To better utilize native pasture at the high altitude region, three-consecutive-year feeding experiments and a total of seven metabolism trials were conducted to evaluate the impact of three forage stages of maturity on the chemical composition, nutrient digestibility, and energy metabolism of native forage in Tibetan sheep on the Qinghai-Tibetan Plateau (QTP). Forages were harvested from June to July, August to October, and November to December of 2011 to 2013, corresponding to the vegetative, bloom, and senescent stages of the annual forages. Twenty male Tibetan sheep were selected for each study and fed native forage ad libitum. The digestibility of DM, OM, CP, NDF, ADF, DE, DE/GE, and ME/GE were greatest (P< 0.01) from the vegetative stage, intermediate (P < 0.01) from the bloom stage, and least (P < 0.01) from the senescent stage. Nutrient digestibility and energy parameters correlated positively (linear, 0.422 to 0.778; quadratic, 0.568 to 0.815; P < 0.01) with the CP content of forage but correlated negatively with the content of NDF (linear, 0.343 to 0.689; quadratic, 0.444 to 0.777; P ≤ 0.02), ADF (linear, 0.563 to 0.766; quadratic, 0.582 to 0.770; P < 0.01), and ether extract (EE, linear, 0.283 to 0.574; quadratic, 0.366 to 0.718; P ≤ 0.04) of forage. For each predicted variable, the prediction of DMI expressed as grams per kilogram of BW (g/kg BW·d) yielded a greater R2 value (0.677 to 0.761 vs. 0.616 to 0.711) compared with the equations of DMI expressed as g/kg metabolic BW by step-wise regression. The results suggest that parameters of forage CP, NDF, and ADF content were most closely related to nutrient digestibility. Contrary to previous studies, in this study, ADF content had a greater linear relationship (0.766 vs. 0.563 to 0.732) with OM digestibility than the other parameters of nutrient digestibility. The quadratic relationship between forage CP content and CP digestibility indicates that when forage CP content exceeds the peak point (9.7% DM in the present study), increasing forage CP content could decrease CP digestibility when Tibetan sheep were offered native forage alone on the QTP. Additionally, using the forage CP, EE, NDF, and ADF content to predict DMI (g/kg BW·d) yielded the best fit equation for Tibetan sheep living in the northeast portion of the QTP.

Selenium (Se) deficiency is a widespread and seasonally chronic phenomenon observed in Tibetan sheep (Ovis aries) traditionally grazed on the Qinghai–Tibet Plateau (QTP). Effects of the dietary addition of Se-enriched yeast (SeY) on the bacterial community in sheep rumen and rumen fermentation were evaluated with the aim of gaining a better understanding of the rumen prokaryotic community. Twenty-four yearling Tibetan rams [initial average body weight (BW) of 31.0 ± 0.64 kg] were randomly divided into four treatment groups, namely, control (CK), low Se (L), medium Se (M), and high Se (H). Each group comprised six rams and was fed a basic diet of fresh forage cut from the alpine meadow, to which SeY was added at prescribed dose rates. This feed trial was conducted for over 35 days. On the final day, rumen fluid was collected using a transesophageal sampler for analyzing rumen pH, NH3-N content, volatile fatty acid (VFA) level, and the rumen microbial community. Our analyses showed that NH3-N, total VFA, and propionate concentrations in the M group were significantly higher than in the other groups (P &lt; 0.05). Both the principal coordinates analysis (PCoA) and the analysis of similarities revealed that the bacterial population structure of rumen differed among the four groups. The predominant rumen bacterial phyla were found to be Bacteroidetes and Firmicutes, and the three dominant genera in all the samples across all treatments were Christensenellaceae R7 group, Rikenellaceae RC9 gut group, and Prevotella 1. The relative abundances of Prevotella 1, Rikenellaceae RC9 gut group, Ruminococcus 2, Lachnospiraceae XPB1014 group, Carnobacterium, and Hafnia-Obesumbacterium were found to differ significantly among the four treatment groups (P &lt; 0.05). Moreover, Tax4fun metagenome estimation revealed that gene functions and metabolic pathways associated with carbohydrate and other amino acids were overexpressed in the rumen microbiota of SeY-supplemented sheep. To conclude, SeY significantly affects the abundance of rumen bacteria and ultimately affects the rumen microbial fermentation.

