地膜覆盖与施氮肥对光合碳在玉米-土壤系统分配的影响

Effects of Plastic Film Mulching and Nitrogen Fertilization on the Distribution of Photosynthetic Fixed Carbon in Maize-Soil System

地膜覆盖(简称"覆膜")与施肥是促进作物增产增收的重要技术措施。光合碳是"大气-植物-土壤"系统碳固定的起点,也是土壤有机碳的重要来源。基于沈阳农业大学棕壤长期定位试验站,利用^(13)CO2对苗期玉米进行田间原位脉冲标记,分析光合碳在植物-土壤系统动态分配,探讨覆膜与施氮肥对其的影响,对深入认识土壤有机碳固定具有重要意义。试验处理包括:裸地施氮肥(N4)、裸地不施肥(CK)、覆膜施氮肥(FN4)和覆膜不施肥(FCK)。结果表明,与不施肥处理相比,覆膜施氮肥提高了玉米茎叶和根的生物量,而裸地施氮肥却降低了玉米生物量。苗期标记后第1 h,玉米-土壤系统光合净固定^(13)C量为194~468 mg m^(-2),其中FN4处理净固定^(13)C量最高,^(13)C同化率为76.8%,其次为FCK和CK处理,平均约为51.7%,N4处理净固定^(13)C量最低,为31.8%;标记结束后(第30 d)^(13)C同化率平均约为36.0%。光合碳分配到茎叶的比例为48.1%~89.5%,根为3.6%~19%,根际土壤和非根际土壤平均分别为9.27%和5.83%。FCK和FN4处理光合碳分配到地下部(根、根际土壤和非根际土壤)的比例在标记后第1 d达到最高,分别为29.97%和39.10%,在标记后第30 d分别下降到23.41%和31.44%。CK和N4处理光合碳分配到地下部的比例分别从标记后第1 h的14.87%和11.98%增加到标记后第30 d的27.86%和48.22%。光合碳在地下部的分配与运转受植物生长和土壤本身理化性质的影响与制约。

Plastic film mulching and fertilizer application are important technical measures to increase crop yield and income. Photosynthetically fixed carbon（C） is the start of C fixation in atmosphere-plant-soil system, and also an important source of soil organic C. Based on the long-term experiment station of Brown Earth in Shenyang Agricultural University, the method of in-situ^13CO2 pulse labeling was employed to analyze the dynamic allocation of photosynthetic C in plant-soil system, and to explore the effect of mulching and nitrogen fertilizer on it during maize seedlings. This study would play important roles in further understanding soil organic C fixation. The treatments included nitrogen fertilization and no fertilization under no-mulching（N4 and CK, respectively） and under mulching（FN4 and FCK,respectively）. The results showed that compared with FCK treatment, the application of nitrogen fertilizer under mulching（FN4） increased maize shoot and root biomass. The contrary effect was found in the N4 treatment. Net fixed^13C by photosynthesis in maize-soil system（sum of^13C fixation in maize shoot and root, rhizosphere soil and bulk soil）ranged in 194-468 mg m^-2. The^13C assimilation rate（the percentage of net fixed^13C in total^13C addition） was the highest in FN4 treatment, with a value of 76.8%, followed by FCK and CK treatments, with an average of 51.7%, and the lowest in N4 treatment, with a value of 31.8%, at the 1 st hour of pulse labeling. The average^13C assimilation rate was about 36% at the 30 th days of pulse labeling. About 48.1%-89.5% of photosynthetically fixed C was allocated to shoots, 3.6 %-19 % to roots, 9.27% and 5.83%, respectively, to rhizosphere soil and bulk soil. Photosynthetic fixed C allocation underground（root, rhizosphere soil and bulk soil） decreased from the highest percentage of 29.97% and39.10% at the 1 st day to the lowest percent of 23.41% and 31.44% at the 30 th days of pulse labeling, respectively, in FCK and FN4 treatments. It increased from the lowest percent of 14.87% and 11.98% at the 1 st hours to the highest percent of 27.86% and 48.22% at the 30 th days of pulse labeling in CK and N4 treatments, respectively. Therefore,the distribution and translocation of photosynthetically fixed C underground are affected and restricted by the growth of plant and soil physical and chemical properties.