黄土高原藓结皮土壤呼吸速率对降雨量变化的响应

Responses of respiration rate of moss biocrusts to the manipulation of rainfall amount on the Chinese Loess Plateau

全球气候变化加剧背景下,干旱和半干旱地区的降雨模式将进一步改变,其造成的土壤水分波动是引起土壤呼吸动态变化的重要因素,但生物结皮土壤呼吸响应降雨模式变化继而影响陆地生态系统碳源/汇功能的机制尚不明确。针对黄土高原风沙土发育的藓结皮,以自然降雨量为对照,分别进行幅度为10%、30%、50%的模拟增雨和减雨处理,并利用便携式土壤碳通量分析仪(LI-8100A)测定了模拟增减雨后的藓结皮土壤呼吸速率,对比分析了其对降雨量变化的响应及机制。结果表明:(1)整个实验周期(2018和2019)增雨和减雨分别显著提高(增幅分别为17.9%—48.2%和27.1%—54.2%)和降低了(降幅分别为1.8%—26.8%和5.2%—20.8%)土壤含水量,但对土壤温度的影响不显著;(2)增雨抑制了藓结皮土壤呼吸速率(降幅分别为7.8%—31.7%和14.7%—39.4%),且随梯度增大抑制作用越明显;减雨则取决于减雨梯度,减雨10%和30%会促进土壤呼吸速率(增幅分别为27.5%、9.6%和23.6%、9.7%)而减雨50%具有抑制作用(降幅分别为15.6%和18.5%)。不同实验周期和不同降雨处理间藓结皮土壤呼吸速率大多差异显著;(3)增雨和减雨下藓结皮土壤呼吸速率与土壤温度均成显著指数正相关关系,同时,低含水量时(小于约15%)与土壤含水量均成显著线性正相关关系,而高含水量(大于约15%)时增雨下成显著线性负相关关系。综上,黄土高原藓结皮土壤呼吸速率对降雨量变化具有明显响应,降雨量整体波动减小时其可能成为一潜在碳源。因此,未来黄土高原土壤碳源/汇功能研究中应考虑降雨模式改变对生物结皮土壤呼吸的影响。

Biocrusts are extensively developed in arid and semiarid climate regions,which cover a large part of land surface with the degraded sparse vegetation.Due to their mulch effects and biological metabolism,biocrusts exert an important influence on almost every ecological process,such as soil water and nutrient cycle,carbon and nitrogen sequestration,soil erosion,biodiversity,and vegetation restoration.Specifically,biocrusts greatly affect carbon exchange and cycling through their photosynthesis and respiration in dryland ecosystems.In arid and semiarid climate regions,the rainfall pattern is expected to be greatly changed due to the acceleration of global climate change,and the change of rainfall pattern will certainly cause the shift of soil water regimes,which fundamentally affect soil respiration.It is widely assumed that biocrust respiration would be affected by the change of soil water regimes,but these effects have not yet been fully investigated.In this study,the impacts of rainfall manipulation on respiration rate of biocrusts were determined through artificially increasing and decreasing ambient rainfall amount by 10%,30%,and 50%,respectively.The plots with well-developed and moss-dominated biocrusts were established in the Loess Plateau of China,and the respiration rates of biocrusts were measured by a soil carbon flux analyzer(LI-8100 A)after the manipulation of ambient rainfall.Our results showed that:(1)the increased rainfall raised soil water content by 17.9%—48.2%in 2018 and by 27.1%—54.2%in 2019.Correspondingly,the decreased rainfall reduced soil water content by 1.8%—26.8%in 2018 and 5.2%—20.8%in 2019.Moreover,the significant(P<0.05)differences were observed in soil water content among the treatments with various rainfall amount and also between the two years.However,the change of rainfall amount had no significant effect on soil temperature.(2)The increased rainfall suppressed biocrust respiration rate by 7.8%—31.7%in 2018 and by 14.7%—39.4%in 2019,but the effects of decreased rainfall on biocrust respiration were dependent on the extent of rainfall reduction.More specifically,the treatments with 10%and 30%of decreased rainfall promoted respiration rate by 27.5%and 9.6%in 2018 and by 23.6%and 9.7%in 2019,respectively;while the treatments with 50%of decreased rainfall lower respiration rate by 15.6%in 2018 and 18.5%in 2019.In addition,all these increasing and decreasing effects on soil respiration were proved to be statistically significant.(3)Both biocrust respiration rate and temperature had a significantly positive correlation(exponential)with rainfall amount;however,the relationship between respiration rate and soil water content was dependent on soil moisture.A linear positive correlation(P<0.05)was obtained between respiration rate and soil water content when soil moisture was<15%,and on the contrary a linear negative correlation(P<0.05)was obtained when soil moisture was>15%.We conclude that the manipulation of rainfall amount has significant impacts on biocrust respiration through regulating their relationships with soil water content and temperature,and these influences should be fully considered in further studying and assessing soil carbon exchange with biocrusts in arid and semiarid climate regions.