酒竹人工林土壤呼吸对氮输入的响应及其因子分析

Effects of nitrogen levels on soil respiration of sympodial bamboo plantation and factor analysis

以西南地区引种栽培的酒竹为对象,开展造林初期不同氮输入措施的试验以评价其对土壤呼吸的影响,并通过10cm深处土壤温度(soil temperature at 10cm depth,T10)、土壤水溶性有机碳含量(soil water-solubleorganic carbon content,WSOC)和土壤含水量(soil water content,SW)探讨其响应机制。结果显示:在不同氮输入处理下酒竹人工林T10、WSOC和SW的变化规律基本与土壤呼吸相似,全年呈现上升—高峰—下降—低谷的过程,雨季和旱季的差异性显著;土壤呼吸速率与T10呈极显著相关的指数关系,而与WSOC、SW呈极显著相关的线性关系;全年温度敏感指数Q10值在2.45～2.78之间,雨季的温度敏感性略低(Q10值在1.66～1.89之间),旱季则较为特殊,对温度敏感,Q10值在4.85～9.54之间,N80和N160处理降低了土壤呼吸的温度敏感性;测得的WSOC数据波动较大,酒竹人工林的氮输入并不能提高T10和SW,但N80和N160相对提高了WSOC。SW和T10解释了全年在N0、N40、N80和N160处理下土壤呼吸变化的96.10%、94.30%、94.48%和92.99%,贡献了绝大部分信息量;雨季与旱季土壤呼吸的主导因素有所不同,雨季为SW,旱季为T10。

Summary Soil respiration is the primary way by which CO2 absorbed by terrestrial plants returns to the atmosphere. And it may have distinctly dynamic patterns at different temporal scales since it is affected by diverse abiotic and biotic factors. Increasing deposition of nitrogen from the traditional cultivation of sympodial bamboos may lead to the sequestration of carbon in vegetation and soil. And the rising temperature and water content may increase the flux of CO2 from the soil, but the response of the ecosystem to simultaneous changes in all of these factors is still unknown. Meanwhile, to provide abundant supply of bamboo timber, afforestation of bamboo species such as Oxytenanthera braunii Pilger ap. Engler, Dendrocalamus brandisii Kurz and D. giganteus Munro is encouraged by the government but without scientific directions. And chemical fertilizers are usually applied into fields unscientifically and blindly in the villages of southwest China. Subsequently, what will happen to the soil structure and how to balance soil nutrient environment in the situation of chemical fertilizer abuse？ In the context of climate change, the amount of nitrogen allocated to the soil is predicted to increase with the productivity of terrestrial ecosystem, and may alter soil carbon storage capacities. To provide the proof of soil respiration responding to the nitrogen input for sympodial bamboo afforestation at the beginning period, we set up four nitrogen fertilization （CO（NH2）2） levels in mid-high mountain of southeast China, i.e. N content of 0, 40, 80, 160 kg/hm2 （expressed on No, N40, N50, N160, respectively）, using the two-year old stump of wine bamboo which were planted every five meters. The soil respiration rate is measured by using trenching method and infrared gas analyzer. The responding mechanism is discussed through analyzing the change of soil temperature at 10 em depth （T10）, as well as changes of soil water-soluble organic carbon content （WSOC） and soil water content （SW）. Results showed that soil respiration rate was quite different between rainy and dry seasons. The soil respiration rate increased at the end of April or in the beginning of May when the rainy season arrived. Its wave crest arrived in July, Aug. and Sept. , and then the rate decreased along with the dry season in Nov., Dec., Feb. and Mar. , then the trough of soil respiration rate appeared. The variation rule of T10, WSOC and SW was similar as this way. Exponential function could be used to describe the relationship between T10 and respiration rate. Meanwhile, WSOC and SW showed a linear relationship with the respiration rate respectively, and the regression test indicted that it was significant. And the temperature sensitivity value Q10 of a whole year was 2.45 - 2.78 nearby. In rainy season, Q10 decreased to 1. 66 - 1. 89, which indicated that the sensitivity of respiration rate responding to temperature decreased. On the contrary, Q10 ascended to 4.85 - 9.54 in dry season. The yearly data of WSOC were unstable, and the nitrogen input could not enhance T10 and SW, but N80 and N160 could increase WSOC relatively. The changes of SW and T10 explained 96.10%, 94.30%, 94.48% and 92.99% of the variation of soil respiration rate in the treatment of No, N40, N80 and N160, which contributed most of the information. The main factor affecting the soil respiration in rainy and dry seasons was quite different, which was SW and T10 respectively. As a consequence, the increase in ecosystem productivity may lead to an increase in carbon turnover in the soil, via an increase in the amount of biomass. But its process and mechanism involving different carbon pools are very complex, and to measure the soil respiration rate alone can not totally reflect the whole change of carbon cycle. Experiments of further control that involves different carbon pools interaction appending to the measurements of CO2 emission will help to clarify the relative importance of bulk soil and micro-relationship in the prime effect.