The ecology and growth patterns of Cleistogenes species in degraded grasslands of eastern Inner Mongolia, China

Abstract

Summary Cleistogenes is an important perennial grass genus found in the pastoral steppes of eastern Inner Mongolia. Despite its dominance in many grassland types, the value of Cleistogenes as a key genus for sustainable grassland development has only recently been recognized. To understand better how to manage Cleistogenes‐dominant grasslands, an experiment was conducted in China, to characterize the growth patterns of two Cleistogenes species (C. polyphylla and C. squarrosa) in relation to environmental parameters. Sampling exclosures were established on uniform grasslands at Mangha and Liuhe gachas. Over two growing seasons (1999–2000) vegetation cover, green and dry biomass by species, species height and tiller density of Cleistogenes were measured at about monthly intervals starting in mid‐May and ending in mid‐October. Cleistogenes polyphylla at Mangha and C. squarrosa at Liuhe accounted for > 50% of green biomass. Neither species made any significant growth before late June, even though soil moisture was available and a large number of tillers were present that had survived the subzero winter intact. In contrast, other species (Prunus sibirica, Potentilla spp. Aneurolepidium chinense) produced up to 500 kg ha−1 biomass in early spring. A relationship between temperature and green weight (wt) tiller−1 indicated that Cleistogenes required an average air temperature > 20 °C to initiate growth, most probably due to its C4 photosynthetic pathway. In this region, temperatures above 20 °C also coincide with periods of most reliable rainfall, which may explain the success of Cleistogenes in grassland degraded by overgrazing. In contrast, competing C3 species (e.g. Stipa spp. and Aneurolepidium chinense) initiate growth earlier in spring when rainfall is highly variable and when small plants are most exposed to severe grazing pressure by livestock emerging from winter in poor condition. Where Cleistogenes spp. completely dominated the grassland, the length of the growing season was shorter and feed shortages in early spring became more acute than for grasslands dominated by C3 species. Livestock producers can minimize this effect by adopting management tactics such as resting pastures in spring to maintain a balance between C3 and C4 perennial grasses. Further research is needed to establish when grazing and strategic rest have most impact on the stability of Cleistogenes‐dominant grasslands.

15N fractionation between vegetation, soil, faeces and wool is not influenced by stocking rate

“…During this period, the mean nitrogen content of aboveground dry matter biomass decreases from about 2.1% to 0.7% (Liu 1993). Growth of C4 plants starts about 30 to 50 days later compared to C3 plants (Bai et al 2004;Liang et al 2002).…”

“…C4 plants start growth later at higher temperature than C3 plants (Ehleringer et al 1997) and thus are in a younger stage of development than the co-occurring C3 plants. The delay in development may be longer than one month (Bai et al 2004;Liang et al 2002), causing young, palatable, and highly digestible C4 plants to co-exist near less digestible C3 plants as indicated e.g. by leaf nitrogen content (Liu 1993).…”

Community Structure and Productivity in Western Mongolian Steppe

“…Instead, they are more likely to be driven by local environmental factors. In the Inner Mongolian steppe, the genus Cleistogenes is an indicator of overgrazing (Kawanabe et al, 1998;Liang et al, 2002). This implies that the dominance of Cleistogenes at site 3 is an effect of grazing intensity.…”

Grazing primarily drives the relative abundance change of C4 plants in the typical steppe grasslands across households at a regional scale

“…Three reasons may explain these results. Firstly, grazing suppresses C 3 plants more than C 4 plants and C 4 plants turn generally green later than C 3 plants (by 6 weeks, see Liang et al 2002), and thus avoid grazing damage in early spring. In addition, C 4 species (mainly C. squarrosa) also have a lower canopy (<10 cm) than C 3 plants (20-50 cm) and thus avoid being grazed by cattle (Wang et al 2003).…”