氮添加对北京东灵山地区灌丛土壤呼吸的影响

Abstract

土壤呼吸是陆地生态系统碳收支的重要组成部分。与森林相比,自然或半自然的灌丛主要分布在养分贫瘠的地区,通常认为它们对环境变化较为敏感。外源氮输入可能会显著影响灌丛的土壤呼吸。迄今为止,人们对大气氮沉降对灌丛土壤呼吸的影响知之甚少。该文通过氮添加试验,研究了北京东灵山荆条(Vitex negundo var. heterophylla)和绣线菊(Spiraea sali-cifolia)灌丛土壤呼吸及其对不同氮添加水平(对照(0)、低氮(20 kg N·hm–2·a–1)、中氮(50 kg N·hm–2·a–1)和高氮(100 kg N·hm–2·a–1))的响应。结果表明：自然条件下,荆条和绣线菊灌丛的土壤总呼吸年通量为5.91和4.23 t C·hm–2·a–1,异养呼吸通量为5.76和3.53 t C·hm–2·a–1,荆条和绣线菊灌丛的总呼吸和异养呼吸均与土壤温度呈显著的指数关系。荆条和绣线菊灌丛土壤总呼吸温度敏感性系数(Q10)的变化范围分别为1.44–1.58和1.43–1.98,异养呼吸Q10的变化范围分别为1.38–2.11和1.49–1.88。短期氮添加抑制了荆条灌丛的自养呼吸,而对土壤总呼吸和异养呼吸影响不明显；氮添加促进了绣线菊灌丛的异养呼吸,而对土壤总呼吸和自养呼吸均无显著影响；氮添加对两种灌丛土壤呼吸年通量及土壤总呼吸Q10均无显著影响。

Aims Soil respiration from terrestrial ecosystems is an important component of terrestrial carbon budgets. Compared to forests, natural or semi-natural shrublands are mostly distributed in nutrient-poor sites, and usually considered to be relatively vulnerable to environmental changes. Increased nitrogen (N) input to ecosystems may remarkably influence soil respiration in shrublands. So far the effects of N deposition on shrubland soil respiration are poorly understood. The aim of this study is to investigate the soil respiration of Vitex negundo var. hetero-phylla and Spiraea salicifolia shrublands and their response to N deposition. <br> Methods We carried out a N enrichment experiment in V. negundo var. heterophylla and S. salicifolia shrublands in Mt. Dongling, Beijing, with four N addition levels (N0, control, 0;N1, low N, 20 kg N·hm–2·a–1;N2, medium N, 50 kg N·hm–2·a–1 and N3, high N, 100 kg N·hm–2·a–1). Respiration was measured from 2012–2013 within all treatments. <br> Important findings Under natural conditions, annual total and heterotrophic respiration were 5.91 and 4.23, 5.76 and 3.53 t C·hm–2·a–1 for the V. negundo var. heterophylla and S. salicifolia shrublands, respectively and both were not affected by short-term N addition. In both shrubland types, soil respiration rate exhibited significant ex-ponential relationships with soil temperature. Temperature sensitivity (Q10) of total soil respiration in V. negundo var. heterophylla and S. salicifolia shrublands ranged from 1.44 to 1.58 and 1.43 to 1.98, and Q10 of heterotrophic soil respiration ranged from 1.38 to 2.11 and 1.49 to 1.88, respectively. Short-term N addition decreased only autotrophic respiration rate during the growing season, but had no significant effects on total and heterotrophic soil respiration in V. negundo var. heterophylla shrubland. In contrast, N addition enhanced the heterotrophic soil respiration rate and did not influence autotrophic and total soil respiration in S. salicifolia shrubland.