黄土和风沙土藓结皮土壤呼吸对模拟降雨的响应

生物结皮土壤呼吸是干旱和半干旱生态系统碳循环的重要组成部分,但目前其对降雨的响应规律尚不明确。针对黄土高原黄土和风沙土上发育的藓结皮,分别进行2、4、6、10、20、30、40 mm的模拟降雨,并使用便携式土壤碳通量分析仪测定雨前和雨后藓结皮的呼吸速率,对比分析降雨量对藓结皮呼吸速率的影响;同时,在40 mm降雨后的0—24 h连续测定藓结皮的呼吸速率变化,分析藓结皮呼吸速率随雨后历时的变化规律。结果显示,7种降雨量后两种土壤上藓结皮的呼吸速率均显著升高,黄土上藓结皮呼吸速度的增幅为2.89—6.38倍,风沙土上藓结皮呼吸速率的增幅为0.73—4.38倍。0—6 mm降雨中,两种土壤上藓结皮的呼吸速率均随降雨量增加而迅速升高,二者成显著线性正相关关系;6—40 mm降雨中,黄土上藓结皮的呼吸速率随降雨量增加而缓慢升高,但风沙土上藓结皮的呼吸速率随降雨量增加而快速降低。两种土壤上藓结皮的呼吸速率随雨后历时表现出相似的变化规律,即雨后迅速升高、之后逐渐降低,并在24 h左右回归到雨前水平;但黄土上藓结皮的呼吸速率在雨后即刻达到峰值,而风沙土上藓结皮的呼吸速率在雨后30 min左右方达到峰值。黄土上藓结皮的呼吸速率一致高于风沙土上的藓结皮,前者在不同降雨量和雨后历时中平均比后者高150.0%和59.6%。此外,藓结皮呼吸速率与表层土壤含水量存有显著相关关系,在含水量较低(小于约4%)时二者显著正相关,在含水量较高(大于约4%)时二者对于黄土上藓结皮为正相关、对于风沙土上藓结皮为负相关。研究表明,黄土高原藓结皮土壤呼吸对降雨响应快速而直接,但其响应规律对于黄土和风沙土上的藓结皮是不同的,总体而言黄土上藓结皮对降雨的响应更为持久有效。

Responses of soil respiration of moss-dominated biological soil crusts to simulated rainfall on loess and aeolian soils in the Loess Plateau of China

The respiration of biological soil crusts is an important contribution to carbon cycling in arid and semiarid ecosystems, but soil crust responses to rainfall have not yet been fully investigated. In this study, we conducted a series of simulated rainfall experiments with different rainfall intensities (2, 4, 6, 10, 20, 30, 40 mm) for moss-dominated biological soil crusts (hereafter moss crusts) on loess and aeolian soils in the Loess Plateau of China. The soil respiration rates of the moss crusts were measured before and after the simulated rainfall with a portable CO₂/H₂O Analyzer (LI-COR LI-840). Afterwards, the soil respiration rates of the moss crusts with 40 mm rainfall were continually measured at 0-24 h (0, 0.25, 0.5, 1, 2, 12, 24 h) after the rainfall. Finally, the soil respiration responses of the moss crusts to rainfall were determined from rainfall intensity and time after rainfall. The following results were obtained in this study. (1) The soil respiration rates of the moss crusts were consistently and significantly increased after the simulated rainfall. Compared with the soil respiration rates before the rainfall, the soil respiration rates of the moss crusts on loess soil were increased by 2.89-6.38 times, whereas the soil respiration rates of the moss crusts on aeolian soil were increased by 0.73-4.38 times. (2) In the 0-6 mm rainfall experiments, the soil respiration rates of the moss crusts, both on loess and aeolian soils, linearly increased with increasing rainfall. Correspondingly, in the 6-40 mm rainfall experiments, the soil respiration rates of the moss crusts on loess soil slightly increased with increasing rainfall, whereas the soil respiration rates of the moss crusts on aeolian soil sharply decreased with increasing rainfall. (3) Changes in soil respiration rates during 0-24 h after the rainfall event were similar for the moss crusts on loess and aeolian soils; they both rapidly increased immediately after the rainfall and then gradually decreased to their original levels before the rainfall during 0-24 h. The soil respiration rates of the moss crusts on loess soil reached their maximum values almost immediately after the rainfall event; however, the soil respiration rates of the moss crusts on aeolian soil reached their maximum values approximately 30 min after the rainfall event. (4) The soil respiration rates of the moss crusts on loess soil were 150.0% and 59.6% higher than that on aeolian soil under different rainfall intensities and at different times after the rainfall, respectively. (5) The soil respiration rates of the moss crusts were significantly positively correlated with surface soil water content (0-5 cm) when soil was dry ( < 4%). However, when soil was wet ( > 4%), the soil respiration rates of the moss crusts on loess soil were positively correlated with surface soil water content, but that on aeolian soil were negatively correlated with surface soil water content. From this study, we concluded that the soil respiration of the moss crusts on the Loess Plateau of China responded directly and sensitively to rainfall events, but the responses were different for the moss crusts on loess and aeolian soils. It appeared that the moss crusts on loess soil responded more efficiently to rainfall compared with that on aeolian soil.