Haishan Niu

Effects of warming and grazing on soil N availability, species composition, and ANPP in an alpine meadow

Uncertainty about the effects of warming and grazing on soil nitrogen (N) availability, species composition, and aboveground net primary production (ANPP) limits our ability to predict how global carbon sequestration will vary under future warming with grazing in alpine regions. Through a controlled asymmetrical warming (1.2/1.7 degrees C during daytime/nighttime) with a grazing experiment from 2006 to 2010 in an alpine meadow, we found that warming alone and moderate grazing did not significantly affect soil net N mineralization. Although plant species richness significantly decreased by 10% due to warming after 2008, we caution that this may be due to the transient occurrence or disappearance of some rare plant species in all treatments. Warming significantly increased graminoid cover, except in 2009, and legume cover after 2008, but reduced non-legume forb cover in the community. Grazing significantly decreased cover of graminoids and legumes before 2009 but increased forb cover in 2010. Warming significantly increased ANPP regardless of grazing, whereas grazing reduced the response of ANPP to warming. N addition did not affect ANPP in both warming and grazing treatments. Our findings suggest that soil N availability does not determine ANPP under simulated warming and that heavy grazing rather than warming causes degradation of the alpine meadows.

Gene or environment? Species-specific control of stomatal density and length

Stomatal characteristics are used as proxies of paleo-environment. Only a few model species have been used to study the mechanisms of genetic and environmental effects on stomatal initiation. Variation among species has not been quantified. In this paper, results from an in situ reciprocal transplant experiment along an elevation gradient in the northeast Tibetan Plateau are reported, in which the relative effects of genetics (original altitude) and environment (transplant altitude) on stomatal density (SD) and length (SL) were quantified. In Thalictrum alpinum, only the environment significantly influenced SD, with the variance component () of the environment found to be much greater than that of genetics () (). In Kobresia humillis, only genetics significantly influenced SD and SL, with the genetics variance component found to be greater than that of the environment (, for SD). These results suggest that the extent to which genetics and the environment determine stomatal initiation and development is species-specific. This needs to be considered when studying genetic or environmental controls of stomatal initiation, as well as when SD and SL are used as proxies for ancient climate factors (e.g., CO2 concentration).

Spatio-temporal variations in the areas suitable for the cultivation of rice and maize in China under future climate scenarios

Predictions of changes in the distribution of areas suitable for the cultivation of rice and maize in China under future climate change scenarios may provide scientific support for the optimization of crop production and measures to mitigate climate change. We conducted a spatial grid-based analysis using projections of future climate generated by the National Center for Atmospheric Research Community Climate System Model version 4 for two representative concentration pathway scenarios (RCP2.6 and RCP8.5), adopted by the fifth phase of the Coupled Model Intercomparison Project to study the areas suitable for the cultivation of rice and maize in China. We investigated the migration of the centers of gravity of the cultivation areas based on climatic and hydrological factors from 2021 to 2100. The results indicated that, under RCP2.6, the areas suitable for the cultivation of rice were located throughout China, except for on the Qinghai-Tibetan Plateau, while the areas suitable for the cultivation of maize were located in northern, southwestern, central, eastern, parts of northeastern and some northern parts of western China. The distributions of both crops under RCP2.6 showed little change over time. In contrast, the areas suitable for the cultivation of rice and maize under RCP8.5 shifted northward and expanded from northwestern to northern China, as a result of greater warming in northern China and the faster warming trend under RCP8.5. This scenario would require much stronger climate mitigation policies to maintain the stable development of agriculture and to slow down the future migration of crop cultivation areas in China. The distribution of areas suitable for the cultivation of rice and maize should be studied further to design appropriate adaptation strategies for dealing with future climate change.

