放牧强度对高寒灌丛草甸土壤CO_2释放速率的影响

在中国科学院海北高寒草甸生态系统定位站，研究放牧强度对土壤CO２释放速率的影响及其与环境条件的关系。结果表明，CO２释放速率具有明显的日变化规律，日最大值在12∶00～14∶00h出现，最低值出现于凌晨6∶00～8∶00h。轻牧和重牧区日释放速率分别为7.774±5.577 g·m－２·d －１和6.977±4.947 g·m－２·d －１。CO２释放速率具有明显的季节变化，最大值均出现在7月，而冬季则最低。CO２释放速率的日变化主要受气温和地表温度的制约，与气温和地表温度呈极显著的正相关(P＜0.01)。CO２释放速率的季节动态与气温和地温(0～30cm)呈极显著的正相关(P＜0.01)。放牧使CO２释放速率降低。

Influence of grazing intensity on performance of perennial grass mixtures in the alpine region of the Tibetan Plateau

Effects of grazing intensity on leaf photosynthetic rate (Pn), specific leaf area (SLA), individual tiller density, sward leaf area index (LAI), harvested herbage DM, and species composition in grass mixtures (Clinelymus nutans + Bromus inermis, Elymus nutans + Bromus inermis + Agropyron cristatum and Elymus nutans + Clinelymus nutans + Bromus inermis + Agropyron cristatum) were studied in the alpine region of the Tibetan Plateau. Four grazing intensities (GI), expressed as feed utilisation rates (UR) by Tibetan lambs were imposed as follows: (1) no grazing; (2) 30% UR as light grazing; (3) 50% UR as medium grazing; and (4) 70% UR as high grazing. Leaf Pn rate and tiller density of grasses increased (P < 0.05), while sward LAI and harvested herbage DM declined (P < 0.05) with the increments of GI, although no effect of GI on SLA was observed. With increasing GI, Elymus nutans and Clinelymus nutans increased but Bromus inermis and Agropyron cristatum decreased in swards, LAI and DM contribution. Whether being grazed or not, Elymus nutans + Clinelymus nutans + Bromus inermis + Agropyron cristatum was the most productive sward among the grass mixtures. Thus, two well-performed grass species (Elymus nutans and Clinelymus nutans) and the most productive mixture of four species should be investigated further as the new feed resources in the alpine grazing system of the Tibetan Plateau. Light grazing intensity of 30% UR was recommended for these grass mixtures when swards, LAI, herbage DM harvested, and species compatibility were taken into account.