Linking phytogenic hillocks with plant ecological strategies in a desert steppe: Adaptation of Stipa breviflora to heavy grazing

摘要

The relationship between plants and phytogenic hillocks in arid ecosystems is receiving increasing attention. Although ecologists have explored the microsystem relationship between plant ecological strategies and phytogenic hillocks, the explanation is still ambiguous due to the lack of relevant information on desert grasslands under grazing disturbance. In the present study, a constructive species, Stipa breviflora (a perennial bunchgrass), was selected as the research object in a desert steppe in northern China to quantify plant traits (i.e., height, density, biomass, and seed production) in different growth phases and epiphytically phytogenic hillock traits (i.e., length, width, height, seed number, and soil nutrients) under heavy grazing (HG), moderate grazing (MG), and no grazing (NG). Immature S. breviflora formed phytogenic hillocks under HG treatment. The phenotypic characteristics of phytogenic hillocks were significantly related to the number of aggregated seeds. Furthermore, soil organic carbon, soil total phosphorus and soil total nitrogen increased at the beginning and subsequently decreased with an increase in the size of phytogenic hillocks (plant-growing soil). The livestock preference index was elevated in all phases under HG compared to MG. Plant height was significantly decreased under HG compared to MG and NG. Seed production showed no significant differences between HG and NG during the adult to aging phases. The results indicated that S. breviflora-derived hillocks support S. breviflora survival by providing a nutritious soil matrix while aggregating its seeds to ensure population regeneration. Moreover, S. breviflora adapted to HG by reducing height and increasing reproductive input, which induced livestock to intake older plants.