Productivity and Quality of Alpine Grassland Vary With Soil Water Availability Under Experimental Warming

Abstract

The plant productivity of alpine meadow is predicted to generally increase under a warming climate, but it remains unclear whether the positive response rates will vary with soil water availability. Without consideration of the response of community composition and plant quality, livestock grazing under the current stocking rate might still lead to grassland degradation, even in meadows with high plant biomass. We have conducted a warming experiment from 2010 to 2017 to examine the interactive effects of warming and soil water availability on plant growth and forage quality at individual and functional group levels in an alpine meadow located in the permafrost region of the Qinghai–Tibetan Plateau. Warming-induced changes in community composition, biomass, and forage quality varied with soil water availability. Under dry conditions, experimental warming reduced the relative importance of grasses and the aboveground biomass by 32.37 g m−2 but increased the importance value of forbs. It also increased the crude fat by 0.68% and the crude protein by 3.19% at the end of summer but decreased the acid detergent fiber by 5.59% at the end of spring. The increase in crude fat and protein and the decrease in acid detergent fiber, but the decrease in aboveground biomass and increase the importance value of forbs, which may imply a deterioration of the grassland. Under wet conditions, warming increased aboveground biomass by 29.49 g m−2 at the end of spring and reduced acid detergent fiber by 8.09% at the end of summer. The importance value of grasses and forbs positively correlated with the acid detergent fiber and crude protein, respectively. Our results suggest that precipitation changes will determine whether climate warming will benefit rangelands on the Qinghai–Tibetan Plateau, with drier conditions suppressing grassland productivity, but wetter conditions increasing production while preserving forage quality.

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

“…These findings may be attributed to one or more of the following mechanisms. First, although the increased soil temperature in this study was lower than those in at least two of the three previous studies (Li et al, 2018;Xu et al, 2018), increased soil temperature may not be correlated with the effect of experimental warming on the content of CP in leaves (Lu et al, 2011). Second, the effect of experimental warming on the content of CP in leaves can decrease with an increasing duration of experimental warming (Bai et al, 2013).…”

“…Second, the effect of experimental warming on the content of CP in leaves can decrease with an increasing duration of experimental warming (Bai et al, 2013). The warming duration was less than nine years for at least two of the three previous studies (Li et al, 2018;Xu et al, 2018), whereas the duration was greater than ten years in this study. Third, experimental warming may accelerate soil nitrogen and phosphorus mineralization and the plant's capacity to assimilate nitrogen and phosphorus, but the drying effect that is induced by experimental warming may suppress soil nitrogen and phosphorus mineralization and the plant's capacity to assimilate nitrogen and phosphorus (Gauly et al, 2013;Dumont et al, 2015).…”

“…Therefore, the CP and NDF contents may not only meet maintain requirements of livestock, but also indicate a relatively high nutritive value of the vegetation. 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).…”

“…For example, experimental warming altered the content of CP (Li and Liu, 2017), EE, Ash, ADF and NDF (Li and Liu, 2017;Xu et al, 2018) in alpine meadows of the Haibei station. The effects of experimental warming on the content of CP, EE and ADF varied with soil water availability in alpine meadows of the Beiluhe experimental station (Li et al, 2018). These findings may be attributed to one or more of the following mechanisms.…”

“…alpine meadows, alpine steppes and forests) to experimental warming on the Tibetan Plateau have been produced. However, only a few of them have examined the effects of experimental warming on the nutritional quality in alpine grasslands on the Tibetan Plateau (Li and Liu, 2017;Li et al, 2018;Xu et al, 2018). Moreover, these previous studies related to the response of nutritional quality in alpine grasslands to experimental warming were conducted during only one growing season, although the effect of experimental warming on nutritional quality can vary among years (Augustine et al, 2018).…”