）叶凋落物,置于PVC分解环中进行原位分解实验,每月测定分解环的土壤呼吸速率。15个月（2019年9月—2021年1月）的实验结果显示,CK、T1和T2处理下的木荷和锥凋落物分解残留率分别为37.94%、40.63%、44.14%和21.92%、40.27%、48.72%;在分解早期（2019年9月—2020年4月）,不同酸处理水平间没有表现出显著差异（P>0.05）,而在分解后期（2020年5月至2021年1月）CK和T2处理间差异显著（P<0.05）。对照组（未覆盖凋落物的分解环）和覆盖木荷凋落物组中,模拟酸雨显著降低了年土壤呼吸通量（P<0.05）,但T1和T2处理间差异不显著（P>0.05）;覆盖锥凋落物组T2处理下的年土壤呼吸通量显著低于CK处理（P<0.05）,但CK和T1、T1和T2处理间差异不显著（P>0.05）。结果表明,高强度的模拟酸雨（pH=3.0）抑制了木荷和锥叶凋落物的分解,但这种抑制作用只在凋落物分解的后期显现。模拟酸雨抑制了土壤呼吸,凋落物覆盖在一定程度上减缓了这种抑制作用,这种减缓效应与凋落物类型及酸雨强度有关。

关键词: 模拟酸雨, 南亚热带, 针阔叶混交林, 凋落物分解, 土壤呼吸速率, 土壤呼吸累积通量