Remote sensing data have been widely used in the study of large-scale vegetation activities, which have important significance in estimating grassland yields, determining grassland carrying capacity, and strengthening the scientific management of grasslands. Remote sensing data are also used for estimating grazing intensity. Unfortunately, the spatial distribution of grazing-induced degradation remains undocumented by field observation, and most previous studies on grazing intensity have been qualitative. In our study, we tried to quantify grazing intensity using remote sensing techniques. To achieve this goal, we conducted field experiments at Gansu Province, China, which included a meadow steppe and a semi-arid region. The correlation between a vegetation index and grazing intensity was simulated, and the results demonstrated that there was a significant negative correlation between NDVI and relative grazing intensity (p < 0.05). The relative grazing intensity increased with a decrease in NDVI, and when the relative grazing intensity reached a certain level, the response of NDVI to relative grazing intensity was no longer sensitive. This study shows that the NDVI model can illustrate the feasibility of using a vegetation index to monitor the grazing intensity of livestock in free-grazing mode. Notably, it is feasible to use the remote sensing vegetation index to obtain the thresholds of livestock grazing intensity.

We studied the dynamics of microbial biomass and nitrogen in old-growth forests and in 3- and 10-year-old plantations established after clear-cutting and slash burning of old-growth western red cedar (Thujaplicata Donn ex D. Don)–western hemlock (Tsugaheterophylla (Raf.) Sarg.) stands on northern Vancouver Island. Ten-year-old plantations, after initially growing well, were experiencing declining growth rates. Three forest floor layers: F (fermentation), woody F (Fw), and H (humus) were sampled four times in May, July, August, and October of 1992. Moisture content was significantly greater in the old-growth forests than in the plantations for F on July 16 (p < 0.05) and Fw (p < 0.10), but was not significantly different for H. Microbial biomass C and N were relatively constant throughout the sampling period, resulting in nonsignificant date effects. Microbial C content was in the order: old-growth forests > 10-year-old plantations > 3-year-old plantations. Microbial N content was significantly greater in the old-growth forest than in the young plantations for both F (p < 0.001) and H (p < 0.05) but was not different between the plantations. Therefore, the hypothesis that the microbial biomass acted as a net sink in the 10-year-old plantations by immobilizing N into the microbial N pool is rejected. Microbial C/N ratios were greater (p < 0.05) in the 10-year-old plantations than in the old-growth forests and in the 3-year-old plantations in H and on July 16 in F, indicating that microbial competition for N was probably a factor in the growth declining in the 10-year-old plantations. Extractable C and N and mineralizable N were generally higher in the old-growth forests than in the 3-year-old plantations and higher in the 3-year-old than in the 10-year-old plantations. As a result of better nutritional conditions, tree and understory foliage in the 3-year-old plantations had higher N concentrations and lower C/N ratios than in the 10-year-old plantations. Trees in the 10-year-old plantations displayed chlorotic symptoms and slow growth which were not observed in the 3-year-old plantations.

Abstract. Litter decomposition and N release are the key processes that strongly determine the nutrient cycling at the soil-plant interface; however, how these processes are affected by grazing or grazing exclusion in the alpine grassland ecosystems on the Qinghai-Tibetan Plateau (QTP) is poorly understood. So far few studies have simultaneously investigated the influence of both litter quality and incubation site on litter decomposition and N release. Moreover, previous studies on the QTP investigating how grazing exclusion influences plant abundance and biodiversity usually lasted for many years, and the short-term effects have rarely been reported. This work studied the short-term (6 months) effects of grazing and grazing exclusion on plant community composition (i.e., plant species presented) and litter quality and long-term (27-33 months) effects on soil chemical characteristics and mixed litter decomposition and N release on the QTP. Our results demonstrate that (1) shorter-term grazing exclusion had no effect on plant community composition but increased plant palatability and total litter biomass; (2) grazing resulted in higher N and C content in litter; and (3) grazing accelerated litter decomposition, while grazing exclusion promoted N release from litter and increased soil organic carbon. In addition, incubation site had significantly more impact than litter quality on litter decomposition and N release, while litter quality affected decomposition in the early stages. This study provides insights into the mechanisms behind the nutrient cycling in alpine ecosystems. We suggest that periodic grazing and grazing exclusion is beneficial in grassland management on the QTP.

Aims This study investigated the influences of herbivore grazing intensity and grazing season on decomposition and nutrient release of dung and litter, which aimed to improve our understandings of grazing affecting nutrient cycling in alpine meadows on the Qinghai-Tibetan Platean. Methods A factorial design experiment comprising 3 grazing intensities (non-grazing, moderate grazing, and heavy grazing) and 2 grazing seasons (summer and winter), was applied to quantify the decomposition and chemistry of dung and litter in an alpine pasture using the litterbag technique. Litterbags were retrieved for analysis of mass loss and nutrient release with 180, 360, 540, and 720 days after placement. Results Grazing activity accelerated the decomposition of dung and litter and increased nutrient release from dung and litter by increasing soil temperature compared with non-grazing pastures, whereas grazing season had no effect on decomposition. The decomposition time was shorter for dung than that for litter. Conclusions Herbivores grazing benefited dung and litter decomposition and nutrient cycling directly by increasing soil temperature, which is likely to promote soil microbial activity due to low temperatures in alpine meadows, and indirectly through herbage ingestion and dung deposition which increase the organic debris concentration used for microorganisms growth and reproduction. This study provides insights into the mechanisms of grazing regulating nutrient cycling in alpine ecosystems.

