Influence of Neltuma flexuosa and rainfall event on the germination of Leptochloa crinita and Pappophorum caespitosum in two different locations along a stress gradient in the central Monte desert

Abstract

In drylands, grass germination occurs after a large rainfall event. However,trees influence the water requirements for germination either by decreasingthe rate of evaporation from soil surface or by interception rainfall with theircanopy. The aim of this work was to evaluate the role of Neltuma flexuosa treeon the germination of Leptochloa crinita and Pappophorum caespitosumgrasses in response to precipitation events of different sizes. The experimentwas conducted in two locations within the Monte desert, Argentina: a semiarid location with an average annual precipitation of 345 mm and an arid location with an average annual precipitation of 156 mm. Six microsites wereestablished under N. flexuosa canopies and six microsites in open areas at bothlocations. Within each microsite, 35 seeds of each grass species were exposedto precipitation events of varying sizes. This procedure was repeated 14 timesacross two growing seasons. Germinated seeds were counted in the laboratory.Generalized linear mixed models were then applied to evaluate the effects ofaccumulated precipitation and the microsite on the grass germination in bothlocations. Results showed that N. flexuosa did not influence the germination ofeither grass species in the arid location. However, in the semi-arid location,N. flexuosa facilitated the germination of P. caespitosum only. Large precipitation events would act as an environmental signal for these perennial grasses,allowing them to germinate in favorable years regardless of the microsite orthe location.