Mycorrhizal response of <Emphasis Type="Italic">Clusia pusilla</Emphasis> growing in two different soils in the field

Arbuscular mycorrhizas (AM) are important for promoting the mineral nutrition, growth and survival of plants used to rehabilitate degraded areas. Clusia pusilla is an evergreen shrub which is tolerant of high irradiance, germinates readily and can be easily reproduced by cuttings. All these characteristics make this species useful in the recovery of deforested areas. The aim of this work was to explore the response of C. pusilla to AM in the field, in two types of soil: the shrubland soil in which the species naturally grows and in a soil of a riparian forest. Eight treatments were performed in each type of soil. The treatments consisted of a non-mycorrhizal control and mycorrhizal plants colonized by one of the three AM inocula tested in the presence or absence of triple superphosphate (150 kg ha^-1). After 11 months of growth in the shrubland soil, C. pusilla seedlings showed an increase in height and dry weight in response to the fertilizer but not to mycorrhizas. In contrast, in the forest soil the arbuscular mycorrhizal fungi (AMF) effect was equivalent to the fertilizer effect, and the two effects interacted positively. The lack of response to AM in shrubland soil was caused by its high sand content, which hinders the retention of the inocula. Due to a higher clay content, the forest soil binds inocula more tightly than shrubland soil. In conclusion, C. pusilla appears to benefit greatly from the addition of AMF in forest soil, though it requires an additional P source for such benefits in shrubland soil. This P source must be organic so that phosphorus is not lost by leaching. Although the growth rate of this species is very low, its survival can be guaranteed with the application of AMF inocula together with P-fertilizer applied at a low rate.