Biol Fertil Soils:中科院亚热带生态所吴金水研究组揭示水稻光合碳

2016年10月24日,《BioLogy and Fertility of Soils》期刊杂志在线发表了中国科学院亚热带农业生态研究所研究员吴金水领衔的农业生态过程方向研究团队的一篇研究论文，研究报道了在施氮水平对水稻光合碳的土壤传输及其微生物利用机制方面取得了新进展。该研究成果题为Rice rhizodeposition and its utilization by microbial groups depends on N fertilization。

作物光合碳以根际沉积物的形式进入土壤，是根际微生物的主要碳源和能量来源。根际微生物能够通过自身代谢活动将这部分碳源或以气体的形式返回大气，或以有机质的形式存储于土壤中。根际微生物对光合碳的利用能够显著影响土壤碳固定过程。但是，微生物如何利用根际沉积碳，根际沉积碳在稻田土壤有机碳流通过程中的作用及其施氮对根际沉积的影响机制等还尚不清楚。

基于此，该团队利用碳同位素(13C-CO2)连续标记技术结合磷脂脂肪酸的稳定同位素探针技术(13C-PLFA-SIP)，探讨了不同施氮水平(0 、22.5 、45、90 和 135 kg N ha-1)对水稻光合碳(通过沉积作用)的土壤传输及其微生物同化的影响。结果表明，施氮显著提高了水稻地上部和根系的生物量，从而导致输入土壤的光合碳量也呈同步增加趋势，而且随着水稻根系生物量的增加，土壤有机质中来自根的13C含量也相应上升，但来源于光合碳的土壤微生物生物量(13C-MBC)在水稻-土壤系统中的比例却降低了，因此，高量施肥使水稻光合碳的土壤传输和积累比率呈现出非线性骤升的规律，而且施氮肥后土壤碳库13C与根中13C的比值下降，这表明施氮后光合碳向土壤的流通量加快而合成量降低;13C-PLFA-SIP分析的结果表明，施氮后，来源于根际沉积的13C-真菌、菌根真菌和放线菌含量增加，而革兰氏阳性菌和革兰氏阴性菌含量减少。因此，真菌是重要的光合碳根际同化者，施氮显著提高了光合碳的土壤微生物同化量(如图)。该研究为深入解析稻田碳循环及水稻土的可持续管理提供理论基础和数据支撑。

RICE rhizodeposition and its utilization by microbial groups depends on N fertilization

原文摘要：

Rhizodeposits have received considerable attention, as they play an important role in the regulation of soil carbon (C) sequestration and global C cycling and represent an important C and energy source for soil microorganisms. However, the utilization of rhizodeposits by microbial groups, their role in the turnover of soil organic matter (SOM) pools in rice paddies, and the effects of nitrogen (N) fertilization on rhizodeposition are nearly unknown. Rice (Oryza sativa L.) plants were grown in soil at five N fertilization rates (0, 10, 20, 40, or 60 mg N kg−1soil) and continuously labeled in a 13CO2 atmosphere for 18 days during tillering. The utilization of root-derived C by microbial groups was assessed by 13C incorporation into phospholipid fatty acids. Rice shoot and root biomass strongly increased with N fertilization. Rhizodeposition increased with N fertilization, whereas the total 13C incorporation into microorganisms, as indicated by the percentage of 13C recovered in microbial biomass, decreased. The contribution of root-derived 13C to SOM formation increased with root biomass. The ratio of 13C in soil pools (SOM and microbial biomass) to 13C in roots decreased with N fertilization showing less incorporation and faster turnover with N. The 13C incorporation into fungi (18:2ω6,9c and 18:1ω9c), arbuscular mycorrhizal fungi (16:1ω5c), and actinomycetes (10Me 16:0 and 10Me 18:0) increased with N fertilization, whereas the 13C incorporation into gram-positive (i14:0, i15:0, a15:0, i16:0, i17:0, and a17:0) and gram-negative (16:1ω7c, 18:1ω7c, cy17:0, and cy19:0) bacteria decreased with N fertilization. Thus, the uptake and microbial processing of root-derived C was affected by N availability in soil. Compared with the unfertilized soil, the contribution of rhizodeposits to SOM and microorganisms increased at low to intermediate N fertilization rates but decreased at the maximum N input. We conclude that belowground C allocation and rhizodeposition by rice, microbial utilization of rhizodeposited C, and its stabilization within SOM pools are strongly affected by N availability: N fertilization adequate to the plant demand increases C incorporation in all these polls, but excessive N fertilization has negative effects not only on environmental pollution but also on C sequestration in soil.

DOI: 10.1007/s00374-016-1155-z

作者：吴金水