Hernández Daniel L, Hobbie Sarah E
Biology Department, Hamline University, Saint Paul, MN, USA.
Oecologia. 2008 Dec;158(3):535-43. doi: 10.1007/s00442-008-1162-3. Epub 2008 Oct 11.
Fire can alter a multitude of ecosystem properties that have the potential to affect rates of litter decomposition and nitrogen dynamics. In this study, we examined the effect of long-term variation in fire frequency in Minnesota oak savanna on rates of litter mass loss of a common tree species (Quercus ellipsoidalis) to determine how site and intraspecific litter characteristics impacted by variation in fire frequency affect rates of decomposition, litter N dynamics, and litter microbial biomass. Although an increase in fire frequency resulted in higher litter temperatures, lower litter moisture, and decreased soil N and P availability, site characteristics had no net effect on rates of mass loss. Rather, litter C:N ratio, which increased with increased fire frequency, was the dominant predictor of rates of decomposition and litter N dynamics. Increased litter C:N led to decreased rates of decomposition and N immobilization, regardless of the characteristics of the site of decomposition. Therefore, it is the indirect effects of long-term variation in fire frequency on litter characteristics rather than fire's direct effects on site characteristics that determine fire effects on decomposition and N dynamics in this system. Slower rates of decomposition and increased N immobilization of litter produced in frequently burned sites may enhance fire-induced N losses, further decelerating rates of N cycling in frequently burned sites.
火灾能够改变众多生态系统属性，这些属性有可能影响凋落物分解速率和氮动态。在本研究中，我们调查了明尼苏达州橡树林稀树草原火灾频率的长期变化对一种常见树种（椭圆叶栎）凋落物质量损失速率的影响，以确定受火灾频率变化影响的立地和种内凋落物特征如何影响分解速率、凋落物氮动态和凋落物微生物生物量。尽管火灾频率增加导致凋落物温度升高、凋落物湿度降低以及土壤氮和磷有效性下降，但立地特征对质量损失速率没有净影响。相反，随着火灾频率增加而升高的凋落物碳氮比是分解速率和凋落物氮动态的主要预测指标。无论分解地点的特征如何，凋落物碳氮比增加都会导致分解速率和氮固定速率下降。因此，在这个系统中，决定火灾对分解和氮动态影响的是火灾频率长期变化对凋落物特征的间接影响，而非火灾对立地特征的直接影响。在频繁燃烧的地点产生的凋落物分解速率较慢且氮固定增加，这可能会加剧火灾引起的氮损失，进一步减缓频繁燃烧地点的氮循环速率。
