Grazing increases litter decomposition rate but decreases nitrogen release rate in an alpine meadow

Abstract

Abstract. Litter decomposition and N release are the key processes that strongly determine the nutrient cycling at the soil-plant interface; however, how these processes are affected by grazing or grazing exclusion in the alpine grassland ecosystems on the Qinghai-Tibetan Plateau (QTP) is poorly understood. So far few studies have simultaneously investigated the influence of both litter quality and incubation site on litter decomposition and N release. Moreover, previous studies on the QTP investigating how grazing exclusion influences plant abundance and biodiversity usually lasted for many years, and the short-term effects have rarely been reported. This work studied the short-term (6 months) effects of grazing and grazing exclusion on plant community composition (i.e., plant species presented) and litter quality and long-term (27-33 months) effects on soil chemical characteristics and mixed litter decomposition and N release on the QTP. Our results demonstrate that (1) shorter-term grazing exclusion had no effect on plant community composition but increased plant palatability and total litter biomass; (2) grazing resulted in higher N and C content in litter; and (3) grazing accelerated litter decomposition, while grazing exclusion promoted N release from litter and increased soil organic carbon. In addition, incubation site had significantly more impact than litter quality on litter decomposition and N release, while litter quality affected decomposition in the early stages. This study provides insights into the mechanisms behind the nutrient cycling in alpine ecosystems. We suggest that periodic grazing and grazing exclusion is beneficial in grassland management on the QTP.

Grazing activity increases decomposition of yak dung and litter in an alpine meadow on the Qinghai-Tibet plateau

“…The mean annual temperature during the experimental period is~2.5°C; the lowest average monthly temperature, approximately −10°C, occurred in January and the highest average monthly temperature, approximately 12°C, occurred in July. Mean annual precipitation is 678 mm, over 80% of which fall during the summer (Sun et al 2018; Fig. S1).…”

“…Organic matter decomposition is dependent on the local climate, including seasonal variations of precipitation and temperature (Gillet et al 2010;Yu et al 2013), the activity of coprophagous invertebrates and soil microorganisms (Banegas et al 2015;O'Hea et al 2010) and its chemical compositions (e.g. contents of C and N) (Song et al 2017;Sun et al 2018). In the native ecosystems, organic matter decomposition is synchronized with plant growth and optimal utilization of C and other nutrients (Gregorich and Janzen 1998), whereas anthropic disturbance may retard or accelerate decomposition as it alters the functional compartments of the ecosystem (Banegas et al 2015).…”

“…Herbivores, as a major consumer of herbage, contribute to the nutrient recycling through the return of dung and urine. Grazing affects the litter decomposition processes by altering environmental condition and litter quality (Sun et al 2018), and the dynamics of nutrient cycling (Semmartin et al 2004(Semmartin et al , 2008. Previous publications show that grazing activity of herbivores with different grazing intensities in grazing season may induce considerable changes in the decomposition of dung or litter in grassland ecosystems (Liang et al 2018;Song et al 2017;Sun et al 2018).…”

“…For example, Shariff et al (1994) reported that moderate grazing pressure results in a higher litter decomposition compared with non-grazing and heavy grazing. Sun et al (2018) suggested that litter has a higher rate of decay in a grazed paddock (1.30 to 1.34 g −1 day −1 ) compared to that in grazing exclusion (1.04 to 1.20 g 10 g −1 day −1 ), regardless of litter quality. While, Song et al (2017) found that grazing sheep significantly reduce litter decomposition rate in the local species-rich communities, whereas litter decomposition rate increases in the local species-poor communities at the meadow steppe.…”

“…Indeed, Luo et al (2010) showed that on the Qinghai-Tibetan Plateau (QTP), warming and grazing may increase litter mass losses by approximately 19% and 8%, respectively, and increasing 1°C will result in an additional 11% loss of litter mass. Thus, organic matter decomposition on the QTP is more sensitive to increasing temperature than on a pasture at low altitude, due to its extreme environmental conditions of high solar radiation (21 MJ m −2 day −1 ) and high altitude (~3700 m) (Liu et al 2012) with low temperature (~1°C) and partial oxygen pressure (Liu et al 2018;Sun et al 2018).…”