Precipitation and seasonality affect grazing impacts on herbage nutritive values in alpine meadows on the Qinghai-Tibet Plateau

Abstract

Aims Grasslands used for animal husbandry are chosen depending on the nutritive values of dominant herbage species. However, the influence of grazing in combination with precipitation and growing season on the nutritive values of dominant species has not been explicated. Methods To unveil the influence of the different grazing intensities on the nutritional values, an ecological study was formulated, namely fencing (G0), light grazing (G1), moderate grazing (G2) and high grazing (G3). This ambitious study was undertaken on the nutritive values of the four dominant species of herbage in an alpine meadow on the Qinghai-Tibet Plateau (QTP) during growing season (June–September) for two successive years, namely 2015 (rainy year) and 2016 (droughty year). Important Findings We found that (i) the nutritive value of Kobresia capillifolia, Polygonum viviparum and Caragana sinica was noticeably increased by grazing, but negligible effect on Potentilla fruticosa nutritive value was recorded. (ii) During the rainy year (2015), compared with G0, Polygonum viviparum and Potentilla fruticosa displayed 5.4 and 1.5% increases in the crude protein (CP) content and 8.5 and 2.4% increases in vitro true digestibility (IVTD), respectively, while the neutral detergent fibre (NDF) decreased by 13.5 and 0.9%, respectively. During the droughty year (2016), compared with G0, C. sinica and Potentilla fruticosa showed increases in the CP content by 4.3 and 1.3% and increases in the IVTD by 10.7 and 0.4%, respectively, during G3, while the NDF decreased by 6.0 and 1.0%, respectively. (iii) The nutritive values of all species were higher in the years when the rains were good. However, the nutritive values suffered heavily during drought conditions. Besides, the highest and lowest values of nutrition were detected in June and in September, respectively. The inter-seasonal and the inter-annual changes in the nutritional values of species were higher for K. capillifolia and Polygonum viviparum than for Potentilla fruticosa and C. sinica, suggesting that Potentilla fruticosa and C. sinica had higher water-use efficiency. (iv) Grazing clearly reduced the drought tolerance of three species and showed no effects on Potentilla fruticosa. (v) Grazing clearly increased the inter-month variation in the nutritional value of K. capillifolia and Polygonum viviparum but showed no effects on Potentilla fruticosa or C. sinica. Evidently, the grazing effects impacting the nutritional value of the dominant species of herbage exhibited conspicuous inter-annual and seasonal variations with species-specific influences and responses. Our findings are expected to have far-reaching implications enabling the authorities to arrive at strategic decisions and designing of relevant policies for the efficient management of the ecosystems ensuring the speed restoration of the QTP under severe grazing and extreme climatic circumstances.

Effect of Long-Term Experimental Warming on the Nutritional Quality of Alpine Meadows in the Northern Tibet

“…The content of CP, ADF (16.26%-55.39%), NDF, EE (2.48%-4.38%), Ash (7.89%-21.95%) and WSC (3.08%-6.76%) in this study were equivalent to the results (CP: 2.71%-19.21%; ADF: 9.06%-48.30%; NDF: 12.16%-76.23%; EE: 0.64%-10.90%; Ash: 3.49%-12.47%; WSC: 1.24%-17.27%) observed in alpine meadows on the Tibetan Plateau by previous studies (Xu et al, 2002;Shi et al, 2013;Sun et al, 2015;Zhang et al, 2015b;Fan et al, 2017;Li and Liu, 2017;Zhang et al, 2017;Li et al, 2018). Increased water availability may have increased the content of CP in this study, which was in line with the results observed in the steppes of Inner Mongolia Autonomous Region, China (Schönbach et al, 2012;Ren et al, 2016a), a C4 tropical grass in Brazil (Habermann et al, 2019), mountain side grasslands in North-West Greece (Roukos et al, 2011) and alpine meadows on the Tibetan Plateau (Yao et al, 2019). This finding may be related to several mechanisms.…”

Pastures and Climate Extremes: Impacts of cool season warming and drought on the productivity of key pasture species in a field experiment

“…Differences in growth phenology relative to the timing of drought may explain this disparity as Biserrula, an annual species, reached peak growth in early spring when the drought treatment was first implemented for this species, suggesting that residual soil water from winter may have been sufficient to support strong early growth despite the spring drought (Fay et al, 2000;Hofer et al, 2017). These differences in legume response, along with the large effects of winter/spring drought on cool season productivity of our tropical grasses-effects that persisted during the more productive, warm season for one (Themeda) of the three C4 species -provide support for the importance of drought timing in relation to species growth phenology (Wilcox et al, 2017;Yao et al, 2019) rather than functional group classifications.…”

“…However, unlike Medicago, a perennial whose swards develop over multiple years (Li et al, 2012), Biserrula is an annual species, regenerating from seed early in spring each year. These life history differences that influence growth seasonality along with the significant effect of winter/spring drought on productivity of the tropical (C4) grasses, highlight the importance of drought timing in relation to species' growth phenology (Wilcox et al, 2017;Yao et al, 2019), which is at least partially reflected in their functional group classifications.…”

Leaf Stoichiometry of Potentilla Fruticosa Across Elevations Ranging from 2400 m to 3800 m in China’s Qilian Mountains (Northeast Qinghai-Tibetan Plateau)

“…1F), suggesting that by the criteria provided by Koerselman and Meuleman (1996), P was limiting to the growth of P. fruticose. Soil P de ciency is common across China (Han et al, 2005;Zhao et al, 2016), including the whole QTP (Niu et al, 2016) and the Qilian Mountains Xu et al, 2018aXu et al, , 2019Cao et al, 2020). However, Reich and Oleksyn (2004) concluded that plant growth in high elevations was more limited by N. This suggests that limitation of nutrient elements for plants is dependent on region.…”

“…Similarly, factors such as transportation and industrial pollution in uence its leaf morphology and the elemental composition of its organs (Lugovskaya et al, 2018). Likewise, salinity (NaCl and Na 2 SO 4 ) in uence its leaves' physiological and biochemical characteristics (Liu et al, 2013), while grazing in uences its nutritive value (Yao et al, 2019).…”