Experimental Warming Increases Seasonal Methane Uptake in an Alpine Meadow on the Tibetan Plateau

Increased understanding of the response of soil methane (CH4) uptake in alpine meadow ecosystems to warming and grazing could reduce uncertainty in estimates of the soil-atmospheric CH4 budget. To determine the effects of warming and grazing on soil CH4 uptake at different timescales (that is, daily, monthly, seasonal, and annual), we conducted a controlled warming and grazing experiment [that is, no warming with no grazing (NWNG), no warming with grazing (NWG), warming with no grazing (WNG), and warming with grazing (WG)] in an alpine meadow on the Tibetan plateau from 2006 to 2009. Soil CH4 uptake was mainly affected by warming and sample date and their interaction. Warming treatment regardless of grazing significantly increased seasonal average CH4 uptake by 31-39% during the growing season (from May to September) and by 162% during the non-growing season (from October to April next year) in 2007–2008, whereas only WNG increased seasonal average CH4 uptake by 87–138% compared with NWNG during the non-growing seasons in 2006–2007 and 2008–2009. Warming in WNG and WG increased annual CH4 uptake by 50–87% compared with NWNG or NWG. Moreover, warming regardless of grazing and warming with grazing (compared with NWNG) significantly increased the contribution to annual uptake of CH4 uptake during the non-growing season in 2007–2008 and 2008–2009. However, moderate grazing did not significantly influence soil CH4 uptake, although grazing with warming decreased CH4 uptake by 43% during the growing season in 2006. Soil moisture explained 16–25% of the CH4 variation during the growing season, but there was no significant relationship between soil CH4 uptake and soil moisture during the non-growing season. Our results suggest that more attention should be paid to the stimulating effect of warming on soil CH4 uptake during the non-growing season due to its greater response to warming and different stimulating mechanisms compared to responses during the growing season in the alpine meadow.

Warming decreased and grazing increased plant uptake of amino acids in an alpine meadow

Abstract Organic nitrogen (N) uptake by plants has been recognized as a significant component of terrestrial N cycle. Several studies indicated that plants have the ability to switch their preference between inorganic and organic forms of N in diverse environments; however, research on plant community response in organic nitrogen uptake to warming and grazing is scarce. Here, we demonstrated that organic N uptake by an alpine plant community decreased under warming with 13C–15N‐enriched glycine addition method. After 6 years of treatment, warming decreased plant organic N uptake by 37% as compared to control treatment. Under the condition of grazing, warming reduced plant organic N uptake by 44%. Grazing alone significantly increased organic N absorption by 15%, whereas under warming condition grazing did not affect organic N uptake by the Kobresia humilis community on Tibetan Plateau. Besides, soil NO 3–N content explained more than 70% of the variability observed in glycine uptake, and C:N ratio in soil dissolved organic matter remarkably increased under warming treatment. These results suggested warming promoted soil microbial activity and dissolved organic N mineralization. Grazing stimulated organic N uptake by plants, which counteracted the effect of warming.

Ecosystem stability in Inner Mongolia (reply): Plant communities

Arising from: Bai, Y., Han, X., Wu, J., Chen, Z. & Li, L. Nature, 431, 181–184 (2004); see also communication from Guo; Wang et al.Some of our findings are questioned by Wang et al.., on the basis that we use inconsistent data and fail to distinguish spatial heterogeneity effects. Here we show that both claims are unfounded. We also address the questions raised by Guo concerning how the steppe communities vary as they mature.

Effects of sampling method on foliar δ (13)C of Leymus chinensis at different scales.

Stable carbon isotope composition (δ13C) usually shows a negative relationship with precipitation at a large scale. We hypothesized that sampling method affects foliar δ13C and its response pattern to precipitation. We selected 11 sites along a precipitation gradient in Inner Mongolia and collected leaves of Leymus chinensis with five or six replications repeatedly in each site from 2009 to 2011. Additionally, we collected leaves of L. chinensis separately from two types of grassland (grazed and fenced) in 2011. Foliar δ13C values of all samples were measured. We compared the patterns that foliar δ13C to precipitation among different years or different sample sizes, the differences of foliar δ13C between grazed and fenced grassland. Whether actual annual precipitation (AAP) or mean annual precipitation (MAP), it was strongly correlated with foliar δ13C every year. Significant difference was found between the slopes of foliar δ13C to AAP and MAP every year, among the slopes of foliar δ13C to AAP from 2009 to 2011. The more samples used at each site the lower and convergent P-values of the linear regression test between foliar δ13C and precipitation. Furthermore, there was significant lower foliar δ13C value in presence of grazed type than fenced type grassland. These findings provide evidence that there is significant effect of sampling method to foliar δ13C and its response pattern to precipitation of L. chinensis. Our results have valuable implications in methodology for future field sampling studies.