Abstract:

Recently, the pattern of precipitation in China has changed, aligned with the consequences of global warming. Soil enzymes are important biological activators of underground energy flow and material circulation, and play a crucial role in soil nutrient transformation. Studying the influencing factors of soil enzyme activity in desert steppes under changing precipitation patterns can provide data support for the in-depth understanding of the biogeochemical cycle of grasslands in arid and semi-arid regions. Based on a field experiment of changing precipitation patterns in a desert steppe of Ningxia conducted in 2014, the changes of soil catalase, invertase, and urease activities were studied during 480-day litter decomposition, and their correlation with meteorological factors, soil physicochemical properties, and the cumulative release of elements from litters in four plant species were also analyzed. Results showed that catalase activity (0.077-0.138 g∙mL^-1∙h^-1) increased gradually, whereas invertase (7.075-19.550 mg∙g^-1∙d^-1) and urease (0.483-0.998 mg∙g^-1∙d^-1) activities had no evident temporal dynamics during litter decomposition. In addition, reduced precipitation had little effect on the three enzyme activities, whereas increased precipitation could improve the activities of sucrase and urease, but the degree of influence was different in litter decomposition times. The factors that significantly affected enzyme activity included monthly average wind speed, monthly average air temperature, monthly precipitation, soil N:P ratio, and soil NH₄⁺-N (P<0.05). Except for the urease activity which had no significant relationship with cumulative release of nitrogen from the litters of Astragalus melilotoides (P>0.05), the three enzyme activities had significant and positive linear relationships with the cumulative elemental release from litters (P<0.05). The results indicate that enzyme activity is primarily controlled by meteorological factors rather than soil properties during litter decomposition. Moreover, increasing precipitation enhances soil water and nitrogen availabilities, thereby stimulating the activities of sucrase and urease. The decomposition rate of litters and amount of carbon and nitrogen released from litters increase with the increase of enzyme activities. Furthermore, soil temperature is considered as a factor regulating enzyme activities. In the future, combined with the data on soil temperature and other soil properties, long-term observation is necessary for exploring the driving factors of enzyme activity under changing precipitation patterns.

Key words: arid and semi-arid regions, precipitation pattern, soil enzyme, litter, meteorological factor, biogeochemical cycle

摘要：

近年来,受全球变暖的影响,中国降水格局发生了改变。土壤酶是地下能量流动和物质循环的重要生物活化剂,在土壤养分转化中扮演着重要的角色。研究降水量变化下荒漠草原土壤酶活性的影响因素,可为深入了解降水格局改变下干旱半干旱区草原生态系统生物地球化学循环提供数据支撑。基于2014年在宁夏荒漠草原设置的降水量变化野外试验平台,研究了凋落物分解过程中土壤过氧化氢酶、蔗糖酶和脲酶活性的变化,分析了其与气象因子、土壤理化性质以及植物种凋落物元素累积释放量之间的关系。结果表明：凋落物分解过程中,过氧化氢酶活性（0.077-0.138 g∙mL^-1∙h^-1）呈逐渐上升趋势,蔗糖酶（7.075-19.550 mg∙g^-1∙d^-1）和脲酶（0.483-0.998 mg∙g^-1∙d^-1）活性无明显的时间动态。减少降水量处理对3种酶活性影响较小。增加降水量处理有助于提高蔗糖酶和脲酶活性,但其影响程度在不同凋落物分解时间之间存在差异;对酶活性影响显著的环境因子依次为月平均风速、月平均气温、月降水量、土壤N:P和土壤NH₄⁺-N质量分数（P<0.05）;除脲酶活性与草木樨状黄芪（Astragalus melilotoides）氮累积释放量无显著的关系外（P>0.05）,其他情况下3种酶活性与植物种凋落物元素累积释放量呈显著正相关的线性关系（P<0.05）。综上,凋落物分解过程中酶活性主要受气象因子调控;增加降水量提高了土壤水分和氮有效性,有利于刺激蔗糖酶和脲酶活性;随着酶活性的增加,植物种凋落物分解速率加快,碳和氮释放量增多;土壤温度是调控酶活性的主要因子之一。今后还需结合土壤温度等数据,从较长的时间尺度上深入探讨降水量变化下荒漠草原酶活性的驱动因素。

关键词: 干旱半干旱区, 降水格局, 土壤酶, 凋落物, 气象因子, 生物地球化学循环