Effects of grazing intensity on seed production of Caragana stenophylla along a climatic aridity gradient in the Inner Mongolia Steppe, China

Abstract

As climatic aridity and grazing intensity increases, shrubs play an increasingly important role in grassland ecosystem functioning and services, and its abundance also generally increases. However, the effects of climatic aridity and grazing intensity on sexual reproduction of shrubs in grasslands remain largely unclear. In order to understand the effects of grazing intensity and climatic drought stress, and their interaction on seed production of shrub species, we examined the seed number, seed weight and seed yield of Caragana stenophylla under three grazing intensities (fenced, mild grazing and severe grazing) across a climatic aridity gradient (semi-arid, arid, very arid and intensively arid zones) in the Inner Mongolia Steppe, northern China during 2012-2013. The seed number, seed weight and seed yield gradually increased from the semi-arid to the very arid zones, but decreased from the very arid to the intensively arid zones in fenced plots. The seed number and seed yield decreased from the semi-arid to the intensively arid zones in mild and severe grazing treatment plots, therefore, grazing enhanced the suppression effect of climatic aridity on seed production of C. stenophylla. The seed number and seed yield gradually decreased as grazing intensity increased. The seed weight was highest in severe grazing plots, followed by the mild grazing plots and then the fenced plots. Precipitation varied interannually during the study period. We observed that the seed number, seed weight and seed yield were lower in the low precipitation year (2013) than in the high precipitation year (2012). As climatic drought stress increased, the negative effects of grazing on seed production of C. stenophylla also gradually increased. Our results indicated that climatic drought stress may contribute to the encroachment of C. stenophylla shrub in arid zones by promoting its seed production. However, grazing had negative effects on sexual reproduction of C. stenophylla, and the combined effects of drought stress and grazing seriously suppressed sexual reproduction of C. stenophylla in the intensively arid zone.

What drives the shift between sexual and clonal reproduction of Caragana stenophylla along a climatic aridity gradient?

“…As severe grazing would significantly limit sexual reproduction [ 42 , 45 ], we carried out the study only in non-grazed and mildly grazed grassland. Within each study site, we established four ~ 3 ha plots (two non-grazed plots and two mildly grazed plots).…”

Effect of different grazing intensities on bacterial community composition and diversity in rhizosphere and non-rhizosphere soils in desert steppe of China

“…Grazing intensity has been shown to alter fine-scale processes in desert steppe and cause divergent responses in the spatial distribution of vegetation and soil fertility (Lin et al, 2010b). Grazing also enhances the suppression effect of climatic aridity on seed production in Caragana stenophylla (Xie et al, 2016). Appropriate and efficient grazing exclusion has been found to cause desirable transitions in the plant communities of desert steppe rangelands; this is an available method for counteracting local grassland degradation and promoting rangeland sustainability (Deng et al, 2014).…”

Reproductive effort of Caragana microphylla under long‐term grazing exclusion in a semi‐arid grassland

“…Moreover, the negative effects of interspecific competition, Cuscata parasitism and insect herbivory on sexual reproduction of C. microphylla had probably not been fully shown under 8‐year grazing exclusion (Guo et al., 2017). These results were consistent with our previous studies on the effect of grazing on the seed production for other shrub species in grasslands, in which we found that seed production of C. tibetica , C. stenophylla and C. pygmaea was higher at the short‐term grazing exclusion site ( C. tibetica : 4 years; C. stenophylla : 2–6 years; C. pygmaea : 8‐year grazing exclusion) than at the continuous grazing site (Chen et al., 2013; Wang et al, 2018; Xie, Chen, et al, 2016).…”

“…The first site (~50 ha in size) is subjected to continuous grazing (grazing intensity: ~two sheep unit/ha); the second site (~10 ha in size) is subjected to exclusion of domestic animal grazing for 8 years (since 2005); the third site (~25 ha in size) is subjected to exclusion of domestic animal grazing for 30 years (since 1983); the forth site (~25 ha in size) is subjected to exclusion of domestic animal grazing for 34 years (since 1979). The four study sites are geographically close to each other (the range of distances was 4–5 km) and have relatively uniform environmental conditions and plant species compositions, and experienced similar relatively high level grazing by domestic animals (~two sheep unit/ha) before applying the grazing management treatments (Bai et al., 2010; Xie, Chen, et al, 2016). No other management measures were applied to these study sites.…”