Effect of clipping and shading on C allocation and fluxes in soil under ryegrass and alfalfa estimated by ¹⁴C labelling

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• 作者：Andreas Schmitt^a ; Johanna Pausch^a ; ^b ; Yakov Kuzyakov^b ; ^c ; ^{kuzyakov@gwdg.de}
• 关键词：Carbon allocation and partitioning ; Isotope labelling ; Grazing effects ; Assimilate reutilization ; Shoot regrowth ; CO2 sources ; Photosynthesis reduction ; Rhizosphere processes
• 刊名：Applied Soil Ecology
• 出版年：2013
• 出版时间：February, 2013
• 年：2013
• 卷：64
• 期：Complete
• 页码：228-236
• 全文大小：1122 K

文摘

Photosynthesis of higher plants drives carbon (C) allocation below-ground and controls the supply of assimilates to roots and to rhizosphere microorganisms. To investigate the effect of limited photosynthesis on C allocation, redistribution and reutilization in plant and soil microorganisms, perennial grass Lolium perenne and legume Medicago sativa were clipped or shaded. Plants were labelled with three ¹⁴C pulses to trace allocation and reutilization of C assimilated before clipping or shading. Five days after the last ¹⁴C pulse, plants were clipped or shaded and the total CO₂ and ¹⁴CO₂ efflux from the soil was measured. ¹⁴C in above- and below-ground plant biomass and bulk soil, rhizosphere soil and microorganisms was determined 10 days after clipping or shading.

After clipping, 2 % of the total assimilated ¹⁴C originating mainly from root reserves were detected in the newly grown shoots. This corresponded to a translocation of 5 and 8 % of total ¹⁴C from reserve organs to new shoots of L. perenne and M. sativa, respectively. The total CO₂ efflux from soil decreased after shading of both plant species, whereas after clipping, this was only true for L. perenne. The ¹⁴CO₂ efflux from soil did not change after clipping of both species. An increased ¹⁴CO₂ efflux from soil under shading for both plants indicated that lower assimilation was compensated by higher utilization of the reserve C for root and rhizomicrobial respiration.

We conclude that C stored in roots is an important factor for plant recovery after limiting photosynthesis. This stored C is important for shoot regrowth after clipping, whereas after shading, it is utilized mainly for maintenance of root respiration. Based on these results as well as on a review of several studies on C reutilization for regrowth after clipping, we conclude that because of the high energy demand for nitrogen fixation, legumes use a higher portion (9-10 % ) of stored C for regrowth compared to grasses (5-7 % ). The effects of limited photosynthesis were of minor importance for the exudation of the reserve C and thus, have no effect on the uptake of this C by microorganisms.