土壤增温、隔离降水及其交互作用对杉木幼苗细根生产的影响

Effects of soil warming and precipitation exclusion and their interaction on fine roots production of Chinese fir(Cunninghamia lanceolata) seedlings

为了揭示我国最重要的人工林树种杉木对全球变暖和降水格局改变的地下响应及其适应性,在福建省三明市陈大国有林场开展杉木(Cunninghamia lanceolata)幼苗土壤增温和隔离降水双因子试验,包括对照(CK)、土壤增温5℃(W)、隔离降水50%(P)和土壤增温+隔离降水(WP)4个处理,用微根管法探讨试验1a期间土壤增温、隔离降水及其交互作用对杉木幼苗细根生产量(以细根出生数量表征)的影响。双因素方差分析发现,土壤增温和隔离降水对细根总出生数量没有影响,但两者的交互作用则极显著。与CK相比,W细根总出生数量显著增加,而WP处理细根总出生数量则显著低于W处理和P处理。土壤增温、隔离降水与季节的重复测量方差分析发现,土壤增温×季节、隔离降水×季节对细根出生数量均有显著影响;与CK相比,W处理春季细根出生数量显著增加,P处理秋季细根出生数量显著增加,而WP处理夏季和冬季细根出生数量显著下降。土壤增温、隔离降水与径级的三因素方差分析表明,土壤增温×隔离降水×径级存在显著影响;0—1 mm径级细根出生数量W处理显著高于CK,但WP处理则显著低于W处理和P处理。土壤增温、隔离降水与土层的3因素方差分析表明,土壤增温、隔离降水与土层之间不存在显著的交互作用;仅在20—40 cm土层发现P处理细根出生数量显著高于CK。研究结果表明,土壤增温和隔离降水对杉木幼苗细根生产的影响存在显著的交互作用,这种交互作用还因不同的季节和径级而异。

Changes in global warming are expected to have profound effects on precipitation. Root production plays a key role in ecosystem carbon, nutrient, and water cycling; however, the response of root production to soil warming and precipitation exclusion is not well understood. The aim of this study was to explore the below-ground responses and adaptability of the most important timber species in southern China, Chinese fir （Cunninghamia lanceolata）, to global warming and precipitation changes. A factorial experiment of soil warming （ambient, ＋5℃） and precipitation exclusion （ambient, -50%） was carried out in the Chenda State-owned Forest Farm in Sanming, Fujian Province. We measured changes in fine root production （fine root birth） after one year of soil warming and precipitation exclusion using the mini-rhizotron method. Results of two-way analysis of variance （ANOVA） showed that soil warming and precipitation exclusion had no significant effect on the total number of fine roots produced, whereas their interaction had a marked effect on the total number of fine roots produced. Compared to the control plots, the total number of fine roots produced increased significantly in the warmed soil plots, but decreased significantly in the warmed soil plus precipitation exclusion plots compared to the warmed plots and the precipitation exclusion plots, respectively. Repeated-measures ANOVA including soil warming, precipitation exclusion, and season showed that the interaction of soil warming and season, and the interaction of precipitation exclusion and season had significant effects on the number of fine roots produced. Compared to the control plots, the number of fine roots produced increased significantly in the warmed soil plots in the spring, and in the precipitation exclusion plots in the autumn, but decreased significantly in the warmed soil plus precipitation exclusion plots in the summer and winter. These results indicate that soil warming, precipitation exclusion, and their interaction influence the season of fine root production. A three-way ANOVA including soil warming, precipitation exclusion, and diameter class showed that the interaction of soil warming precipitation and diameter class had a significant effect on the number of fine roots produced, which was significantly higher in the soil warming treatment than in the control at 0-1 mm. However, the number of fine roots produced was significantly lower in the soil warming plus precipitation exclusion treatment than in the precipitation exclusion treatment and soil warming treatment, respectively. These results indicate that the effect of the interaction of soil warming and precipitation exclusion on the number of fine roots produced mainly occurred at 0-1 mm. The three-way ANOVA including soil warming, precipitation exclusion, and soil layer showed that the three-way interaction had no effect on the number of fine roots produced. Only the precipitation exclusion treatment resulted in a significantly higher number of fine roots than the control in the soil layer of 20-40 cm. This suggests that the interaction of soil warming and precipitation exclusion on the number of fine roots produced had similar effects at different soil layers. It is concluded that the interaction of soil warming and precipitation influenced root production through changing the fine root seasonal distribution and diameter class allocation, which may play important roles in the growth of Chinese fir.