Soil seed-bank germination patterns in natural pastures under different mineral fertilizer treatments

Anna Iannucci

doi:10.5424/sjar/2014124-6852

Abstract

Degraded native grasslands in Mediterranean areas can be improved by encouraging seedling regeneration from soil seed banks using chemical fertilization. The effect of mineral fertilizers on soil seed banks was studied in natural pastures at two locations in southern Italy: Carpino and Rignano Garganico. The aim was to determine if nitrogen (N), phosphorus (P) and combined nitrogen and phosphorus (NP) fertilization can promote increased soil seed density. The seed-bank size and composition were analysed over two growth cycles (2004-2006) at two periods of the year: at the early summer and at the early autumn. The plant species were classified into three functional groups: grasses, legumes and other species (all other dicots). A two-pool model (ephemeral and base pools) derived from the germination patterns was developed to quantify the dynamics of the germinated seed populations. The mean total seed number in the seed bank ranged from 2,915 to 4,782 seed m-2 with higher values in early summer than in early autumn. Mineral fertilizer applications increased the seed-bank size (by 27%, 23% and 46%, for N, P and NP, respectively) and modified the composition in both localities. The three plant functional groups showed different potentials for ephemeral and persistent seed-bank production; however, within each plant group, the proportion between the ephemeral and base pool fractions did not change with fertilizer application. These data show that mineral fertilization can have positive effects on the seed-bank size of ungrazed natural pastures, and can be used to improve degraded Mediterranean pastures.

Highlights

Natural grasslands in the Mediterranean basin occur generally in hilly areas where cropping is not possible because of shallow, stony soils and steep slopes. They consist predominantly of annual species, and their persistence is dependent upon the development and maintenance of a considerable soil seed bank (Sternberg et al, 2003)
In native grasslands, improved productivity is desirable, with the encouraging of seedling regeneration from soil seed banks. This is important in protected areas where the biodiversity of the natural pastures is protected by law, and any recovery is linked to adequate agro-pastoral techniques of management
The relationships between the cumulative germinated seed populations and the germination times for all of the plant functional groups and the treatments can be described by the negative exponential Eq [1] (r2 = 0.89 – 0.96, p < 0.001): y = a (1 – be–t) + ct

Summary

Introduction

Natural grasslands in the Mediterranean basin occur generally in hilly areas where cropping is not possible because of shallow, stony soils and steep slopes. They consist predominantly of annual species, and their persistence is dependent upon the development and maintenance of a considerable soil seed bank (Sternberg et al, 2003). In native grasslands, improved productivity is desirable, with the encouraging of seedling regeneration from soil seed banks. This is important in protected areas where the biodiversity of the natural pastures is protected by law, and any recovery is linked to adequate agro-pastoral techniques of management. Other practices can be forbidden by law, such as reseeding with exogenous ecotypes, as this promotes genetic contamination of the pasture phytocoenoses

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