In order to examine the influence of microsymbionts on plants, arbuscular mycorrhizal (AM) fungi and rhizobia were used to examine the growth of Lathyrus sativus under sulphate salt stress. Seedlings of L. sativus were inoculated with a combination of selected microsymbionts. Plants were grown under greenhouse conditions with five Na 2 SO 4 concentrations (0, 1%, 2%, 3% and 4% (weight : weight)). The inoculations combinations used were the AM fungus, Glomus mosseae and/or the rhizobium, Mesorhizobium mediterraneum. The results showed that sulphate salinity inhibited plant growth and biomass production. However, compared with the control treatments, dual-inoculation of G. mosseae and M. mediterraneum reduced the harmful influence of sulphate salinity. Parmeters including plant height, the extent of AM colonization, total biomass, nodules biomass, P concentration, N concentration and proline concentration confirmed that dual inoculation plays a vital role in promoting the growth of L. sativus under sulphate salt stress. The results suggested that the use of this dual inoculation could be exploited in grassland plantation establishment and in pastoral ecosystem reclamation programmes in arid and semi-arid areas subject to moderate salt contamination.

. 2006. Some characteristics of soil respiration in hybrid poplar plantations in northern Alberta. Can. J. Soil Sci. 86: 257-268. Fast-growing hybrid poplars are being planted in the Canadian prairies to meet the increasing demand for fibre and environmental services of trees and forests; however, the impact of hybrid poplars on C dynamics and storage on previously farmed land is largely unknown for the boreal region. We measured soil CO 2 efflux along a chronosequence (3-, 9-, and 11-yr-old stands) of hybrid poplar (Populus deltoides × Populus × petrowskyana var. Walker) plantations and a control agricultural field from June to August 2004. Measurements were made between 0800 and 1800 with a portable Li-Cor 6400-09 system and were based on 4-5 min averaging. We also measured the response to simulated rainfall and the diurnal fluctuation of soil CO 2 efflux. Soil CO 2 efflux ranged from 1.30 µmol CO 2 m -2 s -1 in the 3-yr-old plantation to 5.41 µmol CO 2 m -2 s -1 in the agricultural control field, or from 0.17 µmol CO 2 m -2 s -1 kg -1 C (based on soil organic C content to a 0.4 m depth) in the 3-yr-old plantation to 1.09 µmol CO 2 m -2 s -1 kg -1 C in the 11-yr-old plantation. Simulated rainfall applied in the 3-yr-old plantation and a newly planted site resulted in an immediate pulse of CO 2 efflux, 2.90 and 2.54 µmol CO 2 m -2 s -1 , respectively, followed by an efflux rate sustained slightly above pre-irrigation levels. No secondary pulse of soil respiration was observed in the 2-h period following water application. Diurnal variation of soil respiration was found to be small between 0600 and 1900 in the agricultural control field, with values that varied from 2.66 to 3.17 µmol CO 2 m -2 s -1 . Continued monitoring of soil respiration and other C cycling processes in the chronosequence will improve our understanding of the potential for C sequestration in hybrid poplar plantations in northern Alberta. Les auteurs ont aussi mesuré la réaction à une pluie artificielle et la fluctuation diurne des efflux de CO 2 du sol. Ces derniers varient de 1,30 µmol de CO 2 par m 2 et par seconde pour la plantation de trois ans à 5,41 µmol pour la culture témoin, ou de 0,17 µmol de CO 2 par m 2 et par seconde, par kilo de C (teneur du sol en C organique à 0,4 m de profondeur), pour la plantation de trois ans à 1,09 µmol pour celle de onze ans. La pluie artificielle a immédiatement entraîné un efflux de CO 2 de 2,90 et de 2,54 µmol par m 2 et par seconde dans la plantation de trois ans et dans une nouvelle plantation, respectivement. Cette réaction a été suivie par un efflux stable, légèrement supérieur à celui observé avant l'irrigation. Aucun signe de respiration secondaire du sol n'a été observé au cours des deux heures qui ont suivi l'arrosage. La respiration du sol varie peu durant le jour, entre 6 h et 19 h, dans le champ cultivé, les valeurs fluctuant de 2,66 à 3,17 µmol de CO 2 par m 2 et par seconde. En poursuivant l'étude de la respiration du sol et d'autres processus du cycle du carbone dans cette chronoséquence...