荒漠生物结皮碳交换对模拟增温和降雨变化的响应

Carbon exchange of desert soil crust in response to simulated warming and changes of precipitation

生物结皮是干旱荒漠区的重要地表覆被,在未来气候变化加剧的背景下,认识其主导的碳交换过程对于准确评估区域甚至全球碳平衡具有重要意义。尽管针对荒漠生物结皮碳循环过程如何响应全球气候变化已开展了一些研究,但仍缺少关于增温和降水变化及其互作效应的试验研究。本文以腾格里沙漠东南缘的藓结皮和藻结皮为研究对象,基于野外模拟增温和5个降水梯度(2、5、8、13、20 mm)下总初级生产力(GPP)、生态系统呼吸(ER)和净生态系统碳交换量(NEE)的监测,评估其碳交换对未来气候变化的响应。结果表明:(1)增温仅显著影响藓结皮日NEE,降水变化显著影响两种生物结皮日GPP、ER和NEE,增温和降水变化之间没有互作效应。(2)5个降水梯度下,增温平均降低了20.8%藓结皮累积GPP,同时增加了9.9%累积ER,净效应表现为累积NEE平均增加102%;然而,增温提升了藻结皮264%GPP,提高藻结皮24.2%ER,其NEE没有显著变化。(3)藓结皮ER和NEE分别与温度和土壤湿度指数正相关和线性负相关,而增温条件下的藻结皮NEE与二者无显著相关关系。未来全球气候变暖可能会促进荒漠藓结皮的净碳固定,而对藻结皮净碳交换量没有显著影响。因此,在预测未来荒漠生态系统的碳收支时,应考虑不同生物结皮碳交换对气候变暖和降水变化的响应差异。

The C exchange processes dominated by biological crusts,an important surface cover in arid desert soil,at the background of the intensified climatic change is of vital importance to access C balance at the regional and even global scale.Despite how desert crustal C exchange responds to climatic change have received many attentions,the effects of warming and changes of precipitation as well as their interactions remain unclear.To evaluate the extent of C exchange of desert crustal soils in response to climatic change,two typical types of crustal(moss-and algal-dominated crusts)soils in the southeastern edge of the Tengger Desert were selected,and their gross primary productivity(GPP),ecosystem respiration(ER)and net ecosystem exchange(NEE)were monitored in field with stimulated warming and five precipitation gradients(2,5,8,13,and 20 mm).The results showed that:(1)warming only significantly affected daily NEE of moss-dominated crustal soil,precipitation significantly affected daily GPP,ER and NEE of moss-and algal-dominated crustal soil,and there was no interactions between warming and precipitation.(2)Across the five precipitation gradients,warming averagely reduced 20.8%of accumulative GPP and increased 9.9%of accumulative ER,leading to an increase in accumulative NEE by 102%on average for moss-dominated crustal soil.However,warming averagely enhanced 264%of accumulative GPP and increased 24.2%of accumulative ER,with a neutral effects on NEE for algal-dominated crustal soil.(3)ER and NEE of moss-dominated crustal soil were positively and negatively correlated to air temperature and soil moisture,respectively,while NEE of algal-dominated crustal soil was not associated with air temperature and soil moisture under warming.These results suggest climatic change might stimulate C immobilization of moss-dominated crustal soil,while its effects on algal-dominated crustal soil were negligible in the desert region.Accordingly,the distinct responses of C exchange for different crustal soils to climatic warming and precipitation should be taken in consideration when we predict the balance of carbon budget in desert ecosystems.