Revegetation and reclamation of soils using wild leguminous shrubs in cold semiarid Mediterranean conditions: Litterfall and carbon and nitrogen returns under two aridity regimes

This study was designed to evaluate the litter produced by Mediterranean shrub legumes subjected to two conditions of aridity. Seasonal litterfall patterns and litter chemistry showed no significant variation with soil aridity. The effects of aridity on the amount of litter produced were related to the plant species. A higher availability of water led to a 110% increase in litter production by Colutea arborescens (3191 vs. 1516 kg ha^–1) and to a 24% increase for Medicago strasseri (5288 vs. 4258 kg ha^–1). The litter provided by Colutea cilicica failed to significantly increase (1651 vs. 1825 kg ha^–1) in less arid conditions. In our experimental conditions, Dorycnium hirsutum showed high mortality and scarce persistence. In general, the litter supplied by these shrub legumes was low in lignin and showed high levels of easily degradable organic-C. Its N content, in the range 18 to 26.5 g kg^–1, was similar to that described by others for multipurpose tropical legumes. Under the semi-arid conditions of central Spain, C. arborescens and C. cilicica gave rise to potential yearly returns of 662 and 693 kg ha^–1 organic-C, and 35 and 44 kg ha^–1 N, respectively. M. strasseri provided a yearly organic-C return (1742 kg ha^–1) similar to that of a mature Mediterranean wood, and to a potential N return (78 kg ha^–1) that substantially exceeded this reference. Compared to the sclerophyllous species typical of the Mediterranean environment, shrub legumes show a much greater potential for enhancing N and organic-C levels, and consequently, for improving the biological activity of degraded soils. This feature is thought to be associated with the rapid and constant renewal of their leaves and their ability to provide the soil with other easily degraded materials.