Mixed cattle and sheep grazing reduces the root lifespan of the community in a desert steppe

Abstract

• Mixed cattle and sheep grazing can significantly shorten root longevity and may accelerate carbon sequestration. • Grazing inhibits fine root longevity of plant community in the temperate desert steppe. • Sheep grazing alone has a greater inhibitory effect on root longevity than cattle grazing alone. • Adjusting the combination of herbivores is an effective strategy to shorten the root lifespan of the community. • The factors affecting root longevity were analyzed by the COX proportional-hazards model. The soil is the primary carbon pool in grassland ecosystems, and the turnover of plant roots is an essential way of organic carbon input. Grazing intensity under a single animal species is usually used to explore the effects of herbivores on grassland, but multi-species grazing is common in grassland utilization. However, few studies have examined the impact of different livestock species and herbivore combinations on the root growth of the grassland community. We used the minirhizotron method to explore the response of root growth in a temperate desert steppe community to cattle and sheep grazing over two years. Among root characteristics and environmental factors, grazing method(cattle grazing; sheep grazing; cattle and sheep grazing; no grazing) is the most significant inhibiting factor affecting root longevity. We found that mixed cattle and sheep grazing significantly reduced the root lifespan of the community, with a median survival time of 120 d, and a survival rate of only 30 % at the end of the observation period. Compared with other treatments, mixed cattle and sheep grazing significantly reduced the number of live roots (0.3724 ± 0.0453 piece/cm 2 ). The change in fine root length of mixed grazing (-0.012 ± 0.0013 mm/cm 2 ) was considerably greater than other treatments. The root lifespan of the community was significantly negatively correlated with the ratio of belowground to aboveground net primary productivity (BNPP/ANPP). The mixed cattle and sheep grazing changed in the patterns of plant carbon contribution, and increased the organic carbon content of the soil. Therefore, under moderate grazing intensity, adjusting the combination of herbivores is an effective strategy to accelerate root turnover rate of the community, accelerate the input of carbon from plant photosynthesis into the soil carbon pool, and may increase soil carbon storage.