Effects of Rest Grazing on Organic Carbon Storage in Stipa grandis Steppe in Inner Mongolia, China

This study was aimed to evaluate the potential effects of rest grazing on organic carbon storage in Stipa grandis steppe of Inner Mongolia, China. Using potassium dichromate heating method, we analyzed the organic carbon storage of plant and soil in Stipa grand＆ steppe after rest grazing for 3, 6, and 9 yr. The results indicated that as the rest grazing ages prolonged, the biomass of aboveground parts, litter and belowground plant parts （roots） of the plant communities all increased, meanwhile the C content of the biomass increased with the rest grazing ages prolonging. For RG0, RG3a, RG6a, and RG9a, C storage in aboveground vegetation were 60.7, 76.9, 82.8 and 122.2 g C m2, respectively; C storage of litter were 5.1, 5.8, 20.4 and 25.5 g C m^-2, respectively; C storage of belowground roots （0-100 cm） were 475.2, 663.0, 1 115.0 and 1 867.3 g C m^-2, respectively; C storage in 0-100 cm soil were 13.97, 15.76, 18.60 and 32.41 kg C m^-2, respectively. As the rest grazing ages prolonged, the organic C storage in plant communities and soil increased. The C storage ofbelowground roots and soil organic C was mainly concentrated in 0-40 cm soil body. The increased soil organic C for RG3a accounted for 89.8% of the increased carbon in vegetation-soil system, 87.2% for RG6a, and 92.6% for RG9a. From the perspective of C sequestration cost, total cost for RG3a, RG6,, and RG9a were 2 903.4, 5 806.8 and 8 710.2 CNY haq, respectively. The cost reduced with the extension of rest grazing ages, 0.15 CNY kg^-1 C for RG3a, 0.11 CNY kg-~ C for RG6a and 0.04 CNY kg℃ for RG9a. From the growth characteristics of grassland plants, the spring was one of the two avoided grazing periods, timely rest grazing could effectively restore and update grassland vegetation, and was beneficial to the sustainable use of grassland. Organic C storage for RG9a was the highest, while the cost of C sequestration was the lowest. Therefore, spring rest grazing should be encouraged because it was proved to be a very efficient grassland use pattern.

Emission characteristics of carbon dioxide in the semiarid Stipa grandis steppe in Inner Mongolia, China

Using the static opaque chamber method, the soil respiration rates （SR） were measured through the continuous experiments in situ in semiarid Stipa grandis steppe in Xilin River Basin of Inner Mongolia, China from June 2001 to June 2003, in parallel, the difference between the SR and the ecosystem respiration rates （TER） were compared. The results indicated that the seasonal variations of the SR and TER were obvious with higher emissions in growing season and a relatively low efflux level in non-growing season, furthermore, the negative effluxes were found in the observation site in winter; the annual CO2 efflux of total ecosystem ranged from 160.5 gC/（m^2·a） to 162.8 gC/（m^2·a） and that of soil ranged from 118.7 gC/（m^2·a） to 152.3 gC/（m^2·a）. The annual SR accounted for about 74.0% to 93.5% of the annual TER, but the results of Analysis of Variance （ANOVA） indicated that the difference between the annual average TER and SR did not reach the significance level of 0.05. The TER was under similar environmental controls as SR, in growing seasons of drought years, the variations of soil moisture at 0-10 cm and 10-20 cm depth could account for 79,1% 95.6% of the changes of the SR and TER, but in non-growing season, more than 75% of the variations of the SR and TER could be explained by the changes of the ground temperature of soil surface layers.

Impacts of grazing and mowing on reproductive behaviors of Stipa grandis and Stipa krylovii in a semi-arid area

Disturbance can affect biomass allocation of plants,but can it influence plant reproductive behavior?To address this issue,we performed field plant community investigations and explored the reproductive behaviors of Stipa grandis and Stipa krylovii in response to grazing and mowing treatments at Maodeng pasture of Xilinguole League of Inner Mongolia,China during 2007–2009.The results showed that,with a similar niche width for the two plant species under mowing and grazing treatments,mowing significantly increased the ratio of ramet to genet number of S.krylovii and the carbon to nitrogen ratio of S.grandis,and grazing significantly decreased the ratio of vegetative to reproductive tiller biomass of S.grandis and increased the ratio of vegetative to reproductive tiller number of S.krylovii.Regression analysis showed that the significantly positive effect of root to shoot biomass ratio was stronger on the ratio of vegetative to reproductive tiller number of S.grandis than on that of S.krylovii.These results indicated that grazing and mowing influenced the reproductive manner and the process of sexual reproduction of S.grandis and S.krylovii.

季节性放牧改变大针茅养分回收和根系养分储存并影响其翌年春季返青生长

秋季养分回收是草地多年生植物保存和高效利用养分的关键机制。放牧对植物养分回收的影响可能改变根系养分储存,进一步影响植物在翌年春季的返青生长。多数研究关注于放牧草地植物养分回收和保存,而其对植物在翌年春季返青生长的影响研究则较少。本研究以半干旱草原多年生优势禾草——大针茅(Stipa grandis)为模式植物,具体评估了4种季节性放牧管理下(不放牧、春季放牧、夏季放牧和秋季放牧)大针茅植株水平的养分回收特征(养分回收度、回收效率和回收通量)、根系养分动态,以及翌年植物返青状况,旨在探究植物养分回收、根系养分储存和翌年返青生长对不同季节放牧的响应。研究结果显示,(i)大针茅氮回收效率为51%–66%、磷回收效率为58%–80%,养分回收通量在秋季放牧下最低,在春季放牧下最高。(ii)大针茅根系养分储存特征在夏季放牧下显著降低,在春季放牧下轻微下降,而在秋季放牧下则无变化。(iii)翌年春季大针茅返青生长状况在早春放牧下最佳,在秋季放牧下最差,这一现象主要受土壤水分的影响,而与根系养分储存无关。本研究为深入了解植物养分循环过程,建立草原保护和合理放牧管理制度提供了理论依据。