Guodong Han

Grassland communities occupy about 25 % of global land area and global warming could alter grassland plant community coverage. A field study was conducted to investigate the impact of soil warming (surface soil temperature increased by 1.3 °C) and nitrogen addition (100 kg N ha ⁻¹ year ⁻¹ ) on a desert steppe community in Inner Mongolia, China, from 2006 to 2011. Although there were strong intra‐ and inter‐annual variations, in general, warming had little effect on coverage of the four major species (two cool season C ₃ species: Convolvulus ammannii and Stipa breviflora , and two warm season C ₄ species: Cleistogenes songorica and Kochia prostrata ) over six growing seasons. The C ₃ /C ₄ coverage ratio consistently decreased with warming, with the decrease being statistically significant for one‐third of sampling dates. Warming caused a reduction (from 27.6 to 25.1 %) in peak season total plant community coverage. N addition did not affect the four main species, four functional groups (perennial grass, perennial forb, shrub and annual‐biennial) or the total plant community over the 6 years, except when precipitation was high (231 mm in 2008). The small reduction in plant community coverage demonstrated the resilience of desert steppe to warming. There could be a shift of C ₃ to C ₄ species because of warming, as indicated by the decrease in C ₃ /C ₄ ratio, but confirmation of this trend requires further study.

Proper grazing management practices can generate corresponding compensatory effects on plant community production, which may reduce inter-annual variability of productivity in some grassland ecosystems. However, it remains unclear how grazing influences plant community attributes and the variability of standing crop. We examined the effects of sheep grazing at four stocking rate treatments [control, 0 sheep ha⁻¹ month⁻¹; light (LG), 0.15 sheep ha⁻¹ month⁻¹; moderate (MG), 0.30 sheep ha⁻¹ month⁻¹; and heavy (HG), 0.45 sheep ha⁻¹ month⁻¹] on standing crop at the community level and partitioned by species and functional groups, in the desert steppe of Inner Mongolia, China. The treatments were arranged in a completely randomized block design over a 9-year period. Standing crop was measured every August from 2004 to 2012. Peak standing crop decreased (P < 0.05) with increasing stocking rate; peak standing crop in the HG treatment decreased 40 % compared to the control. May–July precipitation explained at least 76 % of the variation in peak standing crop. MG and HG treatments resulted in a decrease (P < 0.05) in shrubs, semi-shrubs, and perennials forbs, and an increase (P < 0.05) in perennial bunchgrasses compared to the control. The coefficients of variation at plant functional group and species level in the LG and MG treatments were lower (P < 0.05) than in the control and HG treatments. Peak standing crop variability of the control and HG community were greatest, which suggested that LG and MG have greater ecosystem stability.

We investigated the effect of increasing soil temperature and nitrogen on greenhouse gas (GHG) emissions [carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O)] from a desert steppe soil in Inner Mongolia, China. Two temperature levels (heating versus no heating) and two nitrogen (N) fertilizer application levels (0 and 100 kg N ha⁻¹year⁻¹) were examined in a complete randomized design with six replications. The GHG surface fluxes and their concentrations in soil (0 to 50 cm) were collected bi-weekly from June 2006 to November 2007. Carbon dioxide and N₂O emissions were not affected by heating or N treatment, but compared with other seasons, CO₂ was higher in summer [average of 29.6 versus 8.6 mg carbon (C) m⁻²h⁻¹ over all other seasons] and N₂O was lower in winter (average of 2.6 versus 4.0 mg N m⁻²h⁻¹ over all other seasons). Desert steppe soil is a CH₄ sink with the highest rate of consumption occurring in summer. Heating decreased CH₄ consumption only in the summer. Increasing surface soil temperature by 1.3°C or applying 100 kg ha⁻¹year⁻¹ N fertilizer had no effect on the overall GHG emissions. Seasonal variability in GHG emission reflected changes in temperature and soil moisture content. At an average CH₄ consumption rate of 31.65 µg C m⁻²h⁻¹, the 30.73 million ha of desert steppe soil in Inner Mongolia can consume (sequestrate) about 85 × 10⁶kg CH₄-C, an offset equivalent to 711 × 10⁶kg CO₂-C emissions annually. Thus, desert steppe soil should be considered an important CH₄ sink and its potential in reducing GHG emission and mitigating climate change warrants further investigation.