The magnitude of ecosystem engineering effect of cushion plant Onobrychis cornuta is strongly affected by elevation

Abstract

Cushion plants have been widely documented as ecosystem engineers by protecting the soil seed bank (SSB), enriching soil nutrients, and enhancing soil microorganism activity, including microbial respiration and enzymatic activity. However, the positive effect of cushion plants on the soil fertility and seed banks may vary along elevational gradients due to increasing environmental harshness, such as lower temperatures and reduced precipitation at higher altitudes. Onobrychis cornuta L. is among the most widely distributed cushions in the subalpine zone of mountainous areas from West and Central Asia to Caucasus and Pakistan. We assessed potential facilitative effects of this cushion plant on the SSBs, chemical and biological parameters at three elevational ranges (low: 2400–2650 m a.s.l., intermediate: 2650–2900 m a.s.l. and high: 2900–3150 m a.s.l.). Within each elevational range, twenty O. cornuta cushions were selected, and soil samples were collected at a 5 cm depth, both beneath and adjacent to each cushion, for SSB, chemical and biological analyses. Seed germination method was used for SSB evaluation. We found that, in general, the cushion plant had a positive effect on both SSB density and nutrient availability, with greater SSB density, higher substrate-induced respiration, and increased organic carbon, urease, and moisture content under cushion plants compared to surrounding areas. However, the magnitude of cushion effect on the soil organic carbon, microbial respiration and enzymatic activity increased with elevation while higher density of SSBs under the cushion was observed only at the lowest elevation (2400–2650 m a.s.l.). Our findings show that the magnitude of effect of cushion plants on SSB density and fertility parameters in subalpine areas is strongly dependent on altitude.