氮沉降增加和人类干扰对半干旱草地土壤呼吸的影响

    Effects of increased nitrogen deposition and anthropogenic perturbation on soil respiration in a semiarid grassland

    • 摘要: 土壤呼吸是全球碳循环的主要流通途径,但半干旱草地土壤呼吸对全球变化和人类干扰的响应机制尚不清楚。该研究以科尔沁沙质草地为研究对象,研究氮沉降增加、人类干扰(火烧、刈割)及其交互作用对沙质草地整个植物生长季(2017年5-9月)土壤呼吸的影响。结果表明,土壤呼吸呈明显的季节动态变化,在7月最高。氮沉降增加使根呼吸显著提高42%,土壤呼吸显著增加17%(P<0.001),但对微生物呼吸无显著影响。火烧使根呼吸显著提高25%(P<0.01),但使微生物呼吸降低13%(P<0.001),从而导致土壤呼吸未显著增加(P>0.05)。刈割显著降低了土壤温度,诱导微生物呼吸和根呼吸分别降低13%(P<0.001)和20%(P<0.05),从而显著抑制土壤呼吸(P<0.001)。氮沉降增强了火烧对土壤呼吸的促进作用,但未显著影响刈割对土壤呼吸的抑制作用。氮沉降、火烧和刈割对土壤呼吸的不同影响可对全球变化背景下沙质草地土壤碳循环的预测和天然草地的科学管理提供参考。

       

      Abstract: Soil respiration is the primary pathway for the global carbon cycle, but the response mechanism of soil respiration to global change and anthropogenic perturbation in semiarid grassland in the context of global change is still unclear. In this study, a field experiment was conducted to explore the effects of nitrogen (N) addition, anthropogenic perturbation, and their interactions on soil respiration throughout the growing season from May to September in 2017, in Horqin sandy land, northern China. In the field research, the nitrogen deposition included no nitrogen and nitrogen addition (10 g/(m2·a)), whereas, anthropogenic perturbation consisted of control, burning, and clipping activities. In soil respiration, the components and environmental factors, including soil temperature, soil moisture and soil microbial biomass carbon, were monitored in the whole plant growing season. The monitoring data was used to identify the effects of single factor, such as nitrogen deposition, burning and clipping, and their interaction on soil respiration, as well as the contributions of microbial and root respiration to soil respiration. The results showed that the soil respiration presented obvious seasonal dynamics, with the highest in July. Both soil temperature and soil moisture can regulate the seasonal variability pattern of soil respiration in the semiarid grassland, while nitrogen deposition, burning or clipping cannot alter that. The contribution ratios of microbial respiration to soil respiration were 64.68%, 54.99%, 69.20%, 57.88%, 50.50% and 57.66% under no nitrogen (N0)+control, N0+burning, N0+clipping, nitrogen addition (N10)+control, N10+burning and N10+clipping, respectively, indicating that the microbial respiration was main contributor to soil respiration in this semiarid grassland. The increased nitrogen deposition can remarkably enhance the root respiration by 42% (P<0.001), resulting in a significant increase in soil respiration by 17% (P<0.001). In the nitrogen addition, there was no significant effect on microbial respiration in this semiarid grassland, due to the nitrogen deposition cannot efficiently change soil microbial biomass. It infers that the decrease of soil carbon sequestration induced by nitrogen addition can mainly stem from the increase in the root respiration under the future global nitrogen deposition addition. The burning significantly increased the soil temperature, and thereby enhanced the root respiration by 25% (P<0.01), but it cannot efficiently increased the soil respiration, due to the reduction of microbial respiration that induced by the decrease of soil microbial biomass. Furthermore, the single nitrogen deposition enhanced the positive effect of single burning on soil respiration, indicating that both the nitrogen deposition and burning can be used to synergistically promote the soil respiration in this semiarid grassland. The clipping process significantly reduced the soil temperature by 7% (P<0.001), inducing the root respiration decreased by 20% (P<0.05). Moreover, the clipping significantly decreased the soil microbial biomass, and thus reduced the microbial respiration by 13% (P<0.001), thereby to effectively inhibit the soil respiration (16%, P<0.001). However, the nitrogen deposition and clipping had no significant interaction on the soil respiration. Different influences of nitrogen deposition, burning and clipping on soil respiration can provide the sound basis for the prediction of the soil carbon cycle, and for the scientific management of natural grassland in sandy grassland under the global climate change.

       

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