Legume defoliation affects rhizosphere decomposers, but not the uptake of organic matter N by a neighbouring grass

Saj Stéphane, Mikola Juha, Ekelund Flemming. 2008. Legume defoliation affects rhizosphere decomposers, but not the uptake of organic matter N by a neighbouring grass. Plant and Soil, 311 (1) : 141-149.

https://doi.org/10.1007/s11104-008-9665-6

Article de revue ; Article de recherche ; Article de revue à facteur d'impact

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Résumé : Legume–grass interactions have a great influence on grassland primary production and it was recently shown how defoliation of a legume can increase the transfer of fixed N to a neighbouring grass. It has also been shown that defoliation of a plant can increase soil microbial activity and lead to better soil N availability in the rhizosphere of the defoliated plant. We combined these two perspectives and tested whether defoliation of a legume (Lotus corniculatus) can enhance N nutrition of the neighbouring grass (Holcus lanatus) by increasing growth of soil decomposer biota and the availability of soil organic matter N for grass uptake. We grew mixtures of L. corniculatus and H. lanatus in grassland soil that included 15N-labelled L. corniculatus litter. In half of the systems, we subjected L. corniculatus to a defoliation treatment mimicking insect larvae feeding. At destructive harvests 1, 3, 9 and 30 days after the last defoliation event, we determined how L. corniculatus defoliation affected decomposer microbes, protozoa and nematodes and whether these changes among decomposers created a feedback on the growth and 15N uptake of the neighbouring H. lanatus. Defoliation reduced the growth and litter-N uptake, but increased shoot N concentration of L. corniculatus. Of the soil variables measured, defoliation doubled the number of bacterial-feeding protozoa, but did not affect the abundance of decomposer microbes and bacterial- and fungal-feeding nematodes. Defoliation did not have statistically significant effects on H. lanatus shoot growth, shoot N concentration or litter-N uptake. Our results demonstrate how defoliation-induced changes in legume ecophysiology can affect the growth of decomposers in soil. However, these effects did not appear to lead to a significant change in the availability of soil organic N to the neighbouring grass. It seems that when positive effects of legume defoliation on grass N nutrition are found in grassland ecosystems, these are more likely to be explained by direct transfer of fixed N rather than changes in the availability of soil organic matter N.

Mots-clés Agrovoc : Lotus corniculatus, Holcus lanatus, plante pour herbage, prairie, interactions biologiques, défoliation, matière organique du sol, physiologie de la nutrition, physiologie végétale, Protozoa, Nematoda, litière végétale, biodégradation, légumineuse, graminée, relation plante sol, micro-organisme du sol, rhizosphère