针对三江源区"黑土滩"治理中的牧草种子萌发与生长困难这一突出问题,结合种子丸粒化技术的研究,选用青藏高原优良牧草青海冷地早熟禾(Poa crymophila Keng CV.Qinghai)种子为研究对象,开展5%、10%、15%、20%的肥料(尿素∶磷酸二氢钾=1∶1.3)添加水平对青海冷地早熟禾丸粒化种子发芽和幼苗生长的影响研究。结果表明,随着肥料含量的增加,丸粒化种子发芽天数相应推迟(p﹥0.05),丸粒化种子发芽率均低于对照组(p﹤0.01);经不同肥料水平处理的丸粒化种子种植于未退化草地土壤中,丸粒化种子的出苗率均较对照组有所降低,且15%肥料组低于对照组(p﹤0.05),其株高、根长、叶片数、苗鲜重、苗干重均略高于对照组(p﹥0.05);种植于退化草地土壤中,添加肥料组丸粒化种子的出苗率均较对照组有所降低,同时随着肥料含量的增加(除20%的肥料外),其株高、叶片数、苗鲜重、苗干重与对照组相比,均无显著差异(P﹥0.05)。结论:不同肥料(尿素∶磷酸二氢钾=1∶1.3)添加水平制作的青海冷地早熟禾丸粒化种子,均降低了丸粒化种子的发芽率和出苗率,而对促进幼苗生长的作用不明显,表明了尿素和磷酸二氢钾肥料配合在丸粒化种子幼苗生长上没有显著的协同效应。因此,今后的工作中,需进一步开展尿素或磷钾肥单独添加对青海冷地早熟禾丸粒化种子发芽率和出苗率的影响研究是十分必要的工作,同时建议尝试添加有机肥作为丸粒化种子的养分配料。
The Qinghai-Tibet Plateau encompasses a large quantity of wetlands, some of which have been degraded to varying severity levels. In the literature, a number of degradation indicators have been proposed to evaluate ecological health of wetlands, but their effectiveness in the plateau environment remains unknown. In this study, we assessed the effectiveness of three degradation indicators, soil moisture content at 10 cm deep, vegetative cover, and density of pika burrows. The degradation severity of wetlands in Maduo County on the Qinghai-Tibet Plateau is enumerated at four levels, intact, slight, moderate and severe. Analysis of 106 samples collected in the field demonstrates that the density of pika burrows is the least reliable indicator. By comparison, vegetative cover and underlying soil moisture content are more reliable, even though neither is a perfect indicator as the difference among adjacent levels of severity as revealed by t-test is not always statistically significant. The imperfection of vegetative cover as an indicator is due to its variation among different types of wetlands. The limitation of moisture content is attributed to its non-linear relationship with wetland degradation. Above the threshold of about 50% in moisture content wetlands are unlikely to be degraded. It is recommended that moisture be measured at the point near the surface and vegetative cover be further differentiated by species in order to improve their effectiveness.
In many ecosystems ungulates have coexisted with grasslands over long periods of time. However, high densities of grazing animals may change the floristic and structural characteristics of vegetation, reduce biodiversity, and increase soil erosion, potentially triggering abrupt and rapid changes in ecosystem condition. Alternate stable state theory provides a framework for understanding this type of dynamic. In the Sanjiangyuan atop the Qinghai-Tibetan plateau (QTP), grassland degradation has been accompanied by irruptions of native burrowing animals, which has accentuated the loss of ground cover. Severely degraded areas of alpine meadows are referred to as 'Heitutan'. Here, using the framework of alternate stable state theory, we describe the proximate and ultimate drivers of the formation of Heitutan on the QTP, and we assess prospects for recovery, in relation to the degree of biophysical alteration, of these alpine meadows. Effective rehabilitation measures must address the underlying causes of degradation rather than their symptoms. Heitutan degradation is not uni-causal. Rather it reflects different mechanisms operating at different spatio-temporal scales across this vast region. Underlying causes include overly aggressive exploitation of the grasslands (e.g. overgrazing), amplification of grazing and erosion damage by small mammals when outbreaks occur, and/or climate change. Given marked variability in environmental conditions and stressors, restorative efforts must vary across the region. Restoration efforts are likely toyield greatest success if moderately and severely degraded areas are targeted as the first priority in management programmes, before these areas are transformed into extreme Heitutan.
LI Xi-laiPERRY LW GeorgeBRIERLEY GaryGAO JayZHANG JingYANG Yuan-wu
