Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, China.
Glob Chang Biol. 2013 Jul;19(7):2158-67. doi: 10.1111/gcb.12161. Epub 2013 Apr 18.
Despite the perceived importance of exudation to forest ecosystem function, few studies have attempted to examine the effects of elevated temperature and nutrition availability on the rates of root exudation and associated microbial processes. In this study, we performed an experiment in which in situ exudates were collected from Picea asperata seedlings that were transplanted in disturbed soils exposed to two levels of temperature (ambient temperature and infrared heater warming) and two nitrogen levels (unfertilized and 25 g N m(-2) a(-1) ). Here, we show that the trees exposed to an elevated temperature increased their exudation rates I (μg C g(-1) root biomass h(-1) ), II (μg C cm(-1) root length h(-1) ) and III (μg C cm(-2) root area h(-1) ) in the unfertilized plots. The altered morphological and physiological traits of the roots exposed to experimental warming could be responsible for this variation in root exudation. Moreover, these increases in root-derived C were positively correlated with the microbial release of extracellular enzymes involved in the breakdown of organic N (R(2) = 0.790; P = 0.038), which was coupled with stimulated microbial activity and accelerated N transformations in the unfertilized soils. In contrast, the trees exposed to both experimental warming and N fertilization did not show increased exudation rates or soil enzyme activity, indicating that the stimulatory effects of experimental warming on root exudation depend on soil fertility. Collectively, our results provide preliminary evidence that an increase in the release of root exudates into the soil may be an important physiological adjustment by which the sustained growth responses of plants to experimental warming may be maintained via enhanced soil microbial activity and soil N transformation. Accordingly, the underlying mechanisms by which plant root-microbe interactions influence soil organic matter decomposition and N cycling should be incorporated into climate-carbon cycle models to determine reliable estimates of long-term C storage in forests.
尽管渗出物被认为对森林生态系统功能很重要，但很少有研究试图检验升高的温度和养分供应对根系渗出物速率及相关微生物过程的影响。在这项研究中，我们进行了一项实验，从移栽到受干扰土壤中的青杄幼苗中采集原位渗出物，这些土壤受到两种温度水平（环境温度和红外加热器加热）和两种氮水平（未施肥和 25 g N m(-2) a(-1) ）的影响。在这里，我们表明，暴露于高温下的树木在未施肥的土壤中增加了它们的渗出物速率 I（μg C g(-1) 根生物量 h(-1) ）、II（μg C cm(-1) 根长度 h(-1) ）和 III（μg C cm(-2) 根面积 h(-1) ）。暴露于实验性增温下的根系形态和生理特征的改变可能是导致根系渗出物变化的原因。此外，这些根衍生 C 的增加与参与有机 N 分解的胞外酶的微生物释放呈正相关（R(2) = 0.790；P = 0.038），这与未施肥土壤中微生物活性的刺激和氮转化的加速有关。相比之下，暴露于实验性增温和氮施肥的树木并没有表现出渗出物速率或土壤酶活性的增加，这表明实验性增温对根系渗出物的刺激作用取决于土壤肥力。总的来说，我们的研究结果提供了初步证据，表明根系渗出物向土壤中释放的增加可能是植物对实验性增温持续生长响应的一种重要生理调节，通过增强土壤微生物活性和土壤氮转化来维持。因此，植物根-微生物相互作用影响土壤有机质分解和氮循环的潜在机制应该被纳入气候-碳循环模型，以确定森林中长期碳储存的可靠估